An artistic reconstruction of the passage of the group of sauropods, a small theropod, and an iguanodon. Image credit: Jorge Gonzalez
Bolivia yields an outstanding dinosaur ichnological record. Different ichnosites in the Chuquisaca Department, and the Potosí Department, reveal an outstanding abundance and diversity of theropod, sauropod, ankylosaur and ornithopod footprints. But most of its deposits were restricted to the Triassic period (220 million years old) and to the last moment of the Upper Cretaceous (between 75 and 65 million years ago). A new ichnosite bearing about 350 dinosaur footprints, discovered by Dr. Gustavo Méndez Torrez, along the shore of the Santa Ana River, near the town of Entre Ríos, in the Department of Tarija, offers a glimpse into a Jurassic kindergarten. More important, with this new discovery Bolivia has dinosaur footprints from the entire Mesozoic Era.
During the Late Jurassic, Gondwana was split into a northern and southern continent by the rift system opening the proto-Indian Ocean. The geological and geochemical record suggest that low-latitude environments were arid and tropical ever-wet conditions were absent. Maximum plant diversity was concentrated at midlatitudes, whith forests dominated by a mixture of conifers, cycadophytes, pteridosperms, ferns, and sphenophytes. The vast Botucatú Desert, which ran from Bolivia to Brazil and had its counterpart in Africa, occupied the center of Gondwana. In this scenario, sauropodomorph diversity patterns reached a peak similar with those of theropods and ornithischians.
Map of the tracks. Arrows indicate direction of movement of the sauropod producers. Photo credit: Sebastián Apesteguía.
The dinosaur traces from Tarija are abundant. They are recorded in 10 different levels, most of them correspond to long-necked sauropod dinosaurs, with the exception of few tridactyl tracks. The best preserved trackway exhibits large pedes of about 95 cm and 75 cm in in diameter, sub-ovoidal to roughly sub-rectangular in outline, with three or four claw impressions, and sub-circular manus tracks with two or three digit impressions. The team was able to calculated that the animal’s hips were 3.8 meters above the ground, with a estimated length from nose to tail of 20 meters. Associated with those tracks, the researchers found a large number of small footprints, between 15 cm and 30 cm in diameter. The distribution of these trackways may represent an ichnological example of herd behavior from the Late Jurassic period.
References:
Méndez Torrez, G., Lovera Cruz, L., Céspedes-Llave, A. Á., Esperante, R., Gutiérrez Berrios, C., & Apesteguía, S. (2023). First Jurassic to earliest Cretaceous dinosaur footprints for Bolivia at the Castellón formation (Tacurú Group), Tarija. Historical Biology, 1-20. https://doi.org/10.1080/08912963.2023.2235373
Letters from Gondwana. 