Latimeria, commonly known as the coelacanth, is a fish that captivates scientists and the public alike, often referred to as a “living fossil.” This designation reflects its remarkable persistence, as it represents a lineage that has survived for hundreds of millions of years. Their existence today offers a unique window into ancient marine life and evolutionary history.
The Living Fossil’s Reappearance
The scientific world was astonished on December 22, 1938, when a coelacanth was caught off the Chalumna River, South Africa. Captain Hendrik Goosen, aboard the trawler “Nerine,” brought the unusual blue fish to the attention of Marjorie Courtenay-Latimer, a curator at the East London Museum. Recognizing its distinctive features, Courtenay-Latimer preserved the specimen and sought the expertise of ichthyologist J.L.B. Smith. Smith identified it as a coelacanth, a group previously known only from fossils and believed extinct for 66 million years, since the time of the dinosaurs.
Smith later named the newly discovered species Latimeria chalumnae in honor of Courtenay-Latimer and the Chalumna River where it was found. This discovery excited the scientific community, challenging long-held beliefs about the extinction of this ancient fish lineage. It confirmed the survival of a creature whose ancestors date back over 360 million years.
Distinctive Anatomy
Latimeria possesses unique anatomical characteristics that set it apart from most modern fish. Its most notable feature is fleshy, paired lobed fins, which extend from the body on stalks rather than attaching directly. These fins contain internal bones resembling the limb structures of land vertebrates, and the coelacanth moves them in an alternating pattern, much like a walking gait.
In its snout, the coelacanth has a specialized jelly-filled cavity called the rostral organ, which functions as an electroreceptor. This organ allows the fish to detect weak electrical impulses emitted by prey in the dark, deep-sea environment. The coelacanth’s body is covered in large, thick, armor-like scales, which are rough to the touch due to tiny, tooth-like spikes called denticles. Unlike most modern bony fish that use gas-filled swim bladders for buoyancy, Latimeria has a unique oil-filled swim bladder, which helps it maintain neutral buoyancy in its deep-water habitat.
A Link to Land Vertebrates
Latimeria belongs to the group Sarcopterygii, or lobe-finned fishes, which is significant in evolutionary terms. This group contains the ancient ancestors of all tetrapods—four-limbed vertebrates that eventually colonized land, including amphibians, reptiles, birds, and mammals. The distinctive bony structure within the coelacanth’s lobed fins provides a visible connection to the skeletal elements that later evolved into the limbs of terrestrial animals.
While modern coelacanths are not the direct ancestors of land vertebrates, they represent a surviving branch of this ancient lineage. They serve as a living model for understanding the morphology and potential behaviors of the early fish that transitioned from aquatic to terrestrial environments. Although lungfish are considered the closest living relatives to tetrapods, Latimeria still offers insights into the anatomical adaptations that facilitated this evolutionary step.
Present-Day Status and Survival
Today, two living species of Latimeria are recognized: Latimeria chalumnae and Latimeria menadoensis. Latimeria chalumnae, often called the West Indian Ocean coelacanth, is found primarily off the eastern coast of Africa, particularly around the Comoros Islands. The second species, Latimeria menadoensis, or the Indonesian coelacanth, inhabits waters near Sulawesi, Indonesia.
These deep-sea dwellers reside in underwater volcanic caves and rocky crevices at depths ranging from 100 to 200 meters during the day. At night, they may venture to depths of 700 meters to forage for prey. Latimeria chalumnae is currently classified as Critically Endangered by the IUCN, with an estimated population of 500 or fewer individuals. Latimeria menadoensis is considered Vulnerable. The primary threat to both species is accidental capture as bycatch by local fishermen, often during night fishing for other deep-sea species like oilfish.