When: Late Miocene (~ 11 - 6 Million years ago)
What: Shansitherium is a fossil relative of the giraffe. Giraffes are a commonly used example of an easy to see evolutionary transformation, the neck getting longer and longer, and here is some of the evidence used to show that hypothesis. Shansitherium lived in the late Miocene of China, and falls closer to the giraffe line than any other extant clade of artiodactyls. It possesses horns like that of the modern giraffe and okapi, which probably would have been covered with skin in life (these are called ossicones), but over all looks much more like a moose than a giraffe.
Today the Giraffidaehas only two living species, the giraffe (duh) and the okapi, and is only found in sub saharan-Africa. In the Miocene however this group was far more diverse, with Shansitherium just one example of the over a dozen species that roamed all over not just Africa, but Asia and Europe as well. The late Miocene was a time of cooling and drying climates in much of the world, and this is probably what lead to the reduction of species in this clade.
Reconstruction by Willem van der Merwe.
Reconstruction by Carl Buell.
When: Eocene (~48 million years old)
Where: India and Pakistan
What: Indohyus is a fossil artiodactyl that falls on the lineage leading to whales. The discovery of an almost complete specimen Indohyus helped to answer one of the long standing questions in the early evolution of whales. All living whales are carnivorous (with diets ranging from vertebrate prey to tiny invertebrates), however, all other living artiodactyls are predominately herbivorous. As all fossils assuredly related to whales showed both aquatic and carnivorous adaptations, it was a mystery as to which came first in the evolution of the cetaceans. Enter Indohyus. This fossil lacks any carnivorous adaptions in its dentition, but has several adaptations for spending time submerged - most notable are an ear region that looks a lot like that of previously known fossil whale ancestors and bones with increased density. These features would have allowed the animal to hear better underwater and to stay submerged easier, respectively. Isotopic analysis of its dentition and bones suggests that Indohyus spent a good amount of time in waters, but fed on land plants - much like the modern Hippopotomus. It has been suggested Indohyus fled to the water to avoid predators, like the modern African Mousedeer, which has been documented spending almost five minutes underwater to escape predation. Indohyus was about 3 feet (~1 meter) long from end to end, thus it would have had many potential predators in the early Eocene world.
Phylogenetic analysis place Indohyus at the base of what have traditionally been referred to as ‘archaeocetes’; a paraphyletic lineage of fossils more closely related to whales than to hippos. The term Cetaceamorpha is used for the group that includes all living whales and all fossils more closely related to them than to the hippos. Falling very near Indohyus is an animal called Diacodexis. I will highlight this animal more in a future entry, but to be brief it shows none of the aquatic adaptions of Indohyus, but has simular dentition. Thus, the current hypothesis of basal whale evolution is that small deer-like animals first went into the water, possibly for protection from predators, and then later became carnivorous.
When: Late Eocene (the formation is dated from 37 to 34 million years ago)
Where: Inner Mongolia, China
What:Andrewsarchus was named after Roy Chapman Andrews, a paleontologist from the American Museum of Natural History who led several expeditions to China and Mongolia in the early 1900s. It is a large mammal from the late Eocene of China. This is a very cagey introduction, you notice… why? We do not know nearly as much about Andrewsarchus as one might assume from the popular media. All that is known of this animal is a skull (which is fairly poorly preserved) and isolated teeth, there is not even a lower jaw! The skull is enormous, at 2 feet 9 inches (~83 cm) long and almost 2 feet (~56 cm) wide. Andrewsarchus has been reconstructed numerous times, and the vast majority of these reconstructions, besides inventing a body, even get the basic features of its head wrong. Andrewsarchus was not a ‘giant wolf like animal’ as has been depicted before; its eyes were very small and very low set on the skull, its snout ‘pinches in’ from the sides, and the brain-case was relatively very small, to name a few major differences. I have selected two of the better reconstructions to show above.
The problems I mentioned are just in reconstructing the head wrong… as for the body we have no firm idea what it looked like. It could have been a very robust form, or much more gracile than has been depicted. True, the head is massive but there are examples in the fossil record of animals with massive heads and relatively slender bodies. It could have had fully developed hooves and just 2 toes on each foot or it could have had less reduced feet. There is even a suggestion that it might have been an aquatic animal, rather than a terrestrial hunter.
Andrewsarchus is far from the only fossil species we have that is only a skull (or less!), and we can reconstruct the post-cranial anatomy of many of these other scrappy fossils with more confidence than we can Andrewsarchus. That is because the taxonomic position of Andrewsarchus is so uncertain. It was at first grouped with the Mesonychia, an extinct group of uncertain affinity, but with well known anatomy. However, almost from the very start it was removed and placed as an aberrant mesonychid and the latest phylogenetic analysis place it far removed from all mesonychids, within the order Artiodactyla (the even toed ungulates - cows, pigs, hippos, and whales!). Entelodonts fell as the closet relatives of Andrewsarchus but this position is unstable, and it is possible Andrewsarchus is more closely related to whales within Artiodactyla.
This is one fossil I would absolutely love to find a complete skeleton of one day. It is a very intriguing animal, and is fairly well known to the public, but we truly know almost nothing about it!
Megaloceros - The Irish Elk or Giant Deer
When: Mid Pleistocene to Early Holocene (400,000 to 8,000 years ago)
Where: Throughout Eurasia, ranging from the British Isles to China.
What: Megaloceros had the largest antlers of any known deer. It ranged all over Eurasia, with a vast quantity of fossils known from Irish peat bogs, giving it the common name of ‘The Irish Elk’. As Megaloceros is not an elk, but rather a ‘true deer’ in the clade Cervini, the name ‘Giant Deer’ is sometimes used instead, by people who really care about that sort of thing. Megaloceros stood roughly 7 feet (~2 meters) tall at the shoulder, with antlers up to 12 feet (3.6 m) wide from tip to tip.
These large antlers have received a lot of attention, for obvious reasons. They are thought to be only for display, as their orientations and placement upon the skull are far from ideal for use in fights between males for mates. The size of the antlers has been suggested to be the reason for the extinction of this deer in several different hypotheses, but none of them have stood up to strong scrutiny. Megaloceras is one of many fossil animals for which we have no clear explanation for its extinction.