Toro Toro – a palaeontological treasure of the Andes
Vivi Vajda (Sweden)
In a valley in the Andes, at 2,500m above sea level, is Bolivia’s third largest city – Cochabamba. The town is beautifully surrounded by snow-capped mountain peaks of which the highest is Tunari at 5,088m. For a palaeontologist, the town is an excellent base camp, as it is situated in a geologically complex area and the highly variable geology exhibits marine Ordovician and Silurian shales, Devonian fossiliferous mudstones, and continental Cretaceous sediments.
However, the subject of this article is an expedition I made with others in the area. Toro Toro is a national park in the province of Charcas in the state of Potosí. Toro Toro, which in the Inca language (Quechua) means ‘mud plain’, is known for its karst landscape with countless caves and for the numerous, well-preserved dinosaur tracks.
The expedition begins with a visit to the city’s Natural History Museum (the Museo de Historia Natural Alcide d’Orbigny), named after the famous French naturalist Alcide d’Orbigny (1802 to 1857) who, during an expedition between 1827 and 1833, spent time in Bolivia to describe the country’s geology, flora and fauna. The museum has impressive collections of geological, palaeontological and biological value, and the museum’s director, Ricardo Cespedes, provided us with maps and good advice before departure.
At dawn, we leave Cochabamba in our 4WD jeep. The air is clear and chilly when we take the highway towards the east and we only make a brief stop to buy supplies from the vendors who have already begun to unpack their goods for Saturday’s market. Fantastic road cuttings with thick Silurian deposits whiz by and I have to restrain myself not to give in to temptation and ask the driver to stop. It has to wait for another time as we need to reach Toro Toro before nightfall, given the road conditions.
After a relatively pleasant few hours on the cobblestone roads, we take a break in the beautiful village of Anzaldo and, after a cup of strong Bolivian coffee, we continue towards our goal. We have now travelled more than half the 140km to Toro Toro and I cannot in any way understand why this trip would take another six hours. We soon pass the border between the states of Cochabamba and Potosi, and there the cobblestone road changes into a mud track that winds along steep, breathtaking cliffs.
We drive along a valley and deep down, at the bottom, the River Caine flows. It appears to be a fertile landscape with plenty of corn and fruit plantings, and the people seem to live relatively well. Nature is beautiful and captivating, and the Ordovician, Silurian, Devonian and Permian now come into view. The jeep defeats a last peak and then we can see the village of Toro Toro down in the valley, where houses with red roofs spread out across the landscape below us.
I’m making a rushed visit to the village’s tourist office where we all sign in waiting for our guide, Mario Jaldin. It is compulsory to have a registered guide as company when entering the park, primarily for the protection of the fossil and archaeological heritage, but also to ensure visitor safety. After a quick dinner, we set off together with Mario for a recognisance tour before the sun sets.
The following days, we spend studying the geology, flora and fauna of this stunning landscape. Toro Toro National Park covers an area of over 165km2 and includes several climatic zones, with warm-temperate areas, arid valleys, higher-lying areas with mixed forest and arid plateaus. The park is a paleontological treasure – probably Bolivia’s most important palaeontological site – with well-preserved Palaeozoic and Mesozoic plant and animal fossils reflecting the palaeoenvironment and evolution of the area. The national park is also famous for its archaeological treasures, with over 23 fascinating archaeological sites and a mountain range extends through the park with deep canyons, valleys and waterfalls.
The area is an Eldorado for speleologists, with at least 20 deep cave systems, of which Umajalanta, with its 7km of tunnels, is the most famous. The cave is situated 2,850m above sea level and was examined by an expedition in 1966. Since then, Umajalanta and 11 other caves have been studied by international teams of speleologists. The caves exhibit extraordinary formations of stalagmites and stalactites and, in the dark lakes, the blind, colourless fish of the genus Trichomycterus thrive. These have received considerable attention from ecologists. The genus includes several species that are specially adapted to underground conditions and the species, Trichomycterus chaberti, is endemic to the cave system at Umajalanta.
However, the main attractions of the park, and the very goal of our expedition, are the numerous dinosaur trackways occurring in its Late Cretaceous sediments.
These sediments belong to the Potosi Basin, which is entirely located at the eastern side of the Andes (Eastern Cordillera) and constitute over 1,000m-thick successions of chiefly limestones and sandstones. There are four sites in Bolivia known for Late Cretaceous dinosaur tracks and all are dated to the Campanian to the Maastrichtian, and Toro Toro is the most northerly located of these sites. Since the first specimens were described in 1968, 2,500 tracks have been recorded and these compare well with the better-known dinosaur trackways of Colorado, USA.
The footprints represent entire dinosaur faunas, with sauropods, ankylosaurs, hadrosaurs and raptors. The sequence containing the fossilised footprints belongs to the Toro Toro Formation dated to the Late Cretaceous (about 75 to 70 million years ago) and the lithology consists mainly of coarse-grained sandstones and evaporites, as well as limestone with a relatively high clay content. The sediments also include conglomerates with mafic volcanic clasts. At the time of deposition, the area was a coastal ecosystem with lagoons and lakes where sandstone and limestone were formed in a sabkha-like environment, as in some desert environments today.
At some levels, we find impressive stromatolites formed in temporary lakes that periodically dried out.
The sauropod footprints (Titanosaurids) occur mainly in the sandstones.
They are found together with a dozen specimens of theropod prints, and represent both adult and juvenile individuals seen here as evidence of herd behaviour. These footprints are very well preserved and even the occasional toes can be discerned. They measure up to 45cm in diameter with a depth of 25cm, usually with straight edges suggesting that the surface was relatively dry and plastic when the dinosaurs walked on the site over 70mya.
However, the most common footprints were left by carnivores, such as theropods.
We spend a few days documenting trackway associations. However, the hiking in the mountains is, at times, very uncomfortable due to the thin air and we are recommended to chew coca leaves to defeat mountain sickness or “soroche”. After some negotiations, I receive the permission to sample the sediments surrounding the various dinosaur tracks. I am interested in samples for pollen analysis to identify the past vegetation from the time of the dinosaurs in the region of Toro Toro.
Time passes too quickly and, due to heavy rains upstream, we cannot visit the Umajalanta cave this time. The trip back to Cochabamba goes without any major problems and, the next day, we spend at the paleontological museum in Cochabamba cataloguing samples.
The preliminary results of my pollen analysis shows that the vegetation in Toro Toro area 70mya consisted of a mixture of palm trees and ferns, together with several groups of now extinct flowering plants. Vegetation composition shows that the climate was much warmer in the area compared to the present day, partly due to the fact that the Andes had not yet been formed and consequently the area was located at sea level. However, it was also the result of global climate warming during the Late Cretaceous.
My thanks go to Mario Jaldin (Toro Toro National Park) for his professional guidance. Thanks also to Andrea Santivanez and Elizabeth Ordoñez-Heredia for their assistance in the field.
About the author
When Vivi Vajda wrote this article for Deposits, she held a post funded by the Swedish Royal Academy of Sciences through the Knut and Alice Wallenberg Foundation at the Department of Earth and Ecosystem Sciences, Lund University. She is now Professor in the, Department of Palaeobiology, Swedish Museum of Natural History, Stockholm, Sweden.