Anchiornithidae

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Anchiornithids
Temporal range: Middle Jurassic–Early Cretaceous 165–122  Ma
Anchiornis huxleyi skel hartman 2017.png
Skeletal restoration of Anchiornis huxleyi by Scott Hartman, 2017
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Paraves
Family:† Anchiornithidae
Xu et al. 2016 sensu Foth & Rauhut, 2017
Type species
† Anchiornis huxleyi
Xu et al., 2009
Genera
Synonyms
  • Tetrapterygidae(Chatterjee, 2015)
  • "Anchiornithosaurs" (Rauhut et al., 2016)
  • Anchiorninae [sic] (Xu et al., 2016 sensu Hu et al., 2018)

Anchiornithidae is a family of small paravian dinosaurs. [1] Anchiornithids have been classified at varying positions in the paravian tree, with some scientists classifying them as a distinct family, a basal subfamily of Troodontidae, [2] [3] [4] [5] members of Archaeopterygidae, [2] [6] or an assemblage of dinosaurs that are an evolutionary grade within Avialae [7] or Paraves. [8]

Contents

Description

Anchiornithids share many general features with other paravians, including early avialans. They were small and lightly-built feathered carnivores, similar in biology to Archaeopteryx , early dromaeosaurids like Microraptor , and particularly troodontids. They are almost exclusively known from Late Jurassic Chinese deposits, although Ostromia was discovered in Germany and Yixianosaurus (a putative member of the group only known from forelimbs) is believed to hail from the early Cretaceous. Most had long legs, arms, and hands, although some ( Eosinopteryx ) had slightly reduced forelimbs. [9]

Feathering

Life restoration of Serikornis sungei Serikornis.jpg
Life restoration of Serikornis sungei

Although it is practically certain that every anchiornithid possessed advanced pennaceous feathers, there is still much variety in feathering between genera (or between individuals in the case of numerous genera such as Anchiornis). Most had vaned tail feathers forming a frond-shaped tail, with the tails feathers of Caihong being particularly long and in some cases asymmetrical. [10] However, Eosinopteryx, Serikornis, and Aurornis were preserved with short and downy tail feathering. Some studies on the body feathering of anchiornithids indicate that the feathers were pennaceous, but seemingly lacked barbules, making them "shaggy" or "silky" in life. [11] [8]

Long pennaceous feathers were present on the arms of most anchiornithids. However, these feathers were slender, symmetrical, and unspecialized, probably useless for flight. They formed rows which were attached directly to a large fleshy propatagium connecting the upper and lower arm. [12] [8]

Most anchiornithids also had dense feathering extending down their legs. A few had short leg feathering, but most (Anchiornis and Pedopenna, for example) had very long pennaceous feathers on their legs, giving them the moniker of "four-winged dinosaurs", a trait also shared by microraptorians. Eosinopteryx seemingly lacked any sort of feathers on the lower part of its legs, but its close relative Serikornis possessed both plumaceous (downy) feathers extending onto its toes as well as pennaceous feathers further up the leg. [9] [8]

Distinguishing features

Foth and Rauhut (2017) established several diagnostic features present in anchiornithids: [1]

Systematic history

In 2015 Chatterjee created Tetrapterygidae in the second edition of his book The Rise of Birds: 225 Million Years of Evolution, where he included Xiaotingia , Aurornis , Anchiornis , and even Microraptor; together they were proposed to be the sister group of the Avialae. [13] However this family is invalid as must include the genus Tetrapteryx, which is the junior synonym of Grus – therefore Tetrapterygidae is a junior synonym of Gruidae. [14]

In their description of Wiehenvenator Rauhut and colleagues had informally called the group as "Anchiornithosaurs" which they placed outside of Avialae. [15]

The clade was originally named as "Anchiornithinae" by Xu et al. (2016) and defined as for "the most inclusive clade including Anchiornis but not Archaeopteryx , Gallus , Troodon , Dromaeosaurus , Unenlagia , or Epidexipteryx ". [16]

In 2017 Foth and Rauhut in their re-evaluation of the Haarlem Archaeopteryx specimen (which they classified it in its own distinct genus Ostromia [1] ) found that the anchiornithids are a distinct family closer to the ancestry of birds. [1] They provided their own definition of Anchiornithidae as "all maniraptoran theropods that are more closely related to Anchiornis huxleyi than to Passer domesticus , Archaeopteryx lithographica , Dromaeosaurus albertensis , Troodon formosus , or Oviraptor philoceratops ." [1]

During the description of Halszkaraptor, Cau et al. (2017) incorporated many putative anchiornithids into two different large-scale phylogenetic analyses. The first analysis was a comprehensive study of theropod dinosaurs originally designed by Lee et al. for a 2014 paper on miniaturization in theropods leading up to the evolution of birds. Cau et al.'s usage of this first analysis found support for Anchiornithidae being a distinctive family of avialans. The strict consensus tree of the first analysis is given below: [17]

Avialae

The second analysis was first used in a different paper on theropod size published by Brusatte et al. in 2014. This analysis (which was updated by Cau et al. during a 2015 study on the affinities of Balaur bondoc [18] ) focused specifically on coelurosaurs and found that anchiornithids (represented only by Anchiornis, Xiaotingia, Aurornis, and Eosinopteryx in the analysis) were troodontids rather than avialans, in contrast to the first analysis. [17]

The description of Caihong by Hu et al. (2018) also implemented the Brusatte analysis and found the same result. However, this study also implemented an analysis performed by Xu et al. (2015) during the description of Yi qi . This analysis placed anchiornithids (or as the study calls them, members of "Anchiorninae") either as troodontids or unresolved paravians, depending on whether parsimony or bootstrap analyses are used. [19]

An analysis used in the description of the Jurassic bird Alcmonavis by Rauhut et al. (2019) recovered anchiornithids (represented in the analysis by Eosinopteryx, Anchiornis, and Ostromia) as the most basal avialans. Xiaotingia and Pedopenna were placed as more advanced avialans closer to Archaeopteryx. [20]

In 2019 with the description of the Late Jurassic genus Hesperornithoides , Hartman et al., using every named Mesozoic maniraptoromorph (with the addition of 28 unnamed specimens), which they scored 700 characters and 501 operational taxonomic units, found that most of the anchiornithids are members of Archaeopterygidae, with only Xiaotingia and Yixianosaurus being classified as a troodontid and a dromaeosaurid respectively, Pedopenna found in many possible positions within the Paraves phylogeny, and Ostromia described too late to include in the analysis. [6] Below is their phylogeny:

Archaeopterygidae

The cladogram below shows the results of the phylogenetic analysis by Cau (2020). [21]

Cau (2024) found support for the inclusion of Scansoriopterygidae in Anchiornithidae. [22]

Palaeoecology

A good majority of the known anchiornithid fossils have been recovered from the Tiaojishan Formation in Liaoning, China dating back to 160 million years. [23] [24] The climate during this period of time would have been subtropical to temperate, warm and humid based on the plant life present in the Tiaojishan Formation. [25] This environment was dominated plant by gymnosperm trees. There were ginkgopsids like Ginkoites, Ginkgo , Baiera, Czekanowskia, and Phoenicopsis. There were also conifers like Pityophyllum, Rhipidiocladus, Elatocladus, Schizolepis, and Podozamites. Also, Lycopsids like Lycopodites and Sellaginellities, horsetails (Sphenopsida) like Equisetum, cycads like Anomozamites, and ferns (Filicopsida) like Todites and Coniopteris. [26]

Chinese anchiornithids discovered outside of the Tiaojishan Formation includeYixianosaurus longimanus, which was found in the 125 million-year-old Early Cretaceous Yixian Formation. Fujianvenator prodigiosus was discovered in the 148 to 150 million-year-old Zhenghe Biota of southeastern China, which was dominated by aquatic and semi-aquatic fossils such as fish and turtles indicative of a lacustrine swamp environment. [27] Only one genus of anchiornithid has been found outside of China: Ostromia , which is found in the Painten Formation from Riedenburg, Bavaria, Germany. [1]

Related Research Articles

<i>Archaeopteryx</i> Extinct genus of bird-like dinosaurs

Archaeopteryx, sometimes referred to by its German name, "Urvogel" is a genus of bird-like dinosaurs. The name derives from the ancient Greek ἀρχαῖος (archaīos), meaning "ancient", and πτέρυξ (ptéryx), meaning "feather" or "wing". Between the late 19th century and the early 21st century, Archaeopteryx was generally accepted by palaeontologists and popular reference books as the oldest known bird. Older potential avialans have since been identified, including Anchiornis, Xiaotingia, and Aurornis.

<span class="mw-page-title-main">Troodontidae</span> Extinct family of bird-like dinosaurs

Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discoveries of complete and articulated specimens, have helped to increase understanding about this group. Anatomical studies, particularly studies of the most primitive troodontids, like Sinovenator, demonstrate striking anatomical similarities with Archaeopteryx and primitive dromaeosaurids, and demonstrate that they are relatives comprising a clade called Paraves.

<i>Microraptor</i> Extinct genus of dinosaurs

Microraptor is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China. They date from the early Cretaceous Jiufotang Formation, 125 to 120 million years ago. Three species have been named, though further study has suggested that all of them represent variation in a single species, which is properly called M. zhaoianus. Cryptovolans, initially described as another four-winged dinosaur, is usually considered to be a synonym of Microraptor.

<span class="mw-page-title-main">Maniraptora</span> Clade of dinosaurs

Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Dromaeosauridae, Troodontidae, Oviraptorosauria, and Therizinosauria. Ornitholestes and the Alvarezsauroidea are also often included. Together with the next closest sister group, the Ornithomimosauria, Maniraptora comprises the more inclusive clade Maniraptoriformes. Maniraptorans first appear in the fossil record during the Jurassic Period, and survive today as living birds.

<i>Pedopenna</i> Extinct genus of dinosaurs

Pedopenna is a genus of small, feathered, maniraptoran dinosaur from the Daohugou Beds in China. It is possibly older than Archaeopteryx, though the age of the Daohugou Beds where it was found is debated. A majority of studies suggest that beds probably date from between the late Middle Jurassic and early Late Jurassic Period.

<i>Jinfengopteryx</i> Theropod dinosaur genus

Jinfengopteryx is a genus of maniraptoran dinosaur. It was found in the Qiaotou Member of the Huajiying Formation of Hebei Province, China, and is therefore of uncertain age. The Qiaotou Member may correlate with the more well-known Early Cretaceous Yixian Formation, and so probably dates to around 122 Ma ago.

<i>Yixianosaurus</i> Extinct genus of dinosaurs

Yixianosaurus is a maniraptoran theropod dinosaur genus from the Early Cretaceous of China.

<span class="mw-page-title-main">Scansoriopterygidae</span> Extinct family of dinosaurs

Scansoriopterygidae is an extinct family of climbing and gliding maniraptoran dinosaurs. Scansoriopterygids are known from five well-preserved fossils, representing four species, unearthed in the Tiaojishan Formation fossil beds of Liaoning and Hebei, China.

<span class="mw-page-title-main">Archaeopterygidae</span> Family of dinosaurs

Archaeopterygidae is a group of paravian dinosaurs, known from the latest Jurassic and earliest Cretaceous of Europe. In most current classifications, it contains only the genera Archaeopteryx and Wellnhoferia. As its name suggests, Protarchaeopteryx was also once referred to this group, but most paleontologists now consider it an oviraptorosaur. Other referred genera, like Jurapteryx, Wellnhoferia, and "Proornis", are probably synonymous with Archaeopteryx or do not belong into this group. Jinfengopteryx was originally described as an archaeopterygid, though it was later shown to be a troodontid. A few studies have recovered Anchiornis and Xiaotingia to also be members of the Archaeopterygidae, though most subsequent analyses have failed to arrive at the same result. Uncertainties still exist, however, and it may not be possible to confidently state whether archaeopterygids are more closely related to modern birds or to deinonychosaurs barring new and better specimens of relevant species. Teeth attributable to archaeopterygids are known from the earliest Cretaceous (Berriasian) Cherves-de-Cognac locality and the Angeac-Charente bonebed of France.

<span class="mw-page-title-main">Avialae</span> Clade including all birds and their ancestors

Avialae is a clade containing the only living dinosaurs, the birds, and their closest relatives. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used.

<span class="mw-page-title-main">Paraves</span> Clade of all dinosaurs that are more closely related to birds than to oviraptorosaurs

Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the avialans, which include diverse extinct taxa as well as the over 10,000 species of living birds.

<i>Epidexipteryx</i> Extinct genus of dinosaurs

Epidexipteryx is a genus of small maniraptoran dinosaurs, known from one fossil specimen in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. Epidexipteryx represents the earliest known example of ornamental feathers in the fossil record.

<i>Anchiornis</i> Extinct genus of dinosaurs

Anchiornis is a genus of small, four-winged paravian dinosaurs, with only one known species, the type species Anchiornis huxleyi, named for its similarity to modern birds. The Latin name Anchiornis derives from a Greek word meaning "near bird", and huxleyi refers to Thomas Henry Huxley, a contemporary of Charles Darwin.

<i>Xiaotingia</i> Extinct genus of dinosaurs

Xiaotingia is a genus of anchiornithid theropod dinosaur from Middle Jurassic or early Late Jurassic deposits of western Liaoning, China, containing a single species, Xiaotingia zhengi.

<i>Eosinopteryx</i> Extinct genus of dinosaurs

Eosinopteryx is an extinct genus of theropod dinosaurs known to the Late Jurassic epoch of China. It contains a single species, Eosinopteryx brevipenna.

<i>Aurornis</i> Extinct genus of dinosaurs

Aurornis is an extinct genus of anchiornithid theropod dinosaurs from the Jurassic period of China. The genus Aurornis contains a single known species, Aurornis xui. Aurornis xui may be the most basal ("primitive") avialan dinosaur known to date, and it is one of the earliest avialans found to date. The fossil evidence for the animal pre-dates that of Archaeopteryx lithographica, often considered the earliest bird species, by about 10 million years.

<i>Jianianhualong</i> Extinct genus of dinosaurs

Jianianhualong is a genus of troodontid theropod dinosaur from the Early Cretaceous of China. It contains a single species, Jianianhualong tengi, named in 2017 by Xu Xing and colleagues based on an articulated skeleton preserving feathers. The feathers at the middle of the tail of Jianianhualong are asymmetric, being the first record of asymmetrical feathers among the troodontids. Despite aerodynamic differences from the flight feathers of modern birds, the feathers in the tail vane of Jianianhualong could have functioned in drag reduction whilst the animal was moving. The discovery of Jianianhualong supports the notion that asymmetrical feathers appeared early in the evolutionary history of the Paraves.

<i>Serikornis</i> Extinct genus of dinosaurs

Serikornis is a genus of small, feathered anchiornithid dinosaur from the Upper Jurassic Tiaojishan Formation of Liaoning, China. It is represented by the type species Serikornis sungei.

<span class="mw-page-title-main">Biogeography of paravian dinosaurs</span> Geographic distribution of paravian dinosaurs

The biogeography of Paravian dinosaurs is the study of the global distribution of Paraves through geological history. Paraves is a clade that includes all of the Theropoda that are more closely related to birds than to oviraptorosaurs. These include Dromaeosauridae and Troodontidae and Avialae. The distribution of paraves is closely related to the evolution of the clade. Understanding the changes in their distributions may shed light on problems like how and why paraves evolve, eventually gaining the ability to fly.

References

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