Scansoriopterygidae

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Scansoriopterygids
Temporal range: Middle to Late Jurassic, 165–156  Ma
Epidexipteryx hui slab.jpg
Fossil specimen of Epidexipteryx hui
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Pennaraptora
Family:† Scansoriopterygidae
Czerkas & Yuan, 2002
Type species
† Scansoriopteryx heilmanni
Czerkas & Yuan, 2002
Genera

Scansoriopterygidae (meaning "climbing wings") 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 (dating to the mid-late Jurassic Period) of Liaoning and Hebei, China.

Contents

Scansoriopteryx heilmanni (and its likely synonym Epidendrosaurus ninchengensis) was the first non-avian dinosaur found that had clear adaptations to an arboreal or semi-arboreal lifestyle–it is likely that they spent much of their time in trees. Both specimens showed features indicating they were juveniles, which made it difficult to determine their exact relationship to other non-avian dinosaurs and birds. It was not until the description of Epidexipteryx hui in 2008 that a subadult specimen was known. In 2015, the discovery of an adult specimen belonging to the species Yi qi showed that scansoriopterygids were not only climbers but also had adaptations that could have been used for gliding flight. The recently discovered (in 2019) Ambopteryx also supports this. The earlier described Pedopenna may also be a member of this clade. [1]

Description

Sizes of Yi qi (green), Epidexipteryx hui (orange), and Scansoriopteryx heilmanni (red) compared with a human. Size comparison of scansoriopterygid dinosaurs.png
Sizes of Yi qi (green), Epidexipteryx hui (orange), and Scansoriopteryx heilmanni (red) compared with a human.

Scansoriopterygids are among the smallest non-avian dinosaurs known. The juvenile specimens of Scansoriopteryx are the size of house sparrows, [2] about 16 cm (6.3 in) long, while the subadult type specimen of Epidexipteryx is about the size of a pigeon, about 25 cm (9.8 in) long (not including the tail feathers). [3]

Scansoriopterygids differentiate from other theropod dinosaurs in part by their extremely long third fingers, which were longer than the first and second digits of the hand. In all other known theropods, the second finger is the longest. At least two species, Yi and Ambopteryx , also had a long "styliform" bone growing from the wrist, which, along with the third finger, helped support a bat-like wing membrane used for gliding. This use of a long finger to support a wing membrane is only superficially similar to the wing arrangement in pterosaurs, even though it is physically more bat-like. [4]

Other features shared within the group include short and high skulls with down turned lower jaws and large front teeth, and long arms. Tail length, however, varied significantly among scansoriopterygids. Epidexipteryx had a short tail (70% the length of the torso), anchoring long tail feathers, while Scansoriopteryx had a very long tail (over three times as long as the torso) with a short spray of feathers at the tip. All three described scansoripterygid specimens preserve the fossilized traces of feathers covering their bodies. [2] [5] [6]

Classification

Scansoriopterygidae was created as a family-level taxon by Stephen Czerkas and Yuan Chongxi in 2002. Some scientists, such as Paul Sereno, initially considered the concept redundant because the group was originally monotypic, containing only the single genus and species Scansoriopteryx heilmanni . Additionally, the group lacked a phylogenetic definition. [7] However, in 2008 Zhang et al. reported another scansoriopterygid, Epidexipteryx , and defined Scansoriopterygidae as a clade comprising most recent common ancestor of Epidexipteryx and Epidendrosaurus (=Scansoriopteryx) plus all its descendants. [6]

The exact taxonomic placement of this group was initially uncertain and controversial. When describing the first validly published specimen in 2002 (Scansoriopteryx heilmanni), Czerkas and Yuan proposed that various primitive features of the skeleton (including a primitive, "saurischian-style" pubis and primitive hip joint) showed that scansoriopterygids, along with other maniraptorans and birds, split from other theropods very early in dinosaur evolution. [5] However, this interpretation has not been followed by most other researchers. In a 2007 cladistic analysis of relationships among coelurosaurs, Phil Senter found Scansoriopteryx to be a member of the clade Avialae. [8] This view was supported by a second phylogenetic analysis performed by Zhang et al. in 2008.

A subsequent phylogenetic analysis conducted by Agnolín and Novas (2011) recovered scansoriopterygids not as avialans, but as basal members of the clade Paraves remaining in unresolved polytomy with alvarezsaurids and the clade Eumaniraptora (containing avialans and deinonychosaurs). [9]

Turner, Makovicky and Norell (2012) included only Epidexipteryx hui in their primary phylogenetic analysis, as a full-grown specimen of this species is known; regarding Scansoriopteryx/Epidendrosaurus, the authors were worried that including it in the primary analysis would be problematic, because it is only known from juvenile specimens, which "do not necessarily preserve all the adult morphology needed to accurately place a taxon phylogenetically" (Turner, Makovicky and Norell 2012, p. 89). Epidexipteryx was recovered as basal paravian that didn't belong to Eumaniraptora. The authors did note that its phylogenetic position is unstable; constraining Epidexipteryx hui as a basal avialan required two additional steps compared to the most parsimonious solution, while constraining it as a basal member of Oviraptorosauria required only one additional step. A separate exploratory analysis included Scansoriopteryx/Epidendrosaurus, which was recovered as a basal member of Avialae; the authors noted that it did not clade with Epidexipteryx, which stayed outside Eumaniraptora. Constraining the monophyly of Scansoriopterygidae required four additional steps and moved Epidexipteryx into Avialae. [10]

A monophyletic Scansoriopterygidae was recovered by Godefroit et al. (2013); the authors found scansoriopterygids to be basalmost members of Paraves and the sister group to the clade containing Avialae and Deinonychosauria. [11] Agnolín and Novas (2013) recovered scansoriopterygids as non-paravian maniraptorans and the sister group to Oviraptorosauria. [12] Brusatte et al. (2014) also found Epidexipteryx to be a basal oviraptorosaur along with Pedopenna. [13] The Bayesian analysis of Cau (2018) placed scansoriopterygids in Oviraptorosauria again, while the parsimony analysis placed them in the base of Avialae, and included Xiaotingia in Scansoriopterygidae as sister to the rest of the group. [14] Pittman et al. (2020) again found scansoriopterygids to be basal oviraptorosaurs. [15] Cau (2024) placed Scansoriopterygidae within Anchiornithidae. [16]

The cladogram below follows the results of a phylogenetic study by Lefèvre et al., 2014: [17]

Pennaraptora

Sorkin (2021) argues scansoriopterygids provide evidence that all pennaraptorans evolved from scansorial gliding ancestors. [18]

Provenance and paleoecology

The fossil remains of Epidexipteryx, Scansoriopteryx and Yi were all recovered from the Tiaojishan Formation of northeastern China, and the former two were specifically found in the Daohugou Beds. A study published in 2008 refined the possible age range of this formation, finding that the lower boundary of the Tiaojishan was formed 165 Ma ago, and the upper boundary somewhere between 156 and 153 Ma ago. [19]

The known scansoriopterygids of the Daohugou biota inhabited a humid, temperate forest made up of a variety of prehistoric trees including species of ginkgo and conifer. The understory would have been dominated by plants such as club mosses, horsetails, cycads, and ferns. [20]

The scansoriopterygids would have lived alongside synapsids such as the aquatic Castorocauda , arboreal gliding mammal Volaticotherium and various types of gliding haramiyidans, the rhamphorhynchoid pterosaurs Jeholopterus and Pterorhynchus , as well as a diverse range of insect life (including mayflies and beetles) and several species of salamander. [21] [22]

Paleobiology

Life restoration of a Yi qi in its environment Yi qi restoration.jpg
Life restoration of a Yi qi in its environment

Climbing

In the initial descriptions of the first two scansoriopterygid specimens, scientists studying these animals used several lines of evidence to argue that they were arboreal (tree-climbing), and the first known non-avian dinosaurs with clear climbing adaptations.

Zhang and colleagues considered Scansoriopteryx to be arboreal based on the elongated nature of the hand and specializations of the foot. These authors stated that the long hand and strongly curved claws were adaptations for climbing and moving around among tree branches. They viewed this as an early stage in the evolution of the bird wing, stating that the forelimbs became well-developed for climbing, and that this development later led to the evolution of a wing capable of flight. They argued that long, grasping hands are more suited to climbing than to flight, since most flying birds have relatively short hands. Zhang et al. also noted that the foot of Scansoriopteryx is unique among non-avian theropods; while Scansoriopteryx does not preserve a reversed hallux (the backward-facing toe seen in modern perching birds), its foot was very similar in construction to primitive perching birds like Cathayornis and Longipteryx . These adaptations for grasping ability in all four limbs, the authors argued, makes it likely that Scansoriopteryx spent a significant amount of time living in trees. [2]

In describing Scansoriopteryx, Czerkas and Yuan also described evidence for an arboreal lifestyle. They noted that, unlike all modern bird hatchlings, the forelimbs of Scansoriopteryx are longer than the hind limbs. The authors argued that this anomaly indicates the forelimbs played an important role in locomotion even at an extremely early developmental stage. Scansoriopteryx has a better-preserved foot than the type of Epidendrosaurus, and the authors interpreted the hallux as reversed, the condition of a backward-pointing toe being widespread among modern tree-dwelling birds. Furthermore, the authors pointed to the stiffened tail of Scansoriopteryx as a tree-climbing adaptation. The tail may have been used as a prop, much like the tails of modern woodpeckers. Comparison with the hands of modern climbing species with elongated third digits, like iguanid lizards, also supports the tree-climbing hypothesis. Indeed, the hands of Scansoriopteryx are much better adapted to climbing than the modern tree-climbing hatchling of the hoatzin. [5]

Feathers

Both juvenile scansoriopterygid specimens preserve impressions of simple, down-like feathers, especially around the hand and arm. The longer feathers in this region led Czerkas and Yuan to speculate that adult scansoriopterygids may have had reasonably well-developed wing feathers which could have aided in leaping or rudimentary gliding, though they ruled out the possibility that Scansoriopteryx could have achieved powered flight. Like other maniraptorans, scansoriopterygids had a semilunate carpal (half-moon shaped wrist bone) that allowed for bird-like folding motion in the hand. Even if powered flight was not possible, this motion could have aided maneuverability in leaping from branch to branch. [5]

The adult specimen of Epidexipteryx lacked preserved feathers around the forelimbs, but preserved simple feathers on the body and long, ribbon-like feathers on the tail. The tail feathers, likely used in display, consisted of a central shaft (rachis) and unbranched vane (unlike the vanes of modern feathers, which are broken up into smaller filaments or barbs). [6]

Yi also preserves feathers. These are notably very simple for a member of Pennaraptora (a clade of which scansoriopterygids are usually considered members), being "paintbrush-like", with long quill-like bases topped by sprays of thinner filaments. The feathers covered most of the body, starting near the tip of the snout. The head and neck feathers were long and formed a thick coat, and the body feathers were even longer and denser, making it difficult for scientists to study their detailed structure.

Gliding membranes

At least two species, Yi qi and Ambopteryx longibrachium , developed a patagium, supporting it with the elongated third finger as well as a unique styliform wrist bone akin to similar structures in flying squirrels, bats, pterosaurs and anomalures. Though propatagia are known in birds and similar dinosaurs, scansoriopterygids were the only known dinosaurs to develop true membranous wings, most notably so due to the presence of already fairly derived feathers. [4] [23] [24] [25]

Prior to the discovery of Yi, Italian palaeontologist Andrea Cau had informally suggested that membranes may have been present in Scansoriopteryx , supported by its elongated third finger, due to their similarity to the wing fingers of pterosaurs, [26] a hypothesis he later also applied to Epidexipteryx . [27]

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">Dromaeosauridae</span> Family of theropod dinosaurs

Dromaeosauridae is a family of feathered coelurosaurian theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek δρομαῖος (dromaîos), meaning 'running at full speed', 'swift', and σαῦρος (saûros), meaning 'lizard'. In informal usage, they are often called raptors, a term popularized by the film Jurassic Park; several genera include the term "raptor" directly in their name, and popular culture has come to emphasize their bird-like appearance and speculated bird-like behavior.

<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.

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

Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.

<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>Yixianosaurus</i> Extinct genus of dinosaurs

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

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

Scansoriopteryx is a genus of maniraptoran dinosaur. Described from only a single juvenile fossil specimen found in Liaoning, China, Scansoriopteryx is a sparrow-sized animal that shows adaptations in the foot indicating an arboreal (tree-dwelling) lifestyle. It possessed an unusual, elongated third finger which may have supported a membranous wing, much like the related Yi qi. The type specimen of Scansoriopteryx also contains the fossilized impression of feathers.

<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.

Zhongornis is a genus of primitive maniraptoran dinosaurs that lived during the Early Cretaceous. It was found in rocks of the Yixian Formation in Lingyuan City (China), and described by Gao et al. in 2008.

<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>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>Yi</i> (dinosaur) Extinct genus of dinosaur

Yi is a genus of scansoriopterygid dinosaur from the Late Jurassic of China. Its only species, Yi qi, is known from a single fossil specimen of an adult individual found in Middle or Late Jurassic Tiaojishan Formation of Hebei, China, approximately 159 million years ago. It was a small, possibly tree-dwelling (arboreal) animal. Like other scansoriopterygids, Yi possessed an unusual, elongated third finger, that appears to have helped to support a membranous gliding plane made of skin. The planes of Yi qi were also supported by a long, bony strut attached to the wrist. This modified wrist bone and membrane-based plane is unique among all known dinosaurs, and might have resulted in wings similar in appearance to those of bats.

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

Unenlagiidae is a proposed family of eumaniraptoran paravians that includes the subfamilies Unenlagiinae and possibly Halszkaraptorinae. Fossils of both subfamilies have been found in both Gondwanan and Laurasian deposits. The biology of the group suggests that some members were semiaquatic specialists.

<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">Anchiornithidae</span> Extinct family of dinosaurs

Anchiornithidae is a family of small paravian dinosaurs. 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, members of Archaeopterygidae, or an assemblage of dinosaurs that are an evolutionary grade within Avialae or Paraves.

References

  1. ↑ Hartman, Scott; Mortimer, Mickey; Wahl, William R.; Lomax, Dean R.; Lippincott, Jessica; Lovelace, David M. (2019). "A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight". PeerJ. 7: e7247. doi:10.7717/peerj.7247. PMC 6626525. PMID   31333906.
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  11. ↑ Pascal Godefroit, Helena Demuynck, Gareth Dyke, Dongyu Hu, François Escuillié and Philippe Claeys (2013). "Reduced plumage and flight ability of a new Jurassic paravian theropod from China". Nature Communications. 4: Article number 1394. Bibcode:2013NatCo...4.1394G. doi: 10.1038/ncomms2389 . PMID   23340434.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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  14. ↑ Cau, A. (2018). "The assembly of the avian body plan: a 160-million-year long process". Bollettino della Società Paleontologica Italiana. 57 (1): 1–25. doi:10.4435/BSPI.2018.01 (inactive 2024-11-20). ISSN   0375-7633. S2CID   44078918.{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link)
  15. ↑ Pittman, Michael; Xu, Xing (August 2020). "Pennaraptoran Theropod Dinosaurs Past Progress and New Frontiers". Bulletin of the American Museum of Natural History. 440 (1): 1–355. doi:10.1206/0003-0090.440.1.1. ISSN   0003-0090.
  16. ↑ Cau, Andrea (2024). "A Unified Framework for Predatory Dinosaur Macroevolution". Bollettino della Società Paleontologica Italiana. 63 (1): 1–19. doi:10.4435/BSPI.2024.08 (inactive 2024-11-20). ISSN   0375-7633.{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link)
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  21. ↑ Meng J.; Hu Y.; Li C.; Wang Y. (2006). "The mammal fauna in the Early Cretaceous Jehol Biota: implications for diversity and biology of Mesozoic mammals". Geological Journal. 41 (3–4): 439–463. doi:10.1002/gj.1054. S2CID   84397126.
  22. ↑ Wang X.; Zhou Z. (2006). "Pterosaur assemblages of the Jehol Biota and their implication for the Early Cretaceous pterosaur radiation". Geological Journal. 41 (3–4): 405–418. doi:10.1002/gj.1046. S2CID   131602205.
  23. ↑ Yong, Ed (29 April 2015). "Chinese dinosaur had bat-like wings and feathers". National Geographic . Archived from the original on November 23, 2018.
  24. ↑ Greshko, Michael (8 May 2019). "New species of bat-wing dinosaur discovered". National Geographic . Archived from the original on May 8, 2019.
  25. ↑ Min Wang; Jingmai K. O’Connor; Xing Xu; Zhonghe Zhou (2019). "A new Jurassic scansoriopterygid and the loss of membranous wings in theropod dinosaurs". Nature. 569 (7755): 256–259. doi:10.1038/s41586-019-1137-z.
  26. ↑ Cau, A (2008), Super Theropod Week, Part 1: Scansoriopterygid paleobiology, more than just bird origins!, Theropoda, October 2008
  27. ↑ Cau, A (2012), ritorno del paraviano pterosauro-mimo?, Theropoda, July 2012
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