lineages of archaic birds had evolved,
yet only a few members of a single
lineage, the Neornithes, survived. The
avian dinosaurs that did persist across
the K-T extinction event survived
into a world where many niches
previously occupied by the dominant
dinosaurs were left open for them,
and they evolved, radiated, and diver-
sified; giving rise to the spectacular
diversity of birds we see today, with
over 10,000 species.
But against the background of mass
extinction that also wiped out count-
less numbers of their close, feather-
covered relatives, why is it that
neornithine birds survived? Well, the
answer remains something of an
enigma. Prior to the discovery of
feather impression in a diverse range
of dinosaurs, it was believed that
feathers held the answer, by provid-
ing both insulation and flight.
However, given these features are by
no means unique to birds, this
hypothesis is no longer supported. It
may be that neornithine birds, with
their aerodynamically-contoured
feathers, and advanced flight
muscles, were particularly proficient
flyers, and that they were better able
to escape from poor-quality environ-
ments and efficiently search for safe
and productive habitats following the
turmoil generated by the meteorite.
Still, a key flaw in the ‘flight’
hypothesis is that pterosaurs (which
were not in fact dinosaurs, but a
related lineage) had fully mastered
flight well before birds did, yet they
too were victims of the K-T extinc-
tion. Likewise, other archaic birds
such the enantiornithines were both
highly successful and capable of
flight, yet were snuffed out along
with the dinosaurs in the wake of the
asteroid’s impact. ongoing dispute as to whether
dinosaurs were in fact ectothermic or
endothermic. The latest consensus is
that they were in between, or
‘mesothermic’: that is, they used their
metabolism to generate body heat,
but did not regulate their body
temperatures at a constant, high
temperature. So, it may have been
that the evolution of full endothermy
gave birds an advantage, however
this hypothesis must again be
balanced against the fact that many
archaic birds also perished in the
aftermath of the meteorite.
Another hypothesis (linked to the
ability of feathers to provide insula-
tion) is that birds had an edge over
non-avian dinosaurs in being
endothermic; able to generate
metabolic body heat to maintain a
constant temperature independent of
the vagaries of the environment, and
therefore capable of activity across a
range of conditions. This contrasts
with ectothermy, the thermoregula-
tory strategy of all other extant
reptiles today, in which the regulation
of body temperature is limited to
behavioural mechanisms, and body
temperature must conform largely to
that of the environment. But there is A key feature that distinguishes
modern birds (Neornithes) from other
birds as well as dinosaurs is the
presence of teeth, or more correctly,
the lack thereof. Not only are teeth
heavy structures, reducing aerody-
namic efficiency due to the extra
weight, but a keratinized, lightweight
beak is also highly adept at consum-
ing seeds, whereas teeth are more
suited for consuming flesh or
vegetation. Herein lies a clue to why
neornithines survived – it may be
related to diet. After analysing
thousands of dinosaur teeth, Larson
and his colleagues concluded that,
preceding the K-T impact, dinosaurs