PARASUCHIA
The first known specimen of the order of reptiles now generally
known as the Parasuchia was found in Würtemberg, Germany, in 1826
and very briefly and inadequately described[4] two years later by
Professor George Jaeger. The specimen was a sorry one, and was sadly
misinterpreted by Jaeger. It consisted chiefly of casts of the alveoli
or sockets of a number of teeth, more or less connected by corroded or
decomposed portions of the jaws. He recognized the casts as teeth of
a peculiar reptile, but mistook the roots for crowns, and, naturally
concluding that such obtuse teeth would be of use only for the
mastication of vegetable food—about the last kind of food to which the
phytosaurs were addicted—called the animal _Phytosaurus_, meaning plant
saurian. Because of differences he observed in the shapes of the teeth
he thought that they belonged to two distinct species, which he called
_cylindricodon_ and _cubicodon_; but the differences were due simply to
the different positions they held in the jaws.
[4] “The author showed drawings and some specimens of two hitherto
unknown reptiles from the white, coarse-grained sandstone, of which one
in the form of the skull resembles the gavial, but is distinguished by
the cylindrical form of the lateral teeth of the jaws; he therefore
calls it provisionally _cylindricodon_, and a second species or genus,
of which, however, so far only fragments of the jaws have been found,
because of the four-cornered form of the teeth, _cubicodon_, while at
the same time for the genus or family, to which the remains of these
animals have belonged, he proposes the name _Phytosaurus_, since the
teeth seem to be more adapted to a vegetable diet, even though they
have not been worn away, as in _Iguanodon_.”—_Isis_ (1828), p. 441
(translation).
Fourteen years later Hermann von Meyer, the renowned German
paleontologist, described and figured other remains of the same or an
allied reptile under the name _Belodon plieningeri_. In subsequent
papers during the next twenty-three years von Meyer very fully
described and beautifully illustrated the skulls and other remains
of this and other species, all of which he referred to the genus
_Belodon_, the name by which for many years the animals were generally
known in scientific literature. Von Meyer thought that he recognized in
_Belodon kapfii_, the species most often figured in textbooks, the same
animal that Jaeger had previously described.
Von Meyer was not at all certain about the relationships of his
_Belodon_, though he recognized its affinity with the crocodiles. It
was Huxley who, in a famous paper on the evolution of the crocodiles,
published in 1875, united _Belodon_ and another genus from the Trias
of Scotland, which he called _Stagonolepis_, with the Crocodilia as
representatives of the suborder Parasuchia, one of the three into which
he divided the order. Huxley admitted that the relationships between
the Parasuchia and the Mesosuchia or Eusuchia, the other suborders
which he proposed, were not as intimate as those between the latter
two, which were separated solely on the structure of the palate and
vertebrae, as has been explained in chap. xv. As early as 1869 the
late Professor Cope recognized certain forms which had been previously
described from Carolina as belonging to the group, calling them
_Belodon_, but it was not until 1896 that E. Fraas separated _Belodon
planirostris_ of von Meyer as a member of a distinct genus, to which he
gave the name _Mystriosuchus_.
Here, as a part of the order Crocodilia, the phytosaurs remained
till within very recent years, though there have been some mild
protests against the association, especially by Marsh, Zittel, and
Baur. The famous English paleontologist, Richard Owen, located the
“Belodontia,” as the phytosaurs were often called, in his order
Thecodontia, based chiefly upon the manner of the insertion of the
teeth in sockets. But this has long since been shown to have little
value in the classification of reptiles. Various authors have written
about the phytosaurs in later years, notably Cope, Fraas, Huene, and
Jaekel, but it was J. H. McGregor who first definitely separated the
phytosaurs into a distinct order, in a careful revision of the American
forms. He called the order Parasuchia, after Huxley, dividing into
two suborders, the Phytosauria, after Jaeger, and the Aetosauria, a
group which, for lack of a better place, had previously been classed
with the Crocodilia, either as a member of the Parasuchia or as an
independent suborder by Zittel (the Pseudosuchia). More recently
Huene has shown that certain African reptiles from the Lower Trias
had certain very definite characters entitling them to an independent
position, for which he proposed the order Pelycosimia. Upon the whole,
however, these characters seem to be primitive parasuchian, and the
group may provisionally be placed in the order Parasuchia, as a third
suborder, the Pelycosimia. The order Parasuchia, then, until we know
much more about the latter two groups, may be conveniently divided into
three suborders, the Phytosauria, Aetosauria or Pseudosuchia, and the
Pelycosimia, all of Triassic age.
McGregor was quite right in retaining for the suborder the name
Phytosauria, suggested by Jaeger in 1828, inappropriate as the word is
etymologically, but was hardly justified in substituting the generic
name _Phytosaurus_ for the long and well-known _Belodon_, because it
is quite impossible to say that Jaeger’s very fragmentary specimen
upon which he based the genus _Phytosaurus_ really is the same as
_Belodon_. Professor Fraas very kindly showed the writer the original
type-specimen of Jaeger, now preserved in the Stuttgart Museum,
and both are agreed that it is impossible to prove the identity of
_Belodon_ and _Phytosaurus_ from the very fragmentary and imperfect
specimen. It is quite as probable, for instance, that _Phytosaurus_ and
_Mystriosuchus_ are identical as that _Phytosaurus_ and _Belodon_ are.
Unfortunately, this is not the only case in vertebrate paleontology
where the fragmentary specimens to which names have been given are
inadequate to determine the species, or genus, or even the family
to which they belong; there have been very many such instances. The
pioneers in paleontology were often justified in naming small and
obscure fragments of bones, or single bones. One would be justified
even yet in giving a name to an indeterminable fragment of a bird bone
from the Triassic formation, because the discovery of a bird of any
kind in that formation would be very important for science, even if its
precise kind might never be recognized from the specimen. Nevertheless,
the custom is a very reprehensible one when indiscriminately followed.
For these reasons the writer disagrees with McGregor in substituting
the inappropriate name _Phytosaurus_ for _Belodon_, the name by which
the most typical forms were so long known.
The Aetosauria, which have long been known from a marvelous specimen
found in Würtemberg many years ago and described by the elder Fraas,
need not detain us long. They were relatively small reptiles about
two feet long, almost completely incased in a bony armor, and purely
terrestrial in habit. The skull even yet is not perfectly known, and
it is possible that when it is the group may have to be dissociated
from the phytosaurs. The nostrils were not posterior, and the skull is
short. Other specimens of the same group have been described from the
Upper Triassic rocks of Massachusetts.
The Pelycosimia of Huene are very interesting as showing apparently
primitive forms with which the true phytosaurs may have been intimately
related ancestrally. They, too, have a rather short skull with the
nostrils in front, and were not at all aquatic in habit. Not much is
known about the single genus that is located in the group, aside from
the skull and a few limb bones.
PHYTOSAURIA
The Phytosauria, so far as known, were all reptiles of considerable
size, greatly resembling the crocodiles, and especially the gavials
in form and habit, but differing very greatly in having the external
nostrils situated far back near the eyes; in having no false palate
so characteristic of the Crocodilia; in having a more primitive
shoulder-girdle, consisting of a short coracoid, interclavicle, and
clavicles; and in having the ordinary type of pelvis, that is, with
the pubis entering into the acetabular articulation for the femur.
They were all, like the crocodiles, covered more or less by a bony
armor; there are two openings on each side of the temporal region;
there is no pineal opening; the vertebrae are gently biconcave,
precisely like those of the early or mesosuchian crocodiles; there
is always an opening of considerable size, called the preorbital
foramen, in front of the eyes, as in some crocodiles, many dinosaurs,
and most pterodactyls; there is also an opening through the back
part of the mandibles as in crocodiles; and the double-headed ribs
are attached exclusively to the transverse process of the arch,
precisely as in the crocodiles, dinosaurs, and pterodactyls. From
all these it is evident that the phytosaurs are related most nearly
to the crocodiles and dinosaurs, and are probably an early branch
of the stem from which they, the pterodactyls and the birds, arose,
a branch that persisted only a short time, geologically speaking,
and went entirely out of existence at the close of Triassic times,
leaving no descendants behind. Nevertheless, in this comparatively
brief life-span they developed not a few distinctive forms and became
widely distributed over the earth. Their remains are known from the
Upper Trias of Germany, England, and Scotland, India, South Africa,
and from Massachusetts, North and South Carolina, and many places
in the Rocky Mountains. No true phytosaurs are yet known from South
America, but in all probability they will be discovered there when
the Triassic deposits of that continent have been better explored
for fossils. In the Rocky Mountains, especially, their remains are
widely scattered, they have been found in many localities in Wyoming,
Colorado, Oklahoma, Utah, and New Mexico. Though for the most part
their known remains from these localities are yet fragmentary, not
less than four distinct genera have been described from these regions:
“_Belodon_,” _Angistorhinus_, _Paleorhinus_, and _Episcoposaurus_.
From the Carolinas and Massachusetts a single genus, though described
under numerous names, has been made known, originally called by Emmons
_Rutiodon_ (_Rhytidodon_). And from Europe and India at least as many
more different genera are known. All these genera are, however, so
closely allied that they are placed in the single family Belodontidae.
[Illustration: FIG. 92.—Restoration of _Mystriosuchus_, an Upper
Triassic phytosaur.]
[Illustration: FIG. 93.—Skull of _Mystriosuchus_, a phytosaur: _pm_,
premaxilla; _m_, maxilla; _na_, nasal; _f_, frontal; _p_, prefrontal;
_l_, lacrimal; _pf_, postfrontal; _po_, postorbital; _pa_, parietal;
_sg_, squamosal; _qj_, quadratojugal; _pl_, palatine; _t_, transverse;
_in_, internal nares; _en_, external nares; _pt_, pterygoid; _bs_,
basisphenoid; _eo_, exoccipital. (After McGregor.)]
[Illustration: FIG. 94.—Dorsal vertebrae of phytosaur: _az_, anterior
zygapophysis; _pz_, posterior zygapophysis; _d_, _c_, articulations of
rib.]
[Illustration: FIG. 95.—Scapula and coracoid of _Rutiodon
carolinensis_, an American phytosaur. (After McGregor.)]
[Illustration: FIG. 96.—_Belodon_; restoration of head, from above.]
[Illustration: FIG. 97.—_Mystriosuchus_: restoration of head, from
above.]
In _Belodon_ (Fig. 96), the earliest known and most typical genus,
perhaps, the moderately elongated face has a high crest reaching nearly
to its front end, and this type is known both from Europe and from New
Mexico. Others have the face long and slender, even longer and more
slender than in the ancient teleosaur crocodiles or the modern gavials.
In some forms the teeth are cylindrical and slender throughout, and
there may be as many as fifty on each jaw, or two hundred in all; while
in others only the anterior teeth are cylindrical and the posterior
teeth are flattened and serrate along their cutting edges. In the body
not very great differences have been observed. Some are more slender
than others, and there are minor differences in the shapes and sizes
and numbers of the bony scutes along the back and on the throat.
But they are all alike in their essential characters, a very long
beak with numerous teeth; the foremost ones on the expanded, more
or less spoon-shaped front extremity, are more or less, sometimes
greatly, elongated. The jaws may be likened to a long and slender
pair of tongs with nipping teeth at the front end. The strong, long,
and flattened tail is sufficient evidence that the phytosaurs were
excellent swimmers, but, aside from that and the posterior location of
the external nostrils, directly over the internal, few other aquatic
adaptations are observed in the skeleton. There are no sclerotic bony
plates about the eyes, or at least none have so far been discovered,
although among the numerous known specimens they would confidently be
expected were they really present in the skeleton; and the presence of
bony armor negatives markedly aquatic habits.
Doubtless on the whole the habits of the phytosaurs were not very
unlike those of the modern gavials, which they so strongly resemble
in form, size, and general characters. But they differ very greatly
from the gavials in the extreme posterior position of the nostrils,
and in the greatly elongated teeth of the front end of the beak,
teeth which must have had some especial and peculiar use. Nor is the
position of the nares to be accounted for satisfactorily by reference
to aquatic habits. It has been suggested that the creatures used the
very long and slender beak in prodding and probing in the sand and
mud for soft-bodied invertebrates, worms and the like, for which the
teeth would be especially fitted; and that the posterior position of
the nostrils may be in part, perhaps wholly, accounted for by this
habit, which permitted the reptiles to breathe without extricating the
beak from the mud or shallow waters. That the animals were wholly and
intensely carnivorous in habit is attested by their teeth; although
they are called “plant saurians,” they never had anything to do with
plants in the way of food. Unfortunately so far no specimens have
ever been found showing the remains of stomach contents, nor have any
been found showing impressions of the form of the body or of any of
its parts. Until such specimens are found, as they doubtless will be
eventually, one can be less sure of the precise details in their life
reconstructions. However, the skeleton is now known nearly completely,
and this suffices to give a very approximately correct idea of what the
animals were like when alive.