Palæos:		Unit 230: Rhynchocephalia
The Vertebrates		100: Rhynchocephalia

Rhynchocephalia

LEPIDOSAUROMORPHA
|--SQUAMATA
Rhynchocephalia
|--Pleurosauridae 
`--Sphenodontidae
   |--Clevosaurs 
   `--Sphenodontinae

Taxa on This Page

1. Clevosaurs X

2. Pleurosauridae X

3. Rhynchocephalia

4. Sphenodontidae

5. Sphenodontinae

Descriptions

Rhynchocephalia:  

Range: from the Late Triassic. 

Phylogeny: Lepidosauria : Squamata + * : Pleurosauridae + Sphenodontidae. 001116.

Pleurosauridae: Palaeopleurosaurus; Pleurosaurus. 

Range: Early Jurassic to Late Cretaceous. 

Phylogeny: Rhynchocephalia : Sphenodontidae + *. 

Characters: Elongated (<58 vertebrae.) with long tail; acrodont teeth; incomplete lower temporal bar. Marine, progressive reduction of limbs (normal structure). 

Sphenodontidae: Kallimodon, Homoeosaurus, Sapheosaurus, Pamizinsaurus. 

Range: from the Late Triassic. 

Phylogeny: Rhynchocephalia : Pleurosauridae + * : Clevosaurs + Sphenodontinae. 

Characters: VS-M size. See Clevosaurs entry for basic skull structure. $ Teeth fused to jaw margin (fully acrodont) and not replaced; less than 4 (7?) premaxillary teeth; $ marginal teeth added posteriorly as jaw grows; dentary fits between maxillary teeth and parallel row of palatal teeth; Meckelian canal runs along midline of jaw & is at least partially open; broad mandibular symphysis; prominent coronoid process of dentary, posterior process of dentary ends posterior to coronoid; with posterior surangular facet; frontals not fused (??); $ lacrimal absent; large upper temporal fenestra; complete lower temporal bar; quadratojugal retained; rigid quadrate; well-developed posterior tubercle on posterior margin of ischium; epiphyses present with determinate growth; may have osteoderms (Pamizinsaurus); food crushed thoroughly (insects & birds). 

Links: Introduction to the Sphenodontidae; Turtle, Tuatara, Crocodile Checklist--3; Jurassic Page´s gallery : the terrestrial wildlife (Sapheosaurus); Lebende Fossilien, Intro, Teil 2 (Homoeosaurus). 

References: Evans & Sigogneau-Russell (1997); Reynoso (1996); Reynoso (1997); Reynoso & Clark (1998). 

Image: Kallimodon (among a very good collection of fossil photos) from Herbert Krause. Reproduced by permission. 

Note: The nomenclature of sphenodont taxa tends to be rather confused. The scheme used here is adopted from the sensible system of Mikko Haaramo, who credits Wu, X-C (1994), Late Triassic - Early Jurassic sphenodontians from China and the phylogeny of the Sphenodontia, in Fraser, NC & H-D Sues (eds.), In the Shadow of the Dinosaurs, Cambridge Univ. Press. 001117.

Clevosaurs: Brachyrhinodon, Clevosaurus.  Clevosaurus > Sphenodon? 

Range: Early Jurassic to Early Cretaceous(?).

Phylogeny:  Sphenodontidae : Sphenodontinae + *.

Characters: 1 or more robust "incisor" teeth forming chisel edge ankylosed to premaxilla; palatine dentition; marginal dentition acrodont or absent; shearing (not crushing or piercing) bite with simple orthal (up-and-down) jaw motion; $ long thin posterior process of premaxilla excludes maxilla from margin of nares; $ lacrimal absent; may have dentine "lips"; $ antorbital skull very short (<25% of total skull); triradiate postfrontal broadly contacts frontal; complete lower temporal bar formed by jugal loosely contacting slim quadratojugal; $ dorsal process of jugal elongate; $ large (> 25% skull length) lower temporal fenestra; gap between jugal and quadratojugal small; proximal caudal vertebrae have large transverse processes; caudal autotomy septa may be present distally; humerus strongly bent and expanded at both ends; femur gently S-shaped. 

Note: For reasons I have not been able to determine, no one seems to have gotten around to giving this group a Latinized family name.  

Links: Diapsida; Clevosaurus bairdi (but server is frequently reduced or absent!); Autapomorphies of diapsid clades; Untitled Document; Lecture 12 - Early Jurassic. 

References: Reynoso (1996); Reynoso & Clark (1998); Sues et al. (1994).

Sphenodontinae: Cynosphenodon, Eilenodon, Sphenodon, Zapatadon. Probably: Sphenodon > Eilenodon. However, it may be more useful (and is used here) as Sphenodon + Eilenodon + ??.

Range: from the Early Jurassic. 2 (3?) living species of Sphenodon; fossorial, live in association with sea birds on islands off New Zealand.

Phylogeny: Sphenodontidae : Clevosaurs + *. 

Characters:  Sphenodon is the giant of this largely diminutive group. Generally triangular, teeth with round cross-section; teeth added from posterior of jaw; $ caniniform teeth posterior to edentulous ridge at anterior end of dentary; $ proplinal jaw movement, as judged from wear facets on teeth; prominent coronoid process of dentary; dentary markedly straight ventrally, with small, ventral "chin" projection under symphysial area; retroarticular process reduced; central region of pterygoid long; lower temporal fenestra small (<25% skull length); posterior process of ischium present. 

Links: Sphenodontidae; Tuatara Printout- EnchantedLearning.com; Family: Sphenodontidae; Tuatara Skull Replica from Skulls Unlimited; Untitled Document; Untitled Document; Information about U.S. FDC: 32¢ Opisthias; Growth patterns and ontogenetic variation of the teeth and jaws of ... (Reynoso abstract on tooth development); Today, lepidosaurs are a diverse group of reptiles. With more than ... (sphenodontines remained dominant until the Cenozoic).

References: Reynoso (1996); Reynoso (1997); Reynoso & Clark (1998). 

Image: Sphenodon punctatus. tuatara. ATW040220.

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