Chapter XIII

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.
_latidens_ Dawson, Nova Scotia.
_multidens_ Dawson, Nova Scotia.
_wymani_ Dawson, Nova Scotia.
_fritschii_ Gein. and Deichm., Saxony.
_geinitzi_ Credner, Saxony.
_(?) pictus_ Fritsch, Bohemia.
_wildi_ Woodward, England.
_Smilerpeton aciedentatum_ Dawson, Nova Scotia.
_Hylerpeton dawsonii_ Owen, Nova Scotia.
_intermedium_ Dawson, Nova Scotia.
_longidentatum_ Dawson, Nova Scotia.
_Fritschia curtidentata_ Dawson, Nova Scotia.

=Genus HYLONOMUS Dawson.=

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."

_Hylonomus lyelli_ Dawson. 1, maxillæ and skull bones; 1_a_, 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:

Length of head about cm. 2
Length of neck " " 1.3
Length of trunk " " 7
Length of posterior limb to heel cm. 3
Length of mandible " 1.8
Teeth, 5 in 1 mm.
Length of rib cm. 1.3
Length of humerus " 1.4
Length of femur " 1.8
Length of tibia " 1.2
Length of body of vertebra mm. 2.5

=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.

Length of mandible (imperfect) mm. 9
Length of humerus mm. 7
Length of vertebra mm. 2
Length of tibia (?) mm. 5
Length of thoracic plate cm. 1
Length of six caudal vertebræ mm. 8

=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.

mm.
Length of mandible 11
length of skull 15
Length of femur 9
Teeth, 5 to 6 in 1 mm.

=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_.

_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.]

mm.
Length of skull 8
Length of mandible 5
Length of rib 5.5
Length of femur 6
Length of humerus 5

=Genus SMILERPETON Dawson.=

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.

Length of mandible 1.5 cm.
Length of femur 1.5 cm.
Length of humerus (?) 1.3 cm.
Length of vertebra 3-5 mm.
Length of rib 1 cm.
There are 5 teeth in 2 mm.

=Genus HYLERPETON Owen.=

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.

_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.]

_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:

Length of mandible 4.4 cm.
Length of largest tooth 5 mm.
Length of femur 3.5 cm.
Length of tibia 2 cm.
Length of humerus 2 cm.
Length of radius 1.5 cm.
Length of vertebra 6 mm.
Length of rib 3 cm.
Length of scales 5 to 7 mm.

=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.

Length of mandible 4 cm.
Length of vertebra 5 mm.
Length of rib 3 cm.
Length of humerus 1.5 cm.
Length of femur (?) 1.2 cm.
Length of tibia 8 mm.
Length of mandibular teeth 3 mm.
6 to 7 teeth in 1 cm.

=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 the mandible and the cranial bones have the same slightly waved surface as in the other species. Mandibles 3 cm. long and the teeth, which are about 15 in each ramus of the lower jaw, are simple, with large pulp cavities, those of the maxillary bone slightly enlarging upwards, and intermediate in form between the long, slender teeth of _H. longidentatum_ and the thick, obtuse teeth of _H. dawsoni_.

Coal formations, South Joggins, Nova Scotia, in erect tree, discovered by P. W. McNaughton, 1893.

=Genus FRITSCHIA Dawson, 1882.=

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.

Length of mandible (imperfect) 2.1 cm.
Length of maxilla 2 cm.
Length of rib 1 cm.
Length of humerus 2 cm.
Length of femur 2.4 cm.
Length of radius and ulna 1 cm.
Length of toe in foot 7 mm.
8 teeth in 5 mm.