University of Kansas Publications
Museum of Natural History
Volume 12, No. 2, pp. 155-180, 10 figs.
-----------July 10, 1959-----------
The Ancestry of Modern Amphibia:
A Review of the Evidence
BY
THEODORE H. EATON, JR.
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
[Transcriber's Notes: Several typos have been regulated.
One typo of "ancester" for "ancestor" was corrected.
One instance of "salamanderlike" corrected to "salamander-like".
The captions on some images give relative size. Due to differences in monitor size/resolution, do notconsider the images to be scalable.]
The Ancestry of Modern Amphibia:
A Review of the Evidence
BY
THEODORE H. EATON, JR.
INTRODUCTION
In trying to determine the ancestral relationships of modern orders ofAmphibia it is not possible to select satisfactory structural ancestorsamong a wealth of fossils, since very few of the known fossils couldeven be considered possible, and scarcely any are satisfactory, for sucha selection. The nearest approach thus far to a solution of the problemin this manner has been made with reference to the Anura. Watson's paper(1940), with certain modifications made necessary by Gregory (1950),provides the paleontological evidence so far available on the origin offrogs. It shows that several features of the skeleton of frogs, such asthe enlargement of the interpterygoid spaces and orbits, reduction ofthe more posterior dermal bones of the skull, and downward spread of theneural arches lateral to the notochord, were already apparent in thePennsylvanian Amphibamus (Fig. 1), with which Gregory synonymizedMiobatrachus and Mazonerpeton. But between the Pennsylvanian and theTriassic (the age of the earliest known frog, Protobatrachus) therewas a great lapse of time, and that which passed between any conceivablePaleozoic ancestor of Urodela and the earliest satisfactoryrepresentative of this order (in the Cretaceous) was much longer still.The Apoda, so far as known, have no fossil record.
Nevertheless it should be possible, first, to survey those characters ofmodern Amphibia that might afford some comparison with the earlyfossils, and second, to discover among the known Paleozoic kinds thosewhich are sufficiently unspecialized to permit derivation of the modernpatterns. Further circumstantial evidence may be obtained by examiningsome features of Recent Amphibia which could not readily be comparedwith anything in the fossils; such are the embryonic development of thesoft structures, including cartilaginous stages of the skeleton, thedevelopment and various specializations of the ear mechanism, adaptivecharacters associated with aquatic and terrestrial life, and so on.[Pg 158]