Therizinosaurus

Incisivosaiinis

Caudipteryx

Oviraptor

Protarchaeopteryx

Sinovenator

Troüdon

Microraptor

Sinornithosaurus

Deinonychus

Archaeopteryx

Modern birds

1163 The phylogenetic positions of the Jehol non-avian theropods [in red) among the related groups.

1164 Skull of the holotype of Psittacosaurui meileyingensis (estimated body length I —2 m) from Meileyingzi locality (Jiufotang Formation), Chaoyang. liaoning. Psittacosaurs are a group of herbivorous dinosaur living in the Harly Cretaceous of Asia and a distant relative of Triceratops.

1165 Complete skull of a juvenile Uaoceratops yanzigouensis (total body length less than Im). a small primitive ceratopsian. from Yanzigou locality (lower part of Yixian Formation) in Beipiao. liaoning. (Photo: IVPP)

1167 A skull ofjeholasourus shangyuanensis (estimated body length less than 1 m), a small ornithopod dinosaur, from Lujiatun locality (lower part oFYixiari Formation), Beipiao, Liaoning. (Photo: IVPP)

1166 Reconstruct ion of Uaoceratops yanzigouensis. (Art: Michael VV, Skrepnick/ I'MNH)

mm 168 Skuli of the holotype ofJimhousaums yangi (skull about 50 cm long and 28 cm high), an iguanodont, from Baicaigou locality (middle part of Yixian Formation], Jinzhou, l iaoning. IPhoto: IVPP)

■Ml 69 Holotype of Liaoningosaurus paradoxus (body length less than 40 cm), the smallest ankylosaur found to date, from Wangjiagou locality (middle part of Yixian Formation), Jinzhou, Liaoning. (Photo: IVPP)

BIRDS

Fu-cheng Zhang, Zhang-he Zhou, Lian-hai Hon

Probably more than any other animals, birds have immensely enriched our lives with their colorful plumages and beautiful songs, which always evoke man s artistic inspirations. Side by side with flowers, birds have been the favorite subjects of the Chinese painters over the centuries. Ir is not surprising to find both The Huudred Birds Sing to a Phoenix" in the Cantonese music repertoire and Ottorino Rcspighi's symphonic poem "The Bird" offer equally unblemished musical enjoyment to the people all over the world.

Largely imitating avian (light, we have seen our dream of Hying come true through the inventions ol airplane and spacecraft. Consequently, these inventions have made not only our global village ever more accessible but also ouroutspace travel increasingly feasible. Birds are also our friends, some as pers to accompany and amuse us. and some as toes to rats, helping eliminate such natural disasters as rat calamity "N- and thus maintain a balanced ecosystem to which we also belong. In addition, birds also attract hundreds of thousands bird-watching fans annually worldwide to outdoors to admire their beauty, and as a result, keep the birdwatchers themselves fit.

Birds, with a global distribution of over 9,000 known living species, are the most flourishing land vertebrate group on earth today. The issue of the origin of birds dates back to the old days. The discovery of the Archatopteryx (Fig. 170) fossil from Bavaria of Germany in 1861, for the first time, linked birds with reptiles. Against the backdrop of the classic work Origin of Species published by Charles Darwin two years earlier, the first Arckaeopttryx specimen, with a combination of feathers of modern birds and a long skeletal rail typical of reptiles, stirred an outright public sensation and convinced people that birds evolved from reptilian ancestors. Evolutionism has since prevailed over Crcationism.

Birds have lighr skeleton due to flight adaptation. Compared to other animals, they are usually more difficult to be preserved as fossils. This can probably explain why only 7 skeletons and one feather specimen of Aixbae-

mm 170 Model of Archoeopteryx. the oldest bird, which linked reptile to bird, suggesting a reptile-bird relationship. (Courtesy: Ijrry D. MartitV KU}

1171 A complete skeleton o(Confiiiiusornis sp., a primilive beaked bird, from Sihetun locality (lower part of Yixian Formation) in Heipiao, Liaoning, showing well preserved impression of two long central tail leathers. Note the two special features of this bird; jaws beaked (toothless, Upperi; humerus triangular with elliptic fenestra at its expanded proximal end (Lower). (Photo: IVPP)

172 A Confuciusornis "couple" buried together. The one on the left with a long tail leather is assumed as a male. (Photo: Da-jian Li/ CAS)

opttryx have been found over the past 140 years. Although some other Mesozoic birds were also discovered in other regions of the world, they are all much younger than Anbaeopteryx, with little diversity.

This situation has significantly changed since the 1990s with the discoveries of abundant Mesozoic birds from Liaoning, Hebei, Inner Mongolia, Shandong, Ningxia anil other areas of China. These new fossils have revolutionarized our view of the early evolution and radiation of birds.

The first Mesozoic bird from Liaoning was actually collected by a farmer from the Meiieyingzi locality in Chaoyang in 1987 and then sent to the Beijing Natural History Museum for study; this bird was later named Sinornis. In September of 1990, we discovered three fossil bird skeletons from the Boluochi locality in Chaoyang, Liaoning Province (one of them was later

173 Two Confuciusornis, buried in one slab, from Sihetun locality (tower part of Yixian formation) in Beipiao. Liaoning. The number of Confuciusornis specimens has surpassed the total number of oilier Mesozoic birds combined. (Photo: IVPP)

1174 The distal ends of central tail feather of Confuciusornis. (Photo: IVPP)

1174 The distal ends of central tail feather of Confuciusornis. (Photo: IVPP)

df • ■ L, jrir^s, ihe Mrliesfbtaked bird from iT^^lxT on<&bigg£r afld long-tailed. i)fao-ljan Zeng A jin-leug Hou).

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df • ■ L, jrir^s, ihe Mrliesfbtaked bird from iT^^lxT on<&bigg£r afld long-tailed. i)fao-ljan Zeng A jin-leug Hou).

named Calhayoruts). These fossils were all from the Early Cretaceous Jiufotang Formation, and fit right in the transition form the Late Jurassic A rchiiivph-ryx to the Late Cretaceous birds. However, their discovery was only the beginning of a scries of exciting fossil findings in the area that have lasted to rhts day. For instance, over two dozens of bird skeletons were discovered from this locality alone during the following field seasons in the early 1990s.

In 1993, the first skeleton of Confucttmrnis in a fossil collector's home drew the attention of some colleagues from the 1VPP. It was later named after a renowned Chinese saint, Confucius, who lived more than 2,500 years ago, and recognized as the earliest known bird with a horny beak. A large number of Confuciusornis specimens have since been excavated from the Yixian Formation at several localities in Beipiao and Chaoyang. western Liaoning. Many fossil birds have also been collected from a younger formation, the Jiufotang Formation in that area. Hundreds of specimens of Mesozoic birds have been discovered from thejehol Biota since Smurtth was described, and western Liaoning has increasingly become the hottest area for the study of the origin and early evolution of birds.

Confuciusornis Cimfutinsornis (Figs. 171 — 175) is the earliest known bird without teeth. Unlike most other early birds, Ctinfiiciusornis had a horny beak, just like the birds in your backyard- The loss ol teeth and the appearance of horny beak may also indicate the reduction of the cutting function of jaws, and the shifting of the masticatory process mainly to its gizzard, for which, however, we have not hail any direct fossil evidence.

Confuaiuornis is about the size of Arcbatupteryx. The postorbital of Cunfiiciusornis is large, and ventrally connected with the jugal, suggesting that Arrhaiopteryx may also have a postorbital, thus a typical diapsid skull.

The pectoral girdle bones, scapula and coracoid, are firmly connected, and appear more primitive than in .1 icbaopttryx, Confuciusornis also has a primitive hand similar to that of A >xhueopferyx. Except for the pectoral girdle and forelimb, most of other features of Confuciusornis are, however, more derived, suggesting a more powerful flight capability. For example, the distal tail vertebrae of Coiifmiusotiiis are fused into one solid bone, pygostyle, which is remarkably distinguishable from that of Arcbaeopteryx that has a long caudal tails with 22 unfused vertebrae. A short and steady body of Confuciusornis is,

1176 A specimen of Sapeornis chaoyangensis, the largest known Early Cretaceous bird (about twice as large as Archaeopteryx), from Shangheshou locality [jiufotang Formation) in Chaoyang, Liaoning. Its elongated forelimbs are longer than those of l.angiptervx in proportion: however, its short and robust coracoids are comparable to those oMrWiaeo/j/eryji and theropod dinosaurs. (Photo: IVPPl m

Holotype ofJtbolorttis prima, a primitive bird only slightly more derived than Archaeopierytt. from Dapingfang locality (Jiufotang Formation) in Chaoyang, liaoning. representing the only bird with a complete long skeletal tail after Archaevplcryx. (Photo: IVPP)

Reconstruction ofjehohrvii. (Art: Yong Xu/ IVPP)

Holotype of Cathayornis yandica. an opposite bird (size about a domestic sparrow) and the first complete fossil bird skeleton collected by a Chinese scientist, from Roluochi locality (Jiufotang Formation) in Chaoyang. Liaoning. (Photo: IVPP)

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like modern birds, more adapted for flight than a long and incompact body of Archaeopteryx.

One of the most distinctive features of Confuciusornis is the fenestra at the proximal end of the humerus (Fig. 171), though we are not yet sure about its exact function.

Up to now, probably over one thousand Confuciusornis specimens have been discovered. In many cases, many individuals were preserved in close proximity, indicating mass mortality (Figs. 172, 173). Other birds are relatively less abundant than Confuciusornis. Confuciusornis is not only characteristic of complete skeletal preservation, but it usually contains beautiful feather impressions in areas such as the skull, neck, wing, and tail. These feathers are comparable to those of Archaeopteryx and modern birds, with rachis and barbs; some of them even with barbules. Some Confuciusornis specimens also preserve a pair of long tail feather, suggesting that they may be male individuals (Figs. 171, 172, 175). It is rather often to find male and female lying next to each other preserved on one slab (Fig. 172). We may further conclude that at least by the time of the Early Cretaceous, the sexual dimorphism of feathers in early birds are much like that of modern birds (Fig. 175).

The name of Sapeornis was derived from the SAPE, the abbreviation of the Society of Avian Paleontology and Evolution; this bird's holotype was discovered shortly after the SAPE's 5th symposium meeting, which was held in Beijing in June 2000. Sapeornis (Fig. 176) was collected from a new locality only a few kilometers northwest from the downtown of the Chaoyang City. It is the largest known Early Cretaceous bird. It is not only larger than Archaeopteryx but also larger than many dromaeosaurs from the same region such as Microraptor.

Its elongated forelimbs, relatively short hind limbs, fused carpometacarpus and short pygostyle indicate powerful flight capability. On the other hand, this bird retains some primitive features such as a short and robust coracoid, similar to that of Archaeopteryx and theropod dinosaurs. The coexistence of such a large sized bird with many small to medium sized birds from the same age suggests that by the Early Cretaceous the differentiation of early birds is greater than previously assumed.

Jeholornis Jeholornis (Figs. 177— 179) is a very primitive bird, and phylogenetically only slightly more derived than Archaeopteryx. It is the third bird known to have a long skeletal tail. Its long bony tail contains about

24 — 25 caudal vertebrae. Its tail is even more primitive than that of Archaeopteryx. In fact, the tail bears a lot more resemblance to dromaeosaurids dinosaurs than any other known birds. For instance, the elongated prezygapophysis and chevron of the caudal vertebrae are characteristic of dromaeosaur dinosaurs, providing further evidence for the link between birds and theropod dinosaurs, in particular, the dromaeosaurid dinosaurs.

The holotype of Jeholornis preserved more than 50 seeds as imprint in the belly (Fig. 178). It is the first direct evidence for seed-eating adaptation in the Mesozoic. This bird is clearly a seedeater. There are also other lines of evidence for this conclusion, such as the short, deep and robust jaws, which have only very reduced teeth on the lower jaw. Many intact seeds also indicate that this bird probably has a well-developed crop.

The combination of a much derived pectoral girdles and forelimbs with very primitive tails and hind limbs indicates the mosaic pattern of characters in early evolution of birds. In other words, early birds first developed flight capability and then became modern in the features of the hind limbs and the tail.

Cathayornis Cctthayornis (Fig. 180) is a small-sized enantiornithine bird, slightly larger than a sparrow in size. Enantiornithine birds ("opposite birds") are the dominant Mesozoic avian group, characterized by its unique articulation between the scapula and coracoid that is "opposite" to that of modern birds. Cathayornis is the very first avian specimen collected by professional paleontologists in Liaoning, China. Its discovery in 1990 has boosted the study of early birds in China and trigged a series of discoveries of feathered dinosaurs and early birds such as Confuciusornis in that region.

Cathayornis was from the Jiufotang Formation, which overlies the Yixian Formation (see Chapter 2). Although Cathayornis is much younger than Archaeopteryx in age, they share similarities in the skull structure such as toothed jaws. However, it has a more expanded braincase than Archaeopteryx. It has many advanced features in the pectoral girdle and wing than in Archaeopteryx and Confuciusornis. Compared to the most primitive enantiornithine Protopteryx (see below), Cathayornis has more reduced and shortened digits in the hand.

Boluochia Boluochia (Figs. 181, 182) is another enantiornithine bird from the Jiufotang Formation. It was discovered from the same horizon and locality as Cathayornis. This bird was named after the locality Boluochi, a village near Chaoyang City, western Liaoning. The most distinctive feature

mm 183 Holotype of Uaoxiomis dfhcates. a juvenile or subadult opposite bird (size about a Great Tit|. from Dawangzhangzi locality (middle part of Yixian Formation) in Lingyuan. Ijaoning. (Plioto: IVPP)

mm 184 Reeonst ruct ion of Uaoxiomis delkoies. (Art: Anderson Yang)

mm 184 Reeonst ruct ion of Uaoxiomis delkoies. (Art: Anderson Yang)

185 Hoiotype of Eoenantinrms buhleri, a primitive opposite bird (size about .1 cuckoo) with a relatively short rostrum (denoted by a red arrow) and deep skull, from Heitizigou locality (lower part of Yixian Formation) in Beipiao. Liaoning. (Photo: IVPP)

•*/186 Holotype of Protapteryx fingningmsis (size about a gray starling), the most primitive opposite bird to date, from Sichakou locality (Vixian formation) in Fengning. Hebei, (Photo: IVPP)

m 187 Reconstruction of Protopteryx, with a long, central tail feather. This unbranched feather may represent the ancestral type of feather, providing evidence lor a scale-feather relationship. (Art: IVPP)

of Holuochiti is char the must anterior end of premaxilla is curved into j hook as in some extant raptorial and passerine birds. No tooth has been discovered from the premaxilla. It was therefore proposed that Boluochta probably had a similar lifestyle as some extant raptorial and passerine birds.

Another significant feature of Bnluochia is us long and curved foot claws, suggesting climbing and perching ability. At the distal end of the tarsometa-tarsus the trochleae for the digits are nearly on the same level, further proving that it is a bird with strong perching capability

LiaoxiorniS Liaoxtornis (Figs. 183, I S-i) is the smallest known Mesozoii bird reported from the Yixian Formation in Lingyuan, western Liaoning in 1999. It is about the size of a sparrow.

Liaoxtornis has a large and deep skull. Both upper and lower jaws arc-toothed as in most other Mesozoic birds. Both primitive and derived features can lie found in Liaoxiomis. One of distinctive features of this bird is that the thighbone is longer than the humerus; die pygostyle is longer than the neck. The derived features of Liaoxtornis include: the proximal ends of metacarpal bones being fused together; the number of phalanges of the hand less than that of more primitive birds such as .1 rcbatopteryx at that time. It is distinguishable from other birds by its relatively short rostrum and deep skull. Eoenantiomis is smaller than Qmfuriimrnh, but larger than other enant ¡ornithine birds, consistent with the tendency of body size reduction in the evolution of early birds. The teeth of Loenautiornis arc characteristic of all known toothed birds in having a constriction ar the base of the crown. Another notable feature of fioi/tauliornis is the preservation of bastard wing ¿is in Protopteryx, The bastard wing was not present in Arcbae-opttryx and Confitci/tsumis. It is probably present in ail other enanriornirhines and ornithurines (all extant birds are ornithurine birds).

Protopteryx Protopteryx (Figs, 186, I«7) is about the size of a gray starling. As its name implies it ts "A bird with primitive feathers'. The two central tail feathers of Protopteryx are most distinctive among early birds. Its distal end is not much different from that of other birds in comprising a central shaft or rachis. and barbs on both sides; however, its proximal region is unbranched, that is. lacks differentiated barbs on either side of the rachis. Thus the proximal tail feather is more like an elongated scalelike structure, which was interpreted as an intermediate stage between reptilian scale and avian feather. After the discovery of Protopteryx, similar primitive tail feathers have also been recognized in the specimens o { Cottfuciusontis and some other en ant ¡ornithine birds.

Protopteryx also represents the most primitive of the known enantiornithine birds. Some of its hand bones are longer than those of other enantiornithine birds. On the other hand, it develops the initial procoracoid on the coracoid, indicative of the presence of triosseal canal, which is a derived and key structure adapted for flapping flight of modern birds.

m 187 Reconstruction of Protopteryx, with a long, central tail feather. This unbranched feather may represent the ancestral type of feather, providing evidence lor a scale-feather relationship. (Art: IVPP)

and Confttcit/sornis; the wishbone having a long hypocleideum, and the coracoid elongated.

The juvenile and enantiornithine features of Uaoxiornis indicate that it is a juvenile enantiornithine bird, yet more materials are needed to clarify its phylogenetic position in early avian evolution.

Eoenantiomis Eoenantiornis (Fig. 185) was so named because when it was published in 1999 it represented the most primitive enantiornithine bird

Holotype of Longipteryx chaoyangensis. an opposite bird (size about a dove) with long wings, from Shangheshou locality (Jiufotang Formation) in Chaoyang, Liaoning. (Photo: IVPP)

Protopttryx also preserves bastard wing or alula, which is important lor balance during the slow flight and take-off of birds. It again is a derived feature of birds, suggesting the capacity of more skillful flight in this early bird than in Anbaeopttryx and Confuciusornis.

Longipteryx Longipteryx (i:ig. 188) is a long-winged bird, which was discovered from the same locality of Sapeornts in Chaoyang. Irs fore-limb is markedly longer than the hind limb; the ratio offorelimb to hind limb is about l .i. About nine cervical vertebrae show developed saddle-shaped vertebral body. This is an indicator of high agility of the head and neck.

Lmgipteryx has at least tour uncinate processes on each side; this is the first evidence of such structure in enant ¡ornithine birds. In some modern birds the uncinate processes are attached to the caudal border of the ribs, providing connection between neighboring ribs. The reinforced ribs provide effective attachment for some muscles responsible for flight and respiration.

Longipteryx has long thoracic limb and beak, and it also has strong perching capability. Therefore, it is suggested that the bird probably had a lifestyle comparable to kingfisher. The discovery of Longipteryx also suggests that early enantiornithine birds had undergone a significant radiation in the Early Cretaceous.

Liaoningornis Liaoningornis (Fig. 189) was collected from the Sihetun locality, a site famous for producing the bird Confuciusornis, the feathered dinosaur Sinomithosaurus and many other important vertebrates. Uaoningomis is the only ornithurine bird known from the Yixian Formation. Among ornithurine birds. Liaon/ngomis is a small-sized bird, comparable to the gray starling. It has a nearly completely fused tarsometatarsus. It also has sharp and curved pedal claws, indicating strong perching capability.

Another distinctive feature of this bird is the well-developed keel of the sternum, suggesting that Liaoningornis has more power of flight than enantiornithines and other basal birds. It is also notable that Liaoningornis'sternum is thicker than that of Yanornts and Yixtanornis, both of which are more advanced and younger ornithurine birds also found in western Liaoning (see bellow). The sternum of Liaoningornis also lacks lateral processes.

Yanornis Yanornii (Fig 190) was derived from "Van", name of an ancient country with Chaoyang the capital. It is a large-sized bird, comparable

189 Holotype of Liaoningornis long ¡digitus (Slab A), the only ornithurine bird (size about a sparrow) found in Sihetun locality (lower part of Yixian Formation) in Beipiao, Liaoning. (Photo: IVPP)

to the ring-necked pheasant, This is an orntrhurinc bird from thejiufotang Formation, Long beak, elongated snout and densely distributed reeth art three of the most marked features of Yattornts. The neck vertebrae are long and saddle-shaped, suggesting that Yanornis has head and neck maneuverability comparable to modern birds. The pedal digits are relatively long, but the claws are relatively short. Like modern plover, Yanornis might have spent most of their time 011 the waterside, catching mollusks, fishes or arthropods as food. Tin.- long mouth and flexible long neck are well adapted to this lifestyle.

Yixianornis Yixianornis (Figs. 191, 192) was collected from the Jiufotang Formation in Yixian County, Jinzhou City, Liaoning Province. Compared with Yanornis, Yixianornis has a relatively short head, less teeth in the jaws, and thinner long bones. Like Yanomis, it is an ornithurine bird with a well-developed sternal keel. Yixianornis also preserved well-

190 Holotype of Yannrnis martini, a large ornithurine bird (size about a ring-necked pheasant), from Dapingfang locality (Jiuf'otang Formation) in Chaoyang, Liaoning. (Photo: IVPP)

developed uncinate processes, indicating the presence of a strong ribcage.

Chaoyangia Chaoyangia (Fig. 193) was the first ornithurine bird described from theJehol Biota. It was collected from the same locality of Bnluochia and Cathayornis, the Boluochi site of Chaoyang. It is an incomplete specimen, wirh only partial postcranial bones preserved. Uncinate processes are well preserved in the holotype of Chaoyangia. It has at least nine sacra! vertebrae compared to eight in enantiornithines and seven in Conjuansornn. It also has a well-developed cnemial crest at the proximal tibiotarsus. On the other hand, tt also retains a long pubic symphysis comparable to more primitive birds.

With numerous well-preserved fossils, as well as a high taxonomic diversity represented by both very primitive and quite advanced forms, the Jehol birds have provided important information on the phylogeny and evolution of early birds (Fig. 194). Though still debatable concerning various hypotheses, some consensus has been reached.

Archaeopteryx

Jeholorms

Sapeornis

Confuciusornis

Protopteryx

Eoenantiornis

Cathayornis l.ongipteryx

Yanornis

Yixianornis

Chaoyangia

Modern birds

Holotypc ef Yixianornis grabaui, an ornithurine bird Istighily smaller than Vflnffrois) with well-preserved skeleton and feather imprints, from Qianyang locality (Jiufotang Formation) tn Chaoyang, Liaoning, (Photo: IVPP)

Wing feather of Yixianornis grabatti. same as to those of extant flying birds. {Photo: IVPP)

Holotype of Chaoyangia beishanensis. an ornithurine bird with uncinate processes (denoted by a red arrow) on ribs and developed cnemial crest (denoted by a blue arrow) at the proximal libiutarsus, from Beishan localityQiufotang Formation) in Chaoyang. Liaoning. (Photo: IVPP)

Cladogram showing (he- phylogenetic relationship ofthejehol birds and to Archaeopteryx and modern birds.

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