Archive for the ‘Taxonomy’ Category
I’ve been rather quiet again recently, however, as coauthor of an article just published in PLOS ONE, I’ve good reason to come out of my shell today. The new paper describes and names the Weymouth Bay Pliosaur, a spectacular almost complete skull over 2m long from. As discussed in the open access paper (do take a look), the specimen is sufficiently different from all other pliosaurs to warrant a scientific name of its own, Pliosaurus kevani.
Pliosaurus kevani was named in honour of Kevan Sheehan, the Osmington Mills café owner who collected most of the skull, piece by piece, over a period of eight years during daily walks along the foreshore. Kevan collected chunks up to 60 kg in mass as they weathered out from the Jurassic aged Kimmeridge Clay Formation sea-cliff. The specimen was purchased with funding secured by Dorset County Council’s museum service from the Heritage Lottery Fund Collecting Cultures programme and Dorset and Devon county councils. It was prepared between 2010 and 2011 by Scott Moore-Fay and went on public display in Dorchester County Museum in July 2011.
Richard Forrest, who was involved with the project from the beginning, first had the idea of putting together a ‘dream team’ of British plesiosaur specialists to study and describe the skull. This is the first collaboration of its kind among plesiosaur researchers (as far as I know), and I feel lucky to have had the opportunity to contribute to it under the driving force of our lead author, Roger Benson.
The massive skull has a long snout, circular orbits, huge temporal openings for the jaw musculature, and a deep mandible. Large portions of the skull have been crushed flat during fossilisation, so one of my tasks was to reconstruct the skull to show how it might have appeared before it was flattened. After several versions and much input from Mark Evans, I’m pleased with how it turned out, and I think we have a pretty accurate reconstruction of Pliosaurus. On the basis of this reconstruction I’ve also had a go at restoring the life appearance of the head of P. kevani in profile. Despite its large size and massive teeth, the head is rather gracile.
Pliosaurus belongs to a group of plesiosaurians known as thalassophonean pliosaurs. If you haven’t heard of them before, that’s because the name Thalassophonea, or “sea slayers”, was proposed just this year (Benson & Druckenmiller, 2013) for a natural group of derived giant pliosaurids including Pliosaurus, Liopleurodon, and Kronosaurus. Thalassophoneans were macropredators, that is, giant predators doing the sort of dirty work in the Middle-Late Jurassic and Cretaceous that rhomaleosaurids had done in the Early Jurassic. The paper also discusses the evolution of pliosaurids. The earliest thalattophoneans have a long mandibular symphysis, but in later member it becomes shorter. This trend is related to a shift in the dietary habits of pliosaurs from primarily fish-eaters to macropredators. In conjunction with this trend, we demonstrate that pliosaurids tend to follow Cope’s Rule – they get larger throughout their evolutionary history.
We also name two other new species of Pliosaurus in the paper, P. westburyensis and P. carpenteri, based on material in the Bristol Museum & Art Gallery from Westbury, Wiltshire. Again, there are aspects of the morphology in these specimens that distinguish them from one another, but don’t justify new genus names. So, add these new species to the existing list of valid Pliosaurus species (P. funkei, also known as Predator X, P. brachydeirus, P. rossicus, there might be one or two more, pending thorough description of the material) and we find ourselves with a rather large number of species within a single genus (although some invalid species of Pliosaurus are sunk too). Future research might show greater generic diversity among these species, but that’s really dependent on the discovery of more satisfactory fossil material.
There was a time when I’d leap into tippy-tappy action at the first sniff of a newly named plesiosaur. Unfortunately, I haven’t been keeping Plesiosaur Bites up to date and a few new taxa have passed me by. Of course, when I say “a few”, what I really mean is we are swamped by the things. Little wonder I haven’t been able to keep up.
A few years ago I plotted a graph in my PhD thesis (Smith, 2007, Figure 2.2.) to show the number of valid plesiosaur species and genera named in successive 20-year time intervals since 1821 (when the first plesiosaur was named [Plesiosaurus]). The data ended in 2007, the year I submitted my thesis, but showed that new taxa were being erected at a relatively steady rate throughout the 19th and 20th century (Figure 1). The rate started to pick up during the 1990s and I extrapolated the data into 2008-2020 based on the first seven years of the 21st century. I predicted 30 new genera in the period 2001-2020, which would represent a huge post-2001 leap in the number of new valid plesiosaurs. Well, so much for my crude calculations. It’s only 2012 and my ‘huge’ prediction has already been surpassed.
Figure 1. Tally of the number of new plesiosaur taxa per 20-year interval (from Smith, 2007, Y-axis adjusted for direct comparison with Figure 2 below). 2001-2020 predicted based on 2001-2007 data.
An adjusted prediction for 2001-2020 based on the average rate of new taxa from 2001-2012 is actually pretty staggering (Figure 2). 62 new species and 51 new genera in a 20-year period? Can this be right, or are we about to reach a major drop off – were the last two years just out of the ordinary? Time will tell, but there are no signs yet of the bombardment slowing down, and if my previous prediction is anything to go by, the figure could even be an under-estimate.
Figure 2. Adjusted plot, with the 2001-2020 prediction based on 2001-2012 data.
So, how many plesiosaurs have been actually been named since 2008? Here’s a summary of all the new additions so the group:
Nichollssaura, Gallardosaurus (2009)
Meyerasaurus, Alexeyisaurus (2010)
Abyssosaurus, Westphaliosaurus, Hauffiosaurus tomistomimus, Marmornectes, Zarafasaura (2011).
Albertonectes, Anningasaura, Avalonnectes, Cryonectes, Lusonectes, Djupedalia, Dolichorhynchops tropicensis, Eoplesiosaurus, Pliosaurus funkei, Spitrasaurus wensaasi, Spitrasaurus larsoni, and Stratesaurus (2012). So far.
Presuming I haven’t missed any (and please let me know if I have), that’s 22 new binomial taxa in the space of five years: 18 new genera and 21 new species (I’ve only listed the new species names above where they belong to existing genera, or where two new species have been erected within a new genus). I think this significant increase is due to several factors.
Firstly, historic plesiosaur specimens are receiving a considerable amount of renewed research attention. Many of the new taxa are based on fossils excavated in Victorian times. Anningasaura, Avalonectes, Eoplesiosaurus, Lusonectes, Strateosaurus, all fall into this category. Plesiosaurus continues to be exposed as the waste basket taxon it is.
Secondly, there have been numerous new discoveries in recent years. Sometimes these are the result of chance. Sometimes they are the result of a positive relationships that have developed between collectors or mining/quarrying businesses and palaeontologists. But often they are due to dedicated efforts to explore new strata or geographical areas. Djupedalia, Pliosaurus funkei (‘Predator X’ and ‘The Monster’), Spitrasaurus, and Zarafasaura, come to mind here.
Finally, more palaeontologists are looking at plesiosaurs in general. With fresh eyes. We are seeing differences where we weren’t even looking before, we are examining specimens more closely and more critically, we are applying new techniques and technologies to gain a greater understanding of plesiosaur anatomy, biology and phylogeny. It is inevitable that as more of us look, and as we look in more detail, we begin to unravel the complexity and diversity within Plesiosauria. Similar things are also happening in ichthyosaur research and mosasaur research, and I fully expect this ‘Mesozoic Marine Reptile Renaissance’ to continue into the foreseeable future. I’m looking forward to what the future holds in the world of plesiosaurs, even if I am struggling to keep up. One of these days I might even get around to writing about some of these new taxa and adding them to The Plesiosaur Directory…
Smith, A. S. 2007. Anatomy and systematics of the Rhomaleosauridae (Sauropterygia: Plesiosauria). PhD thesis. University College Dublin, 278pp. (Unpublished) (download PDF – 12.5mb )
Mine’s bigger than yours! The Monster of Aramberri, Predator X, and other monster pliosaurs in the media
During the past decade several dramatically named giant pliosaurs have hit the mainstream media, many claiming to be the biggest yet discovered. But only a trickle of peer-reviewed literature has been published to accompany these news stories. The lack of published data makes it really difficult to sift the facts from the fiction, and it’s easy to get the different stories muddled up, especially in the case of two identically sized congeneric pliosaur specimens from Svalbard: ‘The Monster’ and ‘Predator X’. So in an attempt to iron out the details and assess what we really know about all these specimens, here’s a short summary of the main players.
The Monster of Aramberri
Hit the mainstream media: 2002.
Estimated length in media: 18 m.
Conservative estimated length 15 m.
Material: Partial vertebral column, proximal end of a femur, part of the pelvic girdle, and cranial fragments. The fragment of rostrum collected in 1985 is now lost.
Where: Aramberri, Mexico.
Excavation: The original excavation in 1985 yielded a partial rostrum and vertebral column. The excavation site was reidentified in 2001 and additional material was collected during 2001 and 2002.
Peer-reviewed scientific references: Buchy et al. (2003).
Notes: The material was collected over a period of several years, but the discovery only hit the mainstream media in 2002 when more substantial pieces of the skeleton were discovered. An excellent account of the ‘Monster of Aramberri’ is given here by Richard Forrest. Buchy et al. (2003) described UANL-FCT-R2, the partial vertebral column discovered in 1985 [pictured below], but the majority of the skeleton has not been described and is in the process of being prepared. I’ve confirmed with Marie-Celine that the vertebrae described in 2003 are part of the ‘Monster of Aramberri’, but it is worth noting that the 2003 paper doesn’t explicitly mention ‘The Monster of Aramberri’ by name. Originally referred to Liopleurodon, it isn’t considered so any more (Buchy & Frey, 2003).
Hit the mainstream media: October 2006
Estimated length in media: 15 metres
Conservative estimated length: 13-15 m
Material: anterior part of rostrum, two cervical and numerous dorsal vertebrae, a nearly complete coracoid and right forelimb, and several dorsal ribs and gastralia.
Where: Svalbard, Norway.
Excavation: Discovered in 2006 and excavated in 2007.
Peer-reviewed scientific literature: none.
Notes: ‘The Monster’, not to be confused with ‘The Monster of Aramberri’, was the first pliosaur from Svalbard to be excavated and the first to make the news. A second giant pliosaur (‘Predator X’, see below) was discovered at the same time, but was excavated the following season. Richard Forrest’s 2008 article on the plesiosaurs from svalbard provides a thorough discussion, including comments on ‘The Monster’, but it was written before the second pliosaur hit the mainstream media.
Hit the mainstream media: March 2009
Estimated length in media: 15 m
Conservative estimated length: 13-15 m
Material: Partial skeleton including posterior skull region and anterior cervical vertebrae.
Where: Svalbard, Norway.
Excavation: Discovered in 2006 and excavated in 2008.
Peer-reviewed scientific literature: none.
Notes. The fossil material attributed to this pliosaur was first mentioned in stories covering “The Monster” in 2008, but the name ‘Predator X’ was coined after the specimen was excavated and it hit the media in 2009. According to an SVP poster by Knutsen et al. (2009) both ‘The Monster’ and ‘Predator X’ belong to the same taxon – they are congeneric and they are closest in their anatomy to Pliosaurus. They are both estimated to be the same size, and they are also both from the same geological formation, so with all these similarities it’s easy to confuse the two. ‘Predator X’ inspired the cover story for the 31 October 2009 issue of New Scientist, and was the main subject of a recent History Channel documentary of the same name, which also featured another giant pliosaur – the Weymouth Bay pliosaur. ‘Predator X’ will also appear in the BBC’s upcoming series Planet Dinosaur. Despite its widespread presence in the news and on TV, I was unable to find a suiatable photograph of the actual material.
The Weymouth Bay pliosaur
Hit the mainstream media: October 2009
Estimated length in the media: 16 m
Conservative estimated length: 12 m.
Material: skull and mandible (missing the tip of the manibular symphysis).
Where: Weymouth Bay, Dorset, UK.
Excavation: Discovered in pieces over a period of time – specific details unclear. The specimen was purchased by Dorset County Museum in Dorchester.
Peer-reviewed scientific literature: none.
Notes: There is an excellent account of the Weymouth Bay pliosaur here by Richard Forrest. The skull as preserved is 2.1m long.
So there we have it, four mega-pliosaurs making big news in the space of a decade. All of them have conservative and realistic length estimates around the 15m mark, with the Weymouth Bay pliosaur possibly slightly smaller and ‘The Monster of Aramberri’ possibly slightly larger. But all the estimates are way too wooly to take seriously just yet. So all these monsters will remain jostling for top spot until the scientific papers are published, and until we have a better understanding of pliosaurid proportions.
There are or course plenty of other giant pliosaurs, which frequently pop up in discussions too, including additional real contenders for ‘biggest pliosaur ever!’. While I do plan to write more on giant pliosaurs in the future, I’ve stuck to the ones in the mainstream media for now. You might have noticed that Liopleurodon was conspicuously omitted from this post. Well, although it is entirely relevant to the present topic, it hasn’t been in the news recently so I decided to leave the magical Liopleurodon alone this time around. It will be nice to write about a pliosaur with an actual scientific name for a change, even if that’s opening a can of worms in itself!
Buchy, M.-C. & Frey, E. 2003. Was it really eating granite? We’re searching hard: history of the Monster
of Aramberri (and stories about it). First meeting of the EAVP – abstracts, 39.
Buchy M.-C., Frey E., Stinnesbeck, W. ; López-Oliva J.G. 2003. First occurrence of a gigantic pliosaurid plesiosaur in the Late Jurassic (Kimmeridgian) of Mexico. Bulletin de Societe géologique de France, 174, 271-278.
Knutsen, E., Druckenmiller, P., Hurum, J., Nakrem, H. 2009. Preliminary account of new Late Jurassic pliosaurid material from Svalbard, Norway. Journal of Vertebrate Paleontology, 128A.
Noè, L. F., Smith, D. T. J. & Walton, D. I. 2004. A new species of Kimmeridgian pliosaur (Reptilia; Sauropterygia) and its bearing on the nomenclature of Liopleurodon macromerus. Proceedings of the Geologists’ Association 115, 13-24.
I’m pleased to present a guest article by journalism student Marc Vincent. The subject is the naming of Meyerasaurus, a topic that links in quite nicely with a previous post. Marc produced the article for his university course. The quotes from myself are the result of an interview Marc conducted as part of the project. I reproduce his article here as a slightly condensed version, enjoy!
“In a German museum sits a remarkable fossil with an equally remarkable history. The exquisitely preserved remains on display in the Staatliches Museum für Naturkunde in Stuttgart belong to a plesiosaur – more specifically it is one of the short-necked pliosaurs, a clade (Pliosauroidea) that included the famous forms Kronosaurus and Liopleurodon. Mounted on the wall, its intricate underside exposed for all to see, sits Meyerasaurus victor – 3.35 metres long and dating from the Toarcian age of the Early Jurassic (180-175 million years ago).
Until this year however the animal wasn’t known as Meyerasaurus at all. For decades previously it was known as ‘Rhomaleosaurus’ victor, having thought to have been in the same genus as other, British pliosaur species since the 1960s. Before that it had been known as ‘Thaumatosaurus’ victor for fifty years. The generic name ‘Thaumatosaurus’ was coined by the German palaeontologist Herman von Meyer, but was based on inadequate material.
The British palaeontologist Richard Lyddeker later referred the Stuttgart pliosaur to the genus, which he considered to be the senior synonym of Rhomaleosaurus. However, it is rather likely that he simply rejected the name Rhomaleosaurus without consideration as it had been devised by Harry Seeley, a rival of his.
The referring of the Stuttgart pliosaur to ‘Thaumatosaurus‘ was innocently cemented by the German palaeontologist Eberhard Fraas when he described the specimen in 1910, following Lydekker’s work. The name ‘Thaumatosaurus‘ is today considered a nomen dubum but is still associated with the Stuttgart specimen in the minds of many palaeontologists – thanks to Fraas’ influence.
Unfortunately such a chequered history is common in the nomenclature of fossil animals. In the 19th and early 20th centuries, experts’ thoughts on what constituted a genus, or an order, were very different, so much so that almost every plesiosaur found was casually assigned to the genus Plesiosaurus (in the same way that countless predatory dinosaurs were assigned to Megalosaurus). Today, palaeontologists are slowly fixing the taxonomic muddle left behind by their forebears.
Dr Adam Smith, now Natural Science Curator at Birmingham’s Thinktank science museum, worked alongside Dr Peggy Vincent on a paper (four years in the making) that formally assigned the former ‘Rhomaleosaurus’ victor to the new genus Meyerasaurus.
Meyerasaurus is named after Herman von Meyer, who originally described the specimen. However, there is also an extinct lizard named Meyasaurus, and a dinosaur named Maiasaura, and they all sound remarkably similar when read aloud. Adam wanted to reinstate ‘Thaumatosaurus‘ with ‘Thaumatosaurus’ victor as the new type species, but he was barred by ICZN (International Commission on Zoological Nomenclature) rules.
“The specimen has always historically been associated with the name ‘Thaumatosaurus’ and I’d have liked to reintroduce that name to avoid as much confusion as possible. If you say ‘Thaumatosaurus‘ to most palaeontologists they won’t think of the type specimen, they’ll think of the ‘Rhomaleosaurus’ victor,” he says.
“When it was clear that we weren’t allowed to keep ‘Thaumatosaurus‘ due to ICZN rules, I wanted to introduce the name ‘Thaumatosaura‘ and feminise it, so at least we’d have the same name more or less. But also the species name is masculine, so the binomial name ‘Thaumatosaura‘ victor would have been confusing.”
In 2008 the journal Naturwissenschaften published a paper authored by Adam and Dr Gareth Dyke that included a fresh cladistic analysis of Rhomaleosaurus and related genera in the Rhomaleosauridae. They found that the genus Maresaurus separated the true Rhomaleosaurus species, including Rhomaleosaurus cramptoni, and what was then called ‘Rhomaleosaurus’ victor.
This was a problem as it made the genus Rhomaleosaurus paraphyletic, that is it united animals that didn’t belong together in a single genus, as they were too different. In addition to ‘Rhomaleosaurus’ victor, ‘Rhomaleosaurus’ megacephalus was also found to not be a true Rhomaleosaurus species. Clearly these animals required new generic names, and it was this that inspired the latest paper and the naming of Meyerasaurus victor.
What exactly Smith and Vincent determine to be the diagnostic characteristics of Meyerasaurus are laid out in full in the paper. They include the proportions of the limbs relative to the head and body – a graph in the paper dramatically illustrates the considerable difference in the relative lengths of the humerus and skull in Meyerasaurus and true Rhomaleosaurus – and also characters of the skull and palate.
Put simply, “[Meyerasaurus] has much larger limbs and a smaller skull relative to the body.” In addition, there are important details of the skull and palate bones (often used for diagnostic purposes in pliosaurs due to their frequently very incomplete remains) that, to Adam, indicate that Meyerasaurus deserves separation from Rhomaleosaurus.
With the reassigning of ‘Rhomaleosaurus’ victor to Meyerasaurus, there is no longer any overlap in plesiosaur genera in Early Jurassic Germany and Britain. This raises the question – why not? It is accepted that the region was united during the epoch, as it was almost completely underwater. It may have been a yet unknown geographical feature that kept these fauna separate – or they may have simply been separated in time.
Although the paper notes that more research is needed, Adam’s thoughts on the matter are quite clear. “We know that the deposits in Germany aren’t exactly the same age as the deposits in the UK, and so it seems that that’s the most likely explanation for the generic separation.”
Of course, he’ll also admit that taxonomy is a human invention and, by and large, distinctions at anything above specific level can be pretty arbitrary. “The only definitive level in taxonomy is the species level. There are some people that say even a species doesn’t exist and the only objective entity in biology is the individual, the actual physical individual – that everything else is just a hypothesis.”
“In some ways it doesn’t matter. All that matters is that it’s internally consistent and goes by the ICZN rules. As long as you know what you mean when you say the name Meyerasaurus that’s the important thing.”