AUTHOR=Jiménez-Huidobro Paulina , Caldwell Michael W. 

TITLE=A New Hypothesis of the Phylogenetic Relationships of the Tylosaurinae (Squamata: Mosasauroidea)

JOURNAL=Frontiers in Earth Science

VOLUME=7

YEAR=2019

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2019.00047

DOI=10.3389/feart.2019.00047

ISSN=2296-6463

ABSTRACT=<p>Tylosaurinae (<xref ref-type="bibr" rid="B75">Williston, 1897</xref>), is reconstructed in most analyses as the sister group of the Plioplatecarpinae (<xref ref-type="bibr" rid="B25">Dollo, 1884</xref>). The most distinctive characteristic of the group is an elongated edentulous rostrum on the premaxilla. Members of the tylosaurine subfamily are divided into two genera: <italic>Tylosaurus</italic> (<xref ref-type="bibr" rid="B52">Marsh, 1874</xref>), and <italic>Taniwhasaurus</italic> (<xref ref-type="bibr" rid="B35">Hector, 1874</xref>). When all arguably valid tylosaurine species are included in a single phylogenetic analysis, some clades are well supported, i.e., the clade formed by <italic>T. proriger</italic> (<xref ref-type="bibr" rid="B21">Cope, 1869</xref>) + <italic>T. bernardi</italic> (<xref ref-type="bibr" rid="B26">Dollo, 1885</xref>), or the clade <italic>T. pembinensis</italic> (<xref ref-type="bibr" rid="B57">Nicholls, 1988</xref>) + <italic>T. saskatchewanensis</italic>. In contrast, clade relationships for other species remain unresolved, i.e., <italic>T. gaudryi</italic> (<xref ref-type="bibr" rid="B73">Thevenin, 1896</xref>), <italic>T. nepaeolicus</italic> (<xref ref-type="bibr" rid="B22">Cope, 1874</xref>), and the several species within the genus <italic>Taniwhasaurus</italic>. When <italic>T. gaudryi</italic> (<xref ref-type="bibr" rid="B73">Thevenin, 1896</xref>), <italic>Ta. ‘mikasaensis’</italic> (<xref ref-type="bibr" rid="B17">Caldwell et al., 2008</xref>), and ‘<italic>T’. capensis</italic> (<xref ref-type="bibr" rid="B9">Broom, 1912</xref>) were removed from the analysis, <italic>T. nepaeolicus</italic> appeared as the basal member of the genus. The relationship within the genus <italic>Taniwhasaurus</italic> remains unresolved; however, when the problematic taxa was removed, the genus became monophyletic, with <italic>Ta. oweni</italic> as the sister group of <italic>Ta. antarcticus</italic>. Based on morphological characters present in the holotype of ‘<italic>T’. capensis</italic><xref ref-type="bibr" rid="B9">Broom, 1912</xref>, we suggested a re-assignment to the genus <italic>Taniwhasaurus</italic>, based on the flutes and facets in the crown of the two preserved replacement teeth. The lack of a clear diagnosis of <italic>Hainosaurus</italic>/<italic>Tylosaurus neumilleri</italic> leaves this taxon as a nomen dubium; the few characters visible on the specimen show strong similarities to both <italic>T. pembinensis</italic> and <italic>T. saskatchewanensis</italic>; therefore, the specimen cannot be identified beyond <italic>Tylosaurus</italic> sp. Reassessment of the known materials of the Japanese species <italic>Ta. ‘mikasaensis’</italic> suggests that the various specimens do not display sufficient diagnostic characters to support ‘<italic>mikasaensis</italic>’ as distinct from <italic>Taniwhasaurus oweni</italic>. The hypothesis for a North Atlantic Circle Basin distribution for a species of the genus <italic>Tylosaurus</italic>, from the Coniacian to the Maastrichtian is supported, and a more cosmopolitan distribution is suggested for the genus <italic>Taniwhasaurus</italic> (Santonian to Maastrichtian) with species present along the margins of the Pacific, Indian, and Antarctic Ocean Basins.</p>