f several bones. The frontal and squamosal nearly
meet each other, and both form part of the rim of the orbit. The bones
of the posterior part of the dermal roof are greatly reduced, and there
is none behind the squamosal except the projecting tabular; there is no
indication of quadratojugal, jugal, intertemporal or postparietal. The
foramen magnum is enormous. The external surfaces of the bones of the
skull are nearly smooth.

Is it possible that the "primitive" and "specialized" features of this
animal are actually larval? Are they not just the kind of characters
that would be expected in an immature, aquatic embolomere of
Pennsylvanian time? For several reasons we do not think this is the
case. Except for the anterior part of the braincase, there is no
indication that the skeleton was not well ossified. The postaxial
processes on the humerus, ulna and ulnare could scarcely have been
larval features only, since they are so clearly homologous with those
in adult Rhipidistia; a larval limb should indeed be simple, but its
simplicity is unlikely to involve paleotelic adult characters. The
scapulocoracoid of our specimen is of practically the same shape and
size as that in the only other known individual, the type; this would
be probable if both were adults, but somewhat less likely if they were
larvae of a much larger animal. The form of the stapes, tabular and
otic notch suggest a functional tympanic membrane, which could not have
occurred in a gill-breathing larva. On the other hand, an adult animal
of pigmy size might be expected to have large orbits, large otic
capsules and a large foramen magnum.

We conclude that _Hesperoherpeton_ lived and sought food in the weedy
shallows at the margin of a pond or lagoon, and that for much of the
time its head was partly out of water (Fig. 12). The animal could
either steady itself or crawl around by means of the paddlelike limbs,
but these probably could not be used in effective locomotion on land.
Like the Ichthyostegids, it probably swam by means of a fishlike tail.

[Illustration: FIG. 12. _Hesperoherpeton garnettense_ Peabody. Probable
appearance in life. x 0.5.]

TAXONOMY

Evidently _Hesperoherpeton_ is a small, lagoon-dwelling survivor of
the Devonian forms that initiated the change from Crossopterygii to
Amphibia (Jarvik, 1955). It shows, however, that this transition did
not affect all structures at the same time, for some, as the braincase
with its notochordal