& Michael W. Caldwell (2016)
Reacquisition of the lower temporal bar in sexually dimorphic fossil lizards provides a rare case of convergent evolution.
Scientific Reports 6, Article number: 24087 (2016)
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.
Haiyan Tong, Lu Li, Chaqing Jie and Laiping Yi (2016)
New material of Jiangxichelys ganzhouensis Tong & Mo, (Testudines:
Cryptodira: Nanhsiungchelyidae) and its phylogenetic and palaeogeographical
Geological Magazine (advance online publication)
http: // dx.doi.org/10.1017/S0016756816000108
http: // journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10275067&fileId=S0016756816000108
New material of Jiangxichelys ganzhouensis Tong & Mo, 2010,
including four shells, is described, more fully documenting the morphology of
the species. A partial skull associated with one of the shells is reported for
the first time for that taxon. The new material reveals more similarities
between J. ganzhouensis and ‘Zangerlia’ neimongolensis; the latter species is
therefore included in the genus Jiangxichelys. The phylogenetic analyses
continue to support the monophyly of the J. ganzhouensis, ‘Zangerlia’
neimongolensis, ‘Z.’ dzamynchondi and ‘Z.’ ukhaachelys clade and the separation
of this clade from the type species of Zangerlia, Z. testudinimorpha as
recently suggested. The close affinity between Jiangxichelys and ‘Zangerlia’
spp. provides new evidence for weak physical barriers against the dispersal of
land vertebrates between southern China and northern China and Mongolia during
latest Cretaceous times.