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Palaeospondylus
Extinct genus of vertebrates From Wikipedia, the free encyclopedia
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Palaeospondylus ("early vertebra") is a prehistoric fish, a fossil vertebrate. Its fossils were originally described from the Achanarras slate quarry in Caithness, Scotland, and a second species has been discovered in Australia.[1]
The Scottish fossil as preserved is carbonised, and indicates an eel-shaped animal up to 6 centimetres (2 in) in length. The skull, which must have consisted of hardened cartilage, exhibits pairs of nasal and auditory capsules, with a gill apparatus below its hinder part, and ambiguous indications of ordinary jaws.[citation needed]
The phylogeny of this fossil has puzzled scientists since its discovery in 1890, and many taxonomies have been suggested. In 2004, researchers proposed that Palaeospondylus was a larval lungfish.[2] Previously, it had been classified as a larval tetrapod, unarmored placoderm, an agnathan, an early stem hagfish, and a Chimaera.[3][4] A 2017 study suggested that it was a stem chondrichthyan.[5]
In 2022, researchers reported, based on studies using synchrotron radiation X-ray micro-computed tomography, that the neurocranium of Palaeospondylus was similar to those of the stem-tetrapods Eusthenopteron and Panderichthys, and concluded that Palaeospondylus was between those two phylogenetically.[6] Brownstein (2023) criticized this study, suggesting it would be basal gnathostomes instead.[7] Hirasawa and Kuratani, who are authors in 2022 study, replied to that and reviewed phylogeny again, resulted it would be closer to Acanthostega instead.[8] The 2024 study, using braincase data, ruled out the tetrapod hypothesis.[1]
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Species
- Palaeospondylus australis, early Devonian, Australia
- Palaeospondylus gunni, middle Devonian, Scotland
See also
References
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