Small but with plenty of guts.
Here you'll find both very basal theropods like the coelophysids and more advanced kinds like the compsognathids and even some small tyrannosauroids. At one point, these were all called coelurosaurs ("hollow-tailed reptiles"), though that term now has a different meaning. As in most other Prehistoric Life pages you'll also find some animals which actually are or could be misplaced taxonomically speaking, but are there because scientists once believed they're related with the other examples in the page.
The most common in popular documentary works (other than Compsognathus and Coelophysis) include Ornitholestes, Coelurus, Noasaurus, Elaphrosaurus, "Syntarsus" (probably just more Coelophysis), Procompsognathus, Segisaurus and the alleged theropod Saltopus. In recent media, Guanlong and Scipionyx (the animal of the image) have gained notable consideration as well. Here you can see a (quite affected by Rule of Scary) close-up of Masiakasaurus.
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From Middle Jurassic to Cretaceous
Small but 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 samniticus from Southern Italy made waves when was discovered in 1995, and with reason. This tiny theropod (still a juvenile when it died), still-today of uncertain placement in the theropod family tree - in The New '10s was long believed a compsognathid, but now some even think is actually a juvenile allosauroid - was the very first dinosaur ever found with fossilized internal organs. The windpipe, intestines, feces, part of the liver, skeletal muscles, and even signs of muscle cells and bone cells, 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 rightly 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. And if it is not enough, Scipionyx also preserves evidence of its last meals: in this case several smaller reptiles and some fish. Some think the size of one of these reptiles indicates the baby was a nestling fed by its parents, but this cannot be proven. It had also some teeth longer than the others, and some originally speculated they were sorta "venomous fangs" but this is not accepted anymore (no venom channels are present in the teeth, see also Sinornithosaurus). Scipionyx samniticus means "Scipio's claw from Samnium" (all references to the location it was found), and it has preserved also keratinous sheaths around its small claws other than the inner bone. Its skeleton, the first of a nonbird dinosaur ever found in Italy (a country poor of dino-remains), was articulated and with the classic "death pose" with the head put fairly backwards, and is visible in the Nature History Museum of Milan, Italy, together with a life-size (featherless) model.
Sickle-Foot or Sickle-Hand?: Noasaurus
- Science Marches On has strongly involved a small basal theropod, Noasaurus from Late Cretaceous South America. Discovered in 1980, Noasaurus ("lizard from North-Western Argentina": N=north, O=west A=Argentina) was initially thought similar to dromaeosaurids and depicted with sickle-claws on its feet, making it the “southern dromaeosaur”. 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 (which was found 5 years later). One scientist suggested that both were late megalosaurs, but they are more likely ceratosaurs. The alleged Hook Foot of the noasaur has revealed a Hook Hand, almost like a miniaturized Megaraptor.
Protruding Teeth: Masiakasaurus
- This was confirmed by the more complete skeleton of one close Noasaurus relative described in 2001, Masiakasaurus from Madagascar: this one has revealed its unique protruding teeth, whose purpose remains uncertain - some think it used them to catch fish or insects. Recently, the famous Giant Dromaeosaur Utahraptor has also revealed a dentition similar to Masiakasaurus. Other noasaurines include Velocisaurus ("fast lizard", not that Veloci) and the recently-discovered (2019) Vespersaurus that uniquely ran on only one toe for each foot. These two were all from South-America like Noasaurus and unlike Masiakasaurus. The subfamily might include also the Indian Compsosuchus (known only from neck vertebrae once thought to come from a giant allosauroid), the Madagascan Dahalokely (an unusually robust form), the Patagonian Austrocheirus, which had larger hands than most other ceratosaurs, and tiny Ligabueino also of Patagonia, one of the smallest known nonbird theropods (70 cm long, but could be a juvenile).
Hard-to-classify Theropods
- From Late Cretaceous India comes Jubbulpuria, a late-surviving small ceratosaur of uncertain classification. Laevisuchus ("light-weighing crocodile") also from Late Cretaceous India is known from a single vertebra, and was originally believed an oviraptorosaur: now is believed a noasaurid of uncertain classification. Both lived along with much bigger theropods, Carnotaurus relatives like Indosaurus, and could have become their prey in life. From Australia comes Kakuru, another small theropod of Early Cretaceous whose one remain, a shin, was transformed in opal (a kind of gemstone) during the fossilization. It lived alongside the ornithischians Muttaburrasaurus, Leaellynasaura and Minmi. Several other possibly non-maniraptoran coelurosaurs have been described since the 1990s, such as Bagaraatan from Late Cretaceous Mongolia (possibly a late-surviving primitive tyrannosaur), Nedcolbertia from the Early Cretaceous of the U.S. (an unusually long-legged form, possibly a basal ornithomimosaur), Lourinhanosaurus from Late Jurassic Portugal, long thought to be a megalosaur or allosaur, and Xinjiangovenator from Early Cretaceous China: maybe the same animal as "Phaedrolosaurus", known only from a tooth — the latter was originally believed a large dromaeosaurid, the size of Deinonychus.
Losing Teeth Twice: Elaphrosaurus
- Few other dinosaurs have had such an intricated Science Marches On story than Elaphrosaurus (sometimes misspelled "Elaphosaurus"). This medium-sized, slender-framed theropod (meaning “light lizard”) is known from one skeleton found in the famous Late-Jurassic Tendaguru site in which Giraffatitan (the universally-known “Brachiosaurus”) has been discovered, while other poor remains found in North America and Cretaceous Northern Africa formerly classified as Elaphrosaurus actually don't belong to it — the African ones are now called Spinostropheus. Rightly, the elaphrosaur has usually been shown in dino-sources living along with Giraffatitan in Late Jurassic Africa. The problem is, the skull of the original proper elaphrosaur is not preserved, and we don’t know if it was toothed or toothless. It was in the past often thought a late-surviving coelophysoid because of the shape of its skeleton, and in old paintings it was depicted Coelophysis-like and toothed. Then, scientists proposed Elaphrosaurus was the ancestor of the ornithomimosaurs, and often 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 discovery in The New '10s of Limusaurus, a close relative from China whose skull is quite reminiscent of an ornithomimid's, has shuffled the cards again: now it’s possible Elaphrosaurus really looked like an ostrich-dinosaur, in spite of not being closely related at all. In 2015 a theropod very similar to Limusaurus was found, Chilesaurus, but has revealed was closer to the great megalosaurs & allosaurs. Today Elaphrosaurus and its relatives are classified as Elaphrosaurines, the other subfamily of the Noasaurids other than the Noasaurines. Elaphrosaurus is the biggest-known noasaurid, being up to 6 m long like a Ceratosaurus or a Dilophosaurus, but much slenderer and more fragile than both.
A Successful Name: "-coelurus"
- After Archaeopteryx, Coelophysis, and Compsognathus, the couple Coelurus - Ornitholestes makes the fourth most portrayed Jurassic/Triassic small theropods, despite their scanty remains. This because both lived in Late Jurassic North America alongside many stock dinosaurs like Allosaurus, Stegosaurus, and Apatosaurus, and both were described more than a century ago: thus, they have often been depicted in many old and recent paleo-art — although often confused with each other in the past. Both were slender animals the same length/size of the Real Life Velociraptor, and with a rather inconspicuous appearance. Within their habitat, Coelurus and Ornitholestes arguably played the role of the “small cunning predators” (while Allosaurus and Torvosaurus were the top predators and Ceratosaurus was between the two extremes). 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. Found during the Bone Wars, the incomplete skeleton of Coelurus was the first small theropod remain discovered in USA, a bit later than Compsognathus in Europe. Its full scientific name is Coelurus fragilis, "fragile hollow tail" — recalling that of the contemporary Allosaurus fragilis. Despite its scantiness, the coelurus has had a great historical relevance. As soon as the XIX century, Coelurus gave its name to the Coelurosaurs, aka all small/slender theropods, countered against the Carnosaurs aka large/robust theropods such as Tyrannosaurus rex. "-coelurus" has even become a suffix itself for a bunch of small theropods like Sinocoelurus, Thecocoelurus, and Chuandongocoelurus, or even a prefix: Coeluroides and the non-dinosaur Coelurosauravus (meaning "ancestor of coelurosaurs")!
Carnosaurs and Coelurosaurs
- In the very first classifications, carnosaurs & coelurosaurs were not originally thought to be closely related (with carnosaurs being closer to sauropods), but most later studies indeed believed distinct lineages of theropods, arisen independently in the Triassic and evolved through the epochs until the end of the Cretaceous with a succession of animals like these: COELUROSAURS: Coelophysis —> Compsognathus —> Dromaeosaurids & Ornithomimids; CARNOSAURS: Ornithosuchus (at the time the 4 m long "crocodilian" Ornithosuchus was believed the ancestors of carnosaurs because of its bipedal stance)—> Megalosaurus —> Allosaurus —> Tyrannosaurus. Then, in the 1970s, "coelurosaurs" was restricted to the most generic & primitive small theropods (the subject of this page), while the most recent & specialized sickle-clawed and toothless coelurosaurs were separated in three new groups: Deinonychosaurs (dromaeosaurids + troodontids), Oviraptorosaurs (oviraptorids & relatives), and Ornithomimosaurs (ornithomimids & relatives). The modern meaning of "coelurosaur" was created only in the 1980s after the rise of the new cladistic method of classification; since then, coelurosaurian dinosaurs have re-included deinonychosaurs, ornithomimosaurs & oviraptorosaurus and (ironically) exclude several traditional members of the group like Coelophysis as well as the ceratosaurians Elaphrosaurus and Noasaurus. But the most revolutionary change is another: the former carnosaur Tyrannosaurus rex has been reclassified as an overgrown coelurosaur. In short, big & small theropods were not distinct lineages: big meat-eaters originated independently across the Mesozoic from several distinct small-sized ancestors, and are too different among each other to make a natural lineage. A 2007 analysis seems to indicate Coelurus may have been a basal tyrannosauroid, along with a recently discovered larger-sized relative from the same habitat, Tanycolagreus. These two may form to form the group Coeluridae, which was once treated as a "wastebasket" family including Coelurus, Ornitholestes, and dozens of undetermined small theropods like Calamospondylus, Inosaurus, Jubbulpuria, Kakuru, Ngexisaurus, Ornithomimoides, Teinurosaurus, Tugulusaurus etc. However, even this reduced Coeluridae may not exist; instead, Coelurus may be closer to maniraptorans, with Tanycolagreus as a very primitive coelurosaur or staying with tyrannosauroids.
Ornithomimus Ancestor?: Nqwebasaurus
- Elaphrosaurus was once believed the Jurassic ancestor of the ornithomimosaurian dinosaurs; a possible true ornithomimosaur was found in 2000 in the same continent of the elaphrosaur, but was initially believed a generic toothed small theropod: the African-sounding Nqwebasaurus, which is also considered the oldest known coelurosaur from the southern continents. Unusually found in Early Cretaceous South Africa (dinosaurs from southern Africa are usually Triassic or Early Jurassic), Nqwebasaurus is interesting because the specimen, a juvenile 3 ft long, shows some traits carnivorous and other herbivorous: it had an opposable thumbclaw on each hand, reduced teeth, and the stomach cavity contains gastroliths aka small stones, a trait usually associated with plant-eaters; all this means it could be an intermediate form between early typical theropods and the toothless ornithomimids living in Late Cretaceous.
The First Tyrannosaur Ancestor?: Proceratosaurus
- Before the Early Cretaceous Yutyrannus, Eotyrannus, & Dilong, there were Proceratosaurus and Stokesosaurus other than Guanlong among Jurassic tyrannosaurs. Both the European Middle Jurassic Proceratosaurus and the North American Late Jurassic Stokesosaurus were primitive tyrannosaurs named years before all their Chinese relatives. Discovered in Utah in 1974 by William Lee Stokes (for whom the genus was named) and his assistant James Madsen, Stokesosaurus was one of the first of the Jurassic tyrannosauroids to be found; it's only known from hip elements, but those hip elements have enough to distinct it from other Late Jurassic theropods from the same fauna. Interestingly, Stokesosaurus was found in the Cleveland-Lloyd Dinosaur Quarry in Utah, the same place in which the huge Allosaurus graveyard comes from. Proceratosaurus and Stokesosaurus are today classified in the Proceratosaurid family of tyrannosaurs: because of their scrappy remains, it's hard to get a clear image of what they looked like. Proceratosaurids likely differed from more evolved tyrannosaurs in a plethora of ways: for one, their skull would not be as large or tall. For another, their arms would have been fairly elongate with three functional fingers, each tipped with a claw. Their legs would probably have been quite elongate and gracile, unlike those of later tyrannosaurids, and their neck was longer than other tyrannosaurs. And, considering their relative Guanlong, they may have sported some kind of cranial crest - indeed Proceratosaurus has a small crest on its nose, hence its name "before Ceratosaurus". The fact that the former "Stokesosaurus" species Juratyrant lacks a cranial crest could point to it not existing in Stokesosaurus proper, either. Stokesosaurus likely wasn't the most powerful predator on the block in its time; as it lived in the Morrison Formation, it was living alongside Ceratosaurus, Marshosaurus (a megalosauroid probably basal respect to more evolved relatives, that owes its name to famous dino-hunter Othniel Marsh), Torvosaurus and Allosaurus; all of whom were at least slightly bigger than Stokesosaurus. While Proceratosaurus lived in Europe together with much larger megalosauroids/allosauroids, like Megalosaurus, Metriacanthosaurus, and Eustreptospondylus: like the latest two, it was originally put in the notorious "Megalosaurus wastebin". Even though the earliest tyrannosauroids got eclipsed, their lineage would have the last laugh in the predatory dinosaur rush; the descendants, tyrannosaurids, became the top predator in North America and Asia for most of the Cretaceous Period, pushing out the other large predators before being wiped out in the Cretaceous/Palaeogene extinction 66 million years ago.
Squirrel-Dinosaur: Sciurumimus
- Recently, the famous Late Jurassic Germany fossil sites, the same from which Archaeopteryx and the original Compsognathus come from, gave us two exquisitely preserved animals that may be juvenile megalosauroids, but are placed in this page because of the size of the specimens, only few feet long from nose to tail, as well as the uncertainty surrounding their true affinities. The best-preserved one was announced in 2011 — incidentally, the same year of Yutyrannus: named Sciurumimus ("squirrel mimic": "Sciurus" is Latin for squirrel), this is a reference to its bushy tail covered in filamentous structures which recalls a bit that of the eponymous rodent. The interesting this is: if Sciurumimus is a megalosauroid, it pushes the origin of feathers very far back, if not as far back as Tianyulong.
Feathers or Scales?: Juravenator
- The other is Juravenator ("Jurassic hunter"). Described in 2006, it was first described as a compsognathid, but may be close to Sciurumimus instead. Despite the recentness of its finding, it has already had a complex Science Marches On story. As its tail seems showing signs of scales, it was initially described as a traditionally-scaly theropod, giving fuel to those that still are doubtful about the dinosaurian origins of birds. But recent research has shown that true proto-feathers are also present. The most surprising thing is, this was only revealed under ultraviolet light. According to a recent hypothesis all the theropods traditionally put in the Compsognathid family (Compsognathus and a few others) are actually all juveniles of other genera of bigger theropods, and the compsognathid family should be discarded as artificial; but this is an extremely controversial theory.
From Early Jurassic to Triassic
The Other Compy: Procompsognathus
- 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 as one might believe: it was a small coelophysoid, maybe more primitive than Coelophysis itself. A skull once assigned to it likely came from a non-dinosaurian archosaur. The confusion with Compsognathus carried over into Jurassic Park; the novels explicitly mention Procompsognathus while the movies appear to use Compsognathus.
Big Unbreathing Lizard: Megapnosaurus
- Scientific names are a route full of hurdles. It’s almost unbelievable how many living or extinct animals have been described so far (more than 100,000 genera, 90% of which are insects!). Thus, it's not surprising that sometimes scientists make the mistake of giving their newly described animals already used names. This is what happened to Syntarsus rhodesiensis, a coelophysid that lived in Early Jurassic Southern Africa. In the 2000s, an entomologist discovered the name “Syntarsus” was preoccupied by a living insect (more precisely a beetle), and changed it to Megapnosaurus: “big unbreathing lizard”, under the mistaken impression that the dinosaur's original discoverer had died. Science Marches On however, and most scientists considered until recently "Megapnosaurus" just a late surviving, Early Jurassic species of Coelophysis. Whatever the name, this dinosaur has the distinction to be the first non-avian dinosaur ever depicted with feathers (in 1975, few years before the description of Avimimus), in a time when this hypothesis was only speculation. Ironically, we don't know if this animal was really feathered; if it was, certainly it didn't have true feathers as shown in the depiction of the 1975, but simple downlike fibers or something else. Some remains found in Early Jurassic North America showing a small double-crest similarly to Dilophosaurus were originally labeled as a distinct species of Syntarsus in respect to Syntarsus rhodesiensis: "Syntarsus kayentakatae". Today, it's controversial if it was a late-surviving Coelophysis, the North-American species of Megapnosaurus, or a brand-new genus closer but smaller than Dilophosaurus given the headcrest.
Early Wishbone: Segisaurus
- Other examples of much smaller coelophysids were the Early Jurassic Segisaurus and Podokesaurus, and the Late Triassic Camposaurus, all from North America — at present, the latter is the oldest named dinosaur from that continent. Segisaurus is interesting because, together with Archaeopteryx and Oviraptor, was one of the first non-bird dinosaurs to have revealed a wishbone - a typical bird trait - in a time dinosaurs and birds were still thought not related at all. Later, remnants of wishbones were found in other theropods, Coelophysis among them. Podokesaurus holyokensis was described in Eastern North America at the start of the XX century by Mignon Talbot, making it the first non-bird dinosaur officially named by a woman-researcher. Sadly, its skeleton got destroyed by fire; some think it's a juvenile Coelophysis. Camposaurus was maybe an early specimen of Coelophysis too; it has not to be confused with the Iguanodon relative Camptosaurus, which was much larger and lived well after it.
Hopping Foot: Saltopus
- One of the very first theropods ever lived (but only if herrerasaurians and Eoraptor were not proper theropods), Procompsognathus lived in the Triassic Period in Europe together with Plateosaurus. Another alleged theropod from Triassic Europe was once believed the most ancient dinosaur of this landmass, and was smaller than Procompsognathus both in its size and in its name: Saltopus. A rare Scottish specialty (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. Both Procompsognathus and Saltopus were found at the start of the twentieth century. Saltopus was often 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.
Bird-Ancestors?: Protoavis & "Proavis"
- 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 thought it was older but more advanced than Archaeopteryx). 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 mix-up 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 (thecodonts like Euparkeria or Saltoposuchus), the similar name “Proavis” (“before birds”) was invented for an imaginative missing-link between thecodonts 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, the "proavis" was really found... in the shape of the four-winged Microraptor.
