230 Evolution? The Fossils Say YES!
had found another coelacanth. Soon the fish was flown back to South Africa on the orders of
the prime minister himself, and it was well enough preserved that the internal organs had
survived.
Since 1952, more than 100 additional specimens have been hauled out of the deep waters
around the Comoros and again in South Africa, and a few years ago, another new species
was discovered in Indonesia. It turns out that coelacanths live in very deep waters and only
come to the surface in the dark of night, which is why they had gone undetected for so long.
Unfortunately, they are now so valuable that local fishermen may be hunting them back into
extinction, barely more than 75 years since this living fossil was first discovered. Coelacanths
have long been known from the fossil record (fig. 10.2), but the last known fossil of a coel-
acanth dated back to the Cretaceous, while the dinosaurs still roamed the earth. No wonder
the world was so astonished to find an animal living that had been thought to be extinct for
at least 70 million years.
Coelacanths are part of a group of vertebrates known as “lobe-finned fishes” or Sar-
copterygii, which includes not only the coelacanths but also the lungfishes and a number
of extinct forms known by the paraphyletic grouping “rhipidistia,” as well as their descen-
dants, the tetrapods. Both lobe fins and ray fins share a common ancestor in the Devonian
(fig. 9.1). Recent DNA sequencing has shown that coelacanths and lungfish are more closely
related to each other than either is to tetrapods. While the ray-finned fish now dominate the
world’s waters, lobe fins (once common in the Paleozoic and early Mesozoic) have since
been reduced to a tiny remnant: the living coelacanths, three genera of lungfish, and, of
course, tetrapods. Instead of fins supported by numerous bony rays (as in the fish described
in the last chapter), the fins of lobe-finned fish are supported by robust bones and muscles
forming a lobe, which is then surrounded by fin rays.
The first living lobe fin to be discovered and described scientifically was the South
American lungfish, Lepidosiren, which although highly specialized with whiplike fins, has
lungs rather than gills. In 1837, a specimen of the African lungfish, Protopterus (fig. 10.3),
came to the attention of Richard Owen, England’s foremost anatomist and paleontologist. As
he dissected it, he came across the undisputed evidence that this fish had lungs, although his
creationist leanings refused to admit that this gave it tetrapod affinities. Its teeth consisted
of large ridged biting plates, which had been known from fossils for years, and here was the
source of those mysterious fossils. The clincher came when the Australian lungfish, Neocera-
todus, was discovered. Not only did it have lungs, but its fins were not as highly modified
as those of the African and South American species but still showed the classic lobed form.
Since then, many fossil lungfish have been found, and they look much more like the earliest
coelacanths (fig 10.2) and the earliest “rhipidistians,” so the peculiarities of the living lung-
fishes and coelacanth disappear as you go back in time.
Further study of the living lobe fins reveals another striking characteristic. Not only are
their limbs constructed with robust bones and muscles (like those of a tetrapod) rather than
thin bony fin rays (like most fish), but they also use them differently than most living fish.
Studies of the fin motion of both coelacanths and lungfish have shown that they move their
fins in a “step cycle” similar to the motion of the four limbs of tetrapods. Thus the character-
istic leg motion sequence of four-legged animals was already present in lobe fins that never
walked on land.
This highly specialized anatomy of the modern forms confuses creationists. They point
to the peculiarities of living Latimeria or the specialized fins of some lungfish and argue