New Species of Mastodon (Mammut pacificus) Recognized

I didn’t have to search for this science news.  A link to the complete scientific paper appeared on my facebook page last week, and I knew right away this important new study was blog worthy.  Some pundits complain about the way social media intrudes on privacy, but I love how information relevant to my interests is directed to me.  If people are worried about their privacy, they should not go on the internet.

For almost 100 years paleontologists thought just 1 species of mastodon occurred in North America during the Pleistocene.  They believed the American mastodon (Mammut americanum) ranged from coast-to-coast and from the Rio Grande to Alaska.  However, 10 years ago some scientists noticed mastodon skeletal material from the Rancho Labrea Tar Pits in California differed from mastodon bones found elsewhere in North America.  Mastodon bones are relatively uncommon from Rancho Labrea where they are greatly outnumbered by mammoth (Mammuthus colombi) specimens.  Open dry environments prevailed around this site during the Pleistocene–an habitat favored by grass-eating mammoths.  Mastodons were semi-aquatic browsers, preferring to feed upon leaves, twigs, fruit, and wetland vegetation.  Within the last 10 years scientists discovered 700 mastodon bones during construction of the Diamond Lake Reservoir in Riverside County California.  This was enough material for scientists to anatomically compare California mastodons with American mastodons, and they concluded they were indeed 2 different species.

Map showing distribution of 2 mastodon species is from the below referenced paper.  Click to enlarge.  The red dots represent M. pacificus; the blue dots represent M. americanus.  Scientists aren’t sure which species ranged into Oregon.  It’s not a comprehensive distribution map for M. americanus.  I’m aware of 5 additional locations where mastodons were found in Georgia but not represented on this map.  American mastodons were more abundant in eastern North America than western.

Paleontologists named this new species M. pacificus because all specimens of this species have been found within 620 miles of the Pacific Ocean.  Apparently, this species occurred in California, southern Idaho, and possibly Oregon.  Mastodon material found in Oregon is not diagnostic, meaning there is not enough to make a species identification.  All mastodon material north of Oregon (from Washington, the Yukon, and Alaska) belongs to M. americanum, the species found throughout most of North America north of the Rio Grande.

The Pacific mastodon differs from the American mastodon in several ways.  Their molars are smaller and more narrow.  They also tend to have more sacral fused vertebrae. Pacific mastodons had 6, whereas American mastodons usually had 4 or 5 (but sometimes 6).  Pacific mastodons had thicker femurs in proportion to the length of their legs, but their tusks were smaller in diameter.

Geographical barriers likely caused the divergence of these 2 species.  Habitat favorable for mastodons was more scarce in western North America.  High mountain ranges frequently covered by glaciers during Ice Ages, and large deserts separated these 2 species.  Over time the isolated California population evolved into a different species of mastodon.

Reference:

Dooley, A.; et. al.

“Mammut pacificus sp. nov., a Newly Recognized Species of Mastodon from the Pleistocene of Western North America”

Peer J March 2019

Tags: Mammut pacificus, Pacific mastodon