Monday, 19 November 2012

SVP 2012 - Some Tasty Morsels


 
Evidence of interaction and behaviour between extinct animals is always fascinating since it brings the prehistoric world to life. And, in this section, such evidence features heavily. David Burnham, of the University of Kansas, and colleagues presented a poster said to demonstrate evidence of predation by a plesiosaur on a specimen of Hesperornis.
Hesperornis is a well known Late Cretaceous ornithurine that was an abundant component of the Niobrara chalk sea in Kansas. A left forelimb of this bird demonstrates a series of small conical holes that suggest this specimen was attacked but survived since radiological examination reveals osteomyelitis infection had developed in the distal tibiotarsus.
Comparing the depressions and spacing of the tooth holes suggests that the attacker was most likely to be a small polycotylid plesiosaur. The authors interpret this as evidence that the plesiosaur attacked the bird from behind but was unable to maintain a grip on its intended victim and, thus, was able to make its escape. There appears, on the face of it, a little uncertainty about this since there were so many other predatory fish in the oceans with similar teeth that to be certain that a plesiosaur was responsible for the attack seems a little premature.
 But Bruce Rothschild was present and defending the poster and he was adamant that they were correct and since he knows more about bone pathologies than most people I think we can give him the benefit of the doubt for now. Even so, this is a very cool specimen that highlights the dangers that these large flightless birds must have faced every time they took to the ocean.
Sigilmassasaurus brevicollis was another theropod found in Late Cretaceous rocks (Cenomanian?) of North Africa. Known as Spinosaurus “B” by Ernst Stromer, the taxon was formally named Sigilmassasaurus by Dale Russell in 1996. And now Serjoscha Evers, of Ludwig-Maximilians-University, and colleagues have taken on the task of identifying this mystery taxon. The validity of this animal has always been in doubt since the remains are limited to vertebrae but now new vertebrae, consisting of one dorsal and several cervicals, found in museums in both London and Munich, have presented new data.
Firstly there several characters in line with the original descriptions that demonstrate that they are definitely from Sigilmassasaurus. Secondly the cervicals also demonstrate morphological differences that clearly show that they are not from Carcharodontosaurus – which some authors have considered that these remains belong to. Under CT-scanning, they also have internal arched pneumatic chambers whilst those of carcharodontosaurids are the familiar honeycomb-like small chambers.
What they are similar to, however, are the vertebrae of megalosauroids – especially spinosaurids. This suggests that Stromer may have been right (not for the first time) and that Sigilmassasaurus may represent a new spinosaurid taxon. The authors take this is a further indication that spinosaurids were a more diverse clade of dinosaurs than originally thought.
The small ornithopod Oryctodromeus cubicularis first came to our attention back in 2007 as the first dinosaur that potentially could be described as a possible burrowing or denning dinosaur (Varrichio et al 2007). The remains were found in the Mid-Cretaceous Blackleaf Formation in Montana and were found disarticulated in a partially preserved chamber at the end of a tunnel. Further research into the burrowing hypothesis has continued but has proven hard to quantify.
Now Jamie Fearon and David Varrichio, both of Montana State University, have been examining the forelimb morphology of Oryctodromeus to see if there are any specific adaptions for a burrowing lifestyle. This is problematic in as much that there are no extant analogues around to be able to compare the specimens with. 
But by using a combination of traditional and other geometric statistical analyses, including principal components analysis (PCA), of various ornithopods (including Oryctodromeus) the authors have been able to demonstrate some interesting results.   Iguanodontians and hypsilophodontids share similar basic forelimb morphologies but are distinct from hadrosaurids due to the shape of the deltopectoral crest. However, the PCA reveals that hypsilophodontids are distinct from both iguanodontids and hadrosaurids mainly due to the variance in the morphology of the scapula which is broader at both the proximal and distal ends.
So where does Oryctodromeus figure in all this? Well surprisingly not that close to any of the other groups mainly due to a ventral expansion along the posterior border of the scapula blade. The authors hypothesise that since this is the attachment site for the deltoideus muscle there is a chance that this can be seen as an adaption for digging since extant mammals that burrow today use that very same muscle. I asked the other question that has bugged the burrowing dinosaur theory – was there enough flexibility in the tail for the animal to be able to turn in such a tight area? Jamie Fearon believes that there probably was although she took great pains to point out they were only looking at the forelimb in this current study.
Serration scars are vivid on this example
A very popular poster, and another that has received good publicity, was titled “How to eat a Triceratops….” – a title guaranteed to generate interest. Denver Fowler, of the Museum of the Rockies, and colleagues have been looking at traces of tyrannosaurid carnivory by studying trace marks on numerous bones of Triceratops.
As noted here before, the Hell Creek Formation Project (1999-2011) has yielded 100 specimens of Triceratops and, of this number, there are eight individuals displaying tooth marks with another six that may possibly show evidence of carnivory. The real interesting thing here is that all the bones bar an ilium are from partially articulated or disarticulated skulls.
All bones display typical tyrannosaurid predation marks including puncture wounds and the classic puncture /pull drag marks. Such marks and analysis of the tooth spacing clearly indicate tyrannosaurid predation – in this case Tyrannosaurus rex since it was (and still is) the only known tyrannosaurid from the Late Maastrichtian rocks of Hell Creek.
Closer scrutiny of these marks reveal interesting, indeed, surprising feeding techniques. It appears that these carnivores were actually quite partial to the head of Triceratops. There are several drag marks on the parietosquamosal frills of a few specimens which, on the face of it, is surprising since there is apparently very little flesh there. The authors suggest that this may be indicative of the tyrannosaur manoeuvring the head to get to the succulent neck muscles and they quantify this suggestion by highlighting the fact that there are two occipital condyles displaying deep predatory gouges on them.
At the same time there are lighter feeding traces on bones such as a nasal and premaxilla suggesting that tyrannosaurs could be quite delicate in their feeding. This is not surprising since the premaxillaries of tyrannosaurids have often been described as “nibbling” teeth and now we have the evidence to back that up. But big tyrannosaurids, and Tyrannosaurus in particular, were well suited to large volume dismemberment of a carcass, whether killed or scavenged, and this new research highlights their various abilities in processing their prey to maximise the calorific intake.
What you cannot appreciate reading this, and unless you were at SVP, is the attached images with the poster showing these bones with the signs of carnivory. They are awesome and, in particular, the gauges on the occipital condyles are amazing. I am not sure how far away this paper is from publication but the images will be even better. When it is published take a look and be impressed – great work.
Yet more tyrannosaurid scars
 
This next one is a belter of a fossil. Finding dinosaurs with associated eggs is always fascinating but a partial oviraptorid recovered from the Upper Cretaceous Nanxiong Formation of Jiangzi in China appears to give us truly remarkable insights into the origins of avian reproduction. Tao He, of the Zhejiang Museum of Natural History in China, and colleagues have been looking at this specimen and made some interesting observations.
First of all, only the posterior half of the animal is preserved but it is well articulated. There are two eggs in association and they are both long and asymmetric and are designated as belonging to the Elongatoolithidae. One is located posterior to the sacrum (below caudals 4 – 7) and the other between the ischia. They are both covered in shell which is 1.0mm thick and is streaked by lineated ridges that run the length of the egg. The egg situated between the ischia also displays its blunt end in an apparent caudal direction.
The authors postulate that the relative position of the eggs suggests that they were partially expelled as the animal decayed – something that has been observed in extant drowned pregnant cattle as the calves were expelled after some decomposition(and there were some graphic images to show this). A blunt ended caudally facing egg suggests that theropods did not lay eggs in bound pairs as originally postulated and is actually opposite to what is found today in extant birds.
Two other points of note. Maniraptora have often been described as being monoautochronic – that is the simultaneous production of a single egg by each of a pair of oviducts -  and this specimen is clearly indicative of this. It is also suggestive that laying eggs two by two in a clutch enabled eggs to be proportionally larger and more robust when compared to the overall body size of the adult. This was a great presentation and the displayed images of the specimen were superb.
 
A typical dromaeosaurid
 
Richardoestesia is an enigmatic theropod taxon of uncertain phylogenetic affinities from the Maastrichtian of North America. It has been referred to dromaeosaurids, troodontids and aves but until more definitive remains are found is best left as status to be determined. However, we may be closer to understanding how this taxa eked out a living – by taking a closer look at its teeth.
Microvertebrate fossil specialist Julia Sankey, of the California State University Stanislaus, has been looking at abundant quantities of teeth belonging to Richardoestesia isosceles – a species she named herself back in 2001. Sankey has recognised that the straight tooth morphology is perhaps indicative that the taxon was a fish eater and quantifies this by highlighting that the teeth are much more prevalent in coastal as opposed to inland deposits. Richardoestesia, therefore, could be the first recognised fish eating theropod on the continent of North America.
And finally, in this post, we look at another fascinating case of interaction between taxa but perhaps not quite the animals that you might have expected. Jason Schein, of the New Jersey State Museum, and colleagues have been looking at a hadrosaurid femur recovered from the Main Fossiliferous Layer (MFL) of the lower Hornerstown Formation in New Jersey. The bone displays multiple straight to slightly curved grooves that are typical predation marks of oceanic sharks and the dinosaur was likely a typical bloat-and-float carcass that had been swept out to sea.
This femur, however, may be quite unique. The MFL has proven difficult to age correctly but it does appear likely that these sediments were deposited almost exactly at the contact point between the Maastrichtian and Danian – in fact the MFL has virtually one leg in each stage. Regardless of the complex taphonomic and depositional permutations, the femur represents what may potentially be the youngest non avian dinosaur fossil ever discovered.

References  

Burnham, D.A., Martin, L.D. & Rothschild, B.M. 2012 Plesiosaurs had a taste for birds.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 71.
Evers, S.J., Rauhut, O.W. & Milner, A.C. 2012. Was Stromer right? The affinities of Sigilmassasaurus brevicollis (Theropoda, Tetanurae).  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 91.
Fearon, J.L. & Varricchio, D.J. 2012. Comparative pectoral and forelimb morphology of Ornithopoda: does Oryctodromeus cubicularis exhibit specialization for digging? Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 92 - 93.
He, T., Varricchio, D.J., Jackson, F.D., Jin, X. & Poust, A.W. 2012. An oviraptorid adult-egg association and the origin of avialan reproductive strategies.   Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 108.
Sankey, J.T. 2012. Something’s fishy: was one of the most abundant Late Cretaceous theropods a fish eater? Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 165.
J.T. Sankey, 2001, "Late Campanian southern dinosaurs, Aguja Formation, Big Bend, Texas", Journal of Paleontology 75(1): 208-215 
Schein, J.P., Poole, J.C. & Lacovara, K.J. 2012. A shark-bitten hadrosaurid femur from the basal Hornerstown Formation, New Jersey, USA.: one of the youngest non-avian dinosaur remains known.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 166. – 167.
D. J. Varricchio, A. J. Martin, and Y. Katsura. 2007. First trace and body fossil evidence of a burrowing, denning dinosaur. Proceedings of the Royal Society of London B 274:1361-1368.

1 comments:

Hadiaz said...

"Richardoestesia is an enigmatic theropod taxon of uncertain phylogenetic affinities from the Maastrichtian of North America. It has been referred to dromaeosaurids, troodontids and aves but until more definitive remains are found is best left as status to be determined."

From the looks of it, it's safe to say that Richardoestesia is probably a eumaniraptoran (if not a deinonychosaur).

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