Still slow, but even steadier: an update on the evolution of turtle cranial disparity interpolating shapes along branches

Abstract

In a previous study, we estimated the cranial disparity of turtles (Testudinata) through time using geometric morphometric data from both terminal taxa and hypothetical ancestors to compensate for temporal gaps in the fossil record. While this method yielded reasonable results for the Mesozoic and the early Cenozoic, we found a large drop in cranial disparity for the Miocene, for which we found no correlation with known environmental changes or extinction events. Instead, we speculated that the Miocene dip was a result of poor sampling of fossils or ancestors in this time bin. To countervail this problem, we here updated our original dataset and interpolated changes of shape along the branch lengths and compared them with the previous data. We furthermore explored the impact of topological and temporal uncertainty, demonstrating that the Miocene dip, indeed, is a sampling artefact. All remaining conclusions of the previous study could be more or less supported, nevertheless, including an apparent correlation with global biogeographic events, a minor correlation between cranial disparity and global temperature, and resilience across the K/T extinction event.

Crocodylomorph cranial shape evolution and its relationship with body size and ecology

“…This is consistent with what was found in previous geometric morphometric studies (e.g. Foth, Ascarrunz, et al, 2017;Godoy et al, 2018;Pierce et al, 2008Pierce et al, , 2009Piras et al, 2009;Sadleir & Makovicky, 2008;Wilberg, 2017;Young et al, 2010), indicating that this region of the skull has the highest morphological variation. High variability in crocodylomorph snout length has long been acknowledged (Brochu, 2001;Busbey, 1995;Langston, 1973), even leading early taxonomists (e.g.…”

“…Foth, Fernandez Blanco, et al. () have previously investigated the influence of temporal and topological uncertainty on disparity though time in turtles (Testudinata) and reported comparable impacts. Similarly, although not tested here, it is very likely that alternative time‐scaling methods (e.g.…”

“…I performed a series of sensitivity analyses for disparity-throughtime estimation, given that previous work demonstrated the susceptibility of these kind of analyses to alternative methods for sub-sampling taxa (Guillerme, 2018;Guillerme & Cooper, 2018) and to different phylogenetic hypotheses (Foth, Ascarrunz, & Joyce, 2017). Thus, I used different sub-sampling procedures (i.e.…”

A Review of the Fossil Record of Nonbaenid Turtles of the Clade Paracryptodira

“…The significant amount of morphological variation apparent in the small set of available skulls (see "Skeletal Morphology") attests to much ecological plasticity within the group. The elongate skull with low labial margins of Glyptops ornatus and Pleurosternon bullockii is broadly consistent with gape-and-suction feeding (Pritchard 1984;Foth et al 2017). The higher labial ridges and expanded triturating surfaces of Dorsetochelys typocardium and Uluops uluops, on the other hand, are consistent with dietary generalists (Foth et al 2017).…”

“…The elongate skull with low labial margins of Glyptops ornatus and Pleurosternon bullockii is broadly consistent with gape-and-suction feeding (Pritchard 1984;Foth et al 2017). The higher labial ridges and expanded triturating surfaces of Dorsetochelys typocardium and Uluops uluops, on the other hand, are consistent with dietary generalists (Foth et al 2017). The massive skull of Compsemys victa, by contrast, is unique among turtles by being extremely thick boned, but its overall shape, in particular the toothlike median projection and reduced pterygoids, is highly reminiscent of the extant bigheaded turtle Platysternon megacephalum (Hutchison and Holroyd 2003) and suggests the lifestyle of a macrocarnivorous snapping turtle (Lyson and Joyce 2011;Foth et al 2017).…”