Kalaallitkigun jenkinsi: 215-Million-Year-Old Fossil from Greenland Sheds Light on Origin of Mammals

Exploring Prehistoric Life
Curiosities
Tuesday, October 20, 2020

An artist’s impression of Kalaallitkigun jenkinsi. Image credit: Marta Szubert.

A new genus and species of mammaliaform that lived during the Triassic period has been identified from a partial jaw with teeth found on the eastern coast of Greenland. It represents the earliest known example of a dentary bone with double molariform roots and a crown with two rows of cusps, and offers insight into mammal tooth evolution, particularly the development of double-rooted teeth.

The newly-discovered mammaliaform species was a shrew-like animal about the size of a large mouse, probably covered with fur.

Named Kalaallitkigun jenkinsi, it lived during the Late Triassic period, around 215 million years ago.

Its partial left dentary, with two teeth still preserved in their respective alveoli, was found at the Liasryggen site located on the left bank of the Carlsberg Fjord, Jameson Land, East Greenland.

“I knew it was important from the moment I took this 2 cm (0.8 inches) specimen off the ground,” said Dr. Grzegorz Niedzwiedzki, a paleontologist in the Department of Organismal Biology in the Evolutionary Biology Centre at Uppsala University.

Kalaallitkigun jenkinsi exhibits the earliest known dentary with two rows of cusps on molars and double-rooted teeth.

These anatomical features place it as an intermediate between the mammals and the insectivorous morganucodontans, another type of mammaliaform.

Digital rendering of the holotype left dentary of Kalaallitkigun jenkinsi from the mid-to-late Norian of the Fleming Fjord Formation, East Greenland: (A) the life position of the preserved part of the dentary; (B-D) the dentary in labial (B), lingual (C), and occlusal (D) views; (E-G) the only preserved premolariform in labial (E), lingual (F), and occlusal (G) views; (H-J) the only preserved molariform (m2) in lingual (H), labial (I), and occlusal (J) views. M1-3 mark the position of molariforms (2 is double rooted); pm1-4 mark the position of the premolariforms (1 is single, 2 is double rooted); c marks the position of the canine; (A, G, and B) 1-b4 indicate cusp assignments in the molariform. Abbreviations: ang. reg. – angular region, cre. – crest, premolar. – premolariform, molar. – molariform, cor. pr. – coronoid process, cor. fos. – coronoid fossa, M. tempo. fos. – M. temporalis fossa, V3 no. – V3 notch for the mandibular nerve entering the mandibular canal, Mec. sul. – Meckel’s sulcus, mand. ca. for. – mandibular canal foramen, mas. fos. – masseteric fossa, lat. rid. – lateral ridge, postd. tr. – postdentary trough, med. rid. – medial ridge, and sym. – symphysis. Image credit: Sulej et al., doi: 10.1073/pnas.2012437117.

“The structural changes in the teeth are related to changed feeding habits,” the researchers said.

“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.”

“Our discovery of the oldest mammalian ancestor with double-rooted molars shows how important the role of teeth was in the origin of mammals,” said Dr. Tomasz Sulej, a researcher in the Institute of Paleobiology at the Polish Academy of Sciences.

“I had this idea to look at the biomechanics and the collaboration with the engineers turned out great.”

“It seems that the fossils of close mammalian ancestors must be looked for in even older rocks.”

The discovery is reported in a paper in the Proceedings of the National Academy of Sciences.

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Tomasz Sulej et al. The earliest-known mammaliaform fossil from Greenland sheds light on origin of mammals. PNAS, published online October 12, 2020; doi: 10.1073/pnas.2012437117

Source: www.sci-news.com/