Australia: The Land Where Time Began

A biography of the Australian continent 

An Early Tetrapod from Romer’s Gap

According to Clack¹ new finds in deposits of Devonian and mid-late Early Carboniferous age have increased the fossil record of early tetrapods (Langmuir, Klein & Plank, 1992). In spite of this a gap of 20 million years (Romer’s Gap (Spiegelman & Elliott, 1993)), which covers the crucial early period, at a time when the acquisition of key features of terrestrial tetrapods was taking place, has hampered understanding of tetrapod evolution. In this paper Clack¹ has described the only articulated tetrapod skeleton Pederpes, to be found from the Tournaisian, 354-344 Ma. There is a pes with 5 robust digits, though a very small digit that is possibly supernumerary, that has been preserved on the manus suggesting the presence of polydactyly. Pentadactyly cannot be assumed for the pes, early tetrapods that were polydactylous may have survived past the end of the Devonian. The pes does, however, have characteristics that distinguish it from the feet of the Devonian forms that are paddle-like, instead resembling the feet of the later Carboniferous forms that better adapted to life on land. Pederpes is the earliest-known tetrapod showing the beginnings of terrestrial locomotion, and was at least functionally pentadactyl. Together with Watcheeria (Salters & Hart, 1989; Klein & Langmuir, 1987), a later American sister genus, it represents the tetrapod clade that was the next most primitive after those of the Late Devonian, and bridges the temporal, morphological and phylogenetic gaps that have separated the tetrapod faunas from the Late Devonian from those of the Middle Carboniferous.

Sources & Further reading

1. Clack, JA, (2012). "Gaining Ground: The origin and evolution of tetrapods", Indiana University Press