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Useful Notes: Prehistoric Life - Birdlike Theropods
Let’s talk about the popular word “maniraptors”. This term means “robbing hand”, and refers to their large, grasping hands with three fingers each (although some had lost some digits). Maniraptorans make together a natural subgroup of coelurosaurian theropods containing the most bird-related (and bird-looking) non-avian dinosaurs: dromaeosaurids, troodontids, oviraptorosaurs, and other groups.

Technically, also birds. All maniraptoran coelurosaurs shared forelimbs with a bony-structure more or less similar to birds’ wings, and most had true vaned feathers instead of simple down-like protofeathers and plumaceous feathers seen in non-maniraptoran coelurosaurs. All dinosaurs listed in this page are maniraptors, except for ornithomimosaurs — ironically, they have been considered the dinobirds for almost a century note  –- and some “Liaoning coelurosaurs”, which actually should be placed in the “Other Small Theropods” section, but are here for convenience. For true birds and more primitive small theropods, read the following two pages.

Among bird-like theropods, the most popular one have already been described in Stock Dinosaurs. Very frequent in documentary media have also been: the dromaeosaurid Dromaeosaurus; the troodontid Saurornithoides; the ornithomimid "Dromiceiomimus" (now Ornithomimus edmontonicus); and the oviraptorid Citipati (under the name "Oviraptor"). Other maniraptorans have been common sights as well thanks to their important contribute to the Feather Theory in one certain scientific period: Avimimus (the 1980s and early 1990s), Sinosauropteryx (late 1990s), Microraptor (the 2000s) and, more recently, Anchiornis. Finally, you've good chances to see four overgrown bird-like theropods whose anatomy and habits have been a mystery since their first discover: Deinocheirus, Segnosaurus, Therizinosaurus, and more recently, Gigantoraptor.


The first Raptor Attack: Dromaeosaurus

How can we tell Deinonychus apart from Velociraptor? Other than their different size, this can be done by observing their skull. The Deinonychus head was relatively stocky, with a convex profile and the snout ending with a thin point; the Velociraptor head was narrower and more elongated, with a concave profile and a blunt snout. If you watch carefully the head of the Jurassic Park "raptors" (which has inspired the popular image of the dromaeosaurids), you'll note it's modeled upon the robust skull of Deinonychus. This would demonstrate the latter is the actual animal people think when they think "Velociraptor". However, the JP Deinonychuses have also exagerrately fleshy lips and too large eyes compared with the more realistic portraits of the Deinonychus in dino-books; these two modifications actually make their heads looking like a cross between a Deinonychus and a Velociraptor. About the third stock dromaeosaurid, Utahraptor, this one cannot have been the inspirer of the JP critters (despite being the most similar to them if you count the overall size of the body), both because the Utahraptor's skull has never been found apart from the very end of the snout, and because this dinosaur was found slightly after the production of the first movie.

However, we're going here to talk more about other members of the "raptor" family: Dromaeosaurus and "post-JP raptors". The very first discovered dromaeosaurid (1920s), Dromaeosaurus has an unexpectedly generic meaning: just “running lizard”. This is because its sickle claws were missing in its original skeleton, and scientists believed it was a small tyrannosaur. The image of a hook-footed dinosaur came to light only after the description of Deinonychus in the sixties, and the family Dromaeosauridae itself was created around the same time to include Deinonychus, Dromaeosaurus, and Velociraptor together.

The dromaeosaurids' sickle-shaped pedal claws ere very specialized tools: they were on the second toe of each foot, which was very shortened and strong compared with the other two main toes. When walking and running dromaeosaurids kept their 2nd toe raised up to the ground level, so the whole weight of their body was substained by only two digits of each hindlimb. The sickle-toes were moved by powerful muscles; scientists think "raptors" were able to lower them when used as weapons, just like cats do with their retractable claws. According to a recent hypothesis, the dromaeosaurs' used their sickle-claws like their relatives, the eagles, do with smaller prey; pinning prey down and eating them alive, letting the hapless prey item die from shock and blood loss.

The same size of Velociraptor but with a shorter head and stronger jaws and teeth, Dromaeosaurus is less-frequently portrayed than the Power Trio made up of Utahraptor, Velociraptor, and Deinonychus. Despite this, Dromaeosaurus appears regularly in dino-books and has also made some apparitions in TV documentaries. If you see a dromaeosaurid interacting with Tyrannosaurus rex or Triceratops in Late Cretaceous North America, it would be Dromaeosaurus note  — unless the writers didn't know or just didn't care: some docus have shown Deinonychus in this role. Walking with Dinosaurs dealed with the problem in a bizarre way: here, the dromaeosaurids are officially Dromaeosaurus… but have the shape of Deinonychus.

Actually, every dromaeosaurid in the original series was a Deinonychus, Utahraptor included — which, even though their name clearly means “Utah thief”, were portrayed living in Europe for some reason. And to make the Utahraptors and the Dromaeosauruses distinguishable, they show up with a different coloration. In this show, Utahraptors are also portrayed in the way dromaeosaurids were once represented in paleo-art: naked-skinned, colored like big cats, chasing an iguanodont in pack, jumping on it using their sickle-claws as spurs, and eventually killing it with (a quite exaggerated) ease. Many dino-books have made this thing Up to Eleven with Dromaeosaurus, depicting scenes in which these turkey-sized predators chase and kill in packs adult Edmontosaurus and Triceratops 500 times heavier. Current paleontology suggests that Dromaeosaurus and the other “raptors” hunted small prey and only ate the carcasses of the giant herbivores. The bigger dromaeosaurs (Utahraptor and Achillobator) may have been able to take larger game then their smaller relatives; but likely they were more solitary then the much smaller Velociraptor and Deinonychus. But stop now.


Feathered friends: Bambiraptor, Achillobator & Rahonavis

Dromaeosaurus, Velociraptor, Deinonychus, and Utahraptor together with some other genera such as Adasaurus and Saurornitholestes, used to make the dromaeosaurids before the Jurassic Park times and also few years later (middle 1990s). note  We now know they actually do not match the great variety within their family. Especially since the beginning of the 2000s, mny new dromaeosaur species have been discovered, most of them having received the suffix raptor. Examples are the North-American Bambiraptor (so called because its skeleton was from a juvenile); the European Pyroraptor; and the South American, short-armed Austroraptor. One exception is Achillobator, which lived in Late Cretaceous Mongolia and, with its 6 m long body, was only slightly smaller than Utahraptor. These were all ground-dwelling kinds with a running-plan like the traditionally-intended “raptors”.

But other “new” dromaeosaurids have turned out to be smaller, more specialized animals often with some tree-climbing adaptations. Because of their apparently non-raptor-like nature, some of them were not even initially thought to be dromaeosaurs: this explains why they haven’t got the suffix –raptor. The tiny Rahonavis from Madagascar was initially thought to be some sort of bird. The same about Unenlagia, the first dromaeosaurid discovered in South America. note  While Hesperonychus (whose name is clearly inspired from "Deinonychus") was found only in 2009 and briefly considered the smallest North American dinosaur. Perhaps the most specialized known dromaeosaurid today is Balaur: found in 2010 in Romania, it has uniquely two sickle-claws on each foot. Another non-raptor-looking dromaeosaur found in 2000 (in spite of being a climbing kind it ends in –raptor nonetheless), is now one of the most portrayed bird-like dinosaurs: obviously, we’re talking about Microraptor. See also the “Liaoning Coelurosaurs” entry below.


Similar yet different: Saurornithoides & Saurornitholestes

Many dinosaurs have “-saurus” at the end, but some examples have this reversed: the hadrosaur Saurolophus, the ankylosaur Sauropelta, the carnosaur Saurophaganax, the sauropod Sauroposeidon, and this one as well: Saurornithoides (“bird-like lizard”). One of the several Troodon relatives found in Asia, Saurornithoides shared the same Late Cretaceous habitat with two iconic similar-sized theropods, Velociraptor and Oviraptor.

These three maniraptorans were discovered by the American expedition in Mongolia led by Roy Chapman Andrews in the 1920s. Like Velociraptor, Saurornithoides was considered either a peculiar dwarf megalosaur or a generic coelurosaur until the 1970s, when it and Troodon (then still called “Stenonychosaurus”) were put in their own family, the "saurornithoidids" (now called “troodontids”). Together, troodontids and dromaeosaurids made in turn the larger group called deinonychosaurs. Thus, deinonychosaurs and dromaeosaurids are traditionally not the same thing: the former also include troodontids. However, some analyses in 2013 have recovered troodontids as being avialans, in which case they would actually be closer to modern birds, while other workers think they are neither deinonychosaurs nor avialans. Since the 1990s, the troodontid family has acquired several new relatives, usually from Cretaceous Asia: among them, Archaeornithoides and Sinornithoides (both described in the early 1990s) have received names that are clearly variations of "Saurornithoides". Other interesting discoveries were Byronosaurus with its peculiar teeth, and Jinfengopteryx which has left tracks of feathers. Other troodontids are cited below in the “Liaoning Coelurosaurs” section, ex. Mei and Anchiornis.

Traditionally, Troodon and Saurornithoides have been depicted as cunning nocturnal hunters who used their large, forward-facing eyes (usually shown with cat-like or even gecko-like pupils), as well as their great intelligence to catch small mammals, grasping them with their three-fingered hands weaponed with curved claws and opposable thumbs. More realistically, their eyes were bird-like with round pupils, their hands were not so prehensile, and their great smartness is debatable (see Raptor Attack). Furthermore, according to recent research, at least Troodon was more likely omnivorous (a bit like ornithomimosaurs), because its teeth were tiny and not-so-sharp, resembling those of plant-eating dinos. However, Saurornithoides (and its former species Zanabazar), having a slightly larger head and teeth than Troodon, was more Velociraptor-like than the latter, and maybe it really corresponded to the former portrait of a specialized hunter. Anyway, given their fragile jaws and modest sickle-toeclaws, both dinosaurs would have been able only to hunt small animals that could be swallowed whole, and weren't capable of severing the throat of an animal the size of Protoceratops (unlike the more powerful dromaeosaurids: see the famous Velociraptor/Protoceratops skeleton).

Saurornithoides has also a similar-named, similar-sized and similar-looking relative, Saurornitholestes. But this one was not a troodontid, but one of the few dromaeosaurids known before Jurassic Park note  (that's why it has not the suffix -raptor). Its name is a Portmanteau of Saurornithoides and Ornitholestes. Found in the 1970s after the official description of the dromaeosaurid family, Saurornitholestes lived in Late Cretaceous North America together with Dromaeosaurus; even though has left much more fossil material, it has not received the same level of attention in media. To some point of view it has been luckier than Dromaeosaurus, as the portrayal of a "miniature monster" involving all the other Pre-JP "raptors" has apparently spared Saurornitholestes.


The Mimus family: Dromiceiomimus & Pelecanimimus

Which is the most iconic ornithomimid in pop-consciousness? Well, it depends on age and location. The last-generation dino-fans would respond by saying Gallimimus (no matter which country they live); the long-standing ones living in the USA have a better chance to say Ornithomimus; while those living in Britain will probably ask you Struthiomimus (Of course this is a quite rough distinction, as stock ornithomimids get confused a lot each other in the public mind). Most ornithomimids have bird-related prefixes and the suffix –mimus in their name. Ornithomimus simply means “bird-mimic”, Gallimimus “rooster-mimic” (even though it hardly resembles one…). While Struthiomimus means "ostrich-mimic" - maybe the most apt name, since this group of animals did resemble ground-running birds in shape and possibly habits.

As noted in Stock Dinosaurs, Struthiomimus and Ornithomimus were considered one and the same when the film Fantasia made ornithomimids famous for the first time. This would mean that many fictional ostrich-mimic dinosaurs can equally be called "Ornithomimus" or "Struthiomimus" without being in error. However, Struthiomimus had stronger forelimbs and claws than Ornithomimus, and was definitively recognized distinct in the 1970s. A third ornithomimid was described in the same years in North America, with a name that makes a sort of tongue twister: Dromiceiomimus, “emu-mimic” note . This one was also virtually identical to its neighbors, only with wider eyes and longer legs, and was also cited as the “fastest-running dinosaur”. Since the 2000s this animal has been placed in the genus Ornithomimus, and has disappeared from the official dinosaur list; however, it may return.

Most ornithomimosaurs, however, have been found in Asia: other than the gigantic Gallimimus and the even more gigantic Deinocheirus note , we can mention Archaeornithomimus (“ancient Ornithomimus” because lived in early Cretaceous several million years before the latter), Sinornithomimus ("Chinese "Ornithomimus", a small-sized genus found in the 2000s), Anserimimus ("goose-mimic", but wasn't particularly similar to a goose), and GarudimimusGaruda-mimic”, all archaic yet already toothless animals. Among them, Garudimimus is worth of note because some old books have shown it with a tall, narrow bony crest upon its head, making it resembling a cross between an ornithomimid and an oviraptorid. Actually, it was simply a misplaced bone from another portion of the skull.

But even more basal ornithomimosaurs still retained small teeth. Among them, Harpymimus ("harpy-mimic") from Cretaceous Mongolia had only few teeth on the tip of its mouth; at the opposite end, Pelecanimimus of Early Cretaceous Spain had more teeth (220) than any other known theropod. The latter means “pelican mimic” because its skeleton was discovered with the print of a pelican-like gular pouch. At present, the oldest and most primitive ornithomimosaur is the Early Cretaceous South African Nqwebasaurus (see "Other Small Theropods") Since it was not recognized as an ornithomimosaur initially, it has received the very generic suffix -saurus. However, since the 2000s scientists have decided to break the rule naming some new ornithomimosaur genera with suffixes different than -mimus (ex. Beishanlong and Hexing).

With a description of the integument of Ornithomimus it is now known that ornithomimosaurs were feathered. As it turned out, not only did they have a down-like covering (which was expected, considering that they were more distantly related to birds than deinonychosaurs and oviraptorosaurs were), but the adult specimens also had shafted feathers on their forelimbs which seemed to form primordial wings. In addition, the aforementioned Pelecanimimus shows naked skin on its throat pouch, and some signs seem to indicate the presence of proto-feathers on its body.


Crest or non-crest?: Citipati

In modern media, the animal commonly known as "Oviraptor" (probably Citipati) is usually portrayed with a rhombus-shaped bony crest on its skull-roof. However, in classic paleo-art several "Oviraptor"s appear without this feature, substituted by a small "horn" on their nose. These older portraits are based upon the original Oviraptor crushed skull found nearby the alleged Protoceratops eggs: this skull is actually crestless, but the shape assumed by the crushed bones did seem to show this horny bump, leading paleo-artists in error. Old portraits also show oviraptorids with two small "teeth" protruding from their palate: in a time in which oviraptors were still considered specialist egg-eaters, these "palatine teeth" were said to be an adaptation to make holes into eggshells, aiding the beak to open the nutritious eggs; however, they too could be a mistake based on the original Oviraptor crushed skull. Note however that the egg-robbing theory has not been totally discarded; after all, many modern carnivorous mammals do eat the occasional unattended eggs if they have the chance.

From 1920s up to the 1970s Oviraptor was the only known genus in its own theropod group. Several new oviraptorosaur genuses were classified since the 1980s, mainly in Asia; many of them used to be put in the genus "Oviraptor" before that, for example the crested Citipati and Rinchenia (originally "Oviraptor mongoliensis"), while others have been found without any crest, for example Conchoraptor and "Ingenia" (now called Ajancingenia), both announced in the 1980s. note  One of the most interesting is Nomingia: found in 2000, its vertebrae at the end of its short tail were fused together, just like the "pygostyle" of modern birds. A pygostyle has been as recently as in the 2013 found also in Conchoraptor and Citipati itself. Oviraptorosaurs also included some of the smallest non-bird dinosaurs, and the earliest ones (from Early Cretaceous) preserved teeth as a primitive trait. Some oviraptorosaurs are listed in other sections below, for example Avimimus, Caudipteryx, and the huge Gigantoraptor.


Teeth or non-teeth?: Chirostenotes & Microvenator

There is, however, one genus which has been known from North America since the 1910s, but was recognized as an Oviraptor relative only in the 1980s: Chirostenotes, to this day still one of the few North American oviraptorosaurs. Despite this “privileged” position, Chirostenotes remains a rather obscure dinosaur, and has had a convoluted Science Marches On story. Since it was originally named based on a lone hand (its name means "narrow-handed one"), it was initially considered a “generic toothed coelurosaur” (toothed jaws once assigned to it were renamed Richardoestesia in 1990). The foot was found in 1936, named Macrophalangia ("big toes") and considered an ornithomimosaur. Its toothless jaws were found in 1940, but was named Caenagnathus ("recent jaws") and believed to be a bird. In 1981, the discovery of the Mongolian Elmisaurus ("foot reptile") suggested that all these dinosaurs were related. In 1988, a complete skeleton of Chirostenotes was found, which showed that "Macrophalangia" & “Caenagnathus” were the same as Chirostenotes, and these two names fell in disuse, being named more recently than Chirostenotes. A 2007 analysis suggested Caenagnthus really is distinct, but this is highly contentious. There is also an astounding analogy between the Chirostenotes and the Oviraptor Science Marches On stories. The former, too, was depicted with only a small bump on its nose in old portraits; but the skull used as model was incomplete, and now the dinosaur is thought to have had a large crest similar to that of Citipati, although more rounded in shape.

Chirostenotes was Late Cretaceous like Oviraptor, and lived alongside several North American Stock Dinosaurs. Other two North American oviraptorosaurs are the large Hagryphus and the small Microvenator ("small hunter"). The latter was Early Cretaceous and shared its habitat with the famous Deinonychus. Microvenator has also had a peculiar story. It was originally named "Megadontosaurus" ("big-toothed reptile"), as the teeth of the larger Deinonychus were originally assigned to it. This name was never made official, however. When it was officially named in 1970, it was considered a generic coelurosaur. Later, it was found to be an early oviraptorosaur, possibly close to Chirostenotes. Because of its much smaller size than the latter, some think the Microvenator remain was from a juvenile. Sadly, as the skull was never found, we don't know if it was crested or not, or if had it teeth, or not.


The first known feathered dinosaur: Avimimus

When did the Great Feather Adventure begin? The answer: in 1981, in the Mongolian Gobi Desert, the same place where Oviraptor and Velociraptor were first discovered. That year, a new kind of Late Cretaceous “coelurosaur” was described from a partial skeleton, which astonished the scientist who found it.

He chose to name his find Avimimus - “bird mimic”, the same as Ornithomimus, only with a Latin prefix instead of Greek. Despite this, Avimimus was not an ornithomimid, but an only 5 ft long, late-surviving basal oviraptorosaur. Nothing special per se… except for one thing: it was the very first dinosaur whose skeleton showed some evidence of feathers. Not prints on the rock, however, only a crest on its arm-bones that resembled that of modern birds.

For about 15 years since then, Avimimus has been the only non-avian dinosaur regularly portrayed with feathers – often in an incorrect way: certain depictions popularized by John Sibbick showed it as a short-winged Archaeopteryx with the same head-shape, jaws filled with teeth, and splayed forelimbs, as if was about to take off. It actually had a short head and short arms typical of oviraptorosaurs, so it couldn’t fly. However, it should be noted that Avimimus lacked a crest, and also had serrations in its beak which could have worked as teeth.


Birds are dinosaurs: Sinosauropteryx, Protarchaeopteryx & Caudipteryx

The first unequivocal non-avian dinosaur fossils with actual feathers preserved came to light in the second half of the 1990s in Liaoning (province of China). They were extraordinarily well-preserved, better than almost any other known dinosaur fossil; they were all small-sized (the biggest was only 8 ft long); they hailed mostly from the Early Cretaceous (unlike Avimimus); and they represented almost all of the main coelurosaur subgroups, giving a sort of snapshot of the coelurosaurian fauna of the time.

More than 20 genera have been described so far, and others could still join them in the future: we’ll mention only some examples. Sinosauropteryx (“Chinese feathered lizard”) was the first to be discovered (1996); a compsognathid, it was the very first non-avian dinosaur to have shown prints of feathers; being it was a non-maniraptoran coelurosaur, these were still down-like, unlike modern feathers.

The very first Liaoning coelurosaurs, discovered with vaned feathers in 1997 and 1998, were much closer to birds: these were Protarchaeopteryx (“First Archaeopteryx”) and Caudipteryx (“feathered tail”). Both were basal oviraptorosaurs similar to Avimimus, but only 2-3 ft long and with teeth; they had pennaceous feathers on their forearms and their tail feathers were homologous to those of the famous Archaeopteryx (not casually, these three dinosaurs have been named with the suffix -pteryx). However, the wing-feathers of Caudipteryx and Protarchaeopteryx were short and symmetrical, unlike those of true birds, and thus totally unsuitable for flight.

Soon after, the list of feathered dinosaur fossils increased dramatically each year. The herbivorous Beipiaosaurus is perhaps the most specialized among them, being a small therizinosaur (see at the bottom of the page) with a down-like covering and some thin feathers on its forearm. In 2004, even a feathered tyrannosauroid was discovered: Dilong, a slender coelurosaur with little external resemblance to a T. rex, preserving some down-like feathers.

Other Liaoning coelurosaurs showed up in the third episode "Dino-Birds" of the miniseries Prehistoric Park. The chosen ones were: the buck-toothed oviraptorosaur Incisivosaurus because of its funny look, the troodontid Mei, which is now “the shortest-named dino” along with the alvarezsaurid Kol (the former record-holders were the Australian ankylosaur Minmi and the oviraptorosaur Khaan), and, naturally, the ever-present Microraptor (see below).note  In “Dino-Birds”, Nigel Marven makes a Time Travel to the Cretaceous China to save some Microraptors from extinction; before ending the mission, he encounters several Mei (referred to by their whole scientific name: Mei long) apparently sleeping in the same bird-like position in which the type specimen was found fossilized (they were actually dead), while the other Mei long act as the “danger of the forest”, and to fit their fearsome better role, are oversized and lack feathers.


Four-winged dinosaur: Microraptor

Discovered in 2000, Microraptor is another Liaoning coelurosaur, named “small thief”; as the "-raptor" suffix suggests, it was a dromaeosaurid. It was a find that strongly surprised not only casual paleo-fans but also the entire paleontologist community. And not because it was a feathered dino fossil (such animals were already known from the same site); nor just because it was the smallest non-avian dinosaur known at that point (merely 1.5ft long, but this record is contended now by other non-avian maniraptors). It was its unique body-plan that astonished us all. A four-winged dinosaur!

More precisely, its hindlimbs had a feather-covering incredibly similar to that of its forelimbs, giving it its unbelievable appearance.These wings had the same structure as the wings of true birds, with asymmetrical, vane-like feathers on the forelimbs, likewise on the hindlimbs, and placed in a "fan" at the tip of its long tail: in short, very similar to the kind of plumage of the well-known Archaeopteryx (itself recently found to have had remnants of such large feathers on its legs).

Of course, paleontologists and dino-fans have begun Wild Mass Guessing about its way of life. Since its discovery, Microraptor has been suggested to have been a tree-climber, with forelimbs as developed as the hindlimbs, both fitted with robust claws apt for climbing upright tree-trunks; however, a study published in 2011 suggests it might have been terrestrial instead. The way it traversed the air is also controversial; with true flight like modern birds, or just simple gliding like modern “flying” squirrels, “flying” fish and “flying” lizards? Currently many scientists think Microraptor was actually a flier (although not as good as modern birds): not only that, it seemed to be even better adapted for flight than Archaeopteryx. If this is true, it would mean that flight evolved before the appearance of the so-called “first-bird”, because Microraptor was less close to modern birds than Archaeopteryx was. And since flight was achieved in basal dromaeosaurids, this would mean that… yes, Velociraptor and all other dromaeosaurids may have descended from flying ancestors! One scientist did go Up to Eleven declaring that all maniraptorans descended from flying ancestors: this would mean, Troodon, Oviraptor, and even the huge Therizinosaurus were ancestrally creatures of the air, which, like ostriches or rheas, returned to a more ground-level way of life and increased their size.

Whatever the case was in Real Life, Microraptor immediately became the center of much interest soon after the year 2000, becoming rapidly popular in illustrated books (also because was the considered the smallest dinosaur at the time); it became even more widely-known after being portrayed as one of the main animal characters in the aforementioned Prehistoric Park (where it was portrayed with the classic, splayed-limbs gliding style, now known to be anatomically impossible). Soon afterwards, it started to gain attention by the broader pop-cultural world, and it could at this point be qualified as a true Stock Dinosaur (even if only in the Rarely-Seen section).

Over the years, several interesting specimens of this dinosaur have been found. One of these was originally named Cryptovolans ("hidden flyer") in 2002 and thought to be different from Microraptor due to a few seemingly unique features (a longer tail, for example). Further work showed that they are all present in Microraptor, and so "Cryptovolans" fell into disuse. A specimen announced in 2011 provides a clue to its diet: this one seems to preserve the remains of an enantiornithine bird in its stomach. A specimen published in 2013 shows it ate fish. As remarkable as those stories are, they don't come even close to a 2012 study carried out on one specimen. This study showed that its feathers were likely iridescent in color, troubling a previous suggestion it was nocturnal.

There is another story to be told about Microraptor. Before being discovered properly, the tail of one specimen had been mixed with the front end of a true bird found in Liaoning, Yanornis; the so-created Mix-and-Match Critter was published in media as a new kind of bird-dinosaur, “Archaeoraptor”, but this hoax was exposed after qualified scientists studied the specimen — in fact the world-infamous article that published the fake was so hastily put-together, they didn't even bother to check if it was a true fossil or not... leading to one of the biggest controversies of modern paleontology. But although “Archaeoraptor” itself didn't exist, its tail belonged to a real animal, one that redefined our understanding of dinosaurs even more than an actual “Archaeoraptor” would have. This is an often overlooked detail, especially by creationists and conspiracy theorists who still can't let go of the controversy.


Colorful little guy: Anchiornis

Another, just as extraordinary Liaoning discovery has come in 2009 from Jurassic rocks: Anchiornis (literally “near bird”). This pigeon-sized troodontid or similar form has often been referenced as the smallest non-avian dinosaur known, but this record is actually contended by other theropods, for example another Liaoning troodontid found in 2013, Eosinopteryx —- which is interesting also because it uniquely has not any sickle-claw in its foot. The great interest surrounding Anchiornis is due to another detail: it has, amazingly, preserved not only its whole plumage, but even the original colors. Since colors have almost never preserved in vertebrate fossil record, it’s easy to understand the extraordinariness of such a discovery.

Even the aforementioned Sinosauropteryx and Caudipteryx have left some traces of color, as did probably other feathered dinosaur fossils, such as the basal bird Confuciusornis and the dromaeosaurid Sinornithosaurus. Still, Anchiornis remains the most well-preserved, and it is the only non-avian dinosaur whose precise appearance is known with a reasonable degree of sureness. However, since fossilization processes often change the original patterns of live animals, the true colors of Anchiornis could possibly have faded or even changed a fair bit in 160 million years. We may never know how close our restorations are.


When dinosaurs went up trees: Scansoriopteryx, Epidexipteryx & Zhongornis

Scansoriopterygids were pigeon-sized animals from the latest part of the Middle Jurassic (although some thought they were as young as the Early Cretaceous). They had a body-plan apt for climbing, similar to Microraptor, or rather, even more specialized; they had forelimbs longer than their hindlimbs. First discovered in 2002 in Liaoning, they were found with feather prints around their body like many other Liaoning coelurosaurs, but their placement within the phylogenetic tree is fairly uncertain (are they true avialians, early relatives of deinonychosaurs & avialians or early oviraptorosaurs?). Unluckily, only juvenile specimens are known from the few species of scansoriopterygids described, and some of their peculiar traits might just be juvenile-related and were lost in adults.

The tiny Epidexipteryx (which once contended the “smallest non-avian dinosaur” record with Anchiornis), and the namesake Scansoripteryx, were the only two species recognized for a long time: a third genus, "Epidendrosaurus", has been synonymized with Scansoriopteryx, and there are those who still prefer that name. In 2014 it was suggested that Zhongornis was actually a late-surviving scansoriopterygid. Named in 2008, it was initially considered an intermediate between ancient long-tailed birds and more advanced short-tailed forms (see in another page).

Dino-anteaters, or ancient ostriches?: Mononykus & Alvarezsaurus

Lets leave Liaoning behind and go discover another odd-looking bird-like dinosaur, Mononykus. Discovered in 1993 and initially called “Mononychus” (but that name was already taken by an insect), this is an enigmatic animal which shared Late Cretaceous Mongolia with Avimimus, Velociraptor, Saurornithoides, Oviraptor and several other coelurosaurs.

Only 3 ft long, its name means “one claw” because of its strange, one-fingered hands (the other two digits usually present in coelurosaurian hands were simple stubs on Mononykus). We still don't know how Mononykus could have used its “hooks”: maybe it destroyed termite-mounds with them? One close relative, Shuvuuia (which just means “bird” in Mongolian), was a close relative found in 1999, and lived alongside Mononykus. Unlike the latter, Shuvuuia has left some cranial remains, which show a mobile upper jaw totally similar to a modern bird's; but this discovery has only made their way of life even more enigmatic.

These dinosaurs, along with other relatives, form the Alvarezsaurids, a mainly Cretaceous family named after Alvarezsaurus, a more primitive South American genus discovered incidentally in the same year as Mononykus. It’s significant that Alvarezsaurus was initially thought a late-surviving ceratosaur that convergently became similar to an ornithomimid. Whereas Mononykus was identified as a sort of running bird, closer to a house sparrow than Archaeopteryx was.

Actually, the classification of the family has always been very problematic: they have been variably put next to ornithomimids, to troodontids, or to Archaeopteryx (in this case, they would be the closest bird relatives); this is because their specialized hands made comparisons with other theropods a difficult task. However, the discovery in 2010 of a basal relative called Haplocheirus with a complete, three-fingered hand has since confirmed alvarezsaurs as non-avian maniraptors, slightly more advanced than therizinosaurs. Also note that, since “Mononychus” was changed to “Mononykus”, most alvarezsaurid genera have since called with the suffix –onykus, in a classic Follow the Leader example. One of them has been found in Alberta, living alongside many popular Late Cretaceous dinosaurs: Albertonykus.

Alvarezsaurids also include one of the smallest non-bird dinosaurs ever: Parvicursor ("small runner") was only one foot long and the same size of the aforementioned Anchiornis. It's interesting to note that, unlike most other coelurosaurian groups, the alvarezsaurs failed to produce any truly giant members: Rapator from Early Cretaceous Australia was thought by some to be a giant alvarezsaur, but is instead a megaraptoran. Still uncertain is the classification of Bradycneme, a poorly-known fossil from Late Cretaceous Romania: originally classified as a prehistoric owl, some researches seem indicating it was an European member of the alvarezsaurids.


Deadly Embrace: Deinocheirus

Most bird-like dinosaurs were small and unimpressive in Real Life compared to most other dinosaurs. This definitively couldn’t be said for the following examples: Deinocheirus, Segnosaurus, Therizinosaurus, and Gigantoraptor, all living in Late Cretaceous Mongolia. These are indeed among the largest known theropods, and at the same time, among the most mysterious.

Let's start with Deinocheirus (“terrible hands”, not to be confused with Deinonychus, “terrible claw”). Discovered in the 1970s, only its complete forelimbs are known, along with shoulder-blades and some other fragments from the rest of the skeleton. These forelimbs were similar in shape to those of an ornithomimid… only, they were two times taller than a fully grown human. To give you an idea of the scale, several drawings have shown these immense “arms” encircling an adult man, with the three-fingered hands (each as wide as a TV-set) shown like they’re going to grasp and then lift him. The drawings usually don’t show the whole body, because its shape is totally unknown. Some thought it had forelimbs longer than the hindlimbs, but this is unlikely, since this would have forced the animal to walk on four legs: an impossibility, since its hands were inapt for walking. It’s more probable that Deinocheirus had the same body shape of the classic ornithomimids.

If its forelimbs had the same proportions of a Gallimimus, Deinocheirus could have been as long as a Spinosaurus, and even taller, thanks to the longer neck. Some scientists have even said that it could reach the fifth story of a building if alive today, and could have weighed as much as two elephants, that is to say, two T. rexes. But most experts don’t agree with these extreme ideas, and put Deinocheirus in the same size-range as Tyrannosaurus or Allosaurus. Moreover, being an ornithomimosaur, it would be rather slender-framed, and thus it's unlikely that was as heavy as two elephants: perhaps it was even lighter than T.rex.

The way-of-life of Deinocheirus has been even more enigmatic, and still remains misterious to this day. Early reports described it as a gigantic and fearsome predator, but we now know such an image is highly unlikely. Deinocheirus was either a basal toothed ornithomimosaur or a derived toothless ornithomimid. If the first is true, Deinocheirus could have been an active hunter, and someone could even imagine titanic battles againts the contemporaneous T. rex relative Tarbosaurus or even Therizinosaurus (see below). But wait: even with sharp-toothed jaws, Deinocheirus shouldn’t be seen as such a powerful killer. Its jaws and teeth would be much smaller and weaker than tyrannosaurs', carnosaurs', or even spinosaurids'. Furthermore, its claws seem too blunt to be able to rip the tough skin of a hadrosaur or a sauropod. Maybe Deinocheirus was a sort of giant omnivore, which could have eaten from tree-tops using its forelimbs to pull down branches, and at the same time could have scavenged carrion of large herbivores, hunted small dinosaurs that could be swallowed whole, and maybe even chased Tarbosaurus away from their kills using its “terrible hands” as a scaring device.

To resolve the mystery, dino-fans patiently waited for a complete Deinocheirus skeleton for many years. Material described in 2012 was a step in the right direction: this shows that the original carcass was scavenged by Tarbosaurus. More complete specimens found near the original one were announced in 2013 confirming its ornithomimosaurian affinities, although it displays a feature unknown in any other birdlike theropod: a sail that peaks over the hips, similar to that of the carnosaur Concavenator. Even though they're still attending formal description, these fossils seem to indicate that Deinocheirus actually was one of the biggest and tallest theropods ever, but most likely an herbivore like its neighbor Therizinosaurus.


Mix and Match Critter: Segnosaurus

Most dinosaurs would appear as a bunch of Mix-and-Match Critters if alive today, with traits resembling those of mammals, bird, and crocodiles. But the Mix-and-Match Critter trope can also be applied in a more subtle way. Some relatively unknown dinos actually resembled strange mixes of Stock Dinosaurs, rather than modern animals. Segnosaurus used to be the best example of this in the recent past.

When its incomplete remains were discovered in the 1970s, hailing from Late Cretaceous Mongolia, this 7 m long dinosaur made the scientists' eyes roll in their sockets: how could a dinosaur have the body-shape of a prosauropod, the forelimbs of a theropod, and an Iguanodon-like skull with a round bill at the front and grinding teeth behind? And, even though its pelvis was clearly saurischian in its overall structure, why did it have the pubis uniquely pointing backwards? Taxonomists were totally confused, and placed Segnosaurus in its own group, the “segnosaurs”, along with some less-known relatives (Erlikosaurus, Nanshiungosaurus, and the meaningfully-named Enigmosaurus). These were believed a separate evolutive branch which arose early in dino-evolution, and were classified in between theropods and sauropodomorphs, sauropodomorphs and ornithischians or sometimes even saurischians and ornithischians.

Science Marches On, however, and at the beginning of the 1990s, a much smaller relative, the 3.5 m long Alxasaurus (from Early Cretaceous China) clearly showed a coelurosaurian anatomy. This meant that segnosaurians were not only true theropods, but also members of the Maniraptoriformes. Not only this: thanks to a more accurate comparison, it was discovered that the enigmatic Therizinosaurus was another member of the same group. Today, Therizinosaurus, being far cooler-looking, is much more frequent in books than Segnosaurus, and the whole group is now more frequently called “therizinosaurians”. Therizinosaurus too has had its own Science Marches On story, independent from that of Segnosaurus. We'll get to that in a minute.

The diet of Segnosaurus used to be just as problematic as its classification. One theory made it a fish-eater like Baryonyx, but slippery fish could have easily escaped from its round beak; some paintings have even shown it with webbed feet, based on footprints. Another unlikely hypothesis made segnosaurians termite-eaters because of their large handclaws apparently apt to dig into termite-mounds; but again, these dinosaurs hadn't the typical tubular muzzle of a mammalian anteater, and such lage creatures couldn't have lived on insects alone.note  Today we think therizinosaurs were plant-eating theropods. This also explains their backward-pointing pubis: its function was to give space to the massive gut of a herbivore without losing the bipedality of a theropod.note . Even though other birdlike theropods (ornithomimids, oviraptorids) could have eaten fruits or other kinds of vegetation, only therizinosaurs appeared specialized to a strict herbivorous diet based upon tree-leaves. If it wasn't for their unmistakeably theropodian forelimbs you could easily confound them with ornithopods like Iguanodon if they'd be alive today.


Converted to Veganism:: Alxasaurus, Beipiaosaurus & Nothronychus

Today, therizinosaurs (or segnosaurs if you're more traditional) are a rather well-known group, including both large and small genera. Among the large ones (all Late Cretaceous), most have been found in Asia, just like Segnosaurus and Therizinosaurus: one example is the aforementioned Erlikosaurus. Only one large-sized therizinosaur is known so far from North America: Nothronychus ("sloth-claw"). This one lived at the start of the Late Cretaceous, before the most-famous North American herbivores like the ceratopsids and the hadrosaurs: competition with them could have led it to its early extinction.

Among small therizinosaurs (all Early Cretaceous), other than Alxasaurus and the smaller Beipiaosaurus found in Liaoning, worthy of note is the North American Falcarius — found in 2005, this one has left us with a whole graveyard containing hundreds of specimens. While the first two were rather evolved and shared typical therizinosaurian traits, Falcarius (the "scythe-bearer") has a slender structure more similar to a typical coelurosaur and was perhaps omnivorous. Maybe the most ancient therizinosaur is Eshanosaurus from the Early Jurassic of China, but its collocation in this group is highly controversial, and it may be a sauropod relative instead.


Wolverine Claws: Therizinosaurus

Therizinosaurus could be considered the Non Identical Twin of Deinocheirus: it was a colossal yet awfully bird-like theropod, just like Deinocheirus; specialized to a non-big-prey-based diet, just like Deinocheirus; was discovered in Late Cretaceous rocks from Mongolia, just like Deinocheirus; is known mainly from forelimbs and few other bits, just like Deinocheirus; entered the dinosaur list around the same time as Deinocheirus; and, last but not least, it is another candidate for “the biggest theropod” title, like Deinocheirus! But, unlike Deinocheirus, Therizinosaurus was not a giant ornithomimosaur — it was an even more bizarre animal.

Discovered in the 1950s but not recognized as a dinosaur until the 1970s, its forelimbs were slightly shorter but more powerful than those of the giant ornithomimosaur. But Therizinosaurus had an additional curiosity, one that made it even more awesome: three scythe-like claws on each hand (hence its name, “scythe lizard”), some as long as a human arm. In short, it had the biggest nails known so far within the entire Animal Kingdom. One of these oversized claws was in fact the first known remain, and for several years, scientists thought it belonged to a giant marine turtle.

With such poweful weapons, Therizinosaurus has received in the past the same treatment as Deinocheirus. Some old drawings went as far as to show our “scythe-dino” as a giant carnosaur or deinonychosaur with sickle-claws on each foot (if Therizinosaurus was really shaped that way, it would really have been the most Bad Ass dinosaur one can imagine…). More accurate analyses made in the beginning of the 1990s definitively debunked these fantasies: we now know with a good level of sureness that Therizinosaurus was a bulky-bodied, round-bellied, and quite slow-moving animal, that used its claws mainly to pull down branches. Furthermore, its jaws were arguably weak with a rounded horny tip and small grinding teeth similar to those seen in its relative Segnosaurus.

This obviously doesn't lessen its general coolness: even with this new shape, Therizinosaurus remains an odd-looking, powerful beast, and thanks its massive body, it might even be the biggest and heaviest theropod ever discovered, weighing even more than the famous Spinosaurus. Just like with Deinocheirus, we dino-fans are patiently waiting for new exciting remains of our "Wolverine Claws-osaurus" being excavated.

Meanwhile, a special spinoff of Walking with Dinosaurs from 2002 temporarily recreated our imagination in CGI: in the episode titled “The Giant Claw” Nigel Marven talks about Therizinosaurus, lampshading its whole Science Marches On story from a mighty carnivore to a Gentle Giant. Nigel is in Late Cretaceous Mongolia searching for the possessor of the eponymous “giant claw”, which the zoologist believes to have pertained to a fearsome predator. After goung through several adventures with other famous dinosaurs of the habitat (Protoceratops, Velociraptor, etc.), Nigel witnesses a fight between Therizinosaurus and Tarbosaurus: even though the former unexpectedly reveals itself to be a herbivore, it easily defeats the tyrannosaur by slapping it in the face with its scythe-claws, obligating the predator to flee. Finally, the therizinosaur licks Nigel’s face. Really!


Gigant-[ic] O-[vi]-raptor: Gigantoraptor

Most Oviraptor relatives were small-sized like their group's namesake, except one: Gigantoraptor. Discovered in Asia only in 2007, this dinosaur, despite its name, is not an overgrown dromaeosaur: its name means “gigantic thief” (an evident reference to Oviraptor).

Gigantoraptor grew up to 25ft in length, almost as big as the neighboring tyrannosaur Tarbosaurus, but with the anatomy of the classic oviraptorosaurs: and if their way of life was hard to decipher, imagine what kind of headscratching Gigantoraptor caused. It's all cool, though: three, generally small-sized lineages of non-avian coelurosaurs have at least one oversized member within their ranks: Deinocheirus the giant ornithomimosaur, Utahraptor the giant dromaeosaur, and Gigantoraptor the giant oviraptorosaur. On the other hand, tyrannosaurs and therizinosaurs include many gigantic species, while other coelurosaurs, such as the troodonts, have none. But who knows? Maybe one day a “Gigantroodon” would be discovered…

Together, Deinocheirus, therizinosaurids & Gigantoraptor make a strange case: such overgrown birdlike theropods seem an only-Asian affair, and nobody knows why similar animals have never been found in North America (considering the strong similarity of the two faunas in the Late Cretaceous). Maybe could the competiton with the exclusively American Ceratopsids have prevented North-american maniraptoriformes to reach larger size?

Despite being a very recent find, Gigantoraptor has already recevied some mild media attention, appearing in paleo-documentaries like Planet Dinosaur and Dinosaur Revolution. Its awesome-sounding name could even make it a new member of the Stock Dinosaurs in the future.
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