COLUMBIAN MAMMOTH (MAMMUTHUS COLUMBI) FROM THE LATE IRVINGTONIAN FAIRMEAD LANDFILL LOCALITY, MADERA COUNTY, CALIFORNIA

In May 1993, heavy equipment operators at Madera County's Fairmead Landfill discovered fossils during excavation for a new five-acre expansion cell. As part of a paleontological resource impact mitigation program, paleontological monitoring has continued at Fairmead Landfill for the past fourteen years. Among the two dozen mammal taxa identified from the site are mammoth specimens. Fragmentary remains of mammoth molars, tusks, crania and postcrania are often encountered. This study assigns the mammoth remains to a species and reports on some of the best preserved specimens.

Mammoth species assignment is based on dental metrics of enamel thickness and lamellar frequency. For this project, 14 molars were examined; 11 mandibular and 3 maxillary. Enamel thickness ranged from 2.0 mm to 2.8 mm and lamellar frequency ranged from 4.5 to 7. These ranges are consistent with the enamel thickness and lamellar frequency of the middle Pleistocene Columbian mammoth (Mammuthus columbi).

Two mandibles were examined to determine the individual ages of the animals, using the model based on Laws' (1966) African Elephant Years. Specimen UCMP 140415 is a nearly complete mandible, missing only the left ascending ramus. The right and left m2 are fully erupted and are in wear, with the exception of the last two lamellae. The m3s are not erupted. The remainder of the tooth sockets for the right and left m1s are present. The tooth eruption pattern fits closest to Laws' Group XVI, which would indicate an individual age for this mammoth of 26 ± 2 years. UCMP 141407 is a partial right dentary with dp4 present. All lamellae of the dp4 are in wear, with the anterior of the dp4 exhibiting erosion. The dentary is broken just posterior to the beginning of the socket for the m1 and the m1 is missing. Given the stage of wear of the dp4 lamellae, it is likely that the anterior lamellae on the m1 were in wear. The dp3 socket is absent. Based on the above characteristics, the specimen best approximates the condition of Laws' Group VIII, which suggests an individual of approximately 8 ± 1 year of age.

Other mammoth remains identified during this study include a right tibia (A8-8/9-1), proximal half of a right ulna (A8-8/7-8), a proximal left scapula (UCMP 140405), a partial magnum (95DLB8-1-1), and an atlas (UCMP 140402).