panderichthys skeleton

Panderichthys spp.

Panderichthys, which was recovered from Frasnian (early Late Devonian) deposits in Latvia, is represented by two species. Panderichthys stolbovi is known only from some snout fragments and an incomplete lower jaw. Panderichthys rhombolepis is known from several more complete specimens. Although it probably belongs to a sister group of the earliest tetrapods, Panderichthys exhibits a range of features transitional between tristichopterid lobe-fin fishes (e.g., Eusthenopteron) and early tetrapods.

Panderichthys is a 90-130 cm long fish with a large tetrapod-like head that's flattened, narrow at the snout and wide in the back. The inter-cranial joint, which is characteristic of most lobe-fin fishes, has been lost from the external elements of the skull, but is still present in the braincase. The patterns of external bones in the skull roof and cheeks are more similar to those of early tetrapods than those of other lobe-fins.

The transitional qualities of Panderichthys are also evident in the rest of the body. It lacks the dorsal and anal fins and its tail is more like those of early tetrapods than the caudal fins of other lobe-fins. The shoulders exhibits several tetrapod-like features, while the humerus is longer than those found in other lobe-fins. On the other hand, the distal parts of the front fins are unlike those of tetrapods. As would be expected from a fin, there are numerous lepidotrichs (long and thin fin rays). The distal fin also has a plate of fused bones instead of the ulnare, intermedium, and digits (or radials) found in tetrapods. The endoskeleton of the pelvic fins are not known. The vertebral column is ossified throughout its length and the vertebrae are comparable to those of early tetrapods.

Panderichthys was collected in deposits that were formerly believed to be from a calm freshwater basin, but may prove to be from shallow tidal flats or an estuary. Associated vertebrates include an armored jawless fish (Psammolepis), two placoderms (Asterolepis and Plourdosteus), an unidentified acanthodid acanthodian a porolepiform lobe-fin (Laccognathus), a lungfish (Dipterus), and another elpistostegalian (Livoniana)

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Web:
G.R. Morton's Transitional Forms: Fish to Amphibian:
home.entouch.net/dmd/transit.htm
Books:
Clack, J. A. 2002 Gaining Ground: the origin and evolution of tetrapods.  Indiana University Press: Bloomington.
Janvier, P. 1996. Early Vertebrates. Claredon Press: Oxford.
Long, J.A. 1995. The Rise of Fishes: 500 Million Years of Evolution. John Hopkins Univ. Press. Baltimore and London.
Maisey, J.G. 1996. Discovering Fossil Fishes. Henry Holt & Co: New York.
Scientific Papers
Ahlberg, P. E., Clack, J. A. & Lukésevics, E. 1996: "Rapid braincase evolution between Panderichthyes and the earliest tetrapods." Nature 381(2): 61-64.
Schultze, H.P and M. Arsenault. 1985. "The panderichthyid fish Elpistostege: a close relative of tetrapods?" Paleontology 28: 293-309.
Vorobyeva 1980. "Observations on two rhipidistian fishes from the Upper Devonian of Lode, Latvia." Zool. J. Limn. Soc. 70(2): 191-201.
Vorobyeva, E.I. and H.P.Schultze. 1991. "Description and sytematics of panderichthyid fishes with comments on ther relationship to tetrapods." pp. 68-109. In: H.P. Schultze and L. Treub (eds.). Origins of the higher groups of tetrapods. Controversy and consensus. Cormstock, Ithaca.

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