stegopod!

Photo (Octavio Mateus) and reconstruction (from the paper) of the new stegosaur Miragaia longicollum.

Once again I'm late to the party. Miragaia longicollum is the newly published, long-necked sauropod mimicing stegosaur from the Late Jurassic of Portugal that was featured in loads of blogs yesterday. Attendees of the SVP annual meeting may have actually caught the reconstruction of Miragaia way back in 2007, in Austin. Even though it was only up on screen for a short time, the crazy long neck was immediately obvious, and I've been waiting for it to be published ever since.

Ayway neck elongation in this stegosaur was covered very well by Matt Wedel here. So I won't spend anymore words on it here. Instead I'll delve into the systematics of Miragaia. At the outset let me say that I think the authors have done a great job in this paper and they are thoroughly deserve the publicity they are getting. However this one lttle niggly aspect of the paper has not convinced me and I want to raise the issue here because the fault seems to lie with the whole culture of publication in palaeontology, rather than with these specific authors.

First off Miragaia shares a bunch of characters with the roughly co-eval English stegosaur, Dacenturus. These include fusion of the cervical vertebra to their respective centra, dorsal vertebral centra that are wider than long and olecranon process of the ulna developed into a horn-like prong (you can see this last feature clearly in the photo above). Indeed when the two are included in a cladistic analysis the two form a well supported clade which the Mateus et al. call the Dacenturinae. Another interesting tidbit is that the new data from Miragaia shifts Dacenturus from its usual basal position amongst stegosaurids to a derived position next to Stegosaurus itself. Interestingly though when Mateus showcased this skeleton in 2007 he had identified it AS Dacenturus.
So what makes Miragaia distinct? Obviously its unusually high number of neck vertebrae is a wierd feature (and there are several others listed in the diagnosis) but this cannot be determined in Dacenturus because it is mostly known from the backend of the animal while Miragaia is largely known from the front.

Indeed due to this non-overlapping parts problem just about all of the autapomorphies of Miragaia are not determinable in Dacenturus. So is there a justification for erecting a new taxon? I went through the character taxon matrix in the supplemental material in order to find out if there was any observable differenceand found a few points of difference. All but one f these concerned the continuously variable characters (e.g. ratio of distal width of the humerus to its length)and in most cases the difference was slight so that in more traditional discrete character state coding these features might be given the same state. The one discrete character difference in the matrix concerned the robustness of the dorsal plates but once again the known plates of Miragaia are from the front of the animal while those known from Dacenturus come from further back so we may not be compareing the same thing.

In all there seems justification for at most a new species of Dacenturus (especially since its sister taxon Stegosaurus, houses three species which display more disparity than these two genera). Maybe I'm missing something but f so the authors really could have made the distinction between these two genera clearer.

Does erecting a new taxon make publishing a new fossil easier? It shouldn't, the Miragaia fossils are fantastic enough to deserve publication in the Proceedings. But nonetheless I have heard talk that editors of these high-impact broad science journals are less keen to publish palaeontology if it doesn't involve a new taxon. If this is so, and I hope it isn't, then it is a practice that has to stop, an important fossil that throws new light on evolution or palaeobiology deserves recognition wether or not it represents a new taxon.

Mateus, O., Maidment, S. C. R., Christiansen, N. A. (2009). A new long-necked ‘sauropod-mimic’ stegosaur
and the evolution of the plated dinosaurs Proceedings of the Royal Society B DOI: 10.1098/rspb.2008.1909

Egg Eating Snake

Moving to a new continent is a simulataneous joy and frustration for those with a naturalist bent. On the plus side there is a whole new fauna and flora to discover. On the downside until you become very familiar with it you often haven't got a clue what you find is. This happened to me on a recent short field trip to Golden Gate Highlands National Park. The trip was a total washout, heavy rains and bad weather made it unpleasant in the field and had caused a rockfall that obscured much of the site we wanted to investigate. However while scrabbling around the rockfall I found this beautifull little snake. I didn't know it at the time but I had found a rhombic egg-eater (Dasypeltis scabra), a member of a fascinating group of snakes I had always wanted to see. Sadly I thought it was a night adder so treated it cautiously I didn't give it a very close look. Night adders are quite venemous whereas egg eaters are virtually toothless and quite harmless (unless you happen to be a small bird egg). Only later when I was back home did I identify what it really was.

A little about Dasypeltis snakes for those who don't know. They are an african genus of colubrids that are adapted to feeding exclusively on bird eggs. They are capable of swallowing eggs up to three times the width of their head. They have highly reduced dentitions and use ventral projections from the vertebrae in the gullet region to pierce the shell. The liquid contents are swallowed and the collapsed shell is regurgitated. I would love to see this in action, but my little guy was just sheltering from the bad weather when I found him.

Fossil Human Hair

200 000 year old human hair from a hyaena coprolite. Image from Backwell et al. 2009

Over a week ago Lucinda Backwell, who also works at the BPI at Wits, announced the discovery of fossilised human hair that exceeds the previous oldest known hair (from a 9000 year old mummy) by about 200 000 years. Indeed it is so old it might not even belong to our own species but might instead belong to H. heidelbergensis.
The story was picked up by some of our local papers but doesn't appear to have generated much interest in the blogosphere, so I thought I'd timidly foray into the world of palaeoanthropology and discuss Backwell et al.'s paper here.
What adds some iterest to the story is where the fossil hair was found: inside a hyaena coprolite from Gladysvale Cave in the 'Cradle of Humankind' , South Africa (practically next door to such famous sites as Sterkfontein and Swartkrans). Coprolites are, of course fossilised faeces.
Does this mean a hyaena attacked and killed a Homo species in the Late Pleistocene of South Africa? Well I'm sure our ancestors and relatives may have on occasion fallen prey to spotted hyaenas and some of the larger extinct forms. However this fossil does not record such an event. The coprolite was part of a latrine buried in situ in Gladysvale Cave,and the details of this latrine, such as its location inside a cave, small size and well circumscribed boundaries, all indicate that it was made by a brown hyaena (Parahyaena brunnea). Brown hyaenas are rather smallish and are not known to kill humans. Far more likely is that this represents scavenging on an already deceased member of our genus.



A brown hyaena


It was the cave setting that allowed the latrine to be dated. The latrine is sandwiched between two flowstones which contain enough Uranium to be used for Uranium-Thorium dating. This dating was done as part of a larger project by Robyn Pickering, one of the brightest students to come through the BPI in recent years.
Sadly the hairs are preserved as casts in carbonate. No trace of organics are left so we won't be getting any molecular data for 200 000 year old hominids just yet.
By itself that is about all that the paper can tell us. Perhaps if more such latrines could be found we could then survey more scats for fossil hair and discover how frequent such scavenging events occured. Discovery of even older hair, might start to reveal systematic variation and we might even be able to hazard some guesses as to what kind of hairs our more remote relatives bore. For instance we might be able to get a handle on when modern style short fine body hair evolved. The Gladysvale deposits cetainly go back much further in time so the potential for finding australopithecine hair is there.
This also serves to remind us that coprolites are unique microenvironments that have unusual preservation potentials. Ever snce the oldest known mammalian hair was found in Paleocene coprolites, I've thought that coprolites offer us the best chance to find out just when our unique mammalian pelage evolved. I have looked through coprolites from a Middle Triassic synapsid bearing site in the hopes of finding non-mammalian hair but so far no luck.

UPDATE: Randy rightly asked how the ID was made. Mammalian hair is not completely diagnostic to low taxonomic categories. It helped that several specimens were found in the coprolite. Any one hyaena scat usually contains the hair from just one sitting so is not likely to be mixed with other species. Thus there was a sample of several hairs to work from. Only human hairs were found to match the range of variation seen in the fossil hairs (using characteristics such as scale margins, scale spacing, hair width etc.). Other primates came close but most non-human primates produce finer hair. So the ID is a probabilistic one, hence the equivocation in the title of the paper.

L BACKWELL, R PICKERING, D BROTHWELL, L BERGER, M WITCOMB, D MARTILL, K PENKMAN, A WILSON (2009). Probable human hair found in a fossil hyaena coprolite from Gladysvale cave, South Africa. Journal of Archaeological Science DOI: 10.1016/j.jas.2009.01.023

Before they were giants, a new fossil from the dawn of the age of dinosaurs

I was shut off from the internet all this morning. When I got back online I find the wonderfull news that a brand new dinosaur from Argentina has been described by Ricardo Martinez and Oscar Alcober. And not just any dinosaur, a basal sauropodomorph, indeed THE basal sauropodomorph. How could I not blog about it?
Called Panphagia protos (meaning 'the first that eats all' - a reference to its basal position and probable omnivory) it hails from the Ischigualasto Formation. The authors give its age as the earliest Carnian but this is actually not likely given the shake up that Triassic dating and stratigraphy has been getting over the last few years. The revised stratigraphy puts the Ischigualasto right at the very end of the Carnian and probably extending into the earliest Norian.
In anycase Panphagia is a much more primitive sauropodomorph than anything else described so far including the equivalent aged Saturnalia from Brazil. It doesn't have reduced skull and the neck is barely elongated relative to the neck of basal theropods (this depends on wether or not you include herrerasaurids and Eoraptor among the theropods).
However it does show a handfull of rather subtle sauropodomorph features including an enlarged external naris (also in Eoraptor), basally constricted tooth crowns (also in some teeth of Eoraptor) and a non-articulating gap between the transverse processes of the first sacral vertebra and the ilium in the pelvis. The authors cite a few other characters but none are overwhelmingly convincing. And this is the point. We are dealing with the very roots of the saurischian dinosaur radiation and the different lineages had not yet changed enough to accrue distictive characters to convincingly diagnose them. Indeed the similarity between Panphagia and the contemporary dinosaur Eoraptor (which some claim is the basalmost theropod) is very strong, a point not lost on the authors. If I read the subtext of the article correctly I think the authors are hinting at the possibility that Eoraptor is also a basal sauropodomorph. I have certainly entertained the idea in the past but unfortunately I've never seen the Eoraptor fossils and published details are frustratingly sparse so I cannot claim to have an informed opinion.
How did Panphagia make a living? It was certainly not a full time herbivore, nonetheless its somewhat leaf-shaped, imbricated teeth are not quite the slashing deadly blades weilded by its herrerasaurid and rauisuchian contemporaries. Martinez and Alcober are clearly in favour of an omnivorous diet and I concur. Looking at the jaw I can easily imagine such a set of teeth catch and slicing up small time prey while also shredding soft nutritious vegetable matter (e.g. new shoots and fleshy reproductive structures).


All purpose teeth of Panphagia from Martinez and Alcober 2009

To sum up, the morphology of Panphagia actually presents no real surprises, its pretty much exactly what I would have suspected the earliest of sauropodomorphs to have looked like (is this a sign that we are on the right track and our phylogenies are a pretty accurate reflection of dinosaur evolution?). The bigger surprise s its age. Since there is a more advanced sauropodomorph of similar age (Saturnalia) I wonder wether the survival of the less specialised Panphagia alongside it might just be hinting that the initial radiation wasn't that much older. Put more simply the initial divergence of theropods from sauropodomorphs, and indeed saurischian dinosaurs from ornithischian dinosaurs may have only occured during the Carnian Stage of the Late Triassic, rather than extending back into the Middle Triassic as is often postulated.

Ricardo N. Martinez, Oscar A. Alcober (2009). A Basal Sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the Early Evolution of Sauropodomorpha PLoS ONE, 4 (2) DOI: 10.1371/journal.pone.0004397

Bushfire Tragedy

In these days of instant news from around the globe, the horrible tragedies that strike at humans everywhere start to wash over you without the horror truly sinking in. However every now and then an event really does reach out and touch you. For me this happened this morning as I read about the full extent of the bushfire hell that was unleashed in Victoria this past weekend. Kinglake, Whittlesea, these are places I know and visited many times during my five year stint as a PhD student in Melbourne. Good friends of mine live close to, but thankfully not in, the fire ravaged areas. So I want to send my sincere condolences to all the hundreds who lost their family members, homes, or livelyhoods in the devastating bushfires.
On happier news I also want to congratulate fellow blogger and co-author, Darren Naish and his wife Toni on the birth of Emma Naish.
As for myself, I'm about to head of into the field for a few days so things will be quiet on Dracovenator this week.

Another giant from the tropics: Superlucina

As the blogosphere buzzes about Titanoboa I’m going to review another recent paper that hasn’t received the same degree of publicity but describes another tropical giant that is as equally interesting to me. I’m talking about Superlucina: a new generic named coined for an old species ‘Lucina’ megameris named in 1901. Superlucina megameris is a giant bivalve from the Eocene of Jamaica that was revised and interpreted by Taylor and Glover in the latest issue of Palaeontology. Yes that’s right, a paper about the proverbial Eocene clams. This one is for you Mike ;-)



That’s a big cockle. The giant bivalve Superlucina megameris. From Taylor and Glover 2009.

All joking aside, bivalve molluscs have a reputation for being simple, dull filterfeeders with little interest anyone except perhaps those few crazy taxonomists that specialize on them. Even Chris Taylor, who appears to have a boundless love for the systematic s of all biota confessed that it was hard to get excited about bivalves.
It is a tribute Taylor and Glover that they have produced such a fascinating and readable paper on these maligned creatures. However some of this credit has to go to the organisms themselves, which are fascinating once you look below their dull, clammish exterior.
Superlucina megameris belongs to the family Lucinidae which lead an unusual lifestyle. They are chemosymbiotic sulfide miners that inhabit the interface between the oxic and anoxic zones of marine sediments. By using an elongate muscular foot they build a tunnel up to the sediment surface in order to bring down oxygenated water. They also push holes down into the anoxic sediment below to bring up water with dissolved sulfides. These sulfides are oxidized by bacteria held symbiotically in the bivalve’s tissues and provide much of the nutrition that the bivalve requires.
To understand some of the unusual adaptations of S. megameris and the lucinids I first need to give a quick primer in bivalve anatomy. Bivalves are shell-bearing molluscs so that surround their body with a skirt-like fringe of tissue known as the mantle. The mantle secretes the shell, which in bivalves is divided into left and right valves that are joined dorsally along the hinge. The space between the mantle and the body forms a chamber into which the gills (called ctenidia) protrude. To ventilate the gills a water current needs to be drawn into the mantle cavity, passed over the gills and then expelled. To help with these currents many bivalves have evolved inhalant and exhalent siphons (which are modifications of the mantle. The mantle has a series of flap like, medially directed folds that partially enclose the mantle cavity. The inner fold is controlled by pallial retractor muscles which leave a long linear scar on the inner surface of the shell. This line is called the pallial line. At each end of the pallial line are two shell-closing muscles known as adductor muscles (which also leave prominent scars). Ventrally there is a muscular organ known as the foot. That will do for now.



A schematic , grossly simplified, diagram of bivalve anatomy in cross-section. Drawn hurredly by myself last night.

Ok, now to the interesting stuff. First of all lucinids house their symbiotic bacteria in the tissues of the ctenidia which makes breathing a little difficult, especially since the bacteria need to be supplied with anoxic, sulfide-rich water. In order to compensate lucinids use the anterior end of the mantle folds, as respiratory surfaces. In some large lucinids the anterior end of the inner mantle fold is thickened and pleated with complex folds that act as mantle gills. To keep the oxygenated water separate from the anoxic water, the mantle cavity is partially divided. To help with this division the anterior adductor muscle of many lucinids becomes highly elongate and extends posteroventrally, thus creating a channel between it and the mantle gills. Concomitant with this adaptation lucinids lack the posterior inhalant siphon that many bivalves have and take water in at the anterior end of the animal. In S. megameris the elongation of the anterior adductor muscle is more extreme than in other lucinid. A pustulose channel runs between the anterior adductor scar and the pallial line on internal moulds of S. megameris seems to mark the presence of a unique respiratory channel in this species that was longer than in any other lucinid.



An internal mould of S. megameris from Taylor and Glover 2009. Scars from several anatomical features impressed upon the internal surface of the shell are replicated in the mould. I have colourised these: blue – anterior adductor muscle; red – respiratory channel; yellow – pallial line; green posterior adductor muscle.



A reconstruction of the internal anatomy of S. megameris from Taylor and Glover 2009 showing the division of water inflow. Colours follow the figure above.

S. megameris also differs from other lucinids in its great size. It is the largest lucinid known and is one of the largest burrowing bivalves of all time (epifaunal bivalves like giant clams get even larger).
S. megameris inhabited a transitional zone between an open shelf region and a shallow lagoon filled with seagrass meadows. The presence of seagrass is important because it is the decaying grass that provides the sulfide that fuels the bacteria in their bodies. Although the great size of S. megameris is impressive by itself it is all the more impressive when one compares it to modern shallow water lucinids. These rarely reach a height of 10 cm (less than one third the height of S. megameris) while the vast majority range in height from 0.5 cm to 3 cm. Some chemosymbiotic bivalves inhabiting sulfide rich deep-water cold-seeps reach similar impressive sizes (as indeed did some extinct lucinids from cold seep deposits) and it has been suggested that it was the cold-seep environment that allowed for gigantism in chemosymbiotic bivalves. However the paleoenvironment of S. megameris was definitely not a deep-water cold seep. So why did S. megameris get so big? At this stage we do not know.
Lastly it is interesting to consider the relationships of Superlucina. The genus presents no particularly close similarity with any other but seems most closely related to the genera Miltha, Pseudomiltha and Eomiltha. These also tend to have the most elongate anterior adductor muscles and n some cases toothless hinge lines (like Superlucina). This potential clade was diverse in the past but is now reduced to a handful of mostly rare species, apparently being replaced by more advanced lucinids that have broader shorter anterior adductor muscles, instead using a septum to effectively divide the mantle cavity and have highly plicated mantle gills to efficiently extract oxygen. This takeover appears to have occurred rather recently, I have collected sizeable Miltha specimens from the latest Pliocene or earliest Pleistocene of southern Australia where none now live.


JOHN D. TAYLOR and EMILY A. GLOVER (2009). A GIANT LUCINID BIVALVE FROM THE EOCENE OF JAMAICA – SYSTEMATICS, LIFE HABITS AND CHEMOSYMBIOSIS (MOLLUSCA: BIVALVIA: LUCINIDAE) Palaeontology, 52 (1), 95-109 DOI: doi: 10.1111/j.1475-4983.2008.00839.x

Titanoboa and paleophidiothermometry

Yes that's right a new word to describe the measuring of ancient temperatures using fossil snakes. By now most of you will have heard of the Jason Head and colleagues' paper describing Titanoboa, the largest known snake ever. For those that might not have seen it, Titanoboa was a boa that lived 58-60 million years ago in Colombia. Many fossils (mostly vertebrae) deriving from multiple individuals have been found and the largest of these came from a snake close to 13 metres in length and probably weighing in at 1.2 tons. Fossils from eight individuals were found in this size category indicating that we aren't dealing with a single freakily large individual but a species that regularly attained this gigantic size.
What I'm going to discuss however is the second part of the paper, where the authors attempt to estimate the mean annual temperature of Titanoboa's habitat by using maximum snake size. The idea rests on the observation that the size of snakes, as animals that require external sources for their body heat (ectotherms), and cannot maintain a constant internal temperature (poikilotherms), is constrained by the temperature of their environment. Makarieva and colleagues (2005a, b)observed that the largest species of many terrestrial clades of pokilotherms occur in the tropics, while the largest in the temperate realms were smaller and the largest from the polar regions were smaller still. They argued that there is a minimum mass specific metabolic rate below which an organism simply can't function. As mass specific metabolic rate decreases with increasing size there is a maximum size over which the mass-specific metabolic rate is too low. Increasing ambient temperature allows the metabolic rate to be increased and consequently a larger size can be attained.
Head et al. then used the mathematical relationship between temperature change and the change maximum attainable body size to calculate the mean annual palaeotemperature which Titanoboa experienced. Using modern green anacondas as a model for a modern snake that is probably at its maximum acheivable size (which was taken as 7.5 metres) and the temperature data for their habitat, Head et al. calculated that Titanoboa lived in a sweltering tropical forest that averaged somewhere between 31 and 32 degrees Celcius throughout the year (compare that to the 26-27 degrees averaged by modern lowland equatorial forests that anacondas live in).
It is an interesting idea but I see all sorts of problems. Firstly the size of the fossil snake may not be accurately estimated (actually this is the least likely area of inaccuracy - Head et al.'s methods seem pretty solid in this regard). My main problems are that Makariev's formula has not yet been rigorously tested (I'm not even sure HOW you would go about testing it) and most of all I don't know how we can demostrate that modern green anacondas are up against the theoretical maximal size limit for an ambient temperature of 26-27 degrees. The mere existance of exceptional individuals of anacondas and reticulated pythons reaching length close to or even slightly over 10 metres indicates that it is possible for snakes to exceed 7.5 m in the modern tropics without their metabolic rate dropping to fatally low levels. I suspect other ecological pressures (e.g. prey size, predation, availability of suitable cryptic resting places or something else entirely) may be keeping anacondas from reaching their theoretical maximum body size.



Graph from Head et al. 2009 that shows the curve of theoretical maximum size of a boiine snake against mean annual ambient temperature and the predicted temperature derived from the size of Titanoboa.

Despite all these objections, the results are remarkable in that they appear to work. That is a MAT of 32 degrees is entirely plausible, indeed expected for the tropics of the mid Paleocene Epoch. It is well known that CO2 levels were high in the Paleocene, and the world was in a greenhouse phase. During such phases there were no icecaps and we can find fossil evidence for abundant vegetation and animal life at the poles. It used to be thought that the temperature gradients between the equator and the poles were flatter than in modern times and that although the poles were nice and warm the equatorial regions were no hotter than they are now. We now know we were wrong - the tropics were fiercely hot during such times and this fits perfectly with Head's paleophidiothermometry.

REFERENCES

Jason J. Head, Jonathan I. Bloch, Alexander K. Hastings, Jason R. Bourque, Edwin A. Cadena, Fabiany A. Herrera, P. David Polly, Carlos A. Jaramillo (2009). Giant boid snake from the Palaeocene neotropics reveals hotter past equatorial temperatures Nature, 457 (7230), 715-717 DOI: 10.1038/nature07671

Makarieva, A. M., Gorshkov, V. G.&Li, B.-L. (2005)Gigantism, temperature and metabolic rate in terrestrial poikilotherms. Proc. R. Soc. Lond. B 272, 2325–2328.

Makarieva, A. M., Gorshkov, V. G. & Li, B.-L. (2005b)Temperature-associated upper limits to body size in terrestrial poikilotherms. Oikos 111, 425–436.

Finishing Fish Fortnight

Ok, this is way late but you know how the real world has a habit of intruding on blogging time. Anyway this drawing is one of mine. It depicts what is perhaps the wierdest coelacanth known, Allenypterus montanus, from the Carboniferous of Montana. The bright red coloration was inspired by the resemblance between Allenypterus and the modern Pataecus fronto, a wierd ray-finned fish that is also bright red. There is a lot more I could say about this guy and its relatives - but not today.

Wierdo of the Week; Protuberum cabralensis

Image from Reichel et al 2009

Imagine you found this fossil. At first glance you might think it was some kind of ornamented cranial horn but a closer look would reveal that one end bore two articulation facets on a vaguely hockey-stick shaped head. These features identify the bone as the rib of a tetrapod. But the rib of what, exactly? The row of knobs along the dorsal surface is very unusual and does not bear a close resemblance to any other known tetrapod.

These questions were raised when some of these unusual ribs were unearthed at a locality in middle Triassic sediments of southern Brazil by Father Cargnin, a preist with an interest in palaeontology. Since these ribs were isolated in an assemblage of mixed vertebrates, little could be said about their affinities. About all one could surmise is that they belonged to some exceptionally weird tetrapod. The answer came in 1989 when Father Cargnin found a partial articulated skeleton, with a skull, of the beast with the knobbed ribs at a second locality. It turned out to be a traversodontid cynodont, one of a group of plant-eating close mammal relatives that were common across the globe in the Middle and Late Triassic. Ranging in size between something that was roughly rabbit-sized up to something slightly larger but lower slung than a wolf. As advanced cynodonts they had much of the mammalian adaptive toolkit,probably including endothermy and a furry pelt, but lacked the defining dentary-squamosal jaw joint.





A reconstruction of Exaeretodon a typical traversodontid. From Wikipedia

Considering the unusual nature of the ribs, it is actually remarkable how unremarkable the rest of the animal is. The skull is much like that of any other traversodontid (there are some minor differences in skull proportions and the thickness of the skull roof).



The skull of Protuberum, above (taken from Reichel et al. 2009) in comparison to another traversodontid Massetognathus , below (taken from Romer 1967).
Anyway it has taken some time but Father Cargnin’s lumpy traversodontid has finally been published. It was given the name Protuberum cabralensis by Reichel et al. in the most recent issue of Palaeontology. The entire ribcage of Protuberum from the neck to the hips (and the dorsal edges of the hips themselves) was covered in these lumpy excrescences. The lumps are protrusions of the bone itself, not fused on dermal bones as one would expect since no cynodont is known to be armoured with dermal bones. Nonetheless these lumps would have protruded abone the level of the skin during life and were probably covered in tough, leathery or even keratinized skin. It would have made for an unusual looking animal, particularly if these lumps protruded above a layer of fur. The purpose of the knobs seems to have been defensive, perhaps against predators (they shared the earth with big crocodile relatives called rauisuchians ) or perhaps against each other.

Hat tip to Bill at Chinleana for alerting me to this publication.

References

Romer, A.S. (1967) The Chanares (Argentina) Triassic Reptil Fauna. III. Two new gomphodonts, Massetognathus pascuali and M. teruggii. Breviora 264: 1-25.

MÍRIAM REICHEL, CESAR LEANDRO SCHULTZ, MARINA BENTO SOARES (2009). A NEW TRAVERSODONTID CYNODONT (THERAPSIDA, EUCYNODONTIA) FROM THE MIDDLE TRIASSIC SANTA MARIA FORMATION OF RIO GRANDE DO SUL, BRAZIL Palaeontology, 52 (1), 229-250 DOI: 10.1111/j.1475-4983.2008.00824.x