Further Evolution of the Emu
by Dee Dee Mares

Feathered Velociraptor 
the work of Janice McCafferty of Turtle Path Studios 

Previously I discussed the work of Yale paleontologist, John Ostrom in furthering the bird-dinosaur connection by identifying over 85 similarities between the skeletons of birds and dinosaurs.  Today that list has over 100 shared features such as swiveling wrists, wishbones and hollow, thin-walled bones.  Most similar are the skeletons of the group of modern birds called Ratites and a group of carnivorous dinosaurs called the Maniraptors. It is proposed that from one of these feathered dinosaurs similar to the Velociraptor pictured, all modern birds evolved.

Early feathered dinosaurs developed feathers for body temperature regulation, camouflage or display.  Flight did not evolve until much later. Two theories of the origin of flight are held. The arboreal hypothesis, states that bird ancestors began to fly by climbing trees and gliding down from branches with the help of incipient feathers. As feathers became larger, flapping flight evolved, and birds became fully airborne.  The cursorial hypothesis holds that small dinosaurs ran along the ground at high speeds and stretched out their arms for balance as they leaped into the air after insect prey or to avoid predators. Feathers on forelimbs expanded the arm's surface area to enhance lift - larger feathers developed incrementally to increase lift until sustained flight was gradually achieved.  Possibly both hypotheses hold.  Whichever, it is thought that ancestors of the Ratite group had some ability to glide but had not reached an ability to sustain flight when they branched off from other modern birds.  This is based upon analysis of the skull structure and the lack of fusion between the jaw and skull. Flying birds’ jaws are tightly fused in order to withstand the stress of flight.

A series of evolutionary changes then began in a common ancestor with the total loss of flight as reflected today in the absence of a keeled sternum and the reduction of wing size relative to body.  The word Ratite is derived from the Latin word Ratitae which infers a flat, raft like shape, and refers to the flat breastbone of these flightless birds.  Simultaneously the early Ratites attained their great size.  Large body size could be used as a means of escaping predation as well as improving metabolic regulation in response to cooler climates which developed during the middle to late Cretaceous period.  In addition large size would grant a broader range of food items. Early Ratites possessed short, massive legs with a wide pelvis.  Heavily muscled hindquarters would not sustain high speed running.  This probably reflects their roles as forest dwellers as most of Southern Super Continent of Gondwanaland on which they were evolving was covered with various forests.

The early Ratites were able to travel overland and spread out to reach their present day ranges 80-100 million years ago, just prior to the break up of the super land mass into the separate continents of South America, Africa, India, Antarctica and Australia and New Zealand.  They then began to evolve into the divergent birds that they are now.

Today’s living Ratites are the Emu from Australia , The Ostrich from South Africa , the Rhea and Tinamou from South America , the Cassowary from Australia and the Kiwi from New Zealand .  Among those ratites that have become extinct are the Dodo Bird of Madagascar; The Elephant Bird of Africa (a 1100 pound, 10 foot tall bird whose egg held 2 gallons of liquid); and the Moa of New Zealand.

A second major evolutionary change seems to have begun independently among some of the now geographically divergent birds. The Emu, Ostrich and Rhea became more adapted to running.  This is seen in the narrowing of the pelvis, the loss of the fourth small toe and the legs becoming longer and slimmer allowing greater speed through the few open areas in the grasslands of South America the deserts of Africa and the open tundra of the still merged Antarctica/Australia land mass.

At some time 43 – 45 million years ago prior to the separation of those final two continents the Emu migrated across Eastern Antarctica to Australia .  The formation then of the continental ice shelf over Antarctica later caused Australia to become more arid.  It would have been at this time that the Emus perfected their grassland adaptations.

In future articles I'll continue with the evolution of the bird to modern day. (Not published yet - stay posted)