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While dinosaurs dominated the continents, mammals were timid, small, and agile creatures, often hunted by large reptiles. However, an enigmatic mammal that traversed the dunes of present-day southern Brazil 130 million years ago possessed enough size to confront some of these giants.

Its footprints differed significantly from those of its contemporaries, measuring over 10 centimeters in length and 13 centimeters in width, surpassing any other known mammal track in that geological formation. Researchers suggest that this creature may represent the largest mammal that coexisted with the dinosaurs.

These footprints were discovered in the Botucatu Formation, located in the Paraná Basin, a site notable for its fossil remains, although scarce in skeletons. At that time, the area was part of an extensive desert covering Brazil and parts of southwestern Africa, regions that were part of the supercontinent Gondwana.

The sandstone rocks contain traces of dinosaurs, mammals, lizards, pterosaurs, and arthropods. However, previously recorded mammal tracks were generally much smaller, with dimensions of approximately 4.5 to 5 centimeters in length and just over 6 centimeters in width.

The new discoveries break this pattern, presenting tracks almost twice the size of previous ones. Based on the morphology of the tracks and the proportions of other mammals of the period, it is estimated that the animal could have reached up to 1.55 meters in length, comparable to the size of a capybara or a leopard.

Despite this, without bone evidence, the exact identity of the animal remains unknown. Aline Ghilardi, a paleontology professor at the Federal University of Rio Grande do Norte (UFRN) and author of the study, clarifies that the confirmation is not based on a single trait, but rather on the combined analysis of the footprint anatomy and how they are arranged in the trail.

Researchers argue that the tracks were left by a mammal because the prints are wider than they are long, possess four short, rounded toes, and form narrow trails, consistent with quadrupedal locomotion. These characteristics are typical of mammaliaforms, a group that includes both modern mammals and their distant ancestors.

Precisely identifying which animal left these tracks is an even greater challenge. Ghilardi points out that the footprints do not function as direct fingerprints of a species, mainly because there are no skeletons of mammaliaforms of that age in Brazil. She speculates that the responsible parties could be triconodonts or cladotheres; while triconodonts were an extinct lineage known for three-pointed aligned teeth, cladotheres belong to the ancestral group of most modern mammals, including humans.

The reason why this mammal was considerably larger than others of its time is also a mystery. Pedro Buck, the first author of the study and a professor at the State University of Minas Gerais (UEMG), explains that intense competition with dinosaurs, which were extremely varied, may have kept most mammals at reduced sizes throughout the Mesozoic Era.

Qinghai Lake, China's largest inland saline lake, is situated on the northeastern Tibetan Plateau at an altitude of about 3,200 meters above sea level. Local Tibetans call it Tso Ngongpo, which translates to 'Blue Lake.'

This area features a combination of high-altitude landscapes, internationally significant bird nesting sites, rare endemic species, and an ecosystem that is gradually recovering due to conservation measures and efforts to combat climate change.

Qinghai Lake is located in Qinghai Province, between the counties of Ganzi, Gunhe, and Haiyang. Geographically, it is situated approximately between 36°33′ and 37°14′ North latitude and 99°37′ and 100°44′ East longitude. Its surface elevation ranges from 3,193 to 3,196 meters above sea level.

The size of the lake varies year by year, and estimates differ depending on the measurement method. The lake's area fluctuates between 4,165 and 4,597 square kilometers; one estimate for 2022 was approximately 4,572.7 square kilometers. Qinghai Lake has a length of 101 to 105 kilometers and a width of 63 to 76 kilometers.

The average depth is about 21 meters, with a maximum depth of approximately 25.5 meters. The water volume is estimated to be in the range of 71.6 to 105 billion cubic meters, depending on the period and dataset considered.

The lake basin covers an area of about 29,661 square kilometers and includes the counties of Ganzi, Tianzun, Gunhe, and Haiyang. This cold, semi-arid depression lies at the intersection of three natural zones: the eastern monsoon region, the arid northwest, and the high Tibetan Plateau.

Qinghai is an endorheic lake, meaning its water does not flow out. As a result, salts and minerals accumulate over time. The lake is replenished by direct precipitation and runoff from more than 50 intermittent rivers. The main tributary is the Buh River.

The water in the lake is alkaline and saline. According to a recent hydrochemical study, its pH is about 9.08, and the average mineralization is about 12,024 milligrams per liter. The predominant chemical components are sodium, magnesium, and chlorides.

The climate around the lake is harsh, typical of a high plateau. Average annual temperatures range from approximately minus 0.9 to plus 1.4 degrees Celsius, and annual precipitation varies from 260 to 572 millimeters depending on the location and observation period.

Winters are long, and the ice cover usually lasts four to five months. In summer, daytime temperatures on the shores can reach 15–25 degrees Celsius, making June, July, and August the most comfortable months for visiting.

Qinghai Lake serves as a clear indicator of climate fluctuations on the plateau. From 1958 to 2004, the water level decreased by approximately 0.08 meters per year. However, from 2004 to 2018, it increased by approximately 0.16 meters annually.

The earlier decline was attributed to drought conditions and high evaporation rates. Between 1959 and 2000, the lake received an average of about 357 millimeters of precipitation per year, while evaporation reached approximately 924 millimeters. Researchers believe that climate, rather than local water abstraction, is the main reason for the water level drop, as human water consumption accounted for only about 1% of losses through evaporation.

Since the mid-2000s, increased precipitation and reduced evaporation have contributed to the lake's recovery. According to one satellite observation study, the area of Qinghai Lake increased by an average of 2.89 square kilometers per year between 1986 and 2022.

The lake's wetlands are an important node for two migratory bird routes: the Central Asian-Indian and the East Asian-Australasian. The wetlands around Bird Island are particularly vital as they serve as nesting grounds for colonial waterfowl, including grey cranes, brown gulls, Pallid gulls, and pelicans.

The Qinghai Lake National Nature Reserve developed from the Bird Island Reserve, which was established in 1975 and upgraded its status in 1997. Today, it encompasses the lake itself and key habitats for the Przewalski's gazelle.

One of the most important species in the lake's ecosystem is the Przewalski's carp (Gymnocypris przewalskii), known locally as Huangyu. This fish is endemic to Qinghai Lake and migrates upstream in freshwater rivers for spawning from June to August every year.

Overfishing, diversion of tributaries, and loss of spawning grounds led to a sharp decline in the population. Available data show that fish stocks dropped from about 320,000 tons at the end of the 19th century to about 3,000 tons by the end of the 20th century. Thanks to fishing moratoriums, artificial breeding, juvenile release, and the construction of fish passage facilities, the population has significantly recovered. Recent reports indicate stocks of about 133,000 tons.

The Przewalski's gazelle is found only on the Qinghai-Tibetan Plateau and remains endangered despite population improvements. In the 1990s, its numbers around the lake fell to just over 300 individuals. Currently, the population exceeds 3,400 individuals.

The species continues to face threats related to limited suitable habitats, urban expansion, livestock grazing, and human-wildlife conflicts. Conservation plans are increasingly focusing on involving local communities alongside habitat protection.

Qinghai Lake holds sacred significance for Tibetan communities. Its surroundings include meadows, sand dunes, snow-capped mountains, monasteries, and settlements where traditional pastoralism continues.

The combination of natural and cultural landscapes makes this area one of the most recognizable parts of the northeastern Tibetan Plateau. Travelers often combine a trip to the lake with visits to Xining, Ta'er Monastery, Chaka Salt Lake, the western road around Qinghai Lake, and Jin'intan meadows.

July and August are considered the most picturesque months, when yellow rapeseed fields bloom along some stretches of the shoreline against the deep blue water of the lake. From June to August, visitors can enjoy relatively mild weather, green meadows, and blooming rapeseed.

The period from April to June is generally better for birdwatching, as migrating and breeding species are present in the lake. However, access conditions can change, and some parts of Bird Island are closed for nature conservation purposes.

The lake is also known for the 'Qinghai Lake Tour,' an international road cycling race usually held at the end of July. In winter, the frozen lake transforms into a harsh high-altitude landscape, although travel during this period is more difficult.

Xining, the capital of Qinghai Province, is a common starting point for trips to the lake. The most reliable time to visit is considered to be from late June to early September, when access conditions, vegetation, and weather are generally favorable.

Since the lake is located above 3,100 meters, tourists are advised to allow time for acclimatization, protect themselves from the sun, bring warm clothing even in summer, and avoid strenuous physical activity on the first day. Strong solar radiation, dry air, and rapidly changing weather require thorough preparation.

The beauty of Blue Lake depends on a fragile balance: the closed basin's water cycle, the migration of non-endemic fish, bird nesting sites, and the survival of one of the rarest mammals on the Tibetan Plateau.

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