The earliest-known mammaliaform fossil from Greenland sheds light on origin of mammals

Abstract

Synapsids are unique in having developed multirooted teeth and complex occlusions. These innovations evolved in at least two lineages of mammaliamorphs (Tritylodontidae and Mammaliaformes). Triassic fossils demonstrate that close to the origins of mammals, mammaliaform precursors were “experimenting” with tooth structure and function, resulting in novel patterns of occlusion. One of the most surprising examples of such adaptations is present in the haramiyidan clade, which differed from contemporary mammaliaforms in having two rows of cusps on molariform crowns adapted to omnivorous/herbivorous feeding. However, the origin of the multicusped tooth pattern present in haramiyidans has remained enigmatic. Here we describe the earliest-known mandibular fossil of a mammaliaform with double molariform roots and a crown with two rows of cusps from the Late Triassic of Greenland. The crown morphology is intermediate between that of morganucodontans and haramiyidans and suggests the derivation of the multicusped molariforms of haramiyidans from the triconodont molar pattern seen in morganucodontids. Although it is remarkably well documented in the fossil record, the significance of tooth root division in mammaliaforms remains enigmatic. The results of our biomechanical analyses (finite element analysis [FEA]) indicate that teeth with two roots can better withstand stronger mechanical stresses like those resulting from tooth occlusion, than teeth with a single root.

Symmetry and Aesthetics in Dentistry

“…Mammalian molars evolved from simple, conical precursor forms (haplodontic) with one cusp (protocone) and one root, more or less rotationally or bilaterally symmetric. The triconodontic upper molar scheme shows two roots and three main cusps (paracone, protocone and metacone, with smaller additional cusps), in upper molars arranged more or less in a single row [56,57]. A triconodontic tooth scheme, therefore, shows bilateral symmetry to a frontal plane and to a sagittal plane.…”

Evolution of Atmospheric O2 Through the Phanerozoic, Revisited

“…driver of the subsequent long-term decline in O2. In our reconstruction, O2 levels eventually stabilized at around 25% by the late Triassic, coincident with the evolution of mammals (Sulej et al, 2020). The later evolution of large placental mammals in the early Cenozoic occurs after a long period of gradually rising O2 levels in our reconstruction (Falkowski et al, 2005), but is also accompanied by a decline towards present-day levels, making it difficult to link to changes in oxygen concentration.…”

On the genus Vanikoropsis Meek, 1876 (Gastropoda, Caenogastropoda) from the Paleocene of Denmark and West Greenland with descriptions of three new species

“…The dimensions of the coprolite, with a maximum flattened diameter of 49 mm and a length of at least 125 mm suggest the producer to be among the larger archosaurs from the formation. While mammals have been reported from the formation (Jenkins et al 1994(Jenkins et al , 1997Sulej et al 2020), they can quickly be excluded as possible producers as all Triassic mammals have a body-size significantly smaller than the length and width of the herein described specimen. Assuming that the coprolite stratigraphically belongs to the middle to upper part of the Malmros Klint Formation likely producers include the herbivorous dinosaur Plateosaurus and theropod dinosaurs (Clemmensen et al 2016) and the phytosaurs (Jenkins et al 1994;Clemmensen et al 2016;Niedzwiedzki & Sulej 2020).…”