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OCCASIONAL PAPERS

QMP. ZOOL.
LIBRARY

Of the MAR 2\m

MUSEUM OF NATURAL HISTORYD
The University of Kansas
Lawrence, Kansas

NUMBER 14, PAGES 1-8 FEBRUARY 20, 1973

A PENNSYLVANIAN DISSOROPHID AMPHIBIAN

FROM KANSAS

By
Theodore H. Eaton^

Among rhachitomous labyrinthodont Amphibia of the Late
Paleozoic, the Dissorophidae and Trematopsidae currently are con-
sidered to be separate but closely related families. They are gen-
eralized in most features but show trends toward terrestrial life.
Commonly recognized distinctions between the two families include
the great enlargement of the external nares in the trematopsids,
whereas the dissoropliids ha\'e: 1) transverse plates of bony armor
along the back usually attached to the neural spines; 2) broad,
rounded interpterygoid vacuities; and 3) palatine bone forming part
of the lower rim of the orbit.

Apart from the limitations imposed by incomplete specimens,
these features are neither consistently present in the appropriate
group nor mutually exclusive between the two. For instance, DeMar
(1966a) described a Permian genus Lon<iiscitula with enlarged
nares; yet because of other characters such as dorsal armor, he
placed it in the Dissorophidae. Vaughn ( 1969 ) showed that another
Permian genus, Ecolsonia, has broad, rounded interpterygoid fenes-
trae such as characterize the dissoropliids, but because of the pres-
ence of large nasal openings, Vaughn referred the genus to the
Trematopsidae. It is not known whether or not armor was present
in Ecolsonia.

Amphibamus from the Middle Pennsylvanian Allegheny beds of

^ Curator, Vertebrate Paleontology, Museum of Natural History, University
of Kansas.

2 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY

Linton, Ohio, is the oldest dissorophid; fortunately it can be studied
from a number of specimens (Carroll, 1964). Watson (1940), who
investigated Amphibamus in reference to the origin of frogs, noted
that it is probably more aquatic and more primitive in some ways
(e.g., exclusion of the frontal from the rim of the orbit by the pre-
frontal and postfrontal) than any other dissorophid.

The genus described here from Kansas is from the Late Penn-
sylvanian. Although in most respects it is an unspecialized dissoro-
phid, it does have an enlarged nasal opening. The other known
genera are variably characterized by small or large nostrils, presence
or absence of armor, and wide or narrow palatine fenestrae; all are
of Permian age. It is a part of the thesis of this paper that we should
no longer recognize two families in this group, but only one, for
which the older name, Dissorophidae, would be used. Two other
valid families can be included in a superfamih', Dissorophoidea;
these are the Zatracheidae and Doleserpetontidae. Both are closely
related to dissorophids. Doleserpeton is a minute amphibian, prob-
ably terrestrial, from the Lower Permian fissure deposits at Fort Sill,
Oklahoma. This animal was described by Bolt (1969) as a possible
"protolissamphibian." Its structure, apart from the pedicellate, bi-
cuspid teeth and large pleurocentra, differs remarkably little from
that of Amphibamus.

The specimen named and described here is a nearly complete
skull and skeleton of a small labyrinthodont amphibian, order
Temnospondyli, suborder Rhachitomi, family Dissorophidae, taken
from the Rock Lake Shale member of the Stanton Limestone, Mis-
sourian series. Upper Pennsylvanian, approximately 6 mi NW of
Garnett, Kansas. The locality is that from which Petrolacosaunis,
HesperoJwrpeton, Edaphosaunis ecordi, and other members of the
Garnett fauna were obtained. The dissorophid is in a limy shale bed
containing plant fragments and numerous bones of the primitive
pelycosaur Clepsijdrops.

Actiobates new genus
Type species. — Actiobates peabodyi new species.
Ilolotype. — University of Kansas Museum of Natural History
(VP) 17941; locality, age, and formation as given in preceding para-
graph.

Diagnosis. — Skull broad, shallow, comparable to Amphibamus
and Ecolsonia; cranial roofing bones thin, with pit-and-ridge orna-
mentation externally; basipterygoid joint moveable; frontals entering
margin of orbits; otic notch moderate, its posterior opening slightly

PENNSYLVANIAN DISSOROPHID AMPHIBIAN 3

narrowed; marginal teeth uneven, those of anterior end of max-
illary large.

Actiohates differs from Amphihamiis in having a greatly enlarged
nasal opening and from EcoJsonia in having the frontal and parietals
of nearly equal size, and the postparietals narrow and elongate lat(!r-
alh'. Diagnosis of the species is the same as that of the genus. This
specimen is mentioned by Estes (1965) and Estes and Reig (1973).

Etymology. — The generic name is derived from the Greek actios
meaning shore, and hates meaning one who walks. The specific
patronym is in remembrance of Frank E. Peabody, who initiated the
extensive study of the Garnett fauna.

DESCRIPTION AND DISCUSSION

The skull is flattened by pressure, but has sustained little damage
and slight displacement of bones (Fig. 1). Its medial length is 59
mm, but the lateral edges have been pressed out a few millimeters,
making the skull a little broader than it was in life. At the same
time the nasal and premaxillary parts were spread laterally, leaving
a gap between. In addition there is a small round fenestra between
the tips of the nasals, which is commonly present in dissorophids.
Ventrally, the mandibles were pressed against the lateral parts of
the palate and upper jaw; a full description of this area must await
further preparation. The pterygoid, parasphenoid and otic parts are
remarkably well preserved. In the ventral view (Fig. lb) the stapes
and opisthotic are shown on the left side of the drawing as they are
in the specimen; on the right, they are placed in their original
positions relative to one another and the fenestra ovalis.

The postcranial skeleton and details of the skull not yet available
will be described in a subsequent paper. The vertebral column is
nearly complete, but scattered, because of the rhachitomous division
of each vertebra. The forelimbs, including the girdle and feet, are
complete; similarly, most of one hind limb is complete. A few scat-
tered chevron bones and part of the pelvis are present. Four small
bones are present anteriorly that look like double-ended paddles;
these are probably units of the dorsal armor, but they lack attach-
ment to the neural spines.

One curious featin-e is the presence of an occipital (one basi-
and two exoccipitals in one unit) of a small individual of Clepsij-
drops inside the mouth cavity and pressed up into the orbit. A few
other associated fragments suggest that this was not a chance re-
lationship, but instead, that the amphibian was feeding on the
pelycosaur.

Figure 1 shows most of the visible features of the skull, but some

OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY

Fig. 1. Skull of Actiobates peabodyi, KU (VP) 17941, actual size. A. Dor-
sal view. B. Ventral view. Abbreviations: cl, edge of clavicle; /, frontal; /u,
jugal; la, lacrimal; nix, maxillary; no, nasal; op, opisthotic; or, orbit; pa, pari-
etal; pt)i, premaxillary; po, postorbital; pp, postparietal; pof, postfrontal; pif,
prefrontal; pro, prootic; ps, parasphenoid; pt, pterygoid; qj, quadratojugal; qu,
quadrate; .spt, supratemporal; sq, squamosal; it, stapes; ta, tabular.

PENNSYLVANIAN DISSOROPHID AMPHIBIAN 5

items need to be discussed. Comparison of the expanded nasal
opening with those of most dissoropliids and other labyrinthodonts
shows that tlie anterior part (one-third) has not been changed by the
enlargement, but that the posterior two-thirds resulted from reces-
sion of the edges of the lacrimal and prefrontal bones and some of
the lateral edge of the nasal. The lacrimal and prefrontal are left as
little more than a cross-bar separating the orbit and nostril. What-
ever the reason for this expansion may have been, it need not have
affected the original function of the anterior portion, which was for
the passage of air.

The more lateral and anterior parts of the palate are concealed
beneath by the lower jaws which are crushed against them; it may
be possible to reveal these parts of the palate by further preparation
while reconstiiicting the lower jaw at the same time. Much of the
pterygoid is visible; its joint with the basisphenoid was evidently
moveable. The expanded ventral surface of the pterygoid and that
part of the parasphenoid which is between the basipterygoid
processes are closely scattered with minute (0.25 mm diameter or
less), round, flattened, dome-like teeth. Each tooth occupies, but
may not fill, a round, shallow alveolus. Some of the teeth are much
smaller than the alveolar opening and deeply placed in it; these are
apparently in early stages of eruption. Other teeth nearly fill the
alveolus to the rim, and the largest appear to have fused with the
margin. A few have their rounded peaks worn off exposing the inner
cavity.

The basisphenoid is exposed on either side of the converging,
ventralmost part of the parasphenoid; the bone bears grooves for
the interal carotids. The medial edges of these grooves are bounded
by the parasphenoid except in their anterior parts, where the basi-
pterygoid processes project laterally. The cultriform process of the
parasphenoid is slender and crushed against the skull roof; thus, it
is not possible to see a cranial cavity or foramina. There is no indi-
cation of a sphenethmoid.

No palatine, ectopterygoid, or vomerine teeth can be seen, be-
cause these bones are covered. The few visible teeth of the jaws are
shown in figure lb. There appears to be space for about 30 teeth in
each jaw. Apparently, the largest teeth are two located on the for-
ward end of the maxilla.

Morphologically, the otic region is most interesting. The otic
capsule is represented mainly by the prootic, and is bounded later-
ally by the quadrate process of the pterygoid, anteriorly by the basal
process, medially by the parasphenoid plate, and posteriorly by the

6 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY

anterior edge of the clavicle. At the posterolateral corner of the otic
capsule is the fenestra ovalis, with the stapes slightly displaced, as
seen on the left side of figure lb. Beyond its rounded footplate, the
stapes has a foramen in its shaft; distal to the foramen, the shaft
ciu'ves laterally. The shaft lies dorsal to the quadrate process of the
pterygoid, beyond which its tip shows. Posterior to the foot of the
stapes, lies a short bone which evidently forms a portion of the
wall of the fenestra ovalis. I assume that this bone is the opisthotic,
which is considerably reduced and bears a short paroccipital process
laterally. On the right side of figure lb, the stapes and opisthotic are
shown in their proper positions relative to the fenestra ovalis.

The resemblance of this apparatus to those of frogs and sala-
manders is at once obvious. If we allow a little more reduction of
the opisthotic until it is a small, flat plate, and eliminate its ossifi-
cation (as is usual for the otic region among modern amphibians),
the opisthotic becomes quite precisely the operculum of the otic
capsule. Primitively, the paroccipital process was for muscle attach-
ment. When the bone was reduced, the muscle (opercularis) re-
mained inserted on the operculum; it extends back to the anterior
edge of the scapula in the modern Amphibia. It may have done so
in dissorophids in the early stages of terrestrial life. This alone is not
enough to demonstrate conclusively that Actiobates is directly an-
cestral to Lissamphibia, because we do not yet know the relationship
of the expanded nasal opening to the reduction of the skull in frogs,
salamanders, and caecilians. On the other hand, the condition of
the ear in Actiobates approaches that of the modern Amphibia re-
markablv closelv.

Elements of the hyobranchial apparatus, although not figured,
are present. They are somewhat displaced against the otic region of
the left side of the skull.

SKULL CHARACTERS AND RELATIONSHIPS

The question whether dissorophids and trematopsids represent
one family or two depends on the occurrence of differential charac-
ters or combination thereof. But interpretation of these, in turn,
requires viewing a given character, or characters, as a stage or "state"
in the evolution of certain moiphological features. For instance,
among the Rhachitomi a movealile basipterygoid articulation is
clearly more primitive than a fixed articulation. The moveable
articulation occurs in the two Pennsylvanian genera, but not, so far
as is known, in those of the Permian. On the other hand, union in
a fixed joint could have occurred more than once; if it did, then

PENNSYLVANIAN DISSOROPHID AMPHIBIAN 7

possession of a fixed joint is not, Ijy itself, evidence of a direct rela-
tionship among genera.

Likewise, there is no doubt that the small external nares charac-
teristic of most labyrinthodonts arc primitive with respect to large
external nares. The former occur in AmpJiibamiis, Dissorophus and
most other genera in the Dissorophidae, but not in Actiohates, Ecol-
sonia, Longiscitida, or the genera usually placed in the Trema-
topsidae. Again, the enlarged condition, being specialized, could
liave originated more than once. The size of the external nares is
not a simple character, and the modification of at least three bones
in a particular area of the skull in the same way in more than one
evolutionary line seems improbable. Such an interpretation would
require independent evidence from other characters that genera
having enlarged nares represent separate phyletic lines.

Morphologically it is not possible to determine the relative prim-
itiveness of wide, rounded interpterygoid vacuities as compared
with narrow or small interpterygoid vacuities. However, widiin the
scope of dissorophids and trematopsids, we can suppose that the
wide, rounded state is primitive because it is present in Amphibamiis
and Actiohates of the Pennsylvanian in addition to other dissorophid
genera. The fenestrae are narrow and relatively small in several
trematopsids. If these taxa are closely related and form a natural
group ( whether one family or two), then there is a high probability
that the narrowed condition is secondary. In spite of the fact that
the most primitive labyrinthodonts had no interpterygoid vacuities,
it is reasonable to suppose that rounded interpterygoid vacuities
were present in primitive dissorophids, because they are known in
Ampliibamus.

None of the features of the skull that has been discussed, nor the
occurrence of dorsal armor, seem to be suitable to distinguish the
two families. In the case of each character there is at least one taxon
for which a character state cannot be determined. Furthermore, the
distribution of known characters is discordant. Thus, any arrange-
ment of the genera in separate groups requires that some incon-
sistency in overlapping or contradictory characters be introduced in
their diagnosis. It seems more satisfactory, therefore, to recognize
only one family, the Dissorophidae, for all the animals hitherto
placed in this and the Trematopsidae.

8 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY

SUMMARY

A virtually complete skeleton of a new dissorophid labyrintho-
dont, Actiobates peobodyi, is reported from the Rock Lake Shale
member of the Stanton Limestone, Missourian Series, near Ganiett,
Kansas. The skull is characterized by an expanded narial opening,
characteristic of Permian trematopsids and seen here for the first
time in a Pennsylvanian amphibian. In other respects, the skull is
that of a generalized dissorophid. The distribution of characters
among dissorophids and trematopsids no longer seems to warrant
recognition of more than one family, the Dissorophidae, for both.

LITERATURE CITED

Bolt, J. R.

1969. Lissaniphibian origins: possible Protolissamphibian from the Lower
Permian of Oklahoma. Science, 166:888-891.
Carroll, R. L.

1964. Early evolution of the dissorophid amphibians. Bull. Mus. Comp.
Zool., Harvard, 1.31(7) : 163-250.

DeMar, R. E.

1966a. Longiscitula houfihae, a new genus of Dissorophid Amphibian from

the Permian of Texas. Fieldiana Geology, 16(2):45-53.
1966b. The phylogenetic and functional implications of the armor of the
Dissorophidae. Fieldiana Geology, 16(3):55-88.
Estes, Richard

1965. Fossil salamanders and salamander origins. Amer. Zool., 5:319-
334.

Estes, Richard axd Osvaldo Reig

1973. The early fossil record of frogs: a review of tlie evidence. In J. L.
Vial, Evolutionary biology of the Anurans. University of Missouri
Press, Columbia ( in press ) .
Vaughx, p. p.

1969. Further evidence of close relationship of the Trematopsid and Dis-
sorophid Amphibians with a description of a new genus and spe-
cies. Bull. So. Calif. Acad. Sci., 68(3): 121-130.
Watson, D. M. S.

1940. The origin of frogs. Trans. Roy. Soc. Edinburgh, 60:195-231.