The Theatrical Tanystropheus

Good tidings and well-wishes!

My fellow Triassic aficionados have doubtlessly realized that their beloved period has been unjustly neglected in recent months by my humble blog in favor of perissodactyls and eurypterids among other things. To remedy this situation, I’ve decided to post a bit of coverage on one of the most interesting and controversial archosaurs of the age, Erpetosuchus granti.

E. granti skeletal reconstruction.

The type specimen of this critter hails from the Elgin region of modern Scotland, home of Ornithosuchus, Stagonolepis, and the ever-problematic Scleromochlus among many others. Specimens have been discovered in the local sandstone since the mid-1830’s and have received attention from several of the world’s greatest early paleontologists, geologists, and comparative anatomists, including Louis Agassiz, Charles Lyell, Gideon Mantell, Sir Richard Owen, and “Darwin’s bulldog” himself, Thomas Huxley.

Erpetosuchus skull reconstruction based on the Connecticut specimen (see below).

In his excellent review of Triassic vertebrate assemblages from around the world entitled “Dawn Of The Dinosaurs: Life In The Triassic”, Nicholas Fraser writes:

“Erpetosuchus is another poorly known small archosaur that is difficult to pigeonhole taxonomically. It was a small animal (skull under 9 centimeters long) with gracile front limbs (the posterior half of the animal is unknown). Superficially, the skull bears a resemblance to sphenosuchian crocodiles, with the quadrate angled forward and a deeply emarginated otic region. However, a closer examination of the sutures (although poorly defined in the sandstone molds) reveals that the quadrate does not hook back under thesquamosal, and it is unlikely that there was a quadrate-prootic contact (a character widey distributed among crocodylians). Neither is the quadratojugal positioned anterior rather than lateralto the quadrate. Furthermore, the radiale and ulnare are not elongated, and the coracoid lacks and attenuated [(“gradually thinning”)] posterior process.”

A rather incomplete specimen of Erpetosuchus (or possibly a closely-related animal) was found in the Newark Supergroup near Cheshire, Connecticut in 1995. In their description of the specimen, Paul Olsen, Hans-Dieter Sues, and Mark Norell (of Columbia University, the University of Toronto, and the AMNH respectively) note that

“There are several minor differences between the two skulls [(theirs and that of the Scottish holotype)], such as the relatively smaller antorbital fenestra, the more gently rounded ventral margin of the orbit, and the size of the maxilliary teeth in AMNH 29300 [(their specimen)]. They probably reflect individual variation and preservational features rather than taxonomically significant characters, and we identify AMNH 29300 as Erpetosuchus sp.”

Erpetosuchus cranial reconstruction.

On the subject of the animal’s maxilliary teeth, many paleontologists consider Erpetosuchus‘ arrangement of teeth to be its most bizarre characteristic. Fraser concurs with this notion, saying

“The most unusual feature of Erpetosuchus is the distribution of the marginal teeth. In the upper jaw, they are restricted to the premaxilla and the very anterior portion of the maxilla. In the lower jaw, there are at least two or three acutely conical teeth situated more posteriorly. [The Newark Supergroup specimen] was first recognized on the basis of this peculiar dentition. Just how this dentition functioned is unclear, but it seems plausible that the acutely conical teeth in the front of the jaw captured large insects such as cockroaches, piercing the exoskeleton and preventing them from escaping. Thus immobilized, the tough exoskeleton could be pierced by the teeth in the lower jaw and crushed against the  broad edentulous [(toothless)] region of the maxillia and palate.”

A "galloping" Erpetosuchus reconstruction.

(For an incredibly detailed description of Erpetosuchus‘ known anatomy, do go here)

As I’ve said earlier in this post, the taxonomy of this creature is a matter of controversy among Triassic paleontologists. Olsen, Sues, and Norell have offered their own interpretation in their aforementioned paper:

“The phylogenetic relationships of Erpetosuchus have remained unresolved since the original description of E. granti… Most authors… referred Erpetosuchus to the Thecodontia. Since the pioneering phylogenetic analysis by Gauthier (1984), most authors have considered “Thecodontia” a paraphyleticassemblage of only distantly related basal archosaurian taxa…Walker…considered Erpetosuchus ‘a pseudosuchian at best only distantly related to crocodiles’ and interpreted its skull as displaying ‘a remarkable example of convergence towards the crocodilian condition in the attitude of the quadrate and the formation of an otic notch…

In our analysis, Erpetosuchusis the proximate sister taxon of Crocodylomorpha…Unambiguous synapomorphies linking Erpetosuchus and Crocodylomorpha are medial contact of the maxillae to form a secondary bony palate, absence of a postfrontal [(a bone found behind the frontal in many vertebrates)], and parietals fused without trace of an interparietal structure.”

Hopefully, some of the mysteries surrounding this little-known animal will be solved by the discovery of future Erpetosuchus specimens on either side of the Atlantic.

May the fossil record continue to enchant us all!

Good tidings and well-wishes!

I’ve decided that since I essentially have Wednesday nights off this semester (or what’s left of it…and don’t worry, Dr. Hungerbueher, I still devote plenty of time to my studies), I’ll take advantage of this opportunity by creating “The Theatrical Tanystropheus”s first regular column: the Wednesday Wonders. In this segment, I plan to discuss a bizarre and under-emphasized prehistoric beast each week and what better way to kick this whole project off than to cover the very critter after which this blog is named and nevertheless remained unjustly absent from my previous entries, the notorious Tanystropheus sp.  

First, some background facts. Tanystropheus would appear to be most closely related toTanytrachelos of the Eastern U.S. and Macrocnemus of Italy and is thus considered to be aprolacertiform. The animal lived during the Middle Triassic.

Tanystropheus reconstruction.

A small Tanystropheus longibardicus skeleton.

Upon viewing specimens of Tanystropheus, one is immediately stricken by the creature’s rather interesting neck. For one thing, its anatomy indicates that it was held in a more or less permanently-horizontal position (more on this later). Oh, and it’s rather long as well…

Sarcasm aside, this creature’s neck is almost implausibly lengthy. In fact, because of its sheer proportional exaggeration, some early paleontologists remarked that the animal’s mere existence nearly defies the laws of physics. To give you a better perspective on just how long this beast’s neck actually was, check out this (somewhat dated) reconstruction:

Dracula would have a field day...

Just how long was it? Up to three meters. That’s ten feet, English measurement fans!  As Nicholas Fraser explains in his excellent book “Dawn of the Dinosaurs: Life in the Triassic”:

“Tanystropheushas long been regarded by paleontologists as one of the world’s most improbable creatures. The long neck of most species in this genus is typically composed of 12 extraordinarily large elongate cervical vertebrae (although one referred species, T. antiquus, has only 8 cervicals, and yet another possible tanystropheid from China has 24 cervicals!).”

(Note, the Chinese tanystropheid to which he was referring is Dinocephalosaurus orientalis, additional information about which may be found here and here.)

Alright, we’ve established that the neck was long enough to give the executioner from “Blazing Saddles” and “Robin Hood: Men in Tights” quite a challenge (‘No noose is good noose!’ You’ve gotta love Mel Brooks…). But what was this that I’d mentioned earlier about its notable rigidity? For this, I once again turn to Nicholas Fraser:

“Moreover, most of the neck vertebrae bear a pair of elongate and slender ribs that extend posteriorly [backwards] well past the subsequent vertebrae. The result is a bundle of overlapping neck ribs that would have acted to keep the neck in an almost permanent horizontal position, so movement of the neck would have been severely restricted. Indeed, the comparison of the neck ribs to the ossified tendons of hadrosaur tails seems appropriate-both would have provided a great deal of rigidity.”

So there we have it: Tanystropheus sported a long, stiff, neck that was nearly always held in a horizontal (or at least very straight) position, thus rendering certain reconstructions in complete conflict with the available evidence. With these facts in mind, the obvious question becomes “what the devil was Tanystropheus doing with this neck?” To answer this, the situation grows a bit more complicated…

First of all, it should be noted that specimens of Tanystropheus are nearly always found in strongly marine deposits (of southern Europe) in fair abundance. This, coupled with the fact that such an enormous neck would be nearly impossible to maneuver in a terrestrial environment, strongly suggests that these beasts were highly aquatic. Furthermore, it’s snout contained a series of long, interlocking teeth which are the perfect tools for piercing and grasping slippery fish. Based on this interpritation, in the deeper depths of the sea (to once again quote Mr. Fraser), “fish would only have been aware of a relatively small and apparently innocuous head at the end of a long neck. The recesses of the water would hide the bigger body. All of a sudden it would have been too late, and another fish or cephalopod would have become nothing more than a tasty morsel!”

Tanystropheus cranial profile. Courtesy of the Hairy Museum of Natural History.

However, as is frequently the case in paleontology and functional morphology, the case is far from closed.

It’s been noted that Tanystropheushad a foot structure which bore far greater similarity to that of a land-dwelling creature than to that of a marine beastie. Also, young Tanystropheus sported multicusped cheek teeth towards the back of their mouths, which were later lost as these animals matured. This has suggested to some researchers that juveniles fed upon insects and lived on land before ‘graduating’ into an aquatic, piscivorous (fish-eating) niche.

However, neither of these arguments is necessarily in conflict with the ‘aquatic predator’ scenario. It’s possible that the animal may have spent most of its time walking along the seafloor in search of prey, much like a modern snapping turtle. As for the alternate dentition in juveniles, even the necks of the youngest Tanystropheus were too large to avoid facing the aforementioned difficulties of living in a land-based environment and thus, the idea that they may have eaten insects becomes highly questionable. They were probably receiving their nourishment from different prey items than their mature counterparts, but as far as many paleontologists are concerned, terrestrial arthropods are out of the question.

A 2006 discovery has effectively thrown a monkey wrench into the already mangled mess. The specimen in question was a partial skeleton which contained the first known remains of Tanystropheus soft tissue which revealed two interesting facts:

1) Tanystropheus was draped in rectangle-like, non-overlapping scales for at least part of its body.

2) The base of the animal’s tail was surrounded in part by “wide patches of black material” which have been interpreted to suggest that these creatures had an enormous amount of flesh posterior to its hind-limbs. Or, as Matt Celeskey so eloquently puts it:

Here's Tanystropheus displaying the 'reverse amphibian' scenario, which involves the animal sitting ashore and plucking fish from their watery utopia.

In his book of the same year, Nicholas Fraser also commented on Tanystropheus‘ backside, saying:

“The presence of ‘postclocal’ or ‘heterotopic’ bones on the tail in some specimens clearly shows that there was sexual dimorphism. Perhaps these bones were associated with a copulatory organ, and thus individuals bearing them were probably males. However, the bones are both much more complex than those known to occur in lizards, and also much larger-almost too large to be associated with such an organ, being approximately the same dimensions as the pelvic girdle. An alternative theory is that they supported some kind of brood pouch. If the adults were unable to come out onto land, it might be speculated that the females retained the eggs or embryos in some kind of internal pouch and gave birth to live young at sea. However, there is currently no really plausible explanation for the precise function of these heterotrophic elements.”

I believe that these two observations are likely related…something was going on near Tanystropheus‘ privates. This is not, however, the first occasion in which someone has proposed an unusual function of this region of the animal’s body. In 1973, paleontologist Rupert Wild claimed to have seen fracture planes on a specimen of Tanystropheus caudal vertebrae which, if true, would mean that this animal could drop its tail like a lizard. This idea was later incorporated into BBC’s mediocre “Sea Monsters” mini-series as seen below:

However, other scientists who subsequently reviewed these specimens seldom arrived at the same conclusion. Furthermore, as Italian paleontologist Dr. Silvio Renesto writes in a thread on “The Dinosaur Mailing List”:

“Moreover, as I repeatedly stated in many occasions (and Olivier Rieppel also
wrote in a JVP paper on Macrocnemus) caudal autotomy is not feasible in such a
big animal. The physiological cost is too heavy I presume. As far as I know the
big monitor lizards do not lose their tail and they ARE lizards. In addition if
the animal was aquatic how did it move if the body became totally unbalanced?
The same is true on land.”

Thus, it seems highly unlikely that this animal mimicked modern lizards in this regard. Precisely what Tanystropheus did do with its hindquarters, however, remains one of the many mysteries which surround this wonderfully bizarre beast.

May the fossil record continue to enchant us all!