Category: Marine reptiles

The Giant Turtle That Really Sucked

Posted on by Travis Park in Marine reptiles, Turtles

Turtles are an underappreciated group of tetrapods. Despite a brief flirtation with popular culture in the late eighties and early nineties (although no known species actually eats pizza and wields ninja weapons), the shelled reptiles still don’t get the attention their seriously weird morphology deserves.

The oldest known turtles are from the Late Triassic of China (Li et al. 2008), but the debate still rages on regarding which group turtles actually evolved from, so derived is their morphology (Carroll 2013). There are around 300 living species of turtle, divided into 14 families, the largest of which is the marine leatherback turtle, which can reach 2m in length. Yet this pales in comparison with the largest known fossil turtle, Archelon ischyros, which had a shell over 4 m long! Yet for all of the turtles of different shapes and sizes, none have ever been found like the new species described in a paper published in PLoS One last week.

Here you can clearly see just how huge the largest known fossil turtle, Archelon, really was. Image from Moody et al. 2013.
Here you can clearly see just how huge the largest known fossil turtle, Archelon, really was. Image from Moody et al. 2013.

The paper, written by Nathalie Bardet and colleagues, names a new species of giant turtle, Ocepechelon bouyai from the Late Cretaceous (~65 Ma) phosphates of the Oulad Abdoun Basin in Morocco. In it they describe a skull of a turtle that is unlike any other ever known. Most turtles have beaks with horny ridges that they use to slice through their food. Ocepechelon bouyai however used a completely different method. The snout of its skull was shaped like a pipette tube which it used to suck in its prey, a method known as suction feeding. This feeding method is relatively common in aquatic vertebrates such as fish and marine mammals and some living species of turtle do also use this method of feeding, but it is very rarely reported in Mesozoic marine reptiles, let alone to this extreme degree of specialisation and unique morphology.

Here is a reconstruction of the new turtle species, Ocepechelon bouyai. How weird is that skull morphology!? Image from Bardet et al. 2013.
Here is a reconstruction of the new turtle species, Ocepechelon bouyai. How weird is that snout!? Image from Bardet et al. 2013.

In an unlikely example of convergent evolution (where two separately related taxa evolve similar features), the authors compare this strange animal to modern beaked whales. These marine mammals also possess a long toothless rostrum that they open rapidly to suck in prey. This convergence also extends to other parts of the skull, the nostrils are situated further towards the back of the top of the skull (or posterodorsally if you prefer) and also the squamosals are very well developed like in beaked whales, these would have allowed the attachment of strong throat muscles to help generate the large suction forces necessary for this mode of feeding.

Here's the holotype skull of Ocepechelon bouyai. You can see the elongated, toothless rostrum and enlarged squamosals that make the authors compare it to a beaked whale. Image from Bardet et al. 2013.
Here’s the holotype skull of Ocepechelon bouyai. You can see the elongated, toothless rostrum and enlarged squamosals that make the authors compare it to a beaked whale. Image from Bardet et al. 2013.

This find shows that at the end of the Cretaceous, the shallow seas where Morocco is today possessed a diversity of animals that is still yet to be fully realised. The pipette like rostrum of O. bouyai is unique among tetrapods and shows that this cool group of animals have plenty more surprises up their sleeves. Cowabunga dudes! Ahem…

References

Bardet N, Jalil N-E, de Lapparent de Broin F, Germain D, Lambert O, et al. (2013) A Giant Chelonioid Turtle from the Late Cretaceous of Morocco with a Suction Feeding Apparatus Unique among Tetrapods. PLoS ONE 8(7): e63586. doi:10.1371/journal.pone.0063586

Carroll, R. 2013. Problems of the Ancestry of Turtles in D. B. Brinkman et al. (eds.), Morphology and Evolution of Turtles. Springer, New York, 576 p.

Li, C; Wu, XC; Rieppel, O; Wang, LT; Zhao, LJ (November 2008). “An ancestral turtle from the Late Triassic of southwestern China”. Nature 456 (7221): 497–501.

Richard T. J. Moody, Cyril A. Walker, and Sandra D. Chapman. 2013. Fossil European Sea Turtles: A Historical Perspective in D. B. Brinkman et al. (eds.), Morphology and Evolution of Turtles. Springer, New York, 576 p.

River Monsters, Cretaceous Style: A Freshwater Plesiosaurian from Victoria

Posted on by Travis Park in Australian palaeo, Marine reptiles, Plesiosaurs, Pliosaurs

The tragedy of extinction (necessary evil that it is) is that we’ll never (barring the physicists getting their act together and building a time machine – sort it out guys) get to see all those incredible animals in the flesh, moving around, eating, sleeping, mating, fighting and just doing whatever it was that they did. One of the groups that I feel most dismayed about never being able to see is the extinct marine reptiles.  This group consisted of animals such as the ichthyosaurs, mosasaurs, nothosaurs, thalattosaurs, thalattosuchians and the group which is the focus of this post, the plesiosaurs. All these reptile groups made the transition from being terrestrial animals to secondarily aquatic reptiles at various points during the Mesozoic era but from the reptiles, only turtles and snakes and iguanas have modern representatives in the seas today.

The plesiosaurs first appeared in the Late Triassic (Taylor & Cruickshank 1993) and had become widespread by the Jurassic. Plesiosaurs are distinguished by having a unique body plan which consists of a short, stiff trunk, short tail, all four limbs modified into flippers and highly variable neck length and skull size (Benson et al. 2013). Although there were also intermediate body shapes, the group tend to be fall into either the long necked, small skulled plesiosaurs or the short necked, large skulled pliosaurs. In addition to being adaptable morphologically, they were also adaptive ecologically too, as they are also known from freshwater localities including some from Australia.

Skeletal drawings of the two man body plans of the plesiosaurids: A, the long necked, small skulled plesiosaur and B, the short necked, large skulled pliosaur. Image from Springer Images.
Skeletal drawings of the two man body plans of the plesiosaurids: A, the long necked, small skulled plesiosaur and B, the short necked, large skulled pliosaur. Image from Springer Images.

Freshwater plesiosaurs are known from two localities in Victoria, Australia. These are the Otways and Flat Rocks localities, both of which are from the same formation (Eumarella Formation) and represent a time in the Early Cretaceous when the two localities were part of the same depositional basin. Southeastern Australia in the Early Cretaceous was joined to Australia (although they were in the process of rifting apart) and situated within the Antarctic Circle. The area was a flood plain that was filled with braided river channels that would have burst their banks when the spring thaw floods passed through each year. These flood waters carried with them the remains of animals that had perished in the waters and been carried downstream and it’s their fossils that we search for at these localities today (see here and here for previous posts on each locality).

In a new paper to be published in the next issue of the journal Alcheringa, Roger Benson and colleagues describe a freshwater plesiosaurian tooth (NMV P198945) from the Eumarella Formation in Victoria, Australia. The interesting thing about the tooth is that it is different to any other plesiosaur teeth that have been found at these localities previously. It is much larger than all other plesiosaur teeth discovered; it has a length of 45.1 mm, whereas the other teeth from that locality are between 10-30 mm in length. It has ridges on its enamel which are spaced apart from each other and stop short of the crown apex (the top of the tooth), differing from the smaller teeth from the locality, which possess ridges that are closer together and continue closer to the apex of the crown.

Figure showing NMV P198945 in A, C, undetermined, B, labial, and D, lingual views. Image from Benson et al. 2013
Figure showing NMV P198945 in A, C, undetermined, B, labial, and D,
lingual views. Image from Benson et al. 2013

So what does this new tooth mean for our interpretation of the palaeoecosystem at this locality? Well, this is the first unambiguous evidence of a multitaxic (multiple species) freshwater plesiosaur assemblage known anywhere in the world.  In freshwater river systems today there are equivalents in the form of river dolphins from China and the Amazon. Whilst the Chinese dolphins might actually be extinct, the Amazon dolphins partition food and habitat to avoid directly competing with each other. A similar thing may have been happening in the Early Cretaceous of Victoria with these freshwater plesiosaurs. The estimated size of the animal that this tooth belonged to is a seriously impressive 4-5 m, a true river monster if there ever was one! If those physicists ever do get round to that time machine, I hope they let Jeremy Wade use to do a palaeo special episode for this beastie. Jeremy, you might need a bigger boat…

(For those of you who don’t know who Jeremy Wade is, he is the host of a show on Nat Geo called River Monsters, definitely worth checking out!)

References

Roger B.J. Benson , Erich M.G. Fitzgerald , Thomas H. Rich & Patricia Vickers-Rich (2013): Large freshwater plesiosaurian from the Cretaceous (Aptian) of Australia, Alcheringa: An Australasian Journal of Palaeontology, DOI:10.1080/03115518.2013.772825

Taylor, M. A. and Cruickshank, A. R. I. 1993. A plesiosaur from the Linksfield erratic (Rhaetian, Upper Triassic) near Elgin, Morayshire. Scottish Journal of Geology, 29, 191-196.