# The Osteology of the Reptiles/Chapter 10

Layout 2
CHAPTER X
THE SUBCLASS SYNAPTOSAURIA
6. ORDER SAUROPTERYGIA
A single, large temporal opening, bounded above by the parietal, below by the postorbital and squamosal. No dermosupraoccipitals, tabulars, or quadratojugals. Quadrate fixed. A parietal foramen. Neck elongated, the tail never long. Vertebrae platycoelous. Cervical ribs attached exclusively to the centrum, the dorsal ribs exclusively to the arch by a single head. A single, large coracoid on each side. Girdles stout. Pelvis with large pubo-ischiatic opening, or secondarily a thyroid foramen. No sternum. Parasternals stout.
There is still much doubt as to the derivation and genealogical relationships of this order of reptiles, chiefly because of the structure of the temporal region. The general characters of the skeleton are more or less modified by aquatic adaptations. The boundaries of the temporal region seem to be those of the upper opening of the diapsid reptiles; and there are many who believe that it really is the upper one, and that the order is nearest related to the Proganosauria. The opening, it is seen, is bounded quite like that of some members of the Therapsida, especially the Cynodontia; and these reptiles are confidently believed to have descended from theromorphous reptiles with a typical lower opening. The more general opinion is that the Sauropterygia are related to the anomodont-like reptiles. Some, however, would trace their descent directly from the Cotylosauria; others from the Diapsida, by the loss of the lower arch. The author believes that the first of these views is the correct one, but in the present uncertainty they may be left in an independent group.
Whatever has been their origin, we must await the discovery of their more terrestrial ancestors in the early Trias. The modifications of structure in adaptation to aquatic life are very pronounced, even in the Nothosauria. The order is clearly divisible into two chief groups, the Nothosauria and the Plesiosauria.
A. Suborder Nothosauria
Crawling or swimming reptiles from three to seven feet in length, of exclusively Triassic age. Skull depressed, more or less elongate, the orbits situated far forward, looking upward. Nares about midway between the orbits and extremity. Lacrimals possibly absent. Palate without openings, except the large internal nares, the vomers and pterygoids meeting in the middle line throughout. From twenty to twenty-five cervical, twenty-five to thirty dorsal, two to five sacral, vertebrae, and a moderately long tail. Clavicles stout, the interclavicle vestigial. The elongated coracoids meet in the middle line. Epipodials much shorter than propodials. Phalangeal formula primitive, or with the loss of one phalanx in the fourth finger. Digits probably webbed in life.
The Nothosauria were all aquatic in habit, but not exclusively so like the plesiosaurs, the feet still retaining terrestrial characters, with but minor aquatic adaptations. The parasternals, like those of the Plesiosauria, are very stout, apparently also an aquatic adaptation. The body was never slender, though less broad than that of the plesiosaurs, and it is not probable that they were rapid swimmers. They doubtless lived in the shallow waters, as do the crocodiles, coming frequently to land, and subsisted chiefly upon fishes and invertebrates, for the capture of which their slender, curved teeth were well fitted. A peculiar parallel adaptation to that of the contemporary aquatic Labyrinthodontia is seen in the forward position of the eyes in the flat skull, and also in the unusually stout clavicular girdle of both.
Several families have been proposed, based upon minor characters of the skull chiefly. For the present they may all be placed in a single family, the Nothosauridae.
Family Nothosauridae. Upper and Middle Trias. Anarosaurus Dames, Cymatosaurus Fritsch, Dactylosaurus Gürich, Doliovertebra Huene, Lamprosaurus Meyer, Lariosaurus Curioni, Microleptosaurus Scuphos, Neusticosaurus Seeley, Nothosaurus Münster, Parthanosaurus Scuphos, Pistosaurus Meyer, Proneusticosaurus Volz, Simosaurus Meyer.
B. Suborder Plesiosauria
Marine reptiles from eight to about fifty feet in length, with paddle-like, hyperphalangic limbs. Skull moderately broad to very slender. Nares small, situated remote from the extremity and near the orbits. Orbits with sclerotic plates. No distinct nasals. Internal nares small, situated in front of the external. A pair of posterior interpterygoidal openings divided by the parasphenoid always present; other openings variable on the palate. The squamosals meet in the 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 Nothosauria are incontestable, though the closed palate of the latter indicates that no known form could have been actually ancestral to them.
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 epipodials. Coracoids contiguous throughout.
Jurassic. Plesiosaurus Conybeare, Thaumatosaurus Meyer, Europe.
Fig. 173. Skeleton of Thaumatosaurus (Plesiosauria). After Fraas. One twentieth natural size.
​contiguous 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. Cryptocleidus Seeley, Muraenosaurus Seeley, Tricleidus Andrews, Picrocleidus Andrews, Microcleidus Watson, Sthenarosaurus 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 epipodials only, short.
Upper Cretaceous. Elasmosaurus Cope, Ogmodeirus Williston and Moodie, Leurospondylus Brown, North America.
Family Polycotylidae. Skull very slender. Premaxillae articulating 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 foramen; coracoids contiguous throughout. Ischia elongate. Three or four epipodials, all short.
Upper Cretaceous. Polycotylus Cope, Trinacromerum Cragin, ? Piratosaurus Leidy, North America.
​Family Brachaucheniidae. 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, Ischyrodon 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. Polyptychodon Owen, Europe. Cimoliosaurus Leidy, Oligosimus Leidy, Brimosaurus Leidy, Piptomerus Cope, Orophosaurus Cope, Embaphias Cope, Taphrosaurus Cope, Uronautes Cope, "Plesiosaurus" Conybeare, North America.
7. ORDER PLACODONTIA
Temporal opening bounded by parietal, postfrontal, postorbital, and squamosal. Jaws and palatines with few, very large, flat crushing teeth. A parietal opening. Vertebrae amphicoelous, with hyposphene, hypantrum. Ribs double-headed. Remainder of skeleton unknown.
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 Sauropterygia. 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 improper. 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 vertebrae 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 invertebrates. 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 little in the structure of the skull that would entitle them to an ordinal rank; shell-eating animals with crushing teeth occur in various orders.
Family Placodontidae. Upper Triassic. Placodus Agassiz (Anomosaurus Huene), Placochelys Jaekel, Cyamodus Meyer, Europe.