Reptilia 1 (cont.) Modern snakes and lizards




Дата канвертавання26.04.2016
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REPTILIA 1 (cont.)



  1. Modern snakes and lizards

    1. Lineage dates to Mesozoic

    2. Predominantly terrestrial, some secondarily aquatic species

    3. Predominantly insectivorous/carnivorous

    4. Order Squamata

      1. Systematics and diversity

        1. Squamata originated in the Triassic (210-245 mya) and include:

          1. By far the most abundant group other than birds

          2. 21 families, 4000 species of lizards

          3. 1 family, 133 species of amphisbaenians

          4. 17 families, 2700 species of snakes

          5. Cosmopolitan distribution, occurring throughout the world in a wide range of terrestrial and aquatic habitats, except for Antarctica and the highest elevations and latitudes

            1. Within Serpentes, about 2/3 of species are in a single family, the Colubridae.

      2. General characteristics

        1. Determinate growth (derived character): unlike other reptiles (crocodiles and turtles), don’t grow continuously throughout lives

        2. Kinetic skulls

          1. Skulls are, in general, "lightly" constructed – number, size of bones reduced

          2. Retain mobile joints between various parts of the skull, notably between the quadrate and squamosal (at back of jaw)

          3. Best developed in snakes

        3. Males have unique reproductive organs = hemipenis

        4. Limb reduction (to varying degrees) is common throughout the group

          1. One investigator estimated that it’s happened at least 62 times

          2. Every major group has at least one species with some degree of reduction

          3. Most prominent in

            1. Snakes

            2. Amphisbaenians ("legless lizards")




        1. Tail autotomy is a shared, derived character for Squamata, but has been secondarily lost in some

          1. Autotomy = "voluntary" tail loss

          2. Used as mechanism to avoid predation

          3. Interestingly, breaks occur along specialized fracture plates within tail vertebrae

          4. Muscles are specialized to constrict around break, closing "wound"

          5. Tails generally regenerate, although often different in appearance and internal anatomy




        1. Reproductive biology is varied

          1. Span entire range from oviparous - ovoviviparous - viviparous with full matrotrophy

          2. Sex determination can be either genetic (chromosomal) or temperature-dependent

          3. Parental care ranges from none to some maternal protection of eggs/young

        2. Thermoregulation (seen most often in lizards)

          1. Most species are ectothermic

          2. But can regulate temperatures with precision


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