Many reptile species died during the K-T event, but snakes, lizards and the crocodilians
persevered. Crocodilians have been on the planet for about 240 million
years. There are 23 crocodilian species today, including alligators, crocodiles and caimans. Mesozoic crocodilians were generally larger than living species. Another prehistoric order of reptiles is the sphenodontians. Today, there is one living sphenodontian -- the tuatara, which lives in New Zealand.
The tuatara (Sphenodon punctatus) is the only surviving species of an order that flourished 200 million years ago in New Zealand.
Konrad Wothe/Minden Pictures/Getty Images
The first mammals were
monotremes, or mammals that
reproduce by laying eggs. Mammals are common today, but only three
monotreme species still exist. These are the duck-billed platypus
and a couple of spiny anteaters, or echidnas.
A zookeeper cradles rare twin platypus babies. The platypus is one of the few remaining monotremes on Earth. Jason Edwards/National Geographic/Getty Images
Many reptile species died during the K-T event, but snakes, lizards and the crocodilians persevered. Crocodilians have been on the planet for about 240 million years. There are 23 crocodilian species today, including alligators, crocodiles and caimans. Mesozoic crocodilians were generally larger than living species. Another prehistoric order of reptiles is the sphenodontians. Today, there is one living sphenodontian -- the tuatara, which lives in New Zealand.