Samuel Wendell Williston.

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middle line posteriorly. Coracoids very large, contiguous in midline;
clavicles and interclavicle small, sometimes vestigial. Ilium rod-like,
articulating below with ischium only, above with a well-developed
sacrum of three or four vertebrae.

An extensive and long-lived group of purely marine reptiles,
widely distributed over the earth; as a whole clearly defined, but
with many minor modifications. The neck was extremely variable
in length, with from thirteen to seventy-six cervical vertebrae. The
body was broad, though not nearly so broad as represented in most
modern restorations. The most perfect specimen known — and the
author has seen most of them in the collections of the world — is that
of Thaumatosaurus victor, in the Stuttgart museum, of which a figure
copied from a photograph is reproduced here. The body, it is seen,
is broadly oval, but not flat, protected below by the extraordinary
developments of the pectoral and pelvic girdles and intervening
parasternal ribs. Their phylogenetic relationships with the Notho-
sauria are incontestable, though the closed palate of the latter indi-
cates that no known form could have been actually ancestral to

Family Plesiosauridae. Skull moderately long. From thirty-
five to [seventy-six] cervical vertebrae, the cervical ribs double-
headed. Scapulae not contiguous in the middle; no interclavicular
foramen; epipodials much longer than broad, no accessory epipo-
dials. Coracoids contiguous throughout.

Jurassic. Plesiosaurus Conybeare, Thaumatosaurus Meyer, Europe.

Family Pliosauridae. Skull long, neck short, composed of about
nineteen vertebrae. Cervical ribs double-headed; five pectoral and
about twenty dorsal vertebrae. Premaxillae continuous to parietals
in middle. Scapulae closely approximate in midHne; coracoids con-

Fig. 173. Skeleton of Thaumatosaurus (Plesiosauria). After Fraas.
One twentieth natural size.



tiguous throughout. Two or three epipodials, as broad as long or
broader. Ischia long. Large or very large.
Jurassic. Pliosaurus Owen, Peloneustes Lydekker, Europe.

Family Cryptocleididae. Very much like the following family,
but the neck is shorter, with from thirty- two to forty-four vertebrae;
and the coracoids are contiguous throughout. From two to four
epipodials, all short. Cervical ribs single-headed. Skull short.

Jurassic. Cryptodeidus Seeley, Muraenosaurus Seeley, Tricleidus
Andrews, Picrocleidus Andrews, Microcleidus Watson, Sthenaro-
saurus Watson, Europe.

Fig. 174. Skeleton of Trinacromerum osborni, a Cretaceous plesiosaur, as mounted in the
University of Kansas Museum.

Family Elasmosauridae. Head short, neck very long, with from
more than fifty to seventy-six vertebrae; ribs single-headed. The
scapulae meet in midline; no interclavicular foramen. Coracoids
broadly separated on their posterior half. Ischia short. Two epi-
podials only, short.

Upper Cretaceous. Elasmosaurus Cope, Ogmodeirus Williston and
Moodie, Leurospondylus Brown, North America.

Family Polycotylidae. Skull very slender. Premaxillae articu-
lating with parietals. Neck not longer than head, with from twenty-
three to twenty-six vertebrae; ribs single-headed. The precoracoidal
process separates the scapulae in the midline; an interclavicular fora-
men; coracoids contiguous throughout. Ischia elongate. Three or
four epipodials, all short.

Upper Cretaceous. Polycotylus Cope, Trinacromerum Cragin,
? Piratosaurus Leidy, North America.


Family Brachatjcheniidae. Skull long, neck very short, with but
thirteen vertebrae, shorter than skull. Cervical ribs singleheaded.
Pterygoids not reaching to vomers. Paddles imperfectly known.

Upper Cretaceous. Brachauchenius Williston, North America.

Genera incertae sedis

Triassic. "Plesiosaurus" Conybeare, Europe.

Jurassic. Eretmosaurus Seeley, Colymbosaurus Seeley, Tschyrodon
Meyer, Liopleurodon Sauvage, Spondylosaurus Fischer, Simolestes
Andrews, Europe. Megalneusaurus Knight, Pantosaurus Marsh,,
" Muraenosaurus" Seeley, North America.

Lower Cretaceous. ^'Plesiosaurus'' Conybeare, North America.

Upper Cretaceous. Mauisaurus Hector, New Zealand. Polypty-
chodon Owen, Europe. Cimoliosaurus'Leidy,OligosimusL,eidy,Bri'mo-
saurusl^eidy,Piptomerus CoY)e, Orophosaurus Cope, Embaphias Cope,
Taphrosaurus Cope, Uronautes Cope, "Plesiosaurus^' Conybeare,.
North America.


Temporal opening bounded by parietal, postfrontal, postorbital,
and squamosal. Jaws and palatines with few, very large, fiat crush-
ing teeth. A parietal opening. Vertebrae amphicoelous, with hypo-
sphene, h3rpantrum. Ribs double-headed. Remainder of skeleton

This singular group of littoral, shell-eating reptiles has long been
a problem, because of our ignorance of the skeleton. Some would
include them among the Sauropterygia as a separate suborder;
others would give to them the same rank among the Therapsida. If
the supratemporal and interparietal are really present, as believed
by Huene, they would certainly find no place among the Sauro-
pterygia. But their presence has been denied. On the other hand, if
there should prove to be but a single coracoid on each side in the
pectoral girdle, their location among the Therapsida would be im-
proper. Placochelys has a carapace of bony plates, both above and
below, with isolated ones upon the skull, all of which seem to be
wanting in Placodus. Their presence or absence, however, is of no
more importance than in the Dinosauria, or Squamata, as examples.


As might be suspected in such forms, the number of presacral verte-
brae is reduced.

The temporal vacuity is bounded as in the plesiosaurs, and also in
some theriodonts. The maxillae are large, the nares situated rather
far back, perhaps an adaptation for grubbing in the mud after in-
vertebrates. Possibly there was a moderate adaptation in Placodus
for life in shallow water.

The placodonts were reptiles of considerable size, perhaps eight or
ten feet in length, undoubtedly slow in movement, and with a heavy
skull, as have all shell-eating reptiles.

Until more is known of the skeleton, the group may remain in an
independent position, though there is Uttle in the structure of the
skuU that would entitle them to an ordinal rank; shell-eating animals
with crushing teeth occur in various orders.

Family Placodontidae. Upper Triassic. Placodus Agassiz {Ano-
mosaurus Huene), Placochelys Jaekel, Cyamodus Meyer, Europe,



Primitive, aquatic reptiles with long neck, body, and tail, two or
three feet in length. Structure of skull imperfectly known, probably
with a single, upper temporal opening on each side. Face long and
slender, the nostril near orbits, the premaxillae elongated. Teeth
numerous, long and slender; small teeth on vomers, probably also on
other palatal bones. Vertebrae deeply amphicoelous; intercentra
unknown; eleven or twelve cervicals, eighteen to twenty- two dorsals,
two sacrals and sixty or more caudals. Free ribs on all presacrals
except atlas; dorsal ribs stout, single-headed, articulating with cen-
tra. Numerous parasternal ribs. Scapula fan-shaped; a single cora-
coid; clavicular girdle primitive; pelvis with small pubo-ischiatic
vacuity. Humerus with entepicondylar foramen. Propodials long;
epipodials short, carpus and tarsus primitive ; phalangeal formula of
pes (in Mesosaurus and Noteosaurus at least) 2, 3, 4, 5, 6, the fifth toe

These small reptiles, the first known in geological history with
marked aquatic adaptations, retain many primitive characters,
though highly speciahzed in the scapular girdle with its single cora-
coid, the earhest known. Aside from the Dolichosauria and certain
dinosaurs they are the only known aquatic reptiles with both neck
and tail elongated. Until the skull is better known, however, doubt
remains as to their relationships with other reptiles. By some they
have been placed with the double-arched reptiles; by others among
the Sauropterygia. Because of the articulation of the single-headed
ribs especially, and the probable possession of but a single, upper
temporal opening, their natural association seems to be near the
ichthyosaurs and lizards.^

1 [Much further evidence for this \aew is given by von Huene in his memoir Die
Ichthyosaurier des Lias und ihre Zusammenhdnge, 1922, 4to, Berlin. — Ed.]




FvmiLY Mesosauridae. Lower Permian. Stereosternum Cope
(Notosaurus Marsh), Mesosaurus Gervais, Brazil. Mesosaurus Ger-
vais {Ditrichosaurus Gurich), ? Noteosaurus Broom, South Africa.

Fig, 176. Restoration of Mesosaurus. After McGregor. The posture of the hind leg is

slightly modified.


Marine reptiles with all aquatic adaptations of the tail-propelling
type: elongated face; posterior nares, sclerotic plates, short neck,
elongated body, no sacrum, long, flattened or dilated tail, short pro-


podial and epipodial bones, hyperphalangy, and often hyperdactyly.
Premaxillae long; maxillae short. A parietal foramen; free paroccip-
itals, large stapes; no ectopterygoids or dermosupraoccipitals.
Teeth inserted in sockets or grooves, labyrinthine in structure; none
on palatal bones. The large upper temporal vacuity is bounded by
parietal, postf rontal, and tabular (supratemporal) . No lateral open-
ing. Vertebrae short, deeply amphicoelous, without persistent dorsal
intercentra. Scapulae small; a single coracoid; clavicles and inter-
clavicle present. No sternum, but numerous parasternals. Pelvis
more or less plate-like with small pubo-ischiatic vacuity. Prearticu-
lar bone of mandible distinct.

The ichthyosaurs were exclusively marine reptiles, more perfectly
adapted to aquatic Hfe than any other known ones unless it be the
plesiosaurs. They varied from about two to about thirty feet in

Family Mixosauridae. Cervical ribs for the most part holo-
cephalous. Tail with a preterminal dilatation, slightly decurved.
Chevrons Y-shaped. Epipodials relatively long; feet pentedactylate.
Face less elongate. Teeth more or less anisodont, inserted in sockets.

Middle and Upper Triassic. Mixosaurus Baur, Spitzbergen,.
Switzerland, Germany.

Family Shastosaueidae. Body more elongate. Cervical ribs
dichocephalous. Tail distinctly expanded and decurved distally.
Chevrons Y-shaped. Epipodials relatively long. Feet tetra- or tri-

Both the Mixosauridae and Shastosauridae, which Merriam gives
only sub-family values under the Mixosauridae, are more primitive^
with less perfect aquatic adaptations than the later forms of the
Ichthyosauridae, and especially the Ophthalmosauridae.

Middle or Upper Triassic. Cymbospondylus Leidy, Toretocnemus
Merriam, Merriamia Boulenger, Delphinosaurus Merriam, Shaslo-
saurus Merriam, Phalaradon Merriam, California, Nevada. Pesso-
saurus Wiman, Spitzbergen.

Family Ichthyosauridae. Fewer presacral vertebrae; pelvis
more reduced; tail with a broad terminal fin; epipodials shorter;
dorsal ribs dichocephalous; chevrons separate or fused; hind limbs



usually more reduced; frequently hyperdactylate. Teeth inserted in
grooves. Face longer.

Upper Triassic to Upper Cretaceous. Ichthyosaurus Koenig
{Proteosaurus Howe), Europe, Asia, Africa, Australia, New Zealand,
South and ? North America.

A widely distributed genus as it is ordinarily accepted. It pre-
sents, however, numerous minor modifications, that might justify its

Family Ophthalmosauridae. Differs from the more typical Ich-
thyosauria in the more reduced teeth, the presence of three epipo-
dial bones in the front paddles, the more reduced hind paddle, the
fusion of the ischium and ilium, in the apparent entire absence of
chevrons, and in the more discoidal form of the phalanges.

Upper Jurassic. Ophthalmosaurus Seeley (? Baptanodon Marsh),
Europe and North America.

Cretaceous (Upper Greensand). 7 Ophthalmosaurus Seeley.


Family Omphalosauridae. Marine reptiles with a short, shell-
crushing skull. Mandibles short, the dentaries united in a strong
symphysis, their broad, convex, superior surface beset with several
rows of low-crowned, button-like crushing teeth, the largest about
fifteen millimeters in diameter. Vertebrae amphicoelous. "Palate
plesiosaur-like." Skeleton otherwise unknown.

The incompletely known remains of these reptiles, described by
Merriam, are very suggestive of a new type of shell-eating aquatic
reptiles, but until more is known they are merely suggestive, the
ordinal rank and relationships provisional or conjectural. In them-
selves the characters are not of ordinal rank, but their associations
and their age make it not at all improbable that when fully known
they will justify the rank provisionally given to them. From essen-
tially the same horizon in Spitzbergen similar teeth have been
described by Wiman, which seem to pertain to the same kind of

^ [Von Huene (1922) divides the old genus Ichthyosaurus into several phyletic lines,
the evolution of which he traces from the Triassic to the Upper Cretaceous. — Ed.]

^ [Recent authors (von Huene, Nopcsa) class the Omphalosauria with the Ichthyo-
sauria. — Ed.]


reptiles. Somewhat doubtfully associated with those remains are
others of ichthyosaur-like bones that the describer provisionally as-
sociated with the Ichthyosauria, bearing possibly a like relation to
the known Ichthyosauria that Glohidens does to the typical Pytho-

Middle Triassic. Omphalosaurus Merriam, Nevada. Pessopteryx
Wiman, Spitzbergen.


Quadrupedal, arboreal, terrestrial, or subaquatic reptiles one to six
feet in length, with a single, upper temporal opening between the
parietal and the temporal arch, the quadrate fixed. Ribs in part or
all single-headed, articulating with centra — a single coracoid, an
interclavicle, and clavicles.

This order, as here Hmited, is a provisional one, including several
reptiles, some of them imperfectly known, which cannot be placed in
any other known order. Most of them have hitherto been classified
with the RhynchocephaUa, from which they are distinguished by the
absence of a lateral temporal opening, so far as known. Perhaps when
finally known they will be found to be incoherent. For the present
they may be defined as families.

Family Araeoscelidae. Very slender, arboreal or leaping, hol-
low-boned reptiles of less than eighteen inches in length, with long
legs and long tail. The broad lateral temporal region is formed ap-
parently of a single bone, here identified as the squamosal, the quad-
ratojugal absent. The dermosupraoccipital is apparently large. Lac-
rimal vestigial or absent. A parietal foramen. All cranial bones
paired. Palatal bones with teeth. At least seven cervical verte-
brae, twenty dorsal, two sacral, and a long, slender tail. Vertebrae
amphicoelous with persistent intercentra. Cervical ribs, at least,
single-headed, the dorsal more or less dichocephalous. Coracoid
and scapula closely fused. Humerus with both entepicondylar
and ectepicondylar foramina. Pelvis primitive. Phalangeal formula
primitive. Calcaneum produced.

Araeoscelis, the type of the family, is the earliest definitely known
reptile with a single, upper temporal vacuity, bounded as in the
lizards, and a fixed quadrate. It was a very slender, leaping or

Fig. 179. Skeleton of ^raeoscelis (ProtoTosaurla.). About one fourth natural size.

Fig. 1 80. Restoration of Araeoscelis.



arboricolous, insectivorous, lizard-like reptile from the Lower Per-
mian of Texas. Of Kadaliosaurus, unfortunately, the skull is un-
known. Its slender bones were less hollow, and it has also numerous
parasternal ribs, unknown in Araeoscelis.

Lower Permian. Araeoscelis Williston, Texas. Kadaliosaurus
Credner, Germany.

Family Protorosauridae. Elongate reptiles with long neck and
hind legs and hollow bones, from three to five feet in length. Skull
imperfectly known, probably with an upper temporal opening only.
Sclerotic plates in orbits. Prevomers, palatines, and pterygoid with
small teeth. Vertebrae amphicoelous, with persistent intercentra.
Seven cervicals, sixteen to eighteen dorsals, two or three sacrals, and
a long tail. A single coracoid. Pelvis more or less plate-Hke, with

Fig. 181. Skeleton of Protorosaurus (Protorosauria), modified from Seeley.
About one tenth natural size.

probably a small pubo-ischiatic vacuity. Ribs single-headed, articu-
lating with centrum, those of the cervical region very slender. Epi-
podials about as long as propodials, the hind legs much longer than
the front. Humeri with ectepicondylar (?) foramen; nine or ten
carpals, seven tarsals ; phalangeal formula primitive, the digits long.
Numerous abdominal ribs.

Although the first-described fossil reptiles, the protorosaurs are
still imperfectly known in the details of their structure, especially of
the skull, pectoral, and pelvic girdles. In the elongation of the neck
and the slender legs Protorosaurus very much resembles Araeoscelis,
and doubtless had similar habits, whether or not the structure of the
skuU was the same. The numerous known specimens of Protoro-
saurus differ so much from each other that it is not at all improb-
able that they represent different genera.

Aphelosaurus is still more problematical, inasmuch as all that is
known of it are the trunk and limbs. The limbs resemble those of


Protorosaurus in size, slenderness, and proportions. The single-
headed ribs are described by Thevenin as articulating intercentrally.

Lower Permian. ? Aphelosaurus Gervais, France.

Upper Permian. Protorosaurus v. Meyer, Germany.

The nares were described by Seeley as immediately in front of
the orbits- — ^an error. There may be a small antorbital foramen,
but it is doubtful.

Family Saphaeosauridae. Slender, terrestrial or subaquatic rep-
tiles about two feet in length. Skull with a single temporal opening,
the quadrate fixed and the lateral temporal region moderately broad.
No postf rontals ; postorbitals large. No parietal foramen. Maxillae
and dentaries edentulous, with cutting edges. Vertebrae procoelous
without intercentra; twenty- three presacrals, two sacrals, and fifty
or more caudals. Caudal vertebrae with splitting point (?). Ribs
single-headed, articulating with anterior part of centrum. Coracoid
with two median emarginations. Interclavicle T-shaped, the clavicles
slender. Parasternals numerous, composed of a median unpaired
pices and a lateral splint on each side. Pubes and ischia broadly
separated by pubo-ischiatic opening, the ischia with a stout posterior
tuberosity. An ectepicondylar foramen in humerus. Manus and pes
pentedactylate, with primitive phalangeal formula.

Saphaeosaurus, usually called Sauranodon, has long been classed
as a representative of a distinct family of the RhynchocephaUa. The
skull, as described by both von Meyer and Lortet, has but a single
temporal opening on each side, bounded externally by the postorbital
and squamosal (tabular?) . There is no lower temporal opening. The
structure of the temporal region as described is doubtful. In much
probability the tabular, squamosal, and quadra tojugal are all present.
In all its essential characters it is a Lacertilian with a primitively
fixed quadrate. The vertebrae, as figured and described by Lortet,
are procoelous, perhaps the first known evidence of such in geological

Upper Jurassic. Saphaeosaurus v. Meyer {Sauranodon Jourdan),

Family Pleurosauridae. Very slender, snake-Hke, aquatic rep-
tiles, with short neck, long body, very long flattened tail, and small
pentedactylate legs; attaining a length of nearly five feet. Skull

Fig. 182. Skeleton of Sap/iaeosaur us (Protorosaui'ia.). After Lortet.
One fourth natural size.



elongate, pointed, the nares remote from end. No postfrontals. A
parietal foramen. The single temporal opening is bounded within by
the parietal, without by the postorbital and (?) squamosal. A small
quadratojugal. Teeth pointed and recurved. Acrodont. Palatal
teeth unknown. Five cervicals, forty or forty-one dorsals, two sa-
crals, and more than seventy caudals. Vertebrae amphicoelous, cer-
vical intercentra hypapophysial. Ribs single-headed, articulating as
in the Squamata. Numerous slender, parasternal ribs.

Fleurosaurus, the only certainly known genus of the family, was
long supposed to be a member of the RhynchocephaHa, though it has
also long been known to have but a single upper temporal opening.
Its remarkable adaptation to aquatic Ufe is shown in the elongated
head, posterior nares, short neck, very slender trunk, very small legs,
and enormously elongated tail, with its long chevrons and spines,
which in life was surmounted by a thin crest of scales.

Acrosaurus is probably only the young of Fleurosaurus, as the
author convinced himself by examination of specimens in the Munich
museum. In consequence, the ordinal name once proposed for these
reptiles, Acrosauria, is inappropriate. The structure of the temporal
region still needs confirmation. If there is but a single bone bounding
the temporal opening posteriorly, it is in much probabiHty the real

Uppermost Jurassic. Fleurosaurus v. Meyer {Anguisaurus Miin-
ster, Saurophidium Jourdan), Germany, France. } Acrosaurus v.
Meyer. Germany.


With a single temporal vacuity on each side, bounded by parietal,
tabular, squamosal, and postorbital, secondarily sometimes roofed
over or the arcade obsolete. No lower temporal opening or bar.
Quadrate movably articulated, streptostyhc, secondarily sometimes
fixed. No supratemporals, dermosupraoccipitals, or quadratojugals.
The pterygoids articulate in front with the palatines, never with the
prevomers. Paroccipitals fused with exoccipitals. Interorbital sep-
tum not ossified. Teeth acrodont or pleurodont, often attached to
palatine and pterygoid. Prearticular fused with articular. Ribs
single-headed, articulating with centrum.


A. Suborder Lacertilia (Sauria)^

Subvolant, arboreal, terrestrial, burrowing, subaquatic, or marine
reptiles from a few inches to about forty feet in length; quadrupedal,
bipedal, or limbless; herbivorous, insectivorous, or carnivorous.
Brain-case in front of prootics more or less membranous. Lacrimals
small or vestigial. Posterior arcade sometimes absent. Mandibles
usually united by suture. Vertebrae procoelous, except in the Geck-
onidae and Uroplatidae; not more than two sacral vertebrae. Clav-
icles and interclavicle rarely absent. No entepicondylar, but usually
an ectepicondylar foramen in humerus.

This group is often given an ordinal rank, equivalent to the Ophidia
or even to the Pythonomorpha, but the ultimate distinctions be-
tween them are almost trivial, as will be seen, and in many legless
burrowing lizards the skull structure mimics that of the snakes.
More than eighteen hundred species are known, distributed widely
throughout the world, usually classed in about twenty families and
numerous genera.

Because of their predominantly terrestrial habits, but few remains
of lizards are found in the rocks, aside from the more aquatic or
marine types. Only about fifty genera of extinct forms have been
described and less than one hundred species, and the greater majority
of those are for the most part fragmentary and incomplete, so much
so that their systematic positions are very often uncertain and pro-
visional. Doubtless they have had a long and abundant geological
history from very remote times, but of the true land lizards almost
nothing is known throughout the Mesozoic. But few positive char-
acters are distinctive of the group, though many negative ones are.
The mandibles are usually suturally united in the middle, but a few
forms have them ligamentously attached. The presence of legs is not
distinctive, though at least a vestige of the pectoral girdle remains.
The more or less open brain-case in front is perhaps the most
diagnostic, only partially enclosed by the more or less vestigial post-
optics ("alisphenoids," "postorbitals"). However, in the Amphis-
baenia even this character is doubtful, and in the mosasaurs a dis-
tinct descending plate from the parietals resembles that of the snakes,

1 [For a very comprehensive morphological and taxonomic revision of the Lacertilia,

1 2 3 4 5 6 7 8 9 10 11 12 13 15 17 18

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