Two Nujalikodon cassiopeiae in the
Rhætelv Formation, Greenland. Credit: Pedro Andrade in Patrocínio et al. 2025
In
a recent study by Dr. Sofia Patrocínio and her colleagues, published in Papers
in Palaeontology, a new specimen of Docodonta is described.
This fossil represents
the earliest occurrence of docodontans, and helps narrow the
40-million-year-old (Myr) gap to 33 Myr.
"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, rather than a
simple arrangement of only a few cusps in a row," explained Dr. Elsa
Panciroli, one of the authors of the study.
"This probably made them able to
eat a wider range of foods, making them more ecologically diverse. By the
Middle to Late Jurassic, they are very ecologically diverse—more so than almost
any other early mammal group … "
Despite this, no living docodontans or
their descendants survive today, although it is not clear what caused their
extinction either. Dr. Panciroli elaborates, saying, "It is not possible
to say why they became extinct. Extinction is a natural phenomenon that
happens, often when conditions change (new habitats, changing climates, altered
ecosystems)."
While there is general agreement on
where docodontans fit into the broader evolutionary tree of early mammals,
there remains some debate on the relationships between different docodont
species.
Fossils help provide insight into these
evolutionary relationships. "There are very few places in the world where
the fossils of terrestrial animals are preserved from the Early to Middle
Jurassic. This is why there is such a big gap in our knowledge. It's a problem
not just for the study of mammals, but for all land-living animal groups,"
explains Dr. Panciroli.
One place in which such fossils can be
found is the Kap Stewart Group (Rhaetian‐Sinemurian, Triassic–Early Jurassic), located in the
Jameson Land Basin in central East Greenland.
Here specimen NHMD 1184958 was
recovered. The fossil specimen consisted of a single molar, roots of a second
tooth, and part of the jawbone.
The preserved tooth was a second molar, which allowed the researchers to identify it to the species level. "Every species of mammal has a different arrangement of cusps and ridges on the teeth, which allows us to tell one species from another," explains Dr. Panciroli.
Digital reconstruction of Nujalikodon
cassiopeiae's jaw fragment (NHMD 1184958) showing different views. The
preserved tooth and roots are highlighted in panels C and F. Scale bar = 1 mm.
Credit: Patrocínio et al. 2025
It
was determined that the tooth belonged to a new species, Nujalikodon
cassiopeiae. Further phylogenetic and morphological analyses revealed that this
species was either an early member of the Docodonta or its closest relative,
rather than belonging to any previously proposed early docodant species.
This made Nujalikodon cassiopeiae an
important transitional species for understanding the evolution of early
mammaliaforms. Additionally, it was the oldest definitive docodontan so far
discovered, narrowing the ghost lineage between early docodontans and later
taxa from 40 to 33 Myr.
Furthermore, "this [Nujalikodon
cassiopeiae's teeth] gives us a clue about how their complex teeth may have
evolved from the simpler cusp patterns of their ancestors," elaborates Dr.
Panciroli.
Given the fossil's location, alongside
other early forms of the group recovered in Great Britain and France, it is
likely that the earliest descendants of docodontans emerged in Europe, before
spreading across the northern hemisphere to Portugal, Germany, Russia, China,
and the U.S..
More research is needed to fully understand the evolutionary relationships and trajectory of the docodontans, and hopefully, future fossils will provide these insights.
Source: Oldest known docodontan fossil found in Greenland narrows the evolutionary gap
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