Fossils of the elasmosaur Aristonectes were first reported from the Late Cretaceous of Patagonia in 1941. Recent discoveries in Chile and on Seymour Island (Antarctica) have provided much new information on this elasmosaur and the closely related Morturneria, respectively. F. Robin O'Keefe (Marshall University, Huntington, WV), and his colleagues reported at the 75th Annual Meeting of the Society of Vertebrate Paleontology that these reptiles employed a unique mode of feeding.
The massive lower jaws bear a comb-like structure formed by many slender teeth that project sideways. Similarly, the teeth in the upper jaws extend downward and sideways. Together with other features such as a deeply vaulted palate, this arrangement of teeth suggests that these elasmosaurs employed filter-feeding. They would fill the mouth with sea water and then, using coordinated movements of the throat and tongue, squeeze the water out through the tooth combs, leaving only the food particles to be collected by the tongue.
Aristonectes and Morturneria represented a unique style of food acquisition among marine reptiles from the Mesozoic Era. Baleen whales independently evolved a very similar method of feeding many millions of years after the extinction of the last elasmosaurs.
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CORRESPONDING AUTHOR CONTACT INFORMATION
F. ROBIN O'KEEFE
Marshall University, Huntington, WV, USA
CRANIAL ANATOMY OF MORTURNERIA SEYMOURENSIS AND THE EVOLUTION OF MYSTICETE-LIKE FILTER FEEDING IN AUSTRAL ARISTONECTINE PLESIOSAURS
O'KEEFE, F. Robin, Marshall University, Huntington, WV, USA
OTERO, Rodrigo A., Red Paleontológica U-Chile, Santiago, Chile
SOTO-ACUÑA, Sergio, Museo Nacional de Historia Natural, Santiago, Chile
O'GORMAN, Jose P., Universidad Nacional de La Plata, La Plata, Argentina
CHATTERJEE, Sankar, Texas Technical University, Lubbock, TX, USA
Aristonectine elasmosaurids of the austral Late Cretaceous have puzzled paleontologists since the description of Aristonectes from the Maastrichtian of Patagonia in 1941. The skull is fragmentary, but the large, hoop-like mandible is very derived. The recent description of new Aristonectes material from Chile has greatly augmented our understanding of this taxon, confirming that it is a large elasmosaurid, but one with compressed cervical vertebrae and large flippers. In this study we synthesize new Chilean cranial material, the Patagonian material, and Antarctic material to offer the first confident reconstruction of aristonectine skull anatomy. The reconstruction relies on the holotype of Morturneria seymourensis, an aristonectine from the Maastrichtian of Seymour Island, Antarctica. Our analysis indicates that Morturneria is certainly a valid taxon, smaller than Aristonectes, and that its cranial morphology is less derived than other members of the clade. The skull also has the most complete palate of any known aristonectine.
The skull reconstruction reveals unique cranial adaptations indicating that aristonectines were filter feeders. The occlusal surface of the mandible is covered with bone and the lower teeth project laterally from the jaw in a comb-line structure. The maxilla holds a dense battery of teeth that projects laterally and ventrally; the upper teeth overlap the lowers at a very low angle, lateral to the side of the skull. The cranium is also highly derived. The quadrates lie far behind the occipital condyle, and the braincase is near the center of the skull. The quadrates are carried by massive, dish-shaped extensions of the pterygoids, and the palate is deeply arched to both sides of the midline. These palatal chambers, when combined with the enormous mandible, create a voluminous oral cavity unprecedented among marine reptiles. A large volume of gulped water in the oral cavity would be cleared by movements of the pharynx, hyoids and tongue, expelling the water through the closed tooth batteries and straining out food particles. The internal naris is shielded behind a flange of the pterygoid and vomer, protecting it from water leaving the oral cavity. In summary, new cranial material from Chile has provided the perspective needed to confidently reconstruct the skull of Morturneria for the first time. The skull carries a suite of radical oral adaptions that clearly indicate that aristonectines were mysticete-like filter feeders. They are unique among all Mesozoic marine reptiles in adopting this feeding style.