RANCHO LA BREA MASTODONS, ARE THEY SMALLER THAN MAMMUT AMERICANUM FROM ELSEWHERE IN THE UNITED STATES?

Rancholabrean records of Mammut americanum are common in California, with over 100 reported localities. Most specimens are dental remains representing single individuals. Among the few sites preserving multiple individuals is Rancho La Brea. Miller (1987) and Harris (2001) reported that Page Museum Rancho La Brea mastodons are smaller than other North American specimens but neither author provided supporting evidence. We examined Rancho La Brea mastodon specimens in the University of California Museum of Paleontology (UCMP) to evaluate the previous statement about Mammut size.

UCMP 198852 and 198861 are partial right dentaries. UCMP 198852 M₃ width is 83.0 mm and length is 199.7 mm. UCMP 198861 has an M₁ and M₂. M₁ width and length are 66.5 mm and 108.5mm, respectively. The M₂ width is 79.1 mm and length is 110.5 mm. Age is estimated to be 34-39 and 20 years, respectively. UCMP 198853 and 198858 are partial left dentaries. The M₃ of UCMP 198853 is 83.1mm wide and 190.0 mm long. UCMP 198858 has a broken M₂, preventing standard measurements. Tooth wear suggests UCMP 198853 is ~34 years old while the presence of the M₁ alveolus in UCMP 198858 indicates an individual greater than 18 years in age. UCMP 198859 is a partial cranium with left and right tusk alveoli. The left alveolus dorsoventral diameter is 86.5 mm and mediolateral diameter is 78.2 mm. The right alveolus dorsoventral diameter is 85.6 mm and mediolateral diameter is 79.4 mm. UCMP 198860 is a partial cranium with right M¹ and M². M¹ width is 69.9 mm and length is 97.1 mm. M² width is 74.9 mm and length is 97.2 mm. The individual is estimated to be ~20 years in age.

UCMP Rancho La Brea mastodons have long, narrow teeth compared to Trolinger Spring and Boney Spring mastodons from Missouri and Utah specimens. The M₃ of UCMP 198852 and 198853 are the most pronounced examples. The M₁ and M₂ of UCMP 198861 and M¹ and M² from 198860 are small compared to Missouri specimens. The M₃ of UCMP 198853 and 198852 are similar in width to Utah specimens but are 22 and 32 mm longer, respectively. The M₂ of UCMP 198861 is larger than Brigham Young University specimen 4379, while the M² of UCMP 198860 is about the same length but 5 mm narrower than the aforementioned male specimen from Utah. Further analysis of Page Museum and UCMP Rancho La Brea specimens and comparison to other North American Mammut populations is warranted.