Small beginnings are common for very big things. That was certainly the case for brontotheres, massive herbivorous mammals resembling rhinos that roamed North America and Asia during the Eocene era. Researchers recently discovered that while the majority of Brontotheres species evolved to become nearly as large as elephants relatively quickly as a result of smaller species being outcompeted into extinction, Brontotheres started out as animals the size of dogs.
In point of fact, brontotheres probably hadn’t reached their maximum size yet. They could have delivered species that were considerably more gigantic, had they not all become wiped out because of ecological changes, researchers announced Thursday in the diary Science.
Brontotheres are family members of present day rhinos, ponies and ungulates. Most brontothere species weighed north of 2,200 pounds (1,000 kilograms), and the greatest lived in the South Dakota Barren wasteland, estimating around 8 feet (2.4 meters) tall and 16 feet (4.9 meters) long, with monster Y-formed horns on their noses, as per the Public Park Administration.
According to the park service, Lakota oral histories about violent thunderstorms accompanied by giants served as inspiration for the name Brontotherium, which means “thunder beast” and was first used in the 19th century by paleontologist Othniel Charles Marsh.
About 53 million years ago, the first brontotheres that are known to have existed; According to the scientists, they weighed about 40 pounds (18 kilograms) and were hornless and about the size of a coyote. That unassuming size was typical for vertebrates at that point. Mammals that lived in the shadow of dinosaurs in the Mesozoic era (252 million to 66 million years ago) were typically no larger than badgers. The mass extinction of 75% of Earth’s life caused by an asteroid impact brought an end to the reign of the dinosaurs. The mammals that survived the calamity were typically the size of rats.
However, this would soon alter. Mammals began to occupy those ecological niches after the large dinosaurs vanished, and brontotheres were particularly adept at rapidly evolving into enormous creatures. Only 16 million years after the first brontotheres showed up, “the last individuals from this gathering were multi-ton behemoths with extreme hard bulges over the head,” lead concentrate on creator Oscar Sanisidro said in an email.
“Makes this gathering considerably really fascinating that it is the main in mammalian history to be reliably large,” said Sanisidro, who directed the exploration while at the College of Alcalá in Spain and is currently a postdoctoral scientist at the College of Valencia.
The evolutionary phenomenon known as “Cope’s Rule,” named after the 19th-century paleontologist Edward Drinker Cope, can be seen in the fossil record of other extinct animal groups, which also steadily increased in size over time. Numerous early researchers contended that brontotheres obtained greater because of “an internal engine pushing development towards achieving the biggest and most specific structures,” said Pasquale Raia, a scientist and a teacher at the College of Naples Federico II in Italy. All in all: Regardless of environmental factors, evolution toward large size is inevitable if animals are given enough time.
According to Raia, who was not involved in the research, other scientists later proposed that size increases were instead shaped as species adapted to environmental pressures like food availability, competition for resources, and the presence of predators. However, these scientists struggled to define what might lead to rapid and extreme growth.
The authors looked at evidence from the group’s extensive fossil record, which covers the majority of its evolutionary history, in order to investigate the evolution of brontothere size. In addition, computer models were developed by the researchers to keep track of specifics regarding the evolution of genetic traits in brontothere species. The scientists could then figure out how these changes might be linked to increases in body size through phylogenetic analysis, which examines the evolutionary pathways by which new species take shape.
Patterns of species extinction provided an important clue. Their findings demonstrated that in brontotheres, body size changed in both directions, with new species becoming smaller or larger on occasion. However, smaller species were more likely to die out than their larger counterparts, and a pattern began to emerge in which larger species lasted longer than smaller ones.
Sanisidro stated, “By the late Eocene, all the remaining species were giants.” This example indicated that megaherbivory — turning out to be enormous herbivores — benefited brontotheres; According to the authors, it’s possible that smaller brontothere species were more susceptible to carnivore predation and competition from other plant-eating species.
Sanisidro stated, “We can, for the first time, explain brontothere size evolution from an evolutionary perspective and propose a “pathway” to reach megaherbivory that must be tested in other mammalian groups.”
“A fresh new look to an old and incredibly attractive question:” the study offers Raia stated in an email that it “makes an exceptional move” toward identifying the external conditions that drove brontotheres to be huge and what drives the evolution of body size.
However, as the humid greenhouse conditions of the Eocene began to recede, these titans of herbivory lost their advantage in terms of survival. The thunder beasts eventually perished as previously lush ecosystems became less favorable to them as the climate became increasingly dry.
The scientists stated that additional modeling of ecological factors, such as the rate at which ancient climate shifts affected the abundance of edible vegetation, “would clarify how environmental change led to the brontotheres’ demise.” Sanisidro stated, “By the late Eocene, all the remaining species were giants.” This pattern suggested that brontotheres benefited from megaherbivory, or becoming large herbivores; According to the authors, it’s possible that smaller brontothere species were more susceptible to carnivore predation and competition from other plant-eating species.
Sanisidro stated, “We can, for the first time, explain brontothere size evolution from an evolutionary perspective and propose a “pathway” to reach megaherbivory that must be tested in other mammalian groups.”
“A fresh new look to an old and incredibly attractive question:” the study offers Raia stated in an email that it “makes an exceptional move” toward identifying the external conditions that drove brontotheres to be huge and what drives the evolution of body size.
However, as the humid greenhouse conditions of the Eocene began to recede, these titans of herbivory lost their advantage in terms of survival. The thunder beasts eventually perished as previously lush ecosystems became less favorable to them as the climate became increasingly dry.
The scientists stated that additional modeling of ecological factors, such as the rate at which ancient climate shifts affected the abundance of edible vegetation, “would clarify how environmental change led to the brontotheres’ demise.”
