科研之友
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摘要
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.
- 出版日期2011
