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.

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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.

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April 17, 2009

Rocky Mountain Dinosaur Resource Center

7:47 pm

Tylosaurus skeleton at the Rocky Mountain Dinosaur Resource Center
The monstrous skeleton of Tylosaurus proriger looms over visitors entering the Prehistoric Ocean room at the Rocky Mountain Dinosaur Resource Center.

On my way back to Albuquerque from the WIPS Symposium, I made a detour over to Woodland Park, Colorado, to check out the Rocky Mountain Dinosaur Resource Center. This “new species of museum” (according to its tagline) was founded by Mike and JJ Triebold, of Triebold Paleontology Inc., and Mike was gracious enough to come in on a Sunday to give me a tour of the place.

Mike Triebold with the cast of a giant coelurosaur track
Mike Triebold with a cast of a concretion that had formed within the footprint of a giant coelurosaur.

Mike explained that most of the skeletons on display were casts of specimens that he and his team had molded and mounted (and in many cases, collected and prepared to boot). The displays are constantly changing, as the reconstructed (cast) skeletons are purchased by museums and other collectors, and new skeletons are prepped, cast, & put out for display. In the 20+ years the Triebolds have been in this business, their team has put together some spectacular skeletons:

Juvenile Hadrosaur at the RMDRC
Juvenile Edmontosaurus. Behind and to the left is a larger Edmontosaurus. A Tyrannosaurus rex looms over the scene, and the pachycephalosaur Stygimoloch can be spotted in the background as well.

Conchoraptor gracilis at the RMDRC
Conchoraptor gracilis, nicely showing off the robust oviraptor furcula (wishbone).

Dramatic mosasaur mount at the RMDRC
One of my favorite mounts was this dramatically serpentine mosasaur Platecarpus

Dueling Pachycephalosaurus at the RMDRC
Dueling Pachycephalosaurus—these two have been reconstructed from “Sandy”, the most complete pachycephalosaur specimen known from North America.

I have to say I was quite impressed by what I saw during my visit. The mounts were dynamic and did a good job of showing off the range, skill, and productivity of the center’s staff. The large, open halls packed with skeletons & fossils felt a bit like a mix between traditional museum exhibits and a showroom floor, which I suppose is not an entirely inaccurate description. In some ways (none bad) I felt the crowding of the casts on display made the RMDRC feel a bit like an old cabinet of curiosities, with a desire to show off a great quantity and diversity of objects—in contrast to the current museum practice of calling carefully-picked specimens into the service of a grand idea. That said, I’m curious to see how the RMDRC handles themed exhibits like their newly opened Darwin and Dinosaurs, which was still being assembled during my visit.

In addition to the exhibits, there were a couple other aspects of the RMDRC that are worth a mention: First, the floor staff was extremely courteous, helpful, and informed (something I noticed even before I met Mike for the tour). Second, the Prehistoric Paradise gift shop was extremely spacious and well-stocked, something I’m always happy to see. And finally, in the time it’s taken me to get this post written up, I’m happy to see that Anthony Maltese has started posting a blog from the RMDRC paleo lab, so you can get a glimpse of the specimens they’re working on and other behind the scenes happenings at the Center.

—Matt Celeskey.

File under: Cretaceous, Dinosaurs, Museumabilia, Reptiles.

Comments on record: (1)

March 1, 2009

New PalaeoArt Carnival – Art Evolved

12:28 pm

A new internet carnival for Palaeo-Art, ART Evolved, kicked off today with its first themed gallery. Check out the work of several different paleoartists as they interpret the Ceratopsia. Nice Work!

—Matt Celeskey.

File under: Cretaceous, Dinosaurs, Paleo-Pop, Webbery.

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Miragaia longicollum

12:18 pm

—Matt Celeskey.

File under: Dinosaurs, Jurassic.

Comments on record: (0)

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