THE MICROSAURIAN FAMILY ICHTHYCANTHIDÆ, FROM THE COAL MEASURES OF OHIO.
=Family ICHTHYCANTHIDÆ new family.=
This family is the most recently recognized group of the Linton fauna. Its
members, of which there are two known species, are distinct from all other
Coal Measures Amphibia in the possession of an osseous tarsus (483, 484),
with its associated reptile-like limb bones. There are preserved fine
scutellæ in a large patch near the vertebral column. The vertebral spines
are broad and heavy, with the vertebral centra amphicœlous.
=Genus ICHTHYCANTHUS Cope, 1877.=
Cope, Proc. Am. Phil. Soc., p. 573, Feb. 3, 1877 (Pal. Bull. 24).
Baur, Beiträge zur Morphogenie des Carpus und Tarsus der Vertebraten,
I Theil, p. 16, 1888.
Cope, Trans. Am. Phil. Soc., XVI, p. 289, fig. 1, 1888.
Moodie, Science, n. s., XLI, No. 1044, p. 34, 1915.
Moodie, Am. Jour. Sci., XXXIX, pp. 509-512, fig. 2, May, 1915.
Type: _Ichthycanthus ohiensis_ Cope.
The generic characters are derived from the characters presented by the
posterior dorsal and caudal vertebræ, with adjacent parts. The posterior
limbs are well developed, with distinct tibia and fibula, osseous tarsus,
and 5 digits. Ribs elongate, simple, curved. Abdominal armature consisting
of bristle-like rods in anteriorly directed chevrons. Dorsal vertebræ not
elongate, with simple neural spines. Tail large, its vertebræ ossified,
and furnished with slender chevron bones which terminate in a hæmal spine.
Neural spines broad and directed backwards; the caudal series somewhat
resembling that of a fish. All the centra are amphicœlous.
This genus differs from all those with enlarged and sculptured neural
spines, and from those with abdominal scutes. It is equally distinct from
those without ribs, abdominal rods, or limbs. It is possible that some of
the species referred to _Tuditanus_, in which these parts are unknown,
may belong to it, or that it may be established on a small species of
_Leptophractus_, a genus known only as yet from the skull. With our
present imperfect knowledge of the Linton forms it seems best to refer _I.
ohiensis_ and _I. platypus_ to this distinct genus, _Ichthycanthus_.
=Ichthycanthus ohiensis Cope.=
Cope, Proc. Am. Phil. Soc., 1877, p. 573 (Pal. Bull. 24).
Type: Specimen in the American Museum of Natural History.
Horizon and locality: Linton, Ohio, Coal Measures. Collected by Dr. J. S.
Newberry, in the summer of 1876.
The centra of the dorsal vertebræ are about as long as deep, and their
sides are deeply concave; there are 4 anterior to the pelvis which are
without ribs. The caudal vertebræ are robust, and 7, from the first,
support a small tubercle-like diapophysis. The chevron bones are short and
acuminate; the neural spines are a little shorter, narrow, and truncate,
and directed backwards at the same angle as the chevron bones. They are
much reduced on the eighteenth caudal vertebra, where the chevron bones
are considerably longer.
The abdominal rods are quite slender. The hind limb is quite stout for
this order. The femur is regularly expanded at both extremities, but the
distal is deeply and openly grooved, distinguishing the condyles, while
the proximal end is plane. There is no trochanter visible. The ulna
and radius are well separated, and are three-fifths the length of the
femur. There is a large fibular tarsal bone of a subquadrate outline. In
immediate contact with it is probably the external digit with 5 phalanges
or segments; the ungual is simply conic. The femur is as long as 5 dorsal
vertebræ. The ribs have expanded, undivided heads, and extend to the
abdominal armature.
Measurements of the Type of Ichthycanthus ohiensis Cope.
mm.
Length of last 10 dorsal vertebræ 47
Length of first 23 caudal vertebræ 117
Length of a posterior rib 29
Length of a posterior dorsal vertebra 5
Length of twenty-second caudal vertebra 5
Length of femur 25
Proximal diameter of femur 8
Width of lower leg 9
Length of fibula 15
Length of tarsal bone 6
Length of digit 27
=Ichthycanthus platypus Cope.=
Cope, Proc. Am. Phil. Soc., pp. 574, 575, 1877.
Cope, Trans Am. Phil. Soc., XVI, p. 289, fig. 1, 1888.
Baur, Beiträge zur Morphogenie des Carpus und Tarsus der Vertebraten,
I Theil, p. 16, 1888.
Moodie, Science, n.s., XLI, No. 1044, p. 34, 1915.
Moodie, Am. Jour. Sci., XXXIX, pp. 509-512, fig. 2, 1915.
Type: Specimen No. 79540, and obverse, Department of Geology, Columbia
University. (Plate 23, fig. 1.)
Horizon and locality: Linton, Ohio, Coal Measures.
This amphibian is represented by the same portions of the skeleton as the
preceding species, furnishing a good basis for comparison. It is very well
preserved, displaying the characters, especially of the hind foot, which
is almost entirely represented.
Several features distinguish it from the _I. ohiensis_, one of which is
of more than usual value if correctly indicated by the fossil. There are
10 vertebræ from the anterior end to the sacrum preserved in place, and
none of them supports a rib, nor are there any ribs visible anywhere on
the block of shale. I suspect that they exist on more anterior vertebræ,
or may have been displaced to a more anterior position than they normally
occupy. The abdominal chevrons are more anterior in position than are
those of the _I. ohiensis_. The hind legs are longer than in that species;
in this one the femur equals 7.5 vertebral centra in length. The external
digit, on the other hand, while bearing 5 phalanges, is distinctly
shorter. The fibular tarsal is of a transverse oval, not quadrate, form.
The dorsal centra are shorter and deeper than long; the neural arches are
elevated, with short but distinct zygapophyses, and a flat, subquadrate,
superiorly truncate, neural spine. They bear short, vertically compressed
diapophyses near the base of the arches. The neural spines of the caudal
vertebræ become rapidly more slender, and also diminish in length, while
the zygapophyses are continued to the fifteenth vertebra. The chevron
bones are slender, and inclose a moderate hæmal opening.
[Illustration: MOODIE PLATE 24
1. Photograph of the type specimen of _Pelion lyelli_ Wyman, from
the Ohio Coal Measures. Supposed to represent the ancestral form
of the Salientia. × 2. Original in American Museum of Natural
History.
2. Scales of _Cercariomorphus parvisquamis_ Cope, a microsaur from
the Ohio Coal Measures. × 10. Original in American Museum of
Natural History.
3. Type specimen of _Cercariomorphus parvisquamis_ Cope, from the
Ohio Coal Measures. Original in American Museum of Natural
History. × 0.75.
]
The femur is gradually expanded to the extremities. Proximally there is
a trochanteric ala, besides the obtuse head. Distally the condyles are
well distinguished, the external or fibular being truncate. The fibula is
less than three-fifths the length of the femur, and is expanded at both
extremities. Two proximal tarsals are distinct; the one next the fibula
is larger than the other and transverse suboval in form. It has a median
dividing ridge as though composed of fibulare and intermedium coössified.
The tibiale is subtriangular. There are five distinct phalangeal tarsals.
The toes are, in the order of their lengths, beginning with the shortest,
1-2-5-3-4. Their phalanges (including metatarsals) are, in the proper
order, commencing with the hallux, 3-3-4-5?-5, the distal end of the
fourth finger being lost. These bones are rather stout, and the unguals
are simply conic. The form of the foot is short and wide. The number of
the phalanges is nearly similar to that found in _Amphibamus grandiceps_,
excepting that in that species the fifth digit has but 4. They are more
numerous on most of the digits in _Sauropleura digitata_. Cope (Trans.
Am. Phil. Soc., XVI, 289, fig. 1, 1888) contributed the following note on
_Ichthycanthus platypus_:
"A reëxamination of the type specimen of this species from the Coal
Measures of Ohio, preserved in the Museum of Columbia College, New
York, enables me to refer this species to the Rachitomi. The neural
spines are distinct, showing that it belongs, probably, to the
Eryopidæ. As the skull is not preserved, I can not determine the genus
positively, but refer it for the present to Eryops. I append a figure
of the posterior foot, which displays the characters of the tarsus
of this group for the first time. The number of tarsals is as in a
Theromorph reptile, except that two elements represent the cuboid
bone as in the reptile, _Stereosternum tumidum_ Cope; giving five
elements in the distal tarsal row. There is but one centrale and no
intermedium. Two fragments of caudal vertebræ adhere to the specimen."
Measurements of Ichthycanthus platypus Cope.
mm.
Length of 10 dorsal vertebræ 45
Length of 15 caudal vertebræ 55
Length of centrum of a dorsal 3.8
Total elevation of a posterior dorsal 14
Length of femur 32 Length of first digit 10
Diameter of femur medially 4.5
Diameter of femur distally 8.3
Length of fibula 18
Diameter of fibula proximally 7
Width of sole at second row of tarsal bones 17
Length of foot to end of third digit 31
Length of third digit 22
Length of fifth digit 20
The writer has had the privilege of restudying this interesting specimen
and has already (484) described the foot and tarsus, as follows:
The only known specimen of this anomalous amphibian is incomplete,
representing the posterior half of the skeleton, and an abundance of
ventral scutellæ or calcified myocommata. The block of coal containing
these interesting remains is from Linton, Ohio, and is preserved in the
geological collections of Columbia University, from which institution
Professor Grabau very courteously forwarded it for study.
_Ichthycanthus platypus_ was described by Cope from the Linton, Ohio, Coal
Measures, locating it doubtfully in the Permian genus _Eryops_ on account
of the unusual condition of the tarsus and reconsidering a former decision
in favor of a Coal Measures genus _Ichthycanthus_. In this disposition
of the species into the Permian genus he is followed by Hay (317); but
Baur (28) regarded the form as a member of the Coal Measures genus
_Ichthycanthus_, after commenting on the later definition by Cope. The
type of the genus, _Ichthycanthus_, to which Cope first allied the species
under consideration, is _I. ohiensis_, a supposed amphibian from the Coal
Measures of Linton, Ohio, founded on incomplete material.
The form combines in an unusual and remarkable degree reptilian and
amphibian characteristics. The leg bones, pelvis, and tarsus are all
strikingly reptilian, but the phalanges in the arrangement of elements
are so typically amphibian that if we had no other means of diagnosis we
would incline to locate this Coal Measures species among the Amphibia.
The leg (plate 23, fig. 1) recalls in its structure that of another
Coal Measures species, _Eosauravus copei_ Williston, which is, however,
clearly a reptile. While there is a general degree of similarity between
the foot structure of _Eosauravus copei_ and _Ichthycanthus platypus_,
yet there are very great differences in the phalangeal formula and the
arrangement of the tarsal elements. These differences are clear and
indicate a separation of the two species into distinct classes. The
phalangeal formula in the _Eosauravus_, 2-3-4-5-4, is typically reptilian;
while in the _Ichthycanthus_, 2-2-3-3-3, it is amphibian. The tarsus of
the _Ichthycanthus_ is amphibian in the presence of an intermedium, but
this is very small and the remaining tarsal structures have nothing which
might not be found in an early reptile. There may be a single or even two
centralia in the reptilian tarsus among the early forms.
The amphibian nature of the species having thus been established,
it remains to give a detailed account of its skeletal anatomy, with
comparative references to such other ancient forms as are available.
Little can be said of the vertebral column, since only the molds of a few
vertebræ remain, and these are so obscured by a closely adherent pellicle
of carbonaceous material that their form can not be distinctly discerned.
They are high, with relatively broad neural spines. There are no ribs
preserved. The pelvis is obscured, but it is possible to determine the
presence of an elongate ilium and an ischium. The leg of the left side
is the best preserved of all the elements, and it is to this that our
attention will be confined. The opposite leg is not so complete, yet all
the long bones and a part of the tarsus are preserved with sufficient
clearness to corroborate the findings of the left side.
The femur, as has been stated, is reptilian in appearance. This is due
to the well-rounded articular surfaces, as though the endochondrium were
well developed, and to the large development of the greater and lesser
trochanters, which are quite prominent, though these are distorted and
depressed in fossilization. The bone is stout and well built and its form
suggests an active habit of life. The tibia and fibula are separate, and
do not otherwise have sufficiently noteworthy characters to call for a
special description in this place, except to note an unusual anterior
crest on the tibia. To the lower ends of these bones articulate the first
row of tarsal elements, the tibiale, intermedium, and fibulare. The tarsus
is composed of 9 elements arranged in 3 rows. The proximal row is composed
of the tibiale, the intermedium, and the fibulare. On the edge of the
tibiale there lies a portion of one of the caudal vertebræ, so that the
form of this tarsal element is slightly obscured. The intermedium is a
small, rounded element lying between the larger elements. The fibulare is
rectangular and projects a considerable distance out from the tibia, but
articulates directly with the large lateral distal tarsal. The centrale
is triangular in form and is opposed directly by the tibiale and tarsalia
1 to 3. The phalanges are robust in appearance. The entire foot gives
one the impression of a very broad structure. The ungual phalanges were
apparently bluntly clawed.