the anatomical peculiarities of spenodon and its affinities
Answers
Answer:
Sphenodontia is an order of lizard-like reptiles that has only one living genus and two living species, the Cook Strait tuatara and the Brother's Island tuatara. ... The word tuatara is a native Maori word that means “peaks on back”.
Explanation:
Sphenodon was formerly known on the main islands of New Zealand, but is now restricted to some small islands in the Bay of Plenty and appears to be on the verge of extinction.
General anatomical features
(1) The lizard like body of Sphenodonis about 2 feet long and the tail measures about 1 /3 of the whole length of the body- The animal is nocturnal.
(2) The body and tail are laterally compressed and a series of spines are dorsally present (along the middle line).
(3) Limbs are pentadactyle, legs are short and primitive in nature. Sometimes 10-11 carpels are present.
(4) Hind limbs are typically plantigrade.
(5) The upper surface of the body is covered with small granular scales and the lower surface is covered with transverse rows of large squarish scales.
(6) The head is large and there is prominent ridge over the eye.
(7) There is a foramen above the outer and one above the inner condyle of the humerus.
(8) There are eleven carpal elements in all, four in the proximal row, two centrals and five in the distal row.
(9) In the tarsus the tibial and fibular elements are quite distinct, though firmly united. The intermedium and the centrale are firmly fixed to the tibiale. There are three tarsal bones.
(10) Teeth are pleurodont and homodont like reptiles but they are monophyodont. The teeth are pointed, triangular, laterally compressed and arranged in two parallel rows, one along the maxilla, and the other along the palatine. The teeth of the lower jaw bite in between the two upper rows, all the rows becoming worn down in such a way as to form continuous ridges. Each premaxilla bears a prominent, chisel-shaped incisor, represented in the young animal by two pointed teeth. In the young Sphenodont a tooth has been found on each vomer — a condition unusual among reptiles.
(11) The pubes are united in a Symphysis, infront of which is a cartilaginous epipubis. A large oval foramen intervenes between the ischium, and the pubis. A cartilaginous hypoischium is attached to the ischia behind.
(12) In the skull, there is a complete lower temporal arch. The quadrate is immovably fixed, wedged in by the quadrate- jugal, squamosal, and pterygoid. The premaxilla are not fused together but separated by a suture. There is a broad palate, formed by the plate-like vomer, palatine and pterygoids. The pterygoids meet in the middle line and extend forwards to the vomers. There is an epipterygoid extending from the parietal to the pterygoid and quadrate.
(13) Sphenodon retains the large parietal foramen, in which, is the non-functional median pineal eye.
(14) There is no antorbital foramen.
(15) The anal opening of Sphenodonis transverse.
(16) There is no copulatory organ (Penis) in the male.
(17) The vertebrae are amphicoelous and fully ossified and intercentra are present.
(18) The ribs are single headed and have uncinate processes. There is a sternum and abdominal ribs.
(19) Chevron bones occur in the caudal region of the vertebrae.
(20) There is a median bone, the Pro-atlas, intercalated between the atlas and the occipital region of the skull.
(21) Caudal ribs become fused with the vertebrae.
(22) The lateral temporal fossa is bounded below, by an inferior temporal arch composed of jugal and quadrato-jugal (Palato-quadrate).
(23) Jacobson’s organ is present in a rather primitive form.
(24) A urinary bladder is present.
(25) There is a T-shaped interclavicle.
(26) Coracoid is without fenestra.
(27) It lays 10-13, leathery shelled eggs which are buried few inches below the surface of the soil. The young ones are hatched 13 months later.
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