The remarkable fossil of the "fishapod," Tiktaalik, which lived about 375 million years ago, is a beautiful example of an intermediate form, having the attributes of both fish (scales, fins) and tetrapods (a flat head, mobile neck). The presence of Tiktaalik and other fossils of other organisms that lived around the same time shows clear evidence that tetrapods were derived from fish, implying, that the grouping "fish" is paraphyletic. Imagine now that there was no fossil record. Would it still be possible to determine whether or not "fish" is paraphyletic?
A)Yes, because a phylogeny can be constructed using morphological and molecular characters of modern fish and tetrapods.
B)No, because without a fossil record there is no evolutionary history of fish available for study.
C)Yes, because Tiktaalik is a species of coelacanth, and so phylogenetic reconstructions can be based on coelacanth characters.
D)No, because modern fish and modern tetrapods share no synapomorphies.

Question

Quizplus · Accepted Answer

Even without a fossil record, it is still possible to construct a phylogeny using morphological and molecular characters of modern fish and tetrapods to determine if "fish" is paraphyletic. This would involve comparing the traits that are shared by these two groups and looking for synapomorphies (shared derived characteristics) that define the clade of tetrapods as distinct from fish.

The Remarkable Fossil of the "Fishapod," Tiktaalik, Which Lived About