A tiny jaw from Greenland sheds light on the origin of complex teeth


Date:
October 13, 2020
Source:
Uppsala University
Summary:
Scientists have described the earliest known example of dentary bone
with two rows of cusps on molars and double-rooted teeth. The new
findings offer insight into mammal tooth evolution, particularly
the development of double-rooted teeth.



FULL STORY ==========================================================================
A team of scientists led from Uppsala University have described the
earliest known example of dentary bone with two rows of cusps on molars
and double- rooted teeth. The new findings offer insight into mammal
tooth evolution, particularly the development of double-rooted teeth. The results are published in the scientific journal PNAS.


==========================================================================
The first mammals originated in the latest Triassic period, around
205 million years ago. An ancestor to mammals were the therapsids,
"mammal-like reptiles" referred to as stem mammals or proto-mammals, which originated about 320-300 million years ago. One unique characteristic
of the lineage that included mammals and animals related to mammals
(synapsids) was that they developed complex occlusion. Close ancestors
to mammals, called mammaliaforms, developed rows of cusps on molar-like
teeth adapted for more omnivorous feeding. The origin of this multicusped pattern and double-rooted tooth has thus far remained unclear.

A team of scientists led by Grzegorz Niedzwiedzki from Uppsala University
have investigated the jaw anatomy and tooth structure of a recently
described new mammaliaform species named Kalaallitkigun jenkinsi. It
was discovered on the eastern coast of Greenland and was a very small, shrew-like animal, probably covered with fur. It would have been the
size of a large mouse and lived during the Late Triassic, around 215
million years ago.

"I knew it was important from the moment I took this 20 mm specimen off
the ground," says Niedzwiedzki, researcher at Uppsala University and
the corresponding author of the publication.

Kalaallitkigun jenkinsi exhibits the earliest known dentary with two
rows of cusps on molars and double-rooted teeth. The anatomical features
place Kalaallitkigun jenkinsi as an intermediate between the mammals
and the insectivorous morganucodontans, another type of mammaliaform.

The researchers believe that the structural changes in the teeth are
related to changed feeding habits. In this case study, the animals were switching to a more omnivorous/herbivorous diet and the tooth crown was expanding laterally.

Broader teeth with "basins" on the top surface are better for grinding
food.

This development also forced changes in the structure of the base of
the tooth.

The biomechanical analysis that was carried out within the study
found that multi-rooted teeth are better able to withstand mechanical
stresses, including those of upper and lower tooth contact during
biting, compared to single-rooted teeth. Human teeth, for instance,
have this characteristic. The results suggest that the development of molar-like teeth with complex crowns may have developed together with biomechanically optimised dual roots.

"The early evolution of mammals is a particularly interesting topic in evolutionary studies. This tiny jaw from Greenland shows us how complex mammalian teeth arose and why they appeared," says Niedzwiedzki.

"Our discovery of the oldest mammalian ancestor with double-rooted molars
shows how important the role of teeth was in the origin of mammals. I
had this idea to look at the biomechanics and the collaboration with
the engineers turned out great," says Tomasz Sulej, researcher at the
Polish Academy of Sciences, first author of the publication.

"It seems that the fossils of close mammalian ancestors must be looked
for in even older rocks," says Sulej.


========================================================================== Story Source: Materials provided by Uppsala_University. Original written
by Linda Koffmar.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Tomasz Sulej, Grzegorz Krzesiński, Mateusz Tałanda,
Andrzej S.

Wolniewicz, Błażej Błażejowski, Niels
Bonde, Piotr Gutowski, Maksymilian Sienkiewicz, Grzegorz
Niedźwiedzki. The earliest-known mammaliaform fossil
from Greenland sheds light on origin of mammals. Proceedings
of the National Academy of Sciences, 2020; 202012437 DOI:
10.1073/pnas.2012437117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201013124056.htm

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