LIFE SCIENCE

Revelation! The largest terrestrial mammals in history weighed


The giant rhinoceros, the largest terrestrial mammal in history, lived in Eurasia about 40 to 22 million years ago. Their size grew extremely rapidly, leaving an important evolutionary mystery.

Recently, the scientific research team of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences (hereinafter referred to as the Institute of Paleovertebrates) reported the Junggar giant rhinoceros found in the Qingshuiying Formation of the Early Oligocene in Lingwu City, Ningxia Hui Autonomous Region, and estimated the weight of most of the giant rhinos, including them. The results were published online in the international journal Historical Biology.

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Lingwu giant rhinoceros skeleton Courtesy of the ancient spine

The Lingwu region is rich in fossil diversity, and the giant rhinoceros is a typical representative of it. In the past, scientists have estimated the weight of giant rhinos in a variety of ways at 15 to 20 tons. In this study, the researchers used the limb bones of a variety of living mammals as training data, and the teeth of those without suitable limb bones were supplemented, and the weight of 16 giant rhinos was calculated. Of these, the original Salamulun giant rhino weighed about 1.5 tons, while the progressive Dzungar giant rhino weighed more than 20 tons.

Deng Tao, corresponding author of the paper and director of the Institute of Ancient Spine, introduced that according to the rate of weight gain, the study divided the body size evolution of giant rhinos into three stages.

The ancestral stage is the evolution from the ancestral rhinoceros to the first giant rhinoceros. After the climate-appropriate period of the Early Eocene, global temperatures continued to decline. Affected by this, the living environment of the giant rhinoceros in the early stages became relatively open and arid. During this period, the weight gain of the giant rhino did not exceed the maximum growth rate of the rhinoceros superfamily. But at this rate of growth, the Salamulund giant rhinoceros, which lived from the late Meseocene to the early Late Eocene (42 to 38 million years ago), became one of the largest terrestrial mammals of its time.

The second stage is the evolution of the Eiden macrosnacillus from the Late Ephemerocene to the Late Eocene. It was also the period of rapid weight growth in the evolutionary history of the giant rhinoceros, far exceeding the growth rate of any branch of the rhinoceros superfamily. The middle Erden rhino weighs about 5 tons and is one of the largest animals living in the same environment. In the Paleogenous Period, there was an arid zone in the central and western Parts of China at latitudes of 30° to 50°, and the climate was similar to that of today’s savanna, and the giant rhino was able to migrate long distances in such an environment.

The third stage is the period of differentiation of progressive giant rhinos in the Oligocene, and most of the giant rhinos found so far are the products of this stage. After another violent turning event at the turn of the Eocene and Oligocene, the Genus Erdenosaurus became extinct, with the emergence of larger rhinos, such as the genus Rhinoceros and the Dzungar rhinoceros. At this stage, the rate of weight gain of giant rhinos is usually between the first two stages. Lingwu’s giant rhinoceros fossils are found in a set of light gray-green sandy mudstones that contain a gypsum layer more than 5 centimeters thick. Some fossil bones are also filled with plaster, reflecting the relatively arid environment at the time. At this time, there was a scene of several giant rhinos coexisting. Because of their size, these rhinos may not be able to adapt to the forest environment, so they have not reached Western Europe, which is warmer and wetter than in East Asia.

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The relationship between the evolution of the body type of the giant rhinoceros and the climatic environment Provided by the ancient spine

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Weight evolution of rhinoceros superfamily Provided by the paleovertebrae

In addition to the giant rhinoceros, the research team also selected a variety of rhino superfamily taxa as a comparison and background, and found that many branches showed a trend of body size growth, and the growth rate of the giant rhino was much greater than that of other branches. From the late Oligocene to the early Miocene, after the extinction of the giant rhinoceros, the plate-toothed rhinoceros taxa and the euphalogena rhinoceros taxa began to evolve in an enlarged direction. The plate-toothed rhinoceros feeds on a growing herb. Perhaps due to the lack of a long neck and the inability to feed on the leaves of tall trees, the researchers explain, the weight growth rate and upper limit of the plate-toothed rhinoceros is much lower than that of the giant rhinoceros. (Source: China Science Daily, Hu Minqi, Teng Wenyu)

Related paper information:https://doi.org/10.1080/08912963.2022.2095908



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