and had feathers on just certain body
regions (especially the forearms, hind
legs and tail), and whilst some
species had just one type of feather,
others featured a number of different
types. By the Early Cretaceous (124-
128 million years ago) for example,
Sinornithosaurus and Microraptor
gui had both plumulaceous as well as
pennaceous feathers.
The most likely scenario for the
evolution of feathered
flight is that as lineages
became increasingly
arboreal, this would
have favoured more
aerodynamic feathers
that assisted in leaping
amongst branches. The
development and modi-
fication of pennaceous
feathers on the limbs and tail would
have enhanced arboreal locomotion
by permitting first parachuting, then
gliding, and finally powered flight.
Birds are reptiles too!
Not only are birds dinosaurs, but
they, like dinosaurs, are also reptiles.
Surprisingly, based on multiple lines
of evidence – DNA, fossils and
various embryonic and morphological
features – birds are classified within
the group Archosauria, which
includes crocodiles! This means that
crocodiles are more closely related to
birds than they are to other reptiles,
like snakes and lizards. Molecular
and fossil data date the divergence of
the lepidosaurs (including snakes and
lizards) from archosaurs at about 270-
275 million years ago, whereas
crocodiles and dinosaurs last shared a
common ancestor about 230- 220
million years ago. Despite superficial
appearances, crocodiles share more
features with birds than lizards, in
particular in relation to their bone and
muscular structures. Another
common feature is a single penis (for
those birds that have not lost the
penis as an intromittent organ),
whereas lizards and snakes have two
hemipenes.More broadly, there are multiple
features that birds share in common
with reptiles. These include eggs with
a calcareous shell, the protein beta-
keratin (in feathers and scales), a
‘diapsid’ skull (which differs to that
of mammals), scales (retained on
birds’ legs), and the production of
uric acid in order to eliminate
nitrogenous waste. It is well
established among zoologists that
birds are completely nested within the
reptilian clade; over a century ago
T. H. Huxley, a renowned zoologist
and close colleague of none other
than Charles Darwin, was moved to
declare birds to be ‘glorified reptiles’.This points to the inaccuracy of the
field of ‘herpepology’: our organisms
of interest, the herpetofauna, are thusa group inconsistent with evolution-
ary relationships. Combining
amphibians and reptiles, these two
disparate clades, which diverged
approximately 360 million years ago,
were grouped together as those
‘creeping’ animals (the name being
derived from the Greek herpeton or
herpein; to creep). This makes
herpetofauna a polyphyletic clade,
while the traditional view of Reptilia,
excluding birds, is consequently a
paraphyletic clade (i.e. a grouping
with a common
ancestor but that does
not include all
descendents).These evolutionary
relationships reveal
another inaccuracy in
the very name of the
group we know as dinosaurs, for the
name Dinosauria derives from the
Greek words deinos, meaning
terrible, and sauros, meaning lizard.
Dinosaurs, especially of the avian
kind, are hardly ‘terrible’, and are
strictly not lizards either. These flaws
are unsurprising given that the term
dinosaur was coined by Richard
Owen, a religious man opposed to his
contemporary Charles Darwin’s
theory of evolution.The successful
survivors.Birds were not entirely immune to the
cataclysmic consequences unleashed
when the ancient asteroid crashed
into Mexico. By the end of the
Cretaceous, a number of distinctLeft: specimens
preserved in amber (like
this grasshopper) exhibit
extremely fine structural
detail. Image by Roy
Palmer.
Above right: pterosaurs
had mastered flight well
before birds.This species
of Zhenyuanopterus
dinosaur lived during
the Cretaceous period in
China .Image by Linda
Bucklin.‘Based on DNA, fossils and otherevidence, CROCODILES are moreCLOSELY RELATED TO BIRDSthan snakes and lizards!’2 x qtr page ads