Palaeospondylus

Palaeospondylus
Temporal range: Middle Devonian
Fossil on display at the Cincinnati Museum Center
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Subphylum:
Vertebrata
Infraphylum:
Agnatha?
Genus:
Palaeospondylus

Traquair, 1890
Species:
P. gunni
Binomial name
Palaeospondylus gunni
Traquair, 1890

Palaeospondylus ("early vertebrae") is a prehistoric fish, a fossil vertebrate. Its fossils are described from the Achanarras slate quarry in Caithness, Scotland.

The fossil as preserved is carbonized, 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.[1] Previously, it had been classified as a larval tetrapod, unarmored placoderm, an agnathan, an early stem hagfish, and a chimera.[2][3] A 2017 study suggested that it was a stem chondrichthyan.[4]

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.[5] Brownstein (2023) criticized this study, suggesting it would be basal gnathostomes instead.[6] Hirasawa and Kuratani, who are authors in 2022 study, replied to that and reviewed phylogeny again, resulted it would be closer to Acanthostega instead.[7]

  1. ^ Thomson, K.S. (2004). "A Palaeontological Puzzle Solved?". American Scientist. 92 (3): 209–211. doi:10.1511/2004.47.3425. JSTOR 27858385.
  2. ^ Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 33. ISBN 1-84028-152-9.
  3. ^ 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.
  4. ^ 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.
  5. ^ 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.
  6. ^ 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.
  7. ^ 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.