Temporal range: Late Devonian, 380Ma
|Reconstruction of P. rhombolepis|
Panderichthys is a monospecific genus of extinct sarcopterygian (lobe-finned fish) from the late Devonian period, about 380 Mya of Latvia. Panderichthys, which was recovered from Frasnian (early Late Devonian) deposits in Latvia, is represented by two species. P. stolbovi is known only from some snout fragments and an incomplete lower jaw. P. 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. It is named after the German-Baltic paleontologist Christian Heinrich Pander.
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.
Recent reexamination of existing Panderichthys fossils using a CT scanner shows four very clearly differentiated distal radial bones at the end of the fin skeletal structure. These finger-like bones do not show joints and they are quite short, but nonetheless show an intermediate form between fully fish-like fins and tetrapods.
In January 2010, Nature reported well-preserved and "securely dated" tetrapod tracks from Polish marine tidal flat sediments approximately 397 million years old. Therefore, Panderichthys can only be a "late-surviving relic", showing traits that evolved during the transition from fish-like creatures to tetrapods, but whose date does not reflect that transition. The tracks "force a radical reassessment of the timing, ecology and environmental setting of the fish–tetrapod transition, as well as the completeness of the body fossil record."
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).
- Murphy, Dennis C. "Panderichthys spp.". Devonian Times. Retrieved 21 February 2015.
- Niedzwiedzki, G., Szrek, P., Narkiewicz, K., Narkiewicz, M and Ahlberg, P., Nature 463(7227):43–48, 2010, Tetrapod trackways from the early Middle Devonian period of Poland, 7 January 2010.
- Editor's summary: Four feet in the past: trackways pre-date earliest body fossils. Nature 463.