Notes from recent papers on theropod dinosaurs and early avians. For anatomical terminology, see the Dinosauria.com Anatomical Dictionary, as well as the anatomy section at DinoData.net. For bird-specific anatomy, see this page, this page, this page, this page (bird forelimbs), and this page. For additional information on creationist claims regarding bird evolution, see Dinosaurs and Birds- an Update, All About Archaeopteryx, and Archaeopteryx.
Description: Xu et al., 1999. Nature 399, pp. 350-354.
Provenance: Early Cretaceous, Liaoning, China.
Classification: Therizinosaurid theropod
Abstract:
Non-avian theropod dinosaurs with preserved integumentary coverings are becoming more common; but apart from the multiple specimens of Caudipteryx, which have true feathers, animals that are reasonably complete and entirely articulated that show these structures in relation to the body have not been reported. Here we report on an enigmatic small theropod dinosaur that is covered with filamentous feather-like structures over its entire body.
Xu et al. write:
"The filamentous structures in Beipiaosaurus are similar to, but longer than, those of the compsognathid Sinosauropteryx. They are perpendicular to the limb bones, and are unlikely to muscle fibers or frayed collagen. Their presence in both therizinosaurs and compsognathids indicates that there may be a broader distribution of similar structures in theropod dinosaurs . . . The absence of such structures in most theropod fossils is probably attributable to the lack of such ideal preservation as is found in the Yixian Formation. This again indicates that feathers preceded flight, because both therizinosaurs and compsognathids apparently could not fly and did not descend from flying animals" (p. 354).
Other characters: semilunate carpal.
Description: Chen et al., 1998. Nature 391, pp. 147-152.
Provenance: Late Jurassic-Early Cretaceous, Liaoning, China.
Classification: Compsognathid theropod
Abstract:
Two spectacular fossilized dinosaur skeletons were recently discovered in Liaoning in northeastern China. Here we describe the two nearly complete skeletons of a small theropod that represent a species closely related to Compsognathus. Sinosauropteryx has the longest tail of any known theropod, and a three-fingered hand dominated by the first finger, which is longer and thicker than either of the bones of the forearm. Both specimens have interesting integumentary structures that could provide information about the origin of feathers. The larger individual also has stomach contents, and a pair of eggs in the abdomen.
Other characters: longest tail of any known theropod -64 caudal vertebrae. Unserrated premaxilllary teeth, serrated maxillary teeth; footed pubis; zig-zag gastralia as found in Archaeop. and Confuc.; integumentary structures up to 40mm long;
Description: Qiang et al., 1998. Nature 393, pp. 753-761.
Provenance: Late Jurassic-Early Cretaceous, Liaoning, China.
Classification: Maniraptoran theropod
Abstract:
Current controversy over the origin and early evolution of birds centres on whether or not they are derived from coelurosaurian theropod dinosaurs. Here we describe two theropods from the Upper Jurassic/Lower Cretaceous Chaomidianzi Formation of Liaoning province, China. Although both theropods have feathers, it is likely that neither was able to fly. Phylogenetic analysis indicates that they are both more primitive than the earliest known avialan (bird), Archaeopteryx. These new fossils represent stages in the evolution of birds from feathered, ground-living, bipedal dinosaurs.
Other characters: teeth similar to Archaeop. in shape, but serrated. U-shaped furcula as in Archaeop., Confuc., and many theropods; semilunate carpal; claws on manus; pubic foot; long tail; theropod phalangeal formula 2-3-4-x-x; unfused metatarsals (no tarsometatarsus); hallux proximally placed, not reversed as in birds; tail consisting of up to 28 caudal vert.; symmetrical 'feathers':
"A clump of at least six plumulaceous feathers is preserved anterior to the chest, with some showing well-developed vanes. Evenly distributed plumulaceous feathers up to 27mm long are associated withten proximal caudal vertebrae. Twnety-millimetre plumulaceous feathers are preserved along the lateral side of the right femur and the proximal end of the left femur.
"Parts of more than 12 retrices are preserved attached to the distal caudals. one of the symmetrical tail feathers extends 132mm from the closest tail vertebrae, and has a long tapering rachis with a basal diameter of 1.5mm. The well-formed pennaceous vanes of Protarchaeopteryx show that barbules were present.
"The vane is 5.3mm wide on either side of the rachis. At midshaft, 5 barbs come off the rachis every 5mm (compared with 6 in Archaeopteryx), and individual barbs are 15mm long." (p. 753-754).
Description: Qiang et al., 1998. Nature 393, pp. 753-761.
Provenance: Late Jurassic-Early Cretaceous, Liaoning, China.
Classification: Maniraptoran theropod
Abstract:
Current controversy over the origin and early evolution of birds centres on whether or not they are derived from coelurosaurian theropod dinosaurs. Here we describe two theropods from the Upper Jurassic/Lower Cretaceous Chaomidianzi Formation of Liaoning province, China. Although both theropods have feathers, it is likely that neither was able to fly. Phylogenetic analysis indicates that they are both more primitive than the earliest known avialan (bird), Archaeopteryx. These new fossils represent stages in the evolution of birds from feathered, ground-living, bipedal dinosaurs.
Other characters: teeth in premaxilla, no maxillary of dentary teeth; ten amphicoelous cervical vertebrae, as in Archaeop. and most theropods; 22 caudal vertebrae, as in Archaeop; zig-zag gastralia as in Proarchaeop. and most theropods; U-shaped furcula as in Archaeop., Confuc., and many theropods; semilunate carpal as in dromaeosaurids, oviraptorids, troodontids, Archaeop., and Confuc. Unfused metacarpals and digits (no carpometacarpus); theropod phalangeal formula 2-3-4-x-x; Manus longer than hunerous and radius, as in ceolurosaurs, Archaeop., and Confuc.; claws on manus; unfused pelvic bones; ischium dromaeosaur-like; unfused metatarsals (no tarsometatarsus); first toe proximally situated, not retroverted as in birds; plumulaceous symmetrical feathers up to 14mm long, with rachi and barbs; anteromedially oriented hallux;
"Phylogenetic analysis shows that both Caudipteryx and Protarchaeopteryx lie outside Avialae and are non-avian ceolurosaurs. This indicates that feathers are irrelevant to the diagnosis of birds . . . the presence of feathers on flightless theropods suggests that the hypothesis that feathers and flight evolved together is incorrect. Finally, the presence of remiges, retrices and plumulaceous feathers on non-avian theropods provides unambiguous evidence supporting the theory that birds are the direct descendents of theropod dinosaurs" (p. 760-761).
NGMC 91 and BPM 1 3-13
Description: Qiang et al., 2001. Nature 410, pp. 1084-1088; Norell et al., 2002. Nature 416, pp. 36-37.
Provenance: Late Jurassic or Early Cretaceous, Liaoning, China.
Classification: Dromaeosaurid theropod
Abstract:
Non-avian theropod dinosaurs with preserved integumentary coverings are becoming more common; but apart from the multiple specimens of Caudipteryx, which have true feathers, animals that are reasonably complete and entirely articulated that show these structures in relation to the body have not been reported. Here we report on an enigmatic small theropod dinosaur that is covered with filamentous feather-like structures over its entire body.
Other characters: semilunate carpal; elongate, bifurcating prezygapophyses and chevrons; teeth similar to those of the dromaeosaurid Sinornithosaurus; dromaeosaurid teeth - recurved, no basal constriction, posteriorly serrated; t-shaped lacrimal; long tail with stiffening rods; boomerang-shaped furcula; forelimb proportions similar to other dromaeosaurids; typical theropod hand morphology - phalangeal count 2-3-4-x-x, claws; typical theropod foot morphology - full-length fibula contacts ankle, digit 1 not reversed, unfused metatarsals, elarged raptorial claw on digit 2;
NGMC 91 is covered with feather-like integuments over most of its body. Qiang et al write (p. 1087):
"In NGMC 91 integumentary filaments are distributed across the entire skull, body, limbs and tail, except for the distal hindlimbs. Unlike Sinosauropteryx, the structure and distribution of filaments are heterogenous. There are three basic types . . . single fibers, long 'sprays' of fibres that resemble the plumulaceous feathers of Protarchaeopteryx, and fibers oriented around a central axis in a herringbone pattern that resembles the remiges of Caudipteryx."
BPM 1 3-13:
"BPM 1 3-13 can be unequivocally referred to the Dromaeosauridae on the basis of derived characters, including elongate prezygapophyses and chevrons that span several vertebrae in the tail, a retroverted pubis, and a modified second pedal digit. Although BPM 1 3-13 shows several advanced maniraptoran features, such as an hourglass-shaped sternum composed of two sternal plates with attachment sulci for sternal ribs, and a semilunate carpal that caps metacarpals 1 and 2, it and other dromaeosaurs lack a reversed hallux, unserrated teeth and the short tail of basal avians. The tail is relatively much longer than that of NGMC 91 (which can probably be referred to Sinornithosaurus) and that of Microraptor.
. . .
"The feathers of BPM 1 3-13 are structurally identical to those of modern birds, indicating not only that modern feathers must have evolved in dinosaurs before the emergence of birds and flight, but also that the feather-like structures present in many other non-avian theropods are homologous with feathers" (p. 36).
Description: Xu et al., 1999. Nature 401, pp. 262-266; Xu et al., 2001. Nature 410, pp. 200-203.
Provenance: Early Cretaceous, Liaoning, China.
Classification: Dromaeosaurid theropod
Abstract:
Dromaeosaurids, despite their notoriety, are poorly characterized meat-eating dinosaurs, and were previously known only from disarticulated or fragmentary specimens. Many studies have denied their close relationship to birds. Here we report the best represented and probably the earliest dromaeosaurid yet discovered, Sinornithosaurus millenii gen. et sp. nov., from Sihetun, the famous Mesozoic fish–dinosaur–bird locality in China. Sinornithosaurus not only greatly increases our knowledge of Dromaeosauridae but also provides evidence for a filamentous integument in this group. It is remarkably similar to early birds postcranially. The shoulder girdle shows that terrestrial dromaeosaurids had attained the prerequisites for powered, flapping flight, supporting the idea that bird flight originated from the ground up. The discovery of Sinornithosaurus widens the distribution of integumentary filaments among non-avian theropods. Phylogenetic analysis indicates that, among known theropods with integumentary filaments or feathers, Dromaeosauridae is the most bird-like, and is more closely related to birds than is Troodontidae.
Xu et al. write:
"Sinornithosaurus is placed in dromaeosauridae on the basis of the following shared derived features: t-shaped lacrimal; large supratemporal fossa with a strongly sinosoidally curved anterior frontal margin; t-shaped quadratojugal. . . ; widely open fenestra between the quadratojugal and quadrate; dentary with subparallel dorsal and ventral margins; ossified caudal rods increasing the lengths of prezygapophyses and chevrons" (p. 262).
Other characters: : shoulder girdle and forelimb closely resemble early birds such as Archaeop.; boomerang-shaped furcula resembling that of Archaeopteryx; feathers or feather-like structures:
"The integumental structures of Sinornithosaurus are compound structures composed of multiple filaments with two types of branched structure. First, the tufts of filaments joined at their bases are identical in structure to avian natal down feathers in which mutiple filamentous barbs are basally fused to a single calamus. . . Second, the serial branching of filaments along a central shaft is identical in structure to to the barbs and the rachis of a pennaceous feather, and is also unique to avian feathers. The integumental structures of Sinornithosaurus are are different from most modern avian feathers in their apparent lack of barbules. Thus, Sinornithosaurus appendages could not have formed a closed pennaceous vane.
"The compound filamentous structure of the two types of feathger-like branching in the integumental appendages of Sinornithosaurus strongly indicate that these structures are homologous with avian feathers. A previous phylogenetic analyses indicates that Sinornithosaurus is not a bird but a basal lineage of the dromaeosaurids which . . .have been repeatedly considered to be the lineage of theropods most closely related to birds. Thus, the proposed homology between the integumentary appendages of Sinornithosaurus and avian feathersis supported by observations of detailed, derived morphological similarities, and is strongly corroborated by independent phylogenetic data . . . " (p. 200-201).
Description: Xu et al., 2000. Nature 408, pp. 705-708; Xu et al, 2003. Nature 421, 335-340.
Provenance: Early Cretaceous Jiufotang Formation, Liaoning, China.
Classification: Dromaeosaurid theropod
Abstract:
Non-avian dinosaurs are mostly medium to large-sized animals, and to date all known mature specimens are larger than the most primitive bird, Archaeopteryx. Here we report on a new dromaeosaurid dinosaur, Microraptor zhaoianus gen. et sp. nov., from the Early Cretaceous Jiufotang Formation of Liaoning, China. This is the first mature non-avian dinosaur to be found that is smaller than Archaeopteryx, and it eliminates the size disparity between the earliest birds and their closest non-avian theropod relatives. The more bird-like teeth, the Rahonavis -like ischium and the small number of caudal vertebrae of Microraptor are unique among dromaeosaurids and improve our understanding of the morphological transition to birds. The nearly completely articulated foot shows features, such as distally positioned digit I, slender and recurved pedal claws, and elongated penultimate phalanges, that are comparable to those of arboreal birds. The discovery of these in non-avian theropods provides new insights for studying the palaeoecology of some bird-like theropod dinosaurs.
Xu et al. write:
"The discovery of Microraptor completes some morphological gaps between dromaeosaurid dinosaurs and birds; for example, it has more bird-like teeth than do other dromaeosaurids, a Rahonavis-like ischium, enlarged sacrals and fewer caudal vertebrae" (p. 707).
Other characters: extremely small- trunk length estimated 47mm; tail consisting of 24-25 caudal vert., possessing rod-like extensions of prezygapophyses and chevrons, as in other dromaeosaurs; gastralia; semilunate carpal; Metatarsals II, III, and IV unfused and of unequal length as in other dromaeosaurs, Archaeop., and other early birds, versus fused MTs of equal length in later birds. MT IV bears pronounced flange on posteromedial surface, as in other dromaeosaurs; second pedal digit is specialized raptorial tool as in dromaeosaurs, troodonts, Archaeop., and Rahonavis; Pedal digit I distally placed, but not retroverted, as in Archaeop. and other early birds. Also, large patches of integumentary covering:
"Large patches of integuments are preserved in situ around the skeleton, and the pattern of preservation is similar to that of early birds from the same locality. Integumentary structures are best preserved near the femur, where they run almost perpendicular to the bone. They are long (average 25-30mm), narrow, and have a feather-like contour, whereas those along the tibia and in the hip area are shorter. Some impressions of the integuments contain a structure similar to that of a rachis, suggesting that true feathers may have been present. . . " (p. 707).
Description: Forster et al., 1998, Science 279, pp. 1915-1919.
Provenance: Late Cretaceous, Madagascar
Classification: Enantiornithine bird
". . . although exhibiting avian features such as reversed hallux and ulnar pappilae, retains characteristics that indicate a theropod ancestry, including a pubic foot and hyposhene-hypantra vertenral articulations. Rahona has a robust, hyper-extendable second digit of the hind foot thatthat terminates in a sickle-like claw, a unique characteristic of the theropod groups Troodontidae and Dromaeosauridae. A phylogenetic analysis place Rahona with Archaeopteryx, making Rahona one of the most primitive birds yet discovered" (p. 1915).
Forster et al. write:
"The most striking feature of the nearly complete left foot . . . is the structure of digit II. It is extremely robust relative to other digits . . . and distinctive in morphology . . . The digit ends in an enlarged sickle-shaped claw . . . digit II was found in hyperextension, whereas digits III and IV were flexed. This distinctive morphology of an enlarged digit II is found only in dromaeosaurid and troodontid maniraptorans . . . resulting the predatory 'slashing' foot" (p. 1917).
"In addition to its numerous bird features (for example, a reversed hallux, a splintline fibula, and ulnar pappilae), Rahona retains specific theropod synapomorphies. The accessory hyposphene-hypantra articulations on its dorsal vertebrae are a synapomorphy of Saurischia and are unknown in any other amniote clade. The singular pedal morphology is known only in derived maniraptoran theropods . . . Thus, the combination of morphological characteristics found in Rahona strongly supports its membership in Aves, as well as its theropod ancestry, and thus the dinosaurian ancestry of birds" (p. 1918).
Other characters: bony tail (13 caudal vertebrae); unfused metatarsals (no tarsometatarsus); sacral vertebrae fused into synsacrum; pelvis very similar to theropods and other early birds - vertical pubis, short ischium (45% of pubic length), pubic 'foot,' all elements unfused; birdlike reduced fibula which does not articulate with calcanaeum.
Protopteryx fengnensis
Description: Zhang and Zhou, Science 290, p. 1955.
Provenance: Early Cretaceous, Liaoning, China.
Classification: Enantiornithine bird
Abstract:
A fossil enantiornithine bird, Protopteryx fengningensis gen. et sp. nov., was collected from the Early Cretaceous Yixian Formation of Northern China. It provides fossil evidence of a triosseal canal in early birds. The manus and the alular digit are long, as in Archaeopteryx and Confuciusornis, but are relatively short in other enantiornithines. The alula or bastard wing is attached to an unreduced alular digit. The two central tail feathers are scalelike without branching. This type of feather may suggest that modern feathers evolved through the following stages: (i) elongated scale, (ii) central shaft, (iii) barbs, and finally (iv) barbules and barbicel.
Zhang and Zhou write:
"Discoveries of 'fiber'-like structures in Sinosauropteryx, Sinornithosaurus, Beipiaosaurus . . . have stimulated debates on the origin of feathers . . . Similarities have been found between the elongate integumentary appendages in the Late Triassic archosaur Longisquama and modern avian feathers. Protopteryx preserved some interesting types of feathers with characters between those of scales and modern feathers, thus providing fossil avian evidence for the origin of feathers from elongated scales in reptiles"
"Protopteryx possesses a combination of primitive and advanced characters. It shares with modern birds a procorocoid process and lateral process of the corocoid. On the other hand, the long hand and alular digit, unfused carpometacarpus, and tibiotarsus are similar to those of Archaeopteryx"
Other characters: teeth in premaxilla and dentary; footed pubis;
References
Chen et al, 1997. An
exceptionally well preserved theropod dinosaur from the Yixian Formation
of China. Nature 391, 147-152.
Forster et al, 1998. The theropod
ancestry of birds: New evidence from the Late Cretaceous of Madagascar. Science
279, 1915-1919.
Norell et al, 2002. Palaeontology:
'Modern' feathers on a non-avian dinosaur. Nature 416, 36 - 37.
Qiang et al, 1998. Two feathered
dinosaurs from northeastern China. Nature 393, 753-761.
Qiang et al, 2001. The distribution
of integumentary structures in a feathered dinosaur. Nature 410: 1084-1088.
Xu et al, 1999. A therizinosauroid
dinosaur with integumentary structures from China. Nature 399, 350-354.
Xu et al, 1999. A dromaeosaurid
dinosaur with a filamentous integument from the Yixian Formation of China.
Nature 401, 262-266.