Self (via philosophicalgamer)
Living Fossil - Coelacanth
Coelacanth is a lobe-finned fish that dates all the way back to the Devonian, and were believed to have gone extinct around the end of the Cretaceous. Before its rediscovery in 1938 it was thought to be the “missing link” between fish and tetrapods, though it is apparently no longer the case that it is the link, coelacanth is still closer related to tetrapods than to ray-finned fish. It has remained roughly unchanged for ~400 million years. There are two living species, Latimeria chalumnae (West Indian Ocean Coelacanth (pictured above,)) and L. menadoensis (the Indonesian Coelacanth.) Its rediscovery in 1938 after virtually falling off the fossil record qualifies it as probably the best example of the Lazarus Taxon.
Photo is from the Wikimedia Commons, its information can be found at this link.
Stethacanthus - The Ironing Board Shark
When: Late Devonian to Early Carboniferous (385 - 320 million years ago)
Where: The seas that covered what is now North America and Europe
What: Stethacanthus is an extinct shark. Over all this ancient shark is an excellent example of the amount of conservation the simple shark body plan has seen throughout the eons. It is relatively small, 2.3ft/70 cm long, and has a general form very much like an extant shark. The one major exception to this is the shape of its dorsal fin. It was flattened and covered with enlarged denticles (the particles in shark skin that give it it’s sandpaper texture). The head of Stethacanthus was also topped with enlarged denticles. Though some sort of courtship role has been suggested for the structures, detailed studies have determined that the dorsal fin could be flexed forward, to start to come into occlusion with the patch of denticles on the top of the head. This would give the illusion of a much bigger mouth than Stethacanthus actually possessed, allowing this little pre-historic shark to hopefully scare off potential predators.