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Phylogeny of Theropodentia

By Sheather888
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Theropodents, a specious clade of megafaunal, theropodal rodents, are among the most iconic of Sheatherian megafauna. Found from pole to pole, they are in fact one of its most recent lineages, originating from a mouse-like ancestral form which reached the planet less than fifty million years ago during the middle eocene. Long thought to have originated from a much earlier pre-rodent glire before or immediately after Earth's K-pg event 66 million years ago, the modern consensus on the clade, based on morphological analysis, is a position well up on the rodent family tree within the rodent superfamily Muroidea. Though the fossil record of the family is initially sparse, it is likely that the first true theropodent was a gerbil-like desert-dwelling species native to Servallia roughly 46 million years ago, which hopped and occasionally walked upon its hind limbs in the manner of a jerboa in order to travel efficiently over hot sandy environments. From this original form the lineage appears to have radiated rapidly in the immediate aftermath of the Cretaceous ice age which left West Servallia, still isolated at the time by the remnant ice cap from the rest of the continent to the east, relatively impoverished in large animal life. Primitive Theropodents were quick to fill this open niche, expanding into a variety of larger herbivore, omnivore, and insectivore niches, before gradually spilling northwards as the ice retreated and southwards via island hopping to the south pole before sea levels reached their modern day level. In both new environments they would meet new competition - megagnaths and ungulates to the north, ornithopods to the south - and gradually their diversity would wane before a few specialized forms emerged and again experienced a new radiation of diversity. Three major lineages would gradually diverge; the Bronkjirds (Ungulaginae) would by and large specialize as herbivores, analogues to our own deer and antelopes, developing long ostrich-like legs and necks and strong molars to chew coarse grasses and shoots and hare-like ears to listen for the slightest noise that could foretell danger hiding in the tall grass of the savannah. The Tyrannorats (Dromaeomurinae) specialized oppositely as carnivores, analogs to the dinosaurian Dromaeosaurs, or to modern-day cats and canids, with some of the most specialized teeth of any animal, a pair of multiple-cusped incisors in both upper and lower jaws, which function on their inner portion to shear meat and on their outer point as stabbing canines. With a variety of forms, they range from small ambush predators which rely mainly on their dexterous forearms to snatch their prey to immense endurance hunters which bring their large victims down with enormous jaws alone and exhibit nearly atrophied hands. From a basal member of the clade, the Foons, becoming elongated and armless, abandoned the land for an oceanic existence. They are tied perhaps only with the two species of "unicorn", bizarre predators-turned-vegetarian from the south pole, for the title of most aberrant tyrannorat. The unicorn's skull shows its bizarre specialization in turning a maw designed for the kill into a specialized browsing apparatus, while the foons shows the least heterodont teeth of all, which have moved forward to fill the rodents' ancestral gap between molars and incisors - a hindrance to holding slippery fish.

The most basal of all the Theropodents are a lineage which has remained on an evolutionary path so different from its two sister lineages that it was not until recently that its alliance with them was even determined. The Faeries are a cosmopolitan clade of primitive theropodents which have developed powered flight, relying on a unique system of membranous wings fitted with two separated, mobile wing digits, each supporting on either side of the finger a firm cartilaginous web which is sufficiently strong to support itself yet lightweight enough to permit agile flight. These "feather-fingers", which appear to have evolved from display structures, and which still retain claws, allow for excellent aerial maneuverability versus a stiffer pterosaur-like wing and excellent manual dexterity despite forming the leading edge of the wings. They are less restricted than the fully-webbed fingers of a bat or swiftlet (even though the latter also retains wing claws), and fitted opposite to two free digits, Faeries are excellently-adapted to climbing and are predominately small animals of dense brush, mainly specializing in feeding on seeds and/or small invertebrates (though some species, among them the falcon-like Valkyries have adapted to a predatory lifestyle and hunt in the open air.) Faeries are thought to have split off so early from the rest of their clade that the vast majority of them do not readily move on their hind limbs alone at all, with quadrupedal gaits analogous to very early pterosaurs being most common. The membranes of Faeries are primitive and bulky, making terrestrial movement a bit awkward, and subsequently most species are poorly-adapted to moving on the ground at all, the sole exceptions being Flutterfoxes, with their exceptionally long limbs, some of which hunt in the manner of storks upon the ground. Even so, these animals do not nearly approach the size of the swiftlets which fill a similar niche at much larger sizes. All Faeries are restricted to sizes no larger than medium-sized modern raptors, with wingspans of six to seven feet at their extreme, by their solid bones, and by far their greatest diversity comes in their smallest sizes as grainivores and songbird analogs which may darken the sky with their numbers. Since many species feed on fruit, and most are diurnal, Faeries are similar to the distant Anomolospectrodonts and unique amongst the Theropodents in having re-developed complete color vision.

It is important to note that Theropodents are not monophyletic with Anomolospectrodonts, though both clades share some similarities and originated upon the Servallian subcontinent. Anomolospectrodonts are extremely primitive rodents or near-rodent glires, which split from the order by 66 million years ago and have no close relatives today. Theropodents on the other hand are true muroids, their closest relatives on Earth being the true rats, mice, and even the humble hamster so often kept as a child's pet around the world.


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Typh3n's avatar
I had a similar idea to this that I thought up. In my scenario, large bipedal rodents evolved from jerboa-like rodents, becoming huge desert predators. 

I love your work. Keep it up!