Abstract
The enigmatic tetrapod Acherontiscus caledoniae from the Pendleian stage of the Early Carboniferous shows heterodontous and durophagous teeth, representing the earliest known examples of significant adaptations in tetrapod dental morphology. Tetrapods of the Late Devonian and Early Carboniferous (Mississippian), now known in some depth, are generally conservative in their dentition and body morphologies. Their teeth are simple and uniform, being cone-like and sometimes recurved at the tip. Modifications such as keels occur for the first time in Early Carboniferous Tournaisian tetrapods. Acherontiscus, dated as from the Pendleian stage, is notable for being very small with a skull length of about 15 mm, having an elongate vertebral column and being limbless. Cladistic analysis places it close to the Early Carboniferous adelospondyls, aïstopods and colosteids and supports the hypothesis of ‘lepospondyl’ polyphyly. Heterodonty is associated with a varied diet in tetrapods, while durophagy suggests a diet that includes hard tissue such as chitin or shells. The mid-Carboniferous saw a significant increase in morphological innovation among tetrapods, with an expanded diversity of body forms, skull shapes and dentitions appearing for the first time.
Highlights
The Early Carboniferous Period (Mississippian) saw the dawn of continental tetrapod diversity
Purchased by the museum in the late nineteenth century, the specimen of Acherontiscus caledoniae consists of a skull about 15 mm long and an elongate, diplospondylous vertebral column, the latter in the natural mould
Our results suggest that the evolution of limbless tetrapods with elongate postcrania occurred three times in the late Visean and early Serpukovian: in aıstopods [15], in adelospondyls [15] and in Acherontiscus
Summary
The Early Carboniferous Period (Mississippian) saw the dawn of continental tetrapod diversity. 2 body shape and dental morphologies appear to have remained essentially conservative. By the later Visean stage, tetrapods had begun to assume more varied body morphologies. Some groups had reduced or lost their limbs and developed elongate vertebral columns [5,6,7]. One of the few modifications noted among Tournaisian tetrapods was the appearance of lateral keels on the tooth crowns of a large un-named tetrapod [4]. We report the earliest documented example, from the Pendleian (earliest Serpukhovian stage, late Mississippian), of both heterodont and durophagous dental adaptations in the small, limbless and elongate tetrapod, Acherontiscus caledoniae. We note the contemporary evolution of three clades of limbless, elongate tetrapods, each with its own specialized dentition [5,6,7]
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