Life Through Geologic Time

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.

Living Fossils - Queensland Lungfish

The Queensland Lungfish is the only surviving member of its Family, Ceratodonitidae, and the Order Ceratodontiformes. That doesn’t mean that there aren’t other lungfish, though! There are six extant species, including the Queensland Lungfish. 

The Queensland Lungfish is a lobe-finned fish, sometimes called fleshy-finned fish, which is interesting enough because Tetrapoda descended from Sarcopterygii (Lobe-finned fish.) (Remember, evolution isn’t progress, it’s diversification through change through decent.) (See Tiktaalik song) It is one of the six extant species of Dipnoi (lungfishes) which flourished during the Devonian, and is the most primitive surviving member of Dipnoi. It can survive out of water for several days, but, unlike its four African cousins, it cannot survive total water depletion and must be kept moist. Fossils almost identical to the Queensland Lungfish have been found, indicating that it has remained nigh unchanged since 100 mya , and, therefor, is a viable living fossil.