Abstract
AbstractThe Visean stage of the Mississippian was a time of rapid tetrapod diversification which marks the earliest appearance of temnospondyls, microsaurs and the limbless aïstopods. Tetrapod finds from this stage are very rare and only a dozen sites are known worldwide. Here we announce the discovery of a new Visean site in Fife, Scotland, of Asbian age, and from it describe a new species of the baphetoid Spathicephalus. These specimens represent the oldest known baphetoid by three million years, yet belong to the most specialized members of the clade. Unlike typical baphetoids with large marginal teeth and palatal fangs characteristic of early tetrapods, spathicephalids had very broad flattened heads with a dentition consisting of a large number of small, uniform teeth. Spathicephalids were probably one of the earliest tetrapod groups to use suction feeding on small, aquatic prey. Palynological and sedimentological analysis indicates that the new fossil bed was deposited in a large, stratified, freshwater lake that became increasingly saline.
Highlights
Recent discoveries in the earliest Carboniferous have revealed that tetrapod diversification was well established by the Tournaisian (Smithson et al 2012; Anderson et al 2015; Clack et al 2016) the predominant members of the Carboniferous tetrapod fauna, the a€ıstopods, anthracosaurs, microsaurs and temnospondyls, have not been found among them: these first appear in the Visean, 10 myr later
Some discoveries have been made in the Visean of Scotland (Wood et al 1985; Paton et al 1999), USA (Bolt et al 1988) and Australia (Thulborn et al 1996) Visean tetrapod finds remain very rare, with only a dozen sites known worldwide
Those finds hint that the Visean was a time of morphological innovation among tetrapods, with limbless forms and unusual cranial morphologies appearing for the first time
Summary
Recent discoveries in the earliest Carboniferous have revealed that tetrapod diversification was well established by the Tournaisian (Smithson et al 2012; Anderson et al 2015; Clack et al 2016) the predominant members of the Carboniferous tetrapod fauna, the a€ıstopods, anthracosaurs, microsaurs and temnospondyls, have not been found among them: these first appear in the Visean, 10 myr later. Baphetids are known from the Visean until the late Pennsylvanian but spathicephalid specimens have been found previously only in the Serpukhovian, at two sites in Scotland and one in Nova Scotia (Baird 1962; Beaumont & Smithson 1998) The origins of these two clades and their cranial and dental modifications remain unknown, but presumably were much earlier. We report the discovery and briefly describe a new spathicephalid and its environmental setting from a recently discovered vertebrate-bearing site in the Visean of Fife, Scotland. This specialized taxon is the earliest known member of the baphetoids. These data show that the beds are within the upper part of the tessellatus–campyloptera (TC) palynozone and are of Asbian age (Fig. 1)
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