The marblebill is a large arboreal carnivore with some pronounced specializations. Its body shape reveals its mode of locomotion at a glance: it is a brachiator, swinging from its 'arms'. These, the first pair of limbs, are about three times as long as the others, and end in simple but powerful hooks. Suspended from these hooks the animal swings from branch to branch.

The marblebill's other legs are short in comparison and end in strong claws. With these legs the animal can not just crawl up tree trunks and hop around with agility; they also serve to grasp a victim. The marblebill's favourite prey is the 'Aggie' (Agitator Augur), a tree-dwelling fructivore.

Marblebills live in pairs and are fiercely territorial; a pair spends much of its time threatening its neighbours, resulting in some impressive posturing and ear-splitting screeching. But when hunting, in pairs or alone, they are quite stealthy. A troop of Aggies may suddenly become aware of a lightly swaying branch and a falling baignac; only when they hear the marblebill's triumphant howl does it dawn upon them that one of their comrades had just now been sitting on that branch and eating that baignac.

It is the pre-prandial 'Aa-ia-iaaaaa' howl that explains the species' name. The related species Iaculator Schwarzeneggrii has a more guttural sound.

Blog posts on marblebills
There are several posts on marblebills and related topics. Two dealt with brachiation, the mode of locomotion in which an animal swings by its arms. As said above, the marblebill does so, as do several Earth animals. Here is a comparison of Earth's brachiators with the marblebill: a post from March 2010. Here is one that describes a rather stranger way of swinging through trees, for which no name was yet available: cernuation; April 2010.
In the course of revamping and repainting earlier creatures, the marblebill was one of the first to undergo rejuvenation. Its head and feet underwent the largest changes. The image shown here is an early stage of rebuilding the head. The post appeared in August 2012.

Marblebills are quite specialised, indicating that their arboreal environment must have existed for a very long time. Indeed, the Paleogeas seem to have remained in place and isolated for long epochs.

Habitat: tiered forests
Distribution: South Paleogea (related species on Middle Paleogea)
Mass: up to 60 kg
Length (body and head): 170 cm