Many species of animals and plants have changed over millions of years of evolution, but others hardly. And for this reason they are popularly called “living fossils”. And without a doubt, the best known case of a living fossil is that of theCelacanto. A type of fish that was believedextinct for millions of years, but was found alive in the first half of the 20th century. In December 1938, the fishing boatNerinehe was fishing as usual off the South African coast, in the waters of the Indian Ocean. One of the many times they cast their nets, a strange fish appeared among the catch to the surprise of the fishermen. It was a large fish, about50 kilograms, who could remember a mere, but who had what we call “lobed fins” or “fleshy” fins, as opposed to the typically membranous fins of other fish. In addition, this fish seemed to cling to life: instead of dying within minutes of being out of the water from which they get their oxygen, it struggled for almost 4 hours, dragging itself along the deck thanks to those muscular fins. It was such a strange animal that the captain kept it for the local museum curator to examine.Marjorie Courtenay-Latimer, zoologist. Despite being outside her specialty (Marjorie was an ornithologist), she carried out a very careful dissection and a very detailed description and figuration to send the data to her colleagueJames L. Smith, ichthyologist. When Smith received the material, he could not believe it: he was facing a dissection of a coelacanth, a lobe-finned fish that was believed to have been extinct for 80 million years. This species of coelacanth was calledLatimeria chalumnae, and since then many more specimens have been recovered and at least one more species described.
Today’s coelacanths have not changed much for millions of years. These lobe-finned fish (which we call sarcopterygians ) are relatives of the earliest tetrapods, the first vertebrates to emerge from the water. Also members of the sarcopterygians are the dipnoos, air-breathing lungfish . But they are not the only living beings that seem to have been “frozen in time”, which we usually call “living fossils” because they have kept their shape for millions of years.
Another case is that of the Metasequoias . These trees first became known as fossils, with the genus Metasequoia being described in 1941 from fossil material from the Late Jurassic . Over time, fossil remains from the Cenozoic were also discovered. And some time later, even living specimens were identified in China. These living metasequoyas can reach 50 meters in height, and have even begun to be used as ornamental trees.
Gingkos are also considered living fossils, the last trees of the Ginkgophyta division, which originally appeared during the Permian, were very abundant in the Mesozoic, and are not abundant today, except when they are also used as an ornamental tree.
Among the animals, we also consider living fossils to be the tuatara , reptiles of the genus Sphenodon that have practically not changed their anatomy in 200 million years, and that were much more abundant in the past.
These are just a few of the living things that have not changed in millions of years. And it is that, although we tend to think of evolution as a process of constant change, nature rarely changes, unless it has a good reason for it. When an animal has a characteristic that is an advantage when it comes to survival or reproduction, it tends to be preserved. And it is that, if something works well in one way, why are we going to change it?
But, have these species really been “stuck in time”? Nothing is further from reality. They have changed, of course. But the changes that they have undergone in millions of years are very few, compared to those that, for example, we ourselves have undergone.
References :
Johanson, Z. et al.2006. Oldest coelacanth, from the Early Devonian of Australia. Biology Letters, 2 (3): 443–6.
Fricke, H. et al. 1987. Locomotion of the coelacanth Latimeria chalumnae in its natural environment. Nature, 329 (6137): 331–3.
Chaney, R.W. 1948. The bearing of the living Metasequoia on problems of Tertiary paleobotany. Proceedings of the National Academy of Sciences, 34 (11): 503–515.
Zhou, Z.Y. 2009. An overview of fossil Ginkgoales. Palaeoworld, 18 (1): 1–22.
Jones M.E. et al. 2009. A sphenodontine (Rhynchocephalia) from the Miocene of New Zealand and palaeobiogeography of the tuatara (Sphenodon). Proceedings. Biological Sciences, 276 (1660): 1385–90.
