iHerp_Australia_-_March-April_2018

may have knocked Archaeopteryx off

the perch --so to speak - as being the

earliest bird, a title for which there

are now many contenders. The dis-

covery of Archaeornithura in 2015

dates ‘true’ birds as having arisen a

little over 130 million years ago.

But the evolution of filamentous

‘protofeathers’ preceded powered,

feathered flight by at least 100

million years. Based on

fossil evidence, the first

feathers, in the form of

simple, fibrous, single

filaments, had evolved

in non-avian theropods

by 190 million years

ago. These were by no

means suited to flight,

and are most likely to have been used

for thermoregulation and display,

although a variety of other possible

functions include crypsis, tactile-

sensation, physical defence, water-

repellency, communication, and

species or mate recognition or

selection. Feathers function as an

incredibly good insulating

body cover, which is very

important in aiding modern

birds to maintain a high body

temperature, driven by the

high metabolic rate necessary

for powered flight. They can

help regulate body tempera-

ture and prevent overheating

by being raised and lowered

to alter the amount of insula-

tion, and can shed excess

heat through the blood that

flows through their vanes.

Sinosauropteryx prima is

known from a fossil dated at

about 130 million years ago,

and was a small, lightly-built

coelurosaur with relatively

long legs and tail. It was

covered with tufts of thick

filaments that projected a few

millimetres above its skin, suggesting

an insulating and possibly thermo-

regulatory function. This contrasts

with another coelurosaurian therapod

that also existed approximately 130

million years ago. Beipiaosaurus only

measured 2m in total body length, but

boasted integumentary filaments up

to 150mm long. Their structure

(single and broad – up to 2mm wide)

and localised distribution on the head,

neck and tail means they would

function poorly as insulation, but

would be well suited for display.

Analysis of the melanosomes

(pigment-containing cells) of fossil

dinosaur feathers reveal that feathers

were not uniform in colour, but rather

came in a great range of hues. The

fact that Late Jurassic and Early

Cretaceous dinosaurs with pinnate

feathers exhibited sexual dimorphism

in plumage and colour patterning

likewise presents a strong case that

mate attraction and display functions

were a key role for these more

advanced feather types.

The limitation of fossils of carbon-

ized impressions is

that although they

indicate the presence

of feathers, they are

often poorly

resolved; in contrast,

specimens preserved

in amber (despite

being extremely rare)

exhibit extremely fine structural

detail. Amber-preserved feathers

from the Late Cretaceous reveal the

evolution of a great diversity of

feather types, which were likely to

have served a range of functions in

avian and non-avian dinosaurs. Many

feathered dinosaurs retained scales,

Above left: Archaeopteryx

has for a long time been

considered the ‘first bird’.

Image by Catmando.

Below left: this depiction of a

Velociraptor is at odds with

the traditional view of

dinosaurs. Image by Linda

Bucklin.

Right: Beipiaosaurus boasted

integumentary filaments up to

150mm long. Image by

Catmando.

‘Late Jurassic and Early Cretaceous

dinosaurs exhibited SEXUAL

DIMORPHISM in PLUMAGE and

COLOUR PATTERNING.’

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