Reptiles radiation

Carboniferous 345 Myr Climate cools, marked latitudinal gradients. Extensive forests of early vascular plants, especially club mosses, horsetails, ferns. Coal beds form. Amphibians diversify first reptiles appear. Radiation of early insect orders... 

Permian 290 Myr All land united in one large continent - Pangaea large glaciers form. Reptiles, including mammal-like forms, radiate amphibians decline diverse orders of insects evolve. Conifers appear. Mass extinction at end of period (ca. 95% of all species disappear)... 

Radiation adversely affects limb regeneration of amphibians, alters DNA metabolism, and increases the frequency of chromosomal aberrations and liver lesions (Table 32.25). In some species of amphibians and reptiles, as in many mammals, mortality rates after acute exposure to radiation do not stabilize within 30 days — effectively invalidating the conventional LD50 (30-day postexposure) value. In the rough-skinned newt (Taricha granulosa), for example, the minimal LD50 dose at 200 days after irradiation was 2.5 Gy, compared with 350 Gy at 30 days (Willis and... 

Table 32.25 Radiation Effects on Selected Amphibians and Reptiles... 

The first "true" terrestrial vertebrates, whether taxonomically amphibians or reptiles, were definitely not lizards. However, there is good reason to imagine that they behaved like lizards (Maderson, 1972a 164). Data are available that suggest that a superficial corneous layer of the epidermis, wherein the cells synthesized 3-keratin, was an adaptation protecting the living cells from the deleterious effects of ultraviolet radiation (Maderson et al., 1984, and in preparation). 

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