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| Funcusvermis gilmorei Kligman, Gee, Marsh, Nesbitt, Smith, Parker & Stocker, 2023 |
Abstract
Living amphibians (Lissamphibia) include frogs and salamanders (Batrachia) and the limbless worm-like caecilians (Gymnophiona). The estimated Palaeozoic era gymnophionan–batrachian molecular divergence suggests a major gap in the record of crown lissamphibians prior to their earliest fossil occurrences in the Triassic period. Recent studies find a monophyletic Batrachia within dissorophoid temnospondyls, but the absence of pre-Jurassic period caecilian fossils has made their relationships to batrachians and affinities to Palaeozoic tetrapods controversial. 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, reduced orbits and the tentacular organ. 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, in combination with vicariance patterns driven by plate tectonics. 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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| Digital renderings of holotype, paratype, and referred specimens of Funcusvermis gilmorei. a–c, Composite reconstruction of craniomandibular elements in lateral (a), medial (b) and dorsal (c) views. d,e, Holotype right pseudodentary (PEFO 43891) in medial and ventral views. f, Paratype right pseudodentary (PEFO 46284) in medial view. g–i, Referred left maxillopalatine (PEFO 46481) in medial (g), ventral (h) and dorsal (i) views. j,k, Referred left pseudoangular (PEFO 46480) in medial and lateral views. l–o, Paratype right pseudodentary (PEFO 45800) in medial (l; expanded view in m) and dorsal (n; expanded view in o) views. abcnV, alveolar branch cranial nerve V; adtr, adsymphyseal tooth row; af, adductor fossa; att, attachment tissue; bp, basal pore; cnV, cranial nerve V insertions; cp, coronoid process; dpaf, dorsal pseudoangular facet; dpdf, dorsal pseudodentary facet; dtr, dentary tooth row; dz, dividing zone; ebcnV, external branch cranial nerve V; fr, facial ramus; hp, hamate process; imf, intramandibular foramen; jas, jaw articulation surface; lcm, lateral choanal margin; lecnV, lateral exit cranial nerve V; mtr, maxillary tooth row; om, orbital margin; pap, posterior pseudoangular process; pc, pulp cavity; pd, pedicel; pgp, preglenoid process; ptr, palatal tooth row; rtl, replacement tooth locus; sf, symphyseal foramen; sp, symphyseal prongs; vpaf, ventral pseudoangular facet; vpdf, ventral pseudodentary facet. Arrows indicate anterior direction. |
Systematic palaeontology
Lissamphibia Haeckel, 1866
Gymnophionomorpha Marjanović and Laurin, 2008
Funcusvermis gilmorei gen. et sp. nov.
Etymology. Funcus, Latinized form of the English word funky (funk is an upbeat, rhythmic form of dance music); vermis, worm (Latin); in honour of the 1972 song Funky Worm from the album Pleasure by the Ohio Players. The species name honours N. Gilmore, collections manager at the Academy of Natural Sciences of Drexel University in Philadelphia, PA, USA.
Holotype. PEFO 43891, right pseudodentary, accessioned at Petrified Forest National Park, Arizona, USA.
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| Life restoration of Funcusvermis gilmorei (bottom) and Acaenasuchus geoffreyi (top) in a paleoenvironmental reconstruction of the Chinle Formation, Petrified Forest National Park, Arizona, USA. |
Ben T. Kligman, Bryan M. Gee, Adam D. Marsh, Sterling J. Nesbitt, Matthew E. Smith, William G. Parker and Michelle R. Stocker. 2023. Triassic Stem Caecilian supports dissorophoid Origin of Living Amphibians. Nature. DOI: 10.1038/s41586-022-05646-5
