Chapter V

THE AMPHIBIA OF THE DEVONIAN AND MISSISSIPPIAN OF NORTH AMERICA.

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).

This still remains after nearly 20 years the only evidence of air-breathing vertebrates in the Devonian of the world.

=Dromopus aduncus Branson.=

Branson, Jour. Geol., XVIII, No. 4, pp. 356-358, fig. 1, 1910.

Type and other specimens in Oberlin College Museum.

Horizon and type locality: Near the bottom of the Hinton formation in Giles County, Virginia. (Plate 18, fig. 3.)

The following description of the shales and footprints are from Dr. Branson's paper cited above:

"The Hinton shales, like the Mauch Chunk, seem to have been subaerial
in origin and are made up for the most part of variegated shales
interbedded with thin layers of argillaceous, fine-grained sandstone.
The footprints occur in fine-grained sandstone, and remains of land
plants are not uncommon in the same beds.

"Twenty-two footprints made by one animal walking in a straight
course were collected in a slab. They give the impression of having
been made by a bipedal animal for part of the distance, but after the
fourth print of the right foot impressions of the forefeet appear. The
hindfeet had 5 digits, the middle digit being longest and the 2 inside
of it being only slightly shorter and lying close together. Their
outer ends were slender and flexible and usually curved inward toward
the middle toe. The 2 outer digits formed wide angles with the middle
one and were shorter than the inner ones. The second toe was webbed to
within 8 mm. of the tip, the third toe to within 23 mm. of the tip.
The impression of the web is well preserved in only one impression of
the hindfoot.

"The forefeet had 4 digits. The 3 inner digits were subequal in
length, the 2 inner being more flexible and incurved near the ends.
The outer digit is two-thirds as long as the second. The webbing
extends about half the length of the digits. The heel impression is
broader than that of the hindfoot.

"Measurements of _Dromopus aduncus_ Branson.

Tip of toe to tip of toe in first prints 21 cm.
After appearance of forefeet the impressions are the following
distances apart: 165 mm., 40 mm., 85 mm., 70 mm., 80 mm., 40 mm.,
150 mm., then back to 20 and 21 cm.

mm.
Length of hindfeet 60
Width of hindfeet 20 to 25
Length of forefeet 45"