  THE MICROSAURIAN FAMILY HYLONOMIDÆ, FROM THE COAL MEASURES OF NOVA SCOTIA. Family HYLONOMIDÆ Fritsch, 1883. Fritsch, Fauna der Gaskohle und der Kalksteine der Permformations BÖhmens, Bd. 1, p. 159, 1883. Lydekker, Cat. Fossil Reptilia and Amphibia, IV, p. 201, 1890. The following characterizations of the family are those given by Lydekker (393, p. 201) based on Fritsch (251): Body slender and lizard-like; skull narrow, with smooth or faintly sculptured bones; neural spines of vertebrÆ well developed, and long, slender ribs. Teeth smooth, or with grooved summits. The whole body covered with sculptured scutes. Internal gills may be developed. Fritsch (251, Bd. I, p. 159) gives the following in his original description: "Stegocephali von Baue schlanker Eidechsen mit schlanken langen Rippen. Wirbel amphicoel mit stark entwickelten oberen DornfortsÄtzen. SchÄdelknochen glatt oder schwach verziert. Schuppen gross, verziert, den ganzen KÖrper deckend. ZÄhne glatt oder mit verzierte Spitze. Kiemenbogen bei einigen angedeutet. Mittlere Kehlbrustplatte unbekannt. Coracoidea Ähnlich wie bei Branchiosaurus schlank, winkelig gebogen." Fritsch includes the following genera in the family: Hylonomus, Hyloplesion, Smilerpeton, Seeleya, Orthocosta, and Ricnodon. The family includes the following species: Hylonomus lyelli Dawson, Nova Scotia. Dawson, Quart. Jour. Geol. Soc. London, XVI, p. 274, figs. 14-18, 1860 Dawson, Air-breathers of The Coal Period, p. 44, 1863. Dawson, Phil. Trans. Roy. Soc. London, 1882. pl. 11, p. 634. Credner, Zeit. d. deutsch. geol. Gesell., 1890 (IX Theil, die Stegocephalen und Saurier). Type: Hylonomus lyelli Dawson. The genus Hylonomus is a very important one from a taxonomic viewpoint, since it was regarded by Dawson (216, p. 635) as the typical genus of the order Microsauria, the most abundant group in the Carboniferous. Unfortunately the species of the genus Hylonomus are known only from fragmentary remains. I have reproduced in plate 9 Dawson's figures of the remains of Hylonomus as published by him in 1891. Dawson (216) gave, in 1882, the following definition of the genus Hylonomus: "Form lizard-like, with the posterior limbs somewhat large in proportion to the anterior. Size, small. Mandibular and maxillary teeth numerous, small, conical, pointed. Palatal teeth minute. Abdominal scales oval." MOODIE Hylonomus lyelli Dawson. 1, maxillÆ and skull bones; 1a, sternal bones; 2, mandible; 3, humerus, ribs, and vertebrÆ; 4, posterior limb; 5, pelvis; 6, caudal vertebrÆ. Nearly natural size. Erect tree, Coal formation, South Joggins, Nova Scotia. Photograph by Dawson, published through the courtesy of Dr. Arthur Willey. Original in the British Museum. Credner (186), Fritsch (251, Bd. 1, p. 89, Taf. 12, figs. 1, 4, 15), and Woodward (629) have referred remains of Microsauria discovered in the Coal Measures or lower Permian deposits of Saxony, Bohemia, and Lancashire, England, to the genus Hylonomus. There is much uncertainty as to the validity of these references, due to the uncertain nature of the type of Hylonomus. There are 4 American species of the genus: Hylonomus latidens Dawson, H. lyelli Dawson, H. multidens Dawson, and H. wymani Dawson. All the species are from the Coal Beds at the South Joggins, Nova Scotia. Hylonomus lyelli Dawson. Dawson, Quart. Jour. Geol. Soc. London, XVI, p. 274, figs. 14 to 18, 1860. Dawson, Air-breathers of the Coal Period, p. 44, 1863. Dawson, Phil. Trans. Roy. Soc. London, 1882, pt. II, p. 635, pl. 39, figs. 1 to 14 and 27. Dawson, Acadian Geology, 3d ed., 1880, p. 370. Type: Specimens Nos. R 443 to 445 in the British Museum (393, pt. IV, p. 223). Horizon and locality: Coal formation of the South Joggins, Nova Scotia. This species is by far the most abundant (plate 9) in the erect trees examined by Dawson. Its characters Dawson (216) defines as follows: "General form lizard-like, with the hind limbs rather larger than the fore limbs. Length when mature, 5 to 6 inches. "Head somewhat elongate; bones of skull smooth or with microscopic striÆ, perfectly united, except at the parietal foramen. Occipital condyle double, and apparently bony. Teeth simple, conical, numerous, about forty in each mandible, and nearly equal, except that a few of the anterior ones are rather larger than the others. The teeth are anchylosed to the jaw in a furrow protected by an external bony plate. "VertebrÆ with cylindrical bodies, slightly concave at the ends. When partly exfoliated they appear hour-glass-shaped, in consequence of the internal cartilage having the form of two cones attached by their apices. Zygapophyses conspicuous above; neural arches united to the bodies of the vertebrÆ, and with broad neural spines. Dorsal vertebrÆ with strong lateral processes. Caudal vertebrÆ apparently simple and cylindrical. Number of vertebrÆ in neck and trunk about thirty. "Ribs long and curved, with capitulum and tuberculum, cartilaginous within. "Anterior limb slender, humerus with distinct keel; radius and ulna separate; toes four or five. "Posterior limb with well-developed femur; tibia and fibula shorter, separate; toes five, somewhat long and slender. "Pelvis large, composed of ilium and ischium." Interclavicle and numerous scutellÆ are present. Upper surface protected with imbricated horny scales. In front two rows of horny tubercles and plates, with epaulettes composed of bristle-like fibers projecting from the skin. The animal possibly fed on insects, as is indicated by the coprolitic matter associated with the remains of the species. The following measurements are given by Dawson for the largest individual discovered:
Hylonomus latidens Dawson. Dawson, Phil. Trans. Roy. Soc. London, 1882, pt. II, p. 637, pl. 39, figs. 18-22. Dawson, Proc. and Trans. Roy. Soc. Canada, 1895, p. 74. Type: Specimen No. 3061-1, Peter Redpath Museum, McGill University. The British Museum (393, pt. IV, p. 224) also has a specimen, No. R 447. Horizon and locality: Coal formation at the South Joggins, Nova Scotia. Fragments of 3 specimens from 3 trees represent this species (plate 10). It seems to have been of stouter build than H. lyelli, with the limbs shorter in proportion. Its generic affinities are somewhat doubtful, as it presents in some respects characters intermediate between Hylonomus and Hylerpeton. Mandibular and maxillary teeth broadly conical, about 20 in each mandible 3 in 1 mm.; anterior mandibular teeth somewhat larger than the others, and bent or hooked. Vomer or palate with minute teeth. Thoracic plate large. Scales of abdomen oval, but somewhat narrow, and tending to be oat-shaped.
Hylonomus multidens Dawson. Dawson, Phil. Trans. Roy. Soc. London, 1882, pt. H, p. 637, pl. 39, figs. 23-26. Dawson, Proc. and Trans. Roy. Soc. Canada, 1895, p. 74 Type: Specimen No. 3061-2, Peter Redpath Museum, McGill University. Horizon and locality: Coal formation at the South Joggins, Nova Scotia. This animal is known only by portions of bones of the head and a few other fragments. The scattered bones of the extremities are inseparable from those of H. lyelli occurring with it. As compared with that species, the bones of this are smoother and more delicate. The teeth are more numerous and slender. The crushed distal end of a femur or humerus found near the skull indicates that the limbs were well developed.
Hylonomus wymani Dawson. Dawson, Quart. Jour. Geol. Soc. London, XVI, p. 277, figs. 27-29, 1860. Dawson, Air-breathers of the Coal Period, p. 52, 1863. Dawson, Phil. Trans. Roy. Soc. London, 1882, pt. II, p. 637, plate 39, figs. 15-17. Dawson, Acadian Geology, 3d ed., p. 378. Type: Specimen No. 3061, Peter Redpath Museum, McGill University. There is also specimen No. R 446 in the British Museum (393, pt. IV, p. 224). Horizon and locality: Coal formation at the South Joggins, Nova Scotia. As compared with the H. lyelli the present species is smaller in size, more elongated in form, had the teeth less numerous (about 22 in the mandible), and shorter and more obtuse in form. There are 6 to 7 in I mm. This species is much more rare than H. lyelli, but quantities of minute bones, probably belonging to it, occur in the coprolitic matter. In one specimen 38 vertebrÆ of this species were found partially associated, indicating along, slender body. The body is covered with scales and ventral scutellÆ are present. Dawson questions whether this species may not be the young of H. lyelli. MOODIE Hylonomus latidens Dawson. Skull, portion of skeleton, foot, scapula, sternal bones, humerus, and rib, believed to belong to this species. Erect tree, Coal formation. Nova Scotia. Nearly natural size. Photograph by Dawson, published through the courtesy of Dr. Arthur Willey. Original in the Peter Redpath Museum of McGill University.
Dawson, Phil. Trans. Roy. Soc., London, 1882, pt. H, p. 634. Dawson, Proc. and Trans. Roy. Soc. Canada, 1895, p. 74. Type: Smilerpeton aciedentatum Dawson. The type species was originally referred to Hylonomus, but further study induced Dawson to refer it to a new genus. Dawson gives (216) the following characteristics of the genus: "Form somewhat elongated, and limbs short. Mandibular and maxillary teeth wedge-shaped, with cutting edges. Palatal teeth numerous, some of them large. Abdominal scales oval. A single species is known, S. aciedentatum, from the Coal Measures at the South Joggins, Nova Scotia." Smilerpeton aciedentatum Dawson. Dawson, Quart. Jour. Geol. Soc. London, XVI, p. 275, figs. 19 to 23, 1860. Dawson. Air-breathers of the Coal Period, p. 65, 1863. Dawson, Phil. Trans. Roy. Soc. London, 1882, pt. II, p. 638, plate 40, figs. 28 to 45. Dawson, Proc. and Trans. Roy. Soc. Canada, 1895, p. 75. Dawson, Acadian Geology, 3d ed., p. 376. Type: Specimen No. 3061-3, Peter Redpath Museum, McGill University. The British Museum (393, pt. IV, p. 224) also has a specimen, No. R 433. The important characteristic (plate 12) is found in the form of the mandibular and maxillary teeth, which are of a peculiar wedge-shape, being broad and oval at the base and narrowed to a longitudinal edge at top. Thus, when viewed from the side they appear narrow and blunt, but when the jaw is broken across, and they are viewed from the rear or front, they appear broad and sharp-edged. The effect of this arrangement is that the jaw is armed with a closely placed series of chisels or wedges, giving an almost continuous edge. At the end of the mandible some of the teeth are longer and more conical. Another important character is that the palatal and vomerine bones seem to have bristled with teeth, mostly of very small size; but there are also some larger palatal teeth, of which some are sharply pointed and others blunt with furrowed points. The vertebrÆ are of the same type as those of Hylonomus; but some which appear to be caudal have a pointed spine above, indicating perhaps a flattened tail. The ribs are short and stout. The body seems to have possessed an interclavicle and ventral scutellÆ. Above it was, apparently, clothed with small tubercles and horny scales, and to have had cuticular pendants like those of Dendrerpeton. An additional species of this genus was apparently indicated by some fragmentary remains, but Dawson thought best not to describe them as such, since they might indicate only a young individual of the present species.
Fig. 18. Skeletal elements of Smilerpeton aciedentatum Dawson, from the Coal Measures of Nova Scotia. (After Dawson.) a, shaft of femur, × 2; b, intermaxillary and teeth, × 25; c, sections of teeth, × 25; d and e, palatal teeth, × 25; f, femur, × 2; g, rib, × 2; h, palate; i, caudal vertebrÆ; j, long palatal tooth, × 25; k, bony scale. Owen, Quart. Jour. Geol. Soc. London, XVIII, p. 241, 1862. Dawson, Amer. Jour. Sci. (3), XII, p. 443, 1876. Dawson, Phil. Trans. Roy. Soc. London, 1882, pt. II, p. 634. Dawson, Proc. and Trans. Roy. Soc. Canada, 1895, p. 74. Dawson, Air-breathers of the Coal Period, p. 55, pl. vi, figs. 32-46, 1863. Body stout, with strong limbs. Mandibular and maxillary teeth strong, not numerous, grooved at apex. Palatal teeth numerous, and some of them large. Thoracic plate broad. Abdominal scales pointed or oat-shaped. Type: Hylerpeton dawsoni Owen. Hylerpeton dawsoni Owen. Owen, Quart. Jour. Geol. Soc., XVIII, p. 241. Dawson, Air-breathers of the Coal Period, p. 55, 1863. Dawson, Acadian Geology, p. 380. Dawson, Phil. Trans. Roy. Soc. London, 1882, pt. II, p. 639, pl. 41, figs. 62-85. Dawson, Proc. and Trans. Roy. Soc. Canada, 1894, XII, p. 74. Type: Specimen No. 3061-4, Peter Red path Museum, McGill University. There are also specimens, Nos. R 441 and 442, in the British Museum (393, pt. IV, p. 225). (Plate 7.) Horizon and locality: Coal formation at the South Joggins, Nova Scotia. Bones of skull slightly striated, but not sculptured as in Dendrerpeton. Lower jaw with distinct ascending ramus or coronoid process, a feature not known in any other of the Nova Scotia fauna, but observed by Cope in Brachydectes. Teeth, 12 in each ramus of the mandible, bluntly conical, slightly striated at the apex. Pulp-cavities large and longitudinally striated at the sides, though the teeth are not folded. Maxilla furnished with similar teeth, one of which near the front is larger than the others. Palatal teeth numerous, small, conical, with a few large teeth at the sides. MOODIE Hylerpeton longidentatum Dawson. Mandible and other bones. 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 Peter Redpath Museum of McGill University. MOODIE Smilerpeton aciedentatum Dawson. Mandible, portions of skull, scales, and various bones. 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 Peter Redpath Museum of McGill University. VertebrÆ short, cylindrical, well-ossified, with well-developed zygapophyses and neural spines; ribs strong and much curved, with well-developed division of the proximal ends; pelvis imperfect, but apparently large, with broad ilium. Humerus half the length of the mandible; radius half as long as humerus; femur very large and stout, nearly as long as the mandible; leg bones and phalanges correspondingly stout. The thoracic plate (plate 7) is indicated only by some fragments. The abdominal scales are narrow and pointed (oat-shaped), smooth externally and with a ridge at one side within. The following are the dimensions of the largest specimen:
Hylerpeton longidentatum Dawson. Dawson, Am. Jour. Sci. (3), XII, pp. 440-447, 1876. Dawson, Phil. Trans. Roy. Soc. London, 1882, pt. II, p. 640, pl. 42, figs. 86 to 109. Dawson, Proc. and Trans. Roy. Soc. Canada, 1894, XII, p. 74. Type: Specimen No. 3061-6, Peter Redpath Museum, McGill University. There is also a specimen, No. R 440, in the British Museum (393, pt. IV, p. 225). (Plate 11.) Horizon and locality: Coal formation at the South Joggins, Nova Scotia. Head much elongated, with the bones minutely pitted, and with delicate microscopic strife, but not sculptured. Mandibular and maxillary teeth long and acute, pointing backwards, with the apex of their inner sides finely striated; 20 or more in each ramus of the lower jaw; palatal bones with several long, slender teeth and many minute teeth. The mandibles found are not complete, but there are indications that there was an ascending process as in H. dawsoni, but less developed. The narrowness of the dentary bone is caused in part by the lower posterior edge being bent inward and by the posterior end being broken off above. VertebrÆ short and stout, and apparently well ossified. Ribs long, with double head and much curved. Humerus longer than femur, which is short and stout, if the bone taken for it is rightly determined. Abdominal scales narrow, oat-shaped; thoracic plate large, broadly oval. Measurements of Hylerpeton longidentatum Dawson.
Hylerpeton intermedium Dawson. Dawson, Proc. and Trans. Roy. Soc. Canada, XII, p. 75, 1895. Type: Specimen No. 3061-5, Peter Redpath Museum, McGill University. Horizon and locality: Coal formation at the South Joggins, Nova Scotia. This species is known only by the mandibles and portions of the skull, which are rather shorter than those of adult individuals of the last species. The extremity of Coal formations, South Joggins, Nova Scotia, in erect tree, discovered by P. W. McNaughton, 1893. Dawson, Phil. Trans. Roy. Soc. London, 1882, pt. II, p. 634. Lydekker, Cat. Fossil Reptilia and Amphibia, pt. IV, p. 225, 1889. Type: Fritschia curtidentata Dawson. Body lizard-like; limbs large and well-ossified, mandibular and maxillary teeth conical, grooved at the apex. Abdominal scales slender and rod-like. Fritschia curtidentata Dawson. Dawson, Phil. Trans. Roy. Soc. London, 1882, pt. II, p. 641, pl. 43, figs. 110-128. Dawson, Am. Jour. Sci. (3), XII, p. 444, 1876. Type: Specimen No. 3061-7, Peter Redpath Museum, McGill University. There is also specimen No. R 449, in the British Museum (393, pt. IV, p. 225). Horizon and locality: Coal formation at the South Joggins, Nova Scotia. Represented by 2 specimens (plate 8). Bones of the head very smooth, only a few microscopic punctures. Teeth conical, somewhat obtuse, striated at the inner side of the apices; there are about 30 in each ramus of the mandible, and about 27 in the maxillary bone. Teeth implanted in a furrow. VertebrÆ short and well ossified, 3 in 1 cm. Ribs strong, curved, about 1 cm. in length. Limbs robust, the bones better ossified than in any other known species from Nova Scotia. Toes of foot probably 5, central ones long and slender. Interclavicle of moderate size and somewhat rounded. Ventral scutellÆ needle-like.
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