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117-471: Stem group genera: The Judomioidea are a superfamily of trilobites , a group of extinct marine arthropods . Its species lived during the Lower Cambrian ( Atdabanian ). This Redlichiida -related article is a stub . You can help Misplaced Pages by expanding it . Crown group#Stem groups The concept was developed by Willi Hennig , the formulator of phylogenetic systematics , as

234-459: A Confuciusornis skeleton preserving an egg near its right foot – the first possible egg referable to the genus. The skeleton is from the short-tailed form and thus might represent a female. The egg might have fallen out of the body after the death of the presumed female, although it cannot be excluded that this association of an adult with an egg was only by chance. The egg is roundish in shape and measures 17 mm in diameter, slightly smaller than

351-422: A pygostyle (a bone formed from a series of short, fused tail vertebrae) and a bony sternum (breastbone), but more basal or "primitive" than modern birds in retaining large claws on the forelimbs, having a primitive skull with a closed eye-socket, and a relatively small breastbone. At first the number of basal characteristics was exaggerated: Hou assumed in 1995 that a long tail was present and mistook grooves in

468-666: A 2010 paper, Gareth Dyke and Kaiser showed that the breadth of the Confuciusornis egg was indeed smaller than what would be expected for a modern bird of similar size. In a 2016 book, Luis Chiappe and Meng Qingjin stated that the aperture of a large specimen (DNHM-D 2454) indicates a maximum egg diameter of 23 millimetres (0.91 in). In modern birds, proportionally large eggs are commonly found in species whose hatchlings do fully depend on their parents ( altriciality ), while smaller eggs are often found in species whose hatchlings are more developed and independent ( precociality ). As

585-537: A 2016 review by David Varricchio and Frankie Jackson argued that nesting above the ground evolved only at a much later stage, within Neornithes, and that Mesozoic birds would have buried their eggs on the ground, either fully or partially, as seen in non-avian dinosaurs. Growth can be reconstructed based on the inner bone structure. The first such study on Confuciusornis , presented by Fucheng Zhang and colleagues in 1998, used scanning electron microscopy to analyze

702-438: A central keel, a strut-like coracoid, a large deltopectoral crest, a strong ulna (forearm bone) and an enlarged second metacarpal. The sternal keel and deltopectoral crest (which provides a more powerful upstroke) are adaptations to flapping flight in modern birds, indicating that Confuciusornis may have been capable of the same. However, it may have had a different flight stroke due to being incapable of rotating its arm behind

819-597: A defense mechanism, a method used by several extant species. Such shedding would have been triggered by stress induced by the very volcanic explosions that buried the animals, resulting in a large number of specimens lacking these feathers. In a 2011 paper, Jesús Marugán-Lobón and colleagues stated that even the presence of two separate species, one with and one without long tail feathers, needs to be considered. This possibility would be, however, unsubstantiated at present, as other anatomical differences between these possible species are not apparent. In 2007, Gary Kaiser mentioned

936-410: A femur in cross section. Because the bone was well vascularized (contained many blood vessels) and showed only a single line of arrested growth (growth ring), these authors determined that growth must have been fast and continuous as in modern birds, and that Confuciusornis must have been endothermic . Zhang and colleagues corroborated this claim in a subsequent paper, stating that the bone structure

1053-495: A fossil Confuciusornis specimen, IVPP V13171. They reported the presence of melanosomes were of two types: eumelanosomes and pheomelanosomes . This indicated that Confuciusornis had hues of grey, red/brown and black, possibly something like the modern zebra finch . It was also the first time an early bird fossil has been shown to contain preserved pheomelanosomes. However, a second research team failed to find these reported traces of pheomelanosomes. Their 2011 study also found

1170-427: A function in reproduction at all. Several alternative hypotheses explaining the frequent absence of long tail feathers have been proposed. In their 1999 study, Chiappe and colleagues discussed the possibility that individuals might lack tail feathers because they died during molting . Although direct evidence for molting in early birds is missing, the lack of feather abrasion in Confuciusornis specimens suggests that

1287-409: A large region including Liaoning, Hebei, and Inner Mongolia. Due to the great abundance, preservation, and commercial value of the fossils, excavations by local farmers produced an unusually high number of fossils. Although a portion of these fossils have been added to the collections of Chinese research institutions, more have probably been smuggled out of the country. In 1999, it was estimated that

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1404-416: A link between the presence of certain metals, like copper , and preserved melanin . Using a combination of fossil impressions of melanosomes and the presence of metals in the feathers, the second team of scientists reconstructed Confuciusornis with darkly colored body feathers and upper wing feathers, but found no trace of either melanosomes or metals in the majority of the wing feathers. They suggested that

1521-430: A more "primitive" skull than Archaeopteryx , but it is the first known bird to have lost the long tail of Archaeopteryx and develop fused tail vertebrae, a pygostyle . One controversial study concluded that Confuciusornis may be more closely related to Microraptor and other dromaeosaurids than to Archaeopteryx , but this study was criticized on methodological grounds. The present standard interpretation of

1638-440: A species. In the case of Confuciusornis , only C. sanctus is universally accepted. In 2002 Hou named the genus Jinzhouornis , but Chiappe et al. (2018) and Wang et al. (2018) showed that this genus is a junior synonym of Confuciusornis based on morphometry and examination of known confuciusornithiform specimens. Confuciusornis was about the size of a modern crow , with a total length of 50 centimetres (1.6 feet) and

1755-432: A squirrel. Daniel Hembree, however, while acknowledging that tree climbing was likely, pointed out that the rump was apparently not lifted more than 25° relative to the femur in vertical position, as shown by the location of the antitrochanter in the hip joint. Dieter S. Peters considered it very unlikely that Confuciusornis climbed trunks as turning the thumb claw inwards would stretch the very long wing forwards, right in

1872-432: A stem group allows the order of these acquisitions to be established, and thus the ecological and functional setting of the evolution of the major features of the group in question. Stem groups thus offer a route to integrate unique palaeontological data into questions of the evolution of living organisms. Furthermore, they show that fossils that were considered to lie in their own separate group because they did not show all

1989-415: A straight airfoil . This collectively is strongly indicative that Confuciusornis was capable of powered flight, if not only for short periods of time. Many specimens of Confuciusornis preserve a single pair of long, streamer-like tail feathers, similar to those present in some modern birds-of-paradise . Specimens lacking these feathers include ones that otherwise have exquisitely preserved feathers on

2106-484: A third one, were formally described as a new genus and species of bird, Confuciusornis sanctus , by Hou and colleagues. The generic name combines the philosopher Confucius with Greek ὄρνις ( ornis ), "bird". The specific name means "holy one" in Latin and is a translation of Chinese 圣贤 ( shèngxián) , "sage", again in reference to Confucius. The first discovered specimen was designated the holotype and catalogued under

2223-440: A way of classifying living organisms relative to their extinct relatives in his "Die Stammesgeschichte der Insekten", and the "crown" and "stem" group terminology was coined by R. P. S. Jefferies in 1979. Though formulated in the 1970s, the term was not commonly used until its reintroduction in 2000 by Graham Budd and Sören Jensen . It is not necessary for a species to have living descendants in order for it to be included in

2340-413: A wingspan of up to 70 cm (2.3 ft). Its body weight has been estimated to have been as much as 0.5 kilograms (1.1 lb), or as little as 0.2 kg (0.44 lb). C. feducciai was about a third longer than average specimens of C. sanctus . Confuciusornis shows a mix of basal and derived traits. It was more "advanced" or derived than Archaeopteryx in possessing a short tail with

2457-565: Is a genus of basal crow -sized avialan from the Early Cretaceous Period of the Yixian and Jiufotang Formations of China, dating from 125 to 120 million years ago. Like modern birds, Confuciusornis had a toothless beak, but closer and later relatives of modern birds such as Hesperornis and Ichthyornis were toothed, indicating that the loss of teeth occurred convergently in Confuciusornis and living birds. It

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2574-416: Is commonly found as large assemblages in lake bottom sediments with little to no evidence of extensive postmortem transport, and that it would be highly unusual for gliding animals to be found in such large numbers in deep water. Rather, this evidence suggests that Confuciusornis traveled in large flocks over the lake surfaces, a habitat consistent with a flying animal. A number of researchers have questioned

2691-429: Is consistent with either birds that live in dense forests or gliding birds; the former is consistent with its environment being densely forested, and requiring more maneuverability and stability than speed. The substantial propatagium would have produced a generous amount of lift, while the likewise large postpatagium would have provided a large attachment area for the calami of the feathers, which would have kept them as

2808-423: Is given the designation "crown-", to separate it from the group as commonly defined. Both birds and mammals are traditionally defined by their traits, and contain fossil members that lived before the last common ancestors of the living groups or, like the mammal Haldanodon , were not descended from that ancestor although they lived later. Crown-Aves and Crown-Mammalia therefore differ slightly in content from

2925-632: Is no consensus phylogeny. Stem arthropods constitute a group that has seen attention in connection with the Burgess Shale fauna. Several of the finds , including the enigmatic Opabinia and Anomalocaris have some, though not all, features associated with arthropods , and are thus considered stem arthropods. The sorting of the Burgess Shale fauna into various stem groups finally enabled phylogenetic sorting of this enigmatic assemblage and also allowed for identifying velvet worms as

3042-547: Is the assessment that due to the lack of a keeled sternum and a high acrocoracoid, the musculus pectoralis minor could not serve as a M. supracoracoideus lifting the humerus via a tendon running through a foramen triosseum . This, coupled with a limited upstroke caused by a lateral position of the shoulder joint, would have made it difficult to gain altitude. Some authors, therefore, proposed that Confuciusornis used its large thumb claws to climb tree trunks. Martin assumed that it could raise its torso almost vertically like

3159-461: Is the crown group and all organisms more closely related to it than to any other extant organisms. In a tree analogy, it is the crown group and all branches back to (but not including) the split with the closest branch to have living members. The Pan-Aves thus contain the living birds and all (fossil) organisms more closely related to birds than to crocodilians (their closest living relatives). The phylogenetic lineage leading back from Neornithes to

3276-448: Is the most likely explanation for the presence and absence of long tail feathers. Winfried and Dieter Peters, however, responded in 2009 that both sexes likely had long tail feathers, as is the case in most modern birds that show similar feathers. One of the sexes, however, would have been larger than the other (sexual size dimorphism). These researchers further suggested that the distribution of size and long tail feathers in Confuciusornis

3393-458: Is thought by some to make the Cambrian explosion easier to understand without invoking unusual evolutionary mechanisms; however, application of the stem group concept does nothing to ameliorate the difficulties that phylogenetic telescoping poses to evolutionary theorists attempting to understand both macroevolutionary change and the abrupt character of the Cambrian explosion . Overemphasis on

3510-620: The Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) at Beijing , visited fossil collector Zhang He at his home in Jinzhou , where he showed them a fossil bird specimen that he had bought at a local flea market. In December, Hou learned about a second specimen, which had been discovered by a farmer named Yang Yushan. Both specimens were found in the same locality in Shangyuan, Beipiao . In 1995, these two specimens, as well as

3627-544: The Jehol Biota , which in the next decades would reveal the most important record of Mesozoic birds worldwide. In the late 1990s, Confuciusornis was thought to be both the oldest beaked bird as well as the earliest bird after Archaeopteryx . It was also considered to be only slightly younger than Archaeopteryx – the Yixian Formation , the rock unit where most Confuciusornis specimens have been found,

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3744-616: The National Geological Museum of China in Beijing housed nearly 100 specimens of Confuciusornis , and in 2010, the Shandong Tianyu Museum of Nature was reported to possess 536 specimens of the bird. The majority of specimens, however, are held privately and thus are not available for research. At one time forty individuals were discovered on a surface of about 100 m . This has been explained as

3861-405: The dinosaurs and the pterosaurs . The last common ancestor of birds and crocodilians—the first crown group archosaur—was neither bird nor crocodilian and possessed none of the features unique to either. As the bird stem group evolved, distinctive bird features such as feathers and hollow bones appeared. Finally, at the base of the crown group, all traits common to extant birds were present. Under

3978-466: The last common ancestor of the crown group and their closest living relatives. It follows from the definition that all members of a stem group are extinct. The "stem group" is the most used and most important of the concepts linked to crown groups, as it offers a means to reify and name paraphyletic assemblages of fossils that otherwise do not fit into systematics based on living organisms. While often attributed to Jefferies (1979), Willmann (2003) traced

4095-426: The lungfish , our nearest relatives among the fishes. In addition to a series of lobe-finned fishes , they also include some of the early labyrinthodonts . Exactly what labyrinthodonts are in the stem group tetrapods rather than the corresponding crown group is uncertain, as the phylogeny of early tetrapods is not well understood. This example shows that crown and stem group definitions are of limited value when there

4212-680: The phylogenetic position of Confuciusornis can be shown in this cladogram : Archaeopteryx Jeholornis Sapeornis Confuciusornis Changchengornis Enantiornithes Ornithuromorpha (including the Neornithes ) A close relative, the confuciusornithid Changchengornis hengdaoziensis , also lived in the Yixian Formation. Changchengornis also possessed the paired, long tail feathers, as did several more advanced enantiornith birds. True, mobile tail fans only appeared in ornithuromorph birds, and possibly in

4329-434: The scleral rings supporting the eyes of Confuciusornis and modern birds and other reptiles indicate that it may have been diurnal , similar to most modern birds. Confuciusornis has traditionally been assumed to have been a competent flier based on its extremely long wings with strongly asymmetrical feathers. Other adaptations for improved flight capabilities include: a fused wrist, a short tail, an ossified sternum with

4446-468: The Chinese fossil material with a differing rachis diameter. In 2016, Falk et al. argued in favor of flight capabilities for Confuciusornis using evidence from laser fluorescence of two soft tissue-preserving specimens. They found that, contrary to Nudds and Dyke's assertions, the raches of Confuciusornis were relatively robust, with a maximum width of over 1.5 mm (0.059 in). The wing shape

4563-527: The Crocodilia branch. Basal branch names such as Avemetatarsalia are usually more obscure. However, not so advantageous are the facts that "Pan-Aves" and "Aves" are not the same group, the circumscription of the concept of "Pan-Aves" (synonymous with Avemetatarsalia) is only evident by examination of the above tree, and calling both groups "birds" is ambiguous. Stem mammals are those in the lineage leading to living mammals, together with side branches, from

4680-592: The Enantiornithes were closely related. In 2001, Ji Qiang suggested an alternative position as the sister taxon of the Ornithothoraces . In 2002 Ji's hypothesis was confirmed by a cladistic analysis by Chiappe, who defined a new group: the Pygostylia of which Confuciusornis is by definition the most basal member. Several traits of Confuciusornis show its position in bird evolution; it has

4797-410: The bird crown group. One very simplified cladogram for birds is shown below: † Archaeopteryx other extinct groups Neornithes (modern birds, some extinct like the dodo) In this diagram, the clade labelled "Neornithes" is the crown group of birds: it includes the most recent common ancestor of all living birds and its descendants, living or not. Although considered to be birds (i.e. members of

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4914-486: The body, and its relatively smaller sternal keel indicates that it likely was not capable of flight for extended periods of time. Several contrary claims have been made against that the flight capabilities of Confuciusornis . The first of these regarded problems to attain a steep flight path due to a limited wing amplitude. In Senter's interpretation of the position of the shoulder joint, a normal upstroke would be impossible precluding flapping flight entirely. Less radical

5031-434: The braincase wall, making its exact borders impossible to determine, which is also true for adult modern birds. Various interpretations have been proposed of the morphology and identity of the bones in the temporal region behind the orbits, but it may not be resolvable with the available fossils. Confuciusornis was considered the first known bird with an ancestral diapsid skull (with two temporal fenestrae on each side of

5148-404: The clade Aves), Archaeopteryx and other extinct groups are not included in the crown group, as they fall outside the Neornithes clade, being descended from an earlier ancestor. An alternative definition does not require any members of a crown group to be extant, only to have resulted from a "major cladogenesis event". The first definition forms the basis of this article. Often, the crown group

5265-520: The closest living relatives of arthropods. Stem priapulids are other early Cambrian to middle Cambrian faunas, appearing in Chengjiang to Burgess Shale. The genus Ottoia has more or less the same build as modern priapulids , but phylogenetic analysis indicates that it falls outside the crown group, making it a stem priapulid. The name plesion has a long history in biological systematics, and plesion group has acquired several meanings over

5382-457: The common definition of Aves and Mammalia. This has caused some confusion in the literature. The cladistic idea of strictly using the topology of the phylogenetic tree to define groups necessitates other definitions than crown groups to adequately define commonly discussed fossil groups. Thus, a host of prefixes have been defined to describe various branches of the phylogenetic tree relative to extant organisms. A pan-group or total group

5499-434: The correctness of the rachis measurements, stating that the specimens they had studied showed a shaft thickness of 2.1–2.3 millimetres (0.083–0.091 in), compared to 1.2 mm (0.047 in) as reported by Nudds and Dyke. Nudd and Dyke replied that, apart from the weight aspect, such greater shaft thickness alone would make flapping flight possible; however, they allowed for the possibility of two species being present in

5616-434: The cotyla (which connected with the condyle of the upper jaw), and this part was therefore similar to a retroarticular process as seen in other taxa. The surangular enclosed two mandibular fenestrae. The hindmost part of the surangular had a small foramen placed in the same position as similar openings in the mandibles of non-bird theropods and modern birds. The splenial bone was three-pronged (as in some modern birds, but unlike

5733-463: The crown group. Extinct side branches on the family tree that are descended from the most recent common ancestor of living members will still be part of a crown group. For example, if we consider the crown-birds (i.e. all extant birds and the rest of the family tree back to their most recent common ancestor), extinct side branches like the dodo or great auk are still descended from the most recent common ancestor of all living birds , so fall within

5850-488: The diagnostic features of a living clade, can nevertheless be related to it by lying in its stem group. Such fossils have been of particular importance in considering the origins of the tetrapods , mammals , and animals . The application of the stem group concept also influenced the interpretation of the organisms of the Burgess shale . Their classification in stem groups to extant phyla, rather than in phyla of their own,

5967-515: The divergence of the lineage from the Sauropsida to the last common ancestor of the living mammals. This group includes the synapsids as well as mammaliaforms like the morganucodonts and the docodonts ; the latter groups have traditionally and anatomically been considered mammals even though they fall outside the crown group mammals. Stem tetrapods are the animals belonging to the lineage leading to tetrapods from their divergence from

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6084-412: The earlier histological findings of de Ricqlès that suggest a much shorter, avian-style growth. Alternatively, the observed size distribution might also be explained by the presence of more than one species, although there are no anatomical features that could be correlated with these potential species. It could also be explained by assuming an attritional death assemblage, in which mortality rates (and thus

6201-411: The enantiornithine Shanweiniao . The large, fleshy phalangeal foot pads, small interphalangeal foot pads, presence of only reticulate scales on the underside of the foot (which increases flexibility), and curved foot claws of Confuciusornis are all traits shared with modern tree-dwelling , perching birds, suggesting that Confuciusornis may have had a similar lifestyle. Comparisons between

6318-526: The estimated egg of the specimen would have been around 30% smaller than expected for a modern altricial bird, it is likely that Confuciusornis was precocial. A 2018 study by Charles Deeming and Gerald Mayr measured the size of the pelvic canal of various Mesozoic birds including Confuciusornis to estimate egg size, concluding that eggs would have been small in proportion to body mass for Mesozoic birds in general. These researchers further posit that an avian-style contact incubation (sitting on eggs for breeding)

6435-544: The evolutionary line leading to modern birds. This view was contested by subsequent studies, which pointed out that slow growing bone is not necessarily an indicator for low metabolic rates, and in the case of Mesozoic birds was rather a result of the decrease in body size that characterized the early evolution of birds. A more comprehensive study based on thin sectioning of bones was published by Armand de Ricqlès and colleagues in 2003. Based on 80 thin sections taken from an adult Confuciusornis exemplar, this study confirmed

6552-505: The extinct moa ) The crown group here is Neornithes , all modern bird lineages back to their last common ancestor. The closest living relatives of birds are crocodilians . If we follow the phylogenetic lineage leading to Neornithes to the left, the line itself and all side branches belong to the stem birds until the lineage merges with that of the crocodilians. In addition to non-crown group primitive birds like Archaeopteryx , Hesperornis and Confuciusornis , stem group birds include

6669-461: The extremely fast growth characteristic for modern birds (6–8 weeks), suggesting that that growth was secondarily accelerated later in avian evolution. In 2008 Chiappe and colleagues conducted a statistical analysis based on 106 specimens to explore the relationship between body size and the possession of long tail feathers. The population showed a clear bimodal distribution of the size of the animals with two distinct weight classes . However, there

6786-407: The feather ligaments. Many specimens preserve a pair of long, narrow tail feathers, which grew longer than the entire length of the rest of the body. Unlike the feathers of most modern birds, these feathers were not differentiated into a central quill and barbs for most of their length. Rather, most of the feather formed a ribbon-like sheet, about six millimetres wide. Only at the last one quarter of

6903-582: The feather, towards the rounded tip, does the feather become differentiated into a central shaft with interlocking barbs. Many individuals of Confuciusornis lacked even these two tail feathers, possibly due to sexual dimorphism . The rest of the tail around the pygostyle was covered in short, non-aerodynamic feather tufts similar to the contour feathers of the body, rather than the familiar feather fan of modern bird tails. Laser fluorescence of two Confuciusornis specimens revealed additional details of their soft-tissue anatomy. The pro patagium of Confuciusornis

7020-416: The first finger to the contrary was very large and curved. The stub-like third metacarpal, which supported the calami of the feathers, was probably enclosed in the flesh of the hand. The formula of the finger phalanges was 2-3-4-0-0. The pelvis was connected to a sacrum formed by seven sacral vertebrae . The pubis was strongly pointing backwards. The left and right ischia were not fused. The femur

7137-494: The front half of the synsacrum were excavated at their sides, comparable to the back vertebrae. Robust side processes connected the synsacrum to the ilia of the pelvis. Although earlier descriptions had counted four or five "free", not fused, tail vertebrae, Chiappe e.a. in 1999 reported seven of them. These had round and somewhat concave front articulation facets. Their spinal processes were high and transversely compressed. The side processes were robust and stick out horizontally to

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7254-432: The full bifurcating phylogeny. Stem birds perhaps constitute the most cited example of a stem group, as the phylogeny of this group is fairly well known. The following cladogram, based on Benton (2005), illustrates the concept: Crocodilia Pterosauria Hadrosauridae Stegosauria Sauropoda Tyrannosauridae Archaeopteryx Neognathae (including the extinct dodo ) Paleognathae (including

7371-480: The hand, but this digit appears to have been free of feathers and independent of the body of the wing in Confuciusornis . According to Dieter Stefan Peters, to compensate for the lack of an alula, the third finger might have formed a separate winglet below the main wing, functioning like the flap of an aircraft. Despite the relatively advanced and long wing feathers, the forearm bones lacked any indication of quill knobs ( papillae ulnares ), or bony attachment points for

7488-417: The head of the animal; according to Kaiser, it would have fit precisely through the pelvic canal of the bird. In dinosaurs and Mesozoic birds, the width of the pelvic canal was restricted due to connection of the lower ends of the pubic bones, resulting in a V-shaped bony aperture through which eggs must fit. In modern birds, this connection of the pubic bones is lost, presumably allowing for larger eggs. In

7605-404: The high growth rates proposed by Zhang and colleagues. The fast-growing fibrolamellar bone tissue was similar to that seen in non-avian theropods, and the sampled individual probably reached adult size in much less than 20 weeks. Small body size was not primarily achieved by slowing growth but by shortening the period of rapid growth. The growth rate estimated for Confuciusornis is still lower than

7722-420: The holotype, and that this lack of overlap makes their referral to the species speculative. Only the discovery of a great number of well-preserved specimens shortly after had confirmed that the specimens indeed represent a single species. Together with the early mammal Zhangheotherium , which was discovered at around the same time, Confuciusornis was considered to be the most remarkable fossil discovery of

7839-409: The jaw bones for small degenerated teeth. The skull morphology of Confuciusornis has been difficult to determine, due to the crushed and deformed nature of the fossils. The skull was near triangular in side view, and the toothless beak was robust and pointed. The front of the jaws had deep neurovascular foramina and grooves, associated with the keratinous rhamphotheca (horn-covered beak). The skull

7956-441: The length of the hand and relatively longer than those of any living bird, while the secondary feathers of the lower arm were rather short by comparison. The outermost primary was much shorter than the second outermost primary, creating a relatively round, broad wing. Its wing shape does not specifically match any particular shape found among living birds. The primary feathers were asymmetrical to varying degrees, and especially so in

8073-404: The lower end of the postorbital process. This scaffolding consisted of two bony bridges, the temporal bar and the orbitozygomatic junction, which gave the appearance of the temporal opening being divided similarly to diapsid skulls, though this structure is comparable to bridges over the temporary fossa in modern birds. The mandible (lower jaw) is one of the best preserved parts of the skull. It

8190-475: The lower jaw connected) of the dentary was very robust. The lower margin formed an angle at the level of the front margin of the nasal foramen, which indicates how far back the rhamphotheca of the beak extended. The dentary had three processes that extended backwards into other bones placed further back in the mandible. The articular bone at the back of the mandible was completely fused with the surangular and prearticular bones. The mandible extended hindwards beyond

8307-451: The maxilla. The orbit was large, round, and contained sclerotic plates (the bony support inside the eye). A crescent-shaped element that formed the front wall of the orbit may be an ethmoidolacrimal complex similar to that of pigeons , but the identity of these bones is unclear due to bad preservation, and the fact that this region is very variable in modern birds. The external nares (bony nostrils) were near triangular and positioned far from

8424-464: The narrower one. Often, an (extinct) grouping is identified as belonging together. Later, it may be realized other (extant) groupings actually emerged within such grouping, rendering them a stem grouping. Cladistically , the new groups should then be added to the group, as paraphyletic groupings are not natural. In any case, stem groupings with living descendants should not be viewed as a cohesive group, but their tree should be further resolved to reveal

8541-420: The orbits (eye openings) like in modern birds, but unlike Archaeopteryx and other primitive birds without pygostyles, where these processes end in front of the orbits. The maxilla (the second large bone of the upper jaw) and premaxilla articulated by an oblique suture, and the maxilla had an extensive palatal shelf. The nasal bone was smaller than in most birds, and had a slender process that directed down towards

8658-479: The origin of the stem group concept to Austrian systematist Othenio Abel (1914), and it was discussed and diagrammed in English as early as 1933 by A. S. Romer . Alternatively, the term "stem group" is sometimes used in a wider sense to cover any members of the traditional taxon falling outside the crown group. Permian synapsids like Dimetrodon or Anteosaurus are stem mammals in the wider sense but not in

8775-409: The outermost primaries. It is unclear whether the upper arm carried tertiaries. Covert feathers are preserved covering the upper part of the wing feathers in some specimens, and some specimens have preserved the contour feathers of the body. Unlike some more advanced birds, Confuciusornis lacked an alula , or "bastard wing". In modern birds this is formed by feathers anchored to the first digit of

8892-401: The outline of an upwards curving beak which sharply tapers towards its tip, while a C. sanctus specimen (IVPP V12352) has an upper margin that is almost straight, and a tip that appears to be slightly hooked downwards. Two further specimens (STM13-133 and STM13-162) belonging to an indeterminate species were described in 2020; the former suggests that, unlike modern birds, the beak on both jaws

9009-406: The path of obstructing branches. Peters sees Confuciusornis as capable of flapping flight but specialised in soaring flight. Also a controversy is the strength of the feathers. In 2010, Robert Nudds and Gareth Dyke published a study arguing that in both Confuciusornis and Archaeopteryx , the raches (central shafts) of the primary feathers were too thin and weak to have remained rigid during

9126-433: The pattern might reflect sexual dimorphism , with the streamer-like feathers only present in one sex (likely the males) which used them in courtship displays. This interpretation was followed by the majority of subsequent studies. Chiappe and colleagues, in 1999, argued that sexual dimorphism is not the only but the most reasonable explanation, noting that in modern birds the length of ornamental feathers often varies between

9243-499: The phylogenetic split from the remaining amniotes (the Sauropsida ). Pan-Mammalia is thus an alternative name for Synapsida . A stem group is a paraphyletic assemblage composed of the members of a pan-group or total group, above, minus the crown group itself (and therefore minus all living members of the pan-group). This leaves primitive relatives of the crown groups , back along the phylogenetic line to (but not including)

9360-399: The plumage got periodically renewed. As in modern birds, molting individuals may have been present alongside non-molting individuals, and males and females may have molted at different times during the year, possibly explaining the co-occurrence of specimens with and without long tail feathers. Peters and Petters, on the other hand, suggested that Confuciusornis may have shed the feathers as

9477-438: The point where it merges with the crocodilian lineage, along with all side branches, constitutes pan-birds. In addition to non-crown group primitive birds like Archaeopteryx , Hesperornis and Confuciusornis , therefore, pan-group birds would include all dinosaurs and pterosaurs as well as an assortment of non-crocodilian animals like Marasuchus . Pan-Mammalia consists of all mammals and their fossil ancestors back to

9594-410: The power stroke required for true flight. They argued that Confuciusornis would at most have employed gliding flight , which is also consistent with the unusual adaptations seen in its upper arm bones, and more likely used its wings for mere parachuting, limiting fall speed if it dropped from a tree. Gregory S. Paul , however, disagreed with their study. He argued that Nudds and Dyke had overestimated

9711-445: The rarity of individuals with an intermediate size was caused by Confuciusornis experiencing a growth spurt just prior to reaching adulthood, the shortness of which would have prevented many becoming fossilized during this phase. This initially slow growth followed by a growth spurt would have resulted in a S-shaped growth curve , similar to that inferred for non-avian dinosaurs. Such an extended dinosaurian mode of growth conflicts with

9828-568: The rest of the body, indicating that their absence is not simply due to poor preservation. Larry Martin and colleagues stated in 1998 that long tail feathers are present in about 5 to 10% of the specimens known at the time. A 2011 analysis by Jesús Marugán-Lobón and colleagues found that out of 130 specimens, 18% had long tail feathers and 28% had not, while in the remaining 54% preservation was insufficient to determine their presence or absence. The biological meaning of this pattern has been discussed controversially. Martin and colleagues suggested that

9945-516: The result of entire flocks of birds being simultaneously killed by ash, heat or poisonous gas following the volcanic eruptions that caused the tuff stone in which the fossils were found to be deposited as lake sediments . Since the description of Confuciusornis sanctus , five additional species have been formally named and described. As with many other fossil genera, species are difficult to define, as differences between species can often not be readily distinguished from variation that occurs within

10062-402: The same would have been true for Archaeopteryx . The wrist of Confuciusornis shows fusion, forming a carpometacarpus . The second and third metacarpals were also partially fused, but the first was unfused, and the fingers could freely move relative to each other. The second metacarpal, which supported the flight feathers, was very heavily built; its finger carries a small claw. The claw of

10179-426: The sexes. Controversy arose from the observation that the known specimens of Confuciusornis can be divided into a small-sized and a large-sized group, but that this bimodal distribution is unrelated to the possession of long tail feathers. Chiappe and colleagues argued in 2008 that this size distribution can be explained by a dinosaur-like mode of growth (see section Growth ), and maintained that sexual dimorphism

10296-410: The shoulder joint was sideways, instead of angled upward as in modern birds; this means that Confuciusornis was unable to lift its wings high above its back. According to a study by Phil Senter in 2006, the joint was even pointed largely downwards meaning that the humerus could not be lifted above the horizontal. This would make Confuciusornis incapable of the upstroke required for flapping flight ;

10413-453: The side. Their articulation processes were rather long. The last of these vertebrae had a rectangular profile. Its neural arch had short processes pointing obliquely to above and sideways. The tail ended in a pygostyle, a complete fusion of the last vertebrae. Their number is uncertain. The pygostyle was about 40% longer than the first part of the tail. At its underside the pygostyle bore a well-developed keel, running from front to rear. Its top

10530-407: The simple splenial of Archaeopteryx ), and its lower margin followed the lower margin of the mandible. There was a large rostral mandibular fenestra and a small, rounded caudal fenestra behind it. Though only five specimens preserve parts of the beak's keratinous covering, these show that there would have been differences between species not seen in the skeleton. The holotype of C. dui preserves

10647-402: The skull roof much farther behind in modern birds, making the frontal bone of Confuciusornis small compared to those of modern birds. A prominent supraorbital flange formed the upper border of the orbit, and continued as the postorbital process, which had prominent crests which projected outwards to the sides, forming an expansion of the orbit's rim. The squamosal bone was fully incorporated into

10764-417: The skull) in the late 1990s, but in 2018, Elzanowski and colleagues concluded that the configuration seen in the temporal region of confuciusornithids was autapomorphic (a unique trait that evolved secondarily rather than having been retained from a primitive condition) for their group. The quadrate bone and the back end of the jugal bar were bound in a complex scaffolding that connected the squamosal bone with

10881-432: The spaces between the vertebral body and the neural arch . Their spinal processes were tall and narrow in side view. Their side processes projected horizontally and were deeply excavated at the rear underside. The sides of the back vertebrae also had deep oval excavations. Seven sacral vertebrae were fused into a synsacrum . The front sacral vertebra had a round and concave front articulation facet. The vertebral bodies of

10998-455: The specimen number IVPP V10918; it comprises a partial skeleton with skull and parts of the forelimb. Of the other two skeletons, one ( paratype , IVPP V10895) comprises a complete pelvis and hind limb, and the other (paratype, IVPP V10919–10925) a fragmentary hind limb together with six feather impressions attached to both sides of the tibia (shin bone). It was soon noted that the two paratype specimens only comprise bones that are unknown from

11115-456: The stem group concept threatens to delay or obscure proper recognition of new higher taxa. As originally proposed by Karl-Ernst Lauterbach , stem groups should be given the prefix "stem" (i.e. Stem-Aves, Stem-Arthropoda), however the crown group should have no prefix. The latter has not been universally accepted for known groups. A number of paleontologists have opted to apply this approach anyway. Confuciusornis Confuciusornis

11232-431: The tip of the snout. The borders of the nostrils were formed by the premaxillae above, the maxilla below, and the nasal wall at the back. Few specimens preserve the sutures of the braincase, but one specimen shows that the frontoparietal suture crossed the skull just behind the postorbital process and the hindmost wall of the orbit. This was similar to Archaeopteryx and Enaliornis , whereas it curves back and crosses

11349-421: The toes suggest that they were used for both walking and perching, while the large claws of the thumb and third finger were probably used for climbing. The wing feathers of Confuciusornis were long and modern in appearance. The primary wing feathers of a 0.5-kilogram individual reached 20.7 centimetres in length. The five longest primary feathers ( remiges primarii ) were more than 3 + 1 ⁄ 2 times

11466-566: The underside. The next, the axis, had an expanded spinal process on the top and its side was excavated by an elongated groove in the side. The remaining neck vertebrae all had rather low spinal processes. There is no clear evidence of a pneumatisation, in the form of internal air spaces, of the vertebral bodies of the neck. The front articulation facets of the neck vertebrae were saddle-shaped. Their undersides were pinched. There were at least twelve back vertebrae. They were amphiplatian, flat at both ends, and had rather small intervertebral foramina ,

11583-508: The village of Sihetun, Beipiao, in what would become one of the most productive localities of the Jehol biota. Large-scale professional excavations at this single locality have been carried out by the IVPP from 1997 onwards; recovered fossils include several hundred specimens of Confuciusornis . Many additional sites producing fossils of the Jehol biota have been recognized since, distributed over

11700-398: The weights of these early birds, and that more accurate weight estimates allowed powered flight even with relatively narrow raches. Nudds and Dyke assumed a weight of 500 grams (18 oz) for Confuciusornis , as heavy as the modern teal . Paul argued that a more reasonable body weight estimate is about 180 grams (6.3 oz), less than that of a pigeon. Paul also noted that Confuciusornis

11817-617: The widely used total-group perspective, the Crocodylomorpha would become synonymous with the Crocodilia, and the Avemetatarsalia would become synonymous with the birds, and the above tree could be summarized as Crocodilia Birds An advantage of this approach is that declaring Theropoda to be birds (or Pan-aves ) is more specific than declaring it to be a member of the Archosauria, which would not exclude it from

11934-503: The wings of Confuciusornis would have been white or, possibly, colored with carotenoid pigments. The long tail feathers of male specimens would have also been dark in color along their entire length. A 2018 study of the specimen CUGB P1401 indicated the presence of heavy spotting on the wings, throat, and crest of Confuciusornis . Hou assigned Confuciusornis to the Confuciusornithidae in 1995. At first he assumed it

12051-491: The years. One use is as "nearby group" (plesion means close to in Greek ), i.e. sister group to a given taxon , whether that group is a crown group or not. The term may also mean a group, possibly paraphyletic , defined by primitive traits (i.e. symplesiomorphies ). It is generally taken to mean a side branch splitting off earlier on the phylogenetic tree than the group in question. Placing fossils in their right order in

12168-542: Was a member of the Enantiornithes and the sister taxon of Gobipteryx . Later he understood that Confuciusornis was not an enantiornithean but concluded it was the sister taxon of the Enantiornithes, within a larger Sauriurae . This was heavily criticised by Chiappe who regarded Sauriurae to be paraphyletic as there were insufficient shared traits that indicated that the Confuciusornithidae and

12285-443: Was a simple curved bar lacking a pointed process at the back, a hypocleidium . The sternum was relatively broad and had a low keel which was raised at the back end. This bony keel may or may not have anchored a larger, cartilaginous, keel for enlarged pectoral muscles . The scapulae (shoulder blades) were fused to the strut-like coracoid bones and may have formed a solid base for the attachment of wing muscles. The orientation of

12402-459: Was incised by a long groove between prominent ridges. Confuciusornis had an exceptionally large humerus (upper arm bone). Near its shoulder-end this was equipped with a prominent deltopectoral crest. Characteristically this crista deltopectoralis was with Confuciusornis pierced by an oval hole which may have reduced the bone's weight or enlarged the attachment area of the flight muscles. The furcula or wishbone, like that of Archaeopteryx ,

12519-595: Was large, likely relatively thick, and extended from the shoulder to the wrist, as in modern birds; the extent of the postpatagium is also similar to modern birds. Reticulate scales covered the underside of the foot, and the phalanges and metatarsals supported large, fleshy pads, although the interphalangeal pads were either small or entirely absent. In early 2010, a group of scientists led by Zhang Fucheng examined fossils with preserved melanosomes ( organelles which contain colors). By studying such fossils with an electron microscope , they found melanosomes preserved in

12636-413: Was made up of two separate elements that met at the midline, with feathers growing between them on the upper jaw. Also unlike modern birds, these specimens suggest that the upper beak extended backwards onto the maxilla due to the presence of foramina. The various specimens seem to have a variable number of neck vertebrae, some showing eight, others nine. The first vertebra, the atlas, bore a faint keel on

12753-402: Was no correlation between size and the possession of the long tail feathers. From this it was concluded that either the sexes did not differ in size or both sexes had the long feathers. The first case was deemed most likely which left the size distribution to be explained. It was hypothesized that the smaller animals consisted of very young individuals, that the large animals were adults and that

12870-399: Was not possible for non-avian dinosaurs and Mesozoic birds, including Confuciusornis , as these animals would have been too heavy in relation to the size of their eggs. Kaiser, in 2007, argued that Confuciusornis likely did not brood in an open nest but might have used crevices in trees for protection, and that the small size of the only known egg indicates large clutch sizes. In contrast,

12987-431: Was rather robust, with deep jaws, especially the mandible. The tomial crest of the upper jaw (a bony support for the jaw's cutting edge) was straight for its entire length. The premaxillae (front bones of the upper jaw) were fused together for most of the front half of the snout, but were separated at the tip by a V-shaped notch. The frontal processes that projected hindwards from the premaxillae were thin and extended above

13104-411: Was robust, especially at the front third of its length. The tomial crest was straight for its entire length, and a notch indented the sharp tip of the mandible. The mandible was spear-shaped in side view, due to its lower margin slanting downwards and back from its tip for the front third of its length (the jaw was also deepest at a point one third from the tip). The symphyseal part (where the two halves of

13221-433: Was similar to the modern pheasant-tailed jacana ( Hydrophasianus chirurgus ), a water-bird in which and the female is largest and adult individuals of both sexes have long tails, but only during the breeding season. Confuciusornis differs from the jacanas in that long tail feathers are present in specimens of all sizes, even in some of the smallest known specimens. This suggests that the long tail feathers might not have had

13338-420: Was straight; the tibia only slightly longer. The metatarsals of the foot were relatively short and fused to each other and to the lower ankle bones, forming a tarsometatarsus . A rudimentary fifth metatarsal is present. The first metatarsal was attached to the lower shaft of the second and supported a first toe or hallux , pointing to the back. The formula of the toe phalanges was 2-3-4-5-0. The proportions of

13455-578: Was thought to be of Late Jurassic ( Tithonian ) age at the time. Although two bird genera, Sinornis and Cathayornis , had already described from the Jehol biota in 1992, these were only based on fragmentary remains and stem from the younger Jiufotang Formation , which was considered to be of Early Cretaceous age. Later, both formations have been dated to the Lower Cretaceous ( Barremian to Aptian stages, 131–120 million years ago). In 1995, local farmers began digging for fossils near

13572-430: Was thought to be the oldest known bird to have a beak, though this title now belongs to an earlier relative Eoconfuciusornis . It was named after the Chinese moral philosopher Confucius (551–479 BC). Confuciusornis is one of the most abundant vertebrates found in the Yixian Formation, and several hundred complete specimens have been found. In November 1993, the Chinese paleontologists Hou Lianhai and Hu Yoaming of

13689-617: Was unlike that of a modern ectothermic alligator but similar to the feathered non-avian dinosaur Beipiaosaurus . However, these authors assumed that endothermy in Confuciusornis had evolved independently from that seen in modern birds. This concurred with earlier work by Anusuya Chinsamy and colleagues, who described distinct lines of arrested growth and low vascularity in other Mesozoic birds that are more derived than Confuciusornis . Both features indicate slow growth, which, according to Chinsamy and colleagues, suggests low metabolic rates. Full endothermy, therefore, would have evolved late on

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