DEFINITION OF THE ORDER SALIENTIA, LAURENTI, 1768.
(World-wide distribution.)
Naked, tailless Amphibia of compact form, and with usually procœlous
vertebræ. Caudal vertebræ coalesced into a slender elongate piece, the
urostyle. Two elements of the tarsus ossified and greatly elongated.
Development by metamorphosis; gills never present in adult. Ilium
greatly elongated.
The order is suggested in the Coal Measures by a single species, known
from a single poorly preserved specimen (plate 24, fig. 1). The form
_Pelion lyelli_ Wyman was the first known of the Linton Amphibia, and
its striking frog-like (123, 639) appearance was early noticed. There
is no assurance that the species belongs with this order, but since a
well-developed and highly specialized frog (480, 481) occurs in the Como
Beds (405) of Wyoming, it is not impossible that we may have in the
_Pelion lyelli_ a suggestion (460), at least, of the ancestral structure.
It is certain that the frogs have, in past ages, had a much greater length
of vertebral column than they possess at present, as is witnessed by the
coalescence of several vertebræ to form the urostyle. It is suggested that
the ancestral vertebral column is represented in _Pelion_.
=Family PELIONTIDÆ Cope, 1875.=
Cope, Bull. U. S. Nat. Mus., No. 1, p. II, 1875.
The present family includes but a single species, that of _Pelion lyelli_
Wyman, first described in 1858 (640), from Linton, Ohio.
The family characters are to be found in the broad and obtusely rounded
cranium, in the frog-like scapular arch, the frog-like hind limb, and in
the form of the palate, so far as these structures have been preserved.
It has been suggested that the present form shows decided affinities with
the frogs of to-day and it may possibly be looked upon as the actual
ancestor of the living frogs. The length of the vertebral column would
seem to militate against such a relationship, since it is well known
that frogs have had a short vertebral column since the Jurassic (480,
481). But this is not a good argument, since the developing urostyles of
modern tadpoles show metameric fenestrations in the developing bone which
doubtless correspond to openings between the vertebræ. The notochord
of the tail is segmented, apparently through the influence of former
vertebral structure. At any rate, the suggestion is an interesting one
and, whether sustained or disproven, the present discussion is based on
the probabilities of the case.
=Genus PELION Wyman, 1868.=
Wyman, Am. Jour. Sci. (2), XXV, p. 160, 1858 (_Raniceps_).
Cope, Proc. Acad. Nat. Sci. Phil., 1868, 211 (_Pelion_, suggested in
letter to Cope by Wyman).
Type: _Pelion lyelli_ Wyman.
"The only specimen of the species exhibits an inferior view of a
portion of the skeleton; and the obverse, on which the thoracic
and abdominal armor could have been preserved, has not come under
my observation. The specimen, however, does not exhibit any ribs,
although the vertebræ are well preserved. As observed by Professor
Wyman, the genus presents some points of similarity to the Anura
(Salientia). The prolongation of the angles of the mandible is of this
character, as well as the general form of the head. The bones of the
forearm may be united as in the frogs, and the length and curvature of
the femur are seen among these animals rather than the Salamanders.
The form of the femur is different from that of _Amphibamus
grandiceps_ Cope, which also differs in the presence of dermal scales
and ventral scutellæ." (123.)
[Illustration: MOODIE PLATE 7
_Hylerpeton dawsoni_ Owen. Above: Mandible, teeth, rib, and
bones of extremity. Below: Bones of pelvis and posterior limb and bony
scales. Nearly natural size. Erect tree, Coal formation, South Joggins,
Nova Scotia. Photograph by Dawson, published through the courtesy of
Dr. Arthur Willey. Original specimens in Peter Redpath Museum of McGill
University.]
=Pelion lyelli Wyman.=
Wyman, Am. Jour. Sci. (2), XXV, p. 160, 1858.
Cope, Proc. Acad. Nat. Sci. Phil., 1868, p. 211.
Cope, Geol. Surv. Ohio, II, pt. II, p. 390, pl. XXVI, fig. 1, 1875.
Moodie, Pop. Sci. Monthly, LXXII, p. 562, fig. 1, 1908.
Type: Specimen No. 7909 G, American Museum of Natural History.
Horizon and locality: Linton, Ohio, Coal Measures. (Plate 24, fig. 1.)
This was the first species described from the Linton, Ohio, deposits.
It was made known by Dr. Wyman in 1857 at the meeting of the American
Association for the Advancement of Science for that year. The species was
subsequently studied by Cope. He merely confirmed Wyman's observations.
The following description is based on the descriptions of Cope and Wyman
and on my own study of the type specimen.
This is the most frog-like, in appearance at least, of all the Amphibia
which have so far been discovered in the Carboniferous. The skull
especially has a shape which is strikingly frog-like, and the long hind
limbs lend further likeness to the tailless forms. _Pelion_ may have
been a jumping creature, if we may judge from its long hind legs. Wyman
and Cope have both called attention to the frog-like appearance of the
specimen, and this is apparent at the first glance. It is probable that
the resemblance has some significance as to the ancestry of the Salientia,
and it may indicate the first step in the origin of the tailless Amphibia.
It is possible that the frogs began to be separated from the other
Amphibia during the Carboniferous. The first frogs we know are from the
Jurassic, where they are well-developed ranids. If _Pelion_ be a frog
ancestor, then the history of the group from the Coal Measures to Jurassic
is an unknown story.
The specimen is preserved on its back and it is thus impossible to tell as
to the structure of the skull. Cope was of the opinion that the depressed
areas on the sides of the elongate parasphenoid were the orbits, and if
so the resemblance to the frogs is much more striking. In the frogs there
is a strong process from the pterygoid which projects inward to meet a
corresponding process from the parasphenoid. This forms a heavy rod behind
the palatine vacuity. There is a heavy rod represented in the specimen and
a part of it is certainly the external process of the parasphenoid, but
whether it is to be interpreted as in the frog is an open question. The
outline of the cranium is partially obscured by the mandibles, but the
anterior part is represented by a raised line, as shown in figure 17. In
the anterior part of this space there are two ridges which may be tooth
ridges. If they are teeth there is a great similarity to the premaxillary
and vomerine teeth of _Necturus_, since the ridges are widely separated
at the median line and approximated distally, as they are in _Necturus_.
The mandible is preserved entire and its form is strikingly frog-like. Its
posterior angles project over the quadrate area and seem to have had an
upturned projection such as is found in the mandibles of the Crocodilia.
There are impressions of 20 vertebræ preserved, and they cover a little
more than half of the presacral region. There may have been 28 to 30
presacrals. The vertebræ, as preserved, are somewhat quadrate in outline
and constricted at the middle, as though they were of the typical
microsaurian type. No ribs are preserved.
[Illustration: Fig. 17. _Pelion lyelli_ Wyman, an amphibian from the
Coal Measures of Ohio, the supposed ancestral salientian. (After Wyman.)
× 0.75. _pmx_, premaxilla; _pv_, palatine vacuity; _m_, mandible; _sc_,
scapula-coracoid; _h_, humerus; _r-u_, radius and ulna; _f_, femur; _t_,
tibia.]
There is an impression anterior to the right humerus which may represent a
part of the pectoral girdle, but its form is so obscure that it can not be
determined. The pelvic girdle is entirely wanting in the specimen. Remains
of the fore and hind limbs are preserved. The arms are especially well
preserved and consist of a strong humerus, a separate radius and ulna, and
phalanges, the carpus having undoubtedly been cartilaginous, since there
are no traces of carpal bones. Wyman has figured a small ossicle (fig. 17)
which might be interpreted as a carpal, but it is further removed from the
carpal region than his figure shows and I would interpret it as a fragment
of a phalange, since the first digit seems to be turned aside over the
vertebral column. The right hand is but imperfectly preserved, but the
left hand is nearly entire. There are evidences of 4 digits, possibly 5.
The metacarpals are elongate and rather stout. The phalanges of the distal
series have been lost, so the phalangeal formula can not be determined.
On the whole, the hand has a very broad aspect and is not at all slender,
as in the majority of the microsaurians from the Coal Measures of Ohio.
It resembles in a great measure the broad hand of a toad and may thus be
indicative of a terrestrial life. The humerus is well developed and has
pronounced swellings, as though for the attachment of strong muscles.
These indications would favor the view of the animal being a land dweller.
The femur and a part of the tibia (?) of the right side are all there
is preserved of the hind limb. These elements show the leg to have been
quite long, though weaker than the fore limb. The femur has a large distal
articular surface. The fibula is, apparently, absent, though it may simply
be lost.
The genus _Pelion_ stands alone among the Carboniferous Amphibia. The
form can not be placed in the order Branchiosauria on account of the
well-developed limb bones and the large mandible. It may belong with
the Microsauria. I have placed it under the Salientia in the hope of
learning more about the early relatives of the tailless forms. There is
no assurance at all that it is even ancestral to the Salientia, but the
resemblances are striking.
The following gives the measurements of the type specimens:
Measurements of the Type Specimen.[B]
mm.
Length of specimen, as preserved 110
Median length of the skull 24
Width across the mandibular angles 25
Greatest width of skull 30
Length of vertebral column from occiput
to sacral region 80
Length of left humerus 19
Width of distal end of left humerus 5.5
Length of radius and ulna 11.5
Width of distal end of radius 2
Length of digit II, as preserved 16
Length of digit III, as preserved 14
Length of femur 24
Width of distal end of femur 4
Length of tibia 18
[Footnote B: The type specimen was collected in 1857 by Dr. John V.
Lauderdale, who presented it to Dr. J. S. Newberry.]