Your Daily Fossil

Thylacoleo - The marsupial lion 

Mounted skeleton located in the Victoria Fossil Cave, Naracoorte Caves National Park, South Australia

Close up reconstruction by Jeanette Muirhead.

Reconstruction of Thylacoleo hunting short faced Kangaroos by Mauricio Anton. 

When: Pleistocene (2 million to 46,000 years ago) 

Where: Australia

What: Thylacoleo is another example of an extinct australian megafauna. It was the largest marsupial predator Australia has ever seen, weighing in at 250 lbs (~115kg) on average, with individuals half again as big occurring with some regularity. The common name of ‘Marsupial Lion’ comes from its large size, shortened face, and retractable claws - the latter making it unique among marsupials. The forearms of this predator were very robust and had a semi-opposable thumbs, allowing them to drag down their prey. This interpretation is supported by the morphology of the hindlimbs and pelvis, which suggests Thylacoleo habitually reared up on its haunches. It had a formidable set of teeth as well, the extremely large sets of shearing teeth gave it the most powerful bite force of any known mammal. A find of eight skeletons in a cave in southern Australia suggests these animals lived in packs. 

Thylacoleo is in the clade Diprotodontia, which contains living koalas, kangaroos, and wombats, but is not closely related to any of these forms. Rather it is in the totally extinct subclade Thylacoleonidae; all the members of this clade were carnivorous, but some were only as small as a house-cat. Like many other large endemic australian mammals, Thylacoleo vanished just under 50,000 years ago. It is thought some aboriginal cave art depicts this lost predator. The genus was named based on material shipped back to the English scientist Sir Richard Owen in the mid 1800s. 

Onychonycteris

When: Eocene (all known fossils from a deposit 52.5 million years old)

Where: Wyoming, USA

What:  Onychonycteris is the most basal bat currently known. It differs from living bats in having claws on all five fingers, whereas living bats have lost them. This form also has relatively shorter arms and fingers, as well as longer legs and tail than any other bat, fossil or extant. Onychonycteris was an extremely important find, as allowed us to answer a long standing question about bat evolution: Which came first, flight or echolocation? This taxon was capable of flight, and detailed examination of the cranium revealed that it could not echolocate.  Thus, bats took to the skies before they developed a system for seeing with their ears. 

This amazing fossil is from the Green River fossil lagerstatten in southwestern Wyoming, and is one of two known complete specimens. This example is not the holotype (the specimen which bears the name) as while it looks absolutely gorgeous, the second specimen was arranged on the rock slab in such a way more of the skull could be studied. Additionally, this specimen was actually in the hands of a private collector, and thus not fully available to science.  That is until the specimen was mailed, unannounced, to Dr. Nancy Simmons at the American Museum of Natural History, New York.  She was working on publishing this taxon at the time, and the private collector had been informed of this, so the family sent the specimen to allow her the best examination possible. That was one awesome package to open, believe me! 

Diprotodon - The Giant Wombat

Mounted specimen on display at the Melbourne Museum, Australia 

Reconstruction by Peter Trusler. 

When: Pleistocene (1.6 million to 46,000 years ago)

Where: Australia

What: Diprotodon is the biggest marsupial to have ever lived. The largest specimens found were roughly the size of an extant hippopotomus; 10 feet (3 meters) long, 6.5 feet (2 meters) tall at the shoulder, and with a weight estimate of over 6,000 lbs (over 2,500 kgs). They inhabited forests and grasslands in Australia, and were herbivores that had an extremely varied diet. There was not much that their large grinding cheek teeth could not process. There are multiple ‘bone-bed’ deposits containing almost nothing but Diprotodon skeletons, offering strong support that they also traveled in herds. Many of these deposits are reconstructed as deaths due to droughts; it took a lot of plant material to sustain a Diprotodon. They occupied  simular niches as large ungulate herds today on other continents. 

The closest living relatives of Diprotodon are koalas and wombats. This was the largest member of the apt named Australian mega-fauna. This giant animal and many other Australian mega-fauna went extinct shortly after the arrival of humans on the continent, in a mirror of the extinction of the North American mega-fauna 10,000 years ago. In both extinction events this colonization was accompanied by climate changes, leading to much debate as to how influential human habitation was on the loss of these forms. It is thought that Diprotodon and its close relatives may be the basis for the bunyip of aboriginal folklore.  

Deinotherium - Hoe tusker

When: Mid-Miocene to Early Pleistocene (~10 million to 3 million years ago)

Where: Asia, Africa, and Europe

What: Deinotherium is a proboscidiean. The only two living species in Proboscidiea are the African and Indian elephants, but there are dozens of fossil species in this order. Unlike some other groups that not only have a much greater number of fossil species than living but a much wider variety of morphologies to go along with that, most fossil elephants well… look like elephants!  That being large, graviportal, and trunked.

However, even though there is less extreme differences in morphology within proboscidieans, there are still a lot of variations on the basic elephant body plan.  One great source of variation is in the tusks. The tusks of Deinotherium are enlarged incisors of its lower jaw whereas in modern elephants the tusks are enlarged upper incisors.  The clade containing Deinotheirum spilt off from the rest of the order roughly 40 million years ago, and the last common ancestor had slightly enlarged upper and lower incisors - thus it appears that some elephant clades further enlarged one set over the other. Oh, one last note about Deinotheirum… it was over 3 times the size of the modern african elephant. It was the 3rd largest land mammal ever to lumber accross the Earth!