The Early
Permian dissorophid Cacops displays its fearsome dentition as it preys on the
hapless reptile Captorhinus (illustration by Brian Engh)
The idea
of being bitten by a nearly toothless modern frog or salamander sounds
laughable, but their ancient ancestors had a full array of teeth, large fangs
and thousands of tiny hook-like structures called denticles on the roofs of
their mouths that would snare prey, according to new research by
paleontologists at the University of Toronto.
In
research published online in a recent issue of PeerJ, an open
access journal, Robert Reisz, distinguished
professor of paleontology at University of Toronto Mississauga,
explains that the presence of such an extensive field of teeth provides clues
to how the intriguing feeding mechanism seen in modern amphibians was also
likely used by their ancient ancestors.
The
researchers believe that the tooth-bearing plates “were ideally suited for
holding on to prey, such as insects or smaller tetrapods, may have facilitated
a method of swallowing prey items via retraction of the eyeballs into the
mouth, as some amphibians do today.”
In many
vertebrates, ranging from fish to early synapsids (ancestors of mammals),
denticles are commonly found in dense concentrations on the bones of the hard
palate (roof of the mouth). However, in one group of tetrapods, temnospondyls
(which are thought to be the ancestors of modern amphibians), these denticles
were also found on small, bony plates that filled the large soft part of the
palate. The entire roof of the mouth was covered with literally thousands of
these tiny teeth that they used to grab prey. Since these toothy plates were
suspended in soft tissue, they are often lost or scattered during fossilization.
Denticles
are significantly smaller than the teeth around the margin of the mouth – on
the order of dozens to a couple hundred microns in length. They are actually
true teeth, rather than just protrusions in the mouths of these tetrapods, says
Reisz and his colleagues, Bryan Gee and Yara Haridy, both graduate students in
paleontology.
“Denticles
have all of the features of the large teeth that are found on the margin of the
mouth,” says Reisz. “In examining tetrapod specimens dating back (approximately) 289
million years, we discovered that the denticles display essentially all of the
main features that are considered to define teeth, including enamel and
dentine, pulp cavity and peridontia.”
A look at
the skull of a small amphibamid dissorophid called Passawioops, with the tiny
palatal plates in place in the roof of the mouth, with two close-ups to the
right.
In
reaching these conclusions, the researchers analyzed specimens unearthed from
the fossil-rich Dolese Brothers Limestone Quarry near Richards Spur, Okla. They
were extraordinarily well preserved, making them ideal candidates for study.
The
researchers extracted and isolated the denticle-bearing plates, created thin
section slides and examined them under the microscope – no small feat since
denticles on this animal were only about 100 microns long.
Reisz and
his graduate students suggest that the next big question relates to
evolutionary changes to the overall abundance of teeth: If these ancient
amphibians had an astonishing number of teeth, why have most modern amphibians
reduced or entirely lost their teeth?
The
research was supported by the Natural Sciences and Engineering Research
Council of Canada.
Posts
