A slab of shale obtained in 1955 by Mr. Russell R. Camp from a
Pennsylvanian lagoon-deposit in Anderson County, Kansas, has yielded in
the laboratory a skeleton of the small amphibian _Hesperoherpeton
garnettense_ Peabody (1958). This skeleton provides new and surprising
information not available from the holotype, No. 9976 K. U., which
consisted only of a scapulocoracoid, neural arch, and rib fragment. The
new specimen, No. 10295 K. U., is of the same size and stage of
development as the holotype and it is thought that both individuals are
adults.
The quarry, University of Kansas Museum of Natural History Locality KAN
1/D, is approximately six miles northwest of Garnett, Anderson County,
Kansas, in Sec. 5, T. 19S, R. 19E, 200 yards southwest of the place
where _Petrolacosaurus kansensis_ Lane was obtained (see Peabody,
1952). The Rock Lake shale, deposited under alternately marine and
freshwater lagoon conditions, is a thin member of the Stanton limestone
formation, Lansing group, Missourian series, and thus is in the lower
part of the Upper Pennsylvanian.
Peabody (1958) placed _Hesperoherpeton_ in the order Anthracosauria,
suborder Embolomeri, family Cricotidae. Study of the second and more
complete specimen reveals that _Hesperoherpeton_ is unlike the known
Embolomeri in many important features. The limbs and braincase are more
primitive than those so far described in any amphibian. The vertebrae
are comparable to those of Ichthyostegalia (Jarvik, 1952), as well as
to those of Embolomeri. The forelimb is transitional between the
pectoral fin of Rhipidistia and the limb of early Amphibia. The pattern
of the bones of the forelimb closely resembles, but is simpler than,
that of the hypothetical transitional type suggested by Eaton (1951).
The foot seemingly had only four short digits. The hind limb is not
known.
The new skeleton of _Hesperoherpeton_ lies in an oblong block of limy
shale measuring approximately 100 x 60 mm. After preparation of the
entire lower surface, the exposed bones and matrix were embedded in
Bioplastic, in a layer thin enough for visibility but giving firm
support. Then the specimen was inverted and the matrix removed from the
opposite side; this has not been covered with Bioplastic. The bones lie
in great disorder, except that some parts of the roof of the skull are
associated, and the middle section of the vertebral column is
approximately in place. The bones of the left forelimb are close
together but not in a natural position. The tail, pelvis, hind limbs
and right forelimb are missing. Nearly all the bones present are
broken, distorted by crushing, incomplete and scattered out of place,
probably by the action of currents. The complete skeleton, in life,
probably measured between 150 and 200 mm. in length.
The specimen was studied at the Museum of Natural History, University
of Kansas, with the help of a grant from the National Science
Foundation, number NSF-G8624. The specimen was discovered in the slab
by Miss Sharon K. Moriarty, and was further cleaned by the authors. Mr.
Merton C. Bowman assisted with the illustrations. We are indebted to
Dr. Robert W. Wilson for critical comments.