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 Formerly considered conspecific with Cairo spiny mouse "Acomys cahirinus" but there are differences in the number of chromosomes. It may be conspecific with Chudeau's spiny mouse "Acomys chudeaui" from Morocco and, if that is the case, then the correct species name is "Acomys chudeaui" as this name has precedence. 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