Wednesday, 31 December 2014

Some Late SVP Reviews



As 2014 draws to a close and time, as always seems to be the case for me this year, is at a premium and I have here my first reviews of some of the research presented at SVP in November. Normally I would have finished with my reviews by now but, on this occasion, I will carry on processing some posts – it is not like the research is already out of date after all.

The recent disclosure that palaeontologists were in possession of associated remains of Spinosaurus aegyptiacus caused a worldwide sensation when the news broke in September. A massive publicity campaign funded by the monetary power of National Geographic (NG) ensured maximum exposure for the authors, the accompanying Science paper and, of course, National Geographic themselves.

The animal is spectacular. The authors describe an almost dragon-like aquatic predator that has a reduced sized pelvic girdle supporting hind limbs that are drastically shortened in comparison with the standard theropod design. There are other adaptions described such as the shape of the skull, solid limb bones and the much discussed forelimbs which are very robust and powerful and all of these, plus other adaptions, appear to suggest that Spinosaurus was a very adept and powerful swimmer that preyed on the contemporary large fish of the time. Still nobody is quite sure what the purpose of the sail/hump was.

You will also know that this research has not exactly been universally accepted by all and that questions remain which is fair enough since that is what science is all about. There has been plenty of discussion about this in the Mesozoic Media so I do not really need to delve into this too deeply and, when I had read the SVP abstract, I was keen to attend the presentation and hopefully learn more about the animal and see what else might be revealed in relation to the upcoming monograph – in other words, I wanted to learn more.

However, I was bitterly disappointed since the oral presentation turned out to be nothing more than a boys own story about how the fossils were recovered and a broader advert for how wonderful NG was. Lead author Nizar Ibrahim broke with SVP convention and did not stand at the lectern presenting his research to his peers – rather he was free to walk about on the platform talking to the audience as if he was presenting a television programme. He was good at it mind and I imagine that the publicity machine behind the Spinosaurus campaign was delighted with him.

At the end of this talk, and after yet more copious thanks to NG, Ibrahim stood there expecting, I believe, whoops of delight and rapturous applause. However, the rather muted applause at the end of it was indicative that most delegates felt, as I did, that we had come to find out more about this enigmatic dinosaur and had learnt nothing – in fact there was not a single palaeontological detail of note.

This was unfortunate. Ibrahim and his co-authors have done (and are still doing) some sterling work in finally bringing Spinosaurus to life but the funding has come at a price and I have severe misgivings because of the circus that attaches itself to palaeontology when a big media operation provides the funding. Palaeontology needs as much funding as possible and I understand that when the opportunity arises then we need to grab it with both hands – but the price, in terms of reputation and respectability, may prove to be expensive. I hope that I am indeed wrong in this assertion.

On to the business in hand then. Dinosaur diversity prior to the Cretaceous end extinction has often been debated over the years with the more recent research appearing to confirm that dinosaurs were still significantly diversifying albeit with a hugely reduced taxa rate. Emily Bamforth, of the Roya Saskatchewan Museum and Hans Larsson of McGill University in Montreal, have also been examining this, but in a much wider context, by examining the palaeomacroecological signals in the latest Maastrichtian Frenchman Formation in Saskatchewan, Canada.

By examining a combination of  stratigraphic and palaeoclimatic data and cross referencing with over 7800 fossils from 38 microsites the authors were able to establish that overall taxanomic diversity, which includes the dinosaurs, displayed no overall shift in stability although there was evidence to suggest that some lesser groups were vulnerable and susceptible to change. Indeed, the majority of microsites examined revealed an extraordinarily high diversity of taxa. This adds to the hypothesis that the extinction event at the end of the Cretaceous was very likely catastrophic or was fairly rapid to say the very least.

In the same vein, Thomas Williamson, of the New Mexico Museum of Natural History, and his co-authors have been looking at the chronostratigraphy of the San Juan Basin in New Mexico with particular emphasis on the period around the KT boundary. This area is of particular note since it is one of the very few areas that contain the remains of animals from both sides of the boundary – and trying to constrain the ages of the relative formations and members has been problematic.

But by utilising a combination of magnetostratigraphy, thermochronology and mammalian biochronology the team has been able to provide the best date estimates yet provided. The top of the Ojo Alamo Sandstone is certainly Paleogene and the rest of this formation is almost certainly Paleogene too. The Naashoibito Member is confirmed as being uppermost Cretaceous and is contemporaneous with the much better known Hell Creek Formation.

Mammalian fossil remains prior to the extinction event indicate that their abundance and diversity was somewhat moderate. However, there is good evidence that life recovered incredibly quickly after what is generally accepted to be a catastrophic extinction event and that there was a diverse mammal fauna after only 160 thousand years and, incredibly, that there were large mammals in excess of 100Kg in weight after 300 thousand years.

I believe we all tend to believe that in the event of a catastrophic extinction event, such as that at the end of the Cretaceous, that life would take an incredibly long time to recover but we can now see that life is incredibly resilient and can both quickly recover and proliferate. I am still mystified, however, in what determined how certain groups of animals survived the KT event whilst others disappeared. In any event this is very cool radiometric dating and research and I found it of particular interest.

Limusaurus inextricabilis is a small gracile basal ceratosaur from the Upper Jurassic Shishugou Formation of Xinjiang in China and is perhaps known for its weird manus which displays strong bilateral digit reduction. Josef Steigler, of the George Washington University, and his colleagues have been delving deeper into the implications suggested by this bizarre little creature.

They examined multiple specimens entombed in two blocks (at least 14 articulated specimens) which represent the animal at various ontogenetic stages including very young juveniles and this may be indicative of parental care in Limusaurus. Having examined the remains, which includes CT reconstruction of a very well preserved three dimensional skull, allowed the researchers to reassess the phylogeny of ceratosaurs and found Limusaurus to be nested within Noasauridae.

Some of the featured anatomical details include unfused frontals, the C10 cervical vertebra, shown as an example, has short neural spines and is extremely elongate and the metatarsals of the pes are really quite slender. Further phylogenetic insights suggest that Limusaurus, Elaphrosaurus, Deltadromeus and Spinostropheus are all basal noasaurids. This is not that much of a surprise – Deltadromeus has been recovered as a noasaurid before (Wilson et al 2003) and all of the named taxa have generally been recovered as basal ceratosaurs anyway.

The superbly preserved megalosauroid Sciurmimus albersdoerferi, from the Upper Jurassic of Germany, continues to fascinate and Christian Foth, of the Bayerische Staatssammlung für Paläontologie und Geologie in Bayerische Staatssammlung für Paläontologie und Geologie in Munich, and his colleagues have been examining the specimen under UV light using various filters to glean new insights into the integument and feather preservation in this fascinating little theropod.

The tail feathers are best preserved and display long, gently curved filaments. There are obvious differences in the filaments whereby they overlap each other proximally but the distal portion remain unwrapped. The authors are quick to point out, and correctly so in my opinion, that this filament distortion and clumping may be due to taphonomic forces during fossilisation.

The UV study also reveals that the tail was completely covered in feathers. Other preserved feathers, however, consist of entirely uniform filaments and resemble those of other dinosaurs such as Dilong and Sinosauropteryx.  Other apparent filaments on the dorsal side of the tail are interpreted as being collagen fibres as opposed to feathers whilst others do indeed resemble filaments similar to those found in Psittacosaurus. In any event the authors stress that only the existence of monofilamentous feathers is proven in this specimen – nothing else.

I do not very often discuss sharks here except to mention their teeth that we recover in both Jurassic and Eocene deposits – sometimes the occasional spine. But the renowned mega-shark, Carcharocles megalodon, is never mentioned here but, Discovery Channel notwithstanding, perhaps we should because this is just about as awesome an ancient predator as any theropod or pliosaur. Catalina Pimiento, of the Florida Museum of Natural History, has been looking at the body size patterns and reasons for the extinction of these giant sharks.

C. megalodon had a rather cosmopolitan distribution and swam in the seas throughout the Miocene and Pliocene periods before its disappearance around the Pliocene-Pleistocene boundary. Using Optimal Linear Estimation, which enabled the author to cross reference temporal distribution with body size estimates obtained by the examination of fossil teeth and vertebral centra from around the world, enabled a novel method to determine the point at which time this shark became extinct.

It appears that that the lineage leading from Otodus to C. megalodon (assuming you are a supporter of the Carcharocles lineage as opposed to a Carcharodon evolutionary line) increased in size exponentially and maintained a pretty stable size median throughout its existence and, as such, likely had no detrimental effect on its decline. However, the research does confirm its disappearance across the Pliocene-Pleistocene boundary and this ties in nicely with the disappearance, at the same time, of smaller sized prey animals and the increase in predatory competitors.

It is no coincidence that whales increased significantly after the disappearance of the giant sharks and is indicative of how the disappearance of a large apex predator can affect the balance of the ecosystem on a global scale – something we have discussed here before when looking at the effects of specific theropod extinctions throughout the Mesozoic. More importantly, however, are the implications that the disappearance of a top predator can have in modern ecosystems and it is sadly the case that it is again the shark that is being eliminated in the seas throughout the world that will likely have massive implications for us in the not too distant future.

Have a great new year everyone!

References

Bamforth, E. & Larsson, H. 2014. Terrestrial biodiversity immediately prior to the end Cretaceous mass extinction in central Canada: Patterns and processes. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2014, pp85.
 
Foth, C., Haug, C., Haug, J., Tischlinger, H. & Rauhut, O. 2014. New details on the integumental structures in the juvenile megalosauroid Sciurumimus albersdoerferi from the Late Jurassic of Germany using different auto-fluorescence imaging technique. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2014, pp131-132. 

Semiaquatic adaptations in a giant predatory dinosaur. Nizar Ibrahim, Paul C. Sereno, Christiano Dal Sasso, Simone Maganuco, Matteo Fabbri, David M. Martill, Samir Zouhri, Nathan Myhrvold, and Dawid A. Iurino. Science 26 September 2014:345 (6204), 1613-1616. Published online 11 September 2014 [DOI:10.1126/science.1258750]

Pimiento, C. 2014. Extinction and body size patterns of the giant shark Carcharocles megalodon. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2014, pp205. 

Stiegler, J., Wang, S., Xu, X. & Clark, J. 2014. New anatomical details of the basal ceratosaur Limusaurus and implications for the Jurassic radiation of Theropoda. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2014, pp235. 

Williamson, T., Peppe, D., Heizler, M., Brusatte, S. & Secord, R. 2014. Chronostratigraphy of the Cretaceous-Paleogene transition in the San Juan Basin, northwestern New Mexico. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2014, pp255-256.  

Wilson, Sereno, Srivastava, Bhatt, Khosla and Sahni. (2003). "A new abelisaurid (Dinosauria, Theropoda) from the Lameta Formation (Cretaceous, Maastrichtian) of India." Contr. Mus. Palaeont. Univ. Mich.31: 1-42