234 Evolution? The Fossils Say YES!
robust lobed fins that could become legs and feet, but do the best they can with the relatively
flimsy ray fins to push themselves along on their bellies and wriggle across the ground. In
fact, there are a variety of completely aquatic teleosts, such as the fingered dragonets, genus
Dactylopus, and the grunt sculpin, Rhamphocottus richardsoni, that have modified their ray
fins into separate “fingerlike” features that allow them to creep underwater along the sea
bottom in a motion that resembles a spider or a lobster. However, these “fin fingers” are not
robust or muscular or as flexible as tetrapod fingers, so they cannot manipulate objects with
them. They are jury-rigged features built out of another structure (ray fins) and suboptimally
modified to be “semifingers” (yet another blow to “intelligent design”). The frogfish, Anten-
narius, uses its fins with the fingerlike fin rays to walk along the bottom in a motion very
similar to that of tetrapods (fig. 10.4C).
When it comes to deciphering how lobe fins crawled out on land, we have some remark-
able fossils that demonstrate some of the steps—although preservation of soft features like
the nature of their skin and gills or lungs cannot be demonstrated from the bony skeleton.
The paraphyletic rhipidistians of the Devonian include a variety of peculiar fish with robust
lobed fins such as Eusthenopteron (fig. 10.5). Although rhipidistians are fishlike with an
aquatic body and multiple fins, the lobe fins have key elements that are homologous, bone
for bone, with those in the tetrapod limb. For example, in the pectoral fin, the robust element
closest to the body looks very much like the upper arm bone, or humerus, of primitive tetra-
pods. At the far end of this bone are a pair of bones, which are homologous (and look much
like) the radius and ulna of the lower arm in tetrapods. Beyond those bones are a series of
smaller rodlike bones that are homologous with the wrist and finger elements. The fin is then
surrounded by a series of rays that support the fin membrane itself. If you look at the pelvic
fin, the homologies with the thigh bone (femur), shinbones (tibia and fibula), and ankle and
foot bones (tarsals and metatarsals) are equally apparent.
The similarities don’t stop there. The detailed bone-for-bone structure of the spine of
Eusthenopteron is a dead ringer for that in primitive tetrapods and totally unlike that in any
other group of fish. The detailed patterns of the bones in the skull are also bone-for-bone
identical with those in primitive tetrapods; only the relative proportions change in tetra-
pods, which greatly reduces the bones covering the gills and expands the bones in the front
of the snout (fig. 10.5). The lungs or gills themselves don’t fossilize, of course, but it’s rea-
sonable to assume that Eusthenopteron already had lungs because its primitive sister group
(the lungfish) and advanced sister taxa (the tetrapods) do. In short, you could not ask for
a better fishibian than Eusthenopteron. If you study it in detail with the eyes of anatomist
(instead of reading superficially about it, as creationists do), you can see all the elements of
the tetrapods already in place. Given how easily many modern fish now walk on land, it’s
not hard to imagine Eusthenopteron doing so as well.
The next step is a series of remarkable fossils that demonstrate the step-by-step transi-
tion to becoming a tetrapod (figs. 10.5–10.8). These include a variety of more tetrapod-like
fish (Panderichthys, Elginerpeton, Ventastega, and Metaxygnathus) known from only partial
specimens from the Late Devonian. Panderichthys (figs. 10.6, 10.7, and 10.10) was a very
tetrapod-like lobe-finned fish. Unlike Eusthenopteron, these creatures had flattened bodies
and upward-facing eyes, and frontal bones, like tetrapods, and a straight tails with a well-
developed tail fin. The braincase of Panderichthys was originally classified as belonging to
a tetrapod, not a fish, until the rest of the body was found. The teeth have the character-
istic enfolding of the enamel (“labyrinthodont” teeth) that characterizes the teeth of later