the sister group to squamates, based on chromosomal and gene sequence data
together they form the Lepidosauria
rhynchocephalians have always had low or moderate diversity
most rhynchocephalian radiation occurred during the Triassic and Jurassic
most had disappeared by the Cretaceous
were the dominant tetrapod of Cretaceous South America
only one extant family (Sphenodontidae)
with one extant species; the tuatara (Sphenodon punctatus)
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Feeding Ecology
forage at night, when temperature range between 12°C to 16°C, but are not exclusively nocturnal
prey predominantly consists of arthropods and other invertebrates, but they also occasionally eat skinks, geckos, and seabirds
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Reproduction and Lifecycle
long-lived and late maturity
mating occurs in January, but eggs won't be laid until the October-December of the following year
each clutch contains between 5 and 15 eggs, which hatch 11-16 months after egg deposition
optimum incubation temperature is between 18°C and 22°C
the lowest of any living reptile
eggs absorb moisture during development
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Anatomy and Physiology
lepidosaurs share numerous derived characters:
transverse cloacal opening (the vent)
tongue notched distally and used to capture prey (lingual prehension)
full body ecdysis
imperforate stapes
pelvic bones fused in adults
fracture planes or septa in the caudal vertebrae
rhynchocephalians differ from squamates by:
the presence of gastralia
a narrow quadrate with greatly reduced or lateral concha
lower temporal fenestra enclosed or partially so,
jugal in the mid-temporal arch touching the squamosal posteriorly
prominent coronoid process on the mandible
several anterior teeth of the palatine series enlarged
dentary and mandibular teeth generally enlarged, regionalised, and fused to the dorsal margin of bone
premaxillary teeth replaced by chisel-shaped extensions of the premaxillary bones that have given rise to the tuatara’s other vernacular name, half-beaks
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