Scansoriopteryx
Encyclopedia
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 (tree-dwelling) lifestyle. It possessed an unusual, elongated third finger. The type specimen of Scansoriopteryx also contains the fossilized impression of feathers.
Most researchers regard this genus as a synonym of Epidendrosaurus, with some preferring to treat Scansoriopteryx as the junior synonym, though it was the first name to be validly published.
ized remains of a hatchling maniraptora
n dinosaur, similar in some ways to Archaeopteryx
. It is notable for its "primitive" non-perforated hip socket, and pubis (hip bone) which points forward, unlike some advanced maniraptorans. Most distinctive is its long third finger, which is almost twice as long as the second finger. This is unlike the configuration seen in all other theropod
s, where the second finger is longest. It also has an unusually large first toe, or hallux
.
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. Impressions indicate a relatively long tail.
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), and may be analogous to the insect-digging finger of the mammalian aye-aye
(in most theropod dinosaurs, the second finger is the longest). 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
. The tail was long, six or seven times the length of the femur
, and ended in a fan of feathers.
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.
. Studies of dinosaur relationships have found Scansoriopteryx to be a close relative of true bird
s and a member of the clade
Avialae
.
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. 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. In scientific literature, the genus Scansoriopteryx has been treated as a senior synonym of Epidendrosaurus by some scientists, such as Thomas R. Holtz, Jr. and Alan Feduccia, and as a junior synonym by other such as Kevin Padian.
", 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 lager, 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.
, 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., but this is hotly contested. See the Daohugou Beds
article for details.
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). 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 (see below), suggest that it probably hails from the same beds, and thus is likely a synonym of Epidendrosaurus.
A 2004 study by He et al. on the age of the Daohugou Beds found them to be Early Cretaceous, probably only a few million years older than the overlying Jehol beds of the Yixian Formation
. The 2004 study primarily used radiometric dating
of a tuff
within the Daohugou Bed to determine its age. However, a subsequent study by Gao & Ren took issue with the He et al. study. Gao and Ren criticized He et al. for not including enough specifics and detail in their paper, and also took issue with their radiometric dating of the Daohugou tuff
. The tuff, Gao and Ren argued, contained crystals with a variety of diverse radiometric ages, some up to a billion years old, so using dates from only a few of these crystals could not determine the overall age of the deposits in which Epidendrosaurus (along with the other Daohugou fossils) were found. Gao and Ren went on to defend a Middle Jurassic age for the beds based on biostratigraphy
(the use of index fossil
s) and the bed's relationship to a layer that is known to mark the Middle Jurassic-Late Jurassic boundary.
Another study, published in 2006 by Wang et al., found that the Tiaojishan Formation
(159-164 million years old) underlies, rather than overlies, the Daohugou Beds. After taking into account the great similarity between the Daohugou fauna and the fauna of the Yixian Formation
, the authors concluded that the Daohugou probably represents the earliest evolutionary stages of the Jehol Biota
, and that it "belongs to the same cycle of volcanism and sedimentation as the Yixian Formation of the Jehol Group." Later in 2006, Liu et al. published their own study of the age of the Daohugou beds, this time using Zircon U-Pb dating on the volcanic rocks overlying and underlying salamander-bearing layers (salamanders are often used as index fossils). Liu et al. found that the beds formed between 164-158 million years ago, in the Middle to Late Jurassic.
of Phu Phok, Thailand
(one of which contained an embryo) were originally thought to have been laid by a small dinosaur similar to Scansoriopteryx. However, further study showed that the eggs actually belonged to an anguimorph
lizard
.
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
.
The Epidendrosaurus was also interpreted as arboreal based on the elongated hand and specializations in the foot. 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.
s 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. Scales
were preserved near the base of the tail, and the Epidendrosaurus specimen also preserved faint feather
impressions at the end of the tail, similar to the pattern found in Microraptor.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of avialan
Avialae
Avialae is a clade of dinosaurs containing their only living representatives, birds , and the most immediate extinct relatives of birds.-Competing definitions:...
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...
. Described from only a single juvenile fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
specimen found in 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 is a sparrow-sized animal that shows adaptations in the foot indicating an arboreal (tree-dwelling) lifestyle. It possessed an unusual, elongated third finger. The type specimen of Scansoriopteryx also contains the fossilized impression of feathers.
Most researchers regard this genus as a synonym of Epidendrosaurus, with some preferring to treat Scansoriopteryx as the junior synonym, though it was the first name to be validly published.
Description
The type specimen of Scansoriopteryx heilmanni (specimen number CAGS02-IG-gausa-1/DM 607) represents the fossilFossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
ized remains of a hatchling 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, similar in some ways to Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
. It is notable for its "primitive" non-perforated hip socket, and pubis (hip bone) which points forward, unlike some advanced maniraptorans. Most distinctive is its long third finger, which is almost twice as long as the second finger. This is unlike the configuration seen in all other theropod
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
s, where the second finger is longest. It also has an unusually large first toe, or hallux
Hallux
In tetrapods, the hallux is the innermost toe of the foot. Despite its name it may not be the longest toe on the foot of some individuals...
.
A second specimen, the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
of Epidendrosaurus ninchengensis (IVPP
Institute of Vertebrate Paleontology and Paleoanthropology
The Institute of Vertebrate Paleontology and Paleoanthropology of China is a prominent research institution and collections repository for fossils, including many dinosaur and pterosaurand cat poo specimens...
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. Impressions indicate a relatively long tail.
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), and may be analogous to the insect-digging finger of the mammalian aye-aye
Aye-aye
The aye-aye is a lemur, a strepsirrhine primate native to Madagascar that combines rodent-like teeth and a special thin middle finger to fill the same ecological niche as a woodpecker...
(in most theropod dinosaurs, the second finger is the longest). 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
Oviraptorosauria
Oviraptorosaurs are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot - like skulls, with or without bony crests atop the head...
. The tail was long, six or seven times the length of the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
, and ended in a fan of feathers.
Because the only known specimens are juvenile, the size of a full-grown Scansoriopteryx is unknown–the type specimen is a tiny, sparrow
House 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...
-sized creature.
Classification
Scansoriopteryx lent its name to the family ScansoriopterygidaeScansoriopterygidae
Scansoriopterygidae is a family of maniraptoran dinosaurs, known from three well-preserved fossils unearthed in the Daohugou fossil beds of Liaoning, China....
. Studies of dinosaur relationships have found Scansoriopteryx to be a close relative of true bird
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...
s 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:...
.
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. 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
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
(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. In scientific literature, the genus Scansoriopteryx has been treated as a senior synonym of Epidendrosaurus by some scientists, such as Thomas R. Holtz, Jr. and Alan Feduccia, and as a junior synonym by other such as Kevin Padian.
Implications
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 ArchaeopteryxArchaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
", 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
Gregory S. Paul
Gregory Scott Paul is a freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dinosaurs and his detailed illustrations, both live and skeletal...
that the lager, ground-dwelling maniraptorans like Velociraptor
Velociraptor
Velociraptor is a genus of dromaeosaurid theropod dinosaur that existed approximately 75 to 71 million years ago during the later part of the Cretaceous Period. Two species are currently recognized, although others have been assigned in the past. The type species is V. mongoliensis; fossils...
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
George Olshevsky
George Olshevsky is a freelance editor, writer, publisher, amateur paleontologist, and mathematician living in San Diego, California.Olshevsky maintains the comprehensive online Dinosaur Genera List...
'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.
Provenance
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 FormationYixian Formation
The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans 11 million years during the early Cretaceous period...
, though Wang et al. (2006), in their study of the age of the Daohugou Beds
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...
, 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., but this is hotly contested. See the Daohugou Beds
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...
article for details.
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
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....
period (169 million years ago) to the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
period (122 ma). 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
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
, which was Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
in age. The provenance of Scansoriopteryx is uncertain, though Wang et al. (2006), in their study of the age of the Daohugou (see below), suggest that it probably hails from the same beds, and thus is likely a synonym of Epidendrosaurus.
A 2004 study by He et al. on the age of the Daohugou Beds found them to be Early Cretaceous, probably only a few million years older than the overlying Jehol beds of the Yixian Formation
Yixian Formation
The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans 11 million years during the early Cretaceous period...
. The 2004 study primarily used radiometric dating
Radiometric dating
Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...
of a tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
within the Daohugou Bed to determine its age. However, a subsequent study by Gao & Ren took issue with the He et al. study. Gao and Ren criticized He et al. for not including enough specifics and detail in their paper, and also took issue with their radiometric dating of the Daohugou tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
. The tuff, Gao and Ren argued, contained crystals with a variety of diverse radiometric ages, some up to a billion years old, so using dates from only a few of these crystals could not determine the overall age of the deposits in which Epidendrosaurus (along with the other Daohugou fossils) were found. Gao and Ren went on to defend a Middle Jurassic age for the beds based on biostratigraphy
Biostratigraphy
Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. Usually the aim is correlation, demonstrating that a particular horizon in one geological section represents the same period...
(the use of index fossil
Index fossil
Index fossils are fossils used to define and identify geologic periods . They work on the premise that, although different sediments may look different depending on the conditions under which they were laid down, they may include the remains of the same species of fossil...
s) and the bed's relationship to a layer that is known to mark the Middle Jurassic-Late Jurassic boundary.
Another study, published in 2006 by Wang et al., found that the Tiaojishan Formation
Tiaojishan Formation
The Tiaojishan Formation is a geological formation in Hebei and Liaoning, People's Republic of China, dating to the middle-late Jurassic period . It is known for its fossil plants, and is made up mainly of pyroclastic rock interspersed with basic volcanic and sedimentary rocks...
(159-164 million years old) underlies, rather than overlies, the Daohugou Beds. After taking into account the great similarity between the Daohugou fauna and the fauna of the Yixian Formation
Yixian Formation
The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans 11 million years during the early Cretaceous period...
, the authors concluded that the Daohugou probably represents the earliest evolutionary stages of the Jehol Biota
Jehol Biota
The Jehol Biota includes all the living organisms - the ecosystem - of northeastern China between 133 to 120 million years ago. This is the Lower Cretaceous ecosystem which left fossils in the Yixian Formation and Jiufotang Formation. It is also believed to have left fossils in the Sinuiju series...
, and that it "belongs to the same cycle of volcanism and sedimentation as the Yixian Formation of the Jehol Group." Later in 2006, Liu et al. published their own study of the age of the Daohugou beds, this time using Zircon U-Pb dating on the volcanic rocks overlying and underlying salamander-bearing layers (salamanders are often used as index fossils). Liu et al. found that the beds formed between 164-158 million years ago, in the Middle to Late Jurassic.
Paleobiology
Several tiny fossil eggs discovered in the Sao Khua FormationSao Khua Formation
The Sao Khua Formation is a middle member of the Khorat Group. It consists of an alteration of grayish-reddish brown siltstone and clay, and pale red to yellowish-gray, fine to medium-grained sandstone. Rare pale red to light gray conglomerates, containing carbonate pebbles, are also characteristic...
of Phu Phok, Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
(one of which contained an embryo) were originally thought to have been laid by a small dinosaur similar to Scansoriopteryx. However, further study showed that the eggs actually belonged to an anguimorph
Anguimorpha
Anguimorphs of the infraorder Anguimorpha include the anguids , monitor lizards, the extinct mosasaurs, and helodermatids . The infraorder was named by Fürbringer in 1900 to include all autarchoglossans closer to Varanus and Anguis than Scincus...
lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
.
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 woodpeckerWoodpecker
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...
.
The Epidendrosaurus was also interpreted as arboreal based on the elongated hand and specializations in the foot. 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
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 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 featherFeather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
s 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. Scales
Reptile scales
Reptile skin is covered with scutes or scales which, along with other characteristics, distinguish reptiles from animals of other classes . Scales are made of keratin and are formed from the epidermis...
were preserved near the base of the tail, and the Epidendrosaurus specimen also preserved faint feather
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
impressions at the end of the tail, similar to the pattern found in Microraptor.
External links
- Reconstruction of Scansoriopteryx forelimb anatomy, from Gareth Monger: Paleo Art.