A Late Jurassic salamander (Amphibia: Caudata) from the Morrison Formation of North America

Abstract

Despite some remarkable recent discoveries, the Mesozoic fossil record of salamanders remains limited, particularly for the Jurassic. Here we describe the first articulated salamander skeleton from the Jurassic of Euramerica, recovered from Upper Jurassic deposits of the Morrison Formation, Dinosaur National Monument, USA. The specimen was studied using both conventional methods and high-resolution computed tomography. It shows a combination of primitive and derived character states that distinguish it from all known Mesozoic salamanders and which permit the erection of a new genus and species, Iridotriton hechti . The derived states (including the presence of spinal nerve foramina in the tail) suggest a position on the stem of the Salamandroidea. Together with microvertebrate material from Britain, Portugal, and North America, this specimen confirms the presence of both stem-and crowngroup salamanders in Euramerica from the Middle Jurassic (Bathonian) onwards, paralleling their evolution in Central and eastern Asia. This, in turn, provides qualified support for the current vicariance model of salamander evolution whereby basal caudates on an undivided Laurasian plate became separated into two populations by the incursion of the Turgai Sea in the Middle Jurassic, yielding Cryptobranchoidea in Asia and Salamandroidea in Euramerica.

Amphibians From the Middle Jurassic Balabansai Svita in the Fergana Depression, Kyrgyzstan (Central Asia)

“…2001; Gambaryan and Averianov 2001). Among other Jurassic Laurasian localities there are sites with a dominance of non‐lissamphibian temnospondyls (Shar Teg in Mongolia and the Junggar Basin in the Xinjiang Uigur Automonous Region in China), anurans (some levels at Dinosaur National Monument and Garden Park in USA), albanerpetontids (Guimarota in Portugal), albanerpetontids and salamanders (Kirtlington in England), and salamanders (Skye in Scotland, Daohugou in Inner Mongolia, and Fengshan in Hebei Province, China) (Hecht and Estes 1960; Evans et al . 1988, 2005; Shishkin 1991; Evans and Milner 1993; Evans and Waldman 1996; Wiechmann 2000; Gao and Shubin 2001, 2003; Maisch et al .…”

“…Kokartus is very similar to the contemporaneous Marmorerpeton from the Middle Jurassic (Bathonian) Forest Marble Formation in England and Kilmalaug Formation in Scotland, which is now also regarded as a karaurid (Evans et al . 1988; Evans and Waldman 1996; Borsuk‐Białynicka and Evans 2002; Evans et al . 2005).…”

Modern Imaging Techniques as a Window to Prehistoric Auditory Worlds

“…Evans et al (2005) used X-ray μCT to describe the osteology of a Late Jurassic salamander, Iridotriton hechti, but were unable to describe much of the ear apparatus due to damage and limited scan resolution. Greater sampling of inner and middle ear morphology in fossil forms is clearly needed to gain a better understanding of the evolution of these structures in this group, particularly in connection with the origin and systematics of Lissamphibia.…”

Mitochondrial genomes and divergence times of crocodile newts: Inter-islands distribution of <i>Echinotriton andersoni</i> and the origin of a unique repetitive sequence found in <i>Tylototriton</i> mt genomes

“…In the analyses, we used the Aln-all and Alnpart datasets and employed seven calibration points as follows. (1) The split of Cryptobranchidae and Salamandroidae: ~151-170 million years ago (Ma), based on the fossil record of salamandroid-like Iridotriton (Evans et al, 2005) for the minimum bound and a proposed origin of caudate (Marjanović and Laurin, 2007) for the maximum bound. (2) The split of Cryptobranchidae and Hynobiidae: >145 Ma, based on fossil salamander Chunerpeton; according to Roelants et al (2007) and Zhang et al (2008), slightly younger date was applied compared with the original date suggested by Gao and Shubin (2003).…”