Geoscience Reference
In-Depth Information
Indeed, of the nest categories, most of these are in trees, although a few are on or in
the ground, such as scrape, platform, burrow, and mound nests.
Basedonwhatweknowabouttheevolutionofbirdsfromdinosaurs,birdnests
probably started on the ground, but with underground as another possibility. The
earliest known dinosaur nests, made by the Early Jurassic sauropodomorph
Mas-
sospondylus
of South Africa, were definitely on ground surfaces. At the other end
of the Mesozoic Era, Late Cretaceous
Maiasaura
,
Troodon
, and titanosaur nests
were bowl-like depressions surrounded by raised rims. A burrow entombing the
small Cretaceous ornithopod
Oryctodromeus
and two of its offspring may or may
not have been a nest site, although it was likely used as a den for raising its young.
Of these dinosaurs,
Troodon
was the most closely related to birds, with at least one
species of feathered troodontid known. Moreover, based on dinosaur egg porosit-
ies,nearlyallwerelikelypartiallyburied,whetherinsedimentorvegetation.Sofor
now, paleontologists assume that nearly all dinosaurs nested on or in the ground.
Yet at some point in the Mesozoic Era—probably in the Early Creta-
ceous—nests began going up and into trees. This behavioral and evolutionary
innovation likely happened in many places with multiple lineages of theropods.
However,theproliferationofnestingmusthavebeenhostedinforestedecosystems,
which provided plenty of opportunities for small theropods to go up and into trees,
using these as safe havens from predators looking for eggs, baby theropods, or
theropod parents. Also, just to show the plasticity of such behavior, some modern
birds that we may normally think of as ground nesters—such as wild turkeys
(
Meleagris gallopavo
)—may use trees on an
ad hoc
basis. In one instance, egg
predation from feral hogs on a Georgia barrier island was so pervasive that wild
turkeys began nesting in the trees there. In other words, trying circumstances can
sometimes prompt birds to resort to behaviors that might have been deeply buried
in their evolutionary histories.
As one might imagine, nests consisting of collections of sticks, leaves, feath-
ers, and mud—however artfully or systematically arranged—had poor fossilization
