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PATAGONIA, LAND OF DISCOVERIES: FOUR FOSSIL FINDS THAT REWRITE THE HISTORY OF LIFE IN ARGENTINA - by cronywell

⏱ ESTIMATED READING TIME: 9 MINUTES | 🗓 APR 2026 | 🦴 ARGENTINE PALEONTOLOGY

SEO keywords: paleontology Argentina 2026, Chubut dinosaur, Bicharracosaurus dionidei, Cretaceous reptile Río Negro, fossil crocodile Patagonia, CONICET fossils

PATAGONIA, LAND OF DISCOVERIES: FOUR FOSSIL FINDS THAT REWRITE THE HISTORY OF LIFE IN ARGENTINA

In less than two weeks, scientific teams from CONICET and international partners published four first-rate paleontological findings in Argentine Patagonia: a 70-million-year-old reptile in Río Negro considered the most complete lizard of the late Cretaceous in South America; Bicharracosaurus dionidei, the first Jurassic brachiosaurid known in the southern hemisphere; an 85-million-year-old land crocodile; and a fossil trunk integrated into the scientific heritage in Neuquén. Argentina once again demonstrates why its soil is the living archive of the planet.

🗺 Four provinces, four windows to the past

🦎

70 M.a.

Paleoteius lakui — Late Cretaceous lizard reptile

📍 Río Negro · Allen Formation, Ojo de Agua Salt Mine

🦕

155–160 M.a.

Bicharracosaurus dionidei — First Jurassic Brachiosaurid of the Southern Hemisphere

📍 Chubut · Calcáreo Canyon Formation

🐊

85 M.a.

Notosuchus terrestris (cf.) — Cretaceous land crocodile

📍 Río Negro · Paso Córdoba Natural Protected Area, Gral. Roca

🌲

Millions of years

Petrified fossil trunk — University scientific heritage

📍 Neuquén · City of Neuquén (rescued private site)

Findings in <2 weeks

155M

Years of Seniority (Max)

<12

Known Southern Hemisphere Mesozoic Lizards

🦎 1. Paleoteius lakui: the missing link of Cretaceous lizards

🖼 View image: Patagonian landscape, Río Negro — Paleoteius lakui finding area

https://upload.wikimedia.org/wikipedia/commons/thumb/d/df/Patagonia_Argentina.jpg/1200px-Patagonia_Argentina.jpg

▲ Patagonian landscape, Río Negro — Paleoteius lakui find area — Source: Wikimedia Commons / CC

At the site of Salitral Ojo de Agua, south of the city of General Roca, province of Río Negro, an international paleontological team led by CONICET scientists made one of the most significant findings in recent South American paleontology. The new species of reptile, named Paleoteius lakui, lived approximately 70 million years ago, during the late Cretaceous, at the dawn of the mass extinction that would wipe out three-quarters of life on the planet.

The discovery, published in the scientific journal Scientific Reports with the support of the National Geographic Society, was led by Federico Agnolín, a CONICET researcher at the Laboratory of Comparative Anatomy and Evolution of Vertebrates (LACEV) of the Argentine Museum of Natural Sciences. Despite its small size – just 15 centimeters in length – Paleoteius lakui represents the most complete terrestrial lizard known for that period in the entire Southern Hemisphere.

The value of the find is hard to overstate. While more than 150 species of Mesozoic lizards are known in the Northern Hemisphere, the Southern Hemisphere record barely exceeds a dozen. Moreover, the phylogenetic analysis revealed that Paleoteius lakui does not belong to any known group in South America, which evidences the existence of evolutionary lineages completely unpublished by science.

🔬 Species	Paleoteius lakui
📍 Location	Ojo de Agua Saltpeter, Río Negro — Allen Formation
⏳ Seniority	~70 million years ago (Late Cretaceous)
📏 Size	Approx. 15 cm in length — small land lizard
🧬 Lineage	Scincomorpha — not classifiable in known South American groups
📰 Publication	Scientific Reports (Nature Portfolio) — apoyo National Geographic Society
⚗️ Technology	Microcomputed tomography + 3D models (CNEA)
👥 Team	LACEV-MACN-CONICET, Félix de Azara Foundation, Patagonian Museum

The fossil remains of small animals are generally very scarce... the discovery of Paleoteius fills a void of tens of millions of years.

— Federico Agnolín, researcher at CONICET (LACEV-MACN)

The skull of Paleoteius featured an ornamentation of small protuberances and jaws with numerous thin teeth, probably adapted to feed on insects. To study its internal anatomy without damaging the remains, the team used micro-computed tomography in collaboration with the National Atomic Energy Commission (CNEA), generating high-precision three-dimensional models. The result is the sharpest image ever obtained of a Late Cretaceous terrestrial lizard in South America.

🦕 2. Bicharracosaurus dionidei: the giant that began with a "bicharraco"

🖼 See image: Reconstruction of sauropod type Diplodocus — reference to the Macronaria group to which Bicharracosaurus belongs

https://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Diplodocus_Carnegie_Labeled.jpg/1200px-Diplodocus_Carnegie_Labeled.jpg

▲ Reconstruction of Diplodocus-type sauropod — reference to the Macronaria group to which Bicharracosaurus belongs — Source: Wikimedia Commons/CC

In a remote corner of northwestern Chubut, Dionide Mesa, a baqueano and rural producer, roamed the countryside on horseback as he had done all his life. Every time he came across a huge bone, he called the scientists of the Egidio Feruglio Paleontological Museum (MEF) with the same phrase: "I found a bug!" That usual gesture, repeated for years, ended up being the starting point of the most relevant paleontological discovery in South America so far in 2026.

The new dinosaur, named Bicharracosaurus dionidei after Mesa, is a long-necked herbivorous sauropod that lived between 155 and 160 million years ago during the Late Jurassic. Its remains were found in the Cañadón Calcáreo Formation, a geological unit internationally recognized for its richness in Jurassic fossils. The study was published in the journal PeerJ and was led by German paleontologist Alexandra Reutter in collaboration with teams from CONICET-MEF, the Ludwig-Maximilians-Universität München and the German Research Foundation (DFG).

The scientific relevance of Bicharracosaurus transcends its enormous size – between 15 and 20 meters long and about 20 tons. The phylogenetic analysis determined that it belongs to the group of the Macronaria, a branch that includes Brachiosaurus and Patagotitan, and that its finding makes it the first Jurassic brachiosaurid known in the entire southern hemisphere.

🔬 Species	Bicharracosaurus dionidei
📍 Location	Cañadón Calcáreo Formation, northwest of Chubut
⏳ Seniority	155–160 million years ago (Late Jurassic)
📏 Size	15–20 m long · ~20 tons weight
🧬 Lineage	Macronaria — first Jurassic brachiosaurid in the Southern Hemisphere
🦴 Material	Spine, dorsal ribs, hip fragments
📰 Publication	PeerJ — German-Argentinian team (CONICET-MEF / LMU München / DFG)
🎖 Tribute	Name in honor of Dionide Mesa, baqueano discoverer

Our analysis indicates that Bicharracosaurus is the first Jurassic brachiosaurid known in South America.

— Alexandra Reutter, paleontologist, lead author of the study — LMU München

The most distinctive anatomical feature of Bicharracosaurus dionidei is its neural spines – the bony projections on the vertebrae. While in most sauropods these structures are wider than they are long, in this dinosaur they appear compressed and elongated from front to back, forming an unprecedented morphology within the group. The vertebrae also have complex internal cavities: a kind of hollow architecture that lightens the skeleton without losing structural strength, the key that allowed sauropods to reach colossal sizes.

José Luis Carballido, a researcher at CONICET-MEF and co-author of the study, was direct in assessing the significance of the discovery: "Sauropods were a fundamental part of the terrestrial ecosystems of South America; its diversity was much greater than we thought." Diego Pol, another co-author, stressed that "each discovery provides key information about a time for which there are very few records in the southern hemisphere."

🐊 3. The crocodile that walked upright: 85 million years in Paso Córdoba

🖼 View image: Artist's reconstruction of Notosuchus terrestris — possible species from the Rio Negro fossil (Wikimedia Commons)

https://upload.wikimedia.org/wikipedia/commons/thumb/9/9b/Notosuchus_BW.jpg/800px-Notosuchus_BW.jpg

▲ Artist's reconstruction of Notosuchus terrestris — possible species of the Río Negro fossil (Wikimedia Commons) — Source: Wikimedia Commons / CC

Unlike popular imagination, late Cretaceous crocodiles were terrestrial, agile, upright creatures, more like a mammal than the aquatic reptile we know today. In the Paso Córdoba Natural Protected Area, in the vicinity of General Roca, Río Negro, a CONICET campaign led by Agustina Lecuona (Institute for Research in Paleobiology and Geology, IIPG-CONICET-UNRN) brought to light one of these extinct reptiles.

The discovery began when postdoctoral fellow Facundo Riguetti detected a skull fragment in the rock. By expanding the excavation, the team also recovered vertebrae, parts of the limbs and other bones of the post-skull, which were extracted with CONICET protocols in collaboration with the National University of Río Negro and the Azara Foundation-Maimonides University. The geological formation corresponds to the Bajo de la Carpa Formation, an environment of ephemeral rivers and aeolian sectors similar to today's deserts.

Preliminary analysis suggests that the remains could correspond to Notosuchus terrestris, a species of terrestrial crocodile widely distributed in Patagonia during the Cretaceous. However, the researchers do not rule out that it is a different species – and even new to science – which would further raise the value of the find. Lecuona stressed that the almost complete femur allows us to estimate an adult size of around one meter without counting the tail.

🔬 Probable species	Notosuchus terrestris (to be confirmed)
📍 Location	Paso Córdoba Natural Protected Area, Gral. Roca, Río Negro
⏳ Seniority	~85 million years ago (Late Cretaceous — Lower Tent Formation)
📏 Estimated size	~1 meter not including tail (based on femur)
🏃 Locomotion	Terrestrial · Upright legs · agile mammal-like gait
🦴 Material	Skull, vertebrae, limb bones (postcranium)
👥 Team	Agustina Lecuona, Facundo Riguetti, Mattia Baiano · IIPG-CONICET-UNRN

If, on the other hand, it were not the species mentioned, the finding would be just as or more relevant, since few species of crocodiles are known in Paso Córdoba and they are usually represented by a single specimen.

— Agustina Lecuona, researcher at CONICET (IIPG-UNRN)

🌲 4. The fossil trunk of Neuquén: preserving is also researching

The fourth piece of the Patagonian paleontological mosaic of these weeks did not come from a planned scientific excavation, but from an urgent rescue. The Directorate of Cultural Heritage of the province of Neuquén detected a fossil trunk in a private property within the city of Neuquén and proceeded to remove it to deposit it in the paleontological repository of the Museum of Natural Sciences of the National University of Comahue (UNCo).

"What was done was to remove that material and deposit it in the paleontological repository of the University of Comahue," explained paleontologist Juan Porfiri, director of the museum, who stressed that this type of intervention is part of a systematic policy of safeguarding paleontological heritage. The institution acts as a depository of paleontological, archaeological and historical pieces of the region.

The case brings to the fore the constant threat of illegal fossil trafficking. Argentine Patagonia has documented records of petrified trunks, fossil invertebrates and even dinosaur bone material that have been illegally extracted and offered on internet portals. Active preservation – not just research – is, in this context, an essential way of doing science.

In times when natural memory faces risks of loss and devaluation, the public university reaffirms its role as guardian of knowledge.

— Institutional Declaration, Museum of Natural Sciences — National University of Comahue

🌍 Argentina, the fossil capital of the world

The concentration of findings in such a short time is not a coincidence. Argentine Patagonia is, along with Montana (USA) and some areas of Central Asia, one of the richest and most diverse paleontological sites on the planet. Its geological formations range from the Jurassic to the late Cretaceous, and the conditions of sedimentation and aridity have preserved remains that in other latitudes would have already disappeared.

Behind each find there are decades of institutional work: CONICET, the Egidio Feruglio Paleontological Museum in Trelew, the Argentine Museum of Natural Sciences in Buenos Aires, the National University of Comahue, the National University of Río Negro and dozens of international collaborators weave a scientific network that, despite structural underfunding, continues to produce world-class results. There are also rural dwellers – such as Dionide Mesa in Chubut or Facundo Riguetti in Río Negro – whose trained gaze and their vocation to collaborate with science are essential.

Each of these four discoveries that occurred in April 2026 adds a piece to the puzzle that science has been trying to complete for centuries: what life was like on Earth before humans inhabited it. And the answer, once again, comes from Patagonian soil.

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📚 Primary sources consulted

▸ Reptile Paleoteius lakui — Official CONICET · https://www.conicet.gov.ar/cientificos-del-conicet-hallan-en-la-patagonia-argentina-un-nuevo-reptil-de-70-millones-de-anos/

▸ Paleoteius lakui — Scientific Reports (Nature) · https://www.nature.com/articles/srep

▸ Bicharracosaurus dionidei — Official MEF · https://mef.org.ar/blog/2026/04/17/bicharracosaurus-el-nuevo-gigante-jurasico-de-chubut-que-homenajea-al-poblador-rural-que-lo-hallo/

▸ Bicharracosaurus dionidei — Infobae Education · https://www.infobae.com/america/ciencia-america/2026/04/17/hallan-en-chubut-una-nueva-especie-de-dinosaurio-herbivoro-y-de-cuello-largo-como-lo-descubrieron/

▸ Crocodile 85 M.a. — IIPG-CONICET · https://iipg.conicet.gov.ar/cientificos-del-conicet-hallan-en-rio-negro-un-antiguo-cocodrilo-que-vivio-hace-85-millones-de-anos/

▸ Crocodile 85 M.a. — La Nación · https://www.lanacion.com.ar/sociedad/un-cocodrilo-muy-distinto-a-los-actuales-pero-en-la-patagonia-el-hallazgo-de-un-fosil-de-85-millones-nid22042026/

▸ Fossil trunk Neuquén — Río Negro · https://www.rionegro.com.ar/sociedad/rescatan-un-tronco-fosil-de-millones-de-anos-en-neuquen-y-lo-convierten-en-patrimonio-cientifico/

▸ Reptile Patagonia — El Litoral · https://www.ellitoral.com/informacion-general/paleoteius-patagonia-cretacico-extincion-conicet-fosiles-rionegro-evolucion-scientificreports-lagarto-formacionallen-yacimiento_0_29jnbrywf8.html