Cranial morphology and relationships of a new grippidian (Ichthyopterygia) from the Vega-Phroso Siltstone Member (Lower Triassic) of British Columbia, Canada

ABSTRACT

In 1989, TMP 89.127.3, a basal ichthyopterygian, was collected as a counterpart slab from the Vega-Phroso Siltstone Member (Lower Triassic) of the Sulphur Mountain Formation in east-central British Columbia, Canada. Previous investigations of its postcranial skeleton resulted in ambiguous taxonomic affinities, with it being identified as either Grippia cf. longirostris or Parvinatator wapitiensis. More recently, the part slab of TMP 89.127.3 was collected and prepared, revealing important new cranial data that permits its systematic relationships to be more thoroughly assessed and previously proposed taxonomic affinities to be tested. By integrating both cranial and postcranial data, phylogenetic analysis recovers TMP 89.127.3 and Grippia as members of Grippidia, nested within Eoichthyosauria. TMP 89.127.3 can be distinguished from Grippia by possessing the following autapomorphies: metacarpal I with a notched peripheral shaft; cylindrical anterior teeth with a crown shape index >5.0; and a postfrontal-frontal contact at the rostral limit of the anterior margin of the supratemporal terrace. A new taxon, Gulosaurus helmi, is erected to accommodate this suite of features. The placement of Gulosaurus helmi within Grippidia reaffirms the Early Triassic distribution of this clade to include western and northern Laurasia, which is represented by outcrop in present-day Canada and Norway (Spitzbergen), respectively.

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline/UJVP

ACKNOWLEDGMENTS

We thank J. Gardiner and B. Strilisky of the TMP for access to specimens in their care. Thanks also go to J. McCabe (TMP) for the further preparation of the tooth row of TMP 89.127.3. Much appreciation goes to D. Brinkman for insightful discussions regarding the specimen. We would also like to thank R. O’Keefe, E. Maxwell, and M. Zammit, whose constructive comments improved the manuscript. This research was supported by an NSERC Discovery Grant and University of Calgary starter grant awarded to J. Anderson, and a NSERC Discovery Grant awarded to A. Russell.

Handling editor: Robin O’Keefe.