Type Species: Koskinonodon (= Buettneria) perfectum (Case, 1922)
Other Species: Koskinonodon (= Buettneria) bakeri (Case, 1931)
Systematic Paleontology:
Amphibia Linnaeus, 1758
Labyrinthodontia von Meyer, 1842
Temnospondyli Zittel, 1887-1890
Metoposauroidea Save-Soderbergh, 1935
Metoposauridae Watson, 1919
Koskinonodon Branson and Mehl, 1929
Koskinonodon perfectum (Case, 1922)
Synonyms:
Buettneria perfecta Case, 1922)
Koskinonodon princeps Branson and Mehl, 1929
Buettneria howardensis Sawin, 1945
Buettneria calgariensis Green, 1954
Buettneria major Branson and Mehl, 1929
Borborophagus wyomingensis Branson and Mehl, 1929
Eupelor fraasi jonesi Colbert and Imbrie, 1956
Eupelor fraasi fraasi Colbert and Imbrie, 1956
Eupelor browni Colbert and Imbrie, 1956
Metoposaurus jonesi Case, 1920
Metoposaurus fraasi jonesi Roy Chowdhury, 1965
Metoposaurus fraasi fraasi Roy Chowdhury, 1965
Metoposaurus browni Roy Chowdhury, 1965
Metoposaurus maleriensis Roy Chowdhury, 1965
Type Specimen: UMMP 7475, skull
Figures: Case 1922 Figs. 1-3, pl. 1-2
Type Locality: Breaks of Sand Creek, just south of Cedar Mountain, Crosby County, Texas
Type Horizon and Age: Tecovas Formation, Dockum Group. Late Triassic.
Distribution: Chinle Formation, Arizona and New Mexico; Dockum Group, Texas and New Mexico; Popo Agie Formation, Wyoming; Maleri Formation, India.
Referred Specimens: Numerous. See Long and Murry (1995) for an almost complete listing.
Note: Hunt (1993:79) referred a single skull (NHM 37938) from the Schilfsandstein of Germany to Koskinonodon perfectum. However, Sulej (2002) argues that this specimen is not referable to K. perfectum and therefore that this taxon does not occur in Europe.
Diagnosis: (Hunt, 1993) Metoposaurid that differs from other members of the family in possessing a lachrymal entering the margin of the orbit. (Note: Sulej (2002) demonstrates that this character is not useful for diagnosing Koskinonodon from Metoposaurus.) Koskinonodon and Apachesaurus differ from Metoposaurus in possessing an interclavicle with an enlarged area of rounded pits at the center of the element. Koskinonodon differs from Apachesaurus in possessing a lacrymal that enters the margin of the orbit (Hunt, 1993; Long and Murry, 1995; Sulej, 2002).
Discussion: Koskinonodon perfectum is a large metoposaurid previously referred to the genus Buettneria, which was discovered to be preoccupied (Mueller, submitted). It has an average skull length of about 65 centimeters. Koskinonodon represents one of the last of the labyrinthodont amphibians, which were extremely common worldwide during the late Paleozoic Era but became extinct at the end of the Triassic Period. Koskinonodon is extremely common in Carnian age sediments and may extend into the Norian as well. At Petrified Forest National Park Koskinonodon is one of the most common animals recovered from the Blue Mesa area where bonebeds of these animals occur. The most common elements recovered from these animals are the skulls and pectoral elements such as clavicles and interclavicles. Vertebrae are less common but do occur. Other parts of the postcrania such as the limbs are extremely rare. It appears that the limbs were weak in this aquatic animal and may not have completely ossified making preservation scarce. The skull on display at the Rainbow Forest Museum was collected from the Devil’s Playground area by Park Naturalist Myrl Walker in the 1930’s.
Judging by the weak axial skeleton and intact lateral line system of the skull, Koskinonodon was most likely a fully aquatic form. This animal possesses sharp, conical (labyrinthodont) teeth and most likely fed mainly on fish and other small aquatic forms. Upwards facing orbits (eye sockets) suggest that Koskinonodon was an ambush predator, waiting in the soft mud at the bottom of ponds and attacking prey suddenly from below.
The first metoposaurid material from Arizona was collected by Barnum Brown near Cameron (Ward Bonebed) in 1901 and was described by Lucas (1904) as Metoposaurus fraasi. The holotype consists of an interclavicle (USNM 2152) that may be referable to K. perfectum (Long and Murry, 1995), however Hunt (1993) and Sulej (2002) consider this taxon a nomen dubium.
Koskinonodon bakeri (Case, 1931)
Synonyms:
Buettneria bakeri Case, 1931
Eupelor fraasi jonesi Colbert and Imbrie, 1956
Metoposaurus fraasi jonesi Roy Chowdhury, 1965
Metoposaurus bakeri Baird, 1986
Metoposaurus bakeri Hunt, 1993
Metoposaurus bakeri Long and Murry, 1995
Type specimens: Holotype: UMMP 13055, nearly complete skull. Paratypes: UMMP 14154, partial skull; UMMP 14098, partial skull.
Figures: Case (1931) figs. 1-2, pl. 1
Type locality: Elkins Place Bonebed, 23 miles north of Snyder, Scurry County, Texas.
Horizon and age: “Camp Springs Formation”, Dockum Group. Late Triassic.
Note: Other workers (e. g. Lehman, Chatterjee) have argued that this horizon represents the Cooper Canyon Formation.
Distribution: Dockum Group, Texas; Fundy Basin, Newark Supergroup, Nova Scotia (Baird, 1986).
Referred specimens: UMMP 12946, right femur; UMMP 13027, interclavicle; UMMP 13028, clavicle; UMMP 13029, interclavicle; UMMP 13055, skull; UMMP 13820, skull; UMMP 13823, skull; UMMP 13822, skull; UMMP 14098, skull; UMMP 14154, skull; UMMP 13596, skull; UMMP 14262, skull; MCZ 1054, skull; UMMP 13792, axis; UMMP 13824, clavicle; UMMP 13825, clavicle; UMMP 13903, clavicle; UMMP 13898, clavicle; YPM PU 21742, skull.
Diagnosis: (Case, 1931) K. bakeri is distinguished from K. perfectum by possessing more elongate pits in the frontal and postorbital regions, an incomplete sensory canal system, extension of the palatal vacuities anterior to the orbits, possessing a narrower and more elongate skull, which is of smaller adult size. (Hunt, 1993) K. bakeri can be distinguished from K. perfectum by the exclusion of the lacrymal from the orbit. Differs from Metoposaurus in possessing a more elongate lachrymal, and in lacking a long linear union of the clavicles anterior to the interclavicle.
Discussion: Koskinonodon bakeri is known mainly from the Dockum Group of Texas. E. C. Case excavated numerous specimens from the Elkins Place Bonebed in Scurry County, Texas from which he provided the original description (Case, 1931). A skull from the Newark Supergroup of Nova Scotia has also been referred to this taxon (Baird, 1986; Hunt, 1983). K. bakeri was assigned to the genus Metoposaurus by Hunt (1993) based on the presence of a lachrymal that did not enter the margin of the orbit. However, new material of Metoposaurus diagnosticus from Poland has shown that the lachrymal of Metoposaurus does indeed enter the margin of the orbit (Sulej, 2002). As a result, this taxon was referred back to Koskinonodon based on similarities of the pectrum to that of K. perfectum. Houle and Mueller (2004) have reported on the presence of K. bakeri from the Cooper Canyon (=Bull Canyon) Formation of Texas, although slight differences suggest that these specimens probably represent a subspecies.
References:
Baird, D., 1986. Some Upper Triassic reptiles, footprints, and an amphibian from New Jersey. The Mosasaur 3:125-153.
Branson, E. B., and M. G. Mehl, 1929. Triassic amphibians from the Rocky Mountain Region. University of Missouri Studies 4:155-239.
Case, E. C., 1920. On the perfect thoracic shield of a large labyrinthodont in the geological collections of the Museum of Zoology, University of Michigan. Occasional Papers of the Museum of Zoology, University of Michigan 82:1-3.
Case, E. C., 1922. New reptiles and stegocephalians from the Upper Triassic of Western Texas. Carnegie Institution of Washington Publication 321:1-84.
Case, E. C., 1931. Description of a new species of Buettneria with a discussion of the brain case. Contributions from the Museum of Paleontology, University of Michigan 3:187-206.
Case, E. C., 1932. A collection of stegocephalians from Scurry County, Texas. Contributions from the Museum of Paleontology, University of Michigan 4:1-56.
Colbert, E. H., and J. Imbrie, 1956. Triassic metoposaurid amphibians. Bulletin of the American Museum of Natural History 110:403-452.
Green, F. E., 1954. The Triassic deposits of northwestern Texas. PhD dissertation, Texas Tech University, 196p.
Houle, M., and B. Mueller, 2004. A new occurrence of Buettneria bakeri (Temnospondyli: Metoposauridae) from the Norian (Cooper Canyon Formation, Dockum Group) of West Texas. Journal of Vertebrate Paleontology 24(3):73A.
Hunt, A. P., 1989. Comments on the taxonomy of North American metoposaurs and a preliminary phylogenetic analysis of the Family Metoposauridae; pp. 293-300 in Dawn of the Age of Dinosaurs in the American Southwest, New Mexico Museum of Natural History.
Hunt, A. P., 1993. A revision of Metoposauridae (Amphibia: Temnospondyli) and description of a new genus. Museum of Northern Arizona Bulletin 59: 67-98.
Long, R. A., and P. A. Murry, 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4:18-23.
Lucas, F.A., 1904. A new batrachian and a new reptile from the Triassic of Arizona. Proceedings of the United States National Museum 27:193-195.
Roy Chowdhury, T. 1965. A new metoposaurid amphibian from the Upper Triassic Maleri Formation of Central India. Philosophical Transactions from the Royal Society, Series B 250:1-52.
Sawin, H. J., 1945. Ambians from the Dockum Triassic of Howard County, Texas. University of Texas Publication 4401:361-399.
Sulej, T., 2002. Species discrimination of the Late Triassic temnospondyl amphibian Metoposaurus diagnosticus. Acta Palaeontologica Polonica 47(3):535-546.
Wilson, J. A., 1941. An interpretation of the skull of Buettneria with reference to the cartilage and soft parts. Contributions from the Museum of Palaeontology, University of Michigan 6:71-111.
