Pachycrocuta - The Giant Hyena
Mounted specimen from the Zhoukoudian Museum, Beijing.
Reconstruction by Mauricio Antón
When: Pliocene to Pleistocene (~ 5 million to .5 million years ago)
Where: Europe, Asia, and Africa
What:Pachycrocutais a prehistoric member of the Hyaenidae. Today hyenas are restricted to Africa and western Asia, but their fossil record has revealed they were once much more wide spread. Pachycrocuta has been found in Africa and Asia, but most specimens have been found in Europe, with many localities in the Iberian Peninsula. The largest species was Pachycrocuta brevirostris, which stood over 3 and a half feet (~100 cm) at the shoulder and is estimated to have weighed over 400 lbs (190 kg). This makes it about the size of a modern lioness! Cave deposits in both Spain and China have revealed multiple almost complete skeletons, suggesting that these animals lived in packs and utilized these caves as their dens.
As Pachycrocuta is even more heavyset and adapted for bone crunching than the living bone-crunching hyenas, it has been suggested that this fossil form was even more dependent on scavenging kills than living species. But there really is not much evidence to pack this up other than thought-experiments. As it appears that some large cat species were displaced when Pachycrocuta moved into their ranges, it is more likely it was a direct hunter that would take advantage of pre-killed remains when it could drive away other predators. Like 99% of carnivores today. The predator/scavenger divide is really not a fast or hard line at all. Even more evidence of hunting comes from the remains of interactions between Pachycrocuta and Homo errectus. These two species overlapped and bones of our poor relative have been found in Pachycrocuta dens in China!
When: Cretaceous (~100 million years ago)
What: Melittosphex is a fossil bee. It is the oldest bee fossil ever found, and this tiny tiny (only 3 millimeters long!) specimen, beautifully preserved in amber, can tell us much about the evolution of this amazing group of social insects. The closest relatives to living bees are the wasps, and some wasps are more closely related to bees than they are to other groups of wasps. The crabronid wasps (the digger-wasps) are the wasps most closely related to bees. These wasps are solitary and while the adults feed on nectar, the young larva feed on a spider or insect that mom-wasp procures for them.
Melittosphex is assuredly more closely related to bees than any wasp, with a great deal of anatomical features found only in bees today, such as the morphology of its hindlimbs and the presence of intricately branching hairs on body. Melittosphex also has features reminiscent of its wasp ancestry that are not seen in any living bee species today; specific spurs on its middle pair of legs and a very slender rear most ‘foot’. This combination of features shows that Melittosphex is an excellent example of a transitional fossil, falling between the crabronid wasps and all living species of bees.
Knowledge of Melittosphex and its kin is critically important for determining how the solitary carnivorous (as larva) wasps gave rise to the eusocial herbivorous bees. But that is not all! These ancient bees also help inform us to how the modern plant biota was established. Today’s flora is dominated by angiosperms - the flowering plants, but this is a relatively recent state of things. The earliest known fossils of angiosperms date to only the Jurassic period, and it is not until the early Cretaceous that body fossils are known. It is at about 100 million years ago that the great angiosperm radiation can be seen, and shortly after this the flowering plants begin to dominate. The one specimen of Melittosphex known preserves minute pollen grains between the branching hairs on its body, showing that even 100 million years ago bees were involved in pollination of these flowing plants. It has long been thought that bees and angiosperms evolved in tandem, that each group depends on the other for its success, and little Melittosphex offers more support for this view.
Reconstruction by Nobu Tamura
When: Cretaceous (~122 million years ago)
What: Shanweiniao is a mesozoic bird. It retains many features that are not found in modern birds, including a toothy beak. It was capable of powered flight, and its tail was used to help it fly. This is seen in modern birds, but it is unknown exactly when the bird lineage developed this trait. It is clear that it was present in Shanweiniao as four flight feathers were preserved on the slab, giving the fossil bird its name. Shanweiniao means fan-tailed bird in chinese.
Shanweiniao falls after the spilt of the bird lineage from the rest of theropods, but it is still very far removed from the living avians. The first birds are called enantiornithes. All of these birds were capable of powered flight to some extent, but retained toothed beaks and claws on their wings. It is debated if the enantiornithes are a monophyletic group that has left no descendants, or if this ‘group’ is instead paraphyletic with some members more closely related to living birds than others.
Indricotherium - The largest terrestrial mammal
Skull on display at the American Museum of History of Natural History, New York City
Reconstruction was part of the traveling Extreme Mammals exhibit, photo from when it was at the AMNH.
When: Eocene and Oligocene (~ 34 to 23 million years ago)
Where: Asia and Eastern Europe
What: Indricotherium is the largest terrestrial mammal known. It is a member of the rhinoceros family. Some material was found earlier in the 20th century, but the first fairly complete skull and skeletal elements were found by Roy Chapman Andrews in 1922 while on an expedition for the American Museum of Natural History in Mongolia. Indricotherium would have stood about 16.5 feet (~5 meters) tall at the shoulder and is estimated to have weighed in excess of 20 tons. There were sauropod dinosaurs that were smaller than Indricotherium! This giant was a herbivore and filled a simular niche to the sauropods and modern giraffes, so much so that it is sometimes referred to as the ‘giraffe rhinoceros’. It stripped tall trees bare of leaves using its large front teeth and mobile lips.
In the family tree of mammals Indricotherium is in the order Perrisodactyla (horses, rhinos, and tapirs). Within this group it in the rhinoceros clade. While rhinos today all look pretty much the same their fossil record shows this group used to be extremely diverse, with two completely extinct major sub groupings. Indricotherium is in the group Hyracodontidae (the running rhinos). This lineage divered from that leading to modern rhinos over 55 million years ago. Not all rhinos in this group were giant sized, the very first ones were no larger than wolves! All members of this group lacked horns like Indricotherium.
There is a bit of controversy and confusion surrounding the topic of what genus name to apply to this animal. Indricotherium has been proposed by some workers to be synonymous with Paraceratherium and Baluchitherium, but this is not universally accepted. I have used the name Indricotherium for this entry as both examples shown above are based upon material that has held the name Indricotherium.
Art by Mark Klingler
When: Middle Jurassic (~164 million years ago)
What: Castorocauda is an aquatic mesozoic mammal. It is known from a very well preserved slab specimen, which shows a suite of features indicating an adaptation to aquatic life. Its limbs were powerful, and easily capable of strong swimming or digging. Its tail was flattened, shown both by the soft tissues preserved on the slab, but also by its flattened caudal vertebrae, which are very simular to that of living swimming mammals, such as the beaver, otter, or platypus. This tail is what gives this Jurassic animal its name: Castorocauda translates to ‘beaver tail’. Its teeth were also specalized for aquatic life; they have primary cusps which curve backwards, which is seen in fish eating animals today, such as the seals. Castorocauda was about 17 inches (~43 cm) long, making it one of the larget Jurassic mammals.
Castorocauda would have looked somewhat like a platypus lacking a bill, but its diet was more like that of a seal. In the mammal family tree Castorocauda is far far removed from any living taxa. It is a member of a group called the Docodonta, just a few branches removed from one of the first Mammaliforms: Morganucodon. As Castorocauda clearly had fur in life, this puts fur extremely far down on the mammalian lineage. It has been hypothesized previously that even more basal taxa had fur, but there has been no conclusive evidence. As Castorocauda was completely coated in fur, except for much of its tail, it is extremely likely fur originated much deeper in the mammalian lineage, possibly in the non-mammalian synapsids.
The discovery of Castorocauda also shows that mesozoic mammals were much more ecologically diverse than has been previously proposed. Our ancient kin were not only small rat like insectivorous creatures that ran in the shadows of the dinosaurs; they swam, preyed upon dinosaurs themselves, and even flew (more on that one later)!
Mounted specimen on display at the America Museum of Natural History, NYC
Reconstruction by Charles Knight.
When: Miocene to Pliocene (~12 - 3.5 million years ago)
Where: North America, Europe, Asia, and Africa
What: Gomphotherium is a four tusked extinct proboscidean. Unlike modern elephants which only have enlarged upper incisors as their tusks, Gomphotherium and its kin had enlarged upper and lower incisors. Neither set of tusks grew as large as living elephants, but the lower jaw was heavily modified and elongated to support the lower tusks. If you look at the photograph of the mounted specimen above, you can see that the actual bone of the mandible extends to almost the tip of the upper tusk. Based on the structure of the skull of Gomphotheriumit is thought the animal had a trunk, though again not one as log as the living species of elephants. Gomphotheriumis on the small side compared to the mammoth and mastodon in the photo with it, and also is a bit smaller than the living african elephant, but about the same size as the asian elephant - standing about 10 ft (3.2 meters) tall at the shoulder. These fourtuskers were proportioned very differently from the asian elephant, however. Their legs were much shorter in proportion to their body. The genus Gomphotheriumoriginated in North America, but spread throughout most of the world before going extinct in the Pliocene.
Gomphotheriumin the group Gomphotheriidae (shocking I know). Gomphotheres ranged almost world-wide for over ten million years, and it is possible the last one died less than 10,000 years ago. I say only possible as relationships of gomphotheres, and really proboscideans as a whole, are really not well understood. Gomphotheriidae may be a paraphyletic series of taxa (not a ‘real’ group), with some taxa more closely related to the living species than others. Basically if you are interested in paleontology the study of proboscideans is an area that desperately needs more people in it. You also get to look at other cool extinct forms like Deinotherium!
Mounted skeletons from the Melbourne Museum of Natural History
Reconstruction on display at the Carnegie Museum of Natural History
When: Early Cretaceous (~130 to 100 million years ago)
What: Psittacosaurus is a ceratopsian. Yes, a ceratopsian like Tricerotops or Styracosaurus, even though it has no horns or even a neck frill. You have to start somewhere! Psittacosaurus is an extremely basal ceratopsian, with some studies finding this animal in the first group to branch off from the clade. Italso was most likely bipedal (quick remake all the reconstructions!), as its forelimbs were much shorter than its hind-limbs, and it possibly could not even rotate its hands enough to put its palms flat towards the ground. This isn’t really surprising, as despite the large number of quadrupedal dinosaurs, the last common ancestor of all dinosaurs has been reconstructed to be bipedal. Psittacosaurus was a plant eater, but it did not have the grinding cheek teeth of later ceratopsians, so it swallowed stones to help it grind its food. It is also possible that it fed on nuts, as its beak has been reconstructed to function very well as a nut-cracker.
There are hundreds upon hundreds of fossil specimens known for Psittacosaurus, making it one of the most well understood of all dinosaurs. There are over 10 species known, with the best known Psittacosaurus mongoliensis, reaching about 6.5 feet (~2 meters) long at its extreme maximum. This includes an amazing slab specimen that was preserved in soft mud that shows this little ceratopsian had bristles on the top of its tail. It is thought these were used for communication between individuals, and it is debated if these are homologous (same evolutionary origin)to the feathers of theropod dinosaurs or not. There is almost a full ontogenetic (growth) series of specimens, with oodles and oodles of hatchings to subadults. The close association of many hatchlings and adults shows that these ceratopsians, like many dinosaurs, had a good amount of parental care of the young dinosaurs.
One benefit of so many specimens is that destructive sampling can be used - this is where the original specimen is damaged, or even destroyed, to provide some information about the animal. Cutting long bones and examining the resulting cross-sections has lead to the determination that Psittacosaurus lived to about 10 to 11 years old.
Remember Repenomamus from a couple of days ago? The juvenile dinosaur found inside was a Psittacosaurus.
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.
Repenomamus - the mammal that ate dinosaurs
When: Cretaceous (~138-129 million years ago)
What: Repenomamus is the largest known genus of mesozoic mammal. Two species are known, R. robustus and R. giganticus. Repenomamus robustus was about the size of a living North American Opossum, and R. giganticus was about 50% as big as this, coming in at about 3 feet (~1 meter) long. This is not very big by today’s standards, but as most mesozoic mammals were rat sized or smaller, this was very large indeed for its time! Repenomamus falls within the group Triconodonta, an extinct clade of mammals that falls between the monotremes and the therians (placentals + marsupials). Their name comes from the three cusps, typically in a row, found on their upper and lower cheek teeth. Fossils of triconodonts are found from the late Triassic to the end of the Cretaceous. Though the end Cretaceous extinction is commonly thought of as the extinction of non-avian dinosaurs, some mammal groups were lost here as well, or at least their numbers drastically redued.
Speaking of dinosaurs, the skeleton of Repenomamus robustus was found with bones belonging to a juvenile Psittacosaurus (a ceratopsian) clearly inside its ribs. Proof that this mammal snacked on some baby dinos! The diet of the larget mesozoic mammals has long been controversial, but here is undeniable evidence that at least some of these taxa were carnivorous and ate other vertebrates. On a more personal note, this specimen was described by Yaoming Hu, who tragically died from cancer at a relatively young age, just three years after publishing the specimen.
Mounted specimen on display at the American Museum of Natural History, NYC. I could find no reconstruction I liked so have a picture of Barnum Brown next to the specimen for scale.
When: Miocene and Pliocene ( ~11 to 3 million years ago)
Where: India, Pakistan, and Indonesia
What: Colossochelys is a very large land turtle. It mostly roamed in what is now India, but fossils have been found in Pakistan and parts of Indonesia as well. It reached almost 9 feet (~3 meters) long with an estimated weight of about 1 ton. For comparasen the living Galapagos tortoise is about 6 feet (~2 meters) long, and weighs 880 lb (~400kg). Colossochelys is the largest land turtle ever known, but larger turtles swam though the prehistoric seas, such as Archelon. It is thought that this extinct turtle lived much the same way as giant turtles today do, eating plants and drawing into its shell for protection from predators. They vanish from the fossil record at the dawning of the modern Ice House climate, about 2-3 or so million years ago.
This giant turtle has been known by other names in the scientific literature, and some museum displays have not been updated. So do not get confused! It has been labeled both Geochelone atlas and Testudo atlas in the past. Why the change? Turtle systematics have been in a state of confusion for a while, and both of these genera were found to be massively polyphyletic. This means that they were essentially random groupings of taxa that did not share a close relationship to one another to the exclusion of all other turtles. Colossochelys altas is not at risk for a name change again (due to this reason at least!) as it is the only member of this genus.
Also man, isn’t that just the happiest looking fossil you have ever seen?