Evidences of the earliest land vertebrates are exceedingly scanty in the strata between the close of the Silurian and the opening of the Coal Measures, being represented solely by footprints. In the Devonian our knowledge of the group is confined to a single footprint, and in the Mississippian to series of footprints from several localities. These have been described by Lea ([371]), Rogers (Geology of Pennsylvania, pt. II, 1856, p. 831), Barrell ([21]), Dawson ([223]), and Branson ([50]). The last-named author has described a new species from the Mississippian of Giles County, Virginia. His description of the footprints, with a photograph of one of the series, are published herewith ([plate 18, fig. 3]). Branson ([50]) has given a résumé of the knowledge of Mississippian Amphibia in North America.
Thinopus antiquus Marsh, 1896.
Marsh, Am. Jour. Science, II, p. 374, Nov. 1896, with figure.
Type: Specimen No. 784, Yale University Museum.
Horizon: Near top of Chemung, in the upper Devonian.
[The] "specimen shows one vertebrate footprint in fair preservation, and with it part of another of the same series. These impressions are of much interest, both on account of their geological age and the size and character of the footprints themselves. The one best preserved [[fig. 12]] is nearly 4 inches in length, 2.25 inches in width, and was apparently made by the left hind foot. On the inner side in front of the heel, a portion of the margin is split off, and this may have contained the imprint of another toe. The other footprint was a short distance in front, but only the posterior portion is now preserved in the present specimen. It is probably the imprint of the forefoot.
"The specimen [[plate 18, fig. 4]] ... was ... found in the town of Pleasant, one mile south of the Allegheny River, Warren County, Pennsylvania, by Dr Charles E. Beecher, who presented it to Yale Museum, where it still remains.
"The geological horizon is near the top of the Chemung in the upper Devonian. In the same beds are ripple marks, mud cracks, and impressions of rain drops, indicating shallow water and shore deposits. Land plants are found in the same general horizon. Marine molluscs also occur, and one characteristic form (Nuculana) is preserved in the footprint slab" (Marsh).
