January 30, 2010

Bistahieversor sealeyi

3:34 pm

Congratulations to Drs. Carr & Williamson on the publication of “The Bisti Beast,” whose description is the cover story in this month’s Journal of Vertebrate Paleontology.

  • New Dinosaur: Bistahieversor sealeyi
  • Pronounced: bis-tah-he-ee-VER-sor SEE-lee-eye
  • Name means: Sealey’s Bisti destroyer (Paul Sealey discovered the fossils in the Bisti/De-na-zin Wilderness Area)
  • Named by: Carr and Williamson 2010
  • Relations: Tyrannosauroid, a group that includes Tyrannosaurus rex and its not-too-distant relatives
  • Location: Northwest New Mexico, United States of America
  • Age: Late Cretaceous (Campanian), ~73,000,000 years old
  • Length: ~9 meters (29 feet)
  • Info: Two fairly complete skeletons of a new type of New Mexican dinosaur are helping to fill in gaps in the evolution and distribution of tyrannosauroids, the group of dinosaurs that includes T. rex and its fairly close relatives.
  • Tyrannosauroid fossils have been known from southwestern North America for over 100 years, but mostly in bits and pieces—isolated bones and teeth or, at best, incomplete skeletons of uncertain identity (see Carr & Williamson 2000 for a good overview). Traditionally, researchers have assigned these fossils to well-known tyrannosauroid genera like Albertosaurus or Daspletosaurus, whose more complete remains were originally found further north in Wyoming, Montana, and Alberta.
  • Thanks to recent discoveries, the southwest now has a tyrannosaur all its own. Bistahieversor is the new name given to a complete skull and (mostly unprepared) skeleton from the Bisti badlands of northwestern New Mexico. Its skull and jaws display a healthy list of detailed anatomical characters that distinguish it from all other tyrannosauroids, including a complex joint between the nasal and frontal bones on top of its skull, and a unique hole above its eye. Other tyrannosaur remains from northwest New Mexico, including the partial skull and skeleton of a juvenile, appear to be specimens of Bistahieversor as well.
  • Images:
    NMMNH P-27469, holotype skull and jaw of Bistahieversor sealeyi
    Photograph by David Baccadutre, New Mexico Museum of Natural History and Science.


  • NMMNH P-25049, incomplete skull and skeleton of juvenile Bistahieversor sealeyi
    Both these specimens are on display in the New Mexico’s Seacoast hall of the NMMNHS.

  • Main Reference: Carr, Thomas D. and Williamson, Thomas E., 2010 Bistahieversor sealeyi, gen. et sp. nov., a new tyrannosauroid from New Mexico and the origin of deep snouts in Tyrannosauroidea. Journal of Vertebrate Paleontology, vol. 30 (1), pp. 1–16. doi: 10.1080/02724630903413032
  • Additional Reference: Carr, Thomas D. and Williamson, Thomas E., 2000 A review of Tyrannosauridae (Dinosauria, Coelurosauria) from New Mexico. New Mexico Museum of Natural History and Science Bulletin 17, pp. 113–145.
  • Elsewhere on the web:

—Matt Celeskey.

File under: Cretaceous, Dinosaurs.

Comments on record: (3)

January 27, 2010

The Paleobiology of Coelophysis Part II: Other Critters in the Quarry

6:43 am

or, Token Diversity in a Dinosaur Graveyard

Although fossils of the Triassic theropod Coelophysis bauri are by far the most numerous vertebrate remains preserved in blocks from the Whitaker quarry, several other animals are known from the site as well. Many have just been uncovered or described within the past ten years, and in the course of preparing the NMMNH block (and examining other blocks for comparison), several new fossils have come to light. A brief, annotated list of other fauna known from the quarry appears below:

Invertebrates: As mentioned last time, ostracods (Darwinula sp.) and conchostracans (Shipingia) were found in a sandy layer below the bones, remnants of temporary ponding at the site prior to the Coelophysis burial.


Synorichthys chased by Chinlea, sculpted by Gary Staab

Fish: Schaeffer (1967) reported paleonisciform and coelacanth fish in association with Coelophysis at Ghost Ranch. Both were found in the NMMNH block above the invertebrate layer and just below the lowest tetrapod bones: scaly little redfieldiid paleonisciforms, tentatively assigned to Synorichthys, and bits of fin, scale, and skull from the large coelacanth Chinlea sorenseni. As these fish would have been too large to thrive in the type of ephemeral pond indicated by the invertebrates, we posited that floodwaters washed them in to the site from a larger body of water.

Whitakersaurus bermani: This diminutive sphenodontian (my tiny-tuatara-based restoration at the left) is known from pieces of the upper and lower jaw found within 2 centimeters of the edge of the NMMNH block. The largest piece of the holotype, an incomplete right dentary preserving nineteen tooth-positions, is about 5 millimeters long (Heckert et al. 2008).

Drepanosaurs: Harris & Downs (2002) reported the first drepanosaur material from the quarry—a well-preserved (but isolated) shoulder girdle from the block at the Ruth Hall Museum of Paleontology. In a new review of the drepanosaurs, Renesto et al. (2010) assign that shoulder girdle to the genus Drepanosaurus, and describe a partially articulated but generically indeterminate foot on the edge of the NMMNH block (pictured below).


NMMNH P-57651, the foot of a small drepanosaur, preserved portion roughly 5cm long

Vancleavea campi: By far the most complete specimens of this armor-coated reptile are two beautifully articulated skeletons from the Ruth Hall Museum block, recently described by Nesbitt et al. (2009). Remains of a partial, disarticulated skeleton are associated with some characteristic Vancleavea armor in a mostly unprepared fossil removed from the NMMNH block.


Vancleavea sculpture by Phil Bircheff at the Ruth Hall Museum of Paleontology.

Phytosaurs: An ~80cm long phytosaur skull from the Whitaker/Coelophysis quarry (the holotype of Redondasaurus bermani Hunt and Lucas 1993) is housed at the Carnegie Museum. The skull and lower jaws of a juvenile phytosaur were found in the NMMNH block, currently exposed in left lateral/palatal view on a partially prepared jacket removed from the main block (photo below).


NMMNH P-44920, juvenile phytosaur (Redondasaurus?) skull and jaws, left lateral/palatal view. Photo courtesy of Larry Rinehart.

Postosuchus kirkpatricki: The Carnegie Museum of Natural History and the Ruth Hall Museum of Paleontology both have specimens of this rauisuchian on Whitaker/Coelophysis quarry blocks. These were partially figured in Long and Murry (1995, figs 145–146).


Effigia sculpture by Phil Bircheff
at the Ruth Hall Museum of Paleontology.

Effigia okeefeae: The type specimens of this bipedal suchian were recently discovered in jackets pulled from the quarry during the early excavations by the American Museum (Nesbitt & Norell 2006, Nesbitt 2007). A scapula and coracoid found in the NMMNH block might belong to this animal.

Hesperosuchus agilis: One of the best-preserved specimens of this early crocodylomorph is an articulated skull and partial skeleton now at the Carnegie Museum (Clark et al. 2000). Only a few armor scutes are known from the NMMNH block.

To the best of my knowledge, this little bestiary lists pretty much all the non-Coelophysis animals identified from Ghost Ranch Whitaker quarry fossils. All of them, that is, with one interesting exception, noticed while reviewing specimens on other Coelophysis blocks. Its story will make up the bulk of the next post.

Next time: Truly, Coelophysis?
or, The Mysterious Canadian

Previously:
Introduction

 

—Matt Celeskey.

File under: Bony Fish, Dinosaurs, Recent Discoveries, Reptiles, Triassic.

Comments on record: (2)

January 22, 2010

The Paleobiology of Coelophysis Part I: Introduction

10:26 pm

The Triassic dinosaur Coelophysis bauri is well-known from hundreds of fossils unearthed at Ghost Ranch in northern New Mexico, at a famous quarry first discovered by George Whitaker in 1947. Excavations at the quarry—initially by the American Museum of Natural History in the 1940s & 1950s, and subsequently by the Carnegie Museum in the 1980s—sent about thirty large blocks, each containing dozens of fossils, to museums across North America. Although it has been more than 25 years since the last major excavation, new discoveries continue to be made (e.g.: Nesbitt & Norell 2006, Heckert et al. 2008, Nesbitt et al. 2009) as fossils from the quarry are slowly prepared and interpreted.

One block, excavated by the Carnegie-led team in the 1980s, was given to the then-nascent New Mexico Museum of Natural History. In 2008, it was put on permanent exhibit. Larry Rinehart, who prepared the block for display, invited me to assist in the illustration and interpretation of some of the specimens it contained, as well as to reconstruct some of the different sizes and morphologies that were being uncovered through the analysis of dozens of specimens in this and other blocks from the quarry. The results of these investigations have been published in the past few weeks as a New Mexico Museum of Natural History and Science Bulletin (Rinehart et al. 2009).

In future posts, I hope to showcase some of the specimens, interpretations, and conclusions we came to as a result of these investigations. Note that everything I post here will be based on my own understanding and interpretation of the work, much of which was performed by the other authors. I don’t intend to misrepresent any of the procedures or findings, but if it happens, errors in reporting should be considered mine alone.

With that caveat in mind, I’d like to introduce the main object of the study: the NMMNH Coelophysis block.

NMMNH Coelophysis Block
The NMMNH Coelophysis block (Quarry # C-8-82) after preparation

The NMMNH block is a two ton wedge of reddish Chinle siltstone, trimmed down considerably from the original 12,000 pounds pulled out of the quarry in 1982. Across its exposed surface lie more than two dozen specimens referrable to Coelophysis bauri, plus a couple non-dinosaur bits & pieces. Several jackets removed from the block contain many more fossils of Coelophysis, along with an impressive sampling of Triassic fish and reptiles.


Schematic drawing of selected Coelophysis specimens on the exposed surface of the NMMNH block

Up from the Bottom
or, Lessons from a Triassic Turnover.

When looking at the prepared surface of the NMMNH block, everything you see is upside down—the block was flipped over and prepared from the bottom up. This was done to facilitate access to the primary bone layer by avoiding the reworked, poorer-quality bones found above this layer in other blocks. It also revealed new information about the environment where the Coelophysis were buried. Beneath the main Coelophysis beds were found layers containing rip-up clasts running in the same direction as most of the Coelophysis bones—evidence of rushing water that tore up chunks of the underlying mud as it swept the dinosaur bodies in.

A previous study of the taphonomy of the quarry (Schwartz & Gillette 1994) also concluded that water transported the Coelophysis to their burial site. Based on several lines of evidence, Schwartz and Gillette proposed that the animals died during a prolonged drought and were subsequently washed downstream by a flood, where their carcasses clogged a narrow channel prior to burial. But some tiny fossils near the bottom of the NMMNH block suggested a slightly different scenario to us.

Beneath the rip-ups were the fossils of tiny invertebrates—conchostracans and ostracods—often found in temporary bodies of water. They led us to consider that the quarry was once the site of an ephemeral pond—a topographic depression where water might collect during a wet season, followed by dry periods where the water would disappear. An unfortunate flock of Coelophysis, swept up in the flooding of a nearby river, might have been washed into this low spot in the landscape and buried.


The death/burial poses of the seven most complete Coelophysis specimens on the NMMNH block

As for the cause of death, there seemed little reason to suspect any agent beyond the flood that buried them. In fact, one observation previously cited as evidence for post mortem desiccation—the opisthotonic posture where neck and tail are flexed sharply upward and curled over the back—now seems more likely to indicate the death throes of animals suffering the final effects of disease, poison, or (in this case) lack of oxygen due to burial or drowning (Faux & Padian, 2007).

If the bonebed at the Whitaker/Coelophysis quarry is the end result of a single catastrophe, then it preserves an excellent sampling of a population of early dinosaurs. It may possibly be the largest (in terms of numbers of individuals) Mesozoic dinosaur population we know of. This provides an unparalleled opportunity to study growth and variation within a single dinosaur species. Before getting to that, however, I’d like to spend a post reviewing some of the other, non-Coelophysis fossils found within this and other quarry blocks.

Next time: It’s your Lagerstätte, I’m just buried in it
or, Token Diversity in a Dinosaur Graveyard.

—Matt Celeskey.

File under: Dinosaurs, The Day Job, Triassic.

Comments on record: (10)

July 29, 2009

Suminia, the arboreal anomodont

11:51 am

Suminia getmanovi skeletal reconstructionSkeletal reconstruction of Suminia getmanovi (sue-MIN-ee-a  get-mah-NOVE-eye), an arboreal anomodont therapsid from the Late Permian of Russia. Art by Christina Stoppa.

Paleontologists have described the earliest known animal adapted for life in the treetops, according to a paper in the Proceedings of the Royal Society B, released online today. Jörg Fröbisch, of the Field Museum, and Robert Reisz, from the University of Toronto, found several adaptations for arboreality when they examined fossil skeletons of Suminia getmanovi , a small (20 inches/50 cm) herbivore from the Late Permian of Russia.

The most striking features of the skeleton of Suminia are the relatively large hands and feet. Most of their length is taken up by long, slender fingers and toes tipped with strongly curved, laterally (side-to-side) compressed claws, which are similar in proportion and shape to some modern tree-clinging animals, including dermopterans, megabats, and lizards. The first digits on the hands and feet diverge from the remaining four digits as well, and may have been used as opposable ‘thumbs’ as the animal clung to the branches.

Suminia getmanovi PIN 2212/116 specimen 1Skeleton of Suminia getmanovi, Paleontological Institute (Moscow) specimen number 2212/116 (spec. 1) Photo by Diane Scott.

More subtle features also point toward arboreal habits. The tail of Suminia is relatively long, and the vertebrae show strong processes halfway down its length. These processes could have supported muscles that allowed Suminia to use its tail for balance or, possibly, as a prehensile grasping organ.

Suminia, at 260,000,000 years old, is the first known vertebrate with this degree of arboreal specialization. Fröbisch and Reisz note that the Late Permian Period, and the Kotel’nich locality where Suminia was found, provides some of the earliest evidence for “modern terrestrial ecosystems with large numbers of plant-eaters supporting few top predators.” While large megaherbivores fed on the greenery below, Suminia found a new way to exploit the foliage in the treetops, taking the first known step into a niche that vertebrates would return to several times over the next 260 million years.

Suminia getmanovi flesh reconstructionLife restoration of Suminia getmanovi by Christina Stoppa.

Lawless teeth

In part because of some very poorly-written articles and headlines, and in part because talking about vertebrate relationships is just plain enjoyable, it seems like a good place to put in a little bit of context regarding exactly what Suminia is related to.

Suminia is a synapsid, a group of vertebrate animals that would eventually (some 50-100 million years after Suminia) give rise to the ancestors of today’s mammals. Although some synapsids have been called “mammal-like reptiles,” (because they certainly laid eggs and might have looked something like lizards) there are no true reptiles in the synapsid group. All true reptiles—turtles, lizards, snakes, crocodiles—even dinosaurs and birds—belong to a completely separate group.

Among the synapsids, Suminia is considered a therapsid, a phrase commonly used to indicate a grade of synapsid development in between the earlier pelycosaur-grade (think Dimetrodon) and the later mammal-grade. (Although, since mammals evolved from therapsids, we’re technically therapsids too, and since therapsids evolved from pelycosaurs, we can all claim that title as well.)

Among the therapsids, Suminia is an early member of the anomodont (“lawless tooth”) lineage. Sometime during the Early/Middle Permian period, the anomodont line split off from the line of therapsids that would, by way of a whole bestiary of gorgonopsians and therocephalians and countless cynodonts, eventually lead to mammals. The closest relatives we (and all other mammals) share with Suminia would have lived before the Late Permian, around 275,000,000 years ago (give or take several million years) .

The anomodonts have no living descendants, but their roster includes the great radiation of dicynodonts that survived the end-Permian extinction, became some of the largest terrestrial herbivores of the Triassic, and might possibly have survived into the Cretaceous if the identification of an Australian fossil is correct.


Placerias hesternus, a Late Triassic anomodont from Arizona. (Illustration by me, for the day job)

Contrary to what you might have read regarding this discovery, dinosaurs did not evolve from synapsids, and while Suminia is a human relative, this potential predator of Suminia is a much closer relation.

Some images and info for this post came from this press release.

—Matt Celeskey.

File under: Permian, Synapsids.

Comments on record: (4)

June 2, 2009

Uncovering “Ida” at Laelaps

9:19 pm

darwinius

One of the biggest stories in paleontology this past month was the announcement of a beautifully complete fossil of an Eocene primate scientifically christened Darwinius messilae, and given the popular moniker “Ida.” A massive publicity campaign, including a book release and a documentary hosted by Sir Richard Attenborough, was launched in tandem with the fossil’s description in the online journal PLoS ONE. A backlash erupted throughout the science-minded blogosphere/twitterverse, deriding the more breathless claims that this one specimen was the “missing link” that will “change everything.”

Some of the earliest and most insightful comments came from Brian Switek at Laelaps. Earlier today, Brian compiled a collection of his and others’ Darwinius-related posts into a blog carnival called Uncovering “Ida”—an excellent resource for anyone interested in the interaction between science, publicity, and media (new and old).

—Matt Celeskey.

File under: Mammals, Paleo-Pop, Paleogene, Webbery.

Comments on record: (1)

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