The Osteology of the Reptiles/Chapter 7

by Samuel Wendell Williston

Layout 2

 

CHAPTER VII

A SYNOPTIC CLASSIFICATION OF THE REPTILIA

1. ANAPSIDA. Temporal region of skull roofed over, or secondarily emarginated, not perforated.
   1. Cotylosauria. Skeleton primitive; two coracoids^[1]; at least eighteen dorsal vertebrae, their ribs not expanded.
      1. Seymouria. Most primitive; teeth conical, in single row; intertemporal and otic notch. Insectivorous. Lower Permian.
      2. Diadectosauria. Teeth heterodont, the posterior transversely molariform, crushing. Malacophagous. Lower Permian.
      3. Labidosauria. Teeth anisodont, in two or more rows posteriorly; no supratemporal; interparietal on posterior surface. Lower Permian.
      4. Limnoscelis. Teeth anisodont, conical, in single row; interparietal on dorsal surface. Tail long. Lower Permian.
      5. [Pantylosauria. Teeth blunt or pebble-like, in single rows in upper jaw and dentary, numerous on palate and coronoid; interparietals large on dorsal surface. Lower Permian.]
      6. Pariasauria. Teeth anisodont, the posterior flattened [compressed] and crenulate; an acromion. Middle and Upper Permian.
      7. Procolophonia. Incisors conical, posterior teeth transverse, crushing; no supratemporal; interparietal obsolete or absent. Triassic.
   2. Eunotosauria. Skeleton primitive; two coracoids, ten dorsal vertebrae, their ribs expanded to meet on the dorsum, and a dermal layer of bony plates. Middle Permian.
   3. Testudinata (Chelonia). Skeleton not primitive; a single coracoid; ten dorsal vertebrae, their ribs expanded to meet on the dorsum or a dermal layer of bony plates.
      1. Amphichelydia. No mesoplastra. Cervical vertebrae amphicoelous or concavo-convex, neck not retractile. Upper Triassic to Cretaceous.
      2. Pleurodira. Neck retracted laterally; pelvis united with plastron. Jurassic to Recent.
      3. Cryptodira. Neck retracted vertically; carapace with peripheral plates. Jurassic to Recent.
      4. Trionychoidea. Neck retracted vertically; no peripheral plates. River turtles. Cretaceous to Recent.

2. SYNAPSIDA. A single temporal opening, primitively below the postorbito-squamosal arch; two coracoids.
   4. Theromorpha. Skeleton primitive; vertebrae notochordal with persistent dorsal intercentra; teeth on palate bones; phalangeal formula primitive; propodials horizontal in locomotion.
      1. Pelycosauria. Carnivorous; teeth strongly anisodont with diastema; dorsal spines more or less elongated; interparietal and tabulars present. Lower Permian.
      2. Edaphosauria. Malacophagous; teeth small, isodont. Dorsal spines elongate, with bars; interparietal and tabulars present. Lower Permian.
      3. Poliosauria. Insectivorous; teeth small, conical, subisodont; dorsal spines not elongate. Lower Permian.
      4. Caseasauria. Malacophagous; teeth small, isodont; dorsal spines short. Lower Permian.
   5. Therapsida. Skeleton less primitive; vertebrae amphicoelous, rarely notochordal; dorsal intercentra absent or unknown; phalangeal formula often reduced; propodials turned more or less downward in locomotion.
      1. Dinocephalia. Skull massive; no secondary palate; quadrate large, temporal opening surrounded by postorbital and squamosal; phalangeal formula primitive [?]. Upper Permian.
      2. Dromasauria. Dentition subisodont or absent; no secondary palate; phalangeal formula 2, 3, 3, 3, 3. Permian.
      3. Anomodontia. Edentulous or with long canine, or canine and molars; a rudimentary secondary palate; an acromion; phalangeal formula 2, 3, 3, 3, 3. Upper Permian, Triassic.
      4. Theriodontia. Carnivorous; dentition more or less heterodont, at least one pair of caniniform teeth; phalanges and teeth variable. Temporal opening extending to parietal in later forms. Triassic.
3. SYNAPTOSAURIA. A single temporal opening bounded below by postorbito-squamosal arch; no supratemporal, interparietal or tabulars. A single coracoid (? Placodontia).
   6. Sauropterygia. Vertebrae platycoelous; no dorsal intercentra; dorsal ribs single-headed, articulating with diapophysis; no teeth on palate. Neck more or less elongated.
      1. Nothosauria. Amphibious; feet webbed; phalangeal formula primitive; no interpterygoidal opening in palate. Middle and Upper Triassic.
      2. Plesiosauria. Marine; limbs paddle-like, the propodials long; hyperphalangic; palate with openings. Triassic to close of Cretaceous.
   7. Placodontia. Jaws and closed palate with heavy pavement teeth; vertebrae deeply amphicoelous; dorsal ribs double-headed; body with dermal bones; coracoids and feet unknown. Upper Triassic.

4. PARAPSIDA. A single temporal opening, between parietal and postorbito-squamosal arch; supratemporal (tabular) persistent. Ribs articulating more or less exclusively with centrum. A single coracoid.
   8. Proganosauria. Skeleton largely primitive. Aquatic, the neck and tail elongate. Phalangeal formula 2, 3, 4, 5, 4 (6). Skull imperfectly known; the quadrate fixed. Lower Permian.
   9. Ichthyosauria. Marine reptiles with short neck and all aquatic adaptations. Vertebrae amphicoelous; no dorsal intercentra. Quadrate fixed. Middle Triassic to Upper Cretaceous.
   10. Protorosauria. Aquatic or terrestrial. Not more than seven cervical vertebrae. Vertebrae amphicoelous (? Saphaeosauridae). Quadrate fixed. Phalangeal formula primitive. Lower Permian to Jurassic.
   11. Squamata. Quadrate freely articulated proximally (streptostylic) or secondarily fixed.
       1. Lacertilia (Sauria).^[2] Parietals never united to basisphenoid by descending plates, the brain-case more or less membranous anteriorly.

          (a) Kionocrania. An epipterygoid present^[3]; vertebrae amphicoelous with persistent dorsal intercentra, or procoelous and no dorsal intercentra; eight cervical vertebrae; limbed or limbless. Phalangeal formula primitive. Cretaceous to Recent.

          (b) Platynota. An epipterygoid. Vertebrae procoelous. Nine or more cervical vertebrae. Phalangeal formula primitive. Lower Cretaceous to Recent.

          (c) Pythonomorpha. Marine reptiles; limbs paddle-like, hyperphalangic; seven cervical vertebrae, procoelous; an epipterygoid present. Upper Cretaceous.

          (d) Amphisbaenia. No epipterygoid or temporal arch, the quadrate secondarily fixed; limbless or with vestigial front legs; vertebrae procoelous. Oligocene to Recent.

          (e) Rhiptoglossa. No epipterygoid or clavicles^[4]; five cervical vertebrae; vertebrae procoelous; phalangeal formula 2, 3, 4, 4, 3. Oligocene to Recent.

       2. Ophidia (Serpentes). Brain-case enclosed by descending plates from parietals and frontals; no epipterygoids; no temporal arch; mandibles united by ligament. Vertebrae procoelous, with zygosphenes; no chevrons. Limbless. Cretaceous to Recent.
5. DIAPSIDA. Two temporal openings, separated by postorbito-squamosal arch; no supratemporals or tabulars (? Youngina). A

single coracoid; no cleithrum. Phalangeal formula primitive. Often reduced postaxially.

12. ? Proterosuchia. Skull elongate, with palatal teeth; an antorbital vacuity. Skull only known. Triassic.
13. ? Eosuchia. No antorbital vacuity^[5]; interparietal and tabulars present; a parietal foramen. Only skull known. Upper Permian.

A. DIAPTOSAURIA. No antorbital foramen in skull; no supratemporal, tabulars or interparietals; palate with teeth. Vertebrae amphicoelous. Dorsal ribs articulating with intercentral space or centrum and arch, holocephalous.

14. Rhynchocephalia. Teeth protacrodont or acrodont.
    1. Rhynchosauria. Skull broad, with decurved premaxillae and crushing teeth on palate. No epicondylar foramina; pubo-ischiatic opening small. Littoral reptiles. Upper Triassic.
    2. Sphenodontia. Premaxillae beak-like; pelvis with large pubo-ischiatic vacuity; an entepicondylar foramen; dorsal intercentra persistent. Littoral reptiles. Upper Jurassic to Recent.
    3. Choristodera. Face elongate, the nares terminal; no pubo-ischiatic vacuity; teeth labyrinthine. Subaquatic. Uppermost Cretaceous and Lowermost Eocene.
    4. ? Thalattosauria. Skull elongate, with external nares posterior. Ribs attached by single head to centrum. Limbs paddle-like. Imperfectly known. Aquatic. Triassic.

AA. ARCHOSAURIA. Dorsal ribs, anteriorly at least, articulating with arch only, dichocephalous; no teeth on palate; no parietal foramen; no supratemporal, interparietal, or tabulars; vertebrae variable; dorsal intercentra not persistent; usually an antorbital opening. Typically with large pubo-ischiatic vacuity.

15. Parasuchia. Pelvis more or less plate-like with small pubo-ischiatic vacuity; vertebrae amphicoelous; no false palate; phalanges not reduced; body with dermal scutes.
    1. Pseudosuchia. External and internal nares near extremity of face; legs elongate, the epipodials long. Cursorial reptiles. Triassic.
    2. Pelycosimia. External and internal nares terminal. Legs short and stout. Terrestrial or marsh reptiles. Triassic.
    3. Phytosauria. External and internal nares remote from extremity of slender face. Triassic.
16. Crocodilia. Pubes excluded from acetabulum, not meeting in ventral symphysis. A secondary palate. External nares terminal; vertebrae amphicoelous or procoelous; postaxial digits reduced.
    1. Eusuchia. With dermal plates; no sclerotic plates. Amphibious. Jurassic to Recent.

2. Thalattosuchia. Neck shorter; no dermal plates; sclerotic plates in orbits. Vertebrae amphicoelous; a terminal caudal fin. Front legs reduced, paddle-like. Marine. Jurassic.

DINOSAURIA. More or less upright-walking reptiles.

17. Saurischia. Pelvis normal, the pubes meeting in a ventral symphysis; presacral vertebrae amphicoelous, or some or all opisthocoelous. No predentary or rostral bones in skull. Postaxial digits reduced. No dermal ossicles.
    1. Theropoda. Carnivorous or secondarily herbivorous, bipedal in gait, the front legs more or less reduced. Triassic to close of Cretaceous.
    2. Sauropoda (Cetiosauria, Opisthocoelia). Herbivorous, quadrupedal, the front legs but little or not at all reduced; limb bones not hollow; neck and tail elongate. Jurassic, Cretaceous.
18. Ornithischia (Orthopoda). Herbivorous, a predentary bone in mandible; pubes composed of a spatulate anterior process not meeting in symphysis, and a more or less elongate posterior process. Postaxial digits reduced.
    1. Ornithopoda. Upright-walking, bipedal. Without dermal bones. Lower Jurassic to close of Cretaceous.
    2. Stegosauria. Quadrupedal, with dermal armor of plates and spines; skull small; bones solid. Jurassic to close of Cretaceous.
    3. Ceratopsia. Quadrupedal. Skull very large with bony horns and a posterior expansion fringed with scutes or spines. Uppermost Cretaceous.
19. Pterosauria. Volant reptiles, the bones pneumatic. Fourth finger greatly elongated to support patagium. Vertebrae procoelous.
    1. Pterodermata (Rhamphorhynchoidea). Wing metacarpal not longer than forearm; tail long. Skull with teeth. Jurassic.
    2. Pterodactyloidea. Wing metacarpal longer than forearm; tail short. Skull with or without teeth. Upper Jurassic to Upper Cretaceous.

 

1. [But see footnote on page 126.—Ed.]
2. [For a more comprehensive classification of the Lacertilia, see C. L. Camp, 1923, Bulletin, Amer. Mus. Nat. Hist., xlviii, 289–481.—Ed.]
3. [Absent in Dibamidae.—G. K. N.]
4. [Sometimes present, but small.—Ed.]
5. [According to Broom, a well-preserved antorbital vacuity is present.—Ed.]