Wildlife Wednesday: The Evolution of Rhinos

The Black rhino is my favourite animal and when you look at how they have evolved to become the incredible animal they are today, it’s truly amazing. Rhinos aren’t just a magnificent now but rather they have been their entire existence with them once being world rulers as they were once one of the largest land mammals to ever live.

Earth was inhabited with giant rhinos (Paraceratherium) that stood five meters tall at the shoulder, weighed up to twenty tonnes and had a skull that was over one meter long. With its enormous body and vast range, it illustrates how rhinos lived when they were at their peak and across their 50 million years existence, rhinos have migrated across continents, faced prehistoric hyenas and giant crocodiles, and endured the frigid wilderness of the ice age. But their story begins soon after the extinction of the dinosaurs, in roasting tropical heat.

Rhinos first emerged during a very warm period in Earth’s history, known as the Eocene, where during this time, what is now Asia, Europe and North America was covered in dense forest and this period began 55 million years ago and ended 34 million years ago. The Early rhinos that lived in the Eocene were quite different to today’s rhinos. However, rhinos belong to a group of animals called perissodactyls and no one is quite sure how they evolved except that they first appeared 55 million years ago in India.

During the Eocene period rhinos were called hyracodonts and at this time they barely looked like the rhinos that we know and love today, and instead they seemed to appear more like bulky little horses. It would be in the next period of Earth’s history, the Oligocene, that they would evolve into giants such as Paraceratherium. However, despite being so large, Paraceratherium was not safe from predators as they (and other prehistoric rhinos) were hunted by giant crocodiles and “dog-bears” called Hemicyon. Palaeontologist Pierre-Olivier Antoine of the University of Montpellier in France has found evidence of 10m-long crocodiles eating large rhinos.

“In Pakistan we found many, many specimens,” he says. “Bones of huge rhinos with the conical tooth prints of giant crocs.”

It’s not clear that the crocodiles would have been able to regularly prey on healthy adult rhinos. But they might have snatched young or ill prey when they ventured into water. There are no giant rhinos today and it’s not clear why they disappeared, but they may have been out-competed by a newly-evolved rival: elephants.

Elephants were “totally bad news,” says Mikael Fortelius of the University of Helsinki in Finland.

“They were just so much better at being super-large herbivores on land. They were more versatile and adaptable. The trunk is just such a marvel.”

If elephants thrived and hampered rhinos’ access to key food sources, that may well have spelled trouble for the giants, which needed to eat hundreds of kilos of vegetation every day. Whether rhinos were outcompeted by elephants is a whole other entity but from that point rhinos began to evolve further throughout various periods during Earth’s history. One of the most iconic of all rhinos has its roots in the Miocene period where a group called Elasmotherines. They evolved single horns on their heads, and as global temperatures continued to cool over the next few million years, they evolved into Elasmotherium who appeared around 2.5 million years ago at the beginning of the Pleistocene.

Elasmotherium was three meters tall (so much smaller than Paraceratherium) but they did have a very striking feature, their huge horn. It’s not clear exactly how large the horn was, and palaeontologists generally detest speculating about its exact length. Most, though, think it was enormous and it may have been more than 1m long. Throughout these different periods and evolutionary periods, the Earth had been gradually cooling and after millions of years of cooling, Earth plunged into a full-scale ice age and sheets of ice spread from the Arctic to cover much of Europe and North America. Faced with freezing temperatures, rhinos evolved thick woolly coats

It’s not clear if Elasmotherium was woolly, but plenty of other species were. The woolly rhinos may have had their origin in Tibet, before the ice age began. In 2011, a group of palaeontologists described the fossil of a primitive woolly rhino discovered in Tibet. That suggests woolly rhinos first evolved there, and then dispersed to the west when the Pleistocene ice ages began.

Unlike many prehistoric rhinos, woolly rhinos would be quite recognisable to us. They had a large front horn and second, smaller horn, plus stocky legs, and a bulky body. However, despite their thick coats, woolly rhinos could not have penetrated that deeply into the ice-covered regions. They could not cope with deep snow.

“It’s one of the things that may have contributed to their extinction,” says Schreve. “Because they’ve got such a stocky and compact body with relatively short legs, they’re not good at moving through deep snow, so they need relatively snow-free areas.”

Rather than plodding forlornly across ice sheets, then, woolly rhinos would have lived in an environment known as “mammoth steppe”. The climate was cold and dry, but there were plenty of herbs and shrubs for them to eat. Overall, the woolly rhinos had a harder time than their Eocene and Oligocene ancestors. According to Schreve, the Pleistocene is when life became truly difficult for many rhino species.

Towards the end of the Pleistocene the climate began fluctuating wildly. Temperatures rose and fell as much as 10 °C within a generation. For slow-breeding rhinos, dependent on stable food sources, these changes were disastrous. Predators were also a problem, as while Giant crocodiles didn’t threaten European rhinos a new predator came into the picture, prehistoric hyenas. Schreve has found evidence of hyenas eating baby rhinos. These dog-like carnivores would even have crunched the bones of their prey to get as much nutrition as possible.

“All of the bone is scored with tooth picks, scratches and punctures, so it was an important resource,” says Schreve. “And yes, they seem to be taking and consuming adult rhinos as well.”

If that wasn’t bad enough, woolly rhinos were probably being hunted by humans as well. Humans were probably the last straw, says Schreve.

“You can probably lay some of the blame for extinction at their door, but really they’re the final nail in the coffin,” she says. The woolly rhinos had already “gone through millennia of rapid climate change that they were poorly suited to withstand.”

The combination of unstable climates and human hunting put an end to many rhino species. Until this happened, they were very common in Europe, along with other huge animals like elephants and mammoths. Such animals are now confined to Asia and Africa, if they even exist at all. Today, all the diverse rhinos have been reduced to just five species. They have all been heavily hunted, and in recent decades poached for their horns, so none of them are in a good way.

Africa’s white rhinos are divided into subspecies, northern and southern. While the southern subspecies is in fairly good shape, the northern one has been driven past the point of no return. There are only five left alive, and only one male. He is under constant armed guard to protect him from poachers, and has even had his horn removed to deter them.

The other African species, the black rhinoceros, is critically endangered. There are thought to be seven or eight subspecies, of which three are already extinct and another is nearly gone.

The smallest species is the Sumatran rhino, which unlike the other surviving species is slightly woolly. It is also critically endangered. One subspecies is represented by just three captive individuals. As well as the threat from poachers, rhinos are also hindered by their need to give birth in secluded, shrub-covered areas. Such places are becoming harder to find.

Unlike other rhinos, Javan rhinos are sparing with their horns: only males have them. They are also critically endangered, being confined to a tiny area on the western tip of Java. There may be only 40 left.

It’s not all bad news, though. Indian rhinos are considered vulnerable, and while that’s not ideal it is far better than critically endangered. They survive in northern India and southern Nepal. A recent count suggested that the Nepalese population had grown by 21% in four years.

So, since rhinos first appeared 55 million years ago their population has been put through a lot and they are starting to disappear right in front of our eyes and in my eyes not enough is being done to save them. There is a lot of awareness about the ivory trade but little is spoken about the illegal trade in rhino horns.

If nations do not come together to stop the poachers who kill rhinos for their horns then I’m afraid that my children will only ever see a rhino in a picture and we will be talking about them in the same way we talk about woolly mammoths. As a distant memory but instead of saying there’s nothing we could have done to help them, we can only say that we didn’t try hard enough. There is still time to save some of the species and subspecies of rhinos such as black and Indian rhinos but unfortunately whatever happens now, the age of when rhinos ruled the world, is only something for the history books.

Love,

Savannah

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