Docodontids in their natural setting
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A student palaeontologist, Sofia Patrocínio, from the Faculty of Science and Technology at the University of Lisbon (Nova FCT), has identified a fossil tooth as belonging to a docodontan – a group of mammaliform vertebrates considered close relatives and ancestors of true mammals. This discovery pushes back the known origin of this group by a further 40 million years.
This is the sort of find that often prompts headlines seemingly designed to play into the hands of anti-science groups such as creationists, with claims like *“The science books will need to be rewritten”* or *“Everything you thought you knew about evolution was wrong!”* These sensationalist lines risk creating the false impression that scientists are constantly realising they were “wrong all along”.
In reality – as in this case – what has happened is that a gap in our knowledge has been filled. Our understanding is now slightly more complete than before. Rather than overturning evolutionary theory, this discovery fits perfectly within it, supporting what was already known: there was a gradual transition from small reptiles to early mammals. The main uncertainty was *when* certain steps in that transition occurred.
Creationists who seize on such discoveries to claim scientists are forever changing their minds overlook an inconvenient detail – the timeline. Nearly all of these fossil finds involve organisms that lived hundreds of thousands, even millions of years before creationists believe the Earth and life began. If anything needs rewriting, it’s the creationist books that peddle disinformation to those willing to pay for material that reassures them their preconceived beliefs are correct – even when the evidence says otherwise.
Sofia Patrocínio and her colleagues have recently published their findings in the journal of the Palaeontological Association, Papers in Palaeontology. The discovery is also covered in a news article from Nova FCT, published in Almadense.
What Were Docodontans? Docodontans were small, extinct mammaliforms that lived during the Jurassic period, between about 201 and 145 million years ago. Although not true mammals, they were close relatives and part of the larger group from which mammals evolved.
They are best known from their distinctive teeth, which had complex cusps adapted for an omnivorous diet of insects, plants, and other small food sources. Fossils suggest docodontans were shrew-like in size and appearance, with some adapted to specialised habitats – including burrowing, climbing, and even semi-aquatic lifestyles.
The group is important to palaeontologists because their anatomy preserves key stages in the evolution from reptile-like synapsids to the first true mammals. Discoveries like the one by Sofia Patrocínio help refine our understanding of when and how early mammal traits emerged.
Nova FCT student identified a new ancestor of mammals from a two-millimeter tooth
The fossil measures less than seven millimeters in total and is partially hidden in a rock. However, meticulous work has identified a new species that combines the name of a goddess with that of a constellation. The new species pushes back the emergence of this group of animals by 40 million years.
After several years of researching a molar tooth from an animal that might resemble a mouse and several months until she was able to publish the scientific article, Sofia Patrocínio "closed" this cycle on Friday, June 13, 2025. The result presented in the scientific journal Papers in Palaeontology owes nothing to bad luck, but it does have its share of incidents, as the paleontologist told ALMADENSE.
"There's a funny story from high school: I had to do a project on paleontology and got a failing grade; I was so upset I said it wouldn't happen again," she says in a relaxed conversation, while admitting that she loves what she does. And she does a lot of things, even though many of them aren't even paid. "Paleontology isn't seen as a serious profession." Something she's determined to change.
Sofia Patrocínio is from Cartaxo and graduated in Environmental Education and Nature Tourism. It's been more than half a dozen years since she enrolled in the program, but the price of student housing elsewhere was unaffordable (then, as it is now) , and it was one of the factors that forced her to stay closer to home and enroll at the Polytechnic Institute of Santarém. After that, she interned at Dino Parque da Lourinhã and stayed on to work there.
“It was them [my colleagues at Dino Parque] who encouraged me to do a master's degree in Paleontology at Nova; they said I had a knack for it,” he says, referring to the course at the Faculty of Science and Technology of the University of Lisbon (Nova FCT), which has a campus in the parish of Caparica, Almada.
It was impossible to remove the fossil from the rock due to the risk of damaging it. In the center of the image, the yellowish structure corresponds to the dentary (mandible), and the dark structure is the partially visible molar.Photo: Sofia Patrocínio
In one of her master's degree courses, Vertebrate Paleontology, Sofia Patrocínio and her colleagues were challenged to prepare and describe fossils, some from the Lourinhã Museum collection and some from an excavation in Greenland. The then-master's student worked with needles and a microscope to remove the sediments still clinging to the fossil, which was less than seven millimeters long —even so, she was unable to free the entire piece, as we will see.
She then described the fossil in detail and attempted to identify its group and its phylogenetic relationships with other animal groups—in other words, she attempted to place the animal in its proper position on the tree of life. "It had similarities with several groups, but didn't seem to belong to any. It was most likely a new species," says the researcher. "I had so much study material that I could have continued [with the same topic] for my master's degree."
How does a tooth allow us to identify a new species?
The first step was to include the species in the order Docodonta, a group of mammaliforms—the evolutionary predecessors of mammals—with very distinctive molars. To put it simply, the molars were long and low, with a characteristic cusp pattern. (Cusps are the conical protrusions on molars, which we also have.) But this particular tooth had characteristics that didn't fit into any of the previously known genera or species within docodonts.
Docodont fossils are very rare, but there are fossils with entire jaws, which allowed comparison with the available material and ruled out a tooth with a small defect. "If it were just a change in the tooth's morphology, there might be doubt, but I counted five to seven differences," explains Sofia Patrocínio. Among these differences was a cusp facing the tongue.
While the tooth's original pattern allowed it to be classified as a new species, the layer in which it was found offers another new discovery. To determine the age of fossils, paleontologists "measure" the age of rocks found in the same layer. In this case, the fossil would have formed about 200 million years ago, during the transition between the Triassic and Jurassic periods (the period in which a wide variety of easily recognizable dinosaurs emerged). Even more interesting is that this species would have appeared 40 million years before the oldest known docodont species.
A new species at the transition between pre-docodont mammals and docodonts adds another piece to the puzzle of mammalian evolution, particularly the order Docodonta, which diversified and occupied various environments at the same time as large dinosaurs roamed the Earth. Furthermore, this fossil places the origin of docodonts in Greenland and Europe—connected before the continents separated into their current positions—rather than Russia and Asia as previously thought.
The layers of soil containing the fossils are like shelves in a bookcase, each corresponding to a period of time. By exploring each shelf as if reading the books stored there, the scientists were able to date the layer and the fossils—among them a new species of dinosaur, Plateosaurus trossingensis, identified by a fellow student in Sofia's master's program — and also describe the environment. The fossils were found in an ancient lake, with little oxygen in the water and which served as a passageway for many animals.
200 million years ago, when the 'Nujalikodon cassiopeiae' fossil is believed to have formed, what are now Greenland and Europe were connected, and also in contact with the continental plates of North America and Asia.Adapted from: Patrocínio et al. (2025) Papers in Paleontology
A goddess tooth named after a constellation
Now 25, Sofia Patrocínio boasts the identification of a new species on her resume. "It's strange; it seems like it hasn't sunk in yet." Whoever discovers a new species can give it a name, naturally following the rules used by the scientific community. A species always has two Latin names (first the genus name, which functions almost like our surnames, and then the "proper name" that conveys the distinctive characteristic), as defined by the scientist Carlos Linnaeus in the mid-18th century.
This new docodont was named Nujalikodon cassiopeiae . Nujalik is the goddess of the earth hunt in Inuit mythology—the indigenous population of the Arctic regions of Canada, Alaska, and Greenland—and "nujalikodon" means "Nujalik's tooth." The specific epithet cassiopeiae owes its name to the constellation Cassiopeia, whose five stars appear to form a W, like the cusps of the molar Sofia Patrocínio studied.
Naming the species requires all the prior work of studying fossils, in this case a complete molar, the piece of bone that housed the tooth, and the broken roots of a second tooth. But a large portion of the fossil was not visible; it was still embedded within the rock, and removing it could irreparably damage the tooth. Furthermore, it was extremely small, the molar measuring only two millimeters. Therefore, a scan of the fossil was necessary—a kind of CT scan for very small objects—which was very difficult to achieve, says the researcher. "But without the scan, it was impossible to move forward, nor to submit the article for publication." Then, using the 831 photographs from the scan—as if the fossil had been cut into very thin slices—a three-dimensional model was created on the computer, allowing us to see the details hidden within the rock.
The 831 photographs taken by the scan allowed a three-dimensional reconstruction of the fossil measuring just seven millimeters.Adapted from Patrocínio et al. (2025) Papers in Paleontology
Sofia Patrocínio's work was supported by her advisors, Vicente Crespo, a paleontologist at Nova FCT, and Elsa Panciroli, a researcher at the National Museum of Scotland, and involved collaboration with other researchers. The work was funded by the Foundation for Science and Technology, as part of the GeoBioTec project.
Having completed this stage, the paleontologist hopes to continue studying the evolution of mammalian ancestors with a doctorate from the Instituto Superior Técnico of the University of Lisbon. This time, she will study the inner ear—but she will continue to observe bones and very small structures. In the meantime, she will participate in paleontological excavations, collaborate with a fossil database in Portugal, and, in the activities she organizes for Ciência Viva, try to spark children's interest in paleontology.
Publication:
ABSTRACTThis fossil tooth extends the known existence of docodontans by around 40 million years, placing them much earlier in the evolutionary timeline than previously documented. This is significant because:
The first mammaliaforms emerged in the Late Triassic, but their exact origins remain unclear due to the scarcity of fossils from this period. One of the earliest diverging mammaliaform groups, the order Docodonta, became unusually ecomorphologically diverse compared with other early mammals, and this may be connected to the possession of complex molar cusp morphology. The specimen described here, found in the Rhætelv Formation of the Kap Stewart Group (Rhaetian–Sinemurian) of central East Greenland, provides novel information on docodontan origins and evolution, as well as key biogeographic insights into early mammal dispersal. Nujalikodon cassiopeiae gen. et sp. nov. is the first mammaliaform found in the Rhætelv Formation, and is likely to be Early Jurassic (Hettangian) in age. Comprising an incomplete dentary with a single preserved molar, it was visualized using micro-computed tomography; the molar bears similarities to the putative early docodontan Delsatia, and docodontan Dobunnodon. Phylogenetic analysis places Nujalikodon cassiopeiae as a basal member of Docodonta or a close sister taxon, making it one of the oldest definitive docodontans and pushing the origin of the group back to at least the Early Jurassic. It provides insights into the development of docodontan dental complexity, a key factor in their ecological diversification during the Middle to Late Jurassic. Its presence in Greenland supports the hypothesis that docodontans originated in the region now comprising Europe and Greenland before dispersing across the rest of Laurasia.
Patrocínio, S., Panciroli, E., Rotatori, F.M., Mateus, O., Milàn, J., Clemmensen, L.B. and Crespo, V.D. (2025)
The oldest definitive docodontan from central East Greenland sheds light on the origin of the clade. Pap Palaeontol, 11: e70022. https://doi.org/10.1002/spp2.70022
© 2025 John Wiley & Sons, Inc.
Reprinted under the terms of s60 of the Copyright, Designs and Patents Act 1988.
- It strengthens the fossil record for the transition from reptile-like synapsids to early mammals, filling a critical gap rather than overturning existing theory.
- It confirms evolutionary predictions — that mammaliforms had already diversified long before the rise of true mammals, in line with phylogenetic models.
- It demonstrates the self-correcting nature of science — evidence leads to refinements in understanding, not wholesale abandonment of established frameworks. When the evidence changes, scientists change their minds, unlike theologians who try to change the evidence.
Rather than undermining evolution, this discovery is yet another piece of independent evidence that fits perfectly into its framework — and yet another reminder that creationist models fail when confronted with reality.
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