''Palaeospondylus'' is a fish-like fossil vertebrate. Its fossils are described from the Achanarras slate quarry in

Caithness Caithness ( gd, Gallaibh ; sco, Caitnes; non, Katanes) is a historic county, registration county and lieutenancy area of Scotland. Caithness has a land boundary with the historic county of Sutherland to the west and is otherwise bounded by ...

, Scotland. The fossil as preserved is carbonized, and indicates an

eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...

-shaped animal up to 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. 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. Previously, it had been classified as a larval

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct therapsid ...

, unarmored placoderm, an

agnatha Agnatha (, Ancient Greek 'without jaws') is an infraphylum of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present ( cyclostomes) and extinct (conodonts and ostracoderms) species. Among recent animals, cyclostom ...

n, an early stem hagfish, and a

chimera Chimera, Chimaera, or Chimaira (Greek for "she-goat") originally referred to: * Chimera (mythology), a fire-breathing monster of Ancient Lycia said to combine parts from multiple animals * Mount Chimaera, a fire-spewing region of Lycia or Cilicia ...

. A 2017 study suggested that it was a stem

chondrichthyan Chondrichthyes (; ) is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed of bone tissue. ...

. In 2022, researchers report, based on studies using synchrotron radiation X-ray micro-computed tomography, that the

neurocranium In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...

of ''Palaeospondylus'' was similar to those of the stem-tetrapods '' Eusthenopteron'' and '' Panderichthys'', and concluded that ''Palaeospondylus'' was between those two phylogenetically.

References

* {{Taxonbar, from=Q3889332 Prehistoric vertebrate genera Devonian animals of Europe Prehistoric vertebrates of Europe Fossils of Scotland Caithness History of the Scottish Highlands Devonian genus extinctions

See also

References