Many blogs seem to have their own little Friday gimmick, so being that I plan on sticking around, I thought I would feature a different critter, extinct or extant, every Friday to share some of neat animals I love so much. Other than being the 1st installment, this entry is special because in the continuing evolution/ID debate hannodb suggested that there was never an ancestral rhino without a horn, but this is untrue. Perhaps the biggest terrestrial mammal to ever live, Paraceratherium orgosensis (aka Indricotherium) was an Oligocene (34-23 million years ago) perissodactyl (it had an uneven toe count, like rhinos). *Note, I'm sorry for all the parentheses, I just don't want to assume everyone knows what I'm talking about* These massive animals stood up to 15 feet at the shoulder with a total height of approximately 23 feet, making them the biggest things to live in what it now China. Although this group seems to be entirely extinct and did not lead to the extant lineages of rhinos around the world, they lacked horns juat like their ancestors, which in turn are the ancestors to the horned rhinos living today. To understand where Paraceratherium fits in, we need to go back a bit further in time.
Ancestral rhinoceros appear during the Eocene (55-39 million years ago) in North American and Europe, although these early perissodactyls could not as yet be classified as rhinos. During the Oligocene, however, two groups called the Caenopenes and Acerantheres appeared in North America, but they (like their ancestors) lacked horns and used large incisor teeth as their primary defensive weapon. Hyracodonts were another hornless rhinoceros group, known as the "running rhinos" for their long legs, existing approximately 30 million years ago during the Oligocene. As you can already tell, there is strong evidence for rhinos developing horns over time given the lack of taxa with any horns at all, and the black and white rhinoceros (both found in Africa) are the remaining representatives of a group of rhinos that evolved in Asia about 15 Million years ago during the Miocene, not long after the group of more primitive one-horned rhinos appeared that still have representatives today. I wish I could have more (and better) information here for you, but despite the overwhelming abundance of rhinos in the fossil record no one seems particularly interested in them, making the information hard to track down.
In any case, Paraceratherium was derived from Hyracodonts, opting for large size rather than developing a new kind of defensive weaponry. In the front of its mouth were two sets of large incisors, helping the creature to browse among treetops and higher vegetation almost like modern giraffes. To get a good idea of exactly how huge this creature was, check out this picture someone fortunately snapped, as I have been as yet unable to find other suitable reconstructions on the web to refer you to.
As huge and interesting as this animal is, apparently prehistoric rhinos aren't as "sexy" as other bizarre prehistoric beasts and don't get much attention. Although there have been varying forms, ranging from swift runner to near-hippos, many extinct rhinos seem rather plain next to mammoths or saber-toothed cats, and today are an example of a once prolific kind of animal bottlenecking down to just a handful of forms, outcompeted by the more modern artiodactyls (even-toed ungulates).
I think you're correct. Next to saber tooth tigers, rhinoserouses look pretty tame to me. But then, I'm just a fan of big cats. (I know the tiger in The Jungle Book is supposed to be the "bad guy", but he's really awesome too... lol.) Interesting post though, you almost make me wish I'd taken a biology course this year.
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~I know you believe you understand what you think I said, but I am not sure you realize that what you heard is not what I meant.~
It's true, even though rhinos are pretty neat, I never looked at them too closely other than how to tell a white rhino from a black rhino (it's all about the lips). I did see a hairy Sumatran rhino during my first trip to the Bronx zoo, which, of course, shot projectile urine at me for taking its picture. I'm a big fan of cats too (which is why I have two of my own), and I'm glad you found the post interesting. Why take a credit course when you can learn neat things from me for free (AND without tests *nudge,nudge*)?
"The trouble with having an open mind is people insist on coming along and putting things in it"-Terry Pratchett
Aren't rhino's without horns, just hippos?
Just kidding, just kidding.
But on a serious note, how do they know that one set of bones is an offshoot of another? DNA tests? I assume its more complex than that.
Actually a lot of the hornless rhinos did look like hippos, but hippos are artidactyls (meaning they have an even number of toes) and are more derived than rhinos which are perissodactyls (they have an odd number of toes and the lineage is older). The problem with DNA is that is begins to degrade at death, so even if you find intact genetic information from a preserved wooly rhino (which have been found, much like mammoths in Siberia) it's not really an accurate picture of the creature's genome. I have to research this further to find out exactly how it degrades, being genetics is not my strong suit.
Anyway, cladistics and systematics helps, which is where you look at where and when something lived and look at all the characteristics that make it different from other animals (some big, some small) which help organize it into a taxonomic classification. For instance, rhinos have mammalian characteristics, so they are mammals. They didn't lay eggs and were not marsupials (there are skeletal characteristics that correspond to these reproductive methods) so they are placentals. Among placentals they have odd-toed feet (+ other features) that group them with perissodactyls, and then there are different characteristics that seperate groups of rhino from one another. All the early rhinos were hornless, and then one horn developed and then two horns developed in Asia (while many other groups still had one horn) and the fossil record is good enough that we can tell that the black and white rhinos evolved from the two-horned group while others are more closely related to other groups. There's a lot you can tell from skeletons, but (as always) the devil is in the details and such details are not accessible to the layperson without some training and familiarity with skeletal anatomy first, especially in the skull and teeth. There are still some holes in the record, but if you line up the different fossils chronologically and according to location you can see the changes that took place and what groups are related to others based upon the skeletal characteristics inherited from their ancestors.
Another interesting note; rhino horns don't usually fossilize because they were made of compacted hair, not bone, but we can tell they had horns because of scars on their skulls where the horns were attached.
"The trouble with having an open mind is people insist on coming along and putting things in it"-Terry Pratchett