Mounted specimen from American Museum of Natural History, and currently part of the traveling Extreme Mammals exhibit.
Reconstruction by Charles Knight
When: Eocene (~49 to 39 million years ago)
Where: North America
What: Uintatherium is one of the first large mammalian herbivores. It stood about 6 feet (~1.8 meters) high at the shoulder and was roughly 13 feet (~4 meters) long. This isn’t that large for an animal today, but in the Eocene it was a giant! It lived in the lush sub-tropical forests of mid-Eocene North America, most likely eating a combination of terrestrial bushes and shrubs along with aquatic plants from lakes and marshes. Uintatherium has a nasty pair of upper canines, not what you would expect from a herbivore! It is thought that these teeth were involved in sexual display, as they appear to be much larger in males than females. Uintatherium vanishes from the fossil record in the late Eocene, at about the time the temperature of North America was falling and the vegetation was thinning out.
Uintatherium was also one of the fossils involved in the great ‘Bone Wars’ between Cope and Marsh. It was by far the largest of the fossils to come out of the Fort Bridger fossil localities in Wyoming (this fort gives its name to a land mammal age - The Bridgerian!), and thus highly prized. Cope and Marsh both applied multiple names to specimens from this region which would later prove to all belong to the same species. The name Uintatherium wasn’t even one applied by Cope OR Marsh. Joseph Leidy named this creature in 1872, just barely edging out Marsh’s names of Dinoceras and Tinoceras. So that particular battle in the bone wars was won by someone who didn’t even have much of an interesting in fighting!
Uintatherium is not thought to have any living descendants, it is possible that the Eocene Uintatherium was the last of its kin. However, the position of Uintatherium and its brethren (grouped as the Dinocerata) within the mammal family tree is highly uncertain. They are well accepted as placental mammals, but beyond that? It is highly debated, and in my opinion, nobody has really done a rigorous enough study to support any one position over another.
Reconstruction by Smokeybjb.
When: Late Permian (~275 - 270 million years ago)
Where: Oklahoma, USA
What: Rhynchonkos is a very rare amphibian that lived in the swamp land covering what is now Oklahoma in the Permian. It was about 4.5 inches (~11 cm) long, not counting the tail, with an extremely elongated body and tiny tiny limbs. The elongation of its body compared to other amphibians was accomplished via replication of vertebrae, not elongation of each individual bone. Rhynchonkos had at least 36 pre-sacral (before the hips) vertebrae. Its mouth was full of rows of tiny teeth, and it is likely that it ate insects and small fish in its swampy home. Older literature about this animal refers to it as Goniorhynchus rather than its current name. This change is due to the fact that the fossil taxon was named in 1970, however, a moth was given the name Goniorhynchus in 1896. Stupid insects. At least it wasn’t a beetle this time! The name Rhynchonkos was applied in 1981.
The phylogentic relationships of Rhynchonkos are fairly uncertain. For some time it was held as a close relative of modern caecilians (a group of limbless amphibians), but later fossil finds have cast doubt upon this affiliation. Within other fossil ‘amphbians’ Rhynchonkos has been placed in Lepospondyli (along with our friend Diplocaulus). This group as a whole has a much debated relationship with living amphibians. Some studies have them having nothing to do with living amphibians (lissamphibians), where as others link specific taxa with certain groups of living amphibians. Such as the now disputed Rhynchonkos - caecilian link. It may seem obvious to link this almost limbless fossil with the limbless amphibians, but amphibians (and lizards too!) seem to like to lose their limbs at the drop of a hat. It is very common in swimming and burrowing forms.
Mounted skeleton from Petrified Forest National Park, AZ.
Reconstruction by Jeff Martz.
When: Late Triassic (~225 - 200 million years ago)
Where: South Western United States, North America.
What: Desmatosuchusis an Aetosaur. This is a group of archosaurs that ranged worldwide during the Triassic.In the archosaur family tree, they are on the line leading to crocodiles, not birds, and thus are croc-line archosaur or a member of the Crurotarsi. Desmatosuchus is one of the last aetosaurs known, and is many ways is a fairly representative member of this clade. It was covered in armor plating on its back, belly, and tail. One thing that sets Desmatosuchus apart from its fellows is the two parallel rows of spikes that ran along its back on the edge of its osteoderm plating. The largest of these spikes were roughly above the shoulders and could be up to 18 inches (~45 centimeters) long. Pretty impressive on an animal that is ‘just’ 16 feet (~ 5 meters) long.
Desmatosuchus was an herbivore, so all of this armor was to try to protect it from the variety of predators that it co-existed with, such as some of the first true dinosaurs. The turned up shovel-shaped snout of Desmatosuchus coupled with its relatively weak teeth indicate this animal probably fed on softer plant material, digging though the soil to find roots and tubers. That being said, it has been proposed in the past that it was digging not for flora, but for fauna, feeding upon unearthed grubs and other insects. It is possible that Desmatosuchus had a more broad diet than has been previously assumed.
This is species is actually beautiful
Mounted specimen at the State Museum of Natural History Stuttgart, Germany
When: Middle Triassic (~240 million years ago)
Where: Europe and China
What: Placodus is a marine reptile. At first glance it does not appear heavily adapted for aquatic life, as neither its tail nor its limbs are elongated and flattened, but specimens are routinely found in marine sediments. In lieu of being a fast swimmer Placodus was very robustly built, wide and flat, with knobby armor along its backbone and a very dense set ventral ribs. It did not need to swim fast, as its prey was hard bodied invertebrates which were mostly sedentary on the ocean floor. It plucked them out of their shallow burrows with its procumbent front teeth. In order to crunch down on the shells of mollusks and other hard-shelled animals, the rest of its teeth were very broad and flat. This is very distinctive among reptiles, so much so that that is what its name means: flat tooth.
Placodus is one of the most terrestrial placodonts, it would have moved awkwardly on land with its wide flat body and wide spread legs, but it is likely it spent a good deal of its time on the shore and only went into the ocean to feed. Later placodonts not only acquired more aquatic adaptations, but also became more and more heavily armored, some of them coming to superficially resemble turtles. At one point it was thought these animals were related to turtles, but current hypotheses have them far removed from turtles, and more closely related to the plesiosaurs, a group of obligatory aquatic reptiles.
Am I the only one who lol’d at “knobby armour”?
Thylacosmilus - marsupial sabertooth
When: Late Miocene to Late Pliocene (~10 million to 3 million years ago)
Where: South America, most fossils are from Argentina, but it was fairly widespread.
What: Thylacosmilus at first glance looks much like the famous Smilodon (sabertooth tiger). But a closer look starts to reveal many significant differences, such as the extremely large flanges on its lower jaw, which protect the large canines, and the lack of any teeth anterior to these massive teeth. This animal is very far removed from Smilodon, it is not even a placental mammal. It is a metatherian (marsupials are the living metatherians) more closely related to kangaroos, koalas, wombats, etc than to the saber-toothed tiger. The similarity between Thylacosmilus and Smilodon is an excellent example of convergent evolution - two distantly relating forms converging upon a simular morphology and life habitat. There are an three other examples of mammals that have developed saber-teeth- in fact most of the last 65 million years had some large cat-like saber-toothed mammal present, the modern biota is the outlier.
Thylacosmilus went extinct roughly 3 million years ago, closely coinciding with the formation of the land bridge linking the Americas. Animals from North America emigrated south and those from South America journeyed north; this fauna exchange is referred to as the Great American Interchange. It is at this time we start to find Smilodon fossils in South America. It is thought that the arrival of this relatively larger predator (the largest Smilodon was twice the size of the largest Thylacosmilus) may have been what drove the only known marsupial saber-toothed form to extinction.
16,000 Eyes: The Vision of a Cambrian Superpredator.
→ By John Timmer, Ars Technica
Those of you who get a bit weirded out by spiders and other arthropods would probably have a coronary if an Anomalocaris were to swim in your direction. The animals were about a meter long, and shaped as a flattened oval, a bit like a modern flounder. That’s about the only similarity with a fish, though. Instead of fins, the Anomalocarids propelled themselves through the water using a series of elongated paddle-like structures running down both edges of the body. In front, a pair of appendages could shovel prey into a circular mouth located on its underside.
And then there were the large, bulging eyes, springing from each side of the animal’s head. Until now, we could only guess at what the eyes looked like, but some spectacular, 515-million-year-old fossils from Australia have now shown that they had a huge number of small lenses, arranged much like those in modern insects and other arthropods. The finding suggests that the compound eyes evolved right at the origin of this branch of the evolutionary tree, long before the sorts of hard exoskeletons we now consider typical of arthropods.
First, the fossils themselves, which are absolutely spectacular. We’ve discovered a number of different Anomalocarid species in fossil deposits around the globe but, at best, these simply left behind an impression of the eyes. So, we knew they were roughly pear-shaped and where they appeared on the animal, but nothing about their internal structure. The eyes found in the new fossils clearly show details of the internal structure. They aren’t actually attached to an Anomalocaris, but they match the impressions previously found with them, and we’ve not found anything else in these fossil beds big enough to support an eye of this size.
It takes a microscope to see them, but individual lenses were preserved in each eye. For someone who has seen countless images of the compound eyes of Drosophila, they are startling in how modern they look. Based on their density, the authors estimate that each eye housed 16,000 individual lenses, the most that have ever been seen on any animal we know about. Based on the curve of the eye and what we know about modern compound eyes, they suggest that the animal had very good visual acuity.
(Above) The fossilized remains of 515 million year old eyes. (John Paterson)