Parallels between playbacks and Pleistocene tar seeps suggest sociality in an extinct sabretooth cat, Smilodon. 2008. Biology Letters, published Tuesday, October 28, 2008.
From the press release:
Scientists from UCLA and the Zoological Society of London concluded that the sabertooth cat was social by comparing numbers of present-day carnivores competing for kills in Africa with those of mainly extinct species found in a North American fossil deposit.
Smilodon existed in North and South America between 1.8 million and 10,000 years ago and is one of the most common species preserved at the Rancho La Brea tar pits of Los Angeles, a fossil deposit in which dying herbivores trapped in sticky asphalt attracted numerous dire wolves and sabertooth cats, some of which also died there. Because most living cats are solitary, controversy has persisted over the social life of Smilodon.
The study took a new approach to the question by comparing data from the La Brea fossil record and data obtained from "playbacks" used in Africa, in which the recorded calls of distressed prey and the sounds of lions and hyenas are used to attract carnivores. This technique has been used by scientists to estimate carnivore densities in eastern and southern Africa.
Results showed that large social species made up a far larger proportion of the animals attracted than one would expect, considering their population size compared to other carnivores. Large social carnivores were, in fact, found to attend approximately 60 times more often than expected on the basis of relative abundance. When these results were compared with the records at the tar pits of California, the scientists found that the proportion of Smilodon records matched the proportion of the large social carnivores in the playbacks.
"The extinct sabertooth cat, Smilodon fatalis, has been something of an enigma, with almost nothing known of its behavior," said Chris Carbone, lead author of the paper. "This research allowed us to use the behavior of its present-day relatives to conclude that this extinct cat was more likely to roam in formidable gangs than as a secretive, solitary animal."
Friday, October 31, 2008
Thursday, October 30, 2008
Frenchman Formation Terrestrial Ecosystem Conference 2009
We are now accepting abstracts (up to six pages with illustrations) for posters and oral presentations, dealing with all aspects related to the late Maastrichtian palaeontology of the Frenchman Formation. The deadline for abstract submissions is March 1st, 2008. Registration will be $150 after March 1, but early registrants will receive a reduced rate of $100 for students and $125 for non-students. Your registration fee includes the abstract volume, banquet attendance, lunches, social events, and other benefits.
On May 20th there will be an optional workshop incorporating Frenchman Formation specimens, and fieldtrip to local macro- and microvertebrate sites. Cost for both fieldtrip (including lunch) and workshop is $40.
Please note that the conference will be limited to one hundred participants, so register soon. Conference information is available at dinocountry.com; click on T. rex Centre, and navigate to Coming Events. Registration fees can be paid by calling 306-295-4009 (FAX 306-295-4702), or by contacting t.rex1 @ sasktel.net. Proposed titles and abstracts should be sent to ffte2009 @ gmail.com.
T. rex Smells
Olfactory acuity in theropods: palaeobiological and evolutionary implications. 2008. D. Zelenitsky et al. Proc.Royal Soc. B Online.
The researchers inferred the size of the olfactory bulbs based on the impressions left on skull bones.
"T. rex has previously been accused of being a scavenger due to its keen sniffer, although its nose may point to alternative lifestyles based on what we see in living animals" says Zelenitsky, the lead investigator on the study. "Large olfactory bulbs are found in living birds and mammals that rely heavily on smell to find meat, in animals that are active at night, and in those animals that patrol large areas. Although the king of carnivorous dinosaurs wouldn't have passed on scavenging a free dead meal, it may have used its sense of smell to strike at night or to navigate through large territories to find its next victim."
In addition to providing clues about the biology and behavior of the ancient predators, the study also reveals some surprising information about the sense of smell in the ancestors of modern birds.
They found that the extinct bird Archaeopteryx, known to have evolved from small meat-eating dinosaurs, had an olfactory bulb size comparable to most theropod dinosaurs. Although sight is very good in most birds today, their sense of smell is usually poor, a pattern that does not hold true in the ancestry of living birds.
Scientists study dinosaur smelling skills for the first time and sniff out new angle on bird evolution.Scientists are providing new insight into the sense of smell of carnivorous dinosaurs and primitive birds, and have suggested that Tyrannosaurus rex had the best nose of all meat-eating dinosaurs. Their results tone down the reputation of T. rex as a scavenger [Ed. - Isn’t an enhanced sense of smell use to support the scavenging hypothesis?].
The researchers inferred the size of the olfactory bulbs based on the impressions left on skull bones.
"T. rex has previously been accused of being a scavenger due to its keen sniffer, although its nose may point to alternative lifestyles based on what we see in living animals" says Zelenitsky, the lead investigator on the study. "Large olfactory bulbs are found in living birds and mammals that rely heavily on smell to find meat, in animals that are active at night, and in those animals that patrol large areas. Although the king of carnivorous dinosaurs wouldn't have passed on scavenging a free dead meal, it may have used its sense of smell to strike at night or to navigate through large territories to find its next victim."
In addition to providing clues about the biology and behavior of the ancient predators, the study also reveals some surprising information about the sense of smell in the ancestors of modern birds.
They found that the extinct bird Archaeopteryx, known to have evolved from small meat-eating dinosaurs, had an olfactory bulb size comparable to most theropod dinosaurs. Although sight is very good in most birds today, their sense of smell is usually poor, a pattern that does not hold true in the ancestry of living birds.
Wednesday, October 29, 2008
Tuesday, October 28, 2008
Mitochondrial Phylogeny of the Extinct Cave Bear
Deciphering the complete mitochondrial genome and phylogeny of the extinct cave bear in the Paleolithic painted cave of Chauvet. 2008. C. Bon et al. PNAS Published online before print October 27, 2008.
Abstract: Retrieving a large amount of genetic information from extinct species was demonstrated feasible, but complete mitochondrial genome sequences have only been deciphered for the moa, a bird that became extinct a few hundred years ago, and for Pleistocene species, such as the woolly mammoth and the mastodon, both of which could be studied from animals embedded in permafrost.
To enlarge the diversity of mitochondrial genomes available for Pleistocene species, we turned to the cave bear (Ursus spelaeus), whose only remains consist of skeletal elements. We collected bone samples from the Paleolithic painted cave of Chauvet-Pont d'Arc (France), which displays the earliest known human drawings, and contains thousands of bear remains. We selected a cave bear sternebra, radiocarbon dated to 32,000 years before present, from which we generated overlapping DNA fragments assembling into a 16,810-base pair mitochondrial genome.
Together with the first mitochondrial genome for the brown bear western lineage, this study provides a statistically secured molecular phylogeny assessing the cave bear as a sister taxon to the brown bear and polar bear clade, with a divergence inferred to 1.6 million years ago.
With the first mitochondrial genome for a Pleistocene carnivore to be delivered, our study establishes the Chauvet-Pont d'Arc Cave as a new reservoir for Paleogenetic studies. These molecular data enable establishing the chronology of bear speciation, and provide a helpful resource to rescue for genetic analysis archeological samples initially diagnosed as devoid of amplifiable DNA.
and…
Isotopic evidence for omnivory among European cave bears: Late Pleistocene Ursus spelaeus from the Peştera cu Oase, Romania. 2008. M.P. Richards et al. PNAS 105 no. 2 600-604.
Abstract: Retrieving a large amount of genetic information from extinct species was demonstrated feasible, but complete mitochondrial genome sequences have only been deciphered for the moa, a bird that became extinct a few hundred years ago, and for Pleistocene species, such as the woolly mammoth and the mastodon, both of which could be studied from animals embedded in permafrost.
To enlarge the diversity of mitochondrial genomes available for Pleistocene species, we turned to the cave bear (Ursus spelaeus), whose only remains consist of skeletal elements. We collected bone samples from the Paleolithic painted cave of Chauvet-Pont d'Arc (France), which displays the earliest known human drawings, and contains thousands of bear remains. We selected a cave bear sternebra, radiocarbon dated to 32,000 years before present, from which we generated overlapping DNA fragments assembling into a 16,810-base pair mitochondrial genome.
Together with the first mitochondrial genome for the brown bear western lineage, this study provides a statistically secured molecular phylogeny assessing the cave bear as a sister taxon to the brown bear and polar bear clade, with a divergence inferred to 1.6 million years ago.
With the first mitochondrial genome for a Pleistocene carnivore to be delivered, our study establishes the Chauvet-Pont d'Arc Cave as a new reservoir for Paleogenetic studies. These molecular data enable establishing the chronology of bear speciation, and provide a helpful resource to rescue for genetic analysis archeological samples initially diagnosed as devoid of amplifiable DNA.
and…
Isotopic evidence for omnivory among European cave bears: Late Pleistocene Ursus spelaeus from the Peştera cu Oase, Romania. 2008. M.P. Richards et al. PNAS 105 no. 2 600-604.
Monday, October 27, 2008
It Was 20 Years Ago Today....
Last August some of the volunteers who came out to Dinosaur Provincial Park in 1988 as part of the Tyrrell Museum's volunteer program held a mini-reunion back in DPP. Unfortunately I could not attend (being en route to Mongolia), but my old friend Diane sent along some photos. Everyone still looks great!
Paul Ferguson, Maria Santi, Rita Schulze & Diane. Maria's wearing the field season t-shirt I designed for that year - a not-so-sly dig at the IMAX film crew that took up too much of our time that summer!
J.J. Henderson, Thompson Ferguson, Emily Henderson
The next Palaeo generation!: Thompson, J.J., Caroline Ferguson, & Emily
I could not find any 'before' pix from 1988, but I did find a series of photos showing the excavation in 1985 of the Daspletosaurus now on display at the RTMP Field Station in DPP. I'll post those soon.
Paul Ferguson, Maria Santi, Rita Schulze & Diane. Maria's wearing the field season t-shirt I designed for that year - a not-so-sly dig at the IMAX film crew that took up too much of our time that summer!
J.J. Henderson, Thompson Ferguson, Emily Henderson
The next Palaeo generation!: Thompson, J.J., Caroline Ferguson, & Emily
I could not find any 'before' pix from 1988, but I did find a series of photos showing the excavation in 1985 of the Daspletosaurus now on display at the RTMP Field Station in DPP. I'll post those soon.
Skull Shape & Crocodile Evolution
Cranial shape and correlated characters in crocodilian evolution. 2008. R. Sadleir and P. Makovivky. J. of Evol. Bio. 21: 1578 – 1596.
ABSTRACT: Crocodilians show a high degree of cranial variation and convergence throughout their 80 million-year fossil record that complicates their phylogenetic reconstruction. Conflicting phylogenetic results from different data partitions and character homoplasies typify crocodilian phylogeny, and differences between molecular and morphological phylogenetic hypotheses are believed to be associated with the slender-snout skull shape of Gavialis gangeticus and Tomistoma schlegelii. Slender-snout skulls are one of five identified eusuchian cranial ecomorph shape categories (ESCs) thought to reflect functional or ecological specialization.
This paper tested the effect of transitions among general, blunt and slender ESCs on cranial character-state distributions in phylogeny using the concentrated changes test. In addition, 'tree-free' character compatibility analysis of character independence was conducted on the morphological character matrix to determine if character correlations are observed independent of specific tree topologies.
Results suggest cranial ESCs do affect cranial character-state gains in phylogeny. Concentrated changes identify a broad suite of character-state changes that significantly correlate with transitions to slender, general and blunt ESCs on morphological, molecular and combined-data tree topologies, but numbers of correlated characters for each category differ according to topology.
Character compatibility analysis results do not mirror the concentrated changes test results and reflect hierarchically distributed support throughout the data. As cranial ESCs affect character-state transitions, it is possible that nonphylogenetic variables could affect inferences of crocodilian phylogeny by affecting cranial morphology.
This paper tested the effect of transitions among general, blunt and slender ESCs on cranial character-state distributions in phylogeny using the concentrated changes test. In addition, 'tree-free' character compatibility analysis of character independence was conducted on the morphological character matrix to determine if character correlations are observed independent of specific tree topologies.
Results suggest cranial ESCs do affect cranial character-state gains in phylogeny. Concentrated changes identify a broad suite of character-state changes that significantly correlate with transitions to slender, general and blunt ESCs on morphological, molecular and combined-data tree topologies, but numbers of correlated characters for each category differ according to topology.
Character compatibility analysis results do not mirror the concentrated changes test results and reflect hierarchically distributed support throughout the data. As cranial ESCs affect character-state transitions, it is possible that nonphylogenetic variables could affect inferences of crocodilian phylogeny by affecting cranial morphology.
Friday, October 24, 2008
Heterodontosaurus: Omnivore!
The teeth suggest Heterodontosaurus practiced occasional omnivory: the canines were used for defense or for adding small animals such as insects to a diet composed mainly of plants. Credit: Natural History Museum.
Heterodontosaurs, which means "different-toothed lizards," have an unusual combination of teeth, with large fang-like canines at the front of their jaws and worn, molar-like grinding teeth at the back. In contrast, most reptiles have teeth which change little in shape along the length of the jaw.
"It's likely that all dinosaurs evolved from carnivorous ancestors," said Laura Porro. "Since heterodontosaurs are among the earliest dinosaurs adapted to eating plants, they may represent a transition phase between meat-eating ancestors and more sophisticated, fully-herbivorous descendents."
Researchers suspect that the canines were used as defensive weapons against predators, or for adding occasional small animals such as insects, small mammals and reptiles to a diet composed mainly of plants--what the authors refers to as "occasional omnivory."
Heterodontosaurus also lacks replacement teeth, making it more similar to mammals, not only in the specialized, variable shape of its teeth but also in replacing its teeth slowly, if at all, and developing tight tooth-to-tooth contact. "Tooth replacement must have occurred during growth," the authors conclude, "however, evidence of continuous tooth replacement appears to be absent, in both adult and juvenile specimens."
Thanks to Sukie.
Development Stops The Evolution of Endless Forms
An End to Endless Forms: Epistasis, Phenotype Distribution Bias, and Nonuniform Evolution. 2008. E. Borenstein and D.C. Krakauer. PLoS Comput Biol 4(10): e1000202.
Diversity only a tiny fraction of the endless 'space' of possibilities, and observed phenotypes actually occupy only small, dense patches in the abstract phenotypic space. Researchers demonstrate that the sparseness of variety in nature can be attributed to the interactions between multiple genes and genetic controls involved in the development of organisms – a much simpler explanation than previously suggested.
The new model reproduces patterns that are observed in the fossil record, including increasing variation between taxonomic groups, accompanied by decreasing variation within groups. This pattern is consistent with the Cambrian radiation associated with a rapid proliferation of highly disparate, multicellular animals, and suggests that much of the variation seen today is as a result of simpler genetic controls dating from much earlier in evolutionary time.
The findings presented in this study also bear directly on issues of convergence (when very different organisms independently evolve similar features). By including a model of development, rather different genotypes can produce very similar phenotypes. Consequently, convergent evolution, which the vast space of genotypes would suggest to be rare, is allowed to become much more common.
One of the paradoxical implications of this study has been to show how innovations in development that lead to an overall increase in the number of accessible phenotypes, can lead to a reduction in selective variance. In other words, while the potential for novel phenotypes increases, the fraction of space these phenotypes occupies tends to contract. They concluded that "The theory presented in our paper complements the view of development as a key component in the production of endless forms and highlights the crucial role of development in constraining (as well as generating) biotic diversity."
Researchers have put forward a simple model of development and gene regulation that is capable of explaining patterns observed in the distribution of morphologies and body plans.From the press release:
Diversity only a tiny fraction of the endless 'space' of possibilities, and observed phenotypes actually occupy only small, dense patches in the abstract phenotypic space. Researchers demonstrate that the sparseness of variety in nature can be attributed to the interactions between multiple genes and genetic controls involved in the development of organisms – a much simpler explanation than previously suggested.
The new model reproduces patterns that are observed in the fossil record, including increasing variation between taxonomic groups, accompanied by decreasing variation within groups. This pattern is consistent with the Cambrian radiation associated with a rapid proliferation of highly disparate, multicellular animals, and suggests that much of the variation seen today is as a result of simpler genetic controls dating from much earlier in evolutionary time.
The findings presented in this study also bear directly on issues of convergence (when very different organisms independently evolve similar features). By including a model of development, rather different genotypes can produce very similar phenotypes. Consequently, convergent evolution, which the vast space of genotypes would suggest to be rare, is allowed to become much more common.
One of the paradoxical implications of this study has been to show how innovations in development that lead to an overall increase in the number of accessible phenotypes, can lead to a reduction in selective variance. In other words, while the potential for novel phenotypes increases, the fraction of space these phenotypes occupies tends to contract. They concluded that "The theory presented in our paper complements the view of development as a key component in the production of endless forms and highlights the crucial role of development in constraining (as well as generating) biotic diversity."
Thursday, October 23, 2008
Centrosaurus brinkmani Print by Mark Schultz Now Available
Art by Mark Schultz
Unlike some blogs I’ve never put up a “donation” link, and I have no plans to do this in the future. But, if you’d like to show your support for the blog & get a cool print, drop me a line.
All the money goes to support student research as part of the Southern Alberta Dinosaur Research Group’s on-going work, and, as such it’ll all be donated to the not-for profit Dinosaur Research Institute that administers these funds.
To see the complete print check out this previous posting.
Early Global Warming Produced New Form of Life
Gigantism in unique biogenic magnetite at the Paleocene–Eocene Thermal Maximum. 2008. Dirk Schumann et al. PNAS published ahead of print October 20, 2008.
From the press release:
Researchers have unearthed crystalline magnetic fossils of a previously unknown species of microorganism that lived at the boundary of the Paleocene and Eocene epochs, some 55 million years ago.
Though they are only some four microns long, these newly discovered, spear-shaped magnetite crystals (magnetofossils) – unearthed at a dig in New Jersey – are up to eight times larger than previously known magnetofossils. Magnetofossils are remnants of magnetite crystals produced by a type of bacteria called magnetotactic bacteria that are capable of orienting themselves along the direction of the Earth's magnetic field.
"Previous reports suggested that the source of the magnetic signature in the boundary layer was a type of magnetite that was formed by the impact of a comet," said lead researcher and corresponding author Dr. Hojatollah Vali. "In our previous paper we proved that the magnetic signature comes from biogenic material.
This species of microorganism, explained Vali, lived during a period of abrupt global warming known as the Paleocene-Eocene Thermal Maximum (PETM), when worldwide temperatures rose by 5° to 6° C over a period of 20,000 years.
From the press release:
Researchers have unearthed crystalline magnetic fossils of a previously unknown species of microorganism that lived at the boundary of the Paleocene and Eocene epochs, some 55 million years ago.
Though they are only some four microns long, these newly discovered, spear-shaped magnetite crystals (magnetofossils) – unearthed at a dig in New Jersey – are up to eight times larger than previously known magnetofossils. Magnetofossils are remnants of magnetite crystals produced by a type of bacteria called magnetotactic bacteria that are capable of orienting themselves along the direction of the Earth's magnetic field.
"Previous reports suggested that the source of the magnetic signature in the boundary layer was a type of magnetite that was formed by the impact of a comet," said lead researcher and corresponding author Dr. Hojatollah Vali. "In our previous paper we proved that the magnetic signature comes from biogenic material.
This species of microorganism, explained Vali, lived during a period of abrupt global warming known as the Paleocene-Eocene Thermal Maximum (PETM), when worldwide temperatures rose by 5° to 6° C over a period of 20,000 years.
Wednesday, October 22, 2008
Epidendrosaurus: Jurassic Feathered Dinosaur
A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers. 2008. F. Zhang et al. Nature 455: 1105-1108.
Epidexipteryx, a new feathered dinosaur from the Jurassic Period, likely used its long tail feathers for display and possibly to help with balance while creeping along tree branches. Credit: Zhao Chuang & Xing Lida.
Abstract: Recent coelurosaurian discoveries have greatly enriched our knowledge of the transition from dinosaurs to birds, but all reported taxa close to this transition are from relatively well known coelurosaurian groups.
Here we report a new basal avialan, Epidexipteryx hui gen. et sp. nov., from the Middle to Late Jurassic of Inner Mongolia, China. This new species is characterized by an unexpected combination of characters seen in several different theropod groups, particularly the Oviraptorosauria. Phylogenetic analysis shows it to be the sister taxon to Epidendrosaurus, forming a new clade at the base of Avialae.
Epidexipteryx also possesses two pairs of elongate ribbon-like tail feathers, and its limbs lack contour feathers for flight. This finding shows that a member of the avialan lineage experimented with integumentary ornamentation as early as the Middle to Late Jurassic, and provides further evidence relating to this aspect of the transition from non-avian theropods to birds.
Epidexipteryx, a new feathered dinosaur from the Jurassic Period, likely used its long tail feathers for display and possibly to help with balance while creeping along tree branches. Credit: Zhao Chuang & Xing Lida.
Here we report a new basal avialan, Epidexipteryx hui gen. et sp. nov., from the Middle to Late Jurassic of Inner Mongolia, China. This new species is characterized by an unexpected combination of characters seen in several different theropod groups, particularly the Oviraptorosauria. Phylogenetic analysis shows it to be the sister taxon to Epidendrosaurus, forming a new clade at the base of Avialae.
Epidexipteryx also possesses two pairs of elongate ribbon-like tail feathers, and its limbs lack contour feathers for flight. This finding shows that a member of the avialan lineage experimented with integumentary ornamentation as early as the Middle to Late Jurassic, and provides further evidence relating to this aspect of the transition from non-avian theropods to birds.
Poached Eggs & Embryo Death in Modern Dinosaurs
Temperature-dependent sex-biased embryo mortality in a bird. 2008. Y. Eiby et al. Proceedings of the Royal Society B 275: 2703-2706.
Here, we investigated the causes of this temperature-dependent sex-biasing system. Molecular sexing of chicks and embryos confirmed that male embryo mortality was greater at high temperatures while female embryo mortality is greater at low temperatures, with mortality in both sexes similar at intermediate incubation temperatures. Temperature-dependent sex-biased embryo mortality represents a novel mechanism of altering sex ratios in birds. This novel mechanism, coupled with the unique breeding biology of the brush-turkey, offers a potentially unparalleled opportunity in which to investigate sex allocation theory in birds.
The idea that extreme temperature changes during the extinction event at the end of the Cretaceous played a role in the demise of the non-avian dinos has been mentioned a number of times over the past 20 years. Here’s some experimental evidence for the effect of temperature on the incubation of eggs from living birds.Abstract: Sex ratios have important evolutionary consequences and are often biased by environmental factors. The effect of developmental temperature on offspring sex ratios has been widely documented across a diverse range of taxa but has rarely been investigated in birds and mammals. However, recent field observations and artificial incubation experiments have demonstrated that the hatching sex ratio of a megapode, the Australian brush-turkey (Alectura lathami), varied with incubation temperature; more females hatched at high incubation temperatures and more males hatched at low temperatures.
Here, we investigated the causes of this temperature-dependent sex-biasing system. Molecular sexing of chicks and embryos confirmed that male embryo mortality was greater at high temperatures while female embryo mortality is greater at low temperatures, with mortality in both sexes similar at intermediate incubation temperatures. Temperature-dependent sex-biased embryo mortality represents a novel mechanism of altering sex ratios in birds. This novel mechanism, coupled with the unique breeding biology of the brush-turkey, offers a potentially unparalleled opportunity in which to investigate sex allocation theory in birds.
Overwintering Polar Dinos
Polar dinosaurs on parade: a review of dinosaur migration. 2008. P. Bell and E. Snively. Alcheringa 32: 271-284.
Certain groups also appear more predisposed to overwintering based on their physical inability (related to biomechanics, natural history, or absolute size) to migrate, such as ankylosaurs and many small taxa, including hypsilophodontids and troodontids. Low-nutrient subsistence is found to be the best overwintering method overall, although the likelihood that other taxa employed alternative means remains plausible. Despite wide distribution of some genera, species-level identification is required to assess the applicability of such distributions to migration distances. Presently, such resolution is not available or contradicts the migration hypothesis.
From the press release:
Bell does not dispute the evidence of migration and points to discoveries of large bone beds as evidence that many dinosaurs also traveled. In order to sustain the herd, "it seemed to make sense that they would be moving to and from the poles," he said.
While this view of migration is feasible for some species of polar dinosaurs, it does not hold for all, Bell noted. "Many types of dinosaurs were surviving in polar latitudes at the time, and getting along quite fine," said Bell. "They were not physically able to remove themselves from the environment for a variety of reasons and had to adapt to the cold, dark winters just as the rest of us mammals do today."
Contrary to popular belief, polar dinosaurs may not have traveled nearly as far as originally thought when making their bi-annual migration.Abstract: Cretaceous polar dinosaur faunas were taxonomically diverse, which suggests varied strategies for coping with the climatic stress of high latitudes. Some polar dinosaurs, particularly larger taxa such as the duckbill Edmontosaurus Lambe, 1917, were biomechanically and energetically capable of migrating over long distances, up to 2600 km. However, current evidence strongly suggests many polar dinosaurs (including sauropods, large and small theropods, and ankylosaurs of New Zealand) overwintered in preference to migration.
Certain groups also appear more predisposed to overwintering based on their physical inability (related to biomechanics, natural history, or absolute size) to migrate, such as ankylosaurs and many small taxa, including hypsilophodontids and troodontids. Low-nutrient subsistence is found to be the best overwintering method overall, although the likelihood that other taxa employed alternative means remains plausible. Despite wide distribution of some genera, species-level identification is required to assess the applicability of such distributions to migration distances. Presently, such resolution is not available or contradicts the migration hypothesis.
From the press release:
Bell does not dispute the evidence of migration and points to discoveries of large bone beds as evidence that many dinosaurs also traveled. In order to sustain the herd, "it seemed to make sense that they would be moving to and from the poles," he said.
While this view of migration is feasible for some species of polar dinosaurs, it does not hold for all, Bell noted. "Many types of dinosaurs were surviving in polar latitudes at the time, and getting along quite fine," said Bell. "They were not physically able to remove themselves from the environment for a variety of reasons and had to adapt to the cold, dark winters just as the rest of us mammals do today."
Monday, October 20, 2008
Dino Dance Floor
A Wet Interdune Dinosaur Trampled Surface in the Jurassic Navajo Sandstone, Coyote Buttes, Arizona: Rare Preservation of Multiple Track Types and Tail Traces. 2008. W. M. Seiler and M. A. Chan. Palaios 23: 700-710.
From the press release:
The three-quarter-acre site – which includes rare dinosaur tail-drag marks – provides more evidence there were wet intervals during the Early Jurassic Period, when the U.S. Southwest was covered with a field of sand dunes larger than the Sahara Desert.
Located within the Vermilion Cliffs National Monument, the site has more than 1,000 and perhaps thousands of dinosaur tracks, averaging a dozen per square yard in places. The tracks once were thought to be potholes formed by erosion. The site is so dense with dinosaur tracks that it reminds geologists of a popular arcade game in which participants dance on illuminated, moving footprints.
Seiler says the range of track shapes and sizes reveals at least four dinosaur species gathered at the watering hole, with the animals ranging from adults to youngsters.
The 6 cm-wide tail-drag marks – which are up to 7 m long – are a special discovery because there are fewer than a dozen dinosaur tail-drag sites worldwide, Seiler says. Four tail drags were within the 10 plots he surveyed, and there are others nearby.
"Dinosaurs usually weren't walking around with their tails dragging," he says.
University of Utah geologists identified an amazing concentration of dinosaur footprints that they call "a dinosaur dance floor," located in a wilderness on the Arizona-Utah border where there was a sandy desert oasis 190 million years ago.
The three-quarter-acre site – which includes rare dinosaur tail-drag marks – provides more evidence there were wet intervals during the Early Jurassic Period, when the U.S. Southwest was covered with a field of sand dunes larger than the Sahara Desert.
Located within the Vermilion Cliffs National Monument, the site has more than 1,000 and perhaps thousands of dinosaur tracks, averaging a dozen per square yard in places. The tracks once were thought to be potholes formed by erosion. The site is so dense with dinosaur tracks that it reminds geologists of a popular arcade game in which participants dance on illuminated, moving footprints.
Seiler says the range of track shapes and sizes reveals at least four dinosaur species gathered at the watering hole, with the animals ranging from adults to youngsters.
The 6 cm-wide tail-drag marks – which are up to 7 m long – are a special discovery because there are fewer than a dozen dinosaur tail-drag sites worldwide, Seiler says. Four tail drags were within the 10 plots he surveyed, and there are others nearby.
"Dinosaurs usually weren't walking around with their tails dragging," he says.
Sunday, October 19, 2008
Volcanic Origin For Life On Earth
The Miller Volcanic Spark Discharge Experiment. 2008. A. P. Johnson et al. Science 322: 404
Challengers of the Unknown © DC ComicsFrom the press release:
The original experiments, performed by Stanley Miller at the University of Chicago in 1953 and 1954 (Miller died in 2007), were the first to demonstrate that the basic molecules of life could be synthesized by subjecting hydrogen-rich gases (such as methane and ammonia) to an electric spark, simulating lightning in the primordial atmosphere. Scientists no longer think that the primordial atmosphere as a whole had the make-up assumed by Miller's experiments, but the clouds of gases emitted during volcanic eruptions do have a hydrogen-rich composition. Volcanic eruptions may have been very common during the planet's hot, early stages.
The apparatus used for Miller's original experiment. Boiled water (1) creates airflow, driving steam and gases through a spark (2). A cooling condenser (3) turns some steam back into liquid water, which drips down into the trap (4), where chemical products also settle. Image: Ned Shaw, Indiana University
"It turns out that some of the experiments Miller performed simulated the steam from volcanic eruptions, in addition to the more famous experiments that simulated a hydrogen-rich atmosphere," says H. James Cleaves, of the Carnegie Institution's Geophysical Laboratory, one of the paper's co-authors and Miller's last graduate student. "And when we analyzed samples left over from these volcanic experiments, they contained the most varied mixture of compounds."
Cleaves points out that lighting is very commonly associated with volcanic clouds, and could have been an abundant source of energy to convert simple compounds into organic molecules.
The apparatus used for Miller's "second," initially unpublished experiment. Boiled water (1) creates airflow, driving steam and gases through a spark (2). A tapering of the glass apparatus (inlay) creates a spigot effect, increasing air flow. A cooling condenser (3) turns some steam back into liquid water, which drips down into the trap (4), where chemical products also settle. Image: Ned Shaw, Indiana University
The building blocks of life may have emerged in volcanic eruptions on the early Earth, according to a new analysis of classic experiments performed more than fifty years ago. Using modern techniques to examine samples from the original experiments, researchers discovered previously undetectable organic compounds that point to the possible contribution of volcanism to the beginning of life on Earth.
Challengers of the Unknown © DC Comics
The original experiments, performed by Stanley Miller at the University of Chicago in 1953 and 1954 (Miller died in 2007), were the first to demonstrate that the basic molecules of life could be synthesized by subjecting hydrogen-rich gases (such as methane and ammonia) to an electric spark, simulating lightning in the primordial atmosphere. Scientists no longer think that the primordial atmosphere as a whole had the make-up assumed by Miller's experiments, but the clouds of gases emitted during volcanic eruptions do have a hydrogen-rich composition. Volcanic eruptions may have been very common during the planet's hot, early stages.
The apparatus used for Miller's original experiment. Boiled water (1) creates airflow, driving steam and gases through a spark (2). A cooling condenser (3) turns some steam back into liquid water, which drips down into the trap (4), where chemical products also settle. Image: Ned Shaw, Indiana University
Cleaves points out that lighting is very commonly associated with volcanic clouds, and could have been an abundant source of energy to convert simple compounds into organic molecules.
The apparatus used for Miller's "second," initially unpublished experiment. Boiled water (1) creates airflow, driving steam and gases through a spark (2). A tapering of the glass apparatus (inlay) creates a spigot effect, increasing air flow. A cooling condenser (3) turns some steam back into liquid water, which drips down into the trap (4), where chemical products also settle. Image: Ned Shaw, Indiana University
Crest Function In Hadrosaurs
Paleontologists have long debated the function of the strange, bony crests on the heads of the duck-billed dinosaurs known as lambeosaurs. The structures contain incredibly long, convoluted nasal passages that loop up over the tops of their skulls.From the press release:
Some paleontologists have suggested that the crests heightened the sense of smell by increasing the surface area of the sensory tissue. Others have argued that they regulated temperature, and still others have speculated that the crests acted as sound resonators for communication.
Scientists at the University of Toronto, Ohio University and Montana State University now have used CT-scanning to look inside these mysterious crests and reconstruct the brains and nasal cavities of four different lambeosaur species. At the annual meeting of the Society for Vertebrate Paleontology in Cleveland, Ohio, the team today announced new findings that suggest the crests were used for communication.
"Even though the soft tissues are not preserved in the fossils, the shape of the bones that encase the brain and nasal passages are," said David Evans. "From there, the anatomy of these missing soft parts is easily interpreted."
The portion of the brain responsible for the sense of smell was relatively small and primitive, indicating that the crest did not evolve to improve that sense.
Computer models done by other researchers suggest that the crests could have been used to make low, eerie bellowing calls that could have been used in communication, perhaps to call for mates or warn others of predators.
The CT scans documented a delicate inner ear that confirms that the dinosaurs could hear the low-frequency calls produced by the crest.
"We were surprised to see just how large the centers of the brain associated with higher cognitive functions were," said Witmer. "We suspected that the crested duck-billed dinosaurs used both vocal and visual displays, but now we see that they had the brain power and hearing to pull off these behaviors."
Wednesday, October 15, 2008
The Skull of Tiktaalik
The cranial endoskeleton of Tiktaalik roseae. 2008. J. Downs et al. Nature 455: 925-929.
Today, the team that discovered Tiktaalik in the Canadian Arctic provided new details of its transition from water to solid ground. Further examination of the fossils shows a coordinated series of changes underway not just in the creature's limbs, but in its crocodile-like skull, neck and gills, all helping prepare it for a less aquatic, shallow-water lifestyle.
The researchers published their results today in the journal Nature and discussed them publicly during a symposium at this morning's meeting of the Society of Vertebrate Paleontology meeting in Cleveland.
Read the full story by John Mangels in the Cleveland Plain Dealer.
Today, the team that discovered Tiktaalik in the Canadian Arctic provided new details of its transition from water to solid ground. Further examination of the fossils shows a coordinated series of changes underway not just in the creature's limbs, but in its crocodile-like skull, neck and gills, all helping prepare it for a less aquatic, shallow-water lifestyle.
The researchers published their results today in the journal Nature and discussed them publicly during a symposium at this morning's meeting of the Society of Vertebrate Paleontology meeting in Cleveland.
Read the full story by John Mangels in the Cleveland Plain Dealer.
The SVP conference is progressing very well. I'll post some photos, etc., when I get a chance.
Today In History: Darwin Accepted Into Cambridge
From Today In Science History:
In 1827, Charles Darwin was accepted
into Christ's College at Cambridge, but did not start until winter term because he needed to catch up on some of his studies. He had entered the University of Edinburgh in 1825 to study medicine, intending to follow his father Robert's career as a doctor. However, Darwin found himself unenthusiastic about his studies, including that of geology.
Disappointing his family that he gave up on a medical career, he left Edinburgh without graduating in April 1827. His scholastic achievements at Cambridge were unremarkable, but after graduation, Darwin was recommended by his botany professor to be a naturalist to sail on HM Sloop Beagle
In 1827, Charles Darwin was accepted
into Christ's College at Cambridge, but did not start until winter term because he needed to catch up on some of his studies. He had entered the University of Edinburgh in 1825 to study medicine, intending to follow his father Robert's career as a doctor. However, Darwin found himself unenthusiastic about his studies, including that of geology. Disappointing his family that he gave up on a medical career, he left Edinburgh without graduating in April 1827. His scholastic achievements at Cambridge were unremarkable, but after graduation, Darwin was recommended by his botany professor to be a naturalist to sail on HM Sloop Beagle
Monday, October 13, 2008
Dinos & The Cretaceous Terrestrial Revolution
Dinosaurs and the Cretaceous Terrestrial Revolution. 2008. G.T. Lloyd et al. Proceedings of the Royal Society B 275: 2483-2490.
Click to enlarge
Abstract: The observed diversity of dinosaurs reached its highest peak during the mid- and Late Cretaceous, the 50Myr that preceded their extinction, and yet this explosion of dinosaur diversity may be explained largely by sampling bias. It has long been debated whether dinosaurs were part of the Cretaceous Terrestrial Revolution (KTR), from 125–80Myr ago, when flowering plants, herbivorous and social insects, squamates, birds and mammals all underwent a rapid expansion.
Although an apparent explosion of dinosaur diversity occurred in the mid-Cretaceous, coinciding with the emergence of new groups (e.g. neoceratopsians, ankylosaurid ankylosaurs, hadrosaurids and pachycephalosaurs), results from the first quantitative study of diversification applied to a new supertree of dinosaurs show that this apparent burst in dinosaurian diversity in the last 18 Myr of the Cretaceous is a sampling artefact. Indeed, major diversification shifts occurred largely in the first one-third of the group's history.
Despite the appearance of new clades of medium to large herbivores and carnivores later in dinosaur history, these new originations do not correspond to significant diversification shifts. Instead, the overall geometry of the Cretaceous part of the dinosaur tree does not depart from the null hypothesis of an equal rates model of lineage branching. Furthermore, we conclude that dinosaurs did not experience a progressive decline at the end of the Cretaceous, nor was their evolution driven directly by the KTR.
Click to enlarge
Although an apparent explosion of dinosaur diversity occurred in the mid-Cretaceous, coinciding with the emergence of new groups (e.g. neoceratopsians, ankylosaurid ankylosaurs, hadrosaurids and pachycephalosaurs), results from the first quantitative study of diversification applied to a new supertree of dinosaurs show that this apparent burst in dinosaurian diversity in the last 18 Myr of the Cretaceous is a sampling artefact. Indeed, major diversification shifts occurred largely in the first one-third of the group's history.
Despite the appearance of new clades of medium to large herbivores and carnivores later in dinosaur history, these new originations do not correspond to significant diversification shifts. Instead, the overall geometry of the Cretaceous part of the dinosaur tree does not depart from the null hypothesis of an equal rates model of lineage branching. Furthermore, we conclude that dinosaurs did not experience a progressive decline at the end of the Cretaceous, nor was their evolution driven directly by the KTR.
Frontal Sinuses and Head-Butting
Frontal sinuses and head-butting in goats: a finite element analysis. 2008. Andrew A. Farke. Journal of Experimental Biology 211: 3085-3094.
Abstract: Frontal sinuses in goats and other mammals have been hypothesized to function as shock absorbers, protecting the brain from blows during intraspecific combat. Furthermore, sinuses are thought to form through removal of `structurally unnecessary' bone. These hypotheses were tested using finite element modeling.
Three-dimensional models of domesticated goat (Capra hircus) skulls were constructed, with variable frontal bone and frontal sinus morphology, and loaded to simulate various head-butting behaviors. In general, models with sinuses experienced higher strain energy values (a proxy for shock absorption) than did models with unvaulted frontal bones, and the latter often had higher magnitudes than models with solid vaulted frontal bones. Furthermore, vaulted frontal bones did not reduce magnitudes of principal strain on the surface of the endocranial cavity relative to models with unvaulted frontal bones under most loading conditions.
Thus, these results were only partially consistent with sinuses, or the bone that walls the sinuses, acting as shock absorbers. It is hypothesized that the keratinous horn sheaths and cranial sutures are probably more important for absorbing blows to the head. Models with sinuses did exhibit a more `efficient' distribution of stresses, as visualized by histograms in which models with solid frontal bones had numerous unloaded elements. This is consistent with the hypothesis that sinuses result at least in part from the removal of mechanically unnecessary bone.
Abstract: Frontal sinuses in goats and other mammals have been hypothesized to function as shock absorbers, protecting the brain from blows during intraspecific combat. Furthermore, sinuses are thought to form through removal of `structurally unnecessary' bone. These hypotheses were tested using finite element modeling.
Three-dimensional models of domesticated goat (Capra hircus) skulls were constructed, with variable frontal bone and frontal sinus morphology, and loaded to simulate various head-butting behaviors. In general, models with sinuses experienced higher strain energy values (a proxy for shock absorption) than did models with unvaulted frontal bones, and the latter often had higher magnitudes than models with solid vaulted frontal bones. Furthermore, vaulted frontal bones did not reduce magnitudes of principal strain on the surface of the endocranial cavity relative to models with unvaulted frontal bones under most loading conditions.
Thus, these results were only partially consistent with sinuses, or the bone that walls the sinuses, acting as shock absorbers. It is hypothesized that the keratinous horn sheaths and cranial sutures are probably more important for absorbing blows to the head. Models with sinuses did exhibit a more `efficient' distribution of stresses, as visualized by histograms in which models with solid frontal bones had numerous unloaded elements. This is consistent with the hypothesis that sinuses result at least in part from the removal of mechanically unnecessary bone.
Science Cafe Tonight In Cleveland
Join Dr. Catherine Badgley (Ecology & Evo. Biology, U. of Michigan) and Dr. Michael Ryan (Cleveland Museum of Natural History) for a lively discussion on palaeo and related topics. If you're in town for the SVP conference come on down for a pre-meeting warm up.
Date: October 13, 2008
Time: Drinks start at 6:30 PM, discussion starts around 7:00 PM
Location: Tasting Room, Great Lakes Brewing Company (2701 Carroll Ave, Cleveland)
What is vertebrate paleontology? Paleontology is the study of ancient life - plants, birds, insects, bacteria, and everything in between. Within paleontology, vertebrate paleontology (a.k.a. VP) focuses on animals with backbones (i.e., vertebrae).
Although dinosaurs garner much of the media attention, VP researchers also study ancient fishes, lizards, mammals, snakes, frogs, and a variety of other groups, many of which have no direct living descendants. And although discovering and naming new species is an important aspect of VP research, many scientists focus on other questions such as how these extinct animals lived and died, what ancient climates and ecosystems were like, and how these animals are related to each other.
Come join some of the leading researchers in vertebrate paleontology - including Dr. Catherine Badgley (President of the Society of Vertebrate Paleontology) and Dr. Michael Ryan - for a discussion of "hot topics" in VP and other issues folks will be discussing at the annual meeting.
Saturday, October 11, 2008
Collective Behavior in an Early Cambrian Arthropod
Collective Behavior in an Early Cambrian Arthropod. 2008. X.-G. Hou et al. Science 322: 224.
A unique set of fossils indicates that 525 million years ago marine animals congregated in Earth’s ancient oceans, most likely for migration, according to an international team of scientists.From the press release
Fossil evidence of collective behaviour is extremely rare. But what makes the find even more intriguing is that it indicates that such behaviour was occurring at the beginning of the ‘Cambrian explosion’ – a major event that saw a vast profusion of complex organisms enter the fossil record for the first time.
'What we see in these fossils are shrimp-like animals with a carapace and segmented body, which are similar to arthropods that we know existed in the Cambrian seas,’ said Derek Siveter. ‘What’s unique about the Yunnan [China] fossil material is that it shows individual specimens closely interlocked to form a chain, of which there are several examples.’
These chains may have formed for reproductive purposes, or they may represent a stage in the animal’s life cycle – if so there are no comparable occurrences in modern arthropods.
The team believes the congregation is more likely to be evidence of migratory activity, possibly associated with animals congregating as a defence against predators.
The fossil was preserved in the Chengjian Lagerstatte, a fossil-rich exceptional preservation deposit discovered in 1984 that has been dated to the Lower Cambrian period, 525 million years ago, making it around 10 million years older than Canada’s famous Burgess Shale.
Fossil evidence of collective behaviour is extremely rare. But what makes the find even more intriguing is that it indicates that such behaviour was occurring at the beginning of the ‘Cambrian explosion’ – a major event that saw a vast profusion of complex organisms enter the fossil record for the first time.
'What we see in these fossils are shrimp-like animals with a carapace and segmented body, which are similar to arthropods that we know existed in the Cambrian seas,’ said Derek Siveter. ‘What’s unique about the Yunnan [China] fossil material is that it shows individual specimens closely interlocked to form a chain, of which there are several examples.’
These chains may have formed for reproductive purposes, or they may represent a stage in the animal’s life cycle – if so there are no comparable occurrences in modern arthropods.
The team believes the congregation is more likely to be evidence of migratory activity, possibly associated with animals congregating as a defence against predators.
The fossil was preserved in the Chengjian Lagerstatte, a fossil-rich exceptional preservation deposit discovered in 1984 that has been dated to the Lower Cambrian period, 525 million years ago, making it around 10 million years older than Canada’s famous Burgess Shale.
Friday, October 10, 2008
Centrosaurus brinkmani Print by Mark Schultz
I did want to mention that the palaeoblog's good friend, Mark Schultz, has generously allowed me to produce a print based on the reconstruction he did for me of Centrosaurus brinkmani. The 12"x18" (approx.) colour print will be signed by Mark and available from me or at the CMNH table next Thursday and Friday for $20. 100% of the proceeds go to fund student field work in Alberta with the Southern Alberta Dinosaur Research Group.
Sauropod Gigantism
Sauropod Gigantism. 2008. Science 322: 200-201.
From National Geographic news:
To outgrow their predators, sauropods didn't just need lots of food. They also needed to develop fast, so they could attain their full size before being eaten, experts said. Sauropod bones show that they did indeed grow swiftly. A 10kg hatchling could become a 100000Kg grown-up in about 20 to 30 years—quick by dinosaur time.
"This tells us that they must have been warm-blooded and had a high metabolic rate compared to cold-blooded creatures," said the University of Bonn's Sander.
So why don't we see gigantic elephants and crocodiles roaming around today? Experts think that reptiles, such as crocodiles, still maintain the egg-laying advantage, but their cold blood prevents them from growing fast enough to reach a great size. Mammals have warm blood, but can't grow as big as sauropods due to their slow reproductive strategy and the need to chew their food.
From National Geographic news:
To outgrow their predators, sauropods didn't just need lots of food. They also needed to develop fast, so they could attain their full size before being eaten, experts said. Sauropod bones show that they did indeed grow swiftly. A 10kg hatchling could become a 100000Kg grown-up in about 20 to 30 years—quick by dinosaur time.
"This tells us that they must have been warm-blooded and had a high metabolic rate compared to cold-blooded creatures," said the University of Bonn's Sander.
So why don't we see gigantic elephants and crocodiles roaming around today? Experts think that reptiles, such as crocodiles, still maintain the egg-laying advantage, but their cold blood prevents them from growing fast enough to reach a great size. Mammals have warm blood, but can't grow as big as sauropods due to their slow reproductive strategy and the need to chew their food.
The Origin of Teeth
Dual epithelial origin of vertebrate oral teeth. 2008. V. Soukup et al. Nature 455: 795-798.
Abstract: The oral cavity of vertebrates is generally thought to arise as an ectodermal invagination. Consistent with this, oral teeth are proposed to arise exclusively from ectoderm, contributing to tooth enamel epithelium, and from neural crest derived mesenchyme, contributing to dentin and pulp. Yet in many vertebrate groups, teeth are not restricted only to the oral cavity, but extend posteriorly as pharyngeal teeth that could be derived either directly from the endodermal epithelium, or from the ectodermal epithelium that reached this location through the mouth or through the pharyngeal slits. However, when the oropharyngeal membrane, which forms a sharp ecto/endodermal border, is broken, the fate of these cells is poorly known.
Here, using transgenic axolotls with a combination of fate-mapping approaches, we present reliable evidence of oral teeth derived from both the ectoderm and endoderm and, moreover, demonstrate teeth with a mixed ecto/endodermal origin. Despite the enamel epithelia having a different embryonic source, oral teeth in the axolotl display striking developmental uniformities and are otherwise identical. This suggests a dominant role for the neural crest mesenchyme over epithelia in tooth initiation and, from an evolutionary point of view, that an essential factor in teeth evolution was the odontogenic capacity of neural crest cells, regardless of possible 'outside-in'or 'inside-out' influx of the epithelium.
Watch the video showing a stack of optic deconvoluted layers through 20 m thick cryostat section from an embryo after receiving both GFP ECT graft and DiI END injection.
Abstract: The oral cavity of vertebrates is generally thought to arise as an ectodermal invagination. Consistent with this, oral teeth are proposed to arise exclusively from ectoderm, contributing to tooth enamel epithelium, and from neural crest derived mesenchyme, contributing to dentin and pulp. Yet in many vertebrate groups, teeth are not restricted only to the oral cavity, but extend posteriorly as pharyngeal teeth that could be derived either directly from the endodermal epithelium, or from the ectodermal epithelium that reached this location through the mouth or through the pharyngeal slits. However, when the oropharyngeal membrane, which forms a sharp ecto/endodermal border, is broken, the fate of these cells is poorly known.
Here, using transgenic axolotls with a combination of fate-mapping approaches, we present reliable evidence of oral teeth derived from both the ectoderm and endoderm and, moreover, demonstrate teeth with a mixed ecto/endodermal origin. Despite the enamel epithelia having a different embryonic source, oral teeth in the axolotl display striking developmental uniformities and are otherwise identical. This suggests a dominant role for the neural crest mesenchyme over epithelia in tooth initiation and, from an evolutionary point of view, that an essential factor in teeth evolution was the odontogenic capacity of neural crest cells, regardless of possible 'outside-in'or 'inside-out' influx of the epithelium.
Watch the video showing a stack of optic deconvoluted layers through 20 m thick cryostat section from an embryo after receiving both GFP ECT graft and DiI END injection.
Thursday, October 09, 2008
Surviving the Permian-Triassic Extinction
Anomalously diverse Early Triassic ichnofossil assemblages in northwest Pangea: A case for a shallow-marine habitable zone. 2008. T.W. Beatty et al. Geology 36.
From Science Daily News:
Scientists have solved part of the mystery of where marine organisms that recovered from the biggest extinction on earth were housed. A team of researchers discovered that the shorelines of ancient Canada provided a refuge for marine organisms that escaped annihilation during the Permian-Triassic extinction event.
During the Permian, all the world's land masses joined together into a single supercontinent called Pangea. Near the end of the Permian, during the mass extinction, about 95 per cent of all marine species and 70 per cent of land species died and the recovery of life on Earth took longer than other extinction events because so much biodiversity was lost. There are several theories as to why this mass extinction event took place ranging from the heating of the Earth to a catastrophic event. The authors favour major climate change since increased temperatures and elevated CO2 levels are linked to oxygen stress that is key to the results of their research.
Researchers have been studying the Permian-Triassic extinction event for years, but mostly in Greenland and south China where formations represent areas of deep water and have very low levels of oxygen. The research team studied trace fossils along the ancient shorelines found in rock located in western Alberta, northeast British Columbia, and the barren landscapes of the Canadian Arctic. Trace fossils preserve the activity of organisms and can be burrows or other actions created by the ancestors of modern worms and marine arthropods. The dating of these shorelines is confirmed by the presence of distinct conodonts – a microfossil in which the passing of time is recorded by rapid evolutionary changes.
"These trace fossils present a record of ocean-bottom dwelling organisms and indicate locally well-oxygenated conditions in an ocean otherwise characterized by widespread anoxia," says Beatty - the lead author. "Within this habitable zone, the latest Permian extinction levels are reduced and the recovery time is minimized. The findings support the idea that reduced oxygen levels is a major cause of why the recovery from Earth's greatest extinction was delayed."
From Science Daily News:
Scientists have solved part of the mystery of where marine organisms that recovered from the biggest extinction on earth were housed. A team of researchers discovered that the shorelines of ancient Canada provided a refuge for marine organisms that escaped annihilation during the Permian-Triassic extinction event.
During the Permian, all the world's land masses joined together into a single supercontinent called Pangea. Near the end of the Permian, during the mass extinction, about 95 per cent of all marine species and 70 per cent of land species died and the recovery of life on Earth took longer than other extinction events because so much biodiversity was lost. There are several theories as to why this mass extinction event took place ranging from the heating of the Earth to a catastrophic event. The authors favour major climate change since increased temperatures and elevated CO2 levels are linked to oxygen stress that is key to the results of their research.
Researchers have been studying the Permian-Triassic extinction event for years, but mostly in Greenland and south China where formations represent areas of deep water and have very low levels of oxygen. The research team studied trace fossils along the ancient shorelines found in rock located in western Alberta, northeast British Columbia, and the barren landscapes of the Canadian Arctic. Trace fossils preserve the activity of organisms and can be burrows or other actions created by the ancestors of modern worms and marine arthropods. The dating of these shorelines is confirmed by the presence of distinct conodonts – a microfossil in which the passing of time is recorded by rapid evolutionary changes.
"These trace fossils present a record of ocean-bottom dwelling organisms and indicate locally well-oxygenated conditions in an ocean otherwise characterized by widespread anoxia," says Beatty - the lead author. "Within this habitable zone, the latest Permian extinction levels are reduced and the recovery time is minimized. The findings support the idea that reduced oxygen levels is a major cause of why the recovery from Earth's greatest extinction was delayed."
Nine Bowls of Ichthyosaur Soup
From a "They Might Be Giants" podcast comes the video for one of the songs from their 1st(?) kids LP.
Wednesday, October 08, 2008
The Colour Of Evolution
Speciation through sensory drive in cichlid fish. 2008. O. Seehausen et al. Nature 455: 620-626.
Click To Enlarge
From the press release:
A group of colorful fishes in Africa's Lake Victoria have been the focus of scientific efforts to unravel how new species form. This lake contains more than 500 species of cichlids, which play a leading role because of their rapid speciation and remarkable diversity.
Now a new study suggests that species of Lake Victorian cichlids became new species after changes in how they see led to changes in the mates that they selected. The group say that the phenomenon provides evidence that differences in sensory perception contribute to the development of new species.
For many years, scientists have linked evolution to the environment and suggested that new species arise when populations become geographically isolated from one another, thus forcing them to adapt differently. The idea that organisms living right next to each other can separate into two new species has been proposed, but difficult to prove.
The waters of Lake Victoria, which borders Uganda, Kenya, and Tanzania, are murky and red light penetrates deeper than blue light. In the shallow waters, the male fish tend to be green to blue, and in the deeper waters, the male fish are marked by a brilliant red. "These fish specialized to different microhabitats," Carleton explains, "which in this case is different depths. The visual system then specialized to the light environment at these depths and the mating colors shifted to match. Once this happened, these two groups no longer interbred and so became new species."
Previous research had identified long and short wavelength sensitive variants in one of the genes responsible for tuning the fish's vision to different depths. For this new study, the researchers sequenced hundreds of fish captured in the wild and showed that these visual variants segregate with depth and male color, supporting the idea that these fish have specialized to inhabit these micro niches.
Click To Enlarge
From the press release:
A group of colorful fishes in Africa's Lake Victoria have been the focus of scientific efforts to unravel how new species form. This lake contains more than 500 species of cichlids, which play a leading role because of their rapid speciation and remarkable diversity.
Now a new study suggests that species of Lake Victorian cichlids became new species after changes in how they see led to changes in the mates that they selected. The group say that the phenomenon provides evidence that differences in sensory perception contribute to the development of new species.
For many years, scientists have linked evolution to the environment and suggested that new species arise when populations become geographically isolated from one another, thus forcing them to adapt differently. The idea that organisms living right next to each other can separate into two new species has been proposed, but difficult to prove.
The waters of Lake Victoria, which borders Uganda, Kenya, and Tanzania, are murky and red light penetrates deeper than blue light. In the shallow waters, the male fish tend to be green to blue, and in the deeper waters, the male fish are marked by a brilliant red. "These fish specialized to different microhabitats," Carleton explains, "which in this case is different depths. The visual system then specialized to the light environment at these depths and the mating colors shifted to match. Once this happened, these two groups no longer interbred and so became new species."
Previous research had identified long and short wavelength sensitive variants in one of the genes responsible for tuning the fish's vision to different depths. For this new study, the researchers sequenced hundreds of fish captured in the wild and showed that these visual variants segregate with depth and male color, supporting the idea that these fish have specialized to inhabit these micro niches.
Fun In The Currie Lab
When potential graduate students ask me about places to study I always suggest that they talk to the graduate students of the advisors they might like to work for to get a better understanding of what they're in for. One of Phil Currie’s grad students, Miriam Reichel, put together this little video of some fun moments with all the students in the Currie lab, and gave me permission to post it here. Watch and learn. Enjoy!
Albertonykus borealis
One of the many stories I missed while I was away was the announcement of Albertonykus by Nick Longrich and Phil Currie. The link will take you to the National Geographic story.
Extinction By Asteroid A Rarity
Evidence suggests that 'sick Earth' extinctions more likely
Asteroids are the prime suspect only in the most recent of five mass extinctions, said USC earth scientist David Bottjer. The cataclysm 65 million years ago wiped out the dinosaurs.
"The other four have not been resolvable to a rock falling out of the sky," Bottjer said.
For example, Bottjer and many others have published studies suggesting that the end-Permian extinction 250 million years ago happened in essence because "the earth got sick." The latest research from Bottjer's group suggests a similar slow dying during the extinction 200 million years ago at the boundary of the Triassic and Jurassic eras.
At the 2008 Joint Annual Meeting of the Geological Society of America, USC doctoral student Sarah Greene drew similarities between ocean conditions at the Triassic-Jurassic boundary and after the end-Permian extinction. At both those times, bouquet-like structures of aragonite crystals formed on the ocean floor. Such structures are extremely rare in Earth's history, Greene said.
"The fact that these deposits have only been found at these two specific times that are associated with mass extinction suggests at the very least that maybe there's some shared ocean geochemistry … that could be related to the cause of the extinctions," Greene said.
"The Triassic-Jurassic extinction cause is totally up for grabs at the moment," she added.
Also at the meeting, USC doctoral student Rowan Martindale presented results from her studies of coral reefs during the Triassic-Jurassic extinction.
"The coral reefs look actually very similar to modern coral reefs," she said. "At the end-Triassic mass extinction, you lose all your reef systems. And nobody's figured out why that is."
Martindale identified two distinct types of ancient reefs: one dominated by coral and another consisting mainly of mud and debris, possibly held together by bacteria. A theory for the end-Triassic extinction needs to explain how both types of reefs could have been killed off, Martindale said.
The Joint Annual Meeting was held Oct. 5-9 in Houston. It was the first joint meeting of the Geological Society of America, the Soil Science Society of America, the American Society of Agronomy, the Crop Science Society of America and the Gulf Coast Association of Geological Societies.
Tuesday, October 07, 2008
Robots + Pterosaurs = Pterodrone
From the GSA press release:
Paleontologist Sankar Chatterjee of Texas Tech University, aeronautical engineer Rick Lind of the University of Florida, and their students, Andy Gedeon and Brian Roberts, have reached back in time 115 million years to one of the most successful flying creatures in Earth’s history, the pterodactyl, to conjure a robotic spy plane with next-generation capabilities.
Mimicking the physical and biological characteristics of the Early Cretaceous Brazilian pterosaur Tapejara wellnhoferi — skin, blood vessels, muscles, tendons, nerves, cranial plate, skeletal structure, and more — the scientists are working to develop a Pterodrone — an unmanned aerial vehicle that not only flies but also walks and sails just like the original.
"The next generation of airborne drones won’t just be small and silent," says the multidisciplinary group, "they’ll alter their wing shapes using morphing techniques to squeeze through confined spaces, dive between buildings, zoom under overpasses, land on apartment balconies, or sail along the coastline."
The talk on Tuesday, 7 October, at the 2008 Joint Meeting of the Geological Society of America, Soil Science Society of America-American Society of Agronomy-Crop Science Society of America, and Gulf Coast Association of Geological Societies, in Houston, Texas, will provide illustrations of both the Tapejara and the proposed Pterodrone, with details on the richly improved ability of the robotic spy plane to gather data from sights, sounds, and smells in a variety of environments.
Monday, October 06, 2008
Died This Day: George Gaylord Simpson
June 16, 1902 - October 6, 1984
From Today In Science History:
Simpson is known for his contributions to evolutionary theory and to the understanding of intercontinental migrations of animal species in past geological times. Simpson specialized in early fossil mammals, leading expeditions on four continents and discovering in 1953 the 50-million-year old fossil skulls of dawn horses in Colorado.
Simpson helped develop the modern biological theory of evolution, drawing on paleontology, genetics, ecology, and natural selection to show that evolution occurs as a result of natural selection operating in response to shifting environmental conditions. He spent most of his career as a paleontologist at the American Museum of Natural History. image.
From Today In Science History:
Simpson is known for his contributions to evolutionary theory and to the understanding of intercontinental migrations of animal species in past geological times. Simpson specialized in early fossil mammals, leading expeditions on four continents and discovering in 1953 the 50-million-year old fossil skulls of dawn horses in Colorado.Simpson helped develop the modern biological theory of evolution, drawing on paleontology, genetics, ecology, and natural selection to show that evolution occurs as a result of natural selection operating in response to shifting environmental conditions. He spent most of his career as a paleontologist at the American Museum of Natural History. image.
Saturday, October 04, 2008
New Argentinean Theropod, Aerosteon riocoloradensis
Evidence for Avian Intrathoracic Air Sacs in a New Predatory Dinosaur from Argentina. 2008. P.C. Sereno, et al. PLoS ONE 3(9):e3303.
In addition to describing the new theropod, Aerosteon riocoloradensis, The authors present a four-phase model for the evolution of avian air sacs and costosternal-driven lung ventilation based on the known fossil record of theropod dinosaurs and osteological correlates in extant birds:
(1) Phase I—Elaboration of paraxial cervical air sacs in basal theropods no later than the earliest Late Triassic.
(2) Phase II—Differentiation of avian ventilatory air sacs, including both cranial (clavicular air sac) and caudal (abdominal air sac) divisions, in basal tetanurans during the Jurassic. A heterogeneous respiratory tract with compliant air sacs, in turn, suggests the presence of rigid, dorsally attached lungs with flow-through ventilation.
(3) Phase III—Evolution of a primitive costosternal pump in maniraptoriform theropods before the close of the Jurassic.
(4) Phase IV—Evolution of an advanced costosternal pump in maniraptoran theropods before the close of the Jurassic.
In addition, they conclude:
(5) The advent of avian unidirectional lung ventilation is not possible to pinpoint, as osteological correlates have yet to be identified for uni- or bidirectional lung ventilation.
(6) The origin and evolution of avian air sacs may have been driven by one or more of the following three factors: flow-through lung ventilation, locomotory balance, and/or thermal regulation.
In addition to describing the new theropod, Aerosteon riocoloradensis, The authors present a four-phase model for the evolution of avian air sacs and costosternal-driven lung ventilation based on the known fossil record of theropod dinosaurs and osteological correlates in extant birds:
(1) Phase I—Elaboration of paraxial cervical air sacs in basal theropods no later than the earliest Late Triassic.
(2) Phase II—Differentiation of avian ventilatory air sacs, including both cranial (clavicular air sac) and caudal (abdominal air sac) divisions, in basal tetanurans during the Jurassic. A heterogeneous respiratory tract with compliant air sacs, in turn, suggests the presence of rigid, dorsally attached lungs with flow-through ventilation.
(3) Phase III—Evolution of a primitive costosternal pump in maniraptoriform theropods before the close of the Jurassic.
(4) Phase IV—Evolution of an advanced costosternal pump in maniraptoran theropods before the close of the Jurassic.
In addition, they conclude:
(5) The advent of avian unidirectional lung ventilation is not possible to pinpoint, as osteological correlates have yet to be identified for uni- or bidirectional lung ventilation.
(6) The origin and evolution of avian air sacs may have been driven by one or more of the following three factors: flow-through lung ventilation, locomotory balance, and/or thermal regulation.
Gene Expression In Alligators Suggests Birds Have 'Thumbs'
The Evolution of HoxD-11 Expression in the Bird Wing: Insights from Alligator mississippiensis. 2008. A.O. Vargas, et al. PLoS ONE 3(10):e3325.
From the press release:
Bird wings only have three fingers, having evolved from remote ancestors that, like humans and most reptiles, had five fingers. Biologists have typically used embryology to identify the evolutionary origin (homology) of structures; the three fingers of the bird wing develop from cartilage condensations that are found in the same positions in the embryo as fingers two, three and four of humans (the index, middle and ring fingers). However, the morphology of the fingers of early birds such as Archaeopteryx corresponds to that of fingers one, two and three in other reptiles (thumb, index and middle finger). The fossil record clearly shows that fingers four and five (ring and pinky finger) were lost and reduced in the dinosaur ancestors of birds.
Further, the lack of expression of the HoxD-11 gene in the first finger of the wing makes it most similar to finger one (the "thumb") of the mouse, consistent with comparative morphology. However, the mouse is only distantly related to birds; crocodilians, in turn, are bird's closest living relatives.
To see whether the evidence from mouse HoxD-11 expression held up, Vargas and colleagues have examined the expression of this gene in alligators; they found the expression to be, as in mice, absent only in finger one (the "thumb").
Developmental and evolutionary biologists are familiar with the phenomenon of homeotic transformations, in which one structure begins to develop at a different position within the body. A famous example is the case of the fruit fly mutant antennapaedia, which develops legs on its head instead of antennae. The new work by Vargas et al. rekindles the hypothesis that a "hometic frameshift" occurred in the evolution of the bird wing, such that fingers one, two and three began to develop from the embryological positions of fingers two, three and four.
From the press release:
Bird wings only have three fingers, having evolved from remote ancestors that, like humans and most reptiles, had five fingers. Biologists have typically used embryology to identify the evolutionary origin (homology) of structures; the three fingers of the bird wing develop from cartilage condensations that are found in the same positions in the embryo as fingers two, three and four of humans (the index, middle and ring fingers). However, the morphology of the fingers of early birds such as Archaeopteryx corresponds to that of fingers one, two and three in other reptiles (thumb, index and middle finger). The fossil record clearly shows that fingers four and five (ring and pinky finger) were lost and reduced in the dinosaur ancestors of birds.
Further, the lack of expression of the HoxD-11 gene in the first finger of the wing makes it most similar to finger one (the "thumb") of the mouse, consistent with comparative morphology. However, the mouse is only distantly related to birds; crocodilians, in turn, are bird's closest living relatives.
To see whether the evidence from mouse HoxD-11 expression held up, Vargas and colleagues have examined the expression of this gene in alligators; they found the expression to be, as in mice, absent only in finger one (the "thumb").
Developmental and evolutionary biologists are familiar with the phenomenon of homeotic transformations, in which one structure begins to develop at a different position within the body. A famous example is the case of the fruit fly mutant antennapaedia, which develops legs on its head instead of antennae. The new work by Vargas et al. rekindles the hypothesis that a "hometic frameshift" occurred in the evolution of the bird wing, such that fingers one, two and three began to develop from the embryological positions of fingers two, three and four.
Friday, October 03, 2008
Pachyrhinosaurus Endocast PDF from Larry Witmer
"In association with the publication of the NRC Canada monograph on the new species of Pachyrhinosaurus, P. lakustai (announced last night), I've put up a website providing a range of supplementary information pertaining to the braincase, cranial endocast, and inner ear.
The website provides (1) a link to the NRC page that announces and provides purchasing information for the monograph, (2) an authorized PDF of the Witmer & Ridgely paper, (3) a PDF of higher-resolution versions of the figures, (4) a single "super-PDF" file comprising items 2 & 3 plus a 3D PDF (more on 3D PDFs below), (5) a link to a Movies page with QuickTime animations and CT-slice movies, and (6) a link to a 3D PDF.
3D PDFs provide a means of letting anyone with Adobe Acrobat (including the free Reader) interactively manipulate the 3D models generated by our high-powered (and pricey) software. For example, they allow you to spin and resize things, make braincases transparent, turn on and off individual anatomical parts, etc. We provide 3D PDFs in three files sizes for users with varying interests, computer horsepower, and connection speeds."
Wednesday, October 01, 2008
New Pachyrhinosaurus Monongraph Out Now
A New Horned Dinosaur from an Upper Cretaceous Bone Bed in Alberta by Philip Currie, Wann Langston, Jr., and Darren Tanke should be out now from the National Research Council Press in Canada. More than 25 years(!) in the making it has a cover painting by Mike Skrepnick, and will soon be one of the most important documents on ceratopsid anatomy every published.
If you're in Grande Prairie tonight go to Phil Currie's talk at 7:30pm in the GPRC Theatre and celebrate the latest addition to the ranks of Canada's most important group of dinosaurs. The new taxon name will also be revealed.
More Gobi Photos
OK, I'm back from the gobi but not quite back in my office. Here are a few photos to tie you over until the blog starts back up in ernest next week:
U of A grad student, Phil Bell, prospects in Khermeen Tsav close to our 2007 camp site, and one of the better spots to find Gobiteryx eggs.
Glorious Leader, Yueng-nam Lee (center) with Dr. Nam-Soo Kim and the MBC documentary director, Mrs. Lee, confer over how to best collect a nest of hadrosaur eggs.
U of A grad student, Robin Sissons is blown away by an old quarry at Nemegt. This day was sunny and warm, unlike the previous day that where it rained and was freezing cold...
Phil Currie cooks up dinner in the rain at Nemegt....
... after dinner we huddled around our camp fire in the rain trying to get warm. That's Eva Kopplehus, PC, and Robin from left to right.
Lou Jacobs celebrates his 60th birthday in the gobi - an excellent excuse for a party!
Robin pieces togather a protoceratopsian.
U of A grad student, Phil Bell, prospects in Khermeen Tsav close to our 2007 camp site, and one of the better spots to find Gobiteryx eggs.
Glorious Leader, Yueng-nam Lee (center) with Dr. Nam-Soo Kim and the MBC documentary director, Mrs. Lee, confer over how to best collect a nest of hadrosaur eggs.
U of A grad student, Robin Sissons is blown away by an old quarry at Nemegt. This day was sunny and warm, unlike the previous day that where it rained and was freezing cold...
Phil Currie cooks up dinner in the rain at Nemegt....
... after dinner we huddled around our camp fire in the rain trying to get warm. That's Eva Kopplehus, PC, and Robin from left to right.
Lou Jacobs celebrates his 60th birthday in the gobi - an excellent excuse for a party!
Robin pieces togather a protoceratopsian.
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