What a Tiny Jaw From Greenland Shows About the Origin of Molars
A fossil jaw about 2 centimeters long, found in eastern Greenland and about 215 million years old, has the oldest known molar-like teeth with two roots and two rows of cusps. It belongs to a small, shrew-like animal named Kalaallitkigun jenkinsi, a close relative of the first mammals. Engineering tests in the same 2020 study suggest that two roots help a tooth withstand the stress of biting, which may be one reason complex chewing teeth and divided roots evolved together.
What question were the researchers asking?
Mammals chew in a way most other animals do not. Our upper and lower back teeth meet precisely, and their broad crowns grind food. Close relatives of early mammals were already experimenting with tooth shape in the Late Triassic period. One group, the haramiyidans, had molar-like teeth with two rows of cusps suited to a more plant-based diet. Where that pattern came from was unclear.
What did they find?
The team, led by Tomasz Sulej of the Polish Academy of Sciences and Grzegorz Niedźwiedzki of Uppsala University, described the lower jaw of Kalaallitkigun jenkinsi, an animal about the size of a large mouse.
Its molar-like teeth have two rows of cusps on the crown.
Each of those teeth has two roots.
The crown shape sits between two known groups: the insect-eating morganucodontans and the haramiyidans. This suggests the haramiyidan pattern grew out of the simpler morganucodontan tooth.
The researchers also built computer models of single-rooted and double-rooted teeth and tested them with a method engineers use to study stress in structures (finite element analysis). Teeth with two roots handled stronger forces, like those of upper and lower teeth meeting, better than teeth with one root.
What are the limits?
The study rests on a single small jaw, so the picture may change as more fossils are found. The engineering models show what two roots can do mechanically. They cannot prove why divided roots first appeared.
What does this have to do with your teeth?
Your own molars carry the same basic design. Lower molars usually have two roots and upper molars usually have three, with broad crowns built for grinding. That root anatomy matters in everyday dentistry. It affects how a tooth handles chewing forces, how a root canal is planned and how a molar is removed or replaced. Fossils like this one show how long that design has been in use.
For another look at how teeth evolved, see our post on shark teeth and human dental biology. If you have a question about a molar of your own, start with a dental examination.
Sources
Sulej T, Krzesiński G, Tałanda M, et al. The earliest-known mammaliaform fossil from Greenland sheds light on origin of mammals. Proc Natl Acad Sci U S A. 2020;117(43):26861-26867. doi:10.1073/pnas.2012437117. Retrieved via PubMed.
Uppsala University. Press release on the Greenland mammaliaform jaw (October 2020).
About the author. CJ Henley, DMD, is a general dentist in Jacksonville whose practice focuses on cosmetic and restorative dentistry, dental implants and dental care around head and neck cancer. Meet Dr. Henley.
CJ Henley, DMD, PA · 3675 Hendricks Avenue, Jacksonville, FL 32207 · 904-398-1549
Updated October 2026.