Crackbeak

The Crackbeak, Fortirostrum fructiphagum, is an arboreal hypsilophodont that evolved specialized perching feet. They use their beaks for cracking seeds and fruit (Africa, Asia, and Australia).

High in the luxuriant branches of the tropical forest trees in the north-east of the Australasian continent, a black and white creature throws itself from one branch to another and disappears among the foliage. At first glance it looks like an arbrosaur, one of the tree-living coelurosaurs that are found all over the world. Then it appears again, and its bright face, surmounted by a high crest, is its most obvious feature. This is a crackbeak , a tree-living descendant of the successful hypsilophodonts. Crackbeak ancestors were lightly built running animals, evolved to run swiftly across open country. Now the legs have developed into jumping legs, and the lightweight feet have evolved for perching. The small first toe has turned round to face the rear, so the foot can now be used for grasping branches. The tail is still a long, stiff balancing organ but can now be used as a third leg; pressed against a tree-trunk it gives the animal a firm anchor while feeding. As in the arbrosaurs, the crackbeak has developed a strong system of bones and muscles in the shoulder region to help it climb trees. The front feet have become dextrous hands. Crack-beaks are found in many other parts of the world, particularly in the tropical rainforests of the Ethiopian and Oriental realms, but it is only on the Australasian continent that they are so abundant and varied.

The crackbeak's bill is delicate enough to pick individual berries out of a bunch, yet powerful enough to crack open even the hardest nuts. The beak is used only for picking and cracking; the actual chewing is done by the back teeth. The horny crest on the head, along with the bright colour of the face and dewlap, are used for signalling both to mates and to enemies.

The superficial resemblance in size and shape between the Australasian crackbeak and the arbrosaurs of the northern continents have come about by convergent evolution. They both evolved from lightly built running ancestors and have become lightly built tree-dwelling animals, but whereas the arbrosaurs subsist on a diet of insects and small vertebrates, the crackbeak is strictly vegetarian.

The crackbeak hand, like those of all hypsilophodonts and most of their descendants, has a full complement of five fingers. All the fingers are long and mobile. Both the first and the fifth fingers are opposable, or able to cross over the palm of the hand in order to grasp things. These are very useful to the crackbeak while climbing in the branches and selecting food from between the twigs.