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 Farly Cretaceous of Asia and a distant relative of Triceratops.

Dinosaure JiufotangManiraptoran

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 ofYixiati Formation), Beipiao, Liaoning. (Photo: IVPP|


1166 Reconstruct ion of IJaucemtops yanzigouensis. (Art: Michael VV, Skrepnick/ FMNH)

Therizinosaurus Skeleton

mm 168 Skull 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: IVPPi

Primitive Ceratopsians

■»169 Holotype of Liaoningosaurus paradoxus (body length less than 40 cm), the smallest ankylosaur found lo date, from Wangjiagou locality (middle part of Yixian Formation), Jinzhou, l.iaoning. (Photo: IVPP)

Cathayornis Yandica Primitive Bird


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. It is not surprising to find both "The Huudred Birds Sing to a Phoenix" in the Cantonese music repertoire and Ottorino Respighi'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 Atvhatoptetyx (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 hits since prevailed over Crcationism.

Birds have light 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: Ijtry D. Martin/ KU}

Reptile Bird Relation

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

Prehistoric LifeComplete Lizard Fossils

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)


i>ptfr)x 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 Irom 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 Meileyingzi 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 Buluochi locality in Chaoyang, Liaoning Province (one of them was later

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

1174 The distal ends of central tail feather of Confuciusornis. (Photo: IVPI'I

1174 The distal ends of central tail feather of Confuciusornis. (Photo: IVPI'I

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

named Cathayorun). These fossils were all from the Early Cretaceous Jiufotang Formation, and fit right in the transition form the Late Jurassic A rcbiiivph-ryx to the Late Cretaceous birds. However, their discovery was only the beginning of a series of exciting fossil findings in the area that have lasted to this day. For instance, over two dozens of bird skeletons were discovered from rhis 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 IVPP. 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 Jiulotang Formation in that area. Hundreds of specimens of Mesozoic birds have been discovered f rom the Jehol Biota since Smurtiis was described, and western Liaoning has increasingly become the hottest area for the study of the origin and early evolution of birds.

Confuciusornis C<>nfunnsumis <l:igs. 171 — 175) is the earliest known bird without teeth. Unlike most other early birds, Confuciusornis had a horny beak, just like tin- 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 had any direct fossil evidence.

Confuciusornis is about the size of Arcbaeupteryx. The postorbital of C/ntfuctusorttis 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 rcbaopttryx, Confuciusornis also has a primitive hand similar to that of A irhneoptcryx. Except for the pectoral girdle anil forelimb, most of other features of Confuciusornis are, however, more derived, suggesting a more powerful flight capability. For example, the distal tail vertebrae of Confuciusornis are fused into one solid bone, pygostyle, which is remarkably distinguishable from that of A rchaeoptrryx that has a long caudal tails with 22 unfused vertebrae. A short and steady body of Confuciusornis is,

11 76 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

11 76 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

Archaeopteryx CoracoidTherizinosaurus
Holotype ofJtbolorttis prima, a primitive bird only slightly more derived than Archaeopierytt. from Dapingfang locality (jiufotang Formation) in Chaoyang, Uaoning. 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. l.iaoning. (Photo: IVPP)

fe Jk t

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 Cathayornis (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 delicate*, a juvenile or subadult opposite bird (size about a Great Tit|. from Dawangzhangzi locality (middle part of Yixian Formation) in Lingyuan. Liaoning- (Plioto: IVPP)

mm 184 Reconst ruct ion of Uaoxiomis delicate*. (Art: Anderson Yang)

mm 184 Reconst ruct ion of Uaoxiomis delicate*. (Art: Anderson Yang)


185 Holotype of Eoenantinrms buhleri, a primitive opposite bird (size about a 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. (PhDto: IVPP)


•*/186 Holotype of Protopteryx fingningmsis (size about a gray starling), the most primitive opposite bird to date, from Sichakou locality (Yixian 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 a hook ;is in some extant raptorial and passerine birds. No tooth has been discovered from the premaxilla. It was therefore proposed that Boluochia probably had a similar lifestyle as some extant raptorial and passerine birds.

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

Liaoxiornis Liaoxtornis (Figs. 183, ltf-i) is the smallest known Mesozoic bird reported from the Yixian Formation in Lingyuan, western Liaoning in 1999. it is about the size of a sparrow.

Liaoxiornis 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 rhar the thighbone is longer than the humerus; die pygostyle is longer than the neck. The derived fea:urcs of Lnjuxtorni> include: the proximal ends of metacarpal bones being fused together; the number ol phalanges of the hand less than that of more primitive birds such as .1 rchaeoptcryx at that time. It is distinguishable from other birds by its relatively short rostrum anil deep skull. Eoenantiomis is smaller than Confmi/tsornis, but larger than other enanr ¡ornithine birds, consistent with the tendency of body size reduction in the evolution of early birds. The teeth of lioiiKiutiornis arc characteristic of all known toothed birds in having a constriction at the base of the crown. Another notable feature of floi/iau/ionus is the preservation ol bastard wing ¿is in Protopteryx. The bastard wing was not present in Arcbae-opttryx and Confud/isumis. It is probably present in ail other enanriornirhines and ornithurines (all extant birds are ornithurine birds).

Protopteryx Protopteryx (Figs, 186, IS7) is about the size of a gray starling. As its name implies it is "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 rachts, 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 f Confm'iusoniis and some other en ant ¡ornithine birds.

Protopteryx alst) 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 Confuciusornis; 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 ;ire needed ro clarify its phylogenetic position in early avian evolution.

Eoenantiomis Boenantiornis (Fig. IS 5) was so named because when it was published in 1999 tr represented the most primitive enantiornithine bird

Prehistoric Life

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

Protopteryx also preserves bastard wing or alula, which is important lor balance during the- slow flighr 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 Anhanpttryx and Confuciusornis.

Longipteryx Longiptetyx (l:ig. 188) is a long-winged bird, which was discovered from the same locality of Sapeornts in Chaoyang. Irs forelimb is markedly longer than the hind limb; the ratio of forelimb 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.

hmgipteryx has at least four uncinate processes on each side; this is the first evidence of such structure in enantiornithine birds. In some modern birds rile 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 Sinornithosaurns and many other important vertebrates. Uaoningomis is the only ornithurine bird known from the Yixian Formation. Among ornithurine birds. Uaoningomis 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 Yanornis and Yixtanornis, both ol which are more advanced and younger ornithurine birds also found in western Liaoning (see bellow). The sternum of Liaoningornis also lacks lateral processes.

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

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 teeth are three of the most marked features of Yattornts. The neck vertebrae are long and saddle-shaped, suggesting that Yanomis has head and neck maneuverability comparable to modem birds. The pedal dibits are relatively long, but the claws are relatively short. Like modern plover, Yanomis might have spent most of their time on the waterside, catching mollusks, fishes or arthropods as food. The 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 Yanomis, 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 (Jiufotang 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 the Jehol biota. It was collected from the same locality of Bnluochia and Cathayornis, the Boluochi site of Chaoyang. It is an incomplete specimen, with only partial postcranial bones preserved. Uncinate processes are well preserved in the holotype of Chaoyangia. It has at least nine sacral vertebrae compared to eight in enantiornithines and seven in Confiittitsornis. It also has a well-developed cnemial crest at the proximal tibiotarsus. On the other hand, tt also retains a long pubic symphysis comparable ro 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.













Modern birds

Holotype ef Yixianornis grabaui, an omithwine bird Istighily smaller than Yawnis! with well-preserved skeleton and feather imprints, from Qianyang locality (Jiufotang Formation) in Chaoyang, Liaoning, (Photo: IVPP)

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

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

Cladogram showing the phylogenetic relationship of the Jehol birds and to Atrhaeopteryx and modern birds.

Prehistoric Life

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