Two major types
of dinosaur eggs are recognized: spheroidal and
elongated. These types can be further sub-divided
based on length/diameter ratios, the thickness
of the shell, the type of pores and the surface
of the egg (may be ornamented).
The egg structure consists of a series of basic
vertical units that grow from particular sites
on the surface of the shell.
The organization of these units
determines the classification scheme, being either
spherulitic or prismatic:
1. Spherulitic egg shells show spherical patterns
in the crystalline structure, and they are seen
in sauropods and hadrosaurs.
2. Prismatic egg shells grow into spherical crystals
only in the lower portion of the shell, while
crystals in the upper portion are prisms.
3. Ornithoid eggs (also seen in birds) are generally
laid by theropods. In this type only the very
bottom part of the shell exists as separate or
discrete units (mammilae). The upper and mid-portions
of the shell consist of a mass of biocrystalline
material with a spongy (squamatic) ultrastructure
that comprises a homogeneous layer.
The largest eggs come from sauropods,
in particular the titanosaurs. These eggs are
up to 18cm long and up to 5mm thick, able to contain
5.5 litres of fluid. A metre-long egg would be
several centimeters thick, making respiration
and hatching near impossible. Imagine how thick
an egg several times the size of a human would
be!
How a sauropod from an 18 cm diameter egg could
grow to a 30 metre long animal weighing about
20 tones? There are two possible answers:
1. The animal grows throughout its lifecycle,
perhaps continuing to grow until death. Many reptiles
do a similar thing.
2. The animal undergoes accelerated growth in
5-15 years. Growth patterns from dinosaur bone
such as the 'duck-billed' dinosaur Maiasaura indicate
it reached adult size in 5 years. Elephants take
about 15 years to reach sexual maturity. Maybe
sauropods lied in between.
Other dinosaur eggs are often smaller. The smallest
eggs are perhaps from the prosauropods. Eggs from
South Africa are reported to be only 6.5 cm long
and 5.5 cm wide. The shell is only 0.2/0.3 mm
(0.02 cm!) thick. Theropod eggs are generally
10-15 cm long, and a couple of millimeters thick.
Duckbills (hadrosaurs) also have eggs 10-12 cm
long and 7.9 cm wide
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