title: Reacquisition of the lower temporal bar in sexually dimorphic fossil lizards provides a rare case of convergent evolution.
abstract: Temporal fenestration has long been considered a key character to understand relationships amongst reptiles. In particular, the absence of the lower temporal bar (LTB) is considered one of the defining features of squamates (lizards and snakes). In a re-assessment of the borioteiioid lizard Polyglyphanodon sternbergi (Cretaceous, North America), we detected a heretofore unrecognized ontogenetic series, sexual dimorphism (a rare instance for Mesozoic reptiles), and a complete LTB, a feature only recently recognized for another borioteiioid, Tianyusaurus zhengi (Cretaceous, China). A new phylogenetic analysis (with updates on a quarter of the scorings for P. sternbergi) indicates not only that the LTB was reacquired in squamates, but it happened independently at least twice. An analysis of the functional significance of the LTB using proxies indicates that, unlike for T. zhengi, this structure had no apparent functional advantage in P. sternbergi, and it is better explained as the result of structural constraint release. The observed canalization against a LTB in squamates was broken at some point in the evolution of borioteiioids, whereas never re-occuring in other squamate lineages. This case of convergent evolution involves a mix of both adaptationist and structuralist causes, which is unusual for both living and extinct vertebrates.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Tiago R
authors.initials: TR
authors.lastname: Simões
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Gregory F
authors.initials: GF
authors.lastname: Funston
authors.affiliation: Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Behzad
authors.initials: B
authors.lastname: Vafaeian
authors.affiliation: Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, 19555 N. 59th Dr., Glendale, AZ 85383, USA.
authors.forename: Randall L
authors.initials: RL
authors.lastname: Nydam
authors.affiliation: Faculty of Pharmacy &Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta T6G 2E1, Canada.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Doschak
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.|Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Caldwell
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D005260:Female; D005580:Fossils / Q000033:anatomy & histology*; D008116:Lizards / Q000033:anatomy & histology / Q000145:classification / Q000235:genetics*; D008297:Male; D010802:Phylogeny; D012727:Sex Characteristics; D012886:Skull / Q000033:anatomy & histology*