A Water Bear In Amber

Today’s article is about [water bears]! What in the world is a water bear?? They are incredible, tiny creatures that are closely related to arthropods (animals like insects and spiders). They have other charming names like ‘moss piglets’ and more officially, tardigrades. These little animals are both adorable and amazing. They are able to survive in the most extreme conditions, like the vacuum of space, and intense radiation. And look how cute they are!

Here’s one swimming.

They were even featured in the TV show Octonauts.

A clip from The Octonauts.

This week, a new species was published that was found in a piece of amber from the Miocene (~23-5 million years ago) of the Dominican Republic. Amber is fossilized tree sap. When the sap is liquid, it drips from the trees and small organisms (like insects, pollen, and occasionally small birds and lizards) get trapped in it. When the sap hardens, it can turn into amber and anything trapped inside becomes a fossil. The authors were examining the ants trapped in this piece of amber for months before they discovered the tiny water bear. It is only one of a handful of tardigrade fossils.

Figure 1 from the article showing the water bear from the side.

The authors named this one Paradoryphoribius chronocaribbeus. They ran an analysis of evolutionary relationships to figure out what genus this little fossil belonged in. Because of its unique features, they realized that even though it belonged to a recognized group, it was a new species. So they named it ‘chrono’ meaning ‘time’ for the fossil’s age, and ‘caribbeus’ for where it was discovered.

Artist rendition of the water bear (by Holly Sullivan, Figure 6c from the paper).

Let’s hope we find more!

The Giant Extinct Otter and its Giant Bite

Last week, an [article] was published that talked about the biting ability of the extinct giant otter, Siamogale melilutra. The [discovery] of this otter in south-western China was published in January of this year. It lived during the Miocene (23-5.3 million years ago). Siamogale weighed about 50 kg (110 pounds) and is the largest otter to have been found.

A reconstruction of Siamogale by M. Antón.

Living otters have a range of sizes from 4 kg (9 pounds) to 45 kg (100 pounds). They live all over the world in fresh and marine waters. And they’re really cute.

Otters holding hands. From Wikipedia.

This new paper compared the jaw mechanics of all of the living otters. Jaw mechanics include things like how much force the jaw can handle, muscle volumes, jaw stiffness, and how efficient the jaw is when biting. The authors used the jaw mechanics information from the living species to calculate the mechanics of Siamogale. Then the authors made CT scans of all of the skulls and tested the mechanics using computer software.

Figure 4 from the paper showing the computer models for the Giant River Otter and Siamogale. Red areas have higher stress, blue areas have less stress.

They found that Siamogale had a jaw 6 times stiffer than any of the living otters! This means that Siamogale had a super powerful bite. It probably used this powerful bite to eat foods like clams that have to be cracked open to enjoy. Some of the living otters use tools to help them crack the shells. Other living otters use their powerful bite. Siamogale’s super powerful bite probably let them eat foods that other animals at the time couldn’t eat.

The Snail-Crunching Australian Marsupial

In May (2016), a [study] was published describing a new marsupial from Australia with an interesting set of teeth. Let’s dive right in!

Firstly, what is a marsupial? A marsupial is a type of mammal that has a pouch. When a marsupial baby is born, it crawls into the mom’s pouch to continue growing before it’s ready to live in the world.

kangaroo pouch

Kangaroos have pouches.

When most mammals are born, they are instead born straight into the world, and their parents take care of them until they are ready to live on their own. This type of mammal is called placental, and humans belong to this group. A few mammals still lay eggs, but that’s a story for another day.

Marsupials live in the Americas and Australia and come in a variety of shapes and sizes. Interestingly, marsupial and placental mammals seem to be copying each other in living environments, diets, and lifestyles. There are burrowers, fast-movers, tree-dwellers, large herbivores, and carnivores in both marsupials and placentals. There were even marsupial lions and wolves (see video at the bottom)! This is an example of convergent evolution, where animals get the same characteristics independently of each other.

marsupial vs placental

Similar ‘niches’ or lifestyles in placental and marsupial mammals.

Even more interestingly, there are no aquatic or flying marsupials (so nothing like a marsupial whale or bat) because having a pouch makes those environments difficult to live in.

Now that we know what a marsupial is (and how cool they are!) we can talk about the new one. The fossil, Malleodectes mirabilis (meaning “hammer-tooth”), was found in the Northwest of Queensland, Australia, in rocks of Miocene age (around 14.6 million years ago). It is a left maxilla (the bone that holds teeth in the upper jaw) and it preserves several teeth, including one that had not yet come up.

Fig 4

Figure 4 from the paper. A and B showing the new specimen and it’s unique tooth. C, D, E, and F showing the other Malleodectes specimens and teeth.

Teeth are really important in mammal paleontology because each species has its own unique set of bumps so you can identify species from only finding individual teeth. This fossil has a tooth still in the jaw that is cone-shaped, with a wide base and a small point. The same type of tooth found in other animals that eat snails. The shapes of the other teeth tell us that this animal was able to eat other types of food as well. This combination of tooth types tells us that Malleodectes was the only mammal able to take advantage of this variety of diet in Australia’s Miocene rainforests and makes it completely unique.

Fig 6

Malleodectes by P. Schouten.

Video of a Thylacine, the Tasmanian Wolf, also known as the Tasmanian Tiger.