Palaeospondylus
gunni
Chondrichthyes,
Palaeosponyliformes, Palaeospondylidae
Geological
Time: Middle Devonian (385 Million Years Old)
Size: 25
mm
Fossil Site:
Achanarras Slate Quarry, Caithness, Scotland
Description:
The small fossil fish here has been the cause of controversy since
it was first discovered in 1890 by two cousins named Gunn. It comes
primarily from this single location, with a few found at two nearby
locations as well. Not only is it minute in size, 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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