Yi

Type Species: Yi qi

Classification: Dinosauria – Saurischia – Theropoda – Coelurosauria – Maniraptora – Paraves – Scansoriopterygidae

Time Period: Late Jurassic

Location: China

Diet: Carnivore 

The paravian Yi lived during the Oxfordian stage of the Late Jurassic in modern China. The Tiaojishan Formation captures a snapshot of a mountainous, jungle-like, subtropical paradise dominated by bennettitales, ginkgoes, conifers, and ferns. The environment was cut by mountain streams, hollowed-out azure lakes, and active volcanoes. Yi is known from a single adult specimen. It weighed less than a pound and was likely arboreal (tree-dwelling). Its head was short and blunt-snouted with a downturned lower jaw. It had teeth only in the tips of the jaws: the four upper teeth were the largest and slightly forward-pointing, and the four lower teeth were angled even more strongly forward. It had long, slender forearms and was covered in a thick coat of feathers. Its feathers were stiff and simple in structure; they were ‘paintbrush-like,’ with long quill-like bases topped by sprays of inner filaments. The feathers started near the tip of the snout and spread down to the metatarsus of the foot. The head and neck feathers were long, and the body feathers were even longer and thicker. The longest feathers were six centimeters behind the upper arm and shinbone. Electron microscope studies of preserved melanosomes revealed that the body feathers were black while the head feathers had a more yellowish-brown hue. 

Yi’s most interesting characteristic was a bat-like membrane of skin that served for gliding. It had an unusually elongated third finger that supported the membranous gliding pane of skin, which was preserved as small patches of wrinkled skin. These bat-like wings were supported by a long, bony strut attached to the wrist. This arrangement is unique among all known dinosaurs and makes Yi quite an interesting find. At least one other scansoriopterygid, Ambopteryx, appears to have had a similar bat-like membranous wing. Thus these paravians evolved bat-like wings long before the bats, and they were unique among their paravian brethren. Alas, they did not survive into the Tertiary and are not related to modern bats, which are mammals. 

Scansoriopteryx

Type Species: Scansoriopteryx heilmanni

Classification: Dinosauria – Saurischia – Theropoda – Coelurosauria – Maniraptora – Paraves – Scansoriopterygidae

Time Period: Late Jurassic

Location: China

Diet: Carnivore 

The paravian Scansoropteryx lived in southern Laurasia (China) during the Oxfordian stage of the Late Jurassic. The sole specimen belongs to a hatchling, so the adult size is unknown. The hatchling was sparrow-sized and was likely arboreal (tree-dwelling) due to the unusually large first toe of the foot that may have been reversed in life, giving it a grasping ability for perching on tree limbs. Its elongated third finger is nearly twice as long as the second finger, and this may have supported a membranous ‘bat-like’ wing. It had short legs, and the specimen preserves pebbly scales along the upper foot. The presence of feathers in the same area may imply ‘hind wings’ similar to those of Microraptor and other paravians. The tail ended in a fan of feathers. Its jaws were wide and rounded; the lower jaw contained at least twelve teeth, and they were 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 oviraptosaurs. 

Epidexipteryx

Type Species: Epidexipteryx hui

Classification: Dinosauria – Saurischia – Theropoda – Coelurosauria – Maniraptora – Paraves – Scansoriopterygidae

Time Period: Late Jurassic

Location: China

Diet: Carnivore 

The paravian theropod Epidexipteryx grew only ten inches long and weighed just over a third of a pound. It had a distinctive short snout and large eye sockets. Its teeth were restricted to the front of the jaws, and they were unusually angled forward, a feature seen again only in the Late Cretaceous theropod Masiakasaurus. Skull similarities between Epidexipteryx and later oviraptosaurs has led some researchers to speculate that Epidexipteryx may be the sort of dinosaur that was ancestral to the oviraptosaurs. A key similarity between the two is how the lower jaw curves down and away from the upper jaw, especially towards the end; thus the lower front teeth always pointed forward instead of up into the upper jaw. Researchers speculate that this strange design in Epidexipteryx was to catch specific prey. Its diet was probably small insects, worms, and larvae, especially those found in trees. That it was arboreal (a tree-dweller) is evidenced in its incredibly long fingers. Its second finger was much longer than the first, and the third finger was much longer than the second, growing half as long as Epidexipteryx’s body. This has been interpreted as an adaption for an arboreal lifestyle. Its long fingers enabled it to climb trees while gripping firmly to the trunk. The long fingers could also snatch worms and larvae burrowed into tree holes. As a tree-dweller, it may have made nests for its young. The short forelimbs and long fingers would’ve made walking about the ground a difficult task, and thus prone to predation, so it may have rarely gone down to the forest floor. 

Epidexipteryx was covered in simple body feathers composed of parallel barbs; these body feathers were unique in that some appear to arise from a ‘membranous structure’ at the base of each feather, a facet that some scientists believe is a critical stage in the evolution of modern flight feathers. Epidexipteryx’s most fascinating feathers are found on the tail. Its tail bore unusual vertebrae toward the tip which resembles the feather-anchoring pygostyle of modern birds (and some oviraptosaurs, strengthening the possible oviraptosaur connection); and spreading from this base of its tail were four unusually long feathers. Each was composed of a central rachis and vanes; unlike modern tail feathers, the vanes weren’t branched into individual filaments but made up of a single ribbon-like sheet. These feathers are thought to have been similar to those of a peacock; as strict display feathers, they may have been present only in male Epidexipteryx in order to attract females. If these were indeed strict tail display feathers, they are the first in the fossil record and the precedent of hundreds of different bird species today. 

Ambopteryx

Type Species: Ambopteryx longibrachium

Classification: Dinosauria – Saurischia – Theropoda – Coelurosauria – Maniraptora – Paraves – Scansoriopterygidae 

Time Period: Late Jurassic

Location: China

Diet: Omnivorous? 

The non-avian theropod Ambopteryx is known from a nearly complete skeleton with preserved soft tissues. This small critter was just a foot long snout-to-tail, and it had a wing membrane preserved as a continuous brownish layer on the matrix surrounding the left hand, right forelimb, and abdomen. This thin membrane may have been reminiscent of that equipped by modern bats. Ambopteryx’s head, neck, and shoulders were coated with a dense layer of feather. Its head was short and blunt, and it had a hyper-elongated third finger. Some researchers believe that this finger was used to extract grubs from wood, but others believe it was elongated for the attachment of the patagium (wing membrane) and that, in life, their fingers were encapsulated by membranous tissue and had limited mobility. Unlike most non-avian theropods, it had a short tail that lacked a transitional point and ended in a pygostyle (a set of fused tail vertebrae to support tail feathers and musculature). The only other non-avian theropods known to have a pygostyle were a handful of oviraptosaurs and therizinosaurs. Ambopteryx’s abdominal region contained a small number of gastroliths and crushed bones, likely the remnants of its last meal. The presence of both bones and gastroliths indicate it may have been an omnivore. 

Ambopteryx belongs to the non-avian Scansoriopterygid dinosaur family. Only a few species of these scansoriopterygids are known, but these reveal that they had clear adaptations for an arboreal (tree-dwelling) lifestyle and that they likely glided from branch-to-branch, spending little time on the forest floor. These were some of the smallest dinosaurs, some no larger than a sparrow.