三畳紀の化石が両生類の起源を明らかにする地球科学の新しい研究(New geosciences study shows Triassic fossils that reveal origins of living amphibians)

バージニア工科大学の古生物学者チームは、アリゾナ州で三畳紀の最古のイエシリアの化石を発見しました。この発見は、これまで化石が見つかっていなかった約9000万年にわたるイエシリアの歴史的空白を埋めるもので、科学者を困惑させた。 A team of Virginia Tech paleontologists, led by doctoral candidate Ben Kligman, have discovered the first Triassic-era caecilian fossils, the oldest-known of their kind, in Arizona. The find helps fill a massive gap of roughly 90 million years in the historical record of caecilians where no fossils had been previously found, baffling scientists.

2023-01-25 バージニア工科大学(VirginiaTech)

<関連情報>

• https://vtx.vt.edu/articles/2023/01/science-triassic-era-caecilian-fossils-kligman.html
• https://www.nature.com/articles/s41586-022-05646-5

三畳紀の幹カイギュウは、現生両生類がディソロフォイドに由来することを支持する。 Triassic stem caecilian supports dissorophoid origin of living amphibians

Ben T. Kligman,Bryan M. Gee,Adam D. Marsh,Sterling J. Nesbitt,Matthew E. Smith,William G. Parker & Michelle R. Stocker
Nature  Published:25 January 2023
DOI:https://doi.org/10.1038/s41586-022-05646-5

Abstract

Living amphibians (Lissamphibia) include frogs and salamanders (Batrachia) and the limbless worm-like caecilians (Gymnophiona). The estimated Palaeozoic era gymnophionan–batrachian molecular divergence¹ suggests a major gap in the record of crown lissamphibians prior to their earliest fossil occurrences in the Triassic period^2,3,4,5,6. Recent studies find a monophyletic Batrachia within dissorophoid temnospondyls^7,8,9,10, 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 orbits¹⁷ and the tentacular organ¹⁸. The provenance of these fossils suggests a Pangaean equatorial origin for caecilians, implying that living caecilian biogeography reflects conserved aspects of caecilian function and physiology¹⁹, in combination with vicariance patterns driven by plate tectonics²⁰. 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.