WAVP 2009 Photos

Good tidings and well-wishes!

As promised, I’ve uploaded several of my photos and videos from this year’s annual Western Association of Vertebrate Paleontologists meeting. Along with Dr. Hungerbuehler and myself, fellow students Donny Price and Miles Miller came along for the ride, as well as Reg Tempelmeyer (an old friend of the museum who’s been preparing fossils and digging for us for the better part of a decade). A grand time was had by all, and you can bet that I’ll be attending next year (and hopefully giving a talk and/or poster about my work with Redondasauruswith Dr. Hungerbuehler).

We began with a tour of the paleo prep-lab at Petrified forest National Park in Arizona, delivered by none other than Dr. Jeff Martz of Paleo Errata fame and Dr. Bill Parker of Chinleana. Dr. Martz showed off his most impressive specimens and current projects (the display table filled with phytosaur skulls literally made Dr. Hungerbuehler’s eyes bug out!), but I was asked to refrain from posting them here, so I’ll honor that request. After our stop there, Dr. Parker took us around on a geologically-biased tour of the rest of the park, including one locality particularly fossiliferous locality which was literally covered in petrified wood chunks.

Yours truly posing with a section of petrified wood trunk.

A sliver of petrified wood...these literally covered the ground in the area.

Wood wasn’t the only thing we found, however. Reg’s eagle-sharp eyes spotted a pair of phytosaur teeth, and later on the tour, many of us found pieces of scutes and other bone fragments. Dr. Parker advised us to be on the lookout for a shovel handle, as this allegedly marked the location for an un-recovered Vancleavea specimen. Alas, our searching efforts were in vain, but that didn’t prevent us from taking in the almost surreal beauty which is the painted desert.

Later on, we visited the park’s paleontology museum, in which all of us took an immediate and avid interest.

The museum contains one of the original Revueltosaurus casts as well (we also saw a fleshed-out reconstruction done by Matt Brown which sported a pair of taxidermist cat-like eyes, but again, I’ve been asked not to post it).

A Revueltosaurus cast display, complete with those controversial teeth!

A metoposaur skull (I believe that this is Koskinonodon). Note Dr. Parker's profile (sorry 'bout that).

I guess Dr. H wasn't expecting to have his picture taken...

The museum's Postosuchus mount. Dr. H thought that this cast (along with that of the Desmatosuchus to the right) was made from the same mold as ours.

The museum's dinosaur display showcased the remains of Chindesaurus (pictured) and a Coelophysis hindlimb (just out of my shot).

Here's another shot of me, this time with Yavapai Community College's resident Miocene expert, Dr. Jeb Bevers.

After the museum tour, we diverged for a few hours to rest. I spent a few hours trying to photograph a raven (having been inspired by Bernd Heinrich’s book), but it would appear that their reputation for heightened intelligence has been well-earned, as the bloody thing kept flying out of my shot just as I was about to snap a picture. A few hours later, the group of paleontologists met up at the local college for refreshments and to compare notes/specimens (we brought along a few of our new-found aetosaur plates, including a ventral scute for the inspection of the resident authorities). Donny, Miles, and I were completely psyched to be meeting so many paleontologists from such a variety of disciplines and quickly gained notoriety as the ‘paleo-paparazzi’.

The next day, everyone met up at the park’s auditorium for presentations. Dr. Hungerbuehler represented M.C.C. by delivering a talk about the archosaurian remains from our new Triassic site in the Redonda formation of Eastern New Mexico. For some reason, my name (along with Donny’s, Miles’, and Reg’s) were attatched to the absrtact, but I’m certainly not complaining! Other interesting talks given included (but are by no means limited to):

-Dr. David Elliot of Northern Arizona University described early Devonian heterostracans from the Western U.S.

-Dr. Holroyd from the UCMP discussed the turtles of Alberta’s Hell Creek park and showed interesting fluctuations in the population of various species through the latest Cretaceous, which was probably due to temperature variations. As an avid chelonian fan, I listened to the talk with great delight.

-Dr. David Smith of Northland Pioneer College discussed herbivory in theropods and specifically maniraptorans. He expanded on the idea that herbivory in these animals (primarily therizinosaurs, oviraptorsaurs, and ornithomimosaurs, all of which are almost universally agreed to have been at least largely-herbivorous), to quote from his abstract, “represents the ancestral condition for maniraptorans, but was later reversed in more derived clades, such as dromaeosaurs.” He made a very strong case, the implications of which are quite intriguing.

-Dr. David Gillette of the Museum of Northern Arizona described the anatomy, functional morphology, and mounting of the institution’s Nothronychus.

-Dr. Jeb Bevers reviewed the Miocene fauna of the Milk Creek formation and revealed the remains of what is likely the formation’s first lagomorph.

-Dr. Eric Scott of the San Bernardino County museum in Redlands, California gave a very passionate discussion as to why paleontology and molecular biology should be treated not as rivals but as “complementary tools”. He cited the shortcomings of research into the latter field with regards to horse and bison evolution and urged practitioners of both areas to increase their contacts with each other.

-A host of lectures were given by the staff of the Page Museum in Los Angeles: Dr. Christopher Shaw spoke about a massive, though under-researched, tar pit site similar to the famed La Brea tar pits but potentially several times more fossiliferous! Dr. Ryan Long discussed rarely-encountered bones at Rancho La Brea (such as feline clavicles), and Mrs. Andrea Thomer highlighted a new 3-D data visualization system currently being utilized at the site. 

After the talks, most of us got together to share an enjoyable meal at a local Italian restaraunt (it’s amazing that we got the reservation, considering the facts that there were around forty of us and it was Valentine’s day). The next day, the MCC gang departed for the New Mexico Museum of Nature and Science, but that’s an entirely different story altogether…(Don’t worry, I’ll post videos and pictures of that adventure as well)

May the fossil record continue to enchant us all!

Triassic Research 2008

Good tidings and well-wishes!

I realize that this is very late, but Microecos has posted an excellent review of how the outlook on everyone’s favorite Mesozoic period changed in 2008 accompanied by this totally awesome picture and t-shirt:

http://microecos.wordpress.com/2008/12/31/i-support-scientific-triassicism/

🙂

May the fossil record continue to enchant us all and inspire more wicked attire!

Triassic Critters: Sphenosuchians (aka: ‘Triassic Greyhounds’)

Good tidings and well-wishes faithful readers!

Sometimes, to paraphrase in a Cosby-esque style, evolution does the darndest things! Occasionally, a species which seems perfectly well-adapted for a given lifestyle will suddenly undergo massive physical alterations and inhabit a new and radically different niche. Such is the case for the sphenosuchians…the unlikely anscestors of modern crocodylians.

As loyal readers (again, assuming they exist) can probably tell, I’ve had crocodylians on my mind for a little while now, having reviewed David Schwimmer’s book on Deinosuchusa few posts back. The group has undergone a fascinating history which has seen the rise and fall of a dazzling array of characters. Thus, it is a mistake to claim that crocodylians have remained “unchanged for millions of years”, as the anscestors of the modern species with which we are all familiar have spawned from some of the most unlikely creatures imaginable.

Hesperosuchus bronze: now on display here at the MCC dinosaur museum.

Take a look at the image above. This depicts a Hesperosuchus, the quintessential North American sphenosuchian (since my knowledge in this area extends only to North American creatures, I’ll abstain from discussing their European, African, and Asian counterparts). At first glance, it seems almost impossible to believe that such a beast gave rise to the same crocodiles seen grappling with zebras on the Discovery Channel. It’s a well-known fact that modern crocodiles are not exactly the most energetic members of the animal kingdom…one can easily mistake captive specimens for stuffed dummies when walking beside their enclosures at the local zoo. In stark contrast, everything about Hesperosuchusseems to shout “speed deamon”! The animal’s limbs are long and lanky: perfect for short (or even long) distance sprinting, its skull is lightly-built and its tail (which unfortunately can’t be viewed in this photograph) is long and wispy, rather than stout and heavy as in modern crocodylians.

Upon closer examination, however, the similarities between this animal and a modern counterpart are made apparent.

Crocodylians are distinguished from other reptiles by their fairly non-kinetic (unmovable) skulls: while snakes, lizards and even dinosaurs posses some cranial mobility, crocodylians maintain a comparatively rigid skull, which greatly increases the power of their infamous biting capabilities. Other group features include:

          -The back of the skull (the posterior end) has a unique ‘squared off’ shape.

          -The quadrate bone (which forms part of the jaw joint) extends far downward ventrally (towards the creature’s belly) and firmly contacts most of the posterior jaw bones. This allows crocodylians to widely open their jaws and provides an extended hinge for the musculature responsible for the group’s notoriously-strong jaw closure. It should also be noted that modern species, in addition to the traditional jaw adductor muscles (jaw-closing muscles, see the picture below) sport another pair of muscles which may be found inside of these called the pterygoideus muscles. These provide a quick pull on the mandible (lower jaw) which, combined with the slower perpendicular contraction of the jaw adductor muscles, produces their multi-ton jaw-closing power.

The triangular muscles in the back of this Tyrannosaurus' mouth are the jaw adductor muscles

          -Most vertebrates which posses a reasonably-advanced sense of hearing (such as birds, mammals, and most reptiles) sport what’s known as a Eustachian tube in their ears (see the picture below of a human ear).

The Eustacian canal is located in the lower right-hand corner of this image.

In most archosaurs, such as dinosaurs, this tube is accommodated by a mere skull cavity. However, in crocodylians, birds and mammals, a specific canal in the skull, appropriately called the eustacian canal houses its namesake tube. This feature is what forced the scientific community to recognize sphenosuchians as anscestral crocodylians, as a Chinese specimen of a species called Dibothrosuchus sported a recognisably-crocodylian eustacian canal.

Sphenosuchians, like many Triassic archosaurs, possessed scutes (armor-like external plates of bone). However, these were arranged in two rows along their spines. This brings me to an interesting point. As I brought up in my last post, David Schwimmer in his book “King of the Crocodylians” made the observation that living crocodylians don’t use their scutes for defense so much as for physical support. Modern species (like the one below) occasionally engage in what’s known as a ‘high walk’ wherein their bellies are held off the ground as their limbs are placed directly underneath their bodies rather than sprawling out to their sides.

A young saltwater crocodile (Crocodylus porosus) using the 'high walk' along the banks of an Aulstralian river.

Their scutes attach to the top of the animal’s ribcage via a series of muscles which, when placed in this position, actually pull on the animal’s body and help lift it off the ground, similar to how suspension cables hold up the Brooklyn bridge. This feature is a throwback to their sphenosuchian ancestors, who made extensive use of it as they ran about during their energetic lives. Thus, it is believed that scutes evolved initially for support and were only later utilized for defensive purposes.

 There has been considerable debate as to whether sphenosuchians were bipedal (walking and running on two legs) or quadrupedal (walking and running on all fours). In most species, the hind limbs are more than twice the length of the forelimbs, however, some researchers maintain that they predominantly fell into the latter category for most of their activities. Perhaps they would walk and jog on all fours but revert to their back legs when the need was felt to run at an especially-fast pace.

Besides Hesperosuchus, some paleontologists contend that a second late Triassic North American species, Dromicosuchus, exists as well.  The type specimen of the latter was unearthed in North Carolina in 2003. The animal’s discovery was interesting because it was found directly underneath a large rauisuchian (see the picture below).

A rauisuchian known as Postosuchus. This bronze statue is now also on display at the MCC dinosaur museum.

This fact in and of itself isn’t especially likely to raise any eyebrows; after all, skeletons of various animals are frequently found atop each other at dig sites, particularly those which hail from a river deposit. However, the Dromicosuchus specimen bore damage from rauisuchian teeth on its neck! Since neither of these animals are particularly common, this suggests that the Dromicosuchuswas killed by the larger rauisuchian before it too perished somehow. Fascinating, no?

Personally, I don’t think that the differences given between Dromicosuchus and Hesperosuchus in the scientific paper which followed the discovery explaining why the former should be considered its own genus are justified. One of the explanations given was the fact that the “Dromicosuchus” specimen lacks a lone triangular scute at the base of its skull found in Hesperosuchusspecimens from the American southwest, however this is probably due to the injuries sustained by the rauisuchian bites. The other differences given are, for lack of a better term, “nit-picky” and aren’t substantial enough to justify a new genus (though it may possibly represent a new species or subspecies of Hesperosuchus).

These fleet-footed creatures likely dined on insects and small vertebrates, yet surprisingly they co-existed with early theropods for millions of years in the Late Triassic (such as Coelophysis, the New Mexican state fossil, pictured below), even though by every indication they too were dining on similar prey items.

This picture is currently on display at the New Mexico Museum of Natural History and Science in Albuquerque.

Sphenosuchians are also noteworthy because they, along with dinosaurs and a handful of other archosaurs, survived the mass-extinction which occurred at the end of the Triassic period. This extinction wiped out the phytosaurs (pictured below), which were superficially crocodile-like and occupied the large semi-aquatic predator niche through much of the period.

A phytosaur cast on display in Ghost Ranch, New Mexico. Despite appearances, these animals were not closely akin to crocodylians.

Their extinction, coupled with the increased diversity of theropods which occurred during the Jurassic (the succeeding period), likely drove the sphenosuchians to abandon their traditional role as speedy terrestrial predators and evolve larger, more streamlined bodies to inhabit the waterways as had the phytosaurs before them. As is often the case in evolution, no niche goes unfilled for long.

May the fossil record continue to enchant us all.

Flat Frogs 101

Good tidings and well-wishes!

While much ado is traditionally made regarding the paleontology and evolution of prehistoric reptiles (including everyone’s favorite group of ancestral poultry), relatively little attention is paid to their amphibian counterparts. Despite this, reptiles do not in any sense possess a monopoly on interesting (or even downright bizzare) life-forms, and the amphibians themselves sport a rich and diverse evolutionary history featuring a colorful cast of characters. Since MCC is located in a region of New Mexico primarily recognized for its late Triassic deposits, I shall dedicate this post to arguably the most interesting group of amphibians found in such localities, the Metoposaurs, or, as my instructor likes to call them, “flat frogs”.

Apachesaurus gregorii, image from Wikipedia.

As the above illustration demonstrates, these creatures have earned their nickname due to their distinctive dorso-ventrally-compressed (“flattened from the top and bottom” in layman’s terms) skulls. To get a better idea of just how flat the skulls of these beasts were, check out the image below:

Mastodonsaurus skull (side view).

Before one can fully appreciate metoposaurs, one must possess some basic understanding of amphibian taxonomy. These creatures belong to an extinct group of amphibians known as Temnospondyls, which translates to “split-spines”.

In modern amphibians, vertebral bones are developed in two sets. During development, either one of these sets is reduced while the other becomes the centrum (the main body of the vertebrae) or both become the centrum. Temnospondyls sport the latter orientation. In reptiles (and humans for that matter), it is the front set which is reduced while the rear set becomes the centrum, whereas in Temnospondyls the opposite is normally true, however the late Triassic forms we’ll be discussing feature the more familiar ‘reptilian’ model.

The group emerged during the mid-to-late Carboniferous period, some 310 million years ago, however, since the metoposaurs are main topic of this post, we’ll have to bypass extensively-covering their bretheren. For an overview of the entire gang, do go here.

Metoposaurs have been nicknamed “Crocomanders” due to their superficial resemblance to modern caudates (salamanders, newts, and kin) and their almost-irrefutably crocodilian lifestyle. There is an unusual (and often irritating) trend in fossilized creatures which likely inhabited such a niche: normally, only the skull is preserved. Thus, most of what we know of these animals comes from their cranial anatomy.

The skull is generally sculptured heavily, sporting a labyrinth of grooves and canyons across its surface. In addition to these, however, you may notice some ‘worm-like’ structures on that of the image below (look for the long-ish lines running in front of each eye and curving around the nostrils). Interestingly, these are neither decorations nor muscle-attatchment points. Rather, they contain a sense organ known as the lateral line system. Such an apparatus is most frequently encountered in modern fish, though many present-day amphibian larvae (and a few adults) possess them. These systems detect low-frequency movement through water in a method that is analagous to our sense of hearing. Since these organs only work underwater, we can safely assume that metoposaurs were heavily-aquatic at the very least, as no living animal which isn’t befitting of this description also has a lateral line system.

Mastodonsaurus skull (top view).

 You may also notice a small opening in the skull just behind the eyes, this is what’s known as a third eye (the ‘parietal’, anatomy fans). Many ‘lower’ vertebrates (fish, amphibians, and reptiles) use them to help identify the darkness of a particular area, as they lead directly to the brain and are light-sensitive (‘photoreceptive’). This is largely responsible for the ‘day-night’ cycle which programs most of their daily routines. It may also be used for hormone production and regulating “bio-rhythm”, however it’s specific function generally varies amongst owners.

If you look very carefully, you may notice that this skull contains four openings towards its tip instead of the traditional two. The posterior pair (that which is closer to the rear of the animal) contains the nostrils, but what of the smaller pair in front of them? That, my friends, carries out a very odd function indeed. You’ve probably noticed that the side-view of the skull displayed some rather nasty-looking enlarged fangs on the upper and lower jaws. How, you may ask, can such a flat skull house such comparatively-enormous teeth? Read on.

When the creature’s mouth was shut, the fangs from the upper jaw rested their tips at the bottom of its mouth. However, the lower fangs, due to the solid nature of the palate in contrast to the fleshy makeup of the tongue and surrounding areas, had no such luxury. To cope with this, most metoposaurs (and indeed, most temnospondyls) began to evolve holes (‘fenestrae’) in the roofs of their maws to house them. In some species (such as the European Mastodonsaurus pictured here), these holes penetrated the top of the skull, meaning that when the jaws were closed, the lower fangs actually slid up through and stuck out of them to resemble a pair of horns! (I’ll bet some of you thought these were cute little harmless critters until I dropped that tidbit. Don’t deny it…:))

Metoposaur dentition isn’t limited to these freakishly-large fangs either. These semiaquatic beasts additionally featured two rows of teeth in their upper jaw. Though it may seem odd, this is actually standard for amphibians.

Postcranially (‘behind the skull’), there isn’t much to cover, for, as I said before, very little of these animals minus their skulls is preserved on a semi-regular basis. However, the animals did sport a shoulder girdle which was sculptured in a fashion similar to that documented in the skull.

Only two genera are known from the late Triassic deposits of the American Southwest, Koskinonodon (aka: ‘Buettneria’) and Apachesaurus (additionally, the non-metoposaur temnospondyls Latiscopus and Rileymillerus are known from the region). It is interesting to note that in the lower parts of the upper Triassic (no oxymoron there…), the representative species (Koskinonodon) is both large and relatively abundant, yet the higher and younger you go, the smaller and rarer the metoposaurs become, along with all amphibians. Temnospondyls went nearly extinct at the close of the Juriassic period (some 145 million years ago), and indeed, most paleontologists believed that they had retired to that great, big swamp in the sky around this time for decades, likely due to competition from crocodylians. However, it was later discovered that at least one species (Koolasuchus, not a metoposaur, but a temnospondyl nonetheless) lasted until the early Cretaceous period in Australia (where the water was likely too cold for crocodylians since it was located much farther south than it is today), some 50 million years later!

I hope that this has proved to be of interest and not eccessively verbose. As always, may the fossil record continue to enchant us all.