Starfish first appeared in the fossil record in the Cambrian. The first known asterozoans were the Somasteroidea, which exhibit characteristics of both groups. Starfish are infrequently found as fossils, possibly because their hard skeletal components separate as the animal decays. Despite this, there are a few places where accumulations of complete skeletal structures occur, fossilized in place in Lagerstätten — so-called "starfish beds". By the late Paleozoic, the crinoids and blastoids were the predominant echinoderms, and some limestones from this period are made almost entirely from fragments from these groups. In the two major extinction events that occurred during the late
Western Saharan spiny mouse Western Saharan spiny mouse The Western Saharan spiny mouse or Aïr spiny mouse ("Acomys airensis") is a species of small, insectivorous rodent in the family Muridae found arid regions of western Africa. The Western Saharan spiny mouse is a small mouse with large ears, small eyes and a sharp snout. The fur on its back is tawny, each hair being grey at the base with a rufous sub-terminal band and a grey tip. It takes its name from a line of spiny hairs on the posterior part of the back, in older mice the spiny hairs spread forwards along the