Ever since they were knocked off the top of the food chain sixty-five million years ago, maniraptors have been engaging in a constant guerilla-style warfare with mammals. Most of the time, this just means they dive- bomb your car with their urea-laden excreta, but at certain points their history, they have proven to be a significant threat to the mammalian order. Most recently (as recently as 1,500 years ago), the feathery overcast known as Harpagornis moorei (today commonly known as 'Haast's Eagle', probably known to the aboriginal inhabitants of the islands as 'Ohshitlookout!') terrorized the New Zealand skies. But large theropods like Haast's Eagle and Teratornis, both of whom were potentially large enough to kill and eat an unwary juvenile Homo sapiens, are rarities after the Cretaceous-Tertiary Extinction Event. Before the Yucat√°n received its makeover, the exact opposite was true. This was the age of dinosaurs, before they were reduced from bad-ass killing machines to 'Polly wanna cracker?'

The story of the downfall of the maniraptors is long and sordid, and if it weren't for that big rock, we'd still be cowering in our burrows, instead of making them into quesadillas.

It all started in the early Jurassic with the sinosauropterygiformes. Don't try to pronounce that; you'll only embarrass yourself. Most representative of this family is the slightly more-pronounceable Sinosauropteryx. This was among the first of the dinosaurs with the sort of arms typical to theropods: flexible, strong and adapted for grasping, each finger tipped with a deadly claw. This arm would later reach ridiculous extremes with the coelosaurs: Tyrannosaurus and Therizinosaurus, whose comically-long arms are tipped in scythe-like blades --- ironically, these guys were likely herbivores. The coelosaurs are also notable for the innovation of hollow bones, which reduced their weight and may have contributed to their respiratory efficiency, making them more effective predators (and later enabled them to fly).

The theropod arm evolved over time into a wing. But the skeletal structure of a wing is nothing without the very thing that enables a maniraptor to take to the skies and rain death (and feces) from above: feathers. Feathers have been discovered in a growing number of genera, and it's reasonable to say that pretty much all of the smaller theropods were covered in feathery integument. Velociraptors weren't the scaly, saurian beasts as portrayed in "Jurassic Park". They looked more like Big Bird from "Sesame Street", only with a deadly killing claw on its second toe and a mouth full of sharp, serrated teeth. Snuffy better invest in some herding behavior.

Caudipteryx was one of the earliest dinosaurs to show feather-like coverings, more for insulation and display. Protoarchaeopteryx was probably among the first with wings, although it was incapable of flight; the wings were likely more to help it hunt on the ground by running and leaping. Archaeopteryx was one of the first genera to show flight feathers, though it lacked the keel-like sternum that allows it to attach the powerful pectoral musculature to enable powered flight. Although Archaeopteryx was considered by many to be the first 'bird' (although now the aptly-named Protoavis has taken that trophy), it probably was only capable of gliding flight or running starts from the ground. True powered flight would have to wait a bit.

Eoalulavis showed an important innovation in its wings: it had the earliest-known evidence of an alula. Alulas (or alulae for the pretentious) are feathery 'thumb' on the leading edge of a maniraptor's wing that allows it to fly at slower speeds, enabling it to land more easily and maneuver better at low airspeeds. This was imporant, because it helps to control your airspeed if you're pouncing on a puny mammal, especially when your bones are hollow.

By then, maniraptors had all the necessary adaptations for powered flight. Their bones were filled with hollows, which increased their lung capacity and reduced their weight without incurring any significant penalties in structural strength, thanks to an intricate web of struts and braces. Their brains increased in size relative to their body mass, to handle the extra processing load of flight and visual navigation. Their heavy teeth gave way to keratinized beaks, and their forelimbs lost their claws, since their range of motion was seriously limited anyways by their wings.

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Their dominance was all-but assured, except for one small detail: size. To engage in powered flight, you can't exceed a certain body mass. The modern California Condor (Gymnogyps californianus) and Andean Condor (Vulturus gryphus) are just about as heavy as a maniraptor can get without being forever grounded. Haast's Eagle was probably heavier than the limit, but it likely didn't engage in long-distance flight; it is more plausible that it simply engaged in three-dimensional ambush predation, waiting for its prey on cliff edges and high branches, and slamming down on it with the force of a sledgehammer. Right around the time that maniraptors were flying around happily, scaring the shit out of mammals, Chicxulub got cratered and pretty much everything died in the following millennia. Mammals and maniraptors under a certain body mass managed to hang on through this mass extinction event, and thrive, but in the absence of serious superpredators, mammals, unhindered by the body mass constraints of powered flight, took up the ecological niche, and nothing was ever the same again.

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