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| Qikiqtania wakei Stewart, Lemberg, Daly, Daeschler & Shubin, 2022 |
Abstract
A fundamental gap in the study of the origin of limbed vertebrates lies in understanding the morphological and functional diversity of their closest relatives. Whereas analyses of the elpistostegalians Panderichthys rhombolepis, Tiktaalik roseae and Elpistostege watsoni have revealed a sequence of changes in locomotor, feeding and respiratory structures during the transition, an isolated bone, a putative humerus, has controversially hinted at a wider range in form and function than now recognized. Here we report the discovery of a new elpistostegalian from the Late Devonian period of the Canadian Arctic that shows surprising disparity in the group. The specimen includes partial upper and lower jaws, pharyngeal elements, a pectoral fin and scalation. This new genus is phylogenetically proximate to T. roseae and E. watsoni but evinces notable differences from both taxa and, indeed, other described tetrapodomorphs. Lacking processes, joint orientations and muscle scars indicative of appendage-based support on a hard substrate, its pectoral fin shows specializations for swimming that are unlike those known from other sarcopterygians. This unexpected morphological and functional diversity represents a previously hidden ecological expansion, a secondary return to open water, near the origin of limbed vertebrates.
Systematic palaeontology
Sarcopterygii Romer, 1955
Tetrapodomorpha Ahlberg, 1991
Elpistostegalia Camp and Allison, 1961
Qikiqtania wakei gen. et sp. nov.
Locality. Canada, Nunavut, southern Ellesmere Island, near the eastern arm of Bird Fiord, Nunavut Paleontological Expedition site NV0401, ....
Geological setting. Fram Formation (Upper Devonian, early Frasnian Stage).
Holotype. Nunavut Fossil Vertebrate Collection (NUFV) 137.
Diagnosis. Elpistostegalian tetrapodomorph characterized by the following unique combination of characters: dorsoventral asymmetry in pectoral fin lepidotrichia (also present in T. roseae) and possession of a boomerang-shaped humerus lacking ventral ridge and associated foramina and ectepicondyle (distinct from P. rhombolepis, E. watsoni, T. roseae and more crownward tetrapods).
Etymology. Qikiqtania (pronounced ‘kick-kiq-tani-ahh’) is derived from Inuktitut word Qikiqtaaluk/Qikiqtani, the traditional name for the region where the fossil site occurs. The species designation is in memory of David Wake, an eminent evolutionary biologist and transformative mentor, late of the University of California at Berkeley.
Thomas A. Stewart, Justin B. Lemberg, Ailis Daly, Edward B. Daeschler and Neil H. Shubin. 2022. A New Elpistostegalian from the Late Devonian of the Canadian Arctic. Nature. DOI: 10.1038/s41586-022-04990-w
