Archive for the ‘palaeobiology’ Category
An exciting new paper published this week in the journal Science (Vol. 333, p.870-873) provides the first direct evidence for live birth in plesiosaurs, and may have implications for plesiosaur behaviour (O’Keefe & Chiappe, 2011).
Whether plesiosaurs laid eggs or gave birth to live young has been a topic of speculation for nearly 200 years. They have sometimes been portrayed crawling out of the water to lay eggs in the manner of sea turtles, and while palaeontologists have long suspected that plesiosaur anatomy is incompatible with movement on land, empirical evidence either way has been lacking.
The new evidence comes in the form of a fossil plesiosaur skeleton with a fetus preserved in the body cavity. Both individuals have diagnostic characteristics indicating they are the same species, the small individual displays embryonic features and is in the correct position to be a fetus, and there are no signs of it being eaten (bite marks or acid wear). These numerous lines of evidence confirm that this fossil represents a mother and her unborn fetus. This demonstrates that plesiosaurs did not lay eggs and were therefore able to lose their ties with land and spend their entire lives in the ocean.
The newly described fossil plesiosaur is a polycotylid (Polycotylus), one of the last types of plesiosaurs to evolve. It was discovered in Late Cretaceous rocks in Kansas, USA. Polycotylids were highly derived plesiosaurs with torpedo-shaped body outlines and wing-like flippers, a relatively short neck (as far as plesiosaurs go) and a very short tail. They were almost penguin-like in general appearance and also similar to penguins, they would have been fast and agile swimmers.
An unusual aspect of this fossil is the size of the fetus. Most viviparous reptiles give birth to a brood of several small individuals. In contrast, this new fossil shows that at least some plesiosaurs gave birth to a single very large individual, much like whales do today. Many other marine reptiles including ichthyosaurs and mosasaurs gave birth to live young, but this study suggests that plesiosaurs differed in that they invested energy and time into a single individual. This sort of reproductive strategy is often associated with gregarious behaviour and parental care, so the authors of the paper suggest that maybe plesiosaurs were excellent parents too. This hypothesis is fascinating although it would be quite unusual for reptiles.
Fossils of basal sauropterygians (pachypleurosaurs and nothosaurs), close relatives of plesiosaurs, also show that they gave birth to broods of several small live babies, so it is unclear when the evolutionary shift in reproductive strategy occurred in the sauropterygian lineage. It is certainly possible that the first plesiosaurs were more like their ancestors in terms of reproductive behavior. More fossils will ultimately be required to fill in the bigger picture, but for now, it is wonderful to be able to say with certainly that plesiosaurs gave birth to live young.
O’Keefe, F. R. & Chiappe, L.M. 2011. Viviparity and K-selected life history in a Mesozoic marine reptile. Science, 333, 870-873.
Monstertalk is a new sceptical podcast focussing on all things cryptozoological. The most recent episode (episode 004) delves into the idea that plesiosaurs may still be alive today, lurking in lochs and lakes around the world – the so called Plesiosaur Hypothesis. I was interviewed as a guest on this episode and took part in a long discussion about plesiosaur palaeobiology. I’ll admit that I was hesitant to be interviewed at first because I don’t want to get too bogged down or involved in the living plesiosaurs ‘debate’.
The word debate goes into inverted commas because very few cryptozoologists really take the plesiosaur hypothesis seriously, any discussion on the topic is less of a debate and more of a debunk. The plesiosaur hypothesis is really only pushed by 1. the occasional fundamentalist creationist under the (false) impression that a living plesiosaur would somehow discredit evolution (which it obviously wouldn’t), and 2. the media. The media’s fascination with Nessie is especially irksome, no plesiosaur-based science news story in the popular press is self explanatory or interesting enough, it seems, without the inevitable comparison with a fabled creature that doesn’t look like a plesiosaur anyway. This perpetuates the public’s only frame of reference for plesiosaurs as Nessie and does nothing for palaeontology and even less for science education.
It was partly with this in mind that I decided to accept the invitation to be interviewed on Monstertalk, but moreover it was an excellent opportunity to talk about plesiosaur palaeontology and the real mysteries surrounding these fascinating creatures. Far more interesting than those mythical lake monsters I think, and I hope that’s how the podcast came across. I enjoyed the experience although I still haven’t had the courage to listen to myself twittering on. This episode is available to download as a free MP3 here: http://traffic.libsyn.com/skeptic/004_Monstertalk.mp3 and the show notes are here: http://www.skeptic.com/podcasts/monstertalk/09/08/24/. I highly recommend listening to the other episodes too. Enjoy!
So far, 2008 has seen a healthy number of new papers on plesiosaurs and a few new taxa too. Way back in February, Druckenmiller and Russell (2008a) introduced Nichollsia borealis, a plesiosaur of uncertain affinity, based on a beautifully preserved specimen from Alberta, Canada. More recently, Druckenmiller and Russell (2008b) published a large scale cladistic analysis of plesiosauria to try and make sense of plesiosaur relationships, especially the affinities of Leptocleidus and Nichollsia – this is a substantial piece of work. Both papers stem directly from Druckenmiller’s PhD thesis.
Sato and Wu (2008) erected a new taxon Borealonectes russelli, a pliosaur they identify as a rhomaleosaurid, based on a skull and partial postcranium from the Canadian Arctic Archipelago. rhomaleosaurids also recieved treatment from Smith and Dyke (2008) who described the skull of Rhomaleosaurus cramptoni - the holotype of the family. They also present a full body reconstruction of the 7m long genus, and a cladistic analysis dedicated to pliosaurs.
Rhomaleosaurus skeleton – Figure 2 from Smith and Dyke (2008)
Long necks received attention from Zammit et al. (2008) who investigated the flexibility of an elasmosaurid cervical column, confirming the common presumption that swan-like postures were impossible in beasts such as Elasmosaurus. Bardet et al. (2008) described a partial plesiosaur skeleton from Asturias, helping to elucidate plesiosaur diversity in the Pliensbachian and presenting a rare specimen from Spain.
Finally (for now, I may have overlooked one or two papers), Smith (2008) presented an overview of plesiosaurs aimed at a popular audience. It covers basic aspects of the anatomy and biology of plesiosaurs. I hope this article will fill the void present between technical papers and children’s books and help people ‘get into’ the scientific literature, which can be quite daunting otherwise.
Plesiosaur anatomy – Figure 1 from Smith (2008)
Bardet, N., M.., Fernández, J. C. García-Ramos, Z. P. Suberbiola, L. Piñuela, J. I. Ruiz-Omeñaca, and P. Vincent. 2008. A juvenile plesiosaur from the Pliensbachian (Lower Jurassic) of Asturias, Spain. Journal of Vertebrate Paleontology, 28, 258-263.
Druckenmiller, P. S. and Russel, A. P. 2008a. Skeletal anatomy of an exceptionally complete specimen of a new genus of plesiosaur from the Early Cretaceous (Early Albian) of Northeastern Alberta, Canada. Palaeontolgraphica, 283, 1-33.
Druckenmiller, P. S. and Russel, A. P. 2008b. A phylogeny of Plesiosauria (Sauropterygia) and its bearing on the systematic status of Leptocleidus Andrews, 1922. Zootaxa, 1863, 120pp.
Sato, T. and Wu, X-C. 2008. A new Jurassic pliosaur from Melville Island, Canadian Arctic Archipelago. Canadian Journal of Earth Science, 45, 303-320.
Smith, A. S. 2008. Fossils explained 54: plesiosaurs. Geology Today. 24, (2), 71-75.
Smith, A.S. and Dyke, G.J. 2008. The skull of the giant predatory pliosaur Rhomaleosaurus cramptoni: implications for plesiosaur phylogenetics. Naturwissenschaften, 95, 975-980.
Zammit, M.; Daniels, C. B. and Kear, B. P. 2008. Elasmosaur (Reptilia: Sauropterygia) neck flexibility: Implications for feeding strategies. Comparative Biochemistry and Physiology, Part A 150, 124–130
The long neck of the plesiosaur is a mysterious adaptation for which many hypotheses have been proposed. The most recent suggestion comes from Dr Lesley Noe of the University of Cambridge . After examination of the neck vertebrae of the long-necked plesiosaur Muraenosaurus, whose name translates as ‘Moray eel lizard’, Dr Noe concluded that the natural position of the neck was a downwards curve towards the sea-bed. The ability of the neck to flex in other dirctions was limited and the swan-like pose often seen in restorations of plesiosaurs (pictured) was impossible. Also impossible was the ability to raise the neck out of the water in an arc. The research was originally presented in 2004 at the 52nd Symposium of Vertebrate Palaeontology and Comparative Anatomy, Leicester, England (see abstract), but was more recently presented This October (2006) at the 66th Annual meeting of the Society of Vertebrate Paleontology, in Ottawa, Canada (abstract can be downloaded here). Incidentally, the findings have implications for the famous cryptid sometimes regarded as a plesiosaur, the Loch Ness Monster – the inability to raise the neck out of the water contrasts with reports of Nessie, and so constitutes evidence against a plesiosaur identity for any monster living in the loch.
The plesiosaur neck may have been used for sifting through the sea bed for soft animals such as worms and soft small crustaceans. The idea is backed up by other recent findings – namely the discovery of fossil stomach contents in a plesiosaur containing sea-shells as reported here last year (see news entry). Although the idea is appealing, Dr Noe states (personal communication) that this is probably only part of the story concerning the function of the long neck in plesiosaurs.
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