At a Glance
- A new mammaliaform species, Nujalikodon cassiopeiae, was discovered in Greenland, representing the first of its kind found in the Rhætelv Formation geological layer.
- This Early Jurassic fossil is now the oldest definitive docodontan ever found, significantly reducing a 40-million-year gap in the group’s evolutionary history to 33 million years.
- Docodontans, such as Nujalikodon, are notable for their complex molar teeth, which likely enabled them to eat a diverse range of foods and occupy a wide variety of ecological niches.
- The specimen provides crucial clues about how the intricate cusp patterns on docodontan teeth evolved from the simpler dental arrangements seen in their more ancient ancestors.
- Its location supports the hypothesis that docodontans first originated in the region of Europe and Greenland before dispersing across the northern supercontinent of Laurasia during the Jurassic.
In the remote landscape of East Greenland, paleontologists have unearthed the fossilized jaw of a tiny, shrew-like creature that roamed the Earth during the Early Jurassic period. The specimen, named Nujalikodon cassiopeiae, has been identified as the oldest definitive member of an extinct order of early mammal relatives called Docodonta. This discovery, detailed in a study published in Papers in Palaeontology, provides critical new evidence about the early evolution and geographic spread of the first mammaliaforms. This group includes modern mammals and their closest extinct ancestors.
The significance of Nujalikodon lies in its age and unique dental features. It helps close what was a 40-million-year gap in the fossil record for docodontans, narrowing this “ghost lineage” — a period where a group is inferred to exist but lacks fossil evidence — down to 33 million years. Docodontans were exceptionally diverse for their time, primarily due to their advanced dental features. “Docodontans are one of the earliest groups of mammaliaforms, and have more complex teeth than most other mammaliaforms at this time, with a lot of cusps and ridges,” explained Dr. Elsa Panciroli, a co-author of the study, in a statement to Phys.org. This dental complexity likely allowed them to exploit a wider variety of foods, contributing to their ecological success across the Jurassic.
The fossil, consisting of a partial jawbone with a single complete molar, was recovered from the Kap Stewart Group, a geological formation known for preserving rare terrestrial fossils from the Triassic-Jurassic boundary. Using micro-computed tomography (micro-CT) scanning, the research team, led by Dr. Sofia Patrocínio, created a detailed 3D digital model of the jaw and tooth. The intricate arrangement of the molar’s cusps confirmed it belonged to a new species. “Every species of mammal has a different arrangement of cusps and ridges on the teeth, which allows us to tell one species from another,” Dr. Panciroli noted. The analysis places Nujalikodon as either a foundational member of the docodontan family tree or its closest known relative.
Beyond pushing back the timeline for this important group, the Greenlandic fossil offers powerful clues about their origins. The discovery of Nujalikodon in Greenland, along with other early docodontan fossils found in Great Britain and France, strongly supports the hypothesis that the group first evolved in the landmass that is now Europe and Greenland. From this northern hub, they later dispersed across the supercontinent of Laurasia, reaching modern-day China and the United States. While the docodontans eventually went extinct for unknown reasons, fossils like N. cassiopeiae continue to shed light on a crucial chapter in the deep history of mammal evolution.
References
- Oster, S. & Phys.org. (2025, August 8). Oldest known docodontan fossil found in Greenland narrows the evolutionary gap. Phys.Org; Phys.org. https://phys.org/news/2025-08-oldest-docodontan-fossil-greenland-narrows.html
- Patrocínio, S., Panciroli, E., Rotatori, F. M., Mateus, O., Milàn, J., Clemmensen, L. B., & Crespo, V. D. (2025). The oldest definitive docodontan from central East Greenland sheds light on the origin of the clade. Papers in Palaeontology, 11(3), e70022. https://doi.org/10.1002/spp2.70022
