Cranial shape evolution of extant and fossil crocodile newts and its relation to reproduction and ecology

Abstract

The diversity of the vertebrate cranial shape of phylogenetically related taxa allows conclusions on ecology and life history. As pleurodeline newts (the genera Echinotriton , Pleurodeles and Tylototriton ) have polymorphic reproductive modes, they are highly suitable for following cranial shape evolution in relation to reproduction and environment. We investigated interspecific differences externally and differences in the cranial shape of pleurodeline newts via two‐dimensional geometric morphometrics. Our analyses also included the closely related but extinct genus Chelotriton to better follow the evolutionary history of cranial shape. Pleurodeles was morphologically distinct in relation to other phylogenetically basal salamanders. The subgenera within Tylototriton ( Tylototriton and Yaotriton ) were well separated in morphospace, whereas Echinotriton resembled the subgenus Yaotriton more than Tylototriton . Oviposition site choice correlated with phylogeny and morphology. Only the mating mode, with a random distribution along the phylogenetic tree, separated crocodile newts into two morphologically distinct groups. Extinct Chelotriton likely represented several species and were morphologically and ecologically more similar to Echinotriton and Yaotriton than to Tylototriton subgenera. Our data also provide the first comprehensive morphological support for the molecular phylogeny of pleurodeline newts.

Biogeographic history of Palearctic caudates revealed by a critical appraisal of their fossil record quality and spatio-temporal distribution

“…In particular, these vertebrae are characterized by the dorsally enlarged neural crest typical of the extinct Neogene Eurasian taxa Chelotriton and Lissotriton rohrsi (see below), as well as extant crocodile-newts from southeast Asia (i.e. the Tylototriton / Echinotriton group; [ 93 , 94 ]).…”

“…[ 229 , 237 ]). The first taxa that occur in central and eastern Asia are Procynops (Early Miocene of China), closely related to the extant Chinese genus Cynops , and Chelotriton (present in central Asia in the Early and Middle Miocene), which shows close similarities to the extant crocodile newts Tylototriton and Echinotriton from southeast Asia [ 94 ]. This implies that the expansion to the east of Salamandridae happened not later than the Miocene, with subsequent extirpation from central Asia.…”

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“…The various species within the genus Tylototriton differ in reproductive behaviours to the extent that there can be either terrestrial or aquatic mating and there are variations in the sites they select for oviposition (Pogoda et al, 2020). In this study, the breeding behaviour of T. panhai involved five main stages including i/approach, ii/nuptial dance, iii/ amplexus, iv/spermatophore deposition, and v/fertilisation.…”

“…Hernandez & Pomchote (2020) reported oviposition sites being on land near ponds, where eggs were attached to twigs, plants and even grasses or tree roots, sometimes more than 20-40 cm above the ground to avoid predators. Thus, T. panhai shows a preference for terrestrial oviposition while other congeners among the subgenera Tylototriton and Liangshantriton mainly lay their eggs in water bodies (Pogoda et al, 2020).…”

Morphological variation in the vomer of aquatic and terrestrial spelerpini salamanders

“…For example, crocodile newt ( Tylototriton ) speciation largely occurred under the regime of niche conservatism, but the uplift of the Tibetan Plateau led to speciation with niche lability (Hernandez et al, 2018). Cranial morphology in crocodile newts correlates with reproductive ecology, but it is not apparent if both are constrained by phylogeny (Pogoda et al, 2020).…”