Labyrinthodontia having limbs provided with digits, but retaining posterior flanges on axial bones as in Rhipidistia, without joint-structure at elbow and wrist essential for terrestrial locomotion; neurocranium having separate otico-occipital section, large notochordal canal, no occipital condyle, as in Rhipidistia; nares separate from rim of mouth; pectoral girdle anthracosaurian; vertebrae having U-shaped intercentrum and paired, but large, pleurocentra.
Labyrinthodontia having limbs provided with digits, but retaining posterior flanges on axial bones as in Rhipidistia, without joint-structure at elbow and wrist essential for terrestrial locomotion; neurocranium having separate otico-occipital section, large notochordal canal, no occipital condyle, as in Rhipidistia; nares separate from rim of mouth; pectoral girdle anthracosaurian; vertebrae having U-shaped intercentrum and paired, but large, pleurocentra.
Probably associated with the characters of the order, as given above, are the connection of pectoral girdle with skull, and the presence of a tympanic membrane, the stapes functioning in both sound-transmission and palatoquadrate suspension.
Orbits and foramen magnum unusually large in correlation with reduced size of animal; squamosal forming posterior margin of orbit; circumorbital series absent (except for postorbital); sensory pits on squamosal and frontal.
Orbits and foramen magnum unusually large in correlation with reduced size of animal; squamosal forming posterior margin of orbit; circumorbital series absent (except for postorbital); sensory pits on squamosal and frontal.
Characters defining the family are evidently the more specialized cranial features, which probably evolved during Mississippian and early Pennsylvanian times.
The definition of the genus and species may be left to rest upon Peabody's (1958) original description and the present account, until the discovery of other members of the family gives reason for making further distinctions.
Hesperoherpeton garnettensePeabody (1958), based on a scapulocoracoid and part of a vertebra, was originally placed in the order Anthracosauria, suborder Embolomeri, family Cricotidae. A new skeleton from the type locality near Garnett, Kansas (Rock Lake shale, Stanton formation, Upper Pennsylvanian), shows that the animal has the following rhipidistian characters: Large notochordal canal below foramen magnum, otico-occipital block separate from ethmosphenoid, postaxial processes on three axial bones of forelimb, pectoral girdle (probably) articulated with tabular. Nevertheless,Hesperoherpetonhas short digits, an anthracosaurian type of pectoral girdle, an otic rather than spiracular notch, nostrils separate from the mouth, and vertebrae in which the intercentrum is U-shaped and the pleurocentra large but paired. The stapes reaches the quadrate.
Hesperoherpetonis placed in a new order, PLESIOPODA, on the basis of the characters stated above, and a new family, HESPEROHERPETONIDAE. Specialized characters of the family include: Reduction of circumorbital bones, bringing the squamosal to the edge of the orbit, loss of certain bones of the temporal region, and relative enlargement of the orbits and foramen magnum, in correlation with the diminutive size of the animal. The structural characters ofHesperoherpetonsuggest to us that it lived in the shallow, weedy margins of lagoons, rested with its head partly out of water, and normally did not walk on land.
Eaton, T. H., Jr.1951. Origin of tetrapod limbs. Amer. Midl. Nat., 46: 245-251.Jarvik, E.1952. On the fish-like tail in the ichthyostegid stegocephalians. Meddel. om Grønland, 114: 1-90.1954. On the visceral skeleton inEusthenopteronwith a discussion of the parasphenoid and palatoquadrate in fishes. Kgl. Svenska Vetenskapsakad. Handl., 5: 1-104.1955. The oldest tetrapods and their forerunners. Sci. Monthly, 80: 141-154.Moore, R. C.,Frye, J. C., andJewett, J. M.1944. Tabular description of outcropping rocks in Kansas. Kansas State Geol. Surv. Bull., 52: 137-212.Peabody, F. E.1952.Petrolacosaurus kansensisLane, a Pennsylvanian reptile from Kansas. Univ. Kansas Paleont. Contrib., Vertebrata, Art. 1: 1-41.1958. An embolomerous amphibian in the Garnett fauna (Pennsylvanian) of Kansas. Jour. Paleont., 32: 571-573.Romer, A. S.1937. The braincase of the Carboniferous crossopterygianMegalichthysnitidus. Mus. Comp. Zool. Bull., 82: 1-73.1947. Review of the Labyrinthodontia. Mus. Comp. Zool. Bull., 99: 1-368.1957. The appendicular skeleton of the Permian embolomerous amphibianArcheria. Univ. Michigan Contrib. Mus. Paleont., 13: 103-159.Watson, D. M. S.1926. The evolution and origin of the Amphibia. Phil. Trans. Roy. Soc. London, (B) 214: 189-257.
Transmitted January 13, 1960.
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