Los Rastros Formation

The Los Rastros Formation is an important rock layer from the middle of the Carnian age found in northwestern Argentina. It is part of the Agua de la Peña Group and is located in the Ischigualasto-Villa Unión Basin. This formation is special because many fossils have been discovered there.

Scientists have found tracks made by ancient animals called archosaurs, along with fossils of many insects, fish, bivalves, crustaceans, and plants. These fossils help us learn about the world millions of years ago and what kinds of life existed at that time.

Geology

The Los Rastros Formation lies above the Chañares Formation and/or the Ischicuca Formation, and is covered by the Ischigualasto Formation. It is part of the Agua de la Peña Group in the Ischigualasto-Villa Unión Basin, and can be seen in the Ischigualasto Provincial Park, a World Heritage Site in Argentina. This formation, which can be up to 1,000 metres (3,300 ft) thick, is made of claystones, mudstones, and sandstones. It formed in a deltaic to lacustrine environment during a time when the land was changing after a big split in the earth’s surface.

In 2020, scientists found that the lower part of the Los Rastros Formation is about 234.47 ± 0.44 million years old. This shows that most of the layers above it were put down during or after the Carnian Pluvial Event.

Paleobiota

The Los Rastros Formation is a place where scientists have found many old fossils. The only body fossil of a four-legged animal found here is a poorly preserved amphibian called a temnospondyl.

Ichnofossils

This formation is famous for its animal footprints, especially near a place called Quebrada de Ischichuca. These footprints show animals that walked on two legs with three toes on the ground. Scientists think these might be early dinosaurs or similar animals. Some footprints also show hand prints, suggesting animals that walked on four legs. Other footprints might have been made by groups of small reptiles or even large four-legged animals moving together.

Fish

Invertebrates

Many insect fossils have been found here, including types like cockroaches, beetles, and true bugs. Other small animals found include clam shrimp and freshwater mussels.

Blattoptera

Coleoptera

Hemiptera

Water boatmen have also been found in a place called Gualo.

Other insects

Plants

A lot of plant fossils have been discovered here, including tiny plant pieces and larger plant parts. These plants belong to many different groups, such as Calamitales, Coniferales, Cycadales, Equisetales, Osmundales, and Rhexoxilales.

Seed ferns

Other gymnosperms

Other plants