Tetrapod Zoology

i-5d7a75b2163cb78d05b95bab36c2a053-Claire strikes the pose.jpg

What with yesterday’s Simolestes picture-of-the-day article I couldn’t resist but using – at last – this picture. It was taken by Mark Witton at the Oxford University Museum and depicts the immense pliosaur mandible OUM J.10454, a specimen that comes from the Kimmeridge Clay of Cumnor, Oxfordshire, and was acquired by the museum some time between 1880 and 1888. William J. Sollas (1849-1936) had intended to describe the specimen in the year that he died, but its proper debut in the literature didn’t occur until 1959. The lovely lady posing next to the specimen is Claire, Mark’s sister (at left, you can see the flippers of the Nessie model): for Mark’s original go here.

The Cumnor mandible was first assigned to the pliosaurid species Stretosaurus macromerus by L. B. Tarlo (1959), a taxon which Tarlo regarded as representing a distinct genus because he thought that it had a unique scapula morphology. However, the ‘unique scapula’ later turned out to be a not-so-unique ilium and L. B. Halstead – who is the exact same person as L. B. Tarlo you understand – then sunk Stretosaurus into Liopleurodon (Halstead 1989). No� et al. (2004) showed that the referral of mandibles like, and including, the Cumnor specimen to Liopleurodon is incorrect, and that all the material referred to the species macromerus should instead be regarded as part of Pliosaurus, a taxon which has a longer mandibular symphysis than Liopleurodon. The actual story is far more complex than this, and even after all this we still can’t be sure that the Cumnor specimen really belongs to P. macromerus as Tarlo/Halstead thought.

i-0b45375655987be7a47d3201d43c5291-Aramberri giant flipper recon.jpg

Anyway, the big deal about the specimen is how big it is: it’s 2.8 m long and, when complete, would almost certainly have exceeded 3 m. Tarlo (1959) wrote of this specimen that ‘without doubt it belongs to the largest pliosaur ever recorded, somewhat exceeding the size of the Cretaceous Kronosaurus‘ (p. 51): a consequence of this assertion is that P. macromerus has at times been stated to have been the largest marine reptile of all time (e.g., McWhirter & McWhirter, 1974) [it's since been outclassed in that regard by an ichthyosaur: the 21 27 23 m long Shonisaurus sikanniensis]. Near-complete pliosaur skeletons indicate that the skull was about 17% of total body length, suggesting that the whole animal might have approached 18 m. As Naish et al. (2001) said: ‘The caveat, however, is that this assumes that this skull-to-total-length ratio remains constant throughout growth, and it may well not do’. And, yes, it’s specimens like this that led to the totally speculative 25 m given for Liopleurodon in the BBC’s Walking With Dinosaurs. Dave Martill and I do have some new data on giant size in Jurassic pliosaurs, and I suppose one day we’ll get round to publishing it. To give you some idea how big some of the largest pliosaurs might have been, here’s another image I stole from Mark’s flickr site (from here): it shows a reconstruction of one of the paddles of a new giant pliosaurid from the Upper Jurassic of Mexico (see Buchy et al. 2003) as displayed at the Staatliches Museum f�r Naturkunde in Karlsruhe. Richard Hing acts as scalebar.

If you want to know more about the Kimmeridge Clay, there’s a ver 1 article on some of its fauna here.

Refs – -

Buchy, M-C., Frey, E., Stinnesbeck, W. & L�pez-Oliva, J. G. 2003. First occurrence of a gigantic pliosaurid plesiosaur in the late Jurassic (Kimmeridgian) of Mexico. Bulletin de Societe g�ologique de France 174, 271-278.

Halstead, L. B. 1989. Plesiosaur locomotion. Journal of the Geological Society, London 146, 37-40.

McWhirter, N. & McWhirter, R. 1974. Guiness Book of Records. Guiness Superlatives Ltd., London.

Naish, D., No�, L. F. & Martill, D. M. 2001. Giant pliosaurs and the mysterious ‘Megapleurodon’. Dino Press 4, 98-103.

No�, 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.

Tarlo, L. B. 1957. The scapula of Pliosaurus macromerus Phillips. Palaeontology 1, 193-199.

- . 1959. Stretosaurus gen. nov., a giant pliosaur from the Kimeridge Clay. Palaeontology 2, 39-55.

Comments

#1 Zach Miller
December 15, 2007

Pliosaurs: Reptilian toothed whales of the Mesozoic.
#2 David Marjanovi?
December 15, 2007

the 21 m long Shonisaurus sikaniensis

…the 23 m long Shonisaurus sikanniensis. No?
#3 Hai~Ren
December 15, 2007

Sad that like the ichthyosaurs, the pliosaurs didn’t last all the way to the end of the Mesozoic. I wonder if the mosasaurs had anything to do with that…
#4 djlactin
December 15, 2007

a bit off-topic, but… just wondering. did pliosaurs give live birth? (i iamgine they did, given the difficulties of hauling such a body onto land to lay eggs, but is there any fossil evidence?)
#5 Nathan Myers
December 15, 2007

Thanks to DDeden for having pointed me to the note suggesting that the very heavy bone density in kronosaur and related creatures’ flippers might actually be to counteract bouyancy. That the mass was concentrated there and not, e.g., in scapulae suggests to me their mass might also have made them more useful as weapons in mating competition. Is there any way to test that idea?
#6 David Marjanovi?
December 16, 2007

I wonder if the mosasaurs had anything to do with that…

If, then the other way around: the ichthyosaurs disappeared before the mosasaurs came.

That said, Platypterygius seems to have died out at the Cenomanian-Turonian boundary, which had a little mass extinction, and mosasaurs didn’t become similar to ichthyosaurs till shortly before the very end (Plotosaurus).
#7 chris y
December 16, 2007

Avoiding cheap shots about the jaw apparently having been articulated with a rectangular section axle, who the hell vandalised it like that?
#8 John Conway
December 16, 2007

Wow, that’s one big jawbone. It’s seems really slender in comparison to (what I remember of) Kronosaurus though – do you think that’s right?
#9 neil
December 16, 2007

Testing the mating combat hypothesis should be fairly easy enough, provided we could find a tank big enough to fit two adult males…

Pachypleurosaurs are supposed to have been viviparous, so I don’t see any decent reason why an 18 m pliosaur should have to drag her fat arse across the beach. It would be downright indecent.

“Little mass extinction” has such a nice ring to it, kinda like “tactical nuke.”
#10 Nathan Myers
December 17, 2007

Is there evidence of healed traumas along the edges of the flippers, particularly in larger specimens? If they were beating one another with their flippers, they must have got hurt sometime. Does any modern creature (orca?) have bones like that in its flippers?
#11 David Marjanovi?
December 17, 2007

“Little mass extinction” has such a nice ring to it, kinda like “tactical nuke.”

:-}

Well, the climate was unbelievably hot, and there was some, shall we say, turnover in the global fauna (no idea of the flora). It’s also underresearched, which may contribute to the “little” part, though of course it was less of an event than the Triassic-Jurassic boundary mass extinction, let alone the Cretaceous-Palaeogene one.
#12 Matt
May 22, 2009

The Giant Pliosaurs are some very spectacular animals. It is a shame that most of the material known is fragmentary. Is there a census yet, on which of the species is the largest? My guess would be the top contenders would be (Predator X, Kronsaurus, and Liopleurodon). Although at this point Predator X’s estimates of size may be a bit premature at this point, and Liopleurodon from what Colin has mentioned may be bit smaller than most measurements presented in the public literature are. Maybe it is hard to say at the moment which one truely is the largest.
#13 Matt
May 22, 2009

The Giant Pliosaurs are some very spectacular animals. It is a shame that most of the material known is fragmentary. Is there a census yet, on which of the species is the largest? My guess would be the top contenders would be (Predator X, Kronsaurus, and Liopleurodon). Although at this point Predator X’s estimates of size may be a bit premature at this point, and Liopleurdon from what Colin has mentioned may be bit smaller than most measurements presented in the public literature are. Maybe it is hard to say at the moment which one truely is the largest.
#14 Matt
May 22, 2009

Forget comment 13, something I did accidently posted the same comment twice due to an error my computer made. My apologies
#15 Dinosaurzzz
September 11, 2010

Beaten by Shonisaurus or not, the Cumnor Monster’s mandible is HUMONGOUS!!!
There’s a positive Sea-rex. In fact, pliosaurs were the head of state in the Mesozoic oceans, so why exactly might all these super-sized critters, like these fragmentary finds, never go rightly and permanently classified?
Okay, the Cumnor must be of a 50-foot-long, or even bigger, Pliosaurus macromerus, but there’s the monster of Arramberri, and Predator X, most famously.
They should be put into their places permanently, and that’s my firmest belief.