Arbronychosauroidea Title


As strange as the idea may be here and now, it was not so long ago that paleontologists considered all dinosaurs to be strict ground-dwellers (keep in mind, this was before birds were realized to be dinosaurs themselves). While a few very early workers posited tree-climbing non-avian dinosaurs, in the long, dark stretch of the middle twentieth century, such ideas were forgotten and the terrible saurians became exclusively creatures of the swamp.

It was not until the mid-1980s when some paleontologists again suggested treetops as another home for non-avian dinosaurs, turning to the coelurosaurs, small, agile, and (the imagination reels) possible warm-blooded and feathered predators as the most likely dinosaur climbers. Most scientists, however, treated such ideas as derision: who could imaging a dinosaur like Tyrannosaurus or Triceratops in a tree? It was not until almost the end of the century when Chinese fossil beds began to yield fossils of small, hundred-million-year-old dinosaurs that the orthodoxy was proven wrong. Dinosaurs can climb, and many did.


Climbers must be small and light-weight, and so fossilize poorly. To date, the only known fossils of pre-Cenozoic non-avian dinosaur climbers come from those same Chinese fossil beds. However, this one area shows so much diversity in climbers, from spider-fingered Scansoriopteryx to four-winged Microraptor to the long-handed Yixianosaurus, that it is impossible to think that such creatures were aberrations. Dinosaurs seem to have experimented with climbing many times (one of these experiments leading to the wildly successful birds), and in Spec, they continued to do so long after the Cretaceous. Although the scansoriopterygids and Microraptor (as well as similar species to Microraptor) of the distant past are long gone, their spirit lives on in the arbronychosaurs, the climbing raptors.

Some time very early in the Paleogene (or perhaps even earlier, in the Cretaceous), a group of deinonychosaurs took to the trees. From precisely what progenitor these early arbros sprang is difficult to guess. Several lineages of deinonychosaurs of the Cretaceous appear to have been at least somewhat arboreal, a fact that leads many paleontologists to believe that deinonychosaurs originally sprung from tree-dwelling stock. However, the lightly-built, North American Bambiraptor seems to be a good match to early arbronychosaur fossil, and ma be close to the base of their family tree. The arbronychosauroids, however, have evolved far from their ancestors. The arbro skeleton is strongly pneumatisized, the bones being mostly thin-walled and hollow, with an extensive air-sac system running through the body in a manner very similar to birds. Arbronychosaur hands and feet are also highly modified, with the innermost finger and two innermost toes opposing the other digits. The powerfully prehensile feet and hands of an arbro are reminiscent of a chameleon, but unlike the sluggish color-changing lizards, the deinonychosaurs are quite fleet of foot, and can even manage short hopping sprints ove ground. Fossils indicate arbronychosaurs perfected this body-type in the Paleogene and spread from Asia or North America into Africa and, later, South America.

ARBRONYCHOSAURIDAE (Moulongs and treelurks)

One novel modification of the arbronychosaurids is the modification of the vertebrae at the base of the tail. Arbronychosaurid caudal vertebrae are unusually limber for deinonychosaurs, the ossified tendons around the tail's based having been reduced. The tendons still present at the tail's tip turn the appendage into an extremely mobile pole that may be twisted at almost any angle relative to the body. The modified tail is obviously an aid to balance, but it may play an even more dynamic role in the arbronychosaurid's life. Powerful sweeps of the tail while jumping allows an arbronychosaur to shift its center of balance and even alter direction in mid-leap. The stiff sprays of feathers that often adorn the tails of arbronychosaurids may increase the aerodynamic effectiveness of this appendage even more.

Ringing Moulong (Mokulongia sinensis)

Ringing mulong

Ringing Moulong, Mokulongia sinensis (Eastern Eurasia)

The ringing moulong is a denizen of the bamboo forests of China. 20 centimeters from snout to tail, ringing moulong live in loose communities of immediate family, with a communal nest built of woven leaves in which the eggs of the tribe are incubated. Generally, a tribe will have only a single adult female who lays eggs during the spring and summer, but in areas where food is scarce, several females will lay in the same nest. During such times, the nesting mothers carefully keep track of which eggs are theirs, refusing to incubate any but their own progeny. When gathered in communities, adult males generally stay near the females and guard the nest, while subadult males and females act as hunters, gorging themselves and then regurgitating food into the mouths of chicks and adults.

Treelurk (Arbronychus ferox)

Tree lurk

Treelurk, Arbronychus ferox (Southeastern Eurasia)

A common sight in the jungles of India, the treelurk is the principal predator of the region. These meter-and-a-half-long carnivores stalk the pokemurids and pithecavians that live off fruits and leaves, dispatching their prey with their hooked finger-talons.

PACIFONYCHINAE (Island arbros, blue-winged arbros, and fruit-arbros)

Classical phylogenic systems placed all South American arbronychosaurs within Strigosauridae, the owl-faced arbros, but recent genetic studies have discovered that some South American arbros are only distantly related to Strigosauridae. These taxa have now been placed within their own family, Pacifonychidae, a sister clade to Arbronychosauridae. Pacifonychids, including such widely disparate creatures as the island arbro and the green-billed fruit-arbro are similar to the arbronychosaurids in general appearance. The more basal island and blue-winged arbros could even be mistaken for Old-World species, although the fruit-arbros (genus Pacifonyx) are obviously different from any other group of arbronychosauroid. These highly derived creatures are large, arboreal fruit-eaters, similar to the carpos of Asia.

The upper, sunlit layers of the Amazon Rainforest are home many large, arboreal creatures that may never set foot on solid ground. Birds dwell here in tremendous abundance, as do a few climbing mammals, reptiles, and amphibians, but perhaps the most peculiar denizens of the forest canopy are the placid fruit-arbros (family Pacifonichidae, genus Pacifonyx). Like the more familiar, carnivorous arbros of Asia and South America, fruit-arbros are deinonychosaurs (distant relatives of the ferocious draks) that have taken up a life in the trees. Fruit-arbros are descended from this stock, but these slow-moving, fruit-eating creatures are a far cry from their screaming, sharp-toothed cousins. Indeed, what a fruit-arbro most resembles is a large bird, like the toucans and macaws of Home-Earth, or the carpos of Asia. Fruit-arbros lack stereoscopic vision and their teeth are highly reduced. Their bodies in general are more heavily-built than other arbronychsauroids, their bones strong, and the pubis swept back to accommodate a vegetarian's gut. As most of the features that differentiate the fruit-arbros from the rest of arbronychosauria may simply be attributed to their eating habits, the true affinities of this clade are vague.

Island Arbro (Insulonychus antilliensis)


Island Arbro, Insulonychus antilliensis (Caribbean Islands)

The island arbro (Insulonychus antilliensis) is the only member of family Arbronychosauridae that can be found in the Caribbean. It is impossible to say how these creatures got to their present home - perhaps they rafted or swam from the forests of mainland South America, but these creatures now range across the Greater Antilles, with large populations in Cuba, Dominica, and Jamaica, where they eat birds, mammals, insects and (occasionally) fruit. Island arbos show a great deal of variation across their range (the above is a photograph of I. a. virginiensis, the Virgin Islands subspecies), but genetic tests show that all these races are monospecfic.

Blue-Winged Arbro (Caerulatusaurus dobbsi)


Blue-winged arbro, Caerulatusaurus dobbsi (South America: Amazon Rainforest)

Blue-winged arbro

Head of a blue-winged arbo, Caerulatusaurus dobbsi

Molecular studies confirm that the fruit-arbros' closest living relatives are the island arbro and blue-winged arbro, both of which spring from somewhere near the base of the arbronychosaur tree. While not as mobile as the birds of the forest, fruit-arbros are free to grow to much larger size, and so are able to bully their flying cousins away from food. These deinonychosaurs are also excellent leapers, use their long, stiffened tails for balance as they vault from branch to branch, finding purchase with their sharp, curving talons.

Green-Billed Fruit-Arbro (Pacifonyx tucanoides)

Green billed fruit arbro by bensen daniel

Green-billed fruit-arbro, Pacifonyx tucanoides (South America: Amazon Rainforest)

The green-billed fruit-arbro is the largest of the fruit-arbros, two meters long from head to tail, and the best known of this genus. Green-bills spend their entire lives in the forest canopy, where they feed off of large, heavy fruits such as pawpaws, large figs, and avocados that grow near the sturdy branches around the trunks of the trees.

Blue-Faced Fruit-Arbro (Pacifonyx minimus)


Blue-faced fruit-arbro, Pacifonyx minimus (South America: Amazon Rainforest)

A secretive denizen of the Amazon Rainforest, the blue-faced fruit arbro is the smallest known representative of its genus. Weighing a mere 2 kilograms, this fruit-arbro avoids the competition of fruit-eating birds by living in the densely-packed lower stories of the rainforest, where the birds cannot fly.

STRIGOSAURIDAE (Skreechers and saltaritas)

Strigosaurids make up the bulk of Neotropical arbronychosauroid diversity. These medium-sized-to-tiny predators, with their distinctive dish-shaped faces and stubby tails, are arboreal ambush predators, feeding mostly on avialans (including birds), tree-climbing mammals and lizards, and other arbros. All strigosaurids have excellent senses of vision and hearing, due to their strongly stereoscopic eyes and asymmetrically-placed ears, which allow them to pinpoint the origin of a sound in three dimensions with tremendous accuracy.

Skreecher (Strigosaurus vocalis)


Skreecher, Strigosaurus vocalis ( South America)

A skreecher will wait for hours under a concealing pool of shadow, waiting for a prey animal to chance beneath its perch. When the time is right, the strigosaur will descend with talons wide, breaking the back of its prey with its powerful hands and feet. Smaller species find this waiting game too metabolically expensive; their small size means they must eat almost constantly to maintain themselves. Consequently, the little, insectivorous arbros are more active in pursuit of their quarry, but their killing blow, the leap from a higher branch onto the prey, is used even by these minuscule hunters.

Saltarita (Microstrigosaurus saltaris)

White-cheeked saltarita 2

White-cheeked saltarita, Microstrigosaurus saltaris (Amazon Rainforest)

Saltaritas are ubiquitous in the canopy of the Amazon rainforest. These 50-centimeter-long insectivores winkle grubs out of bark with their long finger-talons.

The rainforests of South America are full of creatures beautiful, strange and fierce, but few would fit into any of those three categories better better than the saltaritas, the ''little jumpers" of the jungle.

"Saltarita" is a generic term used to describe any small, South American arbro, but the folk-name corresponds to reality surprisingly well. Most of the arbros designated "saltarita" are indeed members of the same genus, Microstrigosaurus, (only a few fall into the genus Strigosaurus) and all are closely related, the result of an evolutionary explosion no more than 10 million years ago, when the first arbronychosaurs crossed to South America from the north. 

Saltarita, Microstrigosaurus saltaris (South America---Amazon)

The half-dozen-or-so species of saltarita occupy a niche somewhere between Home-Earth's omnivorous monkeys, hawks, and jungle cats.  Generally traveling alone or in pairs, saltaritas eat almost any animal small enough to fit into their mouths, from insects to mammals to each other.  Many hunt the climbing metatherians that live in the trees, other sspecialize on birds or on insects.  One species even fishes, dangling upside-down from tree-branches to snare fish in long-fingered claws.

The white-cheeked saltarita is small, even within this genus, and specializes in insects and birds. These little creatures are seldom seen, but their cat-like mewing may often be heard in the rainforest. Few specimens have yet been captured, and little is known of their private habits.


The chupie is a Spec cryptid known from no concrete evidence and never formally named. However, in the interests of thuroughness, we feel it should be, at least, mentioned in association with its most probable kin, the arbronychosaurs.

                                              ,Insulonychus antilliensis ( Island arbro )
                                          |   `=Caerulatusaurus dobbsi ( Blue winged arbro )
                        |                 |             ,= P. tucanoides ( Green-billed fruit-arbro )
                        |                  `=Pacifonyx=|
                        |                              `=P. minimus ( Blue-faced fruit-arbro )
                     |  |                      ,=Arboronychus ferox ( Tree lurk )             
                     |   `=Arbronychosauridae=|
                     |                         `=Mokulongia sinensis ( Ringing mokulong )
                     |                 ,= Strigosaurus vocalis ( Skreecher )
                                       `=Microstrigosaurus gracilis ( White-cheeked saltarita )
Community content is available under CC-BY-SA unless otherwise noted.