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A new species of Laccognathus (Sarcopterygii, Porolepiformes) from the Late Devonian of Ellesmere Island, Nunavut, Canada

2011; Taylor & Francis; Volume: 31; Issue: 5 Linguagem: Inglês

10.1080/02724634.2011.599462

1937-2809

Jason P. Downs, Edward B. Daeschler, Farish A. Jenkins, Neil H. Shubin,

Evolution and Paleontology Studies

ABSTRACT Recent work in the Late Devonian (Frasnian) Fram Formation of Ellesmere Island, Nunavut, Canada, has produced the first North American record of Laccognathus (Sarcopterygii, Porolepiformes), a taxon previously known only from Latvia and Russia. Represented by a large sample that includes cranial material from 22 individuals, Laccognathus embryi, sp. nov., is uniquely diagnosed by features including the absence of marginal teeth on coronoids 1 and 2, and the lack of a fifth posthyal branchial arch. The large sample allows detailed morphological description of many parts of the cranial skeleton, including the dermal skull, braincase, palatoquadrate, and branchial skeleton. Comparison of the faunas from the Fram Formation in Nunavut, the Escuminac Formation in Quebec, and the Lode and Gauja formations of Latvia confirms a Laurussian (Euramerican) biogeographic province in the late Middle/early Late Devonian and may indicate tolerance of some forms to varied salinities. A cranial reconstruction of the new taxon reveals a wide head with a width-to-length ratio of approximately 2:1, a large spiracular opening, a small orbit, and a lower jaw in which much of the labial surface faced ventrally. The cranial morphology suggests a benthic animal reliant on sit-and-wait predation. ACKNOWLEDGMENTS The authors thank C F. Mullison and W. A. Amaral for fossil preparation, K. Monoyios for line drawings, K. Luckenbill for line drawings and the cranial restoration, and E. Chesser for her data collection and curation of the material. The Nunavut Ministry of Culture, Languages, Elders and Youth, the Grise Fiord Hamlet, and HTA provided permits that made this research possible. The Polar Continental Shelf Project provided logistical support and the Canadian Museum of Nature provided collections support. The authors recognize everyone who has provided field assistance (1999–2008): W. Amaral, B. Atagootak, J. Conrad, R. Dahn, M. Davis, S. Gatesy, A. Gillis, B. Kilbourne, S. Madsen, K. Middleton, J. Miller, K. Monoyios, C. Schaff, M. Shapiro, R. Shearman, and C. Sullivan. The manuscript was significantly improved by the efforts of two anonymous reviewers. This research was supported by two anonymous donors, the Academy of Natural Sciences of Philadelphia, the Putnam Expeditionary Fund (Harvard University), the University of Chicago, the National Science Foundation grants EAR 0207721 (E.B.D.), EAR 0544093 (E.B.D.), EAR 0208377 (N.H.S.), and EAR 0544565 (N.H.S.), and the National Geographic Society Committee for Research and Exploration grants 7223-02, 7665-04, 8040-06, and 8420-08. Handling editor: Zerina Johanson