DINSAUROMORPHA |--ORNITHISCHIA `--+--SAUROPODOMORPHA | Theropoda |--Ceratosauria `--Tetanurae |--Torvosauroidea `--Avetheropoda |--Carnosauria `--Coelurosauria |--Tyrannosauroidea `--Maniraptora |--+--Oviraptorosauria | `--Therizinosauroidea | |--Beipiaosaurus | `--+--Alxasaurus | `--Therizinosauridae `--+--+--Troodontidae | `--Dromaeosauridae `--AVES
This is the teaching of Maryanska et al. (2002). This view has, thus far, met with a rather chilly reception among dinofolk. On initial reading of the paper, one may be suspicious. A number of key taxa, particularly alvarezsaurs, are scored, but not used in the analysis. Further, there is no comparison with neornithines or any other birds closer to neornithines than Confuciusornis. However, a little work suggests why. If neornithines are entered into the data matrix used by the authors, and the omitted taxa are included, the results are extremely strange. The overall topology is this:
Maniraptora |--Alvarezsauridae `--+--Therizinosauria `--Aves |--Archaeopteryx `--+--+--Troodontidae | `--Dromaeosauridae `--+--Oviraptorosauria `--+--Confuciusornithidae `--Neornithes
Just as confusing, Avimimus and Caudipteryx are basal oviraptors. Undoubtedly, at some point, this will all be explained. After flirting briefly with this topology, we have returned to a more conventional view. ATW031103.
Oviraptor is frequently cited as an example of a bird-like dinosaur. Yet, for some reason, typical life reconstructions have missed one potential bird-like feature. The front surfaces of both jaws clearly show the typical rough, pitted markings of horn-like keratin material, quite possibly a beak. There is no reason to assume that the shape of the structure conformed closely to the shape of the bone. See, for example, the illustration at Oviraptor. While very good art, the bull-dog like cropped face that it shows would lose most of the nutritional value from whatever those odd jaws were designed to crack: nuts, eggs, fruit, or delicious crunchy lizards. Whatever it was, the good stuff would flow freely out the sides. What use is half a mouth? Would selection really favor an eye that was so close to things with sharp edges, whether egg shells or claws? Bone makes a very effective device for crushing and cutting. It would be completely superfluous to cover it with a layer of keratin merely to assume the same shape and function. It is more plausible to invent a long, tough curved beak from thin air (for, as usual, the keratin has dissolved without leaving fossil evidence) than to imagine otherwise.
Another problem with the available life reconstructions starts from the position of the arms girdles. Ingenia is a miniature (1.5 m) version of Oviraptor without some of the cranial bells and whistles. The body structures are very much the same. The Nakasota specimen shows a bony sternum (breast bone) like a bird. Above and/or in front of the sternum are the coracoid bones of the arm girdle, and above those the fused clavicles (furcula). The whole thing makes a rather neat package for both muscle attachment and at least some level of protection. The problem, when one does this, is that the big scapulas don't line up in a pretty way with the ribs and the vertebral column. See the close-up. Note how the scapulas stick up and away from the rib cage in the upper corners of the picture. Part of the problem here is that the anterior part of the spine may have been mounted too low (see the lateral view) for reasons that are not clear. Even so, Ingenia would have had remarkable shoulder blades.
A partial solution might be to give the beast a more vertical stance, leaning somewhat forward from the "shoulders." The clawed arms reach up in a natural position to protect the neck. The back bows outward and back, the neck swings forward somewhat, and the coracoids are raised slightly, which forces the scapulas to lie more closely with the body wall. This seems as if it would make reasonable fighting-threatening stance, with the chest armor facing the adversary. Running (and Oviraptorians would seem likely runners), the body assumes the forward, less balanced posture in which it is normally shown.
Maniraptora: Maniraptoriforms closer to Daffy Duck than to Ornithomimus. Padian et al. (1999).
Range: Early Cretaceous-Late Cretaceous of China & North America. Birds > bird mimics, i.e. Neornithes > Ornithomimus. Holtz (1996a).
Phylogeny: Maniraptoriformes: (Ornithomimosauria + Tyrannosauridae) + *: (Oviraptorosauria + Therizinosauroidea) + ((Troodontidae + Dromaeosauridae) + Aves).
Characters: $ prefrontal reduced or absent; distal 3/4 of tail stiffened; $ enlarged sternum; $ furcula present (? plesiomorphy?); $ lateral shoulder joint; $ arm 75%+ of presacral vertebral length; $ bowed ulna; enlarged semi-lunate carpal; $ enlarged manus digit 3; laterally flattened hand claws(?); some groups with retroverted pubes; no anterior expansion of pubic boot; $ ischium <2/3 length of pubis; distal obturator process on ischium; anterior trochanter near or confluent with proximal end of femur; hyperextendable second digit of the foot, with enlarged ungual; feathers with vanes (?!).
Links: DD: Maniraptora; Maniraptoran Dinosaurs!; Avimimus; Selected Synapomorphies; theropods; maniraptora; Case for Maniraptorid Tyrannosaurs; A New Dinosaur Specimen With Feather-like Structures; Evolution, dinosaurs, BAND, BAMM, BCF, 2F, Cladistics, Birds, Secondary, Flightlessness, Archaeopteryx; The Theropod Ancestry of Birds; taxonomy; Coelurosauria - Paleontology and Geology Glossary.
Image: "Avimimids and Troodontids" © 2000 by Dan Bensen and reproduced by permission. Key: from top left to bottom center: Avimimus portentosus, (Kakuru kunjani), Sinornithoides youngi, Byronosaurus jaffei, (Borogovia gracilicrus), Troodon formosus, (Tochisaurus nemegtensis), Saurornithoides mongoliensis, (Saurornithoides asiamericus), (Saurornithoides isfarensis), (Saurornithoides junior). Parentheses indicate reconstructions based upon scanty evidence.
Notes: The membership of this group, as well as its characteristics, is fairly unclear. No authority supports the trichotomy used here as the sister of Paraves. This is simply a compromise between a number of possible arrangements.
Oviraptorosauria: Oviraptor. LCA Oviraptor + Chirostenotes.
Range: Early Cretaceous(?) to Late Cretaceous of China & North America.
Phylogeny: Maniraptora:: Therizinosauroidea + *.
Characters: Small to medium (1-4 m) sized, lightly built, with a bizarre jaw. $ deep skull; skull strongly fenestrated; $ jaws toothless, forming large base for attachment of presumed horny beak; jaws deep & short; nares high; orbits fairly large; cranial domes or crests in some species which may have had additional horn sheaths; infratemporal fenestra large & square [M+02]; foramen magnum larger than occipital condyle [M+02]; maxilla and premaxilla form secondary palate which may bear a central projection articulating with a similar projection on the central articular process; $ strong medial process on articular; $ upper margin of lower jaw arched; $ dentaries with two long posterior processes; in effect, the lower jaw forms one narrow, centrally peaked (= "coronoid eminence" [M+02]), blade which may have articulated medially with the roof of the broader upper jaw; intramandibular joint absent; vertebral formula 10+13+6+~40; centra pneumatized, including anterior caudal vertebrae; hypapophyses present on caudal & dorsal vertebrae [M+02]; tail short overall (a 2000 article in Nature reports a specimen with a possible pygostyle, or at least a series of fused caudals); scapula thick, flat (in O. philoceratops, has process to articulate with clavicle); clavicles robust and fused (furcula); marked delto-pectoral crest on humerus; ectepicondyle more prominent than entepicondyle [M+02]; semilunate carpal present; three fingers with sharply curved , laterally compressed unguals; unguals with pronounced lip above articulation with penultimate phalanges; propubic; ilium deep in O. philoceratops but not others; pubis long, with small boot; ischium bears large obturator process; greater trochanter prominent, but 4th trochanter reduced; some species are arctometatarsalian; 4 toes, 3 weight-bearing; foot unguals relatively small & weakly curved. Several specimens found on nests with eggs, now believed to be their own.
Links: DD: Oviraptorosauria; Oviraptor (striking life reconstruction of head without beak); Oviraptor philoceratops; Ingenia (another gorgeous Nakasota Museum display); Part One [Overview]; Primitive forms and Caenagnathids; oviraptorosauria; Untitled Document; Dann's Dinosaur Info; Oviraptorosauria -- The Dinosauricon.
References: Currie (2000); Maryanska et al. (2002) [M+02]. ATW010617.
Range: Early Cretaceous (Barremian) - Late Cretaceous (Maastrichian) of China & North America.
Phylogeny: Maniraptora:: Oviraptorosauria + *: Beipiaosaurus + (Alxasaurus + Therizinosauridae).
Characters: 2-8 m long, <100-2000 kg; head unusually small; ant jaws toothless and form bill structure; teeth small, se , slightly flattened and ($) bulbous; braincase and vertebrae pneumatized; neck long and light; $ cervicals elongate (?) and highly pneumatized, with ($) widely-spaced zygapophyses; anterior dorsal vertebrae with tall neural arches; dorsal ribs flat & broad; 5-6 sacrals; tail somewhat short, anteriorly massive; scapula strap-like; large coracoid; forelimbs elongated; humerus massive with expanded ends in some spp; conspicuous, sharply peaked deltopectoral crest posteromedially on humerus (not all spp); manus variable, but generally large and bearing long claws, curved or uncurved; $ very broad pelvis; ilia widely separated; ilia very deep above acetabulum and flare laterally; post-acetabular ilia are short, with unique knob-like protruberances; pubes retroverted (i.e. opisthopubic); tibia 80%+ length of femur; fibula slender & closely appresed to tibia; $ short metatarsus (<1/3rd length of tibia); broad, short, ($) 4-toed feet; foot claws (unguals) pointed, curved and laterally compressed; proximal end of 1st metatarsus reaches tarsus (?). Possible herbivores, and general form converges on prosauropods.
Links: DD: Therizinosauridae; Therizinosauria -- The Dinosauricon (cladogram, essay on systematics); Literature - Segnosauria; DIM - number 12; A therizinosauroid dinosaur with integumentary structures from China; Untitled Document; DGF, Geological Society of Denmark, Geologisk Tidsskrift Nr. 4, 1996.
Note: possibly originated in Central Asia. 010619.
Discussion: Greg Paul's reconstruction shows visually how weird these creatures truly were -- so odd that for some years they were thought to be a Cretaceous relict of an early prosauropod lineage. In many ways, the Therizinosaurs do resemble some aberrant sauropodomorph. In other ways they are just as clearly Theropods. The head best illustrates this mixture. The skull is small, although not any smaller than that of reasonably close relatives, such as the Ornithomimosaurs. The front of the snout is usually curved downward. The front of the jaw is sometimes described as "bill-like," but there is little in the way of lateral expansion. Perhaps it is more like the offset jaw articulation of prosauropods -- designed to create a moving point of contact rather than single tearing force as in carnosaurs. The front of the jaw lacks teeth, which is a bit hard to explain. However, we have little idea what "soft" keratinous structures might have been present, such as a sharp tearing beak. The teeth, especially those in front, are somewhat chisel-like with a constricted base. This might be interpreted as the beginnings of a convergence toward the leaf-shaped teeth of sauropods. The teeth are also very numerous, recalling the beginnings of Ornithischian dentition, and are supplemented by sharp, curved denticles. This would be hazardous duty for a tongue! The back teeth are of a more indeterminate small-theropod grade. On the whole, the back teeth seem designed to cut or hold, while the front teeth sheared and the beak, if any, cut -- a real chimera.
The head is highly pneumatized and mounted on neck vertebrae which were also full of air holes. However the neck differs markedly from sauropods in that it is not heavily reinforced and was probably quite mobile. There are no exaggerated zygapophyses, interlocking caudal ribs or ossified tendons which would have held the neck rigid. The individual vertebrae are not elongated. These features suggest a relatively vertical posture, because there is no obvious way to hold the neck horizontally without continual muscular effort.
This impression is confirmed by the angled pelvis and general back-heaviness of the body. The arms are relatively slender, but long and probably heavily muscled. Both the large coracoids and the marked deltopectoral crest on the humerus suggest this, as do the enlarged ends of the arm bones. In fact, the thin central shaft of the humerus is the most difficult part of the arm to explain: perhaps a savings in weight at the expense of tensile strength. The enormous claws, particularly of Therizinosaurus, are also difficult to interpret. They seem almost too large for digging, and in Alxesaurus they are only slightly curved, a feature which would preclude digging against ordinary earth. One might speculate that these animals lived in a more arid, sand-dominated environment. Alternatively, the claws may have been specialized to strip bark or fronds from some locally common type of vegetation.
The pelvis is equally strange: enormously deep and wide, solidly fused to 5 or 6 vertebrae. The leg proportions tell us that this was no runner. Yet the pelvis would permit the attachment of huge leg, and possibly tail, muscles. The reversed pubic bones suggest additional room for the typical herbivore gut. However, as Paul has illustrated, a large gut hangs almost to the ground in the anticipated semi-vertical posture. At the same time, Therizinosaurs seem to have the classic dinosaur perforated acetabulum (the socket in the pelvis where the leg fits) with the back legs originating fairly close to the mid-line. Frankly, it is almost impossible to see how this arrangement of parts would fit together. Paul solves the problem by angling the femur about 20 degrees out from the mid-line. This leaves the femoral head at a reasonable place and angle to fit in the socket, but gives the animal an absolutely bizarre gait, something like a sumo wrestler -- very stable but not at all graceful. The feet are blocky and short, with an unusual 4 digits: not the usual sort of digging leg, which is longer. However, the probable short, curved claws would make good digging tools.
One possible reconstruction is, again, that Therizinosaurs were essentially desert animals. The gait, large, square feet and very low center of gravity all contribute to generate great stability on uncertain, shifting surfaces. Additional balancing adaptations might be the long mobile arms, as well as the relatively large brain. The bulbous body shape minimizes surface area. The hands and feet might be capable tools for digging in loose or sandy soil for roots, for extracting small lizards or mammals, or for splitting the tough exterior of typical desert plants while avoiding any sharp protective spines or scales. The relatively short tail reflects that tails are a less adequate method of achieving balance in a more-or-less upright posture, since the tail's reduced horizontal distance from the center of gravity also reduces the effect of torque. The small gastroliths found in the gut of some therizinosaurs might evolve simply from the necessity of doing something with the sand and gravel inevitably eaten with a diet of roots or burrowing desert animals. Undoubtedly, there are other plausible reconstructions, but it is interesting to imagine a small group of therizinosaurs plodding slowly over a dune near sunrise, their crested heads lurching and darting about, perhaps covered in white feathers to reflect the sun, stopping occasionally to dig up roots or excavate the burrows of unlucky mammals, making their endless rounds of widely scattered or seasonal oases. ATW 010619.
Note added in Disproof: Russell & Dong (1993) note that there is an "association between therizinosaurids and relatively moist (fluvial and lacustrine) environment Asia." This generalization may hold up with Beipiaosaurus as well, since this early therizinosauroid was found in the notably lake-dominated Yixian. Xu et al. (1999). So its back to the drawing board on the ecological restoration in this Note, although the mechanical analysis still seems to hold up.
References: Currie (2000), Russell & Dong (1993); Xu et al. (1999).
Range: Early Cretaceous (Barremian) of China.
Phylogeny: Therizinosauroidea: (Alxasaurus + Therizinosauridae) + *.
Characters: ~2 m; $ largest skull of Therizinosauroidea and ($) shortest, most bulbous tooth crowns; >37 teeth, with dorsally pointed, triangular interdental plates; cervical vertebrae with small, short spines; "fused posterior dorsals" (= pygostyle?); furcula widely arched; hpocleidium absent; semilunate distal carpal present; long hand (10% longer than femur); several features of hand said to be same as Deinonychus; manual unguals laterally comperssed & strongly curved; ilium with shallow anterior iliac process (similar to that of dromaeosaurs?); posterior andanterior processes of ilium equal; hindlimb short & stout; crest on the tibia; medial surface of fibula flat, without medial fossa; metatarsals III & IV compressed proximally; Mt V slender & strap-like; feet with three functional toes and splint-like proximal 1st metatarsal; integument with "proto-feather" filaments 5-7 cm in association with limbs; filaments contact bones; Xu et al. report possibly hollow and branching at ends.
Links: DD: BEIPIAOSAURUS inexpectus; DIM - number 1; theropode.pdf; Beipiaosaurus -- The Dinosauricon; Beipiaosaurus; Beipiaosaurus (Dutch); Dann Pigdon's Paleo Gallery @ Prehistorics Illustrated page 07; Dinosauria Translation and Pronunciation Guide B; Nieuwe therizinosauride (Dutch); Untitled; New feathered dinosaur found; Beipiaosaurus Fact Sheet - EnchantedLearning.com; *Beipiaosaurus* Recapitulated; A therizinosauroid dinosaur with integumentary structures from China.
References: Xu et al. (1999).
Alxasaurus (= Alxasauridae)
Range: mid-Cretaceous (Albian) of China.
Phylogeny: Therizinosauroidea:: Therizinosauridae + *.
Characters: 4 m; 380 kg; >40 very small teeth on dentary; teeth extend to front of jaw; interdental plates probably present; cervical neural spines small & narrow; zygapophyseal articulations broad; centra amphiplatyan; cervical ribs not fused; 5 sacral vertebrae; short tail, but 13 caudal vertebrae with transverse processes; scapular blade very long and slender with little distal expansion; coracoid probably circular; arms slender & very long; relatively small deltopectoral crest on humerus; ~70 cm manual unguals; elongate ilium with moderate preacetabular expansion; femoral shaft slightly bowed; large, keeled "posterior" (prob. = greater) trochanter separated by cleft from "anterior" (lesser) trochanter; 4 functional toes.
Links: DD Alxasaurus; Alxasaurus Printout- ZoomDinosaurs.com; Alxasaurus -- The Dinosauricon; Alxasaurus; PANGEA (Italian); DinoDictionary.com | A - Dinosaurs Page 2.
References: Currie (2000); Russell & Dong (1993).
Image: Alxasaurus reconstruction from Russell & Dong (1993).
Note: Russell & Dong diagnose Alxasaurus and the Alxasauridae by a number of features. However these are, as they state, almost certainly plesiomorphic. Thus, it may not be wise to recognize a separate family at this point based on a diagnosis which will almost certainly take in a paraphyletic group of stem therizinosauroids. 010619.
Therizinosauridae: Erlikosaurus, Segnosaurus, Therizinosaurus.
Range: Late Cretaceous (Cenomanian - Maastrichian) of China, Mongolia, & Central Asia.
Phylogeny: Therizinosauroidea:: Alxasaurus + *.
Characters: Larger therizinosauroids. Skull & jaw shallow & long; teeth absent from front of jaws; jaw curves downward in anterior; dentary shallow, with weak coronoid process; external mandibular foramen large; palate highly vaulted; long, posteriorly shifted vomers & palatines; vomers fused (?), forming vertical plate; pterygoids reduced rostrally; probable beak on premaxilla; external nares very long, with long nasal process of premaxilla; frontal very large dorsally; basicranium & otic region enlarged & highly pneumatized; cervical ribs fused to vertebrae; 6 sacral vertebrae with long transverse processes and ribs; humerus with both ends strongly expanded; long, massive deltopectoral crest; ligament pits on phalanges shallow; opisthopubic; ilium short with significant preacetabular expansion; postacetabular process very short, with knob-like caudolateral protruberance; femoral head turns at right angle with distinct neck; greater trochanter expanded and separated from lesser by cleft; 4th trochanter present as rugose crest; long ascending process of astragalus; astragalus with reduced condyles, only partly covering distal end of tibia; foot claws large, narrow, & curved.
Links: DD: Therizinosauridae; Question of Segnosaurs; Therizinosaurids; Segnosaurus (Dutch).
References: Barsbold & Maryanska (1990); Currie (2000).
Image: skull and palate of Erlikosaurus, pelvis of Segnosaurus. Both modified from Barsbold & Maryanska (1990).
Note: some of the characters above are from Barsbold & Maryanska (1990) based on materials even more skimpy than those known today. 010618.
Troodontidae: Byronosaurus, Saurornithoides, Sinornithoides, Sinovenator, Troodon.
Range: Early Cretaceous (Late Jurassic?) to Late Cretaceous of China and North America.
Phylogeny: Maniraptora::: Dromaeosauridae + *.
Characters: ~2m long; skull long & low; premaxilla forms dorsoventrally flattened internarial bar [M+03$]; maxilla with broad shelf which contributes to palate; enlarged elongate maxillary fenestra; maxilla broadly contacts naris; nasals narrow posteriorly; skull roof peaks over orbits; $ sharp sagittal crest; quadrate pneumatic, with pneumatopore on posterior face [M+03$]; occiput, basal tubera reduced & located directly below occipital condyle, close to midline [M+03$]; basisphenoid without ventral pneumatic recess [M+03$]; laterosphenoid, postorbital process with possibly pneumatic pit [M+03$]; large brain; lateral depression for middle ear; elaborate craniofacial sinus system; inflated parasphenoid (contra [M+03); jaw symphyses narrow but U-shaped; dentary foramina inside lateral groove which does not reach symphysis [M+03$]; large number of teeth on maxilla and and dentary (~100 total) [M+03$]; interdental plates absent; somewhat heterodont, with anterior teeth smaller and more chisel-shaped (posterior teeth are typically theropod); anterior dentary teeth in continuous groove, with alveoli confluent [M+03$]; teeth bear posterior serrations (also anterior serratrions in some spp.) (contra [M+03]: not in Byronosaurus); most distal posterior serration forming tip of tooth; $ teeth with constriction between root & crown; teeth with large hooked denticles (may be absent from basal forms [M+03]) (functional significance of these unusual tooth characters is unknown); all vertebrae except distal caudals bear well-developed pockets for attachment of interspinous ligaments (absence on caudals may be $); trunk vertebrae with long, slender transverse processes [M+03$]; 6 sacral vertebrae; distal caudals with neural groove & no spine; transverse processes also absent from distal caudals; elongate caudal pre-zygapophyses; chevrons flattened in distal caudal (tail stiffened?); strap-like scapula with small acromion process; coracoid bears prominent biceps tubercle; pubic foot longer anterior to the shaft; $ lateral knob-like trochanter on femur; fibula reduced to splint; $ fusion of astragalus and calcaneum; tall ascending process of astragalus; $ laterally compressed metatarsal II, markedly shorter than Mt III & IV; long, strongly arctometatarsalian III; metatarsal IV stout; tongue-like extension of articular surface on metatarsal III; $ modified pes II allowing retraction of enlarged ungual (?); since second ungual normally retracted, foot functionally two-toed.
Links: DD: Troodon; National Geographic Magazine: July 1996 @ nationalgeographic.com; Troodontidae (rather dated UCMP page); Troodontidae -- The Dinosauricon; Re- Troodontidae (misfits); Troodontidae and All That Jazz; Troodontidae (Mikko's Phylogeny).
References: Makovicky et al. (2003) [M+03].
Dromaeosauridae (=Deinonychosauria): Velociraptor, Utahraptor.
Introduction: Dromaeosaurs are considered dinosaurs, very close to the bird boundary (see The Mistaken Extinction). Greg Paul argues that they evolved from Archaeornithines -- the so-called "Secondary Flightlessness" (2F) hypothesis. For reasons which are not clear, this theory is very popular among educated amateurs, but finds little support among academic paleontologists. In either case, this shows how evolution is not about distinct types, but rather a gradation with countless intermediate stages.
These small to medium-sized predators were made famous through Hollywood fantasy. Everyone will remember them from Jurassic Park, Of course the Jurassic Park velociraptors were far larger than the typical species (two to three times the linear dimensions) and much too malevolent (they were after all just animals, not monsters). They were also able to turn door-knobs and open doors! [adapted from MAK, but with a different slant.]
Range: Early Cretaceous to Late Cretaceous of North America, Japan & North China.
Phylogeny: Maniraptora::: Troodontidae + *.
Characters: Small (2-3m), lightweight predators. Interdental plates present but fused; tall, slender vertical process post to jaw articulation; brain fairly large; tail with thin anterior processes from pre-zaps & hemal arches (tail stiff, but not rigid); furcula present; ossified sternum; arms relatively long; "grasping" hand; pubis retroverted & parallel with ischium; short and unspecialized metatarsals; pes 2 with large raptorial claw, strongly curved and twice length of any other claw; probably feathered. Total mass perhaps 20 kg.
Links: DD: Dromaeosauridae; Dromaeosaurid Anatomy (excellent discussion of functional anatomy); Velociraptor (skull) and Nakasato Virtual Museum Velociraptor (skull) (Nakasato); Fighting Dinosaurs (same); Bambiraptor Home; The Court Of B.feinbergi (many detailed images of Bambiraptor); Dromaeosauridae; What is a Raptor?; The Fernleaf: Karen Carr; A New Dinosaur Specimen With Feather-like Structures; Pretty Butte Paleontology: Catalog of Dromaeosauridae Fossils; ???????? Dromaeosauridae; Re: Dromaeosauridae (was Troodontidae); DINOSAURS: Family Dromaeosauridae; dromaeosauridae; DROMAEOSAURIDAE (German); Arts-Letters.com | Dino Database - Glossary; Deinonychosauria (Dinosauricon); Deinonychosauria; ZOO-PAGE :: Dinosaorusi; Raptors; gaiaphyl.pdf; Feathered dinosaurs..
Image: Sinornithosaurus (reconstruction in Graves Museum by Brian Cooley) photograph by Michael Corriss (retouched by ATW) and reproduced by permission.