Friday, May 26, 2017

[Paleontology • 2017] Luskhan itilensis • Plasticity and Convergence in the Evolution of Short-Necked Plesiosaurs

Luskhan itilensis 
Fischer, Benson, Zverkov, Soul, Arkhangelsky, Lambert, Stenshin, Uspensky & Druckenmiller, 2017

  Reconstruction by Andrey Atuchin.

• A new unusual pliosaur marine reptile is described from the Cretaceous of Russia
• Ecomorphological convergence is assessed in short-necked plesiosaurs
• Pliosaurs repeatedly evolved longirostrine piscivorous forms
• Profound convergence characterizes the evolution of short-necked plesiosaurs

Plesiosaurs were the longest-surviving group of secondarily marine tetrapods, comparable in diversity to today’s cetaceans. During their long evolutionary history, which spanned the Jurassic and the Cretaceous (201 to 66 Ma), plesiosaurs repeatedly evolved long- and short-necked body plans. Despite this postcranial plasticity, short-necked plesiosaur clades have traditionally been regarded as being highly constrained to persistent and clearly distinct ecological niches: advanced members of Pliosauridae (ranging from the Middle Jurassic to the early Late Cretaceous) have been characterized as apex predators, whereas members of the distantly related clade Polycotylidae (middle to Late Cretaceous) were thought to have been fast-swimming piscivores. We report a new, highly unusual pliosaurid from the Early Cretaceous of Russia that shows close convergence with the cranial structure of polycotylids: Luskhan itilensis gen. et sp. nov. Using novel cladistic and ecomorphological data, we show that pliosaurids iteratively evolved polycotylid-like cranial morphologies from the Early Jurassic until the Early Cretaceous. This underscores the ecological diversity of derived pliosaurids and reveals a more complex evolutionary history than their iconic representation as gigantic apex predators of Mesozoic marine ecosystems suggests. Collectively, these data demonstrate an even higher degree of morphological plasticity and convergence in the evolution of plesiosaurs than previously thought and suggest the existence of an optimal ecomorphology for short-necked piscivorous plesiosaurs through time and across phylogeny.

Keywords: Plesiosauria, Thalassophonea, convergence, ecomorphology, morphospace, Jurassic, Cretaceous, Luskhan itilensis, plasticity, evolution

Luskhan itilensis 
  Reconstruction by Andrey Atuchin. 

Plesiosauria Blainville, 1835 
Pliosauridae Seeley, 1874
Thalassophonea Benson & Druckenmiller, 2014 
Brachaucheninae Williston, 1925 sensu Benson & Druckenmiller

Luskhan itilensis gen. et sp. nov

Etymology: The Volga river area is the heartland of Golden Horde from the Mongol Empire. In Mongolian and Turkic mythology, ‘‘luuses’’ are spirits and masters of water, and ‘‘khan’’ means chief. ‘‘Itil’’ is the ancient Turkic name of the Volga.

Holotype, Horizon, and Locality: YKM 68344/1_262, a nearly complete, three-dimensionally preserved skeleton excavated in 2002 by one of us (G.N.U.) in the upper portion of the Speetoniceras versicolor Zone, upper Hauterivian, Lower Cretaceous on the right bank of the Volga river, 3 km north of the Slantsevy Rudnik village, western Russia. The horizon is level g-5 in local stratigraphy

Valentin Fischer, Roger B.J. Benson, Nikolay G. Zverkov, Laura C. Soul, Maxim S. Arkhangelsky, Olivier Lambert, Ilya M. Stenshin, Gleb N. Uspensky and Patrick S. Druckenmiller. 2017. Plasticity and Convergence in the Evolution of Short-Necked Plesiosaurs. Current Biology. DOI:  10.1016/j.cub.2017.04.052 

New species of fossil marine reptile, by Valentin Fischer @UniversiteLiege via @EurekAlert

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