Volume 12, No. 2, pp. 155-180, 10 figs. -----------July 10, 1959-----------...

University of Kansas Lawrence 1959 University of Kansas Publications, Museum of Natural History Editors: E. Raymond Hall, Chairman, Henry S. Fitch, Robert W. Wilson Volume 12, No. 2, pp. 155-180 Published July 10, 1959 University of Kansas Lawrence, Kansas PRINTED IN THE STATE PRINTING PLANT TOPEKA, KANSAS 1959 27-8362 BY THEODORE H. EATON, JR....

In trying to determine the ancestral relationships of modern orders of Amphibia it is not possible to select satisfactory structural ancestors among a wealth of fossils, since very few of the known fossils could even be considered possible, and scarcely any are satisfactory, for such a selection. The nearest approach thus far to a solution of the problem in this manner has been made with reference to the Anura. Watson's paper (1940), with certain modifications made necessary by Gregory (1950), p

In both Anura and Urodela the skull is short, broad, relatively flat, with reduced pterygoids that diverge laterally from the parasphenoids leaving large interpterygoid vacuities, and with large orbits. (These statements do not apply to certain larval or perennibranchiate forms.) The skull in both orders has lost a number of primitive dermal bones in the posterior part; these are: basioccipital, supraoccipital, postparietal, intertemporal, supratemporal, and tabular. The exoccipitals form the tw

Abbreviations Used in Figures In temnospondylous Amphibia the tympanum generally occupied an otic notch, at a high level on the skull, bordered dorsomedially by the tabular and ventrolaterally by the squamosal. In this position the tympanum could receive airborne sounds whether the animal were entirely on land or lying nearly submerged with only the upper part of its head exposed. Among those Anura in which the ear is not reduced the same is true, except that the tabular is lost. In Temnospondyl

Development of the vertebrae and ribs of Recent Amphibia has been studied by Gamble (1922), Naef (1929), Mookerjee (1930 a, b), Gray (1930) and Emelianov (1936), among others. MacBride (1932) and Remane (1938) provide good summaries. In this section reference will be made to the embryonic vertebral cartilages by the names used for them in these studies, although the concept of "arcualia" is currently considered of little value in comparative anatomy. The centrum in Anura (Fig. 5) is formed in th

Hecht and Ruibal (Copeia, 1928:242) make a strong point of the nature of the pectoral girdle in Notobatrachus , as described recently by Stipanicic and Reig (1955, 1956) from the Jurassic of Patagonia, and quite rightly recommend that the significance of the arciferal and firmisternal types of girdle be restudied. That of Notobatrachus is said to be firmisternal; in view of the arciferal condition in the supposedly primitive Leiopelma , Ascaphus , Bombinator , etc., this comes as a surprise. Is

In Ascaphus (Ritland, 1955a; cleared and stained specimens of nearly grown males) distal carpals 1, 2, 3 and 4 are present and separate, increasing in size in the order given (Fig. 9). A prepollex rests against centrale 1; centralia 2 and 3 are fused; the radiale fuses with centrale 4, and the intermedium fuses with the ulnare; radius and ulna are fused with each other as in other frogs. The digits (and metacarpals) are considered by Ritland to be 1-4, in addition to the prepollex, rather than 2

Considering the postembryonic developmental stages of modern Amphibia, there can be no doubt that a gill-bearing, four-legged larva of a salamander, in which lateral line pores and a gular fold are present, represents much more closely the type of larva found in labyrinthodonts than does the limbless, plant-nibbling tadpole of the Anura. Salamander-like larvae of labyrinthodonts are well known, especially those formerly supposed to comprise the order Branchiosauria. Many, perhaps the majority of

The Anura probably originated among temnospondylous labyrinthodonts, through a line represented approximately by Eugyrinus , Amphibamus , and the Triassic frog Protobatrachus , as shown by Watson, Piveteau and others. The known Paleozoic lepospondyls do not show clear indications of a relationship with Urodela, but Lysorophus may well be on the ancestral stem of the Apoda. Between Urodela and Anura there are numerous resemblances which seem to indicate direct relationship through a common stock:

Broom, R. 1918. Observations on the genus Lysorophus Cope. Ann. Mag. Nat. Hist., (9)2:232-239. Bystrow, A. P. 1938. Dvinosaurus als neotenische Form der Stegocephalen. Acta Zool., 19:209-295. Case, E. C. 1935. Description of a collection of associated skeletons of Trimerorhachis . Contrib. Mus. Pal. Univ. Michigan, 4:227-274. Cope, E. D. 1889. The Batrachia of North America. Bull. U. S. Nat. Mus., 34:1-525. de Beer, G. R. 1937. The development of the vertebrate skull. Pp. xxiii + 552. Oxford, Cl