The Fossil Record: Evolution or "Scientific Creation"

Clifford A. Cuffey

Linnean Taxonomy

In Linnean taxonomy, organisms are grouped into categories ranging from species to kingdom; each category is a taxon (pl. taxa). For biologists and paleontologists, the basic unit of taxonomy is the species (Mayr, 1942). Careful examination of morphology, qualitatively and quantitatively, permits us to recognize species in the fossil record (Carlson, 1999; Clarkson, 1986; Prothero, 1998; Valentine, 1986; Ashlock, 1986; Moore, Lalicker, & Fischer, 1952). Species are diagnosable by definable morphologic characteristics based on empirical observations. In taxonomy, species are grouped into progressively larger, more inclusive higher taxa (Carlson, 1999) as a nested hierarchy, from genus to kingdom. Each of these higher taxa are also defined by diagnosable morphologic criteria, and species are assigned to one higher taxon or another by the presence or absence of such criteria.

As an example, horses are placed within Class Mammalia because they have hair, mammary glands, and a variety of other soft part and skeletal features. Within mammals, horses have hoofs at the ends of their toes, and so are placed wit hin Superorder Ungulata, along with cows, camels, pigs, and deer (MacFadden, 1992). Within ungulates, horses are placed within the Order Perissodactyla (Carroll, 1988, p. 644; MacFadden, 1992), along with rhinoceroses and tapirs, most obviously because the largest toe on their front and hind feet is digit III (middle finger of humans; Carroll, 1988, p. 527; MacFadden, 1992). Within the perissodactyls, horses are classified as the Family Equidae, and are distinguished from other perissodactyls by details of skull and tooth anatomy (Carroll, 1988, p. 527-536; MacFadden, 1992). Within the family Equidae, numerous genera and species are recognized ranging from Eocene to present (Simpson, 1951; MacFadden, 1992; Carroll, 1988, p. 533-536; Dott & Prothero, 1994, p. 62, 63). The oldest is Hyracotherium whereas the modern horse is Equus (Simpson, 1951; MacFadden, 1992; Carroll, 1988, p. 533-536). The presence of diagnosable morphologic differences between Hyracotherium and Equus identifies them as distinct taxa (Simpson, 1951; MacFadden, 1992; Carroll, 1988, p. 533-536): the front feet of Hyracotherium have four toes whereas those of Equus have one toe. Such diagnosable differences allow us also to test whether or not Hyracotherium evolved into Equus by examining the rock and fossil record for transitional forms bridging the morphologic gap and in proper geochronologic succession, thus demonstrating descent with modification.

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