Biology:Palaeospondylus
- †Palaeospondylus australis Burrow et al., 2024
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Palaeospondylus ("early vertebra") is an extinct genus of fish described from fossils found in both the Achanarras slate quarry of Caithness, Scotland, and the Cravens Peak Beds of Queensland, Australia.[1]
It lived during the Early and Middle Devonian epochs, around 400 to 390 million years ago.[1]
Description
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.[2]
A fossilized braincase that belonged to P. australis showed that Palaeospondylus lacked both a postorbital process and an intracranial joint, contrary to earlier interpretations.[1]
Phylogeny
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.[3] Previously, it had been classified as a larval tetrapod, unarmored placoderm, an agnathan, an early stem hagfish, and a chimaera.[4][5] A 2017 study suggested that it was a stem chondrichthyan.[6]
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.[7] Brownstein (2023) criticized this study, suggesting it would be basal gnathostomes instead.[8] Hirasawa and Kuratani, who are authors in 2022 study, replied to that and reviewed phylogeny again, resulted it would be closer to Acanthostega instead.[9] The 2024 study, using braincase data, ruled out the tetrapod hypothesis, and instead placed Palaeospondylus as either the sister group of Chondrichthyes or as a member of the gnathostome stem-group.[1]
See also
- Georgina Basin
- Orcadian Basin
References
- ↑ 1.0 1.1 1.2 1.3 Cite error: Invalid
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This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed (1911). "Palaeospondylus". Encyclopædia Britannica (11th ed.). Cambridge University Press.
- ↑ Thomson, K.S. (2004). "A Palaeontological Puzzle Solved?". American Scientist 92 (3): 209–211. doi:10.1511/2004.47.3425.
- ↑ Palmer, D., ed (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 33. ISBN 1-84028-152-9.
- ↑ Hirasawa, T; Oisi, Y; Kuratani, S (2016). "Palaeospondylus as a primitive hagfish". Zoological Letters 2 (1): 20. doi:10.1186/s40851-016-0057-0. PMID 27610240.
- ↑ Johanson, Zerina; Smith, Moya; Sanchez, Sophie; Senden, Tim; Trinajstic, Kate; Pfaff, Cathrin (2017). "Questioning hagfish affinities of the enigmatic Devonian vertebrate Palaeospondylus". Royal Society Open Science 4 (7). doi:10.1098/rsos.170214. PMID 28791148. Bibcode: 2017RSOS....470214J.
- ↑ Hirasawa, Tatsuya (25 May 2022). "Morphology of Palaeospondylus shows affinity to tetrapod ancestors". Nature 50 (7912): 109–112. doi:10.1038/s41586-022-04781-3. https://www.nature.com/articles/s41586-022-04781-3. Retrieved 25 May 2022.
- ↑ Brownstein, Chase Doran (2023). "Palaeospondylus and the early evolution of gnathostomes" (in en). Nature 620 (7975): E20–E22. doi:10.1038/s41586-023-06434-5. ISSN 1476-4687. https://www.nature.com/articles/s41586-023-06434-5.
- ↑ Hirasawa, Tatsuya; Kuratani, Shigeru (2023). "Reply to: Palaeospondylus and the early evolution of gnathostomes" (in en). Nature 620 (7975): E23–E24. doi:10.1038/s41586-023-06435-4. ISSN 1476-4687. https://www.nature.com/articles/s41586-023-06435-4.
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