Scansoriopterygidae
Encyclopedia
Scansoriopterygidae is a family
of maniraptora
n dinosaur
s, known from three well-preserved fossil
s unearthed in the Daohugou
fossil beds (possibly dating to the mid-late Jurassic Period) of Liaoning
, China
.
Scansoriopteryx
(and its likely synonym Epidendrosaurus) 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
in 2008 that an adult specimen was known. 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.
s, about 16 centimeters long, while the adult type specimen of Epidexipteryx is about the size of a Pigeon, about 25 centimeters long (not including the tail feathers).
Scansoriopterygids can be characterized by their extremely elongated third fingers, which are longer than the first and second digits of the hand (in all other known theropods, the second finger is the longest). 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.
-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. 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.
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 scansoriopteryds, along with other maniraptorans and birds, split from other theropods very early in dinosaur evolution. 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 the closest dinosaurian relative of avian birds
, and a member of the clade
Avialae
. This view was supported by a second phylogenetic analysis performed by Zhang et al. in 2008. These authors included the additional taxon Epidexipteryx, and found that it formed a clade with Scansoriopteryx at the base of Avialae. An abbreviated version of Zhang et al.s 2008 cladogram
is presented below.
of northeastern China. The age of these fossil beds is not resolved, and studies have variously proposed dates ranging between some 170 to about 120 mya (Middle Jurassic
to Early Cretaceous
).
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
, cycad
s, and fern
s.
The scansoriopterygids would have lived alongside synapsid
s such as the aquatic Castorocauda and arboreal gliding mammal
Volaticotherium, the rhamphorhynchoid
pterosaur
s Jeholopterus
and Pterorhynchus
, as well as a diverse range of insect life (including mayflies
and beetle
s) and several species of salamander
.
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 lead 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.
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 woodpecker
s. 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
.
ns, 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.
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).
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of maniraptora
Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
n dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s, known from three well-preserved fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s unearthed in the Daohugou
Daohugou Beds
The Daohugou Beds are a series of fossil-bearing rock deposits located in northeastern China, with the type locality around Daohugou village of Ningcheng County south of Chifeng, Inner Mongolia, but extending into southwest Liaoning. The rocks are grey, finely bedded, lacustrine, sandy mudstones...
fossil beds (possibly dating to the mid-late Jurassic Period) of Liaoning
Liaoning
' is a province of the People's Republic of China, located in the northeast of the country. Its one-character abbreviation is "辽" , a name taken from the Liao River that flows through the province. "Níng" means "peace"...
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
.
Scansoriopteryx
Scansoriopteryx
Scansoriopteryx is a genus of avialan 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 lifestyle. It possessed an unusual, elongated third finger...
(and its likely synonym Epidendrosaurus) 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
Epidexipteryx
Epidexipteryx is a genus of small avialan dinosaur, 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. The type specimen is...
in 2008 that an adult specimen was known. 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.
Description
Scansoriopterygids are among the smallest dinosaurs known. The juvenile specimens of Scansoriopteryx are the size of House SparrowHouse Sparrow
The House Sparrow is a bird of the sparrow family Passeridae, found in most parts of the world. One of about 25 species in the genus Passer, the House Sparrow occurs naturally in most of Europe, the Mediterranean region, and much of Asia...
s, about 16 centimeters long, while the adult type specimen of Epidexipteryx is about the size of a Pigeon, about 25 centimeters long (not including the tail feathers).
Scansoriopterygids can be characterized by their extremely elongated third fingers, which are longer than the first and second digits of the hand (in all other known theropods, the second finger is the longest). 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.
Classification
Scansoriopterygidae was created as a familyFamily (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
-level taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
by Stephen Czerkas and Yuan Chongxi in 2002. Some scientists, such as Paul Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
, initially considered the concept redundant because the group was originally monotypic, containing only the single genus and species Scansoriopteryx heilmanni
Scansoriopteryx
Scansoriopteryx is a genus of avialan 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 lifestyle. It possessed an unusual, elongated third finger...
. Additionally, the group lacked a phylogenetic definition. However, in 2008 Zhang et al. reported another scansoriopterygid, Epidexipteryx
Epidexipteryx
Epidexipteryx is a genus of small avialan dinosaur, 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. The type specimen is...
, and defined Scansoriopterygidae as a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
comprising most recent common ancestor of Epidexipteryx and Epidendrosaurus (=Scansoriopteryx") plus all its descendants.
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 scansoriopteryds, along with other maniraptorans and birds, split from other theropods very early in dinosaur evolution. 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 the closest dinosaurian relative of avian birds
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
, and a member of the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Avialae
Avialae
Avialae is a clade of dinosaurs containing their only living representatives, birds , and the most immediate extinct relatives of birds.-Competing definitions:...
. This view was supported by a second phylogenetic analysis performed by Zhang et al. in 2008. These authors included the additional taxon Epidexipteryx, and found that it formed a clade with Scansoriopteryx at the base of Avialae. An abbreviated version of Zhang et al.s 2008 cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
is presented below.
Provenance and paleoecology
The fossil remains of Epidexipteryx and Scansoriopteryx were recovered from the Daohugou BedsDaohugou Beds
The Daohugou Beds are a series of fossil-bearing rock deposits located in northeastern China, with the type locality around Daohugou village of Ningcheng County south of Chifeng, Inner Mongolia, but extending into southwest Liaoning. The rocks are grey, finely bedded, lacustrine, sandy mudstones...
of northeastern China. The age of these fossil beds is not resolved, and studies have variously proposed dates ranging between some 170 to about 120 mya (Middle Jurassic
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
to Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
).
The known scansoriopterygids of the Daohugou biota inhabited a humid, temperate forest made up of a variety of prehistoric trees including species of ginkgo
Ginkgo
Ginkgo , also spelled gingko and known as the Maidenhair Tree, is a unique species of tree with no close living relatives...
and conifer. The understory would have been dominated by plants such as club mosses
Lycopodiopsida
Lycopodiopsida is a class of plants often loosely grouped as the fern allies. Traditionally the group included not only the clubmosses and firmosses, but also the spikemosses and the quillworts...
, horsetails
Equisetopsida
Equisetopsida, or Sphenopsida, is a class of plants with a fossil record going back to the Devonian. They are commonly known as horsetails...
, cycad
Cycad
Cycads are seed plants typically characterized by a stout and woody trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female . Cycads vary in size from having a trunk that is only a few centimeters...
s, and fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s.
The scansoriopterygids would have lived alongside synapsid
Synapsid
Synapsids are a group of animals that includes mammals and everything more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having an opening low in the skull roof behind each eye, leaving a bony arch beneath each, accounting for their name...
s such as the aquatic Castorocauda and arboreal gliding mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
Volaticotherium, the rhamphorhynchoid
Rhamphorhynchoidea
The Rhamphorhynchoidea forms one of the two suborders of pterosaurs and represent an evolutionary grade of primitive members of this group of flying reptiles. This suborder is paraphyletic in relation to the Pterodactyloidea, which arose from within the Rhamphorhynchoidea, not from a more distant...
pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
s Jeholopterus
Jeholopterus
Jeholopterus was a small anurognathid pterosaur from the Daohugou Beds of northeastern China , between 168 and 152 million years ago), preserved with hair and skin remains.-Naming:...
and Pterorhynchus
Pterorhynchus
Pterorhynchus was a genus of rhamphorhynchid "rhamphorhynchoid" pterosaur from the Late Jurassic-age Daohugou Formation of Inner Mongolia, China....
, as well as a diverse range of insect life (including mayflies
Mayfly
Mayflies are insects which belong to the Order Ephemeroptera . They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies...
and beetle
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
s) and several species of salamander
Salamander
Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
.
Paleobiology
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 lead 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
Cathayornis
Cathayornis is a genus of enantiornithine bird from the Jiufotang Formation of Liaoning, People's Republic of China and, in the case of the possible species C...
and Longipteryx
Longipteryx
Longipteryx is a genus of prehistoric bird which lived during the Early Cretaceous . It contains a single species, Longipteryx chaoyangensis. Its remains have been recovered from the Jiufotang Formation at Chaoyang in Liaoning Province, People's Republic of China...
. 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.
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 woodpecker
Woodpecker
Woodpeckers are near passerine birds of the order Piciformes. They are one subfamily in the family Picidae, which also includes the piculets and wrynecks. They are found worldwide and include about 180 species....
s. 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
Hoatzin
The Hoatzin , also known as the Hoactzin, Stinkbird, or Canje Pheasant, is a species of tropical bird found in swamps, riverine forest and mangrove of the Amazon and the Orinoco delta in South America...
.
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 maniraptoraManiraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
ns, 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.
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).