Thursday, 26 July 2012

More on Tyrants: Alioramus - Part 1



When the Alioramus monograph was published back in February this year, it arrived to what appeared to me to be universal praise and acclaim. For 24 hours it received an extremely positive press and you would have thought that there would have been a plethora of discussions and comments at all the usual blogs and websites. But, for whatever reason, this never actually materialised and the monograph very quickly disappeared from the palaeoworld front page. In fact the original press release for Alioramus altai in October 2009 provoked more response and a much greater coverage.
Indeed, I have not seen a single review of this work anywhere and I’m pretty sure I would have found one by now (but if you have reviewed this paper, please feel free to send me the detail or link – I would love to read it). And yet this monograph deserves a much greater press and appreciation than it has received and I am glad to discuss it further here.
To really understand a dinosaur, or any other extinct animal for that matter, and provided that the fossil remains are extensive and well preserved, then you need to read a monograph. This is the only way to get “under the skin” of an extinct taxon and get a real feel for the very essence of the beast. Unexpectedly perhaps, modern monographs of tyrannosaurids are conspicuous by their absence. Indeed, only Brochu’s superb treatment of Tyrannosaurus rex back in 2003 has broken a very long run of absence.
I first became aware of Alioramus altai during SVP at Bristol - I remember it very well. It was the Saturday morning session and we were treated to a string of superb theropod presentations which featured (amongst many) Dal Sasso’s and Maganuco’s magnificent work on Scipionyx and Roger Benson’s very cool work on tetanuran theropods. However, Alioramus altai was soon introduced by Norell et al and I remembered being surprised at the completeness of the specimen which was soon reinforced by the following presentation by the same team describing the braincase of the animal. Just two presentations later, Phil Currie presented his and Myashita’s new phylogeny of Tyrannosauroidea which was only new in as much that it more or less consolidated previous phylogenetic work.
Phil Currie’s passionate discourse when discussing the more traditional phylogenetic aspects of deep skulled tyrannosaurids was excellent and I must admit to getting carried away with the occasion and rather arrogantly dismissed Alioramus as a tyrannosaurid of very little consequence. But, as I have mentioned in the past, I now know how wrong of me that was and regret what was said – and even now I still feel the need to apologise to those concerned.
However, things quickly moved on and Alioramus altai was officially introduced to world in October the same year. Steve Brusatte, lead author from the American Museum of Natural History, described Alioramus  as when “Compared to Tyrannosaurus, this new animal is like a ballerina” because of its skeletal pneumatisation and its obvious gracility. The ballerina quote stuck and featured in nearly news article about the animal and there was a flood of interest throughout the palaeoworld and in the public eye generally.
Just over two years later and the monograph of Alioramus altai was published and it is truly an exceptional document.  As I sat down with it to start reading it I was struck by how much of it there was. At 197 pages in length  it was obvious to me straight away that there had been an extraordinary amount of time and effort in producing this awesome publication and I was determined to give it a lot of time and attention  – I felt I owed  Alioramus and the authors at least that much. Part 2 soon.

References
Benson, R.B.J. 2009 Middle Jurassic theropods and the early evolution of Tetanurans (Dinosauria, Theropoda).  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2009, Pg.62A
Bever, G.S., Brusatte, S.L., Carr, T.D. and Norell, M.A. 2009. The braincase of a new tyrannosaurid from the Late Cretaceous of Mongolia.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2009, Pg.63A.
Christopher A. Brochu (2003): Osteology of Tyrannosaurus Rex: Insights from a nearly complete Skeleton and High-Resolution Computed Tomographic Analysis of the Skull, Journal of Vertebrate Paleontology, 22:sup4, 1-138.
Stephen L. Brusatte, Thomas D. Carr, Gregory M. Erickson, Gabe S. Bever, Mark A. Norell (2009) "A long-snouted, multihorned tyrannosaurid from the Late Cretaceous of Mongolia". Proceedings of the National Academy of Sciences. 106(41): 17261–17266.
Brusatte, S.L.; Carr, T.D.; Norell, M.A. 2012: The osteology of Alioramus, a gracile and long-snouted tyrannosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Mongolia. Bulletin of the American Museum of Natural History, (366) doi: 10.1206/770.1
Dal Sasso, C. and Maganuco, S. 2009. Osteology, ontogenetic assignment, phylogeny, paleobiology, and soft-tissue anatomy of Scipionyx samniticus.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2009, 84A
Miyashita, T. and Currie, P.J. 2009. A new phylogeny of the Tyrannosauroidea (Dinosauria, Theropoda).  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2009, Pg.149A.
Norell, M.A., Brusatte, S.L., Carr, T.D., Bever, G.S., and Erickson, G. 2009. A remarkable long-snouted, multihorned tyrannosaurid from the Late Cretaceous of Mongolia.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2009, Pg.155A.

Saturday, 21 July 2012

Describing a cryptoclidid forelimb from the Lower Oxford Clay Formation


I have still been receiving a lot of interest in the plesiosaur we recovered early last year and I did promise some more detail for those of you who have asked for it. So what follows is a description of the right forelimb in its entirety. That will be it for a while until preparation of the specimen restarts which may be later this year but is more likely to be early 2013. So enjoy for now!


In April 2011, a partial cryptoclidid skeleton was found by the writer in an undisclosed quarry near Peterborough in Cambridgeshire, UK (exact location available). The specimen OCWG 160411.01 was extracted soon after by members of a specialist conservation group and other volunteers with permission of the quarry owners.
The specimen was recovered from the Peterborough Member of the Lower Oxford Clay Formation (Middle Callovian) in Bed 10 – the Kosmoceras jason zone (Callomon 1968) .  Bed 10 is usually described as a finely laminated organic-rich mudstone and is exposed at the base of working brick quarries where excavation of the clay ceases due to the presence of abundant septarian concretions (Hudson 1978).
OCWG160411.01 represents a partially articulated skeleton comprising of a fairly complete right forelimb, both humeri, a femur, various vertebrae, odd pelvic elements, and many other limb elements as well as multiple rib fragments. The right forelimb is described here.
Unusually for skeletal elements from the clay, this specimen is remarkably uncrushed and there appears to be very little other taphonomic distortion. As is the norm for plesiosaurs found in the clay, the specimen was found belly-up. The right forelimb is very well preserved and is missing only the phalanges.
Preparation of the forelimb was carried out by the writer and, with no pyrite contamination, was fairly straightforward. Any encrusting sediment, shell debris and matrix was removed by mechanical means including air pen and dental picks whilst finer detail was preserved by utilising pin vices and scalpels. The elements were consolidated by a weak solution of Acryloid B72.
The humerus is considerably larger than the femur which is a characteristic of cryptoclidid plesiosaurs. It measures 290mm in proximodistal length. The proximal articular surface is large and slightly convex and displays numerous tubercles and rugosities. The deltopectoral crest is enlarged and tapers directly off of the capitulum.
The shaft ventral to the proximal head is straight for a short length and has a circumference of 196mm. However, the shaft compresses down as it tapers distally to the distal expansion of the humerus. As is often the case with plesiosaurs, there is a heavily rugose patch of bone on the ventral surface of the humerus situated proximally above mid-shaft and extends from the preaxial to the postaxial margins. The shaft on the preaxial margin displays no foramina but there are a few on the postaxial margin with the largest oval-shaped foramen situated in isolation more or less on the cusp of the dorsal surface just as the humerus expands (eg see Benson et al 2011).
The distal expansion of the humerus is dorsoventrally flattened and expands to 196mm at the widest point between the entepicondyle and ectepicondyle.  Articular facets for the radius and ulna are readily apparent and distinct and the humerus is 44mm thick dorsoventrally at the distal-most point of the bone. The radial facet is bigger than the ulna facet but the size disparity is not as great as it is in other cryptoclidid plesiosaurs such as Cryptoclidus eurymerus (Phillips, 1871). The distal extremity is also rugose but there are no tubercles present.
The ventral surface of the expansion immediately below the proximal rugosity is generally smooth but soon displays striations and foramina that trend with the distal expansion of the humerus. Likewise, the dorsal surface displays similar tendencies but there is only a small rugose patch of bone situated ventral to the proximal head.
In dorsal aspect

The radius is 84mm in length proximodistally along the preaxial margin and is longer than it is wide. It is an unusually shaped element displaying numerous articulating facets. The largest of these is the articulation with the humerus. It is angled obliquely, concave, is 76.79mm in length and has an average dorsoventral depth of 33.82mm. The preaxial margin is concave. The distal most facet articulated with the radiale and is 51.89mm in length and gently concave. Postaxial to this articulation is the oblique intermedium facet and is 26.04mm in length.  The postaxial margin forms the large foramen with the ulna. The notch is 20.62mm in length proximodistally and 22.25mm dorsoventrally. Both the ventral and dorsal surfaces of the radius are covered in numerous scars and foramina.
The ulna is small when compared to the radius and is 75.37mm in length from the preaxial to the postaxial margin. Like the radius, the largest facet is the articulation for the humerus. It is 64.23mm in length and slightly convex. The preaxial margin forms the foramen with the radius although the notch is not so heavily sculpted as in the radius. Ventral to the notch and obliquely angled is the articulating facet for the intermedium. It is 48.59mm in length and the surface is flat. Postaxial to this facet and very obtuse is the articulation with the ulnare which is also strongly oblique but trends anterodorsally and is flat surfaced. This facet is 45.12mm in length. The postaxial margin is strongly convex.  The ventral and dorsal surfaces of the ulna are heavily pitted and rugose – much more so than the radius.

In ventral aspect

The ventral surface of the ulna also displays a quite distinct fossa situated ventral to the intermedium facet that trends dorsomedially and is formed by a distinct ridge that also trends from the intermedial facet. The postaxial margin of the fossa is formed by a prominent ridge that projects from the intermedium facet and forms the proximodorsally orientated margin of the foramen notch that is formed by the ulna and radius.      
The proximal carpals include the radiale, the intermedium and ulnare – there are no ancillary bones present. The ulnare is another strange shaped element similar to the radius and is 41.56mm from the postaxial margin to the articulating facet with the intermedium.  Proximally there is a convex facet that trends dorsolaterally for the ulna and, distally, a rugose convex facet for articulating with metacarpal 5. A further post axial facet is present for articulating with distal carpal 3. The intermedium and distal carpal 3 facets are flat faced. The ulnare tapers and thins down toward the postaxial margin which is dorsoventrally compressed and both the dorsal and ventral surfaces are gently concave and similarly textured.
The intermedium (or centrale in some literature eg Caldwell 1997) is a dense heavily constructed bone that is hexagonal in shape with every facet articulating with another element. It articulates with the radius, ulna, radiale, ulnare and distal carpals 2 and 3. Again all articulating surfaces are flat and the dorsal and ventral surfaces are heavily pitted – particularly the ventral surface. Here there is a heavily sculpted fossa that extends distally from the ulna articulating facet to the facet of distal carpal 3. The centrale is 48.06mm in width at its widest point between the radial and distal carpal 2 articulating facets.
The radiale is almost oblong in shape and is 47.41mm in length from the preaxial to postaxial margin. There are three flat surfaced articulating facets for the radius, intermedium and distal carpal 2 whilst the facet for distal carpal 1 is slightly concave. Similarly to the ulnare, the radius tapers and thins down toward the preaxial margin where it becomes dorsoventrally compressed and both surfaces are gently concave and textured alike.
There are three distal carpals since metacarpal 5 articulates directly with the ulnare. Distal carpal 1 is small – only 32mm from the preaxial margin to where it articulates with distal carpal 2.  Distally it articulates only with metacarpal 1. Distal carpal 2 is another polygonal element and very similar to the intermedium in a much as it is a very thick bone that displays six articulating facets. In addition to the radiale, centrale and distal carpals 1 and 3, it also articulates with metacarpals 2 and 3.
Close up ventral aspect

Interestingly, distal carpal 2 ventrally displays an almost identical trending fossa as both the ulna and intermedium have and is considerably more rugose and pitted than the dorsal surface. These fossae appear to constitute an enlarged proximodistal depression that angles obliquely across the ventral surface of the forelimb. What the significance of such a depression may be is beyond the scope of the writer at this point in time.
The postaxial articulation of distal carpal 2 with distal carpal 3 is pinched forming a more pronounced concavity on both the dorsal and ventral surfaces and the element gently tapers toward this point.
Distal carpal 3 is the most complex element of the three and is also multi-faceted as it articulates with the intermedium, ulnare, distal carpal 2 and metacarpals 3, 4 and 5. It tapers preaxially to mirror the condition in distal carpal 2 and equally compresses down postaxially to form the articulation with metacarpal 5. This is another heavily rugose and pitted element which, unusually in this specimen, displays a dorsal surface more heavily pitted than the ventral side. Distal carpal 3 is 47.91mm in proximodistal aspect.
The five metacarpals are all present. Metacarpal 1 is dorsoventrally compressed preaxially. Metacarpals 2, 3 and 4 are cylindrical in shape and display both proximal and distally expanded articulating ends. The first four metacarpals also display lateral facing facets for articulation with each other (Andrews 1910).
As mentioned previously, metacarpal 5 articulates with the ulnare as a result of shifting proximally to become, in effect, an additional distal carpal. Despite being dorsoventrally compressed postaxially, metacarpal 5 also articulates with distal carpal 3, metacarpal 4 and the first phalange of digit 5. This phalange is the only one that was found in situ although there are others recovered from the quarry. It is broken approximately half way down the shaft and appears to be fairly typical in as much as it is also cylindrical in shape and compressed mid-shaft although this particular bone is also dorsoventrally compressed on the postaxial margin.

Taxanomic Assignment

OCWG 160411.01 was identified as a cryptoclidid plesiosaur on the day of its discovery due to the larger proportional size of the humerus relevant to the femur but was difficult to assign to a specific genera. When the specimen was excavated there were, unfortunately, no cranial remains and no teeth which has proven to be a significant stumbling block.
To try and identify this particular specimen has involved many hours of looking through the literature as well comparing the specimen with those in other collections – particularly the Leeds Collection in the Natural History Museum (London).
The earliest indication of identification was when looking at the Leeds specimens in the Hunterian Museum in Glasgow. GLAHM V1809, labelled as Cryptoclidus richardsoni, was the first specimen that was actually similar to OCWG 160411.001 but it was also apparent that it could also be mistaken for Muraenosaurus. Indeed, Brown (1981) stated that the humerus of Muraenosaurus leedsii is almost identical to that of Cryptoclidus richardsoni and specimen GLAHM V1809 displays many morphologies similar to OCWG 160411.001.
C. richardsoni (Lydekker 1889) has a rather convoluted history and has been the subject of various analyses. The taxon has also been reassigned to C. eurymerus and, Muraenosaurus leedsii (Seeley 1874) over the years. If it was C. richardsoni, then this specimen would be important since this particular taxon is amongst the rarest of plesiosaurs known. And yet it was clear that more comparison was required and, with these thoughts in mind, the specimen was taken to London where we were granted access to the Leeds Collection in the NHM (London).
There were many specimens on our list to check out but chief amongst these was a specimen of Muraenosaurus leedsii BMNH R2864 (Andrews 1910). Although Andrew’s description of BMNH R2864 is very similar to OCWG 160411.01, comparative study of the specimens reveal only limited similarities. However, the new specimen is exceptionally well preserved whilst the Andrews specimen is dorsoventrally flattened and has suffered other significant taphonomic distortion so a true comparison was unrealistic.
In fact many of the specimens in this collection are preserved in a similar fashion and it would appear that OCWG 160411.01 is unusually well preserved and, as such, is an important specimen. Other specimens of Muraenosaurus and particularly Cryptoclidus were observed but it was apparent that there was no comprehensive comparison that could be made. The different degree of preservation, the extreme variance in bone morphology and ontogentic disparity made it virtually impossible and, without the skull, was problematic.
Eventually it appeared that OCWG 160411.01 was, in all probability, a specimen of Muraenosaurus and this was further supported after further study of the radius (S. Moore-Fay, pers.comm) and some of the vertebrae (R. Frost, pers.comm), who also noted that the neural arches of the vertebrae are not fused and supported earlier supposition that the specimen was a juvenile or sub-adult.
Conclusion
OCWG 160411.01 represents a juvenile or sub-adult specimen of Muraenosaurus sp. that, although largely incomplete, is very well preserved and will be useful for further taxanomic study of the taxon – especially when the rest of the specimen is prepared. The genus Muraenosaurus is likely due for revision at some point in the future (R. Frost, pers.comm) and this specimen will add further important information to the dataset. 

References

Andrews, C.W. 1910. A descriptive catalogue of the marine reptiles of the Oxford Clay. Vol.1, London, British Museum of Natural History. 

Roger B. J. Benson, Hilary F. Ketchum, Leslie F. Noè and Marcela Gómez-Pérez (2011). "New information on Hauffiosaurus (Reptilia, Plesiosauria) based on a new species from the Alum Shale Member (Lower Toarcian: Lower Jurassic) of Yorkshire, UK". Palaeontology 54 (3): 547–571. 

Bown, D.S. 1981. The English Upper Jurassic Plesiosauroidea (Reptilia) and a review of the phylogeny and classification of the Plesiosauria. Bulletin of the British Museum of Natural History 35: 253-347.

Caldwell, Michael W. (1997) 'Limb osteology and ossification patterns in Cryptoclidus (Reptilia:
Plesiosauroidea) with a review of sauropterygian limbs', Journal of Vertebrate Paleontology, 17: 2, 295-307.
Callomon, J. H. 1968. The Kellaways Beds and the Oxford Clay. 264–290. In Sylvester-Bradley, P. C. and Ford, T. D. (eds). The geology of the East Midlands. Leicester University Press, Leicester, xx + 400 pp. 

Hudson, J.D. 1978. Concretions, isotopes, and the diagenetic history of the Oxford Clay (Jurassic) of central England. Sedimentology, Volume 25 (3) 339-370.  

R. Lydekker. 1889. Catalogue of the Fossil Reptilia and Amphibia, Part II. 


Phillips, J. 1871. Geology of Oxford and the Valley of the Thames. Oxford.

H. G. Seeley. 1874. On Muraenosaurus leedsii, a plesiosaurian from the Oxford Clay, Part I. Quarterly Journal of the Geological Society of London 30:197-208.



 




Sunday, 8 July 2012

Did Feathers Enable Global Domination by Dinosaurs?


When Yutyrannus was unleashed on the world in April there was a flood of publicity in both the worldwide media as a whole as well as copious amounts of coverage in the palaeoworld – and rightly so. This was the first time that a large tyrannosauroid had been discovered with good evidence of a feathered covering and naturally this has led to speculation that even tyrannosaurids such as Tyrannosaurus may have been feathered.
My initial reaction to this was well publicised and generated a lot of coverage. However, some people grabbed the wrong end of the stick and assumed I was some kind of “feather denier” but this was soon sorted out. My adversity to feathered tyrannosaurids is purely a cosmetic issue and has nothing to do with science and, ultimately, this is the most important thing. And I actually have Andrey Atuchin’s awesome rendition of Yutyrannus as my desktop so I am not THAT averse to feathers!
So then, Yutyrannus, and what an intriguing discovery this has turned out to be. Like I said, there have been multiple articles regarding this animal even though it is still yet to be formally described and so there is only a limited amount of data to work with. But until the proper paper is published (perhaps a year and more?) we can all speculate a little as to its taxanomic affinities.
Firstly, and slightly problematical, is the provenance of these specimens. To remind you, there are three virtually complete specimens representing an adult, sub-adult and a juvenile that were apparently recovered from the Lower Cretaceous Yixian Formation of Liaoning Province in China. “Apparently” because the remains were purchased from a fossil dealer and, although the sediments the bones are encased in are almost certainly from the Yixian, there still has to be an element of caution. It has been recorded that the dealer also confirmed that these specimens were recovered from the same quarry (well he would) and were cut into smaller pieces to aid handling and transportation. So not ideal provenance – that’s for sure.
But the specimens themselves are superb regardless. The unusual fenestrated and rugose midline crest is the most prominent feature of the skull and is reminiscent of those found in Guanlong and Concavenator. On the face of it, Yutyrannus appears to be a typical basal tyrannosauroid based upon several characteristics in the cranium and especially the large three-fingered manus and yet there are other characters you would expect to find in more derived tyrannosauroids. The most obvious of these is the typically large and deep skull and there are additional features in the maxilla, lacrimal, squamosal and quadratojugal (amongst others) that lend sway to its tyrannosauroid affinities.
Interestingly, and as pointed out when the announcement was made in Nature, there does seem to be something carcharodontosaurian in nature about Yutyrannus. Indeed, Yutyrannus and Concavenator are remarkably similar. However, Andrea Cau did some sterling work in trying to nestle Yutyrannus in Carcharodontosauria but, regardless of the permutations, Yutyrannus sits nicely in Tyrannosauroidea. And Andrea points out that the carcharodontosaurian resemblance may simply be a case of convergent evolution.

A final point to make here is that despite the obvious completeness and preservation of the specimens there must be allowance made for the fact that the specimens are crushed flat and there is a possibility that one or two features are not as they seem and MAY be artefacts of preservation. In addition, and as mentioned earlier, we can but hope that there has been no interference with the specimen to “improve” it. I know this seems unlikely but remember Archaeoraptor? This is why it is so important to wait for the full paper.
Obviously the most interesting thing about Yutyrannus is the preservation of filamentous structures which are obviously analogous to feathers. They are big – around 15cm to 20cm long so are not to be sniffed at.  Despite the lack of coverage in certain areas (commonplace in the Yixian and other parts of the Jehol Group) it does appear likely that Yutyrannus would have been more or less fully covered.
Why Yutyrannus was feathered remains a matter of conjecture. Apart from the usual suggestions such as temperature control, sexual display and intraspecific communication, the authors suggest that Yutyrannus was perhaps adapted to exist in a cold climate and, indeed, this theory may have some merit. The Early Cretaceous of western Liaoning was a time of cold temperatures with a mean average temperature of 10° Celsius and a feathery integument would have been very useful and kept the animal insulated and warm.
I have always been fascinated by thought of how did feathered dinosaurs preen? One assumes that they did preen otherwise the feathers would have soon have become dishevelled and of no use. Most (but not all) extant dinosaurs have a gland – the uropygial gland – which is situated at the base of the tail and this produces, unsurprisingly, uropygial oil which the bird collects with its beak and distributes throughout its feathers to help keep them supple and strong.
The birds supplement this by grooming with a foot claw and, indeed, some birds display a comb-like structure that enables them to do this more efficiently. Dust baths also help condition the feathers and help remove parasites, excessive uropygia oil and also helps to dry wet feathers. It would be fascinating to see large theropods preening and grooming and one can only imagine what a spectacle a dust bath may have looked like! And there may be a further importance attached to preening.
Some extant birds, especially those that are monogamous, will often preen each other’s feathers (allopreening) and this is quite often part of a courtship ritual and is interpreted as strengthening the bond between such birds. This leads us nicely to the latest feathered dinosaur to hit the headlines – the stunning little theropod that is Sciurumimus albersdoerferi.
Like Yutyrannus, Sciurumimus has arrived on the scene like a bullet from a gun. We first got a sneak peak of the fossil last year and, indeed, I featured it here on the night the story broke. There has been plenty of coverage regarding this amazing fossil all over the blogosphere and on the web and I won’t be going over it again except for the fact that this taxon has been recovered in phylogenetic analyses as a megalosauroid.

Megalosauroids are an ancient group situated at the base of Theropoda and Dinosauria as a whole. The fact that this taxon is not a coelurosaur is also significant. This suggests that there is a strong possibility that most (some say all) theropods may have been feathered to at least some extent and that because the feathered ancestor of animals such as Sciurumimus must have been at the very base of Dinosauria then, by implication, there is even the possibility that all dinosaurs may have been feathered to a degree.
Of course, this requires an element of speculation and ultimately more fossils to be found before general acceptance can be assumed but it is a remarkable and challenging thought never the less. I tend to believe that feathers evolved several times within dinosaurs throughout their long existence and that they evolved for different reasons.   And maybe now, with the discoveries of animals such as Yutyrannus and Sciurumimus, there is a more profound and challenging notion to consider.
The feather may have been the single most important factor in the global domination of the world by dinosaurs. This one astonishing evolutionary step may have helped them regulate body temperature and aid in species recognition. If that was the case then it follows that feathers would have been used to aid natural selection – perhaps the male with the biggest or brightest plumage was most likely to be the most vigorous or strongest. The same feathers would then have probably been used for courtship ritual. We now enter an ever more complex world.
As feathers evolved and became more derived then preening would have been essential. It then follows that preening may have become part of courtship or a bonding ritual. Since preening and grooming is suggestive of an increasingly complex interaction between species this suggests that perhaps dinosaurs living in socially interactive groups were more complex than first thought. Indeed grooming in primates also dictates hierarchy although, granted, you cannot compare primates with archosaurs - but it does raise intriguing ideas.
If dinosaurs evolved in such a fashion then we should not be surprised at their worldwide success for over 150 million years.  Perhaps dinosaurs were highly evolved creatures that lived in complex social groups with what may have been advanced intelligence for such a time as the Mesozoic. Sciurumimus, by its very existence, with feathers in place may be indicative of just that. Perhaps tyrannosaurs hunting in packs are not so farfetched after all. 

References

Rauhut, O. W. M.; Foth, C.; Tischlinger, H.; Norell, M. A. (2012). "Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany". Proceedings of the National Academy of Sciences. doi:10.1073/pnas.1203238109

Xu, Wang, Zhang, Ma, Zing, Sullivan, Hu, Cheng & Wang. 2012. A gigantic feathered dinosaur from the Lower Cretaceous of China. Nature doi:10.1038/nature10906

Wednesday, 4 July 2012

Debunking ReptileEvolution.com

This is important and a must read. Darren Naish over at Tetrapod Zoology with a balanced yet methodical dismantling of the strange world of David Peters. Check it out here and spread the word.

Sunday, 1 July 2012

Extinction Event Caused Sauropod Hiatus?



There has always been something about the Cloverly Formation that I have found fascinating. I have to confess that I am not quite sure when this fascination began or why but whenever there are new discoveries or literature to be assessed regarding these units I am always eager to find out as much as possible.
The Cloverly Formation is an Early Cretaceous formation comprised of non-marine strata that stretch from Wyoming to Montana and has revealed a diverse community of vertebrate fossils that are, of course, dominated by dinosaurs. The most famous residents of these beds are unquestionably Deinonychus and Tenontosaurus but there are many more specimens that have come to light over the years and some of these are giants.
Michael D’Emic, of Georgia Southern University, has featured here on this blog a few times now and with Brady Foreman, of the University of Wyoming, has just published a paper in the latest edition of the Journal of Vertebrate Paleontology focussing on new insights into the origins of the so-called sauropod hiatus that occurred during the Early Cretaceous.
The absence of sauropod remains from the mid-Cenomanian until the Maastrichtian has proven to be problematic with no satisfactory explanation.  Suggestions as to why this hiatus took place include an extinction event brought about by the expansion of the Western Interior Seaway, competition from more advanced herbivores such as hadrosauroids who, in turn, were evolving at the same time as another suggested factor in the disappearance of sauropods  – the angiosperms.
Not everyone has been convinced by this selective extinction process and suggest that it may simply be a sampling bias (Mannion & Upchurch 2010, 2011) in as much that there is no evidence for sauropods during this period simply because the environments that they preferred were not conducive for fossilisation. To help try and solve the mystery, the authors decided to re-examine material from North American sauropods from before the hiatus and have come up with some pretty interesting results.
Material referred to Paluxysaurus jonesi, Sauroposeidon proteles and other undiagnosed elements were reappraised. It appears that differences between Paluxysaurus and Sauroposeidon are minor and that some characters support the synonymising of the two taxa, with Sauroposeidon taking nomenclatural priority. For example, autapomorphies are displayed in the centrum of the mid-cervical vertebrae, the spinoprezygapophyseal laminae of the anterior caudal vertebrae and the morphology of the scapula in Paluxysaurus – all referable to Sauroposeidon.
Other material is still difficult to assess. Teeth, by way of example, display characters found in brachiosaurids and titanosaurs, as well as Sauroposeidon. Other elements including vertebrae, limb bones and some juvenile material also remain undiagnosed. Indeed, the authors’ report one caudal vertebra has been mis-identified as belonging to a sauropodomorph but is actually more likely to belong to Tenontosaurus.
Since this research has highlighted the likelihood that Paluxysaurus and Sauroposeidon are one and the same taxon, cladistic analysis (D’Emic, in press) has recovered Sauroposeidon, perhaps a little surprisingly, as a basal somphospondylan. Sauroposeidon lacks certain synapomorphies of both brachiosaurids and titanosaurs yet displays other characters attributable to the Somphospondyli. This supports a possible Laurasia-Gondwana faunal interchange which, the authors point out, compliments current thinking on the origins of Acrocanthosaurus (Brusatte & Sereno 2008).
This research also leaves a dearth of evidence in support of Early Cretaceous titanosaurs in North America. The authors suggest the first proper evidence for titanosaurs on the continent resides with the fossils of Alamosaurus from the Maastrichtian and, the authors point out that the lack of titanosaurs pre-hiatus also renders any sampling bias, as a method of explaining the hiatus, unlikely since it appears that titanosaurs were never there in the first place.
This line of research, therefore, favours an extinction event during the mid-Cretaceous to explain the sauropod hiatus. It is worth pointing out, as the authors do, that two other groups also disappear at the same time – allosauroids and basal iguanodontians and this is despite the fact that it appears that their habitat remained stable long after they had disappeared.
The authors favour, with appropriate caveats, that a combination of the transgressions of the Western Interior Seaway and competition from hadrosauroids were likely factors contributing to the sauropods extinction. There is evidence for a fall in sea temperature and a not insignificant extinction of marine invertebrates during the transgression. However, what this actually means and how it relates to the sauropod hiatus is unclear at this time.
Hadrosauroids were beginn ing to flourish and diversify at this point and despite what would appear to be two groups of animals which display widely differing feeding techniques, the authors submit that competition may have arisen between the two groups at different stages throughout ontogeny. I thought that this was a really interesting point and was something that is easily overlooked when considering competition between groups since we tend to consider only adult animals when the subject is discussed.
Different ontogenetic growth stages in large dinosaurs would inevitably demand different food resources and the fast evolving hadrosauroids, with their relatively advanced feeding and “chewing” techniques would make for stern competition for the sauropods. And the fact is that the Early Cretaceous sauropods did indeed disappear at the same time as these hadrosauroids were proliferating.
This combination of transgression events, hadrosauroid diversity and sauropod disappearance may indeed be linked but there is much more research and sampling to be done before a conclusive answer can be decided upon. And I expect some counter arguments to be published in the not too distant future too.  Mannion and Upchurch (2010, 2011) came in for particular scrutiny in this paper and it will be interesting to hear and/or read their latest thoughts on the subject.

References

Brusatte, S. L., and P. C. Sereno. 2008. Phylogeny of Allosauroidea (Dinosauria:Theropoda): comparative analysis and resolution. Journal of Systematic Palaeontology 6:155–182. 

Mannion, P. D., and P. Upchurch. 2010. A quantitative analysis of environmental associations in sauropod dinosaurs. Paleobiology 36:253–282. 

Mannion, P. D., and P. Upchurch. 2011. A re-evaluation of the ‘mid-Cretaceous sauropod hiatus’ and the impact of uneven sampling of the fossil record on patterns of regional dinosaur extinction. Palaeogeography, Palaeoclimatology, Palaeoecology 299:529–540. 

Michael D. D'Emic & Brady Z. Foreman (2012): The beginning of the sauropod dinosaur hiatus in North America: insights from the Lower Cretaceous Cloverly Formation of Wyoming, Journal of Vertebrate Paleontology, 32:4,883-902.