The second great division of Avetheropoda, Coelurosauria is beyond
any doubt the most diverse group of theropods, even without factoring in birds. There are giant superpredators (tyrannosaurids),
toothless racers (ornithomimids), two kinds of
sickle-clawed birdlike hunters (dromaeosaurids and troodontids), strange sloth-like herbivores with giant hand
claws (therizinosaurians), little animals with an
unknown diet and bizarre mandibles and sometimes head crests (oviraptorids and
elmisaurids, on the same page), and
some of the smallest known classic theropods (compsognathids). They all tend
to have relatively long arms, except for the tyrannosauroids which secondarily shortened
them, probably for weight reduction, and the alvarezsaurids,
who reduced their arms to powerful single-clawed stubs,
possibly for digging. All members of
Coelurosauria may have been feathered or derived from ancestors who had that
Tyrannoraptora has been named for the combination of Tyrannosauroidea and Maniraptoriformes, which corresponds in membership to my old Maniraptoriformes, back when I had Arctometatarsalia. An important historical development in Tyrannoraptora is the Tyrannosauroidea/Arctometatarsalia saga, wherein Tyrannosauroidea was introduced to Coelurosauria as a member of a larger grouping known as Arctometatarsalia, which also was to include ornithomimosaurians, elmisaurids, and troodontids. The key character linking these diverse groups was the third metatarsal's relationship with the second and fourth mts. In arctomets, the third metatarsal was pinched off at the top in front view. Later, it became clear that most groups of "arctomets" had acquired this condition convergently; this category includes the elmisaurids, which are closely related to the oviraptorids, the ornithomimosaurians, and the troodontids, which had been classified in a group with the ornithomimosaurians because they shared similar swellings in a bone of the braincase (Bullatosauria, or "inflated lizards"), but now appear to be closer to the dromaeosaurids. Tyrannosauroidea and Ornithomimosauria, or Ornithomimosauria and Alvarezsauridae, are about the only groups that people will occasionally still link as arctomets, but even these small versions of Arctometatarsalia are going by the wayside, as it becomes more and more evident that the arctomet was just a good anatomical idea that several different groups found at different times, or an idea present at the base of, say, Tyrannoraptora, that was further expanded upon or lost by the more derived groups (this second option seems better as we get more information on the basal members of those groups, something we didn't have before).
`--+ "Nexus of basal coelurosaurians"
Compsognathidae: Compsognathids are renowned as the smallest known adult classic dinosaurs, measuring somewhat over a meter in length fully grown in some cases (although their lofty status appears to be in doubt; see Microraptor). Compsognathids were small, fleet theropods with very long tails and reduced arms. Indeed, until the discovery of Sinosauropteryx's three clawed hands it was believed compsognathids had only two fingers per hand, a result of the ambiguous condition of the hands in Compsognathus specimens. These animals were small game hunters, as shown by the discovery of mammal and lizard remains in the belly region of several specimens.
Compsognathidae may be an artificial assemblage of a variety of small basal coelurosaurs, some of which may pertain to a true Compsognathidae, others to basal Tyrannosauroidea (it turns out that basal tyrannosauroids were not all that different from generalized basal coelurosaurs). It would be nice if we could get a good analysis of basal coelurosaurians in general, but then again it might not help much.
Material from the EK of Thailand may be referable to this family.
|Taxon or Taxa:||Time/Place:||Comments:|
|Huaxiagnathus orientalis Hwang, Norell, Ji Q., and Gao K., 2004||early Aptian (EK) of China||Based on two skeletons, including one very good nearly complete specimen, Huaxiagnathus (known as "Huaxiasaurus" in early reports), is a big compsognathid (well, big for a compy, with the subadult type at maybe 1.6 m long). The skull is also very large and robust for a compy, with a deep maxilla giving a very rectangular skull in side view. There are unusual blobs in the rib cage of the type specimen which could have been something it ate. Because of the preservation, no integument has been found, fuzzy or not.|
|?Sinosauropteryx prima Ji Q. and Ji S., 1996||early Aptian (EK) of China||This taxon, known from three virtually complete specimens
including possible stomach contents (lizards and mammals), unlaid eggs, and "protofeathers," is similar
in many ways to Compsognathus. Although most scientists
accept that the fibers seen on Sinosauropteryx have at least
something to do with feathers or "protofeathers," others claim
they are actually part of a soft ridge, like those seen on marine iguanas.
There is evidence that negates this, though (for
example, the fibers seem to cross each other often, and are found in
places where a ridge would not be present unless compsognathid anatomy is
quite a bit wilder than expected). Study of structures in the fibers
indicate that Sinosauropteryx had a banded tail of reddish brown
and white feathers, with reddish feathers over other parts of the body as
Of the original three specimens referred to this taxon, two (including the holotype) might not be compsognathids, instead being more like basal carnosaurians, while the third might be a compy. They had long tails, short arms, and big first digits on the hands.
|Mirischia asymmetrica Naish, Martill, and Frey, 2004||?Albian (EK) of Brazil||Well-known for several years as the undescribed Santana Formation compsognathid, or as its specimen number SMNK 2349 PAL, Mirischia's remains include a possible preserved air-sac and chunk of intestine, along with a pelvis, hindlimb material, and dorsal and sacral verts. Its species name comes from the fact that the two hips differ in prominent details that have often been considered taxonomically significant, but now, maybe not so much.|
|Compsognathus longipes Wagner, 1859||?Tithonian (LJ) of Germany and France||Compsognathus is known from most of two skeletons, one from Germany and a second, larger one from France (incidentally, this French Compsognathus was originally described as a different species, C. corallestris Bidar, Demay, and Thomel, 1972, that was believed to have had flippers, but this was shown to be incorrect). The type, a partially-grown individual, has the remains of a lizard in its belly region; other odd structures in the body could be eggs. The French specimen has disarticulated small reptile remains in its gut region as well. It has a long pubic boot with little forward expansion, similar to that of Coelurus, which is often missed in restorations (which are also typically done from the juvenile specimen).|
|Taxon or Taxa:||Time/Place:||Comments:|
|Aristosuchus pusillus Seeley, 1887 (originally Poikilopleuron [Owen, 1876])||late Barremian (EK) of England||Often confused with Calamospondylus, Aristosuchus
appears to be a valid compsognathid based on the structure of its pubis;
other remains may be referable. At a possible length of 2 m, it
would have been a rather large compsognathid.
Alternatively, it could be a basal tyrannosauroid, which are not that unlike compsognathids. There is a chance that the tyrannosauroid-like cervicals of "Calamospondylus" foxi (Calamosaurus) and the pelvis of Aristosuchus represent the same type of animal.
|?Juravenator starki Göhlich and Chiappe, 2006||latest Kimmeridgian (LJ) of Germany||After several years as the skull and
cervicals known as "Borsti," this compsognathid now sees the
light of day, and as a nearly complete skeleton, no less (the specimen was
in a block of limestone and CAT scanning revealed the rest of the body). Only the last third of the tail is
individual appears to have been a juvenile.
Unlike Sinosauropteryx, this animal had at least a featherless mid-tail with typically dinosaurian small pebbly scales.
It was found in what can only be described as an endearing death pose (except for one wonky leg): arms tucked in shyly, head turned so it appears to be looking over the shoulder, and an aesthetically-pleasing curve to the tail.
Some researchers have called the cladistic analysis in the description into question, but when all is said and done, this animal will probably still end up as a compy-like basal coelurosaurian of some stripe.
|Sinocalliopteryx gigas Ji S., Ji Q., Lü J., and Yuan C., 2007||early Aptian (EK) of China||Sinocalliopteryx was a large compsognathid (the largest known at the time of description), larger than Huaxiagnathus but rather similar. It is based on a complete skeleton, with filament-style integument and a dromaeosaurid leg in its abdomen (eaten, not left there by an amputee dromaeosaur). Another individual was fossilized after having indulged in confuciousornithid birds.|
"Nexus of basal coelurosaurians" (incertae sedis, of
course): There are
a number of interesting basal coelurosaurs that I'm not confident placing
anywhere specifically, and are not the run-of-the-mill tooth taxon or
what-have-you that usually makes up the i.s. sections.
A new basal coelurosaurian, based on two partial skeletons from the middle Turonian (LK) of New Mexico, is currently being described. Also, a possible basal coelurosaurian femur is known from the EK Wealden Formation, and a 7-8 meter long form has been uncovered in the LK of Argentina, with partial skeleton and skull.
|Taxon or Taxa:||Time/Place:||Comments:|
|Aniksosaurus darwini Martinez and Novas, 2006||Cenomanian-Turonian (LK) of Argentina||Aniksosaurus is a small but robust basal
coelurosaurian of uncertain affiliation. It is known from the
remains of at least five partially grown individuals found in a single small bonebed, with
no other animals. Five right tibiae at the discovery locality give
us the minimum number of individuals; either five were present, or this
animal was related to the six-legged turkeys seen around Thanksgiving on
football broadcasts. Other bones include a few vertebrae, arm bones,
and ilia. These individuals were probably around 2 meters long and 70 cm
tall at the hips. The name had been floating around since the mid
Interestingly, the remains were found in a volcanic tuff, which for the non-geology audience members is a former ash bed; thus, a volcano was going off when these five animals died. A volcano puffing away in the background is a cliché of kids' dinosaur books, but it fits here.
|Aorun zhaoi Choiniere, Clark, Forster, Norell, Eberth, Erickson, Chu H., and Xu X., 2013||Callovian (MJ) of China||Aorun is among the oldest known coelurosaurians. It is known from a partial skeleton of a young individual (less than a year old), found low in the Shishugou Formation that has also produced, mostly at higher levels, such theropods as the tyrannosauroid Guanlong, alvarezsaurid Haplocheirus, ceratosaurian Limusaurus, tetanuran Monolophosaurus, carnosaurian Sinraptor, and fellow basal coelurosaur Zuolong.|
|Bicentenaria argentinus Novas, Ezcurra, Agnolín, Pol, and Ortíz, 2012||Cenomanian (LK) of Argentina||Known from the partial remains of several individuals, Bicentenaria is an example of that class of small (~3 m scale in this case) basal coelurosaurians that don't quite fit with a larger group; a perfect "coelurid", for those of you born before 1985 or so.|
|Nedcolbertia justinhofmanni Kirkland, Britt, Whittle, Madsen, and Burge, 1998||Barremian-early Aptian (EK) of Utah||Known from three partial skeletons, Nedcolbertia is similar in many ways to Ornitholestes, but also is like the compsognathids.|
|Ornitholestes hermanni Osborn, 1903||Kimmeridgian (LJ) of Wyoming||Sometimes considered the same as Coelurus, but actually a much different theropod, Ornitholestes was once pictured as capturing early birds for food, hence the name. The type consists of a partial skeleton and most of the skull. Many recent illustrations picture it with a nasal horn, but further investigation of the type indicates that this was based on a broken and displaced nasal. Ornitholestes has a rather small head for its size, and unusually short lower limb elements suggest it may not have been as good of a runner as other small theropods. In some ways it is similar to allosaurids. It and Proceratosaurus (often its partner in crime during the 1990s and 2000s) are known for strong heterodonty; the teeth in the front of the skull differ from those behind them by being smaller and more conical in shape. Some researchers put Ornitholestes at the base of Maniraptora.|
|Santanaraptor placidus Kellner, 1999||Albian (EK) of Brazil||This new theropod is known from ischia, hindlimbs, and three caudals, with associated soft-tissue impressions. A small theropod, with a femur length of 13 cm, it seems to be a rather basal coelurosaurian, possibly related to Ornitholestes. It could be a basal tyrannosauroid; we'll see.|
|Scipionyx samniticus Sasso and Signore, 1998||Aptian (EK) of Italy||"Skippy," as it is known informally, is based on the small partial skeleton of a juvenile (?hatchling) coelurosaurian (characters uncertain due to youth and missing areas) that preserves traces of intestines, the trachea, muscle fibers, and other organs, the first ever classic dinosaur to have its remains show such soft parts. It is also the first named classic dinosaur from Italy. It could be a compsognathid, or something of that ilk.|
|Tanycolagreus topwilsoni Carpenter, Miles, and Cloward, 2005||Kimmeridgian (LJ) of Wyoming and Utah||This new Morrison theropod is based on most of a skeleton, including a partial skull and most of the limbs. Originally, it was thought to be a specimen of Coelurus, but the two have very different proportions. It would have been about 4 meters long when fully grown, and had a blunt snout. Overall, it was well-proportioned, unlike the hyper long-legged Coelurus or the shrunken-headed Ornitholestes. The Wandering Hand that was first attached to Ornitholestes, then to Coelurus, appears to belong to this animal, along with a premaxilla once referred to Stokesosaurus. Its interesting name had been known informally for several years before publication.|
|Tugulusaurus faciles Dong, 1973||Valanginian-?Albian (EK) of China||This small theropod is based on a fragmentary postcranial skeleton including caudals, both "thumbs," and partial hindlimbs. It has been suggested that it may be a chimera, with carnosaurian forelimb material mixed with coelurosaurian (possibly ornithomimosaurian) hindlimbs, but new research indicates that it is a valid if idiosyncratic basal coelurosaurian. Distinctive characters include the forward placement and posterior reduction of the caudal neural arches, and very short 1st metacarpal. It was originally regarded as an ornithomimosaurian.|
|Zuolong salleei Choiniere, Clark, Forster, and Xu X., 2010||Oxfordian (LJ) of China||Zuolong is another in the nexus of early coelurosaurs, known for their small size and generalized Compsognathus-Coelurus-Ornitholestes-like appearance. Zuolong is known from much of a skull, a sampling of vertebrae from across the body, a humerus, forearm, and thumb claw, a scapula, enough of both legs that you could put together most of one, and partial hips. The type individual was about 3 m long, although there are hardly any preserved neural arches, so it seems likely that there was still some growing to be done.|
Other Coelurosauria i.s. (mostly pretty scrappy):
|Taxon or Taxa:||Time/Place:||Comments:|
|"Arkansaurus fridayi" (N.N.) Sattler, 1983||EK of Arkansas||Originally described as a basal ornithomimid, this animal, based on a partial foot, may actually be closer to basal coelurosaurians like Nedcolbertia.|
|?Asiamericana asiaticus (N.D.) Nesov, 1995||Coniacian (LK) of Uzbekistan||This tooth genus has had a long odyssey from possible spinosaurid to possible fish to possible relative of Richardoestesia (which itself could be close to a lot of things). The name refers to the fact that similar undescribed teeth are known from North America.|
|?"Beelemodon" (N.N.) Bakker, 1997||?Kimmeridgian (LJ) of Colorado||This taxon is based on small teeth, which could belong to any of a variety of small Morrison theropods, showing a resemblance to those of most any basal coelurosaur, including compsognathids, basal oviraptorosaurians, and basal eumaniraptorans.|
|Calamospondylus oweni (N.D.) Fox, 1866||Barremian (EK) of England||Calamospondylus is a small theropod, based on a missing pelvis, different from that of Aristosuchus.|
|"Coelurus" gracilis (N.D.) Marsh, 1888 (?Deinonychus)||late Aptian-early Albian (EK) of Maryland||This indeterminate theropod is based on a hand claw similar to that of the contemporaneous Deinonychus.|
|"Dryosaurus" grandis (N.D.) Lull, 1911 (=Ornithomimus affinis Gilmore, 1920) (?Arkansaurus)||late Aptian-early Albian (EK) of Maryland||As one of my regular readers has pointed out,
the somewhat familiar "Coelosaurus" affinis is actually a
superfluous name for "Dryosaurus" grandis. Gilmore
coining the new species Ornithomimus affinis name when he
transferred the material from Dryosaurus to Ornithomimus,
which already had a species grandis
(note that it was not Coelosaurus when Gilmore named it, but that's
Assigned for a long time to Ornithomimidae, this animal may instead be a more basal coelurosaurian, possibly related to Nedcolbertia and "Arkansaurus".
|Euronychodon portucalensis (N.D.) Antunes and Sigogneau-Russell, 1991||late Campanian-early Maastrichtian (LK) of Portugal||This taxon, possibly related to the troodontids, is based on teeth similar to those of the ubiquitous Paronychodon.|
|"Euronychodon" asiaticus (N.D.) Nesov, 1995||Coniacian (LK) of Uzbekistan||Another Paronychodon-type critter, the geographic and temporal separation of this animal from Euronychodon proper reduces the chance it belongs in the same genus.|
|Paronychodon lacustris (N.D.) Cope, 1876||Campanian-Maastrichtian (LK) of Montana, Wyoming, and New Mexico||Based on odd, unserrated, and rather common teeth that some have suggested are the deformed teeth of other theropods, Paronychodon is a dubious theropod.|
|Richardoestesia: Currie, Rigby, and Sloan, 1990||R. gilmorei (type) Currie, Rigby, and Sloan, 1990||late middle Campanian (LK) of Alberta||Based on a toothy jaw once
referred to Chirostenotes,
which is now known to be toothless,
this animal could be some sort of basal coelurosaurian, and/or the same as
Paronychodon. A tooth
referred to R. isosceles may have something to do with the
seemingly nondinosaurian tooth genus Asiamericana, suggesting
possible Asian relatives.
I frankly don't know what to do with this animal. It's more of a tooth genus for a specific type of tooth than anything else (and "Richardoestesia" teeth litter the Upper Cretaceous rocks of North America, so it's downright annoying that the best we have for the rest of the skeleton is a partial jaw). It may have been a bug-eater. Odds are it's some kind of dromaeosaurid-like thing.
Richardoestesia has been the beneficiary of one of the odder nomenclatural disputes of the cladistic era of dinosaur research. It was supposed to have been Ricardoestesia, but an editor of the original document added an 'h" to all occurrences of the name save one use in a caption. Then it got inadvertently stuck in the revised spelling by a first reviser, people weren't sure which to use and got angry on Internet mailing lists, and eventually pretty much everyone decided that the version with the extra "h" should be used.
|R. isosceles Sankey, 2001||late middle Campanian (LK) of Texas|
|Timimus hermani Rich and Rich, 1994||Albian (EK) of Australia||When first described, this animal was thought to be an early ornithomimid. More recently, it was compared to the unenlagiine dromaeosaurids, and even more recently to the tyrannosauroids. It's only based on a femur.|
|Zapsalis abradens (N.D.) Cope, 1876||middle-late Campanian (LK) of Montana||This tooth taxon is usually synonymized with Paronychodon, albeit as a large individual. It could be a dromaeosaurid.|
|Taxon or Taxa:||Time/Place:||Comments:|
|Coelurus fragilis Marsh, 1879||Kimmeridgian (LJ) of Wyoming, Utah, and ?Colorado||Coelurus is known from a good chunk of a postcranial skeleton. This wasn't recognized until 1980, when a study stated that a second species, C. agilis Marsh 1884, was not only the same species but the same individual as the type specimen of C. fragilis. Before this, Coelurus was often confused with Ornitholestes. The type, from a young individual, shows a collection of interesting features, including very long hindlimbs and short but gracile forelimbs. A possible dentary fragment suggests a gracile skull as well. It, along with Tanycolagreus, could be on the line leading to tyrannosaurids.|
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