Chapter X

ORDER CAUDATA DUMÉRIL, 1806. COAL MEASURES TO RECENT.

Naked-skinned, elongate, tailed salamanders, mud-puppies, efts, newts,
etc. External gills present or absent in adult condition, but always
present in young. Limbs short, with usually 4 digits on hand and 5 on
foot, but this is subject to much difference. Limbs never very stout.
Carpus and tarsus cartilaginous. Skull roof without the postparietal,
postorbital, and supratemporal. Skull elements never ornamented and
never cut by the lateral-line canals. Vertebræ consisting of a single
element; ribs short, attached to an elongate transverse process.
Caudal ribs seldom present. Parietal foramen lacking. No ventral
armature. Fresh-water inhabitants.

=Suborder PROTEIDA Cope, 1868.=

This order agrees generally with the Caudata, but presents one most important feature of difference in the presence of the opisthotic. It is this point which gives the Proteida its intermediate position between the extinct amphibians and the recent species, and seems to indicate a connecting line from the Coal Measures down to the present. The structure of the hyobranchial arches sustains this view.

The hyoid apparatus differs from that of other adult Caudata and resembles that of their larvæ in having three epibranchials, instead of one only. The second basibranchial is also connected with the first, which is not the case with the other Caudata. Three extinct genera are placed tentatively in this suborder.

=Family COCYTINIDÆ Cope, 1875.=

Cope, Bull. U. S. Nat. Mus., No. 1, p. 12, 1875.

The present family, as here defined, includes the forms whose structure seems to ally them with the modern salamanders. The character on which most dependence is placed is that of the branchial apparatus, lacking in _Hyphasma_. The forms are all incompletely known and the family will doubtless require revision on acquisition of additional material. Three genera, each with a single species, are:

_Cocytinus gyrinoides_ Cope. Linton, Ohio, Coal Measures. Based on the
ventral impression of the skull, with the well-developed branchial
apparatus.

_Erierpeton branchialis_ Moodie. Mazon Creek, Illinois, shales. Based
on impression of mandibles and branchial apparatus.

_Hyphasma lævis_ Cope. Linton, Ohio, Coal Measures. Based on
incomplete and obscure amphibian body, lacking limbs.

=Genus COCYTINUS Cope, 1871.=

Cope, Proc. Am. Phil. Soc., 1871, 177.

Cope, Geol. Surv. Ohio, II, pt. II, 360, 1875.

Type: Cocytinus gyrinoides Cope.

Vertebræ and ribs osseous; teeth on the premaxillary bone, none on the maxillary; hyoid elements largely developed, an axialhyal with basihyal on each side, closely united with the corresponding ceratohyal, at the end of which is an element in the position of a stylohyal; hæmal or basibranchials 3, the anterior 2, each supporting i pleural branchihyal, and the third supporting one also, the first hæmal branchihyal on the inner side of the ceratohyal, approaching the median line, and with elongate pleural element.

The reference by Cope of this genus to the Caudata is one of the most interesting facts connected with the Paleozoic Amphibia. He says: "The present genus is, then, to be referred to the neighborhood of _Amphiuma_ and _Protonopsis_, but forming the type of another family" (123). He regards the branchial apparatus as being more fish-like than that of any of the modern genera. It is possible that _Cocytinus gyrinoides_ was a larval branchiate and consequently aquatic form. It should be more fully compared with _Erierpeton branchialis_ from the Mazon Creek shales when better known, as well as with _Hyphasma lævis_ from the Linton locality.

All three of these forms are included, provisionally, under the Cocytinidæ.

=Cocytinus gyrinoides Cope.=

Cope, Proc. Am. Phil. Soc., XII, p. 177, 1871.

Cope, Trans. Am. Phil. Soc., p. 278, 1874.

Cope, Geol. Surv. Ohio, II, pt. II, pp. 364-365, pl. xxxix, fig. 4,
1875.

Type: Specimen No. 8613 G, American Museum of Natural History.

Horizon and locality: Linton, Ohio, Coal Measures.

Two specimens of this interesting amphibian are known, one of them fairly complete (No. 2564, Am. Mus. Nat. Hist.). The type specimen consists of the inferior bones of the cranium in a fairly complete state of preservation, with the muzzle and its teeth; also 8 anterior vertebræ, with their short recurved ribs.

The condition of the hyal elements in the type specimen is as follows: the hæmal elements of the first branchial arch are partially concealed on both sides of the ceratohyal. An expanded truncate face for attachment to the axial element is visible on both sides, but the body of the bone is flat and presents the edge of the specimen.

The first pleural element proceeds from just behind the axialhyal; it is longer than the other pleural elements. A slender bone is visible extending from the space between the ceratohyal and mandibular angle; it may, therefore, pertain to the suspensorium of the jaw as well as to that of the hyiod arch, or be squamosal as well as stylohyal. The second hæmal bone is slender, but with an enlarged axial extremity; that of the right side is not so well preserved as to be safely determined. The third hæmal elements are the smallest, and originate immediately in front of the occipital condyles and diverge outwards and backwards. They are little curved, subcylindric, and slightly expanded at the extremities.

Of the pleural elements the first and second are little curved and the first is marked by a pit or foramen on the under side near the distal end, which is clearly visible on both sides of the specimen. The third and fourth pleurals are more curved and the outer ends slightly expanded and directed backwards.

_Dendrerpeton acadianum_ Owen. Mandibles, parts of anterior extremities, humerus, etc. Nearly natural size. Erect tree, Coal formation South Joggins, Nova Scotia. Photograph by Dawson, published through the courtesy of Dr. Arthur Willey. Original specimen in the British Museum of Natural History.]

The obverse of the specimen (fig. 16) shows that the anterior axialhyal is wedge-shaped. The lateral basihyals are massive. The second hæmal branchihyal is dilated, fan-shaped distally, and supports two pleural elements. The muzzle projects over the lower jaw and was rather broadly truncate. The premaxillary teeth are cylindric and 6 in number on each side. The maxillary bone is represented by a lamina at each lateral extremity of the premaxillary. The mandibular rami are very stout, as are also the ceratohyals. The vertebræ have possessed some apophyses, apparently keel-shaped diapophyses. The ribs are slightly curved.

Measurements of the Type.

mm.
Length of specimen 32
Length of skull 12
Posterior width of skull 11
Length of premaxilla 5
Length of mandible 10
Length of axialhyal 3
Length of postbranchial 4
Width of vertebra 1
Length of vertebra 3
Length of rib 6

The other specimen of this species (fig. 16_a_) is interesting in having 40 consecutive vertebræ preserved, and 19 pairs of ribs attached in their natural relations to the skull and hyal elements. There are a few hyal elements preserved, but nothing is added to our previous knowledge. The ribs are quite as in the type specimen, as are also the vertebræ. The animal was apparently a slender, eel-shaped amphibian comparing favorably with the modern _Amphiuma_ in this respect. There are no indications of limbs or limb girdles.

Fig. 16_a_. Nearly complete specimen of _Cocytinus gyrinoides_ Cope, from the Coal Measures of Linton, Ohio. Original in the American Museum of Natural History. × 0.95.

Measurements (No. 2564, American Museum of Natural History).

mm.
Length of entire specimen 113
Length of skull 15
Width of head posterior 15.5
Length of vertebra 2
Length of rib 4

=Genus ERIERPETON Moodie.=

Moodie, Kans. Univ. Sci. Bull., VI, No. 2, p. 328, 1912.

Type: _Erierpeton branchialis_ Moodie.

The generic characters are found, first of all, in the presence of hyobranchial arches which indicate its relationship to the formerly described _Cocytinus gyrinoides_ Cope, from Ohio. The only other known extinct genera of Caudata which possess, or at least have preserved, the hyobranchial arches are the Jurassic _Hylæobatrachus_ from Belgium and Lysorophus from the Permian of Texas. The present form is widely distinct from both of these genera in the shape of the mandible and the form and arrangement of the hyobranchial bars. The genus _Erierpeton_ finds its closest ally in _Cocytinus_, in the family Cocytinidæ, which possibly belongs in the order Caudata and the suborder Proteida of Cope.

=Erierpeton branchialis Moodie.=

Moodie, Kans. Univ. Sci. Bull., VI, No. 2, pp. 329-330, pl. 1, fig. 3;
pl. 2, fig. I, 1912.

Type: Specimen No. 801 (222) 5, Yale University, Museum.

Horizon and locality: Mazon Creek shales, near Morris, Illinois.

The amphibian remains designated by the above name consist of a distinct mandible and some rather indefinite body impressions (plate 3, fig. 4). Three elongate impressions occur between the rami of the mandibles (fig. 15, A), which, I suppose, must represent hyoid bones belonging to the hyobranchial arches. The lateral elements are paired and the median impression is straight and lies between the paired impressions of the hyoids. The paired portions probably represent the hypohyals or hypohyals plus the ceratohyals, and the unpaired portion of the first basibranchial, according to the nomenclature of Wiedersheim (Comparative Anatomy of Vertebrates, 1897, p. 86). If the impressions have been correctly interpreted the present specimen is of very great interest, since it is the first evidence we have of the hyobranchial arches in the Amphibia of Mazon Creek, and the second in the Carboniferous of North America. Dawson doubtfully identified (216) some elements of the Joggins Amphibia as hyoids, but was uncertain as to their position. Cope described fully the well-developed hyobranchial apparatus of _Cocytinus gyrinoides_ (123) from the Coal Measures of Ohio. Among other Paleozoic Amphibia Williston (614) has described branchial arches in the peculiar form _Lysorophus tricarinatus_ Cope, from the Permian of Texas.

The form of the impression of the mandible in the present specimen is unlike anything known to the writer among other Carboniferous or later Amphibia. The rami are long, slender, deep, slightly curved, and pointed anteriorly. The anterior symphysis was not a complete sutural union, but was occupied partly by cartilage or other connective tissue.

There are no definite traces of the appendicular skeleton. The traces of the body (fig. 15, A) indicate an elongated, rather slender animal, but further than this nothing can be said in regard to its structure.

The occurrence of a typically caudate form in the Carboniferous is unusual and complicates still further our understanding of the origin and relationships of the early Amphibia.

Measurements of the Type.

mm.
Length of entire impression 50
Length of mandible along median line 10
Width of mandibular ramus 9
Length of basibranchial 2.5
Width of basibranchial 0.75
Length of hypohyal 2.4
Width of hypohyal 1.5

=Genus HYPHASMA Cope, 1875.=

Cope, Proc. Acad. Sci. Phil., p. 16, 1875.

Cope, Geol. Surv. Ohio, II, pt. II, p. 387, 1875.

Type: _Hyphasma lævis_ Cope.

"Vertebræ osseous, the posterior dorsals, and probably the caudals, furnished with fan-like neural spines; limbs unknown--(?) wanting. Thoracic shields present. Ventral armature, consisting of rhomboidal scuta, forming packed rows arranged in chevrons, directed backwards, on top of which are the usual rod-like scales arranged in packed chevrons, with the angle directed forward.

"The general appearance of the type of this genus is that of a Ptyonius, but the ventral armature is different from anything observed in the known genera of this group. The larger external scuta are like those of the species of Colosteus (Sauropleura), but their series have a different direction. The inner chevrons are those of many other genera" (123).

=Hyphasma lævis Cope.=

Cope, Proc. Acad. Sci. Phil., p. 16, 1875.

Cope, Geol. Surv. Ohio., 11, pt. II, p. 387, pl. 37, fig. 4, 1875.

Type: Specimen No. 9023 (in counterpart), American Museum of Natural History.

Horizon and locality: Linton, Ohio, Coal Measures.

"In the only known specimen the vertebræ have low and squarely
truncate neural spines near the head, and some distance anterior to
the tail they are quite conspicuous and delicately line-grooved.
The body is slender and probably limbless. The thoracic scuta are
large and close to the head; the median is produced at both ends,
but chiefly anteriorly while the lateral are narrow; all are without
sculpture The head is seen from below. The mandibular rami are not so
slender as in most species of _Ptyonius_, but are rather stout. They
are a little incurved distally, so that the form of the muzzle is
somewhat narrowed, but not produced. The teeth are not visible. Ten
rows of the outer layer of scuta in 0.005 m." (123).

The specimen is very indistinctly preserved and the characters given by Cope can not all be made out. It is puzzling to see just on what he bases his conclusion. It is possible that the specimen is a poorly preserved _Ptyonius_. The outlines of the vertebræ are so indistinct that I am uncertain about them. In certain lights there appear to be regular impressions which resemble the spines of the vertebræ of Ptyonius, but they are doubtful. The skull appears totally distinct from any known species of _Ptyonius_, but it is very imperfect. The condition of the pectoral elements is very uncertain and I can not be sure that what Cope described as thoracic "scuta" are such. The interclavicle, however, is clearly preserved as a diamond-shaped structure. It is almost smooth, with a few faint radiating lines near the base. It measures 5 mm. in greatest breadth by 8 mm. in length.

Measurements of the Type.

mm.
Length of specimen as preserved 64
Length of skull 15
Greatest width of skull 8
Width of body 8
Length of 7 cervical vertebræ 15
Length of median thoracic scuta 10
Width of same 4
Width of clavicle 2
Length of mandibular ramus 12