To celebrate ‘World Rhino Day’ here is an evolutionary history of these iconic giants.
The day before yesterday was an important day. The 22nd of September is famous not only for being Bilbo Baggins’ birthday and the day the ‘West Wing’ debuted but it is of course World Rhino Day.
World Rhino Day has been running for the past six years and has become quite a big deal. #worldrhinoday is trended on instagram and twitter and Prince William himself even gave a passionate speech to mark the occasion. One of the main aims of World Rhino day is to abolish the myth that rhino horn has medicinal properties. It is actually made of keratin which also makes up hair and nails. This myth results in the poaching and slaughter of 1,000 rhinos each year, which translates to around three per day. With three of the five extant rhino species being critically endangered and a 90% decline of the global rhino population since the beginning of the 20th century, it’s clear that this incredible group of species is in trouble.
To celebrate ‘World Rhino Day’ and to spread the word about these remarkable animals here is an evolutionary history of the rhinoceros.
– 50 million years ago
In the past 50 million years there have been about 30 genera and over 60 species of rhino. They have come in different forms, many dictated by the climate at the time. Rhinos are part of the Perissodactyla, also known as the odd-toed ungulates. Their living relatives are horses, zebras and tapirs. About 50 million years ago, at the start of the Eocene, the rhino lineage split off from the rest of the Perissodactyls and became their own group of species.
– 30 million years ago
Rhinos split into a number of diverse groups and filled many different niches. It was during the Oligocene that one of the most famous (at least to paleontologists) rhino species existed, Paraceratherium. This gigantic, hornless rhino weighed up to 15 tonnes, was five meters high at the shoulder and claims the title for the largest land mammal that ever existed.
There are some superficial similarities (convergent evolution) between Paraceratherium and Giraffes and Elephants. All of these species use their size elongated structures (necks or trunks) to get at the leaves at the tops of trees that are unattainable for most browsers. It is not known exactly why Paraceratherium became so large. It may relate to a shift from forest to grassland during the Oligocene, and so these animals would have had to travel further to find trees.
– 15 million years ago
During the Miocene the planet cooled gradually. Rhinos continued to diversify and became abundant in terms of species and numbers. Paleontologists in southern France excavated a pond that dated back to this period and contained over 100 individuals from nine different species of rhinos. Rhinos came in many different shapes and sizes and were found all over the globe. One bizarre example of a Miocene rhino is Diceratherium. It had two horns, but unlike the white and black rhinos of today who have a front and back horn, Diceratherium had side-by-side horns, a left and a right.
– 2.5 million up to 11,000 years ago
During the Pleoistocene the world experienced a series of ice ages where glaciers spread down from the Arctic to much of Europe, Asia and North America. This didn’t wipe out the rhinos as they adapted to the colder temperatures. Woolly rhinoceroses (e.g. Coelodonta antiquitatis) with their thick coats roamed much of the Northern Hemisphere during this time. These incredible beasts would have shared the landscape with our early ancestors who made the incredible journey out of Africa. It has even been suggested that hunting pressures from humans lead to their extinction.
There are only five species of rhino that are alive today: white, black, indian, sumatran and javan. Three of the five (black, sumatran and javan) are critically endangered. The javan rhinoceros is considered one of the rarest animals on the planet with only about 60 surviving in the wild. Many rhino subspecies have become extinct in recent years and some subspecies only exist in captivity. There are only three individuals left of the northern white rhino subspecies.
Rhinos are fascinating animals. They are keystone species involved in many important ecological processes. The white rhino plays a vital role in grazing facilitation in savannah grasslands.
The past 50 million years of rhino evolution is a fascinating story. But sadly, if the current poaching crisis cannot be resolved then the rhino timeline is about to come to an end.
Feature Image: www.jamesorrphoto.com