Comparative osteology of the hynobiid complex Liua‐Protohynobius‐Pseudohynobius (Amphibia, Urodela): Ⅰ. Cranial anatomy of Pseudohynobius

Abstract

Hynobiidae are a clade of salamanders that diverged early within the crown radiation and that retain a considerable number of features plesiomorphic for the group. Their evolutionary history is informed by a fossil record that extends to the Middle Jurassic Bathonian time. Our understanding of the evolution within the total group

Middle Jurassic stem hynobiids from China shed light on the evolution of basal salamanders

“…According to AmphibiaWeb (2021) and Frost (2021), Cryptobranchidae have two extant genera, including Andrias and Cryptobranchus; and Hynobiidae have nine extant genera, including Batrachuperus, Hynobius, Liua, Onychodactylus, Pachyhynobius, Paradactylodon, Pseudohynobius, Ranodon, and Salamandrella. Previously, the enigmatic hynobiid genus Protohynobius (Fei and Ye, 2000) was synonymized with the genus Pseudohynobius (Peng et al, 2010;Xiong et al, 2011); however, our recent study indicates that Protohynobius has multiple generic-level morphological differences from the latter (Jia et al, 2021), and therefore was retained here as an independent taxon. The data matrix contains 12 extant species in all 12 extant genera of Cryptobranchoidea, nine monotypic fossil genera from the Mesozoic strata of China (Beiyanerpeton, Chunerpeton, Liaoxitriton, Linglongtriton, Neimengtriton, Nuominerpeton, Pangerpeton, Qinglongtriton, Regalerpeton) and the Late Jurassic Karaurus as outgroup taxon.…”

“…The tall and flexible dorsal tail fin of Neimengtriton seems ideal for swimming and steering when in water, but is sufficiently thin and low not to be a hindrance when walking on land. Interestingly, this taxon has several features that are widely present in extant terrestrial hynobiids (Jia et al, 2021), including skull In the latter image, skull roof bones and caudosacral vertebrae are shaded dark gray, sacral vertebra is shaded whitish, rest of skeleton is shaded medium gray, and soft tissue traces are shaded light gray. See supplemental information for abbreviations.…”

Palatal morphology predicts the paleobiology of early salamanders

“…Previous studies on fossil salamanders generally focus on the taxonomy, whereas the paleoecology and the evolutionary history of the ecological decoupling particularly in metamorphosed taxa had received insufficient attention, which to some extent are contributed by the lack of taphonomic analyses (Wang et al, 2019). The main obstacles are (1) sufficient and reliable ecological indicators in the bony skeleton have not yet been established for extant cryptobranchoids and early salamanders (Xiong et al, 2016;Jia et al, 2021b) and (2) soft anatomical structures (e.g., labial fold, caudal fin) and stomach contents that are ecologically informative, as commonly seen in lacustrine deposits of certain neotenic species (Dong et al, 2012), are rarely preserved in metamorphosed taxa. Here we quantitively investigate the turnover of paleoecology in the earliest known salamanders based on the shape and non-shape variables of the palate.…”

“…Besides the neotenic Regalerpeton as aforementioned, living habitat preferences of these metamorphosed taxa and paleoecological disparity patterns of Cryptobranchoidea remain largely unexplored mainly due to yet established osteological indicators for ecology (see Discussion). The configuration of vomerine teeth has long been identified as useful for the classification of living cryptobranchoids (Zhao and Hu, 1984) and was recently claimed to be ecologically informative (Jia et al, 2021b), but such statements have not received rigorous tests with inclusion of fossil taxa.…”

“…Our series of studies on living and fossil cryptobranchoids noticed that besides vomerine teeth, the palate varies in shape and proportion, and could potentially serve as an indicator for paleoecological reconstruction (Jiang et al, 2018;2021a;2021b; Figure 1 and Figure 1-figure supplements 1-23). To test these hypotheses and to address the constraints underlying the morphological disparity of the palate, here we conducted a 2D landmark-based geometric morphometric analysis on the palate of all living and most aforementioned basal genera of cryptobranchoids, stem and other basal crown urodeles based primarily on micro-CT scanned specimens.…”