Palaeospondylus

Palaeospondylus Temporal range: Middle Devonian PreꞒ Ꞓ O S D C P T J K Pg N
Fossil on display at the Cincinnati Museum Center
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Infraphylum:	Agnatha?
Genus:	Palaeospondylus Traquair, 1890
Type species
Palaeospondylus gunniTraquair, 1890

Palaeospondylus ("early vertebrae") 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 ]}

Artist's reconstruction of Palaeospondylus as an agnathan.

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]

Species

• Palaeospondylus australis, early Devonian, Australia
• Palaeospondylus gunni, middle Devonian, Scotland

See also

• Paleontology portal

• Orcadian Basin

References

1. Carole J Burrow, Gavin C Young, Jing Lu (2024), "A 3D braincase of the early jawed vertebrate Palaeospondylus from Australia", National Science Review, doi:10.1093/nsr/nwae444
2. Thomson, K.S. (2004). "A Palaeontological Puzzle Solved?". American Scientist. 92 (3): 209–211. doi:10.1511/2004.47.3425. JSTOR   27858385.
3. Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 33. ISBN   1-84028-152-9.
4. Hirasawa, T; Oisi, Y; Kuratani, S (2016). "Palaeospondylus as a primitive hagfish". Zoological Letters. 2 (1): 20. doi: 10.1186/s40851-016-0057-0 . PMC   5015246 . PMID   27610240.
5. 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): 170214. Bibcode:2017RSOS....470214J. doi:10.1098/rsos.170214. PMC   5541543 . PMID   28791148.
6. Hirasawa, Tatsuya; et al. (25 May 2022). "Morphology of Palaeospondylus shows affinity to tetrapod ancestors". Nature . 50 (7912): 109–112. doi:10.1038/s41586-022-04781-3 . Retrieved 25 May 2022.
7. Brownstein, Chase Doran (2023). "Palaeospondylus and the early evolution of gnathostomes". Nature. 620 (7975): E20 –E22. doi:10.1038/s41586-023-06434-5. ISSN   1476-4687.
8. Hirasawa, Tatsuya; Kuratani, Shigeru (2023). "Reply to: Palaeospondylus and the early evolution of gnathostomes". Nature. 620 (7975): E23 –E24. doi:10.1038/s41586-023-06435-4. ISSN   1476-4687.

•  This article incorporates text from a publication now in the public domain :  Chisholm, Hugh, ed. (1911). "Palaeospondylus". Encyclopædia Britannica (11th ed.). Cambridge University Press.