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SVPCA
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Palaeospondylus, a jawless vertebrate from the Devonian of Scotland
 
SVPCA Conference
 
Platform presentation (20 minutes)
Authors
 
*Jan den Blauuwen
 
 
Zerina A Johanson
 
 
Michael Newman
 
 
Moya Meredith Smith
 
Abstract
 
Recent suggestions that the enigmatic Devonian vertebrate Palaeospondylus represented the larvae of the Devonian lungfish Dipterus have been repudiated by comparisons to extant larval lungfish and the discovery of Dipterus specimens within the size range of Palaeospondylus. New information provides evidence for affinity with the jawless vertebrates. For example, histological sections show that all Palaeospondylus elements are composed of a mineralized cartilage most similar to that recently described in Euphanerops, principally in the preservation of large chondrocyte cells. Also, as with Euphanerops, there is no prismatic cartilage preserved, making an affinity with the chondrichthyans most unlikely. Reinterpretation of the chondrocranium suggests that the posterior region is particularly informative: the first few anterior rounded vertebrae differ substantially from the more posterior, and are interpreted as unfused occipital segments. The ‘cranial ribs’, extending along either side of these occipital segments, are reinterpreted as elongated parachordals. This results in an elongated occipital region posterior to the otic capsules, a characteristic also seen in osteostracans such as Norselaspis. However, the occiput is fused in Norselaspis, and the lack of fusion of the occipital region in Palaeospondylus is more similar to the condition in Heterostraci.
London 2020