Roy Lee Moodie

THE MICROSAURIAN FAMILY AMPHIBAMIDÆ, FROM THE COAL MEASURES OF MAZON CREEK, ILLINOIS.

Family AMPHIBAMIDÆ new family.

Small, lizard-like, terrestrial or semi-aquatic, megacephalic microsaurians, known from 3 species. The family characters are the huge size of the head as compared to the body, the short, stumpy body with about 25 short dorsal vertebrÆ, a very short tail, phalanges clawed, pubis of calcified cartilage, sclerotic plates in the orbit to the number of 29 or 30 in each, ventral armature well developed. Teeth anisodont, sharp, conical, non-striate.

Two genera are associated in this family: Amphibamus grandiceps Cope, known from three nearly complete skeletons; A. thoracatus Moodie, known from a single incomplete skeleton; Cephalerpeton ventriarmatum Moodie, anterior portion of body and skull. The species are all from the Mazon Creek shales and the family seems unrepresented elsewhere. It may be necessary to compare the AmphibamidÆ with the HylonomidÆ when the latter group is better known, but in the light of our present knowledge the two families are distinct.

The genera may be distinguished as follows:

I. Size small, less than 3 inches in total length, skull with deeply incised tympanic notches (ear-slits) Amphibamus

II. Size relatively large, body-length 6 inches or more, teeth distinctly anisodont, skull with nearly even posterior table, limbs very long, ventral armature highly developed Cephalerpeton

Genus AMPHIBAMUS Cope, 1865.

Cope, Proc. Phila. Acad. Nat. Sci., 1865, pp. 134-137. Geol. Surv. Ills., 11, pp. 135-141, pl. xxxii, 1 text-fig.

Hay, Proc. Am. Phil. Soc., XXXIX, p. 120, 1900.

Moodie, Jour. Geol., XVII, p. 81, fig. 24, 1909.

Type: Amphibamus grandiceps Cope.

The publication of the type species of this genus began the researches of Professor Cope on the extinct Amphibia of North America, which he continued for so many years with such excellent results (105-177). The description was based on a single specimen (plate 3, fig. 7) belonging to Mr. Joseph Evans, of Morris, Illinois, who loaned it to Dr. Worthen for the Illinois Geological State Survey (107), in order that it might be described. The type has been destroyed by fire; so I am informed by Mr. L. E. Daniels, of Rolling Prairie, Indiana. There are two other known specimens of the species. One is in the collection of Mr. Daniels and the other No. 794, of Yale University Museum.

This genus may be clearly separated from all the other microsaurians by characters which are peculiar to the form. Among these may be mentioned the possession of sclerotic plates in the eyes; the large size of the orbits in comparison with the dimensions of the skull; the short, broad form of the body; the very short tail; the possession of a calcified cartilaginous pubis; clawed phalanges; presacrals 22. The character which places the genus distinctly in the Microsauria is the possession of long, slender, curved ribs, first detected on Mr. Daniels's specimen (plate 14, figs. 1, 2), by Dr. Hay (316). Its stegocephalian characters are evident in every particular of its anatomy the roofed skull, the arrangement of the cranial elements, the presence of a well-developed ventral armature, and the digital formula (4 for the hand and 5 for the foot).

The genus Amphibamus was regarded by Cope as a representative of a new order of vertebrates which he called (105) Xenorachia. He later (123) abandoned this, however. Fritsch (251), Zittel (642), and others regarded Amphibamus as a branchiosaurian. The exact position of the form was uncertain until 1900, when Dr. Hay (316) described the long, curved ribs and suggested its place among the Microsauria. He, however (Cat. Foss. Vert., p. 410), made the mistake of including the branchiosaurian family ProtritonidÆ, under Microsauria, thus confusing the subject further. The genus (462) has not the slightest relationship with the Branchiosauria.

Amphibamus grandiceps Cope.

Cope, Proc. Phila. Acad. Nat. Sci., pp. 134-137, 1865; Geol. Surv. Ills., 11, pp. 135-141, pl. xxxii, and 1 woodcut, 1866.

Hay, Proc. Am. Phil. Soc., XXXIX, p. 120, 1900.

Moodie, Jour. Geol., XVII, No. 1, p. 82, fig. 24, 1909.

Moodie, Kan. Univ. Sci. Bull., VI, No. 2, pp. 343-349, pl. 1, figs. 1 and 2; pl. 5, fig. 3; pl. 7, fig. 1; pl. 11, 12, 13, 1912.

Type: Specimen has been destroyed. There is an excellent specimen (plate 4, figs. 5. 6), No. 794 (1234), in Yale University Museum, and another nearly as good in the possession of Mr. L. E. Daniels, of Rolling Prairie, Indiana.

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

The form of the skull of Amphibamus grandiceps Cope is not unlike that of Tuditanus minimus Moodie (462) from the Linton, Ohio, beds, but it is less acuminate than in that form. The large size of the orbits is especially striking. The shape of the skull is triangular, with concavities in the posterior table which correspond to the ear-slits so characteristic of Metoposaurus (242) from the Keuper of Germany. The narrowed posterior table of the skull is truncate, as in several other genera of Microsauria, notably Tuditanus and Saurerpeton. In structure the skull differs but little from many of the other Carboniferous forms, but the arrangement of the elements of the skull is more regular than in other genera.

The premaxillaries are very small elements in the anterior tip of the skull. They border the nares. The skull is rather peculiar among the Microsauria in the possession of a distinct lacrimal. I have detected this element in the cranium of Stegops divaricata Cope. As here defined the lacrimal is triangular, with its posterior border formed exclusively by the prefrontal. Its other relations are the normal ones. The nasal is elongate, with the usual relations of that element. The frontal is slightly longer and broader than the nasal. It apparently forms a portion of the inner border of the orbit. The parietal foramen lies in the anterior fourth of the parietal, a rather unusual position for this structure. The parietals, as in so many of the Microsauria, together form the largest element of the skull and are roughly a triangular area in the postero-median portion of the skull. The postparietal and the tabulare are clearly distinguishable and they have the usual relations for those elements. The maxillary, jugal, and quadratojugal together form the greater part of the maxillary border. The postero-lateral angle of the skull is, as visual, formed by the squamosal. The orbit is bounded posteriorly by the postorbital and the postfrontal, which include in the angle between them the quadrangular squamosal. The orbit is especially remarkable for its size as compared with the dimensions of the skull, being without a parallel among other known Microsauria. Around the border of the orbit in the specimen Cope studied (105) there were found 14 quadrangular plates which he called "superciliary plates." Hay (316) was inclined to regard them as sclerotic plates. In the Yale Museum specimen (plate 4, figs. 5, 6) there are 20 of these plates, and there seems to be no doubt that they are sclerotic elements. In the restoration (fig. 26) 29 sclerotic plates are given, but there is no assurance that this number is the exact one. They may also have been slightly larger, but not as large as in Branchiosaurus.

Skull: pmx, premaxilla; n, nasal; fr, frontal; par, parietal; la, lacrimal; pf, prefrontal; pof, postfrontal; po, postorbital; pp, postparietal; spt, supratemporal; mx, maxilla; j, jugal; qj, quadratojugal; sq, squamosal; tab, tabulare.

Skeleton: ic, interclavicle; cl, clavicle; sc, scapula; h, humerus; r-u, radius, ulna; r, carpus; pu, pubis; il, ilium; f, femur; t, tibia; fb, fibula; ts, tarsus; x, ischium.

The vertebral column is preserved nearly entire in the Daniels specimen and quite entire (478) in the Yale specimen. Cope, in his study of the type (105, 107), thought there could be no more than 13 presacrals, but the specimen was poorly preserved and indecisive on this point. Dr. Hay (316) was inclined to the opinion that there were less than 20. The Yale specimen shows 22 centra, which are elongate, hour-glass-shaped bodies, with the neural spine a long, low crest running the entire length of the centrum, with a median elevation, so that in lateral view the spine would be triangular in form. The body of the centrum is expanded laterally into a diapophysis which extends anteriorly. The posterior vertebrÆ, at least, had the notochord largely persistent. The osseous part of the vertebra seems to have been but a thin shell, and the structure of the zygapophyses can not be determined. That they were dorsal in position is, however, evident from several vertebrÆ. The points of these structures project laterally. The tail is short and the caudal vertebrÆ weakly developed.

There are distinct impressions of at least 12 pairs of ribs in the Daniels specimen. They are long, slender, and curved, and there is no definite assurance that there were as many ribs as are indicated (fig. 26) in the restoration (462). The ribs are intercentral (469) and probably occupied the full length of the vertebral column. There may have been as many as indicated in the restoration.

One of the most interesting features of the Yale specimen is the preservation of a small patch of skin, evidently from the back, lying to one side near the head, measuring 5 mm. in length by 3 mm. in width. The fragment shows the skin to be of tuberculated scales, 4 of which occupy the length of 1 mm. The scales are somewhat hexagonal, almost rounded, and were relatively quite thick. They lie in a close mosaic (fig. 27).

The Yale specimen has, very well preserved, a portion of the ventral scutellÆ, of the throat, chest, and belly. The arrangement of the plates on the throat and chest is almost exactly the reverse of what Credner has described (190) for Branchiosaurus amblystomus Cred. On the throat, in the present form, the chevron points anteriorly, and it is the anterior prolongation of the belly scutes with the postero-lateral projection of the gular scutes which form the chest and arm scutellation. The belly chevrons point anteriorly, as in Branchiosaurus, the rods formed by the scutes being straight and not curved as in Branchiosaurus. The entire ventral armature preserved is displaced to the left of the animal and only the anterior portion is preserved.

The pectoral girdle is only partially known. The scapula is crescent-shaped. The other elements are indicated only by fragments and nothing is known of their form.

The arm elements are nearly all known. The humerus is slender and expanded at the ends, with its articular surfaces well developed. The separate radius and ulna are of approximately the same size and length. The carpus is unossified. The complete phalangeal formula for the hand of Amphibamus is unknown. The third digit seems to have 4 elements. The formula 2-2-3-2 has been suggested (462).

The pelvis is very satisfactorily known. The ilium is a long, slender, straight rod, with expanded ends. The ischium is shown on both sides of the vertebral column in the Yale specimen. Its form is almost identical with that of Paleohatteria longicaudata Credner, from the Rothliegenden of Saxony. The ischia are apparently approximate in the median line, though this character is somewhat obscured by the impression of the caudal vertebrÆ. Their relation with the ilium, other than that they were posterior to it, is uncertain. The pubis is, apparently, calcified cartilage. It is a squarish plate, somewhat corrugated, lying anterior to the ilium in the Daniels specimen. The elements of the pelvis were undoubtedly hung loosely in the flesh, as in modern salamanders, since there is no indication of articular surfaces.

The hind limb is well known, the type having a nearly complete leg with the foot. The Daniels and the Yale specimens supplement and substantiate the type. The femur is longer than the humerus, but more slender, with its articular surfaces about as well developed as in the humerus. The element is a simple rod of bone without muscular crests of any kind. The tibia and fibula are, likewise, slender separate rods of bone. The tarsus is unossified. The phalangeal formula is 2-2-3-4-3, and is fairly definite.

In the type specimen the matrix in the orbit was blackened as if by the pigmentum nigrum of the choroid. The same has been noticed in other specimens. Professor Cope thought this indicated that the animal was nocturnal.

There are many characters in Amphibamus which seem to approximate the reptilian type of structure. Among these may be mentioned the character of the articular surfaces of the limb bones, the intercentral position of the ribs, the incipient double-headedness and the curvature of the ribs, the presence of a cartilaginous calcified pubis, the length of the limbs, and the clawed character of the phalanges.

Amphibamus was a low, flat, short, and undoubtedly a creeping, crawling animal, possibly spending a portion of its time in the water; but it could not have been a swimmer. It was one of nature's first attempts at constructing a land vertebrate.

Measurements of Amphibamus grandiceps Cope.

Collection of Mr. L. E. Daniels, of Rolling Prairie, Indiana:

Amphibamus thoracatus Moodie.

Type: Specimen No. 4306, U. S. National Museum.

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

The type is a part of the collection of Mr. R. D. Lacoe, in the U. S. National Museum. The fossil is very poorly preserved, but the remains are to be seen on both halves of the nodule, so that considerable can be made out as to its structure.

The chief diagnostic characters which will at once distinguish the species are the elongate arm, large interclavicle, shape of the vertebra, and triangular skull.

The portions of the animal which are preserved are the impression of the skull with one orbit, the right humerus and radius with portions of others, and traces of ventral scutellÆ. These remains are so intermingled with the remains of plants that it has been quite difficult to distinguish bone impression from plants. This, however, has been done by whitening the fossils with ammonium chloride, when the texture of the fossils serves to distinguish the one from the other. Parts of the plants have been converted into galena and kaolin, as have also parts of the bones, so the task has been rendered doubly difficult. There can be no doubt, however, that the observations recorded below are correct. The position of the arm in relation to the pectoral girdle and the position of the girdle in relation to the skull impression first called attention to the possible presence of a fossil amphibian.

There is little to be said of the skull. It is merely an impression in the nodule. It is triangular in form, with the snout an acute angle. The angle is, however, exaggerated by the compression to which the fossil has been subjected. The right side of the skull lies over a portion of some plant. The animal is preserved on its back, so that this gives a good opportunity for the study of the pectoral girdle, which is partially preserved. The interclavicle is very large and from it the species has been given its specific name (thoracatus—armed with a breast plate). It is an exaggerated T, with the stem very short with its anterior margin curved, and ending in a rather sharp, elongate point. The interclavicle recalls, in a measure, the same element of the Branchiosauria, although it is much more expanded anteriorly and has a shorter spine. In these respects it resembles more nearly a reptilian interclavicle (fig. 14 B) .

The clavicle is of the simple triangular shape so characteristic of the Microsauria. It is somewhat displaced backward and its inner margin is slightly obscured. The humerus is elongate, apparently cylindrical, and with expanded ends, resembling very closely the humerus of Amphibamus grandiceps, although its proportions are much greater than in that species. Its length is almost equal to the length of the skull, while in A. grandiceps the length of the humerus is only half that of the skull. The radius (ulna?) resembles in its general proportions those of the humerus. It is a more elongate, slender, lighter bone. The impression of the other bone of the forearm is obscured.

A portion of a single vertebral centrum from the posterior part of the dorsal series is preserved. It is apparently amphicoelous; its width is nearly half greater than its length.

Genus CEPHALERPETON Moodie.

Type: Cephalerpeton ventriarmatum Moodie.

This genus is founded on remains of a nearly entire individual of a relatively large microsaurian from the Mazon Creek shales. The genus is most immediately related to the AmphibamidÆ, of which two species are already known, Amphibamus grandiceps Cope and A. thoracatus Moodie. The present genus differs from these species in many respects, notably in size. The skull in Cephalerpeton is nearly as long as half the entire body of Amphibamus grandiceps Cope, inclusive of the tail. Other structural differences are the anisodont teeth, the large size and the more median position of the orbits, and the absence of the posterior tympanic notch in Cephalerpeton. The form of the skull recalls that of Melanerpeton and Pelosaurus (190) of Europe, but those genera are branchiosaurian, while the present form, from the structure of the vertebrÆ and the long, curved ribs, is an undoubted microsaurian. Nothing like it occurs in any of the amphibian faunas thus far made known. It is most nearly approached by a member of the genus Erpetosaurus, but from this genus the present form is readily distinguished by the smooth skull bones, the absence of a posterior table to the skull, and the presence of a highly developed ventral armature. The interorbital width is less than the transverse diameter of the orbit.