Prehistoric Life/Dinosaurs/Other Small Theropods

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/wiki/Prehistoric Lifework

Bird thieves, or what? Ornitholestes and Coelurus

• After Coelophysis and Compsognathus, the couple Coelurus - Ornitholestes makes the third most portrayed Jurassic/Triassic theropods, despite their scanty remains. This because both lived in Late Jurassic North America alongside many stock dinosaurs like Allosaurus, Stegosaurus, and Apatosaurus, and thus are often depicted interacting with them. Both were slender animals the same length/size of the Real Life Velociraptor, and with a rather incospicuous appearance. Within their habitat, Coelurus and Ornitholestes arguably played the role of the “small cunning predators” (while Allosaurus and Ceratosaurus were the top-predators). Although there are no evidences, their preys were possibly lizards, mammals, frogs and insects, and sometimes, also ate the eggs and hatchlings of bigger dinosaurs. In the “Time of the Titans” episode of Walking with Dinosaurs we can see some Ornitholestes behaving in such a way. In many paleo-artistic works Ornitholestes has been shown behaving like a jackal, tearing chunks of flesh from the kills of Allosaurus or Ceratosaurus and fleeing safely from these larger predators. Whatever the case, it is usually shown as a solitary hunter – justified, as the only known Ornitholestes skeleton was found alone. Coelurus was often confused with Ornitholestes in the past, and arguably behaved in a similar way above. First found during the Bone Wars, Coelurus was the first small theropod discovered in USA, and has had a great historical relevance. As soon as the XIX century, Coelurus was chosen as the prototype of the Coelurosaurs, aka all small/slender theropods - the well-known modern meaning was created only few decades ago. Ornitholestes was found a bit later, at the beginning of the 20th century. Its name, “bird thief”, was given because it was though a specialist predator well-adapted to grasp “first bird” Archaeopteryx with its prehensile hands. Such a thing would be not technically impossible, being the two animal contemporary as well… only, the “proto-bird” lived in Europe. In many modern portraits, Ornitholestes used to be shown with a horn-like crest on its nose, seen even in Walking with Dinosaurs; however, we know now that it didn’t have this feature. Walking With also added some speculative erectile quills on its neck: though not demonstrated, these might be possible, especially as Ornitholestes has recently been classified as a bird-like maniraptoran in some analyses (albeit still of uncertain placement within the clade). The link with maniraptors is furtherly renforced by one usually-skipped detail: Ornitholestes had a retractable toe similar to that of deinonychosaurs and early birds. About Coelurus, a recent analysis seems to indicate it may have been a basal tyrannosauroid, along with a recently discovered larger-sized relative from the same habitat, Tanycolagreus.

False relationships: Elaphrosaurus and Noasaurus

• Few other dinosaurs have had such an intricated Science Marches On story than Elaphrosaurus. This medium-sized, slender-framed theropod (meaning “light lizard”) is known from one skeleton found in the famous Jurassic Tendaguru site in which Giraffatitan (the universally-known “Brachiosaurus”). The problem is, its skull is not preserved, and we don’t know if it was toothed or toothless. In old paintings, it was depicted Coelophysis-like and toothed. Then, scientists proposed Elaphrosaurus was the ancestor of the ornithomimosaurs, and depicted it toothless. In the nineties, when theropod classification was strongly improved, Elaphrosaurus was recognized as a much more primitive animal related with Ceratosaurus, and still is today: this caused its mouth to return toothed. However, the very recent discovery of Limusaurus, a close relative whose skull is quite reminescent of an ornithomimid's, has shuffled the cards again: now it’s possible Elaphrosaurus really looked like an ostrich-mimic dinosaur, in spite of not being closely related at all. Science Marches On has also involved another small basal theropod, Noasaurus from Late Cretaceous South America. Initially, Noasaurus was thought similar to dromaeosaurids and depicted with sickle-claws on its feet, making it the “southern dromeosaur”. However, more careful researches showed Noasaurus was far more archaic than a “raptor”: even though hard to believe, it was closely related with its neighbour Carnotaurus. While its alleged Hook Foot has revealed a Hook Hand, like a miniaturized Megaraptor. One close Noasaurus relative, Masiakasaurus from Madagascar, has revealed its unique protruding teeth, whose purpose remains uncertain - some think it used them to catch fish.

Tyrannosaurs went a long way: Guanlong

• Well, it’s true. The undisputable charm of T. rex is also due to the long travel it made to become the Ultimate-King. Tyrannosaurs were already around in the Jurassic, but were still small, uncospicuous animals similar to an Ornitholestes or an Elaphrosaurus in shape. But this is an extremely recent knowledge, confirmed as recently as in 2006. The merit belongs to a very undinosaur-sounding dinosaur: Guanlong. Today, Guanlong may be the most famed dinosaur with “long” (in Chinese means dragon). The trend to call Chinese dinosaurs with this suffix has started only in the early 2000s; since then “dino-long”s have become more and more common, with at least one new-entry for every year. Easily recognizable thanks to its bizarre helmet-like crest, the 10-ft-long Guanlong lived in Late Jurassic; despite its vaguely Coelophysis-like look, Guanlong was the most ancient tyrannosaur known in 2006. In the last years has lost the record in favor of Proceratosaurus (a Middle Jurassic European theropod known for a century from a partial skull with a horn on the nose); however, the sensationalism which surrounded the fact “the first The First Tyrannosaur!” soon gave it a great attention in media. Guanlong appeared as the protagonist of one documentary appositely dedicated to it (a very rare honor for such a recently-discovered dinosaur); and was also portrayed in the third movie within the Ice Age series in place of the stock dromaeosaurids. Could it become a stock dinosaur in the next future?

A dinosaur with plenty of guts: Scipionyx

• When talking about dinosaur fossils, our mind immediately thinks “bones”. Sometimes, also skin prints, footprints, and petrified eggs. And then, the rare “mummies” with hardened muscles like the famous hadrosaurian ones. But things such as hearts, guts, livers, lungs, kidneys, are not usually heard about; this because the preservation of soft tissues and internal organs in vertebrates in an extremely rare event. So, the Early Cretaceous Scipionyx from Italy made sensation when was discovered in 1995, and with reason. This tiny theropod (still a juvenile when it died), now known to be a compsognathid, was the very first dinosaur ever found with fossilized internal organs. The windpipe, intestines, liver, and muscles, all these were preserved in the fine limestone which has preserved the usual bones as well. Since the relative positions of dinosaurian organs could only be guessed before Scipionyx, this has been celebrated as one of the most important discoveries within the whole paleontological science. As for now, no other prehistoric dinosaur has left such complete remains of internal organs. Like many other compsognathid specimens, it also preserves evidence of its last meals: in this case several smaller reptiles and some fish.

Big dead lizard: Megapnosaurus (once called "Syntarsus")

• Scientific names are a route full of hurdles. It’s almost unbelievable how many animals (living or extinct) have been described so far. Thus, it's not surprising that sometimes zoologists make the mistake to call their new-found animals with names already-in-use. This it what happened to Syntarsus, a close relative of Coelophysis that lived in Early Jurassic Southern Africa, with some remains also found in North America. In the 2000s, an entomologist discovered the name “Syntarsus” was preoccupied by a modern-day insect, and changed it to Megapnosaurus (“big dead lizard”). Many dino-fans complain about this change, to the point “Megapnosaurus” has become one of the least-beloved dinosaurian names… Science Marches On however, and if Megapnosaurus is just a late surviving, Early Jurassic species of Coelophysis, this name will become invalid as well. Whatever the name you prefer, this dinosaur has the distinction to be the first non-avian dinosaur ever depicted with feathers (in 1975), in a time when this hypothesis was only speculation. Ironically, we don't know if this animal was really feathered; the closer to birds Ceratosaurus and Carnotaurus show extensive areas of scales and/or bony scutes in the back, so it may be unlikely. Other examples of much smaller coelophysoids were Segisaurus and Podokesaurus, both from North America.

The other compies: Procompsognathus and Saltopus

• Procompsognathus lived in the Triassic Period in Europe together with Plateosaurus. It shared with Compsognathus the same overall shape, the same size (about 4 ft long), the same country (Germany) and a very similar name (“before Compsognathus”). Despite all this, Procompsognathus was not related to its Late Jurassic namesake, nor was it its direct ancestor at all: it is usually thought to be a small coelophysoid, but could also have been a non-dinosaurian archosaur. In 1990, Procompsognathus has gained notoriety thanks to its apparition in the first Jurassic Park novel, depicted as a scavenger which paralyzed its victims with a totally speculative venomous bite. This is indeed the original "Compy" in the Jurassic Park world. Before, Procompsognathus was an obscure animal, as is lampshaded in the novel itself – with Alan Grant thinking the drawing made by the child who saw the “compy” alive was not fake, just because “even dino-lovers don’t know Procompsognathus”. However, seven years later, Spielberg decided to play straight Stock Dinosaurs and chose the more familiar Compsognathus in the same role in Jurassic Park 2. Considering that the “procompy” is known from much scantier remains than the usual 'Compy', this might be partially justified. Another alleged theropod from Triassic Europe is Saltopus. A rare Scottish speciality (almost all British dinosaurs have been found in southern England), being merely 2 ft long, Saltopus was sometimes referred as “the smallest dinosaur” in old books (when Compsognathus wasn't already), but now it seems to be only a non-dinosaurian dinosauromorph. Not to be confounded with Saltoposuchus, a tiny crocodilomorph from Triassic Europe also common in old books because was once thought the common ancestor of dinos, birds and crocs.

The other first-bird: Protoavis

• Yes, Archaeopteryx was not alone. There was also "Protoavis". Discovered in 1990, this very incomplete Triassic fossil from Texas has originated much discussion among paleontologists: Its describer thought that it, and not Archaeopteryx, was the true "first bird", basing this upon some skeletal features. He chose to name its “sensational” find Protoavis, which just means “first bird”. Not surprisingly, our animal has often been mentioned in books and documentaries in those years, even portrayed with small imaginary “wings” on its forearms. However, its legacy with birds is now heavily contested if not totally discredited. This alleged “protobird” is more probably a primitive theropod, a basal saurischian, or a non-dino archosaur, and it was likely described from a mixup of dinosaurian and non-dinosaurian bones, thus not even a real animal. But others still think "Protoavis" really contains the bones of an early bird-relative, perhaps the most ancient coelurosaur known. (Nonetheless, it almost certainly wasn't an actual bird.) There is also a Hilarious in Hindsight detail about the “first-bird” argument. Many decades before the discovery of "Protoavis", in a time when birds were still thought to have directly descended from a bipedal archosaur (the aforementioned Saltoposuchus), the similar name “Proavis” (“before birds”) was invented for an imaginative missing-link between Saltoposuchus and Archaeopteryx. This critter was depicted as a tree-climbing animal with small wings and capable to glide from a tree to another, but still not capable to fly actively. Then, in year 2000, somewhere in the Chinese province of Liaoning…