Coelacanths are an ancient group of lobe-finned fish that belong to the order Coelacanthiformes. They are more closely related to lungfish and tetrapods (which include amphibians, reptiles, birds and mammals) than to ray-finned fish. Coelacanths have a long evolutionary history, dating back to the Devonian Period, about 400 million years ago. They were thought to have gone extinct at the end of the Cretaceous Period, about 66 million years ago, until a living specimen was caught in 1938 off the coast of South Africa. Since then, two living species have been identified: the African coelacanth (Latimeria chalumnae) and the Sulawesi coelacanth (Latimeria menadoensis).
The anatomy and lifestyle of coelacanths
Coelacanths are large, powerful predators that can grow up to 6.5 feet (2 meters) long and weigh up to 198 pounds (90 kilograms). They have heavy, mucilaginous bodies covered with thick scales, and four limb-like fins that can move in different directions. They also have a unique feature: a hollow, spiny tail fin that gives them their name (coelacanth means “hollow spine” in Greek). Coelacanths have a three-lobed caudal fin, also known as a trilobate fin or a diphycercal tail. A secondary tail extending past the primary tail separates the upper and lower halves of the coelacanth’s body.
Coelacanths are slow-growing and long-lived fish that can live up to 100 years. They are live-bearers that give birth to well-developed young after a gestation period of about five years. They inhabit mesopelagic waters, below the continental shelf, at depths of 650 to 1,300 feet (200 to 400 meters). They are nocturnal and feed on fish and cephalopods.
The evolutionary significance of coelacanths
Coelacanths are considered living fossils because they have changed little over millions of years. They are one of the oldest lineages of lobe-finned fish, which are the ancestors of land vertebrates. Lobe-finned fish have fleshy fins with bones and muscles that allow them to move on land. The other living group of lobe-finned fish are the lungfish, which can breathe air and survive in dry conditions.
Coelacanths and lungfish are more closely related to each other than to any other living fish. They share some features that are not found in ray-finned fish, such as a notochord (a flexible rod that supports the spinal cord), a spiral valve intestine (a corkscrew-shaped organ that aids digestion), and a rostral organ (a sensory organ in the snout that detects electric fields). Coelacanths and lungfish also have a common ancestor with tetrapods, which are four-limbed vertebrates that include amphibians, reptiles, birds and mammals. Coelacanths and lungfish are therefore considered sarcopterygians, or fleshy-finned fish.
The conservation status of coelacanths
Coelacanths are rare and endangered fish that face many threats from human activities. They are vulnerable to habitat loss, pollution, climate change, and accidental bycatch by commercial fishing. Coelacanths are also highly prized by collectors and scientists who want to study their unique biology. Coelacanths are protected by international laws and agreements, but their populations are still declining. According to the International Union for Conservation of Nature (IUCN), the African coelacanth is classified as critically endangered and the Sulawesi coelacanth is classified as endangered.
Coelacanths are important for understanding the evolution of life on Earth. They are living relics of a long-gone era that reveal how fish evolved into land animals. They are also fascinating creatures that have adapted to survive in harsh environments. Coelacanths deserve our respect and protection as they continue their ancient journey through time.