Fossilized mastodon tusks and other fragments believed to be as much as 220,000 years old were discovered at a construction site, according to the developer.
Officials at Corky McMillin Cos. said Wednesday that two tusks, an upper jaw fragment with three teeth and vertebrae from a single animal were uncovered during grading for a new housing development.
"This is the first mastodon to be found in Carlsbad, and we're excited to have uncovered two nearly complete tusks," said San Diego Natural History Museum paleontologist Tom Demere.
Developers have said they will donate the fossils to the museum.
Other mastodon remains have been found in San Diego County, including a tusk, teeth and bone fragments found in 2001 at a construction site in Oceanside.
The mastodon, which has been extinct for about 11,000 years, is a distant cousin to the present-day elephant as well as ancient mammoths.