Palaeospondylus, An Enimatic Larval Fish from Devonian Scotland

Palaeospondylus gunni

Class Chondrichthyes; Palaeosponyliformes; Palaeospondylidae

Geological Time: Middle Devonian (385 Million Years Old)

Size: 15 mm

Fossil Site: Achanarras Slate Quarry, Caithness, Scotland

Palaeospondylus Devonian Fossil FishThis small fossil fish has been the cause of controversy since two cousins named Gunn first discovered it in 1890. It comes primarily from this single location, with a few found at two nearby locations as well. Not only is it Diminitive, but it has structures unlike that found on most other fish. It possesses a strange basket-like apparatus on its snout, a well-developed cartilaginous vertebral column (hence the generic name), but no apparent fins. A prominent feature of the head of every specimen is a pair of unusual rods termed the occipital lamellae. These are identical with the cranial ribs found on lungfish. The only lungfish so far known from these deposits is the 30-centimeter long Dipterus valenciennsi, for which the smallest examples are about 60 millimeters in length. If the rostral apparatus of Palaeospondylus is interpreted as a larval attachment organ, then it may well be the larva of Dipterus.

Recent studies seem to confirm Palaeospondylus to be a lungfish, but why is it so different in appearance from Dipterus? The current thinking is that it underwent a sharp metamorphosis, rather than a gradual transition from juvenile to adult. Some researchers prefer to attribute the anterior attachment organ with those of lampreys, arguing for Palaeospondylus as a parasite. Whichever the case: oldest known fossil vertebrate larva or oldest known vertebrate parasite, Palaespondylus gunni is a unique example of the early lives of fish on this planet.

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