Weekly Wonders: Prodeinotherium

24 01 2010

Good tidings and well-wishes!

(NOTE #1: Despite WordPress’ argument to the contrary, this post was in fact written on Saturday, January 23rd, so it counts!)

(NOTE #2: Due to the unfortunate fact that I’ve been unable to locate any reconstructions of Prodeinotherium, all of the images displayed in this post depict it’s more famous relative Deinotherium unless otherwise indicated)

As amusement park caricaturists are well-aware, celebrities often become synonymous with a given trait. For instance, if you’re anything like me, when you consider “big chins”, Jay Leno comes to mind, and when someone gives mention to “greasepaint moustaches”, your mind turns to Groucho Marx. In fact, the latter example became so fundamental to the man’s identity that, according to legend, he’d routinely go without his trademark nasal attire to avoid public detection.

This trend isn’t at all unlike that which accompanies how our brain learns to recognize various animals. Attempting to imagine a horse without its hooves or a bird without its feathers often proves to be an extraordinarily difficult feat. Yet, the fossil record clearly indicates that such creatures once existed. In addition, it would appear that, even during their presence, both characteristics have displayed a significant amount of diversity within their respective group’s evolutionary tree. Which brings us to elephants…

Proboscidean trunks, so characteristic of the order’s modern representatives, have likely undergone a similar amount of variety during their 35-million-year-old history, yet it’s notoriously difficult to be more specific to this end due to the fact that they simply don’t fossilize. Thus, with the obvious exception of frozen Mammuthus primigenius specimens, any attempt to reconstruct their appearance on extinct genera must be made on the basis of the skull in question. Yet this is hardly a foolproof method. For instance, most illustrations of Platybelodon, Amebelodon, and their kin display a short, flap-like proboscis which came to be unchallenged within the paleontological community’s collective psyche until Dave Lambert made the assertion that, on the basis of morphological evidence, the trunks of these animals were much more like those of modern elephants. However, when it comes to controversial trunks, no group can challenge the family of this week’s featured beast, the Deinotheriidae.

Prodeinotherium teeth being measured.

According to Jeheskel Shoshani and Pascal Tassy’s definitive text “The Proboscidea: Evolution And Paleoecology Of Elephants And Their Relatives”, no one was quite sure what to make of the Deinotheriidae in the years following its discovery in the form of isolated teeth which were assigned to extinct rhinos, tapirs, and ground sloths before “a partial skeleton was unearthed during the collapse of an embarkment on the Prague-Brunn railroad in 1853”. Even now, their taxonomic allegiances remain a point of dispute: though most authorities place them within the proboscidea, others maintain that they represent a sister group.

Traditional Deinotherium reconstruction.

While their direct ancestry is fairly ambiguous, the earliest Deinothere known to science is the hippo-sized Chilgatherium harrisi from the late Oligocene of Ethiopia, which is consistent with the theory that the proboscidea initially emerged in Africa. The group appears to have persisted for 20 million years until the latest-known genus, Deinotherium bozasi of Kenya, finally went extinct in the late Pleistocene (their extinction may have been directly related to the spread of grasslands and competition from the Elephantids during the Pliocene). During the course of the family’s evolution, relatively few significant anatomical alterations were obtained (especially when one considers the uncanny diversity of the Gomphotheriidae) other than a progressive increase in size. Geographically, the Deinotheriidae was more ‘adventurous’, having spread to Eurasia during the early Miocene with Prodeinotherium sp. leading the charge.

A lone Deinotherium patrols a Spanish plain during the late Miocene.

The earliest Prodeinotherium species, P. hobleyi, is known from early Miocene deposits in Eastern Africa. As the genus spread, new species began to appear in Pakistan (P. pentapotamiae) and France (P. bavaricum). During the mid-Miocene, these animals started to become replaced by Deinotherium species: D. bozasi, D. giganteum, and D. indicus, respectively. This raises an intriguing question: did Deinotherium emerge from one ancestral species, or did each aforementioned Deinotherium species evolve from its local Prodeinotherium counterpart? Hopefully, further research will clear up the genus’ mysterious origins.

An enormous Deinotherium giganteum pursues a pair of Australopithecus in a promotional image for BBC's 'Walking With Beasts" mini-series.

In “Evolving Eden: An Illustrated Guide To The Evolution Of The African Large-Mammal Fauna”, Alan Turner lists the following characteristics of the Deinotheriidae family:

“Members… have high crested teeth… They are well known in the African fossil record, especially in the Pliocene of eastern areas with the species Deinotherium bozasi… Deinotheres are distinguished from other proboscideans by the absence of upper tusks and the presence of distinctive, downwardly curved tusks in the lower jaw and by the elongated shape of the skull.”

Prodeinotherium is distinguished from its more famous namesake by it’s proportionally smaller size, forelimbs, and molars.

Right, then. Now that we’ve discussed the evolution and distinguishing characteristics of this week’s animal and the family to which it belonged, it’s time for the fun part: analyzing it’s dietary behavior and soft-tissue anatomy (that sentence alone seems sufficient enough to qualify yours truly as a grade-A nerd, but who’s complaining?).

Yet another traditional Deinotherium reconstruction.

One of the first things any budding paleo-mammology enthusiast grows to learn and appreciate is the importance of mammalian teeth: a fact which is just as prominent in the Deinotheriidae as in any family of mammals. Shoshani writes:

“The… shearing teeth of deinotheres were ideally suited for processing soft foliage. Loss of the upper tusks and the downturned nature of the lower tusks would have permitted more direct access of food to the mouth, and could justify an interpretation of a short, tapir-like proboscis in these animals [(more on that later)]. Many deinothere tusks show evidence of wear, although no consistent wear pattern or location has been identified. The fact that deinotheres had long legs but short necks enables one to argue against frequent use of their tusks for, and [it’s been suggested] that these tusks could have been used as sources of purchase for manipulation of a short proboscis or even for recognition of individuals by members of the same species.”

In “Mammoths, Sabertooths, And Hominids: 65 Million Years Of Mammalian Evolution In Europe” Jordi Agusti makes the following observation:

“The shape of muscle insertion areas in the neck vertebrae and posterior skull of deinotheres reflects a marked specialization for enhanced movement in the vertical plane. Compared with those of a modern elephant, the muscles that pull the head up and those that bring it down [could] act through a wider arc. This was very likely related to the action of the downward-pointing tusks, although the precise function of the tusks remains a matter of debate. Since the deinotheres were clearly obligate browsers- as indicated by the morphology of their cheek teeth- it seems likely that the tusks were used in concert with the trunk to gather foliage from the branches of trees.”

As I hinted at the onset of this post, the trunks of the Deinotheriidae are by a wide margin the family’s most controversial feature. To explain why, allow me to reference an excellent 2008 post on the subject fromThe World We Don’t Live In“:

“When [the legendary paleontologist Henry Fairfeld] Osborn first reconstructed Deinotherium back in 1910, he drew it with a short, flap-like trunk much like a tapir’s, but later dropped that reconstruction for no known reason…This reconstruction was revived by [Georgi] Markov [along with his colleagues N. Spassov & V. Simeonovski in 2001] . From a study of the skull’s shape, they deduced that Deinotherium must have had a short, tapir-like snout hanging over its descending lower jaw. A long trunk was not necessary, as a browser standing 5 m high at the shoulder had little need to reach the ground. The tusks remained free for whatever purpose they served, and the nostrils, at the end of the proboscis, could smell and inspect food.”

Deinotherium reconstruction with a short, tapir-like trunk.

However, not everyone buys into this interpretation, as many paleo-artists still reconstruct Prodeinotherium and its kin with lengthy, sinuous trunks which resemble those of their modern relatives. Nevertheless, it goes to reveal that, as with a great many congregations of organisms, the scientific community still has much to learn about the evolution and diversity of the proboscidea.

May the fossil record continue to enchant us all!

UPDATE: God, I love my readers! Doug has courteously scanned a few of Mauricio Anton’s amazing Prodeinotherium illustrations which I’ve displayed below (note that the latter sketch compares a P. hobleyi to a modern African bush elephant (Loxodonta africana). Many thanks!!

‘Weekly’ Wonders (Mini Version): Gomphotaria

18 01 2010

Good tidings and well-wishes!

(NOTE: In light of my recent preparation for the onset of my fourth semester later this week, this post will be on the small side comparatively. My apologies go to any and all pinniped enthusiasts who might be reading this.)

While popular culture maintains that cetaceans and sirenians are fascinating, majestic, and wonderfully mysterious animals, considerably less reverence is maintained for another group of modern marine mammals: the pinnipeds. Perhaps this unfortunate tendency is the result of the fact that, while whales, dolphins, manatees, and dugongs roam the seas without ever having to return to the recesses of ‘our world’ and are thus perceived to be ‘earth-bound aliens’ of sorts, their oceanic grace and manuverability, seals, sea lions, and walruses are still very much tied to the terrestrial habitats of their ancestors. Thus, they’re invariably denied the admiration reaped by their distant relatives simply because of the fact that they seem too similar to ourselves by comparison.

However, though you wouldn’t know it by following the mainstream media, pinnipeds are actually a surprisingly diverse group with a rich history of their own, which has been studded by a menagerie of intriguing genera including this week’s beast: Gomphotaria pugnax, a unique Miocene mollusk-eater from the coast of modern California.

Gompotaria skull. (Courtesy of http://www.coastalpaleo.blogspot.com)

Before moving on to coverage of this bizarre and somewhat ferocious-looking beastie, a review of it’s phylogeny is in order. Gomphotaria  is a member of the Dusignathinae, a group whose exact affinites are rather controversial. According to the paleobiology database, it’s been alligned with the Otariidae, the Odobenini, and the Odobenidae with the majority of recent authors asserting that it was a superfamily belonging to the latter. In the masterful second edition of the textbook “Marine Mammals: Evolutionary Biology”, authors Annalisa Berta, James L. Sumich, and Kit M. Kovacs write “The Dusignathinae includes the extinct genera Dusignathus, Gomphotaria, [and] Pontolis…Dusignathine walruses  developed enlarged upper and lower canines, whereas odobenines evolved only the enlarged upper canines seen in the modern walrus.”

Right, then. On to the featured critter itself!

Lawrence Barnes and R.E. Raschke formally described Gomphotaria in a 1991 paper, a key excerpt of which reads as follows:

“Both upper and lower canines are enlarged and procumbent and worn anteriorly, indicating that the animal may have probed the substrate in search of benthic invertebrates for food. Extreme breakadge and subsequent wear of large, single-rooted cheek teeth indicate that at least some, if not all, the food species (e.g. mollusks) probably had hard shells. Absence of a highly vaulted palate, present in walruses, indicates that G. pugnax did not suck bivalve tissues using the tongue-piston method employed by walruses [(the modern walrus, Odobenus rosmarus, feeds by attatching its strong lips to the prey item in question before rapidly withdrawing its tongue which creates a vacuum. The pinniped’s vaulted palate eases the process)] .”

Gomphotaria reconstruction, courtesy of Wikipedia.

May the fossil record continue to enchant us all!

‘Weekly’ Wonders: Platyhystrix

3 01 2010

Good tidings and well-wishes!

One can easily recognize when a prehistoric creature has made its way into the public consciousness by observing how frequently vaguely similar extinct organisms are mistaken for it. Anyone who’s ever attempted to give a tour of a natural history museum or present a paleontology lecture to a high school audience is acutely aware of such a group’s propensity for identifying any large theropod as a “T. rex“, any small one as a “Velociraptor“, any hairy proboscidean as a “Woolly Mammoth”, and any extinct mammal with enlarged canines as a “Saber Toothed Cat”.  To this end, it would appear that despite (or perhaps because of) its incessant misidentification as a dinosaur, the non-mammalian synapsid Dimetrodon has become one of these relatively well-known beasts in light of the fact that nearly every layman I’ve encountered proclaims that any extinct quadrupedal tetrapod with a sail is a member of the genus. However, it’s no secret that Dimetrodon certainly didn’t have a monopoly on this description, as many of its contemporaries such as Edaphosaurus and the eccentric Secodontosaurus fit the bill quite nicely as well (to say nothing of the Triassic Arizonasaurus). But perhaps the most interesting of these look-alikes wasn’t even a synapsid or amniote at all: instead, one could easily make the case that this critter was in fact the temnospondyl Platyhystrix rugosus.

Platyhystrix as drawn by Matt Celeskey of hmnh.org

The temnospondyli order was arguably the most successful group of non-amniotic terrestrial vertebrates to have ever existed and as such, was far too large and diverse to allow the constraints of this particular blog entry to boast adequate coverage of the congregation as a whole (for a nice introduction, do go here). For our purposes, we need only to concentrate upon the dissorophidae superfamily: a clade which has acquired a decent amount of attention due to its inclusion of Doleserpeton which may have been related to the ancestor modern frogs and other lissamphibians. The most obvious feature which unites this superfamily is the presence of bony plates which were either fused to the neural spines or lying just above them. Additional characteristics include long, slender limb elements and relatively large orbits (‘eye sockets’). For the full list, check out the Palaeos entry. Dissorophids made their grand debut in the late Carboniferous (aka: ‘the Pennsylvanian’ for my fellow American paleo-nerds) and persisted onwards throughout much of North America and Europe until at least the late Permian, although some authors contend that  Micropholis of the early Triassic may have belonged to the group.

Right then, now that we’re taxonomically up to speed, let’s have a look at Platyhystrix itself. In his exquisite new book “The Rise Of Amphibians: 365 Million Years Of Evolution”, Robert Carroll writes:

“Isolated pieces of laterally compressed and ornamented neural spines have long been recognized from Lower Permian and even Upper Carboniferous sites in North America, but rarely with even fragments of the skull or appendicular skeleton…the most complete sequence of neural spines, showing a pattern broadly resembling the ‘sail’ of edaphosaur pelycosaurs, from the area of the atlas arch to the 15th dorsal vertebra…Subsequently, [a skull was prepared in 1981], originally collected by David Baldwin in 1881 from the lower Permian Cutler Formation in New Mexico, which showed an extremely rugose texture, closely associated with spines initially attributed to Aspidosaurus. The lateral edges of the skull table are ridged as in Broiliellus and Dissorophus. Comparable neural spines designated Astreptorhachis ohioensis, from the Upper Pennsylvanian Conemaugh Group of Ohio, support the earlier divergence of this group, near the time of emergence of the amphibamids.”

Platyhystrix neural spine.

This essentially wraps up all known information about Platyhystrix as of this writing, excluding the rather amusing fact that the genus literally means ‘flat porcupine’ (also, the critter would have been approximately 1 meter long in life). However, the animal does warrant further consideration due to its role in one of the most interesting riddles paleobiology has yet to definitively solve: the enigma of ‘sail-backed’ prehistoric faunas.

In another excellent Matt Celeskey illustration, a Platyhystrix attempts to evade an attacking Ruthiromia.

(Click here to see the original post containing the above illustration)

For those significantly less nerdy than yours truly, this mystery stems from the fact that those long-extinct vertebrates which sport massive sails running down their backs are almost invariably found in either the same or nearby deposits as contemporary species with roughly the same feature. The most famous example of this is manifested by the case of Ouranosaurus and the ever-popular Spinosaurus. Although the two dinosaurs have to the best of my knowledge never been found within the same deposits, they nonetheless lived at roughly the same period of time and at similar locales (approximately 110 million years ago in Northern Africa). The situation is made more interesting, however, by the fact that the lower Permian of Texas and New Mexico has yielded not only Platyhystrix, but Dimetrodon, Edaphosaurus, and Secodontosaurus as well, all of which are easily recognized by their prominent dorsal ‘fins’. These latter beasts exhibit far more diversity, for while Spinosaurus and Ouranosaurus each have relatively broad and laterally-compressed neural spines, only those of Platyhystrix are even roughly comparable. Dimetrodon and Secodontosaurus each had fairly rod-like structures while the sail of certain Edaphosaurus species was riddled with horizontal bars. Although both groups of vertebrates are united in the fact that their respective habitats were most likely warm, wet swamps, it’s difficult to see just how this sort of environment would have produced such extravagant animals. Hopefully, additional information on these curious organisms and the ancient terrains which housed them will shed light on this most intriguing of questions.

A pair of Edaphosaurus take a leisurely stroll while a relatively small Platyhystrix scuttles about in the foreground.

May the fossil record continue to enchant us all!

Week Of Wonders: Sebecus

19 12 2009

Good tidings and well-wishes!

Terrestrial crocodylomorphs have been gracing the various postings of this blog since its earliest days and thus, I felt it would be quite fitting to throw the spotlight upon one of these magnificent creatures for the conclusion of ‘The Theatrical Tanystropheus’s first week-long ‘special’. So, without further ado (boy, that’s a first!), I now present the star of today’s installment of my ‘Week Of Wonders’ series:  Sebecus icaeorhinus.

A crocodylomorpha 'family portrait'. Sebecus itself can be observed crouching down in the stream on the left (more on that later).

As per the general protocol of this space, a discussion concerning the animal’s taxonomic affiliations is in order. Though you wouldn’t know it from looking at modern specimens, the crocodylomorpha has undergone a fascinating evolutionary history featuring dozens of intriguing players which ranged from streamlined aquatic predators to turtle-crushing behemoths to stout terrestrial omnivores. Until fairly recently, the superorder was divided into the suborders Eusuchia, Mesosuchia, Thalattosuchia, and Protosuchia. However, a handful of papers published earlier this decade have since re-arranged this antiquated setup.

The crocodylomorpha's place within the sauropsida class.

Under the new system, Sebecus and its relatives have been placed within the Mesoeucrocodylia taxa, which includes the Eusuchia, Thallatosuchia, and now-obsolete Mesosuchia suborders. The group is united by the following characteristics:

-The secondary palate is expanded toward the rear.

-The vertebrae are amphicoelous (concave at both ends).

When we attempt to more specifically define Sebecus‘ taxonomic place, however, problems emerge. There simply isn’t enough space for me to describe the current state of the Sebecosuchia suborder, so I’ll send everyone to ‘Why I Hate Theropods‘ for a nice overview. In 2007, sebecosuchians were treated to a fairly extensive revision which, among other things, dissected the Sebecus genus by re-naming “S. huilensisLangstonia huilensis, and “S. querejazus” Zulmasuchus querejazus (These updates along with several others put forth that year [see above], have effectively reduced the genus to a single species: S. icaeorhinus).

A sebecosuchian tooth

Nonetheless, the Sebecosuchia is characterized by the following traits (from ‘palaeos.com’):

“Active terrestrial predators. Tall, narrow rostrum [(‘snout’)]; sides of rostrum tall and nearly vertical; teeth long, curved, laterally compressed  (very similar to theropod teeth) [(in point of fact, they’re so similar that until the late 1930’s, several paleontologists used them as evidence behind the idea that non-avian theropods had survived the K-T event)] ; 4 teeth on premaxilla; 10-11 teeth on maxilla; no enlarged maxillary teeth; teeth widely spaced, intercalate; posterior ends [(‘rear ends’)]of maxillae meet on palate anterior to [(‘in front of’)]palatine; broad maxilla forms sides of rostrum, and narials forms flat dorsal [(‘top’)] portion, terminating in a premaxilla with substantial diastema; maxilla and premaxilla do not overlap; no maxillary fenestra [(‘holes’)]; nares [(‘nasal openings’)] face antero-laterally [(‘forward and to the side’)] or dorso-laterally [(‘upward and to the side’)]; maxilla and, especially, premaxilla deeply sculptured with deep pits connected by channels; rostrum widens abruptly in front of orbits [(‘eye sockets’)]; orbit relatively small; angular and surangular large, long and strongly curved dorsally [(‘upwards’)].” 

Sebecus skull (heavily reconstructed).

The suborder is furthermore divided into three families: the Baurusuchidae, the Bretesuchidae, and the Sebecidae. Naturally, Sebecus falls within the latter alongside Langstonia, Ayllusuchus, Barinasuchus, & Ilchunaia.

A modern Alligator modified to resemble a juvenile Sebecus.

As with many taxonomic identification systems, the characters mentioned earlier almost exclusively refers to cranial features. How, then, can we assert that Sebecus and its relatives were terrestrial predators? Well for starters, the comparatively rare limb bones (and the even scarcer articulated skeletons) of these beasts tend to bear a much greater resemblance to those of rauisuchians than to the traditional crocodilian physique (in fact, their proportions suggest that they likely severed all ties to any sort of liquid habitat). However, the skull itself offers a significant amount of evidence towards the land-based hunter interpretation, for the teeth of these crocs conform to a ziphodont mold, meaning that they’re compressed from side to side, slightly recurved, and serrated along their edges: a pattern which frequently found in terrestrial carnivores, but is rarely seen in their aquatic counterparts.

A pair of Baurusuchus square off, exhibiting the generally-accepted terrestrial crocodylian stance.

In his excellent 2002 book, “King Of The Crocodylians: The Paleobiology Of Deinosuchus”, David R. Schwimmer (not to be confused with the actor who famously portrayed a geeky pseudo-paleontologist) writes (note that, for the sake of modern accuracy, any mention of ‘Sebecus‘ should be replaced with ‘Sebecus and its kin’) (NOTE: Certain parts of the following quote are debatable and/or inaccurate. See the ‘comments’ section for details) :

“The sebecosuchids were… the last terrestrial crocodylomorphs in the fossil record, and the namesake genus Sebecus apparently survived and flourished in isolation in South America, when it was separated from both Africa and the Northern Hemisphere during much of the Tertiary period. Sebecus filled the role of dominant large predator there until the Pleistocene, when North American predators (eg: big cats) entered South America via the Central America land bridge When Sebecus went extinct, less than 1.0 Million Years ago, it was the last remaining mesoeucrocodylian below the neosuchian grade- and at the same time the last crocodylomorph below the eusuchian grade!”

May the fossil record continue to enchant us all!

Week Of Wonders: Ophiacodon

18 12 2009

Good tidings and well-wishes!

Longtime readers of ‘The Theatrical Tanystropheus‘ may have observed my general tendency to ignore non-avian dinosaurs within its confines. This trend is largely due to the simple fact that nearly every lay person with whom I become engaged in a discussion concerning paleontology seems to be utterly convinced that the subject should simply be re-named ‘dinosaur-ology’ to disambiguate its intended purpose. In other words, the average person seems to think that either paleo is concerned only with the 165-million year reign of the dinosauria (to the exclusion of their descendants of course) or, worse, that anything which becomes extinct is automatically classified as a ‘dinosaur’ by the scientific community (Zach Miller of ‘When Pigs Fly Returns’ recently created a post through which those of us in the blogosphere can vent our frustrations with this latter aggravating phenomenon).

However, at this time, I feel that it’s necessary to remind everyone precisely whose responsibility it is to remedy this regrettable situation: those of us currently taking residence in the paleontological community. If we cannot bring our own academic fields into the public consciousness, who can?

Since this rant has already taken up too much space, I’ll descend from my soap box and redirect those interested to this exquisite diagnosis of the problem from both perspectives in order to move on to the subject at hand.

Virtually no prehistoric organism of any era is more commonly mistaken for a dinosaur than the infamous Dimetrodon , even though the animal is quite demonstrably more closely akin to us than it is to any ‘terrible lizard’ (which is actually a mis-translation. Check this out!). However, I’d like to dedicate this particular post to an early relative of the famed beastie which was somewhat less showy (though just as interesting) and accordingly receives far less attention from the popular media and scientific community alike: Ophiacodon sp. of the early Permian.

Ophiacodon reconstruction

Ophiacodon was a moderately large (species ranged from 2 to nearly 4 meters in length) pelycosaurs, a wonderfully diverse group of non-mammalian synapsids hailing from the Carboniferous and (mostly) early Permian (though some species held out until the second half of the latter period). The pelycosauria order was among the first group of amniotes to evolve, paving the way for virtually every organism most of us instantly picture when we hear the word ‘animal’, including ourselves.

A trio of Pelycosaurs: Cotylorhynchus in the background, Ophiacodon in the midground, and Varanops in the foreground.

However, most of the scientific community recognizes them for pioneering another characteristic: the ‘synapsid skull’. According to the invaluable ‘palaeos.com’ entry on the pelycosauria:

“[The cranium] features a single, large opening on the side of the skull (the temporal region) behind the orbit (eye socket). This special opening allowed the development of larger and longer jaw muscles, and hence stronger jaws that could be opened wider and closed forcefully, enabling the animal to dispatch struggling or larger prey. It was this simple evolutionary adaptation that gave the pelycosaurs the edge in the struggle for survival. All that was needed was a prolonged period of drought, such as the sudden period of aridity during the Kasimovian Period, to kill off many of the large stem tetrapods that kept the pelycosaurs insignificant, and these creatures were able to emerge as the dominant life-form on Earth during the Permian period, while the captorhinids remained small and relatively insignificant.”

An Ophiacodon skull which exhibits the traits mentioned in the previous paragraph.

Ophiacodon itself was more specifically the name-giving genus of the Ophiacodontidae family, a group from whence the sphenacodontids and edaphosaurids would later emerge. The most obvious traits uniting the family’s members are their disproportionally-large elongate skulls and massively wide shoulder girdles (the latter was almost certainly utilized to help support the former). Their awkward proportions and cone-like teeth have traditionally led most scientists to believe that these were semiaquatic piscivores, however, this interpretation is likely a definitive example of being wrong and right simultaneously.

A collection of Ophiacodon teeth.

Fairly complete Ophiacodon skeletons have revealed that the creature’s wrists and ankles were weakly attatched to their respective limbs, suggesting that the animal’s legs were largely incapable of equipping it with an efficient means of terrestrial locomotion. This fact throws additional weight to the idea of Ophiacodon being an obligate fish-eater, but precisely how the beast captured its scaly prey (fun fact: skin impressions of Ophiacodon and its relatives reveal that these animals were scale-less throughout much of their bodies but nevertheless sported dermal scutes on their bellies)  remains highly debatable.

Ophiacodon skeletal mount.

Many Permian workers have maintained that Ophiacodon may have swung its skull from side to side through a body of water while pursuing fish. However, one huge factor obstructs this view: the skull itself. As the 181st entry of the Carnegie Institute Of Washington’s Publication pointed out in 1913,

“the skull [of Ophiacodon] is remarkably narrow, high, and long. The very small nares [(‘nasal openings’)] are at the extreme front end, the small orbits are far posterior [(‘very far behind them’)]. The upper side is flattened in the frontal and parietal region: it’s greatest width is just behind the orbits… Immdeiately in front of the orbits the upper surface narrows; thence to the nares the border, formed chiefly by the nasals, is gently convex in outline. Doubtless in life the very broad sides of the face were gently convex, but, as preserved, the thin bones forming them are nearly in contact, producing a light concavity between the thickened alveolar border of the maxilla and the thickened nasal border; the bones of this region are scarcely thicker than writing paper for the most part…”

Ophiacodon skull replica in aerial view.

This most certainly is not the skull of an animal which actively pursues fish by laterally swinging its skull as the aforementioned Permian paleontologists have argued because if it’s utilized in this fashion, an immense amount of drag will hinder its progress (try striking a fast moving fish underwater with the broad side of an oar and you’ll see what I mean).

A fishing Ophiacodon reconstruction.

So just how did Ophiacodon and its kin use their bizarre skulls? Recently, the paleontology department of the Houston Museum of Natural Science has put forth the following idea for Dimetrodon’s dietary habits: the creature may have used its massive size to tackle large and cumbersome freshwater sharks (such as Xenacanthus) with whom it shared its semi-aquatic environment. Though Dimetrodon was much more heavily-built than any ophiacodont, this scenario provides an intriguing hypothetical answer to one of the fundamental questions about these latter animals which has plagued the scientific community for several decades.

May the fossil record continue to enchant us all!

Week Of Wonders: Carinodens

17 12 2009

Good tidings and well-wishes!

Aside from dinosaurs, pterosaurs, mammoths, and ‘saber-toothed cats’, few groups of ancient fauna can claim strong international fan bases like the various extinct marine reptiles of the world can. You can argue that it stems from the age-old mythology of sea-serpents or that it merely extends from the human fear of the ocean’s depths, but you simply can’t deny the universal appeal of these aquatic beasties. However, as with nearly any paleontological bestiary, nothing sells interest to the general public quite like an intimidating animal of a bygone age: and with all due respect to the plesiosauria, icthyosauria, and thalattosauria (along with many others), no collection of marine reptiles proves to be quite as terrifying to imagine alive as the mosasauridae. (To get an idea of just how monstrous some of these things were, do go here).

Yet every congregation of Goliaths is sure to have its David, and to the mosasaur family, ‘David’ is known as Carinodens sp, a ‘pint-sized’ species of the Netherlands.

Carinodens reconstruction, courtesy of 'oceansofkansas.com'.

At 3.5 meters in length, it’s safe to say that were any of us to find ourselves in the company of Carinodens during a late Cretaceous swim, we’d hesitate before referring to the creature as a ‘dwarf’ of any kind. Yet when one considers the fact that certain mosasaurs may have reached 15 meters from nose-tip to tail-tip, the animal’s miniscule distinction seems appropriate.

As usual, before we can fully appreciate the eccentricities of Carinodens itself, an introduction to the seagoing critter’s phylogeny is required.

Carinodens jaw fragment.

The beast belongs to the mosasaurinae subfamily which, according to D.A. Russel in “Systematics and morphology of American mosasaurs” is defined by the following features:

“Small rostrum present or absent anterior [(‘in front of’)] to premaxillary teeth. Fourteen or more teeth present in dentary and maxilla. Cranial nerves X, XI, and XII leave lateral wall of opisthotic through two foramina [(‘openings’)]. No canal or groove in floor of basioccipital or basisphenoid for basilar artery. Suprastapedial process of quadrate distally expanded. Dorsal edge of surangular thin lamina of bone rising anteriorly to posterior surface of coronoid…At least 31, usually 42–45 presacral vertebrae [(meaning ‘those before the hip region’)]present. Length of presacral series exceeds that of postsacral, neural spines of posterior caudal vertebrae [(‘tail vertebrae’)] elongated to form distinct fin. Appendicular elements [(‘those dealing with the arms and legs’)] with smoothly finished articular surfaces, tarsus and carpus well ossified.”

More specifically, Carinodens is a member of the Globidensini tribe, the members of which are famous for their unorthodox dental arrangements.

Carinodens' larger relative, Globidens. Courtesy of 'oceansofkansas.com'

Traditional reconstructions have overwhelmingly depicted globidansine mosasaurs as shell-crushing oyster eaters, although it’s been suggested that cephalopods and arthropods may have been on the menu as well. In 2005, the question of what precisely Carinodens and its relatives ate was visited by the Maastricht Museum of Natural History’s A.S. Schulp, who utilized the discovery of a recently-discovered group of material to create a ‘mechanical mosasaur’ which was designed to crush various marine animals between its jaws. The experiment revealed that

“a biomechanical model of the bite force of Carinodens applied to a mechanical jaw model provides a constraint on the possible prey items this mosasaur could have processed. Echinoids, smaller bivalves, and gastropods are considered to have been likely prey items. Carinodens was probably less successful in crushing larger bivalves such as scallops and oysters which exceeded 100 mm in size. Particularly rounded gastropods, such as winkles, may not have provided sufficient grip to be crushed… The fact that the dentition of Carinodens was well adapted for crushing hard-shelled prey items does not imply that it did not eat softer food. Animals such as shrimp are quite easily processed, so there is no reason to exclude such animals a priori from the menu.”

May the fossil record continue to enchant us all!

Courtesy of oceansofkansas.com

Week Of Wonders: Coryphodon

16 12 2009

Good tidings and well-wishes!

When asked to cite my favorite sub-discipline of biology by interested parties, I often find myself at an uncharacteristic loss for words. As an academic marriage of geology and bio, my beloved field of paleontology certainly can’t qualify as a finalist for this distinction. This fact results in a three-way tie between evolutionary studies (which, I hardly need tell my fellow nerds, covers an enormous intellectual area), psychobiology (which nicely combines my love of the humanities and social sciences with my passion for evolutionary biology), and the centuries-old subject of comparative vertebrate anatomy.

This latter science is a beautiful thing in that it so very often lends an enormous amount of scientific credence to the notion that ‘looks can be deceiving’. For the proponents of this science have shown that their beloved domain can do much more than assist us in our efforts to ascertain the identities of the various chimeras which have proclaimed their existence to the scientific community through the ages: it can also reveal that those creatures which, at first glance, appear to be entirely mundane are actually far more interesting than anything which we could have possibly imagined. Last spring, I utilized this column to feature the strange case of Sivathertium: a moderately-large giraffid which, according to most any initial inspection, resembled a moose with an elongated skull. Nearly six months later, I’d like to draw the attention of my readership to the anatomical story of another bizarre animal: Coryphodon sp. of the Eocene.

Let’s begin by examining the animal’s skeleton as displayed below:

Coryphodon sp. Skeleton (Courtesy of Wikipedia)

Mammal enthusiasts are likely to assume that this beastie was merely a type of prehistoric Hippopotamus as suggested by its relatively stout limbs, barrel-like chest, and fearsome jaws.

However, perhaps we should now compare it to a skeleton of an actual Hippopotamus:

The two aren’t exactly uniform in composition, are they?

In their excellent book, “Mammoths, Sabertooths, And Hominids: 65 Million Years Of Mammalian Evolution In Europe”, Jordi Augusti and Mauricio Anton write:

“the skeleton of Coryphodon [is] a mixture of traits reminiscent of those of different kinds of animals. The trunk vertebrae have surprisingly weak neural spines for such a big animal [(Coryphodon was approximately 1 meter in height and 2.25 in length)], suggesting a partly amphibious lifestyle, like that of modern hippos. The long bones of the limbs resemble in structure those of heavy perissodactyls like rhinos and tapirs, while the feet, retaining all five digits, are like those of modern elephants in structure. In side view, the head vaguely resembled that of the Paleocene arctocyonids, with huge canines, although this animal was not an omnivore like the latter, but a specialized vegetarian.”

Coryphodon foot reconstruction, which, as the authors have pointed out, really resembles that of an elephant more than anything else.

Although Coryphodon certainly bore distinct resemblances to various members of the artiodactyla, perissodactyla, proboscidea, and arctocyonidae, this intriguing herbivore owed its phylogenetic allegiance to none of these groups. So what the hell was it?

The animal actually belonged to the extinct order pantodonta: one of the first groups of herbivorous mammals to truly attain relatively large sizes.  A list of the group’s distinguishing characteristics may be located here.

Restorations of some pantodonts of the North American Paleocene. A. Coryphodon. B. Barylambda. C Titanoides primaevus. D. Caenolambda. E. Pantolambda cavirictus. E. Pantolambda bathmodon. (Courtesy of paleocene-mammals.de)

As the preceeding image indicates, pantodonts were a wonderfully diverse lot despite their aforementioned similarities. While our hippo-like Coryphodon likely behaved in the manner of the modern creature to which its skeleton was compared at the onset of this article, Barylambda was built like an eccentric ground sloth and likely acted accordingly, Titanoides was a fairly large terrestrial herbivore whose dietary habits largely consisted of tough vegetation, and Pantolambda was a vaguely cat-like creature which nevertheless maintained an herbivorous diet. For an immeasurably more complete description of these incredible organisms, do go here.

A behind-the-scenes look at the Coryphodon cranial reconstruction which was recently employed at the AMNH's recent 'Extreme Mammals' exhibit.

There are certainly many more questions to be answered concerning this magnificent group of creatures (most notably, that of ‘to what other congregation of mammals is the pantodonta most closely related?’), and one would hope that they will soon be answered with the advent of additional research and a host of rising specialists.

May the fossil record continue to enchant us all!