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Panderichthys
''Panderichthys'' is a 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. A recent study uncovered tetrapod tracks dating back to before the appearance of ''Panderichthys'' in the fossil record, which suggests that ''Panderichthys'' is not a transitional fossil, but nonetheless shows the traits that evolved during the fish-tetrapod evolution 〔
==Geological and environmental information==
''Panderichthys'' was alive during the late Devonian (Frasnian) in Lode, Latvia. Lode is known to be a marginal marine environment and it has been hypothesized that ''Panderichthys'' was adapted for movement in shallow and debris filled waters.〔Clack, Jennifer A. "Devonian climate change, breathing, and the origin of the tetrapod stem group." Integrative and Comparative Biology 47.4 (2007): 510-523.〕 ''Panderichthys'' was collected in deposits that were formerly believed to be from a calm freshwater basin, but have proven to be from shallow tidal flats or an estuary. The Lode Formation, where ''P. rhombolepis'' was found, occurs within a 200 meter thick layer composed of fine grained sandstone and clay along with finely dispersed clays. Nearly every major taxa of late Devonian vertebrates are represented within the Lode Formation. Most of the specimens are well preserved due to anaerobic substrate conditions as well as rapid burial in depressions on the submarine delta slopes. ''P. rhombolepis'' was discovered in the Gauja Regional formation within the lower Frasnian section. Taphocoenosis was characterized as in finely displaced clay and silty clay as well as low water activity. Within this environment it has been hypothesized that ''P. rhombolepis'' was a large predator and fed upon dipterids, small and juvenile sarcopterygians, and ''Latvius''.〔Upeniece, Ieva. Paleoecology and juvenile individuals of the Devonian ''Placoderm'' and ''Acanthodian'' fishes from Lode site, Latvia. Diss. University of Latvia, 2011.〕 Associated vertebrates found in the same deposits 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'').〔
During the Frasnian in which ''Panderichthys'' was extant, there was a drop in oxygen in the atmosphere as well as an increase in the abundance of plants. Due to the fact that oxygen is much less soluble in water than air, the decreased oxygen in the atmosphere would have caused the oxygen concentrations in the any type of water to decrease substantially. This in turn would have caused any aquatic animal that could breathe air to have an advantage and be more likely to thrive.〔 In addition to its ability to move in shallow water, ''Panderichthys'' could also breathe air. Its strong pectoral fins in theory could allow it to prop up its head in shallow water and take a breath. The enlargement of the spiracular chamber itself as well as its opening to the outside suggests that ''Panderichthys'' was part of a transition to an increased capacity for air breathing that was completed in tetrapods.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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