Scansoriopteryx

Scansoriopteryx; Temporal range: Callovian to Kimmeridgian, 165–156 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Skeletal restoration of the type specimen
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	† Scansoriopterygidae
Genus:	† Scansoriopteryx ; Czerkas & Yuan, 2002
Species:	†S. heilmanni
Binomial name
	†Scansoriopteryx heilmanni; Czerkas & Yuan, 2002
Synonyms
	Epidendrosaurus ninchengensis; Zhang et al., 2002;

Last updated April 22, 2024

Scansoriopteryx ("climbing wing") 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.^[1]

Most researchers regard this genus as a synonym of Epidendrosaurus, with some preferring to treat Scansoriopteryx as the junior synonym,^[2]^[3] though it was the first name to be validly published.^[4]

History

The provenance of the Scansoriopteryx type specimen is uncertain, as it was obtained from private fossil dealers who did not record exact geologic data. Czerkas and Yuan initially reported that it had likely come from the Yixian Formation, though Wang et al. (2006), in their study of the age of the Daohugou Beds, suggested that it probably hails from the same beds, and thus is likely a synonym of Epidendrosaurus. The Daohugou Beds supposedly date to the mid-late Jurassic Period,^[5] but this is hotly contested. See the Daohugou Beds article for details.

The type specimen of Scansoriopteryx (type genus of the Scansoriopterygidae) and its arboreal adaptations were first presented in 2000 during the Florida Symposium on Dinosaur/Bird Evolution, at the Graves Museum of Archaeology & Natural History, though the specimen would not be formally described and named until 2002.^[1]

Description

The type specimen of Scansoriopteryx heilmanni (specimen number CAGS02-IG-gausa-1/DM 607) represents the fossilized remains of a hatchling maniraptoran dinosaur, similar in some ways to Archaeopteryx . A second specimen, the holotype of Epidendrosaurus ninchengensis (IVPP V12653), also shows features indicating it was a juvenile. The specimen is partially disarticulated, and most bones are preserved as impressions in the rock slab, rather than three-dimensional structures.^[6] Because the only known specimens are juvenile, the size of a full-grown Scansoriopteryx is unknown; the type specimen is a tiny, sparrow-sized creature.^[6]

Scansoriopteryx is also notable for its wide, rounded jaws. The lower jaw contained at least twelve teeth, larger in the front of the jaws than in the back. The lower jaw bones may have been fused together, a feature otherwise known only in the oviraptorosaurs.

One distinctive feature of Scansoriopteryx is its elongated third finger, which is the longest on the hand, nearly twice as long as the second finger. This is unlike the configuration seen in most other theropods, where the second finger is longest. The long wing feathers, or remiges, appear to attach to this long digit instead of the middle digit as in birds and other maniraptorans. Shorter feathers are preserved attached to the second finger.^[7] A relative of Scansoriopteryx, Yi , suggests that this elongated third finger supported a membranous wing of some kind alongside feathers.^[8]

Scansoriopteryx had a non-perforated hip socket, which is more open in most, but not all, other dinosaurs. It also had a pubis (hip bone) which pointed forward, a primitive trait among theropods, and unlike some maniraptorans more closely related to birds, where the pubis points downward or backward.^[7] The legs were short, and preserve small pebbly scales along the upper foot (metatarsus), as well as possible impressions of long feathers in the same area, possibly similar to the "hind wings" of Microraptor and other basal paravians.^[7] It also had an unusually large first toe, or hallux, which was low on the foot and may have been reversed, allowing some grasping ability.^[1]

The tail was long, six or seven times the length of the femur, and ended in a fan of feathers.^[6]

Paleobiology

Climbing

In describing Scansoriopteryx, Czerkas & Yuan cited evidence for an arboreal (tree-dwelling) 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 well-preserved foot, 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 short, stiffened tail of the Scansoriopteryx specimen 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.^[1]

The Epidendrosaurus was also interpreted as arboreal based on the elongated hand and specializations in the foot.^[6] The describing authors stated that the long hand and strongly curved claws are 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 lead to the evolution of a wing capable of flight. They stated 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 Epidendrosaurus is unique among non-avian theropods. While the Epidendrosaurus specimen does not preserve a reversed hallux, the backward-facing toe seen in modern perching birds, its foot was very similar in construction to more primitive perching birds like Cathayornis and Longipteryx . These adaptations for grasping ability in all four limbs makes it likely that Epidendrosaurus spent a significant amount of time living in trees.

Feathers and scales

Scansoriopteryx fossils preserve impressions of wispy, down-like feathers around select parts of the body, forming V-shaped patterns similar to those seen in modern down feathers. The most prominent feather impressions trail from the left forearm and hand. 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, Scansoriopteryx had a semilunate (half-moon shaped) bone in the wrist 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.^[1] Reticulate scales were preserved in the proximal portion of the second metatarsal,^[7] and the Epidendrosaurus specimen also preserved faint feather impressions at the end of the tail, similar to the pattern found in Microraptor.^[6]

Paleoecology

The holotype skeleton of Epidendrosaurus was recovered from the Daohugou fossil beds of northeastern China. In the past, there has been some uncertainty regarding the age of these beds. Various papers have placed the fossils here anywhere from the Middle Jurassic period (169 million years ago) to the Early Cretaceous period (122 ma).^[9] The age of this formation has implications for the relationship between Epidendrosaurus and similar dinosaurs, as well as for the origin of birds in general. A Middle Jurassic age would mean that the bird-like dinosaurs in the Daohugou beds are older than the "first bird", Archaeopteryx , which was Late Jurassic in age. The provenance of Scansoriopteryx is uncertain, though Wang et al. (2006), in their study of the age of the Daohugou, suggest that it probably hails from the same beds, and thus is likely a synonym of Epidendrosaurus.

Classification

Scansoriopteryx lent its name to the family Scansoriopterygidae. Studies of dinosaur relationships have found Scansoriopteryx to be a close relative of true birds and a member of the clade Avialae.^[10]

The status of the name Scansoriopteryx has been controversial. The type specimen was described only a few months after a very similar specimen, Epidendrosaurus ninchengensis, was described online, though the name Epidendrosaurus was not published in print until after Scansoriopteryx.^[1] These two specimens are so similar that they may be the same genus, in which case Article 21 of the International Code of Zoological Nomenclature (ICZN) would give priority to Scansoriopteryx. The journal in which Scansoriopteryx appeared has a very small circulation, but was distributed on roughly 2002-09-02, before the print appearance of Epidendrosaurus, but well after the later's appearance on the Internet, enough time for the name Epidendrosaurus to have come into wide use by experts. This situation was used as an example in a proposed amendment to the ICZN by Jerry Harris that would consider electronic articles with Digital Object Identifiers (DOIs) that are subsequently available in print to qualify as "publication" for naming purposes. Harris noted that while the name Epidendrosarus appeared first, Scansoriopteryx was the first to be published in print and is therefore the valid name, but the fact that the ICZN does not recognize online names as valid has led to confusion over which has priority.^[4] In scientific literature, the genus Scansoriopteryx has been treated as a senior synonym of Epidendrosaurus by some scientists, such as Alan Feduccia,^[3] and as a junior synonym by others such as Thomas R. Holtz, Jr. ^[11] and Kevin Padian.^[2]

Alternate interpretations

Czerkas and Yuan used the suite of primitive and birdlike characters in Scansoriopteryx to argue for an unorthodox interpretation of dinosaur evolution. They stated that Scansoriopteryx was "clearly more primitive than Archaeopteryx ", based on its primitive, "saurischian-style" pubis and robust ischia. Scansoriopteryx also lacks a fully perforated acetabulum, the hole in the hip socket which is a key characteristic of Dinosauria and has traditionally been used to define the group. While the authors allowed that the hole may have closed secondarily, having evolved from a more traditional dinosaurian hip socket, they cited the other primitive features to argue that it is a true primitive trait, which would make Scansoriopteryx among the most birdlike and the most primitive known dinosaurs. Czerkas and Yuan called it a "proto-maniraptoran", supporting the hypothesis of Gregory S. Paul that the larger, ground-dwelling maniraptorans like Velociraptor evolved from small, flying or gliding forms that lived in trees. The authors took this idea further than Paul, however, and lent support to George Olshevsky's 1992 "birds came first" hypothesis, that all true theropods are secondarily flightless or at least secondarily arboreal, having evolved from small, tree-dwelling, Scansoriopteryx-like ancestors. Czerkas and Yuan also argued that, contrary to most phylogenetic trees, maniraptorans form a separate lineage from other theropods, and that this split occurred very early in theropod evolution.^[1]

In 2014, Czerkas, along with Alan Feduccia, published a paper further describing Scansoriopteryx and stating their opinion that certain archaic features of the skeleton and the hypothesis that it was arboreal ruled out the possibility that it was a theropod or even a dinosaur, but that Scansoriopteryx and all birds evolved from non-dinosaurian avemetatarsalian archosaurs like Scleromochlus .^[7] This conclusion has been overwhelmingly rejected by other paleontologists due to the clear morphological similarities scansoriopterygids have to other maniraptoran dinosaurs.^[12]

Related Research Articles

Theropoda, whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally carnivorous, although a number of theropod groups evolved to become herbivores and omnivores. Theropods first appeared during the Carnian age of the late Triassic period 231.4 million years ago (Ma) and included the majority of large terrestrial carnivores from the Early Jurassic until at least the close of the Cretaceous, about 66 Ma. In the Jurassic, birds evolved from small specialized coelurosaurian theropods, and are today represented by about 10,500 living species.

"Archaeoraptor" is the informal generic name for a fossil chimera from China in an article published in National Geographic magazine in 1999. The magazine claimed that the fossil was a "missing link" between birds and terrestrial theropod dinosaurs. Even before this publication, there had been severe doubts about the fossil's authenticity. A further scientific study showed it to be a forgery constructed from rearranged pieces of real fossils from different species. Zhou et al. found that the head and upper body belong to a specimen of the primitive fossil bird Yanornis. A 2002 study found that the tail belongs to a small winged dromaeosaur, Microraptor, named in 2000. The legs and feet belong to an as-yet-unknown-animal.

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.

Caudipteryx is a genus of small oviraptorosaur dinosaurs that lived in Asia during the Early Cretaceous, around 124.6 million years ago. They were feathered and extremely birdlike in their overall appearance, to the point that some paleontologists suggested it was a bird. Two species have been described: C. zoui, in 1998, and C. dongi, in 2000.

Protarchaeopteryx is a genus of turkey-sized feathered theropod dinosaur from China. Known from the Jianshangou bed of the Yixian Formation, it lived during the early Aptian age of the Early Cretaceous, approximately 124.6 million years ago. It was probably a herbivore or omnivore, although its hands were very similar to those of small carnivorous dinosaurs. It appears to be one of the most basal members of the Oviraptorosauria, closely related to Incisivosaurus, or a taxon slightly less closely related to birds than oviraptorosaurs were.

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.

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.

Beipiaosaurus is a genus of therizinosauroid theropod dinosaurs that lived in Asia during the Early Cretaceous in the Yixian Formation. The first remains were found in 1996 and formally described in 1999. Before the discovery of Yutyrannus, Beipiaosaurus were among the heaviest dinosaurs known from direct evidence to be feathered. Beipiaosaurus is known from three reported specimens. Numerous impressions of feather structures were preserved that allowed researchers to determine the feathering color which turned out to be brownish.

<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.

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

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.

The scientific question of within which larger group of animals birds evolved has traditionally been called the "origin of birds". The present scientific consensus is that birds are a group of maniraptoran theropod dinosaurs that originated during the Mesozoic Era.

<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. Basal members of Paraves are well known for the possession of an enlarged claw on the second digit of the foot, which was held off the ground when walking in some species. A number of differing scientific interpretations of the relationships between paravian taxa exist. New fossil discoveries and analyses make the classification of Paraves an active subject of research.

Epidexipteryx is a genus of small paravian 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.

Haplocheirus is an extinct genus of theropod dinosaur from the Middle Jurassic Shishugou Formation of Xinjiang in China. It is generally considered to be an alvarezsauroid, although some researchers have questioned this assignment. The genus contains a single species, H. sollers, which is known from a mostly complete skeleton including the skull.

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.

Yi is a genus of scansoriopterygid dinosaurs 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.

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 2 3 4 5 6 7 Czerkas, S.A., and Yuan, C. (2002). "An arboreal maniraptoran from northeast China." Pp. 63-95 in Czerkas, S.J. (Ed.), Feathered Dinosaurs and the Origin of Flight. The Dinosaur Museum Journal 1. The Dinosaur Museum, Blanding, U.S.A. PDF abridged version
1 2 Padian, Kevin. (2001) "Basal Avialae" in "The Dinosauria" in "The Dinosauria: Second Edition" University of California Press. 2004.
1 2 Feduccia, Alan; Lingham-Soliar, Theagarten; Hinchliffe; Richard, J. (November 2005). "Do feathered dinosaurs exist? Testing the hypothesis on neontological and paleontological evidence". Journal of Morphology. 266 (2): 125–166. doi:10.1002/jmor.10382. PMID 16217748. S2CID 15079072.
1 2 Harris, J.D. (2004). "'Published works' in the Electronic Age: recommended amendments to Articles 8 and 9 of the Code". Bulletin of Zoological Nomenclature. 61 (3): 138–148.
↑ Wang, X.; Zhou, Z.; He, H.; Jin, F.; Wang, Y.; Zhang, J.; Wang, Y.; Xu, X.; Zhang, F. (2005). "Stratigraphy and age of the Daohugou Bed in Ningcheng, Inner Mongolia". Chinese Science Bulletin. 50 (20): 2369–2376. doi:10.1360/982005-581.
1 2 3 4 5 Zhang, F.; Zhou, Z.; Xu, X.; Wang, X. (2002). "A juvenile coelurosaurian theropod from China indicates arboreal habits". Naturwissenschaften. 89 (9): 394–398. Bibcode:2002NW.....89..394Z. doi:10.1007/s00114-002-0353-8. PMID 12435090. S2CID 556221.
1 2 3 4 5 Czerkas, S. A., & Feduccia, A. (2014). Jurassic archosaur is a non-dinosaurian bird. Journal of Ornithology, 1-11.
↑ Xu, X.; Zheng, X.; Sullivan, C.; Wang, X.; Xing, L.; Wang, Y.; Zhang, X.; o’Connor, J. K.; Zhang, F.; Pan, Y. (2015). "A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings". Nature. 521 (7550): 70–3. doi:10.1038/nature14423. PMID 25924069. S2CID 205243599.
↑ Ren, D.; et al. (2002). "On the biostratigraphy of the Jurassic fossil beds at Daohugou near Ningcheng, Inner Mongolia". Geol. Bull. China. 21: 584–591.
↑ Senter, P (2007). "A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda)". Journal of Systematic Palaeontology. 5 (4): 429–463. doi:10.1017/S1477201907002143. S2CID 83726237.
↑ Holtz, Thomas R., Jr. (2007). Dinosaurs: the most complete, up-to-date encyclopedia for dinosaur lovers of all ages. New York: Random House. ISBN 978-0-375-82419-7.
↑ Agnolin, Federico L.; Motta, Matias J.; Brissón Egli, Federico; Lo Coco, Gastón; Novas, Fernando E. (2019). "Paravian Phylogeny and the Dinosaur-Bird Transition: An Overview". Frontiers in Earth Science. 6. doi: 10.3389/feart.2018.00252 . hdl: 11336/130197 . ISSN 2296-6463.

External links

Reconstruction of Scansoriopteryx forelimb anatomy, from Gareth Monger: Paleo Art.

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[czerkas2002-1] 1 2 3 4 5 6 7 Czerkas, S.A., and Yuan, C. (2002). "An arboreal maniraptoran from northeast China." Pp. 63-95 in Czerkas, S.J. (Ed.), Feathered Dinosaurs and the Origin of Flight. The Dinosaur Museum Journal 1. The Dinosaur Museum, Blanding, U.S.A. PDF abridged version

[Padian2001-2] 1 2 Padian, Kevin. (2001) "Basal Avialae" in "The Dinosauria" in "The Dinosauria: Second Edition" University of California Press. 2004.

[Feducciaetal2005-3] 1 2 Feduccia, Alan; Lingham-Soliar, Theagarten; Hinchliffe; Richard, J. (November 2005). "Do feathered dinosaurs exist? Testing the hypothesis on neontological and paleontological evidence". Journal of Morphology. 266 (2): 125–166. doi:10.1002/jmor.10382. PMID 16217748. S2CID 15079072.

[harris2004-4] 1 2 Harris, J.D. (2004). "'Published works' in the Electronic Age: recommended amendments to Articles 8 and 9 of the Code". Bulletin of Zoological Nomenclature. 61 (3): 138–148.

[Wangetal06-5] Wang, X.; Zhou, Z.; He, H.; Jin, F.; Wang, Y.; Zhang, J.; Wang, Y.; Xu, X.; Zhang, F. (2005). "Stratigraphy and age of the Daohugou Bed in Ningcheng, Inner Mongolia". Chinese Science Bulletin. 50 (20): 2369–2376. doi:10.1360/982005-581.

[zhang2002-6] 1 2 3 4 5 Zhang, F.; Zhou, Z.; Xu, X.; Wang, X. (2002). "A juvenile coelurosaurian theropod from China indicates arboreal habits". Naturwissenschaften. 89 (9): 394–398. Bibcode:2002NW.....89..394Z. doi:10.1007/s00114-002-0353-8. PMID 12435090. S2CID 556221.

[feduccia_czerkas2014-7] 1 2 3 4 5 Czerkas, S. A., & Feduccia, A. (2014). Jurassic archosaur is a non-dinosaurian bird. Journal of Ornithology, 1-11.

[yiqi2015-8] Xu, X.; Zheng, X.; Sullivan, C.; Wang, X.; Xing, L.; Wang, Y.; Zhang, X.; o’Connor, J. K.; Zhang, F.; Pan, Y. (2015). "A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings". Nature. 521 (7550): 70–3. doi:10.1038/nature14423. PMID 25924069. S2CID 205243599.

[ren2002-9] Ren, D.; et al. (2002). "On the biostratigraphy of the Jurassic fossil beds at Daohugou near Ningcheng, Inner Mongolia". Geol. Bull. China. 21: 584–591.

[senter2007-10] Senter, P (2007). "A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda)". Journal of Systematic Palaeontology. 5 (4): 429–463. doi:10.1017/S1477201907002143. S2CID 83726237.

[holtz-11] Holtz, Thomas R., Jr. (2007). Dinosaurs: the most complete, up-to-date encyclopedia for dinosaur lovers of all ages. New York: Random House. ISBN 978-0-375-82419-7.

[12] Agnolin, Federico L.; Motta, Matias J.; Brissón Egli, Federico; Lo Coco, Gastón; Novas, Fernando E. (2019). "Paravian Phylogeny and the Dinosaur-Bird Transition: An Overview". Frontiers in Earth Science. 6. doi: 10.3389/feart.2018.00252 . hdl: 11336/130197 . ISSN 2296-6463.

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