Mastodon Diet Is Food for Thought
by Michael Campbell
Two
University of Kansas researchers recently made a discovery about the
diet of ancient elephants with information from a surprising source.
The pair studied preserved plaque removed from the teeth of the mastodons
to show that they did not just eat the leaves of trees and bushes, as
previously was thought.
"They were eating a lot of grass," said Katrina Gobetz,
a South Windsor, Conn., graduate student at the KU Museum of Natural
History. "I don't think anyone has ever said that mastodons were eating
grass."
Gobetz and Stephen Bozarth, adjunct assistant professor
of geography, studied plant cells trapped in hardened plaque from mastodons
that died 11,000 years ago, during the last ice age. They found that
86 percent of the cells came from grasses.
Gobetz and Bozarth's study was published in 2001 in
the journal Quaternary Research. The dental deposits lasted because
they calcified while the mastodons were still alive and the deposits
turned into a hardened substance known as calculus. This process, which
also occurs in a human mouth, is why hygienists have to scrape teeth
so hard during a dental visit.
"The calculus was what was on the tooth when the mastodon
died," said Gobetz's adviser, Larry Martin, curator of paleontology
at the museum. "She [Gobetz] is just a paleo dental hygienist, cleaning
it off."
Gobetz cautioned that the study could not determine
whether mastodons primarily grazed or ate a mix of grass and leaves,
or browsed.
"I can't eliminate [browsing], but my evidence, at
least for Kansas mastodons, is that the cells associated with the leaves
of shrubs and bushes are not showing up in their teeth," she said.
One source of confusion in the research involves the
relative toughness of grass cells and leaf cells. Grasses are easier
to detect than trees because grasses have lots of hardened cells, called
phytoliths, that are tough enough to withstand chewing.
The young tree leaves preferred by browsing animals
have few phytoliths to get trapped in the calculus. Gobetz stressed
that these results are preliminary because she looked only at animals
from the same area.
"These were all Kansas mastodons," she said. "It may
be that they were eating grass because this is the beginning of the
Plains and mastodons from this area were just forced to eat grass."
The hardest part of the study for Gobetz was removing
the calculus from the teeth. The gunk had bonded so tightly to the teeth
that she sometimes needed a hammer and chisel to get it off. After removing
the calculus, Gobetz dissolved it in acid to free the phytoliths trapped
inside.
The phytoliths survived the acid because they were
filled with silica, a hardened crystal also found in sand. The plants
absorbed silica through their roots and deposited it in the phytoliths.
Gobetz then teamed with Bozarth to identify the cells,
which are distinctive enough to allow identification of groups of plants
and sometimes even individual species. The success of this study has
inspired Gobetz to look at calculus from several other animals, including
mammoths and ancient rhinoceroses.
Michael Campbell is a student in the KU School of
Journalism.
