Pre-dating the dinosaurs by millions of years and once thought to have gone extinct with them, 65 million years ago but....
Although now represented by only two known living species, as a group the coelacanths were once very successful with many genera and species that left an abundant fossil record from the Devonian to the end of the Cretaceous period, at which point they apparently suffered a nearly complete extinction. It is often claimed that the coelacanth has remained unchanged for millions of years, but, in fact, the living species and even genus are unknown from the fossil record. However, some of the extinct species, particularly those of the last known fossil coelacanth, the Cretaceous genus Macropoma, closely resemble the living species. The most likely reason for the gap is the taxon having become extinct in shallow waters. Deep-water fossils are only rarely lifted to levels where paleontologists can recover them, making most deep-water taxa disappear from the fossil record. This situation is still under investigation by scientists.
They first appeared in the fossil record in the Middle Devonian. Prehistoric species of coelacanth lived in many bodies of water in Late Paleozoic and Mesozoic times.
Coelacanths, are lobe-finned fish with the pectoral and anal fins on fleshy stalks supported by bones, and the tail or caudal fin diphycercal (divided into three lobes), the middle one of which also includes a continuation of the notochord. Coelacanths have modified cosmoid scales, which are thinner than true cosmoid scales. Coelacanths also have a special electroreceptive device called a rostral organ in the front of the skull, which probably helps in prey detection. The small device also could help the balance of the fish, as echolocation could be a factor in the way this fish moves.
The average weight of the living West Indian Ocean coelacanth, Latimeria chalumnae, is 80 kg (176 lb), and they can reach up to 2 m (6.5 ft) in length. Adult females are slightly larger than males. Based on growth rings in their ear bones (otoliths), scientists infer that individual coelacanths may live as long as 80 to 100 years. Coelacanths live as deep as 700 m (2300 ft) below sea level, but are more commonly found at depths of 90 to 200 m.
Coelacanth this one near Ichthyostega ( prehistoric animals), the first fish that emerged the superfcie.