Reconciling The Divergence of Placental Mammals

Robust Time Estimation Reconciles Views of the Antiquity of Placental Mammals. 2007. Kitazoe Y., et al., PLoS ONE 2(4): e384.

From the press release:

Despite great progress over the past decade, the evolutionary history of placental mammals remains controversial. While a consensus is emerging on the topology of the evolutionary tree, although with occasional disagreement, divergence times remain uncertain. Both paleontological and morphological studies suggest that the radiation of placental orders and super orders occurred close to the Cretaceous–Tertiary (K–T) boundary about 65 million years ago (mya). In contrast, molecular studies have suggested markedly older origins for many superordinal groups and that some extant orders diversified before the K–T boundary.

Example of placental mammals

However, this discrepancy may not be real, but rather appear because of the violation of implicit assumptions in the estimation procedures, such as abrupt acceleration of evolutionary rate entangled with gradual variation and large-scale convergent evolution in molecular level.

Researchers have identified a strong and short-term acceleration of mitochondrial genome along the lineage leading to Laurasiatheria. The revised time at the root of placental mammals was much younger than the preceding reports, 84 million years ago instead of around 122 million years ago. As a result, the estimated distribution of molecular divergence times is broadly consistent with quantitative analysis of the North American fossil record and traditional morphological views. They emphasize the necessity to scrutinize the implicit assumptions adopted by the models of molecular evolution and to develop procedures which rely little on those assumptions.

CLICK TO ENLARGE

Figure: Molecular divergence times and evolutionary rates of placental mammals.A and B show the MVS-FIR and ML-FLOG trees, respectively. The numbers 1–61 denote the ancestral nodes. The red numbers 1–8 indicate the internal nodes with fossil constraints which are as follows: 1, 49–61; 2, 52–58; 3, 45–63; 4, 43–60; 5, <63;>12; 7, 36–55; 8, 54–65 (all in mya) [see 4], [15]. The colors of the branches denote inferred evolutionary rates (in units of ×10−9/site per year) as follows: black, <0.2;>0.7.

CT Scanning

When I was in Alberta last month Eric Snively and I had some CT scanning done at Canada Diagnostics in Calgary. Hopefully we'll have the research completed to present at SVP this year.

Yes, Eric was on crutches at that time.

Earth's Earliest Forest

Giant cladoxylopsid trees resolve the enigma of the Earth's earliest forest stumps at Gilboa. 2007. W. E. Stein, et al. Nature 446: 904-907.

Abstract [edit]: Late Middle Devonian fossil tree stumps, rooted and still in life position, discovered in the 1870s from Gilboa, New York, and later named Eospermatopteris, are widely cited as evidence of the Earth's 'oldest forest.

Here we report spectacular specimens from Schoharie County, New York, showing an intact crown belonging to the cladoxylopsid Wattieza (Pseudosporochnales) and its attachment to Eospermatopteris trunk and base.

This e<vidence allows the reconstruction of a tall (at least 8 m; right), tree-fern-like plant with a trunk bearing large branches in longitudinal ranks. The branches were probably abscised as frond-like modules. Lower portions of the trunk show longitudinal carbonaceous strands typical of Eospermatopteris, and a flat bottom with many small anchoring roots.

The tree-fern-like morphology described here is the oldest example so far of an evolutionarily recurrent arborescent body plan within vascular plants. Given their modular construction, these plants probably produced abundant litter, indicating the potential for significant terrestrial carbon accumulation and a detritus-based arthropod fauna by the Middle Devonian period.

Alice In Sunderland

Bryan Talbot's new book ALICE IN SUNDERLAND (Talbot’s Alice webpage), deals “with the themes of storytelling, history and myth in a form I’ve been describing as a "dream documentary". It is not one story but literally dozens, short and long, the central spines being the history of Sunderland and the story of Lewis Carroll and Alice Liddell (the “real” Alice), both of whom had connections with the city and surrounding area. For example Jabberwocky, the most famous nonsense poem in the English language, was written here.”

This page is an aside talking about the pre-history of the region in England's north-east.

Thanks to the Kirby Weblog for the heads up.

Australopithecus With Gorilla-Like Jaw

Gorilla-like anatomy on Australopithecus afarensis mandibles suggests Au. afarensis link to robust australopiths. 2007. Y. Rak, A. Ginzburg, and E. Geffen. PNAS 104: 6568-6572.

Juvenile Australopithecus afarensis specimen, A. L. 333-43b (left), and Au. robustus specimen SK 34. Note the similarity in the size and shape of the coronoid process and the mandibular notch.

Abstract: Mandibular ramus morphology on a recently discovered specimen of Australopithecus afarensis closely matches that of gorillas. This finding was unexpected given that chimpanzees are the closest living relatives of humans.

Because modern humans, chimpanzees, orangutans, and many other primates share a ramal morphology that differs from that of gorillas, the gorilla anatomy must represent a unique condition, and its appearance in fossil hominins must represent an independently derived morphology. This particular morphology appears also in Australopithecus robustus.

The presence of the morphology in both the latter and Au. afarensis and its absence in modern humans cast doubt on the role of Au. afarensis as a modern human ancestor. The ramal anatomy of the earlier Ardipithecus ramidus is virtually that of a chimpanzee, corroborating the proposed phylogenetic scenario.

Hamadasuchus rebouli from the Cretaceous of Morocco

Some papers from the latest Zoological Journal of the Linnean Society:

Cranial osteology and phylogenetic relationships of Hamadasuchus rebouli (Crocodyliformes: Mesoeucrocodylia) from the Cretaceous of Morocco. 2007. HANS C. E. LARSSON and HANS-DIETER. Zoological Journal of the Linnean Society 149: 533

Abstract: This paper presents a detailed description of the skull and part of the mandible of the crocodyliform reptile Hamadasuchus rebouli from the Kem Kem beds (Upper Cretaceous: Albian–Cenomanian) of south-eastern Morocco. This taxon of deep-snouted ziphodont crocodyliform can be diagnosed by a number of autapomorphies. Phylogenetic analysis of a diverse array of crocodylomorph taxa found strong support for a clade comprising H. rebouli, Peirosauridae, and Sebecus.

The name Sebecia nom. nov. is proposed for this grouping, which is diagnosed by numerous characters, including the participation of the quadratojugal in the mandibular condyle. The distribution of this diverse and long-lived clade lends further support to the biogeographical hypothesis that faunal connections existed between Africa and South America well into mid-Cretaceous times.

Manual Morphology of Compsognathus longipes

On the manual morphology of Compsognathus longipes and its bearing on the diagnosis of Compsognathidae. 2007. ALAN D. GISHLICK and JACQUES A. GAUTHIER. Zoological Journal of the Linnean Society 149: 569–581.

Abstract: Compsognathus longipes sits at an important point in theropod evolution at the base of Coelurosauria. Despite its relative completeness and oft-cited morphology, however, the manual morphology has been unclear. This work provides the first detailed study of the morphology of the manus of Compsognathus longipes.

It shows that Compsognathus longipes had two fully formed functional digits as well as a reduced, perhaps even non-functional, third digit. That conclusion runs counter to the usual interpretation that Compsognathus longipes had only two phalanges, rather than the expected complement of three, in digit II.

This work also identifies a unique suite of metacarpal I morphologies that are used to diagnose a subclade among species often referred to as ‘Compsognathidae’. These features are used to construct an apomorphy-based definition of a new clade name: Compsognathidae.

And a nice article on mosasaur teeth:

Ontogeny, anatomy and attachment of the dentition in mosasaurs (Mosasauridae: Squamata). 2007. M. W. CALDWELL. Zoological Journal of the Linnean Society 149: 687–700.

Early Amphibians Had A Big Bite

Terrestrial-style feeding in a very early aquatic tetrapod is supported by evidence from experimental analysis of suture morphology. M.J. Markey and C.R. Marshall. PNAS, Published online before print April 16, 2007.

Acanthostega. Photo by Jonathan Blair/NGS

Abstract [edit]: There is no consensus on when in the fish-tetrapod transition suction feeding, the primary method of prey capture in the aquatic realm, evolved into the direct biting on prey typical of terrestrial animals.

Here, we show that differences in the morphology of selected cranial sutures between species that span the fish-tetrapod transition (the Devonian osteolepiform fish Eusthenopteron, the aquatic Devonian tetrapod Acanthostega, and the Permian terrestrial tetrapod Phonerpeton) can be used to infer when terrestrial feeding first appeared.

Using this procedure, we find that the suture morphologies of Acanthostega are inconsistent with the hypothesis that it captured prey primarily by means of suction, which suggests that it may have bitten directly on prey at or near the water's edge.

Thus, our data strongly support the hypothesis that the terrestrial mode of feeding first emerged in aquatic taxa.

Read the press release at Nat. Geo. News.

New 42 Million Year Old Omomyid Primate Discovered

From the press release:

Jim Westgate (Lamar U.) and colleagues. announced their discovery at the annual meeting of the American Association of Physical Anthropologists in Philadelphia, Pa., March 29, 2007.

Molar, pre-molar and incisor teeth from a new omomyid primate genus and three other new primate species were recovered from 42 million-year-old tropical, mangrove palm swamp deposits of the Eocene age Laredo Formation exposed in Lake Casa Blanca International State Park in Laredo.

The association of primate fossils with the skeletal remains of oysters, sharks, rays, giant aquatic snakes and crocodiles, along with mangrove palm fruits and pollen, indicates that the middle Eocene shoreline of the Gulf of Mexico lay 150 miles inland of its present position, Westgate said.

Omomyids lived 34 to 50 million years ago during the Eocene Epoch and were one of two groups of known Eocene primates. The other, adapids, were more lemur-like. Fossils of these Eocene primates have been found in North America, Europe, Asia, and Africa. The Eocene primates are the earliest known primates.

Monstersaurus

From the twisted mind of Pete Von Sholly comes these 'Horrora All-Plastic Assembly Kit' boxes. Yup, just like the old Aurora box kits, you really can buy these and other cool boxes from Morbid Monster.com. No actual plastic kit is included, alas!

Croatian Sauropod Track Controversay

Dinosaur prints lead to crediting row. 2007. R. Dalton. Nature 446:708.

Mike Caldwell of the U of Alberta is at the center of controversy over a series of sauropod tracks that he and colleagues from the Croatian Natural History Museum in Zagreb discovered in 2004 on the island of Hvar.

“But before the researchers could publish their study in the scientific literature, a competing group from the University of Zagreb went to the site and then published an article reporting the tracks. The article did not credit the discovery team, and an angry Caldwell has demanded its retraction. The disputed article was published last December in the journal Cretaceous Research (The first record of dinosaurs in the Dalmatian part (Croatia) of the Adriatic-Dinaric carbonate platform (ADCP). 2006. A. Mezga et al. Cretac. Res. 27: 735-742.)

Lio

Lio is a new strip I'm slowly warming up to. A bit of 'Calvin and Hobbes' but filterd through Edward Gorey.

Chimps Using Caves

Savannah chimpanzees, which can make weapons to hunt other primates for meat, can also seek refuge in caves, much like our earliest human ancestors.

link

From Charles Q. Choi at LiveScience:

Researchers investigated the Fongoli community of 35 savannah chimpanzees in southeastern Senegal, one of the hottest and driest habitats chimps live in today. Pruetz and her colleagues recently found that Fongoli chimps apparently could manufacture spears to hunt other primates, such as bushbabies.

The research into chimpanzees' possible use of caves began when Pruetz's field assistant Mboule Camara saw the apes coming from Sakoto cave, the largest cavern within the chimp's home range. The cave is more than 15 feet deep and located at the head of a shallow ravine that was formed through water runoff from a plateau.

To determine why they might use the cave, Pruetz recorded temperature data within the cave as well as at the different habitats the chimpanzees used, such as the woodlands and grasslands. She discovered that chimps most often use the stone cave as shelter during the hottest and driest times of the year, from October to May, findings detailed in an upcoming issue of the journal Primates. It is the first study to document regular cave use by chimps.

310 Million Year Old Kendall County Cave Fossils

Remnants from a cave embedded in a limestone quarry southwest of Chicago have yielded a fossil trove that may influence the known history of north central Illinois some 310 million years ago.

Plotnick and a group of students discovered the cave while on a class field trip about four years ago. It is revealed by darker color surrounded by the lighter limestone, and by the sand and mud containing fossilized material that choke the cave from bottom to top.

"What's really valuable about the cave is the level of preservation of the material," said co-presenter Kenig. "We see charcoal that preserves biological features at the cellular level. Charcoal is an indication of fire burning ancient trees. The cave also beautifully preserved molecular indicators of these fires."
Findings include nearly-pristine plant spores, leaves and scorpion parts. Needles from a conifer were dated and discovered to be the oldest ever from North America. "The oldest conifers previously described are at least 2 million years younger," said Plotnick. The specimen is now in the collection of Chicago's Field Museum.

The scientists think that a shallow sea covering today's north central Illinois during the geological Ordovician period about 450 million years ago formed the limestone. The caves were eroded in the limestone at the beginning of the Pennsylvanian period, about 315 million years ago. Within a few million years, sand, mud and organic debris from plants and animals -- some burned and turned to charcoal -- washed into the cave through surface openings, where it remained preserved but not compacted since that time. link

Initial research findings were presented April 12 by University of Illinois at Chicago earth and environmental sciences professor Roy Plotnick at a regional meeting of the Geological Society of America in Lawrence, Kan.

T. rex Protein Sequenced

Analyses of Soft Tissue from Tyrannosaurus rex Suggest the Presence of Protein. 2007. Science 316: 277 - 280

Abstract: We present evidence from multiple analyses of Tyrannosaurus rex (MOR 1125) fibrous cortical and medullary tissues remaining after demineralization that support the preservation of collagen I, the main organic component of bone, in low concentrations in these tissues. We propose a possible chemical pathway that may contribute to this preservation. The presence of endogenous protein in dinosaur bone may validate hypotheses about evolutionary relationships, rates and patterns of molecular change and degradation, and chemical stability of molecules over time.

Read one of the press releases, and:

Protein Sequences from Mastodon and Tyrannosaurus Rex Revealed by Mass Spectrometry. 207. J. M. Asara, et al. Science 316: 280-285.

Abstract: Fossilized bones from extinct taxa harbor the potential for obtaining protein or DNA sequences that could reveal evolutionary links to extant species. We used mass spectrometry to obtain protein sequences from bones of a 160,000- to 600,000-year-old extinct mastodon (Mammut americanum) and a 68-million-year-old dinosaur (Tyrannosaurus rex). The presence of T. rex sequences indicates that their peptide bonds were remarkably stable. Mass spectrometry can thus be used to determine unique sequences from ancient organisms from peptide fragmentation patterns, a valuable tool to study the evolution and adaptation of ancient taxa from which genomic sequences are unlikely to be obtained.

First Dinosaur Comic?

In a recent (and much too rare) phone conversation with my old amigo, Steve Bissette, he mentioned that he thought he’d turned up the first dinosaur comic. A few days later this post turns up on his MyRant blog. Scroll down to the bottom through the discussion of who did what when in zombie comics.

Bruce Naylor, 1950 - 2007

As I noted last week, Dr. Bruce Naylor, Director of the Royal Tyrrell Museum of Palaeontology, passed away recently. The RTMP site has his obituary up on their front page. The Palaeoblog sends its condolences out to Bruce's family and friends.

More RTMP Photos

'Lillian' the Albertosaurus has been retired from her place in the dino hall at the Royal Tyrrell Museum. In her place will be a new ceratopsian exhibit seen under construction here. I think that's the new Dry Island ceratopsid on the banner.



Donna M. works in the prep lab as seen through the vistor viewing window.

Cretaceous Roadrunner-Like Tracks

Earliest zygodactyl bird feet: evidence from Early Cretaceous roadrunner-like tracks. 2007. M.G. Lockley, et al. Naturwissenschaften, published online: 27 March 2007

Co-author Jerry Harris kindly sent me a PDF of his latest paper:
Abstract: Fossil footprints are important in understanding Cretaceous avian diversity because they constitute evidence of paleodiversity and paleoecology that is not always apparent from skeletal remains. Early Cretaceous bird tracks have demonstrated the existence of wading birds in East Asia, but some pedal morphotypes, such as zygodactyly, common in modern and earlier Cenozoic birds (Neornithes) were unknown in the Cretaceous.

We, herein, discuss the implications of a recently reported, Early Cretaceous (120–110 million years old) trackway of a large, zygodactyl bird from China that predates skeletal evidence of this foot morphology by at least 50 million years and includes the only known fossil zygodactyl footprints. The tracks demonstrate the existence of a Cretaceous bird not currently represented in the body fossil record that occupied a roadrunner (Geococcyx)-like niche, indicating a previously unknown degree of Cretaceous avian morphological and behavioral diversity that presaged later Cenozoic patterns.

Fig. 2 Tracks of Shandongornipes muxiai. a Map of holotype trackway (LRH-DH01). b–e Photographs and schematics of individual tracks in trackway (digit numbers labeled), including b photograph of first (left foot, LRH-dz70), c outline drawing of third (left foot, LRH-dz68), d outline drawing of fifth (right foot, LRH-dz66), and e photograph of fourth (left foot, LRH-dz67). f Segment of a trackway made by extant roadrunner G. californianus near St. George, Utah; segment includes same left–right sequence preserved in LRH-DH01 (a) and shown at same scale. g Schematic of fourth Shandongornipes print (LRH-dz67). h Individual G. californianus right footprint [from Elbroch and Marks (2001); used with permission] rotated with hallux in approximately same orientation as Shandongornipes print in (g)

New RTMP Galleries

The Royal Tyrrell Museum of Palaeontology in Drumheller is revamping its galleries. The old globe that greeted visitors as they entered the museum has been replaced by a hall of full-size dinosaur sculptures by Brian Cooley recreating a Late Cretaceous scene from Alberta. It should be finished soon but the public can wander through it even as it's being worked on.

I'm not sure who did the bronze sculpture above.