Fossil Vertebrates

Fossil Cottontails

Lower premolars of fossil Desert Cottontail, Sylvilagus audubonii   Lower premolars of fossil Nuttall's Cottontail, Sylvilagus nuttallii

Left: The left lower third and fourth premolars of a fossil Desert Cottontail (Sylvilagus audubonii) from Pendejo Cave, southern New Mexico. The specimen dates from the Pleistocene Epoch (the "Ice Age") and is approximately 30,000 years old. The specimen is on loan for research to the Laboratory for Environmental Biology from the United States Army Air Defense Center and Fort Bliss,Texas. Right: Part of a right lower jaw of a fossil Nuttall's Cottontail (Sylvilagus nuttallii) with lower third and fourth premolars and first and second molars. This specimen is from Dry Cave, also located in southern New Mexico and also 30,000 or more years old. Both specimens are magnified, though to different degrees: the third premolar of both is about 2.5 mm in width (about 1/10 inch).

Sylvilagus audubonii: Many fossils, including this one, have a certain beauty about them. The black is enamel, darkened during fossilization; the medium brown material, surrounded by the enamel, is dentine. In many mammals, including rabbits, the enamel covering the chewing surface when the tooth erupts quickly wears away, leaving the dentine exposed. The lighter brown, outside of the enamel, is tooth cement, a material softer than enamel and dentine that helps support the tooth. Several cracks are visible, formed during the fossilization process. The Desert Cottontail is widespread in western North America and occurs in the area of the cave today.

Sylvilagus nuttallii: This specimen has undergone little change since death, looking very similar to remains of recently deceased animals. Nuttall's Cottontail does not occur in southern New Mexico at present, being restricted to areas farther north.

Characters that separate fossil teeth of the two species are found in differences in the degree of crinkling of the enamel.


Last updated: 3 Nov 2007