Triassic stem caecilian supports dissorophoid origin of living amphibians

Article

关键词: EARLY EVOLUTION;    ALBANERPETONTID AMPHIBIANS;    MORPHOLOGICAL DIVERSITY;    CRANIAL MORPHOLOGY;    TEMNOSPONDYL;    PHYLOGENY;    GYMNOPHIONA;    INTERRELATIONSHIPS;    REDESCRIPTION;    ASSEMBLAGE;   

DOI  :  10.1038/s41586-022-05646-5

来源: SCIE

【 摘 要 】

Living amphibians (Lissamphibia) include frogs and salamanders (Batrachia) and the limbless worm-like caecilians (Gymnophiona). The estimated Palaeozoic era gymnophionan-batrachian molecular divergence(1) suggests a major gap in the record of crown lissamphibians prior to their earliest fossil occurrences in the Triassic period(2-6). Recent studies find a monophyletic Batrachia within dissorophoid temnospondyls(7-10), but the absence of pre-Jurassic period caecilian fossils(11,12) has made their relationships to batrachians and affinities to Palaeozoic tetrapods controversial(1,8,13,14). Here we report the geologically oldest stem caecilian-a crown lissamphibian from the Late Triassic epoch of Arizona, USA-extending the caecilian record by around 35 million years. These fossils illuminate the tempo and mode of early caecilian morphological and functional evolution, demonstrating a delayed acquisition of musculoskeletal features associated with fossoriality in living caecilians, including the dual jaw closure mechanism(15,16), reduced orbits(17) and the tentacular organ(18). The provenance of these fossils suggests a Pangaean equatorial origin for caecilians, implying that living caecilian biogeography reflects conserved aspects of caecilian function and physiology(19), in combination with vicariance patterns driven by plate tectonics(20). These fossils reveal a combination of features that is unique to caecilians alongside features that are shared with batrachian and dissorophoid temnospondyls, providing new and compelling evidence supporting a single origin of living amphibians within dissorophoid temnospondyls.

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