Evolutionĭuring the late Cretaceous era, monitor lizards or their close relatives are believed to have evolved into amphibious and then fully marine forms, the mosasaurs, which reached lengths of up to 17 m (56 ft). Monitor lizards are oviparous, laying from seven to 37 eggs, which they often cover with soil or protect in a hollow tree stump. This allows monitor lizards to create mammalian-equivalent pressure differentials between the pulmonary and systemic circuits, which in turn ensures that oxygenated blood is quickly distributed to the body without also flooding the lungs with high pressure blood.Īnatomical and molecular studies indicate that all varanids (and possibly all lizards) are partially venomous.
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Whereas most reptiles are considered to have three chambered hearts, the hearts of monitor lizards - as with those of boas and pythons - have a well developed ventricular septum that completely separates the pulmonary and systemic sides of the circulatory system during systole. Monitor lizards have a high aerobic scope that is afforded, in part, by their heart anatomy. The general consensus is that monitor lizards have the highest standard metabolic rates of all extant reptiles. The active nature of monitor lizards has led to numerous studies on the metabolic capacities of these lizards. Monitor lizards are infamous for their active nature, maintaining large territories and employing active pursuit hunting techniques that are reminiscent of similar sized mammals. Finer morphological features such as the shape of the skull and limbs do vary though, and are strongly related to the ecology of each species. The genus Varanus is considered unique among animals in that its members are relatively morphologically conservative and yet show a range in size that is equivalent to a mouse and an elephant.
![argus monitor lizard california argus monitor lizard california](https://i1.wp.com/reptile-wrangler.com/wp-content/uploads/2019/08/11700799_10205868075038909_5287117258052083128_n-1.jpg)
However, three arboreal species, Varanus bitatawa, Varanus mabitang, and Varanus olivaceus, are primarily fruit eaters. Monitors lizards are, as a rule, almost entirely carnivorous. Ī total of 78 species are currently recognized however, given that several species-groups are in need of taxonomic review, this number is certain to be increased with future research. While most monitor lizards are carnivorous, eating eggs, smaller reptiles, fish, birds and small mammals, some also eat fruit and vegetation, depending on where they live. Most monitor species are terrestrial, but arboreal and semiaquatic monitors are also known.
![argus monitor lizard california argus monitor lizard california](http://pm1.narvii.com/7431/987cbff30d163f1a8ebfe1897f7be55d2b772b12r1-800-600v2_00.jpg)
The adult length of extant species ranges from 20 cm (7.9 in) in some species, to over 3 m (10 ft) in the case of the Komodo dragon, though the extinct varanid known as megalania ( Varanus priscus) may have been capable of reaching lengths of as much as 7 m (23 ft). Monitor lizards have long necks, powerful tails and claws, and well-developed limbs. They are native to Africa, Asia and Oceania, but are now found also in the Americas as an invasive species. Monitor lizard is the common name of several large lizard species, comprising the genus Varanus.