Thursday, October 30, 2014


In the dino to bird theory, there is a good deal of claimed exaptation.
Abducted wrists, feathers and enlarged brains are claimed to have evolved before they were used for flight. These are simply stories. These stories are made up in response to evidence that contradicts the dino to bird theory.
Exaptation and the related term co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another.

Carpal asymmetry [abducted wrists] would have permitted avian-like folding of the forelimb in order to protect the plumage, an early advantage of the flexible, asymmetric wrist inherited by birds.
However, it is likely that mobility of the wrist was initially associated with other functions, such as predation (Padian 2001).
It had originally been proposed that this flexibility could be attributed to hunting, but the same changes are seen in maniraptorans that were herbivores and omnivores so it is unlikely that hunting provides the answer. Instead, the authors of the new study propose, the ability to fold the hands backwards would have protected the feathers of the arms. This would have prevented the feathers from getting damaged or from being in the way as the dinosaurs moved about, although the authors recognize that this hypothesis requires further evidence.
Perhaps more significant, however, is how this wing-folding mechanism may have allowed birds to take to the air. Birds do flex their wrists while flapping their wings to fly, and so it appears that the wrist flexibility that first evolved in dinosaurs was later co-opted for flight in birds. This is what is known as "exaptation," or when a previous adaptation takes on a new function. Indeed, as more is discovered about the evolution of birds, the more traits paleontologists find that evolved for one function but have been co-opted for another at a later point (feathers themselves being the most prominent
example). There is relatively little separating birds from their feathered dinosaur ancestors.

As Darwin elaborated in the last edition of The Origin of Species,[14] many complex traits evolved from earlier traits that had served different functions. By trapping air, primitive wings would have enabled birds to efficiently regulate their temperature, in part, by lifting up their feathers when too warm. Individual animals with more of this functionality would more successfully survive and reproduce, resulting in the proliferation and intensification of the trait.
Eventually, feathers became sufficiently large to enable some individuals to glide. These individuals would in turn more successfully survive and reproduce, resulting in the spread of this trait because it served a second and still more beneficial function: that of locomotion. Hence, the evolution of bird wings can be explained by a shifting in function from the regulation of temperature to flight.
Exaptation is a term used in evolutionary biology to describe a trait that has been co-opted for a use other than the one for which natural selection has built it.
It is a relatively new term, proposed by Stephen Jay Gould and Elisabeth Vrba in 1982 to make the point that a trait’s current use does not necessarily explain its historical origin. They proposed exaptation as a counterpart to the concept of adaptation.
For example, the earliest feathers belonged to dinosaurs not capable of flight. So, they must have first evolved for something else. Researchers have speculated early feathers may have been used for attracting mates or keeping warm. But later on, feathers became essential for modern birds’ flight.
This further supports the hypothesis that "flight feathers" that first evolved in dinosaurs for non-aerodynamic functions were later adapted to form lifting surfaces.[15]

Several ancient dinosaurs evolved the brainpower needed for flight long before they could take to the skies, scientists say.
Bird brains tend to be more enlarged compared to their body size than reptiles, vital for providing the vision and coordination needed for flight.
Scientists using high-resolution CT scans have now found that these "hyper-inflated" brains were present in many ancient dinosaurs, and had the neurological hardwiring needed to take to the skies. This included several bird-like oviraptorosaurs and the troodontids Zanabazar junior, which had larger brains relative to body size than that of Archaeopteryx.

Placed in context of avian evolution, the grasping foot of Deinonychus and other terrestrial predatory paravians is hypothesized to have been an exaptation for the grasping foot of arboreal perching birds. Here we also describe “stability flapping”, a novel behaviour executed for positioning and stability during the initial stages of prey immobilisation, which may have been pivotal to the evolution of the flapping stroke. These findings overhaul our perception of predatory dinosaurs and highlight the role of exaptation in the evolution of novel structures and behaviours.

See page 261 of "Riddle of the Feathered Dragons"

Did preadaptations for flight precede the origin of birds (Aves)? The origin of flight in birds is one of the great evolutionary transitions and has received considerable attention in recent years (Padian and Chiappe 1998; Clarke and Middleton 2008; Dececchi and Larrson 2009; Benson and Choiniere 2013; Dececchi and Larrson 2013). The evolution of birds is often considered coincident with the origins of flight, but many traits associated with flight evolved before the origin of Aves (Padian and Chiappe 1998).

This suggests that the initial conquest of the air was achieved using lower metabolic rates than are characteristic of today's avian flyers. It appears that the closest non-avialan relatives of birds were physiologically preadapted for powered flight and only anatomical adaptations were involved when birds first ventured into the air. 


  1. I get it. The bird brain enlarged for purposes unrelated to flight, and was later co-opted for flight. But I'm not interested in bird brains. I have a human brain and would like to know whether it was exapted from a prior existing purpose (an adaptation for a specific function), or was it exapted from some cause that had no specific function, such as sheer complexity or sheer rapid fetal growth rates.

  2. Read the material again. I am not suggesting that bird brain enlarged for purposes unrelated to flight.