New South American Site Reveals Extraordinary Fossils from the End of
the Age of the Dinosaurs
Pittsburgh, Pa., USA: The discovery of a spectacular fossil site in
Argentina is helping shed new light on life at the end of the Cretaceous,
the time period just before the non-avian dinosaurs went extinct.
presented this Monday at the Geological Society of America’s GSA Connects
2023 meeting by Matthew Lamanna, a paleontologist and the principal
dinosaur researcher at Carnegie Museum of Natural History, describes
exciting fossil finds from a site known as the Cañadón Tomás Quarry in
southern Argentina’s Patagonia region.
“In general, dinosaurs and other continental vertebrates from the
Cretaceous tend to be less known from the Southern Hemisphere than they are
from the Northern, and that creates an imbalance in our understanding of
biodiversity, evolution, and paleobiogeography,” says Lamanna. “We know
enough about continental vertebrates in the Late Cretaceous to know that
there were some very different kinds of animals thriving in the Southern
Hemisphere. One thing that we'd really like to know is, how did non-avian
dinosaurs in the southern half of the world fare at the
The Cañadón Tomás site was first discovered in early 2020 due to petroleum
interest in the region. Oil companies were required to carry out a
paleontological impact study before they could begin work, and the study
soon uncovered dinosaur fossils.
“The paleontological impact study was done by people from the Museo de La
Plata and they found some bones belonging to hadrosaurs
(large-bodied duck-billed dinosaurs). This information was shared with the
paleontology crew of the Universidad Nacional de la Patagonia San Juan
Bosco (UNPSJB), who started to explore the area, finding some bones. At the
end of 2020, a few bones were recovered in the outcrop that today is
Cañadón Tomás, and little by little, we began to expand that excavation
hoping to find something interesting,” says
Noelia Cardozo, a PhD student at the UNPSJB and member of the Cañadón Tomás
Continued excavations at the site have revealed dozens of bones from
hadrosaurs. These plant-eaters are common and well known in Northern
Hemisphere sites from Late Cretaceous times, but they are comparatively
rare and poorly known from Southern Hemisphere sites. Interestingly, the
hadrosaur fossils at Cañadón Tomás appear to belong to individuals of
“The site could capture a social group, potentially even a herd of
individuals that were related to each other that were all buried together.
These are the kinds of things that we’ll be investigating as we dig into
the site more,” says Lamanna.
In addition to the hadrosaur fossils, the team discovered the remains from
two individuals of non-avian predatory dinosaurs: a tooth, likely from an
abelisaurid, and a claw, likely from a noasaurid or a
While the dinosaur fossils at Cañadón Tomás are exciting and provide
crucial insight into Southern Hemisphere non-avian dinosaurs before their
extinction, it’s other fossil finds of rare and small-bodied vertebrates
that have the research team most excited.
The team discovered a vertebra of a snake, likely a madtsoiid, the
first Cretaceous snake found in this region of Patagonia known as the Golfo
San Jorge Basin. What really put the site high on their radar, according to
Lamanna, was the discovery of the upper jaw containing teeth of a small
mammal known as a reigitheriid.
“For me, the most exciting discovery from this site so far was the small
fragment of the jaw of a mammal,” says Cardozo. “Because this formation is
mainly well known for its record of dinosaurs, that’s what I expected to
find. But when that little piece [of jaw] appeared, we knew it was
different from everything that we had been working on so far.”
In March 2023, Cardozo and fellow UNPSJB student Ivanna Mora had spent only
two hours sieving through rocks and sediment when they discovered the
mammal jaw—relatively speaking, a lightspeed find in the world of
paleontology. The fossil is now the first Cretaceous mammal of any kind
found in the Golfo San Jorge Basin. According to Lamanna, the jaw is “one
of the best fossils of its kind of mammal ever discovered.”
Mammals in the Cretaceous were typically small, rodent-sized creatures—not
as foreboding and as easy to capture the imagination as dinosaurs. However,
understanding mammalian life at the end of the Cretaceous is crucial to
having a full picture of life leading up to the extinction of non-avian
dinosaurs, as well as understanding how mammals expanded and proliferated
following the extinction.
While research and excavations at the Cañadón Tomás site are still in a
preliminary stage, the fossil discoveries thus far have shown that the site
is extremely promising.
“Cañadón Tomás is a site of great interest not only for the great
diversity, but also for the great quantity of materials that are being
discovered at the site,” says UNPSJB Ph.D. student Bruno Alvarez. “As
excavation work continues, more and more materials are being found. There
is still a lot of work left to do at Cañadón Tomás with a lot of field work
to complete, and we suspect there will be many more fossils to discover and
Lamanna notes that people should “keep their eyes peeled for new
discoveries” from Cañadón Tomás.
“We think [Cañadón Tomás] holds so much potential to not only inform our
understanding about Cretaceous-Paleogene faunal dynamics and extinction
dynamics in the Southern Hemisphere, but it’s probably also going to
produce new species of animals. Right now, it’s one of the sites I’m
involved with that has me the most excited and fired up,” says Lamanna.
Leer en español.
Extraordinary New Fossil Locality Casts Light on Central Patagonia’s
Last Cretaceous Continental Vertebrates
Contact: Matthew Lamanna, LamannaM@carnegiemnh.org
71: D22. Recent Developments in Biogeography and Biostratigraphy
Mon., 16 Oct., 9:50–10:05 a.m.
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