eutherian

3

Critters! Animal people appear in Killjoys a lot, so I needed to spend a little time thinking about how they’d look as background characters. Since the whole theme in-universe for KJ is “what if the ‘fantasy’ in ‘urban fantasy’ was candyland bullshit”, all the animal folks are cute, colorful, and fall into a few narrow ‘species’.

I say ‘species’ because they’re technically all ONE species (called Eutherians) that just display a wide variety of traits. Early Eutherians were essentially highly magical chameleons, mimicing traits of whatever animals seemed most successful (usually over the course of a few generations) to better endure their environments. Modern descendants have lost that ability, but still display a pretty high species-wide magic saturation. This manifests mostly in their garish coloration, symbol-based markings, and the ability to burst into perfectly synchronized group songs (which sounds cute but is found by non-Eutherians to be terribly creepy in practice).

The three most common types of Eutherian are rabbits, bears, and the slightly rarer cats. Haven’t decided if there should be more kinds yet.

headless-horsepossum  asked:

I have a vague idea that opossums have pretty close ancestors going pretty far back into prehistory. Do you maybe have some Words about my many-toothed, trash-eating associates? Or ancient marsupials in general, maybe?

All living mammals belong to one of three clades, based on their methods of giving birth to their young.  Members of the clade Prototheria, or “monotremes”, lay eggs; members of Eutheria, or “placentals”, carry their fetal offspring in their uterus until they are fairly physically developed before giving live birth; and members of Metatheria, or “marsupials”, give birth to live young at the fetal stage and carry them in an external “pouch”.  While Prototheria is a very old and primitive group of mammals, Eutheria and Metatheria are believed to have emerged at around the same time.

The oldest known member of Eutheria is Juramaia, a tiny shrew-like animal that lived in China approximately 160 million years ago.  How Juramaia gave birth to its young is unknown; the internal reproductive organs used to classify placentals and marsupials do not typically fossilize, forcing paleontologists to classify extinct mammals based on their skeletal similarities to modern mammals.  However, as all living members of Eutheria are placentals, Juramaia was likely a placental as well.

The oldest known member of Metatheria, Sinodelphys, also lived in China, but lived about 35 million years later than Juramaia (although currently undiscovered older members of Metatheria are believed to have existed).  At the time of this writing, Eutheria and Metatheria are believed to be sister clades that share a common ancestor, one which predates both Juramaia and Sinodelphys, likely dating back to the Early Jurassic period.  Sinodelphys bears an extraordinary resemblance to a modern-day opossum—a ratlike animal that lived in trees, hunting insects and other small prey.  Again, however, it may not actually have been a marsupial; it may have given birth in some other way, but possessed skeletal features that place it within Metatheria regardless.

Based on the location of Sinodelphys’ fossils, Metatheria is believed to have originated in China, but eventually spread through all the continents of the world.  However, shortly after the extinction of the dinosaurs, metatherians died off on all continents except South America and Australia.

The reasons for these metatherian die-offs are not entirely clear.  It was once thought that they were outcompeted by eutherians, but metatherians frequently coexisted with eutherians that occupied similar niches.  (Between you and me, this also strikes me as a bit of anthropocentrism – paleontologists assuming that eutherians, the mammal group to which we coincidentally happen to belong, became dominant by virtue of being naturally “better”.)

Whatever the reasons for their extinctions elsewhere, metatherians did exceptionally well in South America.  The dominant carnivores in South America, from 65 to 3 million years ago, were the sparassodonts – large marsupials that convergently evolved to resemble big cats, such as Thylacosmilus, pictured above.  They competed with the borhyaenids – marsupials that resembled hyenas – as well as terrestrial crocodilians and “terror birds”.

Meanwhile, about 23 million years ago, a different group of marsupials emerged.  Small and unassuming, they lived in the trees, high above their clashing macropredatory cousins.  They belonged to the order Didelphimorphidae, and they were the first true opossums.

Three million years ago, volcanic activity formed the Isthmus of Panama, connecting the two continents and allowing animal and plant life to transfer between the two.  Most South American marsupials went extinct – again, for reasons unclear.  The opossums, however, transferred northward, and became incredibly successful, thanks to their adaptability and ability to eat almost anything.  Today they range from Costa Rica to Canada, in both rural and urban environments.  While their strange South American relatives may be gone, it seems that opossums are here to stay.

3

Basilosaurus

Mounted skeleton on display at the Smithsonian.  

When: Late Eocene (40-34 million years ago)

Where: North American and the MIddle East. 

What: Basilosaurus is an extinct whale. The word ‘saurus’, which means lizard, is in its name as the first fossils found in the early 1800s were isolated vertebra which were misidentified as reptilian. Soon thereafter additional material was found which easily diagnosed Basilosaurus as a form of whale.  However, due to the rules of nomenclature, the first name that is applied is the name of the taxon for all time. The first Basilosaurus material was found in Louisiana, USA and specimens were commonly found throughout the southern United States. At one point vertebra were turning up so often they were used as furniture by the locals. 

Basilosaurus is not closely related to any modern whales, diverging from the cetacean lineage prior to the odontocete (toothed whale) mysticete (baleen whales) spilt. Though it is not the longest whale ever known, at 'only' 72 feet (22 meters) long , it reached this length in a manner unlike modern cetaceans. All of this elongation comes from duplications of vertebra past the ribs whereas modern whales of this length are just overall bigger in all aspects - Basilosaurus was extremely narrow for its body length. Basilosaurus did not swim like modern whales, which move the whole tail as one unit, instead it is thought it swam much more like an eel, with the movement undulating though the long body - though in a vertical fashion rather than horizontal. Another interesting aspect of Basilosaurus is it retained extremely small hind limbs, which were useless in locomotion. These tiny appendages were most likely used as copulatory guides, such as seen in some snakes, to make sure that the proper bits of a mating pair lined up. 

shinymegacrobat  asked:

Pokemon cant be mammels coz they all lay eggs???

Platypus and echidnas lay eggs! Egg laying mammals appeared in the Triassic along with the dinosaurs, it was only much later, in the late Jurassic/Cretaceous that eutherians (non egg laying mammals, so marsupials and placentals) came about.

Also breeding mechanics in Pokemon are wrong on so many levels, eggs are by far not the worst of it. Heck you can make plants and rocks lay eggs, so I wouldn’t worry about mammals

2

Leptictidium

When: Eocene (~48-40 million years ago)

Where: Found at the Messel fossil site in Germany

What: Leptictidium is one of the more common mammals found in the Messel fossil pit in Germany. The adults ranged from about two (~60 cm) to three (~90 cm) feet in length, with most of this length being in the long tail. Leptictidium had extremely short forelimbs relative to the length of its legs, and has been reconstructed as the first bipedal mammal. There is debate as to its precise mode of locomotion, with some researchers proposing that the animal was a fast runner and others suggesting it was saltatorial (hopping). More recent studies have supported a hopping and leaping mode of locomotion. Thanks to the extraordinary preservation of fossils from Messel, we know the tail was bald for much of its length, that Leptictidium had a short ‘trunk’, like the elephant shrews of the modern day, and that this animal ate insects and small vertebrates. Contemporaries of Leptictidium include the tiny horse Propalaeotheirum and the predatory giant flightless bird Gastornis

Leptictida is the larger clade that includes Leptictidium and its kin. The first members of this group appear in the latest Cretaceous of western North America and the order quickly spreads throughout the northern continents, lasting until the early Oligocene about 30 million years ago, when the forests worldwide started to give way to grasslands. Previously leptictids were thought to be related to either the living lipotyphla (hedgehogs, shrews, and moles) or elephant shrews, but recent studies of the relationships of mammals have placed them outside of placental mammals entirely, making them stem eutherians and not members of Placentalia.