A crocodile next-generation gender determined according to the temperature

A crocodile, a cold-blooded, spine reptiles to lay eggs. It is so far found one of the earliest and most primitive animals alive. Appeared in the Triassic period to the cretaceous period of the Mesozoic, and was a contemporary of dinosaurs animals, belongs to the carnivorous animals. Accepted a crocodile on a total of 23 varieties, high ecological value and scientific value and economic value. A crocodile eggs is to use the sun's heat and weeds by wet heat of fermentation of incubation. Are bred in a crocodile during the second week, if the incubation temperature below 30 degrees, the eggs hatch into female crocodile, if the temperature is higher than that of 34 degrees, hatch into male crocodile. The sex of the baby crocodile is determined by the incubation temperature, but the mother crocodile will balance the proportion of pregnant woman. Why the crocodile gender is determined by the temperature? Because the DNA in crocodile cannot determine gender, the gender is determined by temperature, this is the biological characteristics of Mesozoic species. As to why crocodiles and other biological DNA but not determined by the temperature of gender? There is no perfect explanation, but there are some hypothesis, to be the experiment confirmed.