Fish Tales 225symmetrical, but the vertebral column does curve upward within the upper lobe of the tail
(fig. 9.13). Most of these Mesozoic fish groups have died out, but there are a few survivors,
such as the garfish and the bowfin.
The final step in fish evolution (fig. 9.12) is the great radiation of the teleost fishes, which
make up 98 percent of all the fishes alive today. Nearly every fish you eat or see in the aquar-
ium or in the lakes, rivers, or oceans is a teleost. There are about 20,000 species of teleosts,
more than all the amphibians, reptiles, birds, and mammals combined. Teleosts branched off
from the more primitive fishes during the Cretaceous and then underwent explosive evolu-
tion into hundreds of different families, most of which are still alive today. We mammal
chauvinists like to think of the last 65 million years as the “age of mammals,” but in terms of
diversity, the teleosts were evolving far faster than the mammals, and we could easily think
of it as the “age of teleosts.”
Teleosts are easily distinguished from the more primitive chondrosteans and holosteans
(fig. 9.13). Most have greatly reduced the bone in their skulls, so their heads are supported
by a framework of thin bony braces and struts connected by muscles and tendons, not solid
walls of bone found in the primitive forms. In particular, the bones of their mouth are much
reduced and connected by flexible tendons, so they can protrude and open very easily. Many
teleosts have abandoned the old snap-trap jaw mechanism of catching prey by biting with
jaws and teeth. Instead they have mouths that open suddenly and create suction, slurping
down their prey. (The next time you feed fish flakes to your aquarium fish, notice how they
protrude their mouths and suck the food in and do not bite it). Teleosts also continue the
trend of reducing bone in the rest of their skeletons as well, so that most of their bones are
very light and delicate. Finally, teleosts have a completely symmetrical tail, with only a tiny
trace of the upward flexure of the spine near the base.
In summary, vertebrates have come a long way from acorn worms, sea squirts, lancelets,
and lampreys to the incredible array of teleosts in the waters of the world. This short chapter
does not do justice to their long and incredibly rich evolutionary story. I strongly recommend
that you read further on this topic if you are interested.
For Further Reading
Benton, M. J. 2014. Vertebrate Palaeontology. 4th ed. New York: Wiley-Blackwell.
Carroll, R. L. 1988. Vertebrate Paleontology and Evolution. New York: Freeman.
Forey, P., and P. Janvier. 1984. Evolution of the earliest vertebrates. American Scientist 82:554–565.
Gee, H. 1997. Before the Backbone: Views on the Origin of Vertebrates. New York: Chapman & Hall.
Long, J. A. 2010. The Rise of Fishes, 2nd ed. Baltimore, Md.: Johns Hopkins University Press.
Maisey, J. G. 1996. Discovering Fossil Fishes. New York: Holt.
Moy-Thomas, J., and R. S. Miles. 1971. Palaeozoic Fishes. Philadelphia: Saunders.
Norman, J. R., and P. H. Greenwood. 1975. A History of Fishes. London: Ernest Benn.
Pough, F. H., C. M. Janis, and J. B. Heiser. 2002. Vertebrate Life. 6th ed. Upper Saddle, N.J.: Prentice Hall.
Prothero, D. R. 2013. Bringing Fossils to Life: An Introduction to Paleobiology. 3rd ed. New York: Columbia
University Press.
Schaeffer, B., and D. E. Rosen. 1961. Major adaptive levels in the evolution of actinopterygian feeding
mechanisms. American Zoologist 1:187–204.
Shu, D.-G., H.-L. Luo, S. Conway Morris, X.-L. Zhang, S.-X. Hu, L. Chen, J. Han, M. Zhu, Y. Li, and
L.-Z. Chen. 1999. Lower Cambrian vertebrates from China. Nature 402:42–46.