Welcome to the blog of the Mesozoic vertebrates research group of the Bayerische Staatssammlung für Paläontologie und Geologie

Thursday, 26 July 2012

Coniophis, the origin of snakes, and long ghost lineages

Although snakes might not be the favourite critters of most people, these animals are certainly among the most amazing land-living vertebrates today. Legless, with greatly elongate bodies, and astonishing feeding adaptions, such as venomous fangs and hyperextensible jaws, snakes are also among the most successfull vertebrate groups, with almost 3000 species known today. However, the fossil record of snakes is still rather poor, and this is especially true for their origin. Thus, the evolution of the remarkable anatomical adaptations of snakes, and their functional and ecological context remain enigmatic.

Skull reconstruction of Coniophis and a modern snake (modified from Longrich et al. 2012, and Pough et al. 2004)
Nick Longrich and colleagues have now published new material of the latest Cretaceous snake Coniophis from North America that has some bearing on these questions. Although the taxon has been known for 120 years, only isolated vertebrae had been described so far. Longrich and colleages now described skull remains and additional vertebrae that throw new light on the anatomy and ecology of this early snake. The new remains show that the skull of Coniophis had the typical hook-shaped teeth and intramandibular joint of snakes, which help to expand the gape to swallow larger prey. However, the upper jaw was firmly attached to the other skull bones, much as in lizards, and thus not allowed the extensic movements between differetn skull bones that we see in modern snakes. Thus, Coniophis presents an interesting mosaic of characters that helps understanding how the feeding apparatus of snakes evolved.
However, one other aspect of the new paper I find somewhat more problematic. There is a long-standing debate whether snakes evolved from aquatic or land-living ancestors, and, if the latter was the case, whether these animal were terrestrial, tree-living, or burrowing. On the basis of the environment that Coniophis was found in and the features of the vertebrae, Longrich and colleagues deduce that this was a land-living and most probably burrowing animal. So far so good, but the next step goes further: on the basis of these findings, the authors suggest that the ancestor of snakes was probably terrestrial and burrowing. However, Coniophis comes from the Maastrichtian stage of the Cretaceous, some 65 million years ago, whereas the oldest known certain snakes date back to the late Early Cretaceous, some 100-120 million years ago. Now, that leaves us with two possibilites: First, the apparently primitive morphology of Coniophis is actually secondarily derived and has evolved from a "typical" snake, which seems unlikely. Second, Coniophis is a member of a primitive lineage of snakes which, according to its relationship with more dervied snakes, must reach back to the late Early Cretaceous at the least and thus have a ghost lineage (an evolutionary lineage without fossil record) of at least 35 million years. Given the fallacies of the fossil record in general and the poor fossil record of snakes in particular, the second explanation seems much more likely, and is also the one favoured by Longrich and colleagues. However, 35 million years are a very long time; indeed, this is more than half the length of the entire Cenozoic, the "age of mammals". The interpretation that a randmom member of such a long-lived evolutionary lineage that lived such a long time after its origin represents the original ecology of the clade is maybe not impossible, but nevertheless rather questionable. Assuming we would not have any good fossil record for either group, would you assume that elephants originated from marine animals, because their closest relatives, the Sirena, are marine today? Thus, although Coniophis provides exciting new insights into the evolutionary history of snake anatomy, I would be careful in interpreting its importance for the question of the ecological origin of snakes.

Longrich, N.R., Bhullar, B.-A.S. & Gauthier, J.A. 2012. A transitional snake from the Late Cretaceous period of North America. Nature, published online.

Wednesday, 11 July 2012

What, if anything, is Lepidotes?

There are certain taxa of Mesozoic vertebrates that every palaeontologist knows. One of these is certainly Lepidotes. Originally named by the great Louis Agassiz in 1832 based on a fish from the Early Jurassic of south-western Germany, the genus soon became a "wastebasket" for any remain of a Mesozoic fish with thick bony scales. Thus, there is a plethora of Mesozoic fish species referred to the genus Lepidotes, spanning the time from the Early Jurassic to the latest Cretaceous, or a time span of some 130 million years. Many of the fishes that were not referred to Lepidotes became species of Semionotus, another wastebasket taxon. Disentangling this mess seemed a task that no palaeontologist was willing to tackle.

Yes, this is a Lepidotes! Lepidotes gigas from the type horizon of the genus, the Posidonia Shale, at the BSPG.

Lepidotes and the other bony-scaled fishes represent a number of primitive lineages that were common in the Mesozoic, but dwindled to a mere nine or ten species today, which seem insignificant in comparison to the more than 25,000 species of the modern ray-finned fishes (teleosts). Nevertheless, these few species are the only available evidence for the evolutionary history that led to the origin of the modern fishes - with the exception of the fossils. However, interpreting the evolution of fishes in the Mesozoic is severely hampered by the lack of hypotheses on the interrelationships of many of the important lineages. Referring every second fish with thick bony scales from Mesozoic deposits to one of two genera certainly doesn't help in this respect. Lepidotes and several other Mesozoic fishes - most notably the almost as inflated Semionotus - are usually included in a group called Semionotiformes - which is widely used, despite the fact that most experts in fossil fishes recognized that semionotiforms are not a natural group.

Not a Lepidotes: Macrosemimimus fegerti under UV light. Foto H. Tischlinger.
This was the situation when Adriana López-Arbarello started with a project on semionotiform fishes in 2006. The German Research Foundation (DFG) financed this impossible seeming task, first for two years, but with extensions of anther two years. And thus Adriana went to work, logically first with revising materials referred to Lepidotes and Semionotus, starting with the original species of these two genera. Thus, over the years, she and her co-workers published new descriptions of the type species of Semionotus, a redescription of Neosemionouts, and coined new names for two other groups of species that were originally referred to Lepidotes, Scheenstia and Macrosemimimus. She further studied new semionotiforms, three of which are already published, Tlayuamichin from the Cretaceous of Mexico,  Sangiorgioichthys sui from the Triassic of China and Lepidotes pankowski from the Cretaceous of Morocco. But, apart from this taxonomic work, she mainly used the detailed studies of many specimens and the visits to collections to collect data for an analysis of the interrelationships of these fishes.

This analysis was now published in the journal PLoS One. It represents the largest and most explicit phylogenetic analysis of semionotiform fishes. Adriana found many interesting results, most importantly the division of semionotiforms into two separate lineages, one of them including Semionotus and its relatives and the other Lepidotes and the fishes more closely related to this genus. This might still not be too surprising - but the latter lineage was found to lead to the modern gars, and the former includes a group that was so far considered to be an own lineage of Mesozoic fishes, the macrosemiids. Based on these relationships, Adriana decided to use the name Lepisosteiformes for the Lepidotes-gar lineage (Lepisosteiformes being the group that modern gars belong to) and restrict Semionotiformes for the Semionotus-macrosemiid lineage. Both lineages were united in the group Ginglymodii.

The interrelationships of ginglymoidian fishes according to López-Arbarello (2012).

These results have far-reaching implications. For one thing, ginglymodians are a more diverse group than previously recognized, being represented by many different lineages with often long ghost lineages (extensions of the lineage for which fossil evidence is still missing), indicating that these fishes were also taxonomically more divers. Furthermore, ginglymodian fishes were ecologically divers, and the recognition of Lepidotes and its kin as fossil relatives of modern gars helps to understand the evolutionary history of these fishes.

So, Adriana has made an important step in her studies of the interrelationships of Mesozoic fishes that stand at the base of modern groups. Does that mean that everything is known now about the evolution of the Ginglymodii, and she can turn to other things? Certainly not, Adriana's work represents only a beginning. There are many more species of Lepidotes and Semionotus to be revised and to be included in the analysis of the interrelationships, and detailed studies of other groups of Mesozoic fishes are necessary to further elucidate the origin of modern clades of bony fishes. However, her paper presents a first reference frame for such studies. It includes a wealth of anatomical and character data that are of importance for the interpretation of the interrelationships of Mesozoic fishes and presents hypotheses of interrelationships that are sure to spark discussion and renewed interest in these groups in ichthyologists. Thus, it will provide fertile ground for future studies of the role that Mesozoic fishes play in our understanding of the origin of our modern vertebrate diversity.

Monday, 9 July 2012

Jurassic abelisauroids in England? Why (and how) to deal with fragmentary specimens

Vertebrate paleontologists often have to deal with fragmentary remains; complete skeletons, such as that of Sciurumimus, are extremely rare. The vast majority of specimens in vertebrate palaeontology consist of isolated teeth or bones, or often even only parts of these. Thus, palaeontologists are often faced with the challenge of interpreting these fragments, identifying their identity and evaluating their evolutionary or biogeographic significance. Many of us have published on such remains and sometimes have drawn far-reaching conclusions on the basis of a few isolated bones or teeth. I myself am certainly guilty of this, having announced the first dromaesaurid (sickle-clawed dinosaur, a relative of the famous Velociraptor) from the southern hemisphere on the basis of a tooth and a few foot bones, or having described the first Jurassic tyrannosauroid from Europe on the basis of a single ilium. Of course, claims on the basis of such material are often contested. A good example for this are dinosaur remains from the Cretaceous of Australia, which almost all consist of isolated bones, and which have been interpreted very differently by different scientists.

Recently, my Argentinean colleagues Martín Ezcurra and Federico Agnolín re-interpreted a distal end of a tibia (the shin bone) of a small predatory dinosaur from the Middle Jurassic of England as one of the oldest representatives of the abelisauroids, a group of peculiar predatory dinosaurs which are mainly known from the southern hemisphere. This specimen would thus not only be one of the oldest representative of abelisauroids, but also the oldest record of this group from the northern hemisphere. This interpretation obviously had far-reaching implications for the evolution and biogeography of this dinosaur group, which were clearly lined out by Ezcurra & Agnolín.
Example of an abelisauroid: Carotaurus sastrei (by Nobu Tamura)

Since I am currently working on a Middle Jurassic abelisaurid from Argentina - which Diego Pol and me recently published as Eoabelisaurus mefi - I was, of course, very interested in this re-interpretation of the small theropod (the predatory dinosaurs) specimen from England. However, reading the article, I was unconvinced of the interpretation presented by Ezcurra and Agnolín. Thus, I got out my photographs of predatory dinosaurs that I took in many different collections over the years, asked a few colleagues for images of other specimens that I thought might be of interest (which many of them provided; special thanks here to Roger Benson, Lindsay Zanno, Jacques Gauthier and Brooks Britt), and then wrote a short article arguing against the interpretation presented by Ezcurra & Agnolín. In this article, I could show (I hope) that the characters used by Ezcurra & Agnolín to refer the specimen to abelisauroids have a wider distribution within theropods, and that the bone in question can thus only be identified as an indeterminate predatory dinosaur.
The bone of contention: distal end of a shin bone of a small predatory dinosaur.

So, having thus publicly disagreed with my colleague Martín Ezcurra, does that mean that I think that he is a poor anatomist? Certainly not; on the contrary, I value Martín's detailed anatomical observations very highly and generally think that he does excellent work! Indeed, a few months ago, Martín started working as a PhD student here at Ludwig Maximilian University in Munich with my friend and colleague Richard Butler, and in all things theropod, I often consult with him. The article by him and Federico Agnolín is also not an example of poor science. The two presented testable characters for the referral of the element in question to abelisauroids, which only made it possible for me to criticise their work. Thus, this is proper scientific procedure: You present your data and the hypothesis derived from it. This hypothesis is then out there to be tested in the light of new data or other observations, which is exactly what I did in this case: I presented observations that showed that their data is not sufficient to support their conclusions. Only by putting the data and your ideas on it out there can science progress; being wrong sometimes is not a failure, but a necessary prerequisite of scientific progress! (Which, however, does not mean that any bogus idea is beneficial to science. It should be backed by hard data, repeatable observations, and logical deduction. See Darren Naish's blog "tetrapod zoology" for an example of what is not very helpful for science.)

So does that mean that I think we should not deal with fragmentary material any more? Also not, since that would mean that we have to ignore some 80 % of the vertebrate fossil record, and would thus loose an enormous amount of potentially important information. In the interpretation of such materials, we have made enormous progress in the past twenty to thirty years: Previously, most referrals of such fragmentary specimens was based on rather vague notions of "overall similarity", but, with the development of large data sets of anatomical characters that are typical for certain groups (so-called apomorphic characters), we can be much more specific on what basis we refer fragmentary remains to a specific clade. Of course, with incomplete material, there is always the possibility that more complete remains might prove us wrong, or that new finds or observations on other materials might show that these characters are more widely distributed than previously thought, but with this data we can formulate specific hypotheses that are then testable by such new data. There is also the danger of overinterpreting minute differences that might not be of systematic significance (for example due to individual variation or just abnormalities), but who can say when we reach this level in animals that are extinct?

As scientists, we should always remain critical. It is often said that "extraordinary claims need extraordinarily good evidence", and we are wise in remembering this when reading about the implications of interpretations of fragmentary specimens. Thus, I am not convinced that there were tyrannosaurs in the Cretaceous of the southern hemisphere, as claimed by Roger Benson and colleagues based on a single pubis. However, I am also not entirely convinced that there were carcharodontosaurids in the Late Jurassic of Tanzania, a claim made by myself on the basis of some teeth and a few vertebrae. Nevertheless, at our current state of knowledge, these are the best hypotheses to explain the available data. New finds, or new observations might prove us wrong, but such is the nature of scientific investigation.

Friday, 6 July 2012

Bellubrunnus and what we do and don't know about Jurassic pterosaurs

Pterosaurs - the flying reptiles - were an important component of Mesozoic terrestrial ecosystems, yet their fossil record is strongly biased towards some exceptional localities. One of them are the Late Jurassic limestones of southern Germany. These rocks have not only yielded the first pterosaur to be described scientifically - Pterodactylus, first described by Collini in 1784, and still kept in our collections here in Munich -but, together with the famous Santana beds of Brazil and the Yixian Formation of China, they have yielded one of the most diverse pterosaur faunas in the world.

However, if you thought that we already know everything about the Late Jurassic pterosaurs from southern Germany, think again - David Hone of the University College London and his coauthors (among them once again the master of UV photography, Helmut Tischlinger) have just published a new species of long-tailed pterosaur from the laminated limestones at Brunn, eastern Bavaria. They called the new taxon, which is based on a wonderfully preserved specimen that technically belongs to our collections, though it is currently housed in Solnhofen, Bellubrunnus - the beauty from Brunn. And Bellubrunnus is not the only new pterosaur from the Late Jurassic limestones of southern Germany: Just recently, two of the authors of the new paper - Eberhard "Dino" Frey and Helmut Tischlinger - together with Christian Meyer from the Museum in Basel described the oldest azhdarchid pterosaur (the group that the giant Cretaceous forms belong to), Aurorazhdarcho, from the Solnhofen limestones, and several other new pterosaurs have recently been found.

Skeleton of Bellubrunnus. Length c. 14 cm.
Why, you may ask, is that so? Well, apart from the obvious - that pterosaur diversity was greater than hitherto recognized - this is due to a pecularity of the geological setting that is little known outside Germany: What is often lumped together as "Solnhofen limestones" actually represent several geological units that span the time from the "middle" Kimmeridgian (c. 152.5 million years ago) to the Early Tithonian (c. 148 million years ago). They thus span several million years, but so far, mainly the Solnhofen Formation has yielded abundant fossil material, including most known pterosaur specimens and the iconic Archaeopteryx. However, this is mainly due to the fact that this is the only unit that has systematically been explored in the past 200 years, since the Solnhofen slabs were the best for lithography and are also used as building materials. Nevertheless, the underlying Rögling and Thorleite formations (and their equivalents) and the overlying Mörnsheim Formation are also very fossiliferous, at least in parts. These units are now being explored more systematically, and, apart from taxa shared between the different units, we also see a lot of new species coming out. The locality that Bellubrunnus comes from, the quarry at Brunn, is thus quite a bit older than the "classical" Solnhofen limestones, and only the systematic excavations by Martin Röper of the Bürgermeister Müller Museum in Solnhofen (another one of the authors on the paper) are starting to reveal the ecosystem of that time. Likewise, a new systematic excavation in the Mörnsheim Formation at the Schaudiberg close to Mörnsheim has already resulted in the recovery of several new taxa, and in a quarry close to Wattendorf worked in by Matthias Mäuser of the Naturkundemuesum Bamberg and Winfried Werner of the BSPG the so far oldest fauna from the Late Jurassic limestones is currently being exhumed. We can thus expect many more new discoveries.

Geological profile through the Upper Jurassic of southern Germany, with placement of several localities indicated. Slightly modified from Fürsich et al. (2007; Palaeogeogr., Palaeoclim., Palaeoecol. 243: 92-117 )
The Upper Jurassic limestone formations of southern Germany thus represent an almost unique opportunity to study the changes in a Jurassic ecosystem over a geologically short period of time. That some taxa are common to all of the different units, whereas others, such as the pterosaurs, seem to show marked differences between the faunas might indicate different evolutionary dynamics in different groups. However, it will also not be easy to tell evolutionary changes in these groups from possible effects of environmental changes between the different units. Thus, everything is known about the Late Jurassic pterosaurs of southern Germany? Far from that, the work has just begun...

Hone, D. W. E., Tischlinger, H., Frey, E. & Röper, M. 2012. A new non-pterodactyloid pterosaur from the Late Jurassic of southern Germany. PLoS One 7(7): e39312. doi:10.1371/journal.pone.0039312

Thursday, 5 July 2012

Virtual Jurassic

You might have wondered, why a blog (and also our website) that is dedicated to Mesozoic vertebrates sports a nice landscape picture in its header. Well, the answer is simple: The landscape you see there is made up by rocks of the Cañadón Asfalto Formation, the most productive geological unit for Middle Jurassic vertebrates in the southern hemisphere, and center of my fieldwork activities since more than ten years. This Middle Jurassic unit (we now know that the formation is considerably older than previously thought, being somewhere between 174 and 167 million years old) is exposed along the middle course of the Chubut river, in Chubut Province, Argentinean Patagonia. The picture you see is the sequence of the Cañadón Asfalto Formation on the eastern bank of the river, opposite to the village of Cerro Cóndor.

The village of Cerro Cóndor. Small, but world-famous amongst palaeontologists.

In the past twelve years, since we started our exploration project in 2000, the Cañadón Asfalto Formation has yielded an incredible wealth of fossils. Dinosaurs had already been described in the 1970ies by famous Argentinean palaeontologist José Bonaparte, but, during the years, we and other teams that collaborate with us found almost every vertebrate you might expect in a Jurassic ecosystem, from fishes, via frogs, turtles and pterosaurs up to mammals. And, of course, many more dinosaur remains, including three new taxa we described in the past years, Condorraptor, Manidens and Eoabelisaurus, the last of which was just described recently by my Argentinean colleague Diego Pol and me.

My cooperation partner in Argentina is the Museo Paleontológico Egidio Feruglio, where Diego works as a researcher. This institution has now dedicated a new exhibition to the Jurassic of Chubut. However, no need to run and book tickets to go to Trelew to see this exhibition: It is a virtual exhibition of the Jurassic ecosystem of the Cañadón Asfalto Formation! Thus, from your home computer, you can enter a building that resembles the real museum building in Trelew, walk through the entrance hall, where due credit is given to those who made the exhibition possible, and then go through a scientist's office into the exhibition.

The virtual exhibition hall of the Museo Paleontológico Egidio Feruglio
Here you see wonderful dioramas with plants and animals known from the Cañadón Asfalto Formation. You can go closer to these, and then click on the items, so that a window pops up and gives you additional information and figures of the actual fossil material. At the end of the museum, there is even a small cinema, where you can see movies about the (temporatily slightly misplaced) Cretaceous carcharodontosaur Tyrannotitan.

All in all, this virtual exhibition gives an excellent overview of the Jurassic in Chubut. Thus, take some time to stroll through a museum from your comfy armchair and discover the wonders of Jurassic life in southern Gondwana! Of course, it is not as good as wandering through the original exhibition, but certainly a great idea to further dissiminate scientific results. Another small wonder of the world wide web...

Disclaimer: I was not involved in this virtual exhibition, but came across it rather by accident. In any way, this was too good to not write about it ;-)

Sciurumimus - looks like a squirrel, tastes like chicken...

Yesterday, me, my student Christian Foth, Helmut Tischlinger and Mark Norell finally got to publish the new theropod dinosaur from the Late Jurassic of southern Germany in the Proceedings of the National Academy of Sciences. The specimen had made the round in the press already last year, since it was exhibited at the Munich Show, a big mineral, jewel and fossil fair here in Munich. The fossil had been found in systematic excavations in a limestone quarry at Painten, north-eastern Bavaria, by a crew of fossil enthusiast and commercial collector Raimund Albersdoerfer, somewhen in the mid 2000s. Raimund rapidly recoginzed the scientific value of the find and looked for scientists to colaborate with in its description - I was the fortunate one that he found. Thus, it was through his courtesy that the specimen came to the Bavarian State Collection here in Munich for scientific analysis. Even more than that, Raimund himself requested that the specimen be included in the register of cultural objects of national importance, which insures that it will stay in Germany and that its current repository has to be made known to the authorities. This is a nice example of how science can profit from interaction with private collectors.

The new theropod photographed under UV light. (c) Helmut Tischlinger.

The specimen is certainly one of the most beautiful dinosaur fossils I have ever seen. It is a small theropod dinosaur (total length c. 70 cm) preserved lying on its right side in complete articulation. It comes from thin-banked to laminated limestones that lie below the famous Solnhofen limestones (from where the primary bird Archaeopteryx is derived), and is thus slightly older, dating back to the Late Kimmeridgian (some 151-152 million years old). Helmut Tischlinger, another private collector, world leading expert on UV-photography of fossils, and one of our co-authors on the paper actually saw the specimen shortly after its discovery in an unprepared state, so there can be no doubt as to its authenticity. But even apart from the exquisite state of preservation of the skeleton, there is more to the animal than what meets the naked eye - UV photography revealed the preservation of soft tissue in several parts of the skeleton. Especially striking were especially long dorsal filaments in the anterior part of the tail. These features led to the nickname that we used during the scientific investigation - "the squirrel". This later translated into the scientific name of the animal, Sciurumimus, meaning squirrel mimic (there are rumours on the web of this specimen being nicknamed "Otto". I have never heard of that name in reference to this specimen, and it was certainly no nickname we ever used). If you think this name is rather complicated - we first pondered whether to name it "Oachkatzlschwoaf", the Bavarian dialect name for a squirrels tail, which is even hard to pronounce for non-Bavarian Germans.

Skin remains and filaments preserved dorsal to the tail base. (c) Helmut Tischlinger.

Though a number of primitive characters were obvious from the beginning, when we first started working on this fossil, we were impressed by the overall similarity with Juravenator, which is of exactly the same age and comes from an adjacent basin, especially in the proportions. It took Christian and me three trips to Eichstätt to look at the original specimen of this taxon to make sure that it is not just another specimen or species of Juravenator. Thanks are due here to the director of the Jura Museum, Dr. Martina Kölbl-Ebert, who gave us access to Juravenator, even though we couldn't tell her why we needed to see it, since the existence of Sciurumimus was still a well hidden secret.

Our further resarch showed that Sciurumimus is not only clearly distinct from Juravenator, but that it is actually considerably more basal in the theropod family tree than other feathered dinosaurs known, being related to megalosaurids, large, predatory dinosaurs, such as the Middle Jurassic Megalosaurus. Thus, it it was not particularily closely related to birds, yet its entire body seems to have been covered in thin, hair-like filaments. It thus indicates that feathers might have been much more widely spread among dinosaurs than previously recognized. Surely, this is not an entirely new idea, but it is always nice to see your hypothesis confirmed by hard evidence...

Life reconstruction of the fluffy juvenile of Sciurumimus. I wonder if adults would have been as fluffy...

The function of these feathers was certainly not flight, but most probably thermoregulation. These structures resemble the down feathers of modern birds, which are great to keep your body warm (as anybody knows who has used a down jacket). This in term indicates that these dinosaurs probably had some kind of mechanism to actively regulat their own body temperature.

Much has been written in the media about the significance of this find, so I don't want to dwell too much on this here, and more information will become available with a detailed description that we are currently working on. In the meantime, Sciurumimus has found a comfortable home as a permanent loan to the Bürgermeister Müller Museum in Solnhofen, the very town whose name is world famous because of the well-preserved fossils in this area. There, the original fossil can be admired by everyone who visits the beautiful valley of the Altmühl, formerly the tropical archipelago of Solnhofen...

Wednesday, 4 July 2012

Mesozoic blogging...

Finally, the Mesozoic Vertebrate Research Group of the Bayerische Staatssammlung has decided to start a blog on new develoments in the field of Mesozoic vertebrates, their evolution and their world. We will try to keep you updated, not only on out own research, but also on other important news from the distant past...