The Giant Turtle That Really Sucked
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.
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.
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.
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…
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.