water, into which they let themselves fall with a splash, whatever the height of the tree, and then swim away, or hide at the bottom for many minutes. Otherwise they exhibit few signs of animal intelligence. “The iguana,” says H. W. Bates (The Naturalist on the Amazons), “is one of the stupidest animals I ever met. The one I caught dropped helplessly from a tree just ahead of me; it turned round for a moment to have an idiotic stare at the intruder and then set off running along the path. I ran after it and it then stopped as a timid dog would do, crouching down and permitting me to seize it by the neck and carry it off.” Along with several other species, notably Ctenosura acanthinura, which is omnivorous, likewise called iguana, the common iguana, is much sought after in tropical America; the natives esteem its flesh a delicacy, and capture it by slipping a noose round its neck as it sits in fancied security on the branch of a tree.
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| Fig. 2.—Head of Iguana rhinolophus. |
Although chiefly arboreal, many of the iguanas take readily to the water; and there is at least one species, Amblyrhynchus cristatus, which leads for the most part an aquatic life. These marine lizards occur only in the Galapagos Islands, where they are never seen more than 20 yds. inland, while they may often be observed in companies several hundreds of yards from the shore, swimming with great facility by means of their flattened tails. Their feet are all more or less webbed, but in swimming they are said to keep these organs motionless by their sides. Their food consists of marine vegetation, to obtain which they dive beneath the water, where they are able to remain, without coming to the surface to breathe, for a very considerable time. Though they are thus the most aquatic of lizards, Darwin, who studied their habits during his visit to those islands, states that when frightened they will not enter the water. Driven along a narrow ledge of rock to the edge of the sea, they preferred capture to escape by swimming, while if thrown into the water they immediately returned to the point from which they started. A land species belonging to the allied genus Conolophus also occurs in the Galapagos, which differs from most of its kind in forming burrows in the ground.
IGUANODON, a large extinct herbivorous land reptile from
the Wealden formation of western Europe, almost completely
known by numerous skeletons from Bernissart, near Mons,
Belgium. It is a typical representative of the ornithopodous
(Gr. for bird-footed) Dinosauria. The head is large and laterally
compressed with a blunt snout, nearly terminal nostrils and
relatively small eyes. The sides of the jaws are provided with
a close series of grinding teeth, which are often worn down to
stumps; the front of the jaws forms a toothless beak, which
would be encased originally in a horny sheath. When unworn
the teeth are spatulate and crimped or serrated round the edge,
closely resembling those of the existing Central American
lizard, Iguana—hence the name Iguanodon (Gr. Iguana-tooth)
proposed by Mantell, the discoverer of this reptile, in 1825.
The bodies of the vertebrae are solid; and they are convexo-concave
(i.e. opisthocoelous) in the neck and anterior part of the
back, where there must have been much freedom of motion.
The hindquarters are comparatively large and heavy, while
the tail is long, deep and more or less laterally compressed,
evidently adapted for swimming. The small and mobile fore-limbs
bear four complete fingers, with the thumb reduced to
a bony spur. The pelvis and hind-limbs much resemble those
of a running bird, such as those of an emu or the extinct moa;
but the basal bones (metatarsals) of the three-toed foot remain
separate throughout life, thus differing from those of the running
birds, which are firmly fused together even in the young adult.
No external armour has been found. The reptile doubtless
frequented marshes, feeding on the succulent
vegetation, and often swimming in
the water. Footprints prove that when on
land it walked habitually on its hind-limbs.
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| Skeleton of Iguanadon bernissartensis. (After Dollo.) |
The earliest remains of Iguanodon were found by Dr G. A. Mantell in the Wealden formation of Sussex, and a large part of the skeleton, lacking the head, was subsequently discovered in a block of ragstone in the Lower Greensand near Maidstone, Kent. These fossils, which are now in the British Museum, were interpreted by Dr Mantell, who made comparisons with the skeleton of Iguana, on the erroneous supposition that the resemblance in the teeth denoted some relationship to this existing lizard. Several of the bones, however, could not be understood until the much later discoveries of Mr S. H. Beckles in the Wealden cliffs near Hastings; and an accurate knowledge of the skeleton was only obtained when many complete specimens were disinterred by the Belgian government from the Wealden beds at Bernissart, near Mons, during the years 1877–1880. These skeletons, which now form the most striking feature of the Brussels Museum, evidently represent a large troop of animals which were suddenly destroyed and buried in a deep
