Archive for the ‘Anatomy’ Category
So, time for more Planet Dinosaur plesiosaurs… In part 1 of we familiarised ourselves with the taxonomy and appearance of the plesiosaurian stars of the fourth episode of the BBC’s Planet Dinosaur, ‘Fight for Life’. Now we’re all set up to pick apart, with ruthless abandon, the animators’ painstaking efforts to bring these animals to life.
Plesiosaur swimming is an active area of research and frankly we don’t know exactly how they swam. There are some fundamental uncertainties in our understanding of plesiosaur locomotion, in particular, how did the four limbs move relative to each other? Sure, we might also be off in our estimations of dinosaur gaits too, but at least we have the footprint evidence to understand the basics. For example, theropod dinosaurs like Allosaurus, which also appeared in this episode, put one foot in front of the other. Yet the animators still didn’t quite manage to capture this satisfactorily as to my eye the walk cycles in the Planet Dinosaur dinos are pretty wooden. So, with this in mind, what chance did the plesiosaurs have?
Well, I’m probably overstating the point. It is true that we don’t know exactly how plesisoaurs swam, but we do have a good understanding of the limb strokes in general, and we know how they didn’t swim. So let’s start there. Derived aquatic animals generally swim either by undulating their body (e.g. crocs, dolphins etc.) or by keeping their body sturdy and using their limbs (e.g. turtles, penguins). Plesiosaurs are in the latter category and their skeleton is constructed accordingly to resist flexibility. They have tightly articulating dorsal vertebrae, robust ribs, and a strong rigid ventral skeleton consisting of flat plate-like girdles, bridged by a strong mesh of gastralia (belly ribs).
To my distress, some early movement cycles of the Kimmerosaurus included not only a limb-based phase, but also a wriggling phase with long lateral undulations of the whole body, with the flippers pulled in flush to the flanks. In this regard, the Planet Dinosaur plesiosaurs originally wanted to have their cake and eat it. Thankfully these side-to-side wiggling phases, and also an up-down wiggling phase, didn’t appear in the final show. However, there is still a little too much dorso-ventral flexibility in the plesiosaur bodies on occasion. The Kimmerosaurus sometimes appear rather too bendy, and in one scene the pliosaur pretty much breaks its own spine, but I was pleased to see these deviations kept to a minimum.
It is generally agreed that the plesiosaur flipper stoke was essentially a modified form of underwater flying with a major up-down component and minor back-forth component. They were not used to row and it is unlikely that the flippers could be pulled back to be flush with the flanks of the body, even though they do this every now and again in the show. The limb-stroke of the forelimbs also looks a bit off at times in Planet Dinosaur. It is my understanding that the digital models are rigged with approximate points of flexibility – they don’t have anatomically correct skeletal anatomy inside – so it is only to be expected that the points of joints and range of motion may not always be spot on. It’s also worth bearing in mind than animators are not biologists, yet they’re ultimately responsible for the construction of biological critters.
When I saw the trailer for Planet Dinosaur I noticed the flippers in the pliosaur being pulled back almost flush with the body and feared for the worst. This happens in the scene when the pliosaur comes to blows with the Kimmerosaurus. But this was a one off and for the most part the pliosaur is cruising around with healthy deep limb strokes. Plesiosaurs may have changed their gait depending on the the velocity and maneuverability they wished to achieve, so it is also reasonable to suppose that all four limbs sometimes moved in unison for a burst of speed, as also depicted in the show. Overall, I thought the Kimmerosaurus‘ elegant prancing and dancing, twisting and turning, was wondrous. It would be unfair, and perhaps premature given our current state of understanding, to pick on it too much.
I had some problems with the interactions between the animals and their underwater environment, the water resistance wasn’t always convincing. At times the plesiosaurs seemed to move via some sort of invisible jet propulsion. Either that, or the momentum being generated from the limb stokes was overestimated. This might be put down to limitations in the technology, and I suppose there is a certain amount of intuition required for perfecting these details. similar explanation could also be invoked to explain why some of the dinosaur walk cycles in the series don’t always cut it when it comes to mass and momentum.
A quick note on that characteristic feature of the plesiosaur, the long neck, which was correctly restored as a relatively inflexible structure. Not a swan-like pose in sight, and no graceful necks arching out of the water. Other recent documentaries (e.g. Sea Rex 3D) just couldn’t resist including such outdated but iconic imagery, presumably against better advice. The evidence for plesiosaur feeding habits from the gutter-like trace fossils, or Lebensspuren (for that it their proper name), was discussed by Darren Naish on the old version of his Tetrapod Zoology site. These structures might have been produced by plesiosaurs, they might not, but it is a reasonable suggestion that fits with other evidence from stomach contents (McHenry et al., 2005).
On several occasions in the program the plesiosaurs break the surface, where, dowsed in harsh sunlight, I’d be hard pushed to tell whether the splashes are CGI or real (if I didn’t already know). These scenes were really excellently excecuted. The pliosaur comes up for air at one point and snorts out a powerful jet of water spray from its external nostrils. It isn’t certain that plesiosaurs breathed through their tiny external nostrils, especially if they employed the method of underwater olfaction explained in the show (these plesiosaurs want to have their cake and eat it again!), but, well, why not, it looked nice didn’t it!
The scientific exposition sections included some dodgy versions of my Rhomaleosaurus reconstruction as a stand in for Predator X, which was therefore anatomically incorrect for a pliosaurid. I believe that the Kimmerosaurus illustration was also based on my Rhomaleosaurus reconstruction. The tooth mark evidence in the skull of a plesiosaur comes from an elasmosaurid specimen formerly referred to the nomen dubium ‘Woolungasaurus‘, and now known as Eromangasaurus australis (following some confusion resulting from two researchers accidentally stepping on each others toes a little and publishing reviews of the material almost simultaneously – the specimen had a short stint as Tuarangisaurus australis and Eromangasaurus carinognathus) (Kear, 2007). Anyway, it certainly isn’t Plesiosaurus as the reconstruction was mysteriously labelled in the show. The interpretation of the bite marks is pretty speculative as who knows for sure the position of the the animal in the water column? But pliosaurs sometimes ate long-necked plesiosaurs, that is certain.
As scientists, palaeontologists have the luxury of not having to commit to any single hypothesis. We can say without shame that we don’t know, at least not with certainty, how plesiosaurs hunted, how they breathed, how they swam. We can interpret evidence tentatively and you’ll have noticed the frequent use of non-commital language in this review such as ‘probably’ and ‘unlikely’. But this doesn’t help artists, script writers or animators who, charged with the task of restoring these long-dead beasties, are forced to plump for one option of the other (under the format used by Planet Dinosaur at least). With all the pitfalls presented to them along the way, I think the Planet Dinosaur team did a sterling job bringing Predator X and Kimmerosaurus back to life. And no, I’m not being apologetic, or sympathetic, just because I was involved. I’m really enjoying this series and look forward to the other episodes.
Kear, B. 2007. Taxonomic clarification of the Australian elasmosaurid genus Eromangasaurus, with reference to other austral elasmosaur taxa. Journal of Vertebrate Palaeontology, 27, 241-246.
McHenry, C., Cook, A., and Wroe, S. 2005. Bottom feeding plesiosaurs. Science, 310, 75.
Astute viewers of BBC’s plesiosaur-fest on Planet Dinosaur this week may have spotted my name dash across the screen at the end credits. ‘Fight for Life’, the fourth in the series, was the first episode, and so far as I’m aware only episode, to plunge us into the Mesozoic oceans and introduce us to some marine life. I’ll obviously skip the dinosaurs and concentrate just on the plesiosaurs.
Having seen the earliest designs of the marine reptiles for this episode, and later the first test animations, the show might have been heading for a disaster. You can thank me now, if you wish, for helping to purge swan-necks from the show and for banishing bodily undulations from the plesiosaurs’ locomotory repertoire. Looking back at the huge gulf in accuracy between the early designs I saw and the finished renderings helps me to put them into perspective, and so I look upon the anatomical issues that remain with some relief in the knowledge that they could have been so much worse. But I would certainly tweak aspects of the anatomy and movement if I had the chance. Of course, budget and deadlines all played a factor and limited the amount of back and forth possible in the design process. And it also doesn’t help that so little is actually known about the stars of the show, both Kimmerosaurus and Predator X. The designers depend on existing reconstructions and restorations for visual guidance and this is often lacking.
The cryptoclidid plesiosaur Kimmerosaurus is closely related to Cryptoclidus. It was named in 1981 on the basis of an isolated skull (Brown, 1981). Some referred material, including some anterior cervical vertebrae, was later identified and subsequent comparison of these vertebrae with those of Colymbosaurus, a genus known inconveniently from everything but a head, led Brown et al. (1986) to suggest both genera belonged to the same taxon. Whether congeneric or not, the similarities in the overlapping anatomy are close enough that skeletal data from Colymbosaurus was used as a basis for filling in the gaps in our knowledge of the postcranium of Kimmerosaurus in Planet Dinosaur. Another problem though, is that Colymbosaurus is a bit of a prickly taxon itself, but I won’t confuse matters any further. Taxonomy aside, we know that at least one moderately large (up to around 6m) long-necked plesiosaur skulked around in the Late Jurassic. Plesiosaurs from the Tithonian of Svalbard have been tentatively referred to Kimmerosaurus.
Predator X is a pliosaur with more media hype than it probably deserves, and a ridiculous name betraying how little we actually know about it. A foray into the twitterverse provided some insightful public reactions to the name that follwed the program, some of which I’ll share here:
Right. There’s a dinosaur called ‘Predator X’ that’s a rubbish name. It should be called a Furiousaurus. I’ll write a letter. To someone.
I would enjoy Predator X more, but I haven’t seen Predators IV-IX yet.
Naming a dinosaur ‘Predator X’ makes it sound like the anonymous defendant in a sexual assault trial.
And @JohnLoony was justified to ask the legitimate question:
“Planet Dinosaur” on BBC1 featured a big marine pliosaur called “Predator X”. Why doesn’t it have a proper Latin classification name?!??
Firstly, it’s not a dinosaur, this should really have been made clearer in the program. Secondly, there is a reason why it doesn’t have a proper scientific binomial name: it hasn’t been described yet. ‘Predator X’ is really just the name for the individual animal and isn’t intended to be a stand in name for the taxon, although I think that’s how it was received by many viewers. Such is the power of media hype. I’ve skimmed over the history of Pred X in a previous article where I’ve explained that preliminary research by Knutsen et al. (2009) allies Predator X with Pliosaurus. I can’t bring myself to constantly refer to this animal as Pred X every time, so I’ll tend to go with the term pliosaur from now on instead…
So, let’s review what we saw. Overall I was quite pleased with the appearance of the pliosaur, which was based on reconstructions of Pliosaurus. But there are problems. The dentition is way off and altogether rather too generic, with the diagnostic large caniniform teeth omitted completely. I was never consulted about the teeth of the pliosaur so I dodge all responsibility here, but I do know the animators had issues with the teeth of Kimmerosaurus too, its mouth wouldn’t shut unless they shrunk and tweaked the angle of the teeth a bit. In the case of both Kimmerosaurus and the pliosaur, the modelers had wrongly endowed them with a slight overbite, so the tooth rows don’t quite line up as they would have in life – no wonder they couldn’t get the teeth to interlock. The teeth were added at a later stage in the design procedure, after the overall body shape had been finalised, so it was too late to go back. As a workaround, they angled the teeth in the mandible more horizontally and shrunk them a bit. Dodgy stuff. The puffy eyelids in the pliosaur seemed a bit unnecessary and I’d have preferred more musculature at the rear of the jawline, but overall the head is pretty good in my opinion.
I thought the head of Kimmerosaurus, with its nice long tooth rows of many tiny teeth, was rather good too. I spotted the far too deeply concave temporal fenestrae quite early on in the design process and despite my concerns (they were supposed to be filled out later on) they still managed to find their way into the finished renderings. The dinosaurs in the series have also suffered the same fate. At least the eyes weren’t placed in the temporal fenestrae in Kimmerosaurus as has occurred in other plesiosaur restorations.
The bodies of both animals are also generally good, with satisfyingly streamlined outlines and beefy musculature around the base of the limbs, fitting for animals that propel themselves through the water by flipper power. The slightly flattened tip of the tail in the pliosaur was a compromise between a fully developed tail fin, a feature I and others suspect many plesiosaurs had, and no tail fin at all. I liked it. I liked the grizzled appearance of the pliosaur’s skin, but while I was pleased to see the end of the obligatory black and white pattern so often attributed to large pliosaurs (post WWD Liopleurodon), I was a bit disappointed that every single plesiosaur was basically grey. I’d have loved a few greens, or at least some differentiation between the predator and prey. Also, despite my suggestion, no parasites or patholoies to be seen on any of the beasties, which I thought was a lost opportunity.
Well, I think I’ve gone on far enough for now so I’ll leave discussion of the behaviour, animation and range of motion for part 2. Suffice to say there are issues. Comparisons with the WWD episode ‘Cruel Sea’ are also justified and I may head into such territory on a later occasion too.
Brown, 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 (Natural History): Geology, 35, 253-347.
Brown, D. S., Milner, A. C., and Taylor, M. A. 1986. New material of the plesiosaur Kimmerosaurus langhami Brown from the Kimmeridge Clay of Dorset. Bulletin of the British Museum (Natural History), Geology, 40, 225-234.
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.
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 second paper in the two-part report on by Albright et al. on plesiosaurs from the Upper Cretaceous Tropic Shale of southern Utah (Journal of Vertebrate Palaeontology, Volume 27(1) p. 41-58), introduces two new genera and species of polycotylid plesiosaur and contributes to the systematics of polycotylid plesiosaurs. The first new genus and species, Palmula quadratus possesses a unique combination of characters amongst polycotylid plesiosaurs – distinctly polygonal epipodials combined with small overall adult size. Palmula is also the only named representative of a new subfamily proposed by Albright et al, the Palmulainae, a clade diagnosed by polygonal epipodials.
The other new plesiosaur, Eopolycotylus rankini, is an almost complete specimen named after David O. Rankin who discovered the fossil in 2001. “I’ve been fossil hunting since I was 9 years old” explains Rankin, who made his first large pliosaur find at the age of 14. So what is it like to have a plesiosaur named after you? “I’m very excited about it” says Rankin, “Its like having your own little piece of history, and science.” Rankin also assisted the excavation team who excavated Eopolycotylus rankini in 2003. The team from the Museum of Northern Arizona in Flagstaff was headed by Dr David Gillette who is a coauthor of the paper.
E. rankini is a representative of a second new subfamily, the Polycotylinae, which also includes the majority of known polycotylids. As in all other polycotylines the epipodials of Eopolycotylus are broader than long, contrasting with the condition in Palmulines.
More photographs of the Eopolycotylus excavation are available on David Rankin’s website. A Palmula and Eopolycotylus ‘genus page’ will be added to the Plesiosaur Directory in the near future.
N.B. I have this article, and the other JVP plesiosaur articles discussed here, as PDFs which I would be happy to share.