The Coelacanth

Modern coelacanths are deep-sea fishes of the family Latimeriidae. The name refers to their hollow fin spines (Greek: koilos, "hollow"; akantha, "spine"). The modern coelacanths are bigger than most fossil coelacanths and are powerful predators with heavy, mucilaginous bodies and highly mobile, limblike fins. They average 5 feet (1.5 m) in length and weigh about 100 pounds (45 kg).

Scientists assume that coelacanths appeared about 350 million years ago. They were abundant over much of the world. It was long supposed that coelacanths became extinct about 60 million years ago, but in 1938 a living member was netted in the Indian Ocean near the southern coast of Africa. Rewards were offered for more specimens, and in 1952 a second was obtained from near the Comoros Islands. Several others have been caught in that area. It was later discovered that these fishes were well known to the islanders, who considered the flesh edible when dried and salted; the rough scales were used as an abrasive.

Before these finds scientists long assumed that coelacanth was the ancestor of amphibians. Many illustrations show the evolutionary way of thinking: the coelacanth developing primitive limbs which developed themselves to full-size limbs with which the coelacanth was eventually able to conquer dry land.

But, as the evidence shows, the coelacanth has always been a coelacanth.

Coelacanth-fossil

Coelacanth alive

So why no fossils for over 70 million years?

First, note that fossil hunts are done on dry land. That's partly because it's easier, and partly because watery environments are usually undergoing deposition, which covers everything up. On land, rocks are eroding, and fossils get revealed.

So, where do dry-land rocks come from? Well, some were formed on land, and some in fresh water, and some in shallow sea water. But very few were formed in deep sea water. Plate tectonics makes it clear why this should be. The deep ocean floor is constantly being destroyed, sucked down into the earth at subduction zones. It is unlikely for a piece of deep ocean floor to wind up as a dry-land rock.

Now, imagine a creature that lives only in the open ocean, and is unlikely to venture close to shore. (Perhaps it lives in the depths.) That creature will leave no fossils that we are likely to find. So, the answer is, yes. It is possible to leave no fossils.

Does Latimeria live in the depths? Well, close. They've been seen in caves about 200 meters down, and they die from decompression when brought to the surface.

Also, if a creature lives in a small geographic area, it is possible that no one ever looked in the right place. The first colony of Latimeria is off one single island (Grand Comoro) in the Indian Ocean. And, the whole population there is only a few hundred fish. The second colony hasn't been located yet, so it can't be large.