A New Order of Fishlike Amphibia From the Pennsylvanian of KansasEaton, Theodore H. (Theodore Hildreth)
Science
A New Order of Fishlike Amphibia From the Pennsylvanian of Kansas
Eaton, Theodore H. (Theodore Hildreth)
Amphibians, Fossil; Paleontology -- Pennsylvanian
The squamosal of _Acanthostega_ (Jarvik, 1952) is articulated under the
tabular and reaches forward and down, much as if it were an opercular
in reversed position. Internally, it must lie against the otic capsule
below the tabular, partially concealing the stapes. The bone that we
suppose to be the squamosal of _H. garnettense_ is of similar shape, of
about the same size and has internally an articular surface at one
corner, bounded by a pair of ridges in the shape of a V. This articular
surface probably fitted on a lateral process extending from the roof of
the neurocranium, over the front of the otic capsule.
The premaxillary extends posterolaterally to a distance 5.5 mm. from
the midline and attains a width at its broadest point of about 1.5 mm.
The posterior edge is slightly concave and in part forms the anterior
border of the naris.
[Illustration: FIG. 1. _Hesperoherpeton garnettense_ Peabody. Skull,
dorsal view. Postorbital processes of the neurocranium are shown in
dotted outline. KU 10295, × 4.]
The nasal is triangular and, with the lacrimal, forms the medial border
of the naris. The length of the medial side of the nasal bone is
approximately 5.0 mm., the transverse width is 3.8 mm., and the extent
of the posterolateral border is 5.5 mm.
The maxillary meets the premaxillary lateral to the naris, borders the
naris posteroventrally, and continues posteriorly beneath the orbit, of
which it forms the external border. The maxillary is about 8.5 mm.
long, and immediately anterior to the orbit has a maximum width of 1.3
mm.
The lacrimal fills the remaining rim of the narial opening between the
nasal and maxillary, and extends to the anterior edge of the orbit. The
length, from naris to orbit, is 4.2 mm.; the width ranges from 1.0 mm.
anteriorly to 2.5 mm. posteriorly.
[Illustration: FIG. 2. _Hesperoherpeton garnettense_ Peabody. Skull,
lateral view, showing relatively large orbit and absence of smaller
circumorbital bones. KU 10295, × 4.]
The external naris is approximately 1.0 mm. in diameter. It is slightly
anterodorsal to the internal naris and 4.0 mm. lateral to the midline.
The dorsal margin of the orbit appears to be formed by the frontal. The
anterior part of this margin, however, may be formed by a prefrontal,
which is not clearly set off by a suture. The frontal extends 3.8 mm.
in the midline, and anteriorly and laterally borders the nasal and
lacrimal, respectively. A faint pattern of pitting radiates on the
surface from the center of ossification of the frontal. There is also a
pit indicating the presence of a supraorbital sensory pore.
The parietal bones enclose the pineal opening, approximately 2.5 mm.
posterior to the suture with the frontal. The foramen is about 0.5 mm.
in diameter. Laterally the parietal meets the medial angle of the
postorbital and the medial border of the supratemporal. No bone of this
animal shows the deep pitting and heavy ornamentation characteristic of
many primitive Amphibia.
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