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hole nests, with ground nests made on the ground surface and hole nests below the
surface. From there, each type can vary. For example, ground nests can range from
simple hastily scraped depressions made by some lizards, to large mounds of ve-
getation amassed by alligators. Hole nests are also diverse, ranging from the blunt,
shallow holes of freshwater turtles and tortoises, to the more elaborate excavations
of sea turtles and crocodiles.
On the other hand, bird nests are as crazily diverse as birds themselves, almost
defyingfacilecategorization.Birdnestsrangefromsimplescrapesintheground,to
better defined excavations, to tunnels in the ground or in vertical bluffs, to elabor-
ately woven and architecturally complex structures made of a wide variety of nat-
ural and man-made materials. Some birds resemble reptiles in their nesting beha-
vior by constructing nests on the ground or as underground burrows, but flight has
also made it easier for birds to build nests well above ground surfaces, such as in
trees, cliff faces, or buildings. Furthermore, by “in trees,” this is sometimes literal
for woodpeckers that actually bore into tree trunks with their beaks, hollowing out
areas to lay their eggs and raise hatchlings inside trees.
Howdiddinosaursfitin“reptilevs.bird”modelsfornestingbehavior?Itturns
out they were somewhere in between, although definitely leaning toward behaviors
we observe today in some reptiles and ground-nesting birds. For one thing, every
dinosaur nest structure recognized thus far is a ground nest. Hole nests like those
of sea turtles or crocodilians, or more fancy structures such as those of some tree-
dwelling birds, aren't yet known for dinosaurs. Of course, this current lack of evid-
ence does not necessarily mean that no dinosaurs made either underground or ar-
boreal nests. For instance, one good candidate for underground nesting would have
been the small Cretaceous ornithopod
Oryctodromeus cubicularis
, which made
dens for raising its young (discussed more in the next chapter). For arboreal nests,
a few small feathered tree-climbing, gliding, and flying non-avian dinosaurs are
known from Early Cretaceous rocks of China. So these dinosaurs feasibly could
