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Dinosaur reproduction and egg clutch masses

From: Ben Creisler

New in PLoS ONE:

Jan Werner & Eva Maria Griebeler (2013)
New Insights into Non-Avian Dinosaur Reproduction and Their
Evolutionary and Ecological Implications: Linking Fossil Evidence to
Allometries of Extant Close Relatives.
PLoS ONE 8(8): e72862.

It has been hypothesized that a high reproductive output contributes
to the unique gigantism in large dinosaur taxa. In order to infer more
information on dinosaur reproduction, we established allometries
between body mass and different reproductive traits (egg mass, clutch
mass, annual clutch mass) for extant phylogenetic brackets (birds,
crocodiles and tortoises) of extinct non-avian dinosaurs. Allometries
were applied to nine non-avian dinosaur taxa (theropods, hadrosaurs,
and sauropodomorphs) for which fossil estimates on relevant traits are
currently available. We found that the reproductive traits of most
dinosaurs conformed to similar-sized or scaled-up extant reptiles or
birds. The reproductive traits of theropods, which are considered more
bird-like, were indeed consistent with birds, while the traits of
sauropodomorphs conformed better to reptiles. Reproductive traits of
hadrosaurs corresponded to both reptiles and birds. Excluding
Massospondylus carinatus, all dinosaurs studied had an intermediary
egg to body mass relationship to reptiles and birds. In contrast,
dinosaur clutch masses fitted with either the masses predicted from
allometries of birds (theropods) or to the masses of reptiles (all
other taxa). Theropods studied had probably one clutch per year. For
sauropodomorphs and hadrosaurs, more than one clutch per year was
predicted. Contrary to current hypotheses, large dinosaurs did not
have exceptionally high annual egg numbers (AEN). Independent of the
extant model, the estimated dinosaur AEN did not exceed 850 eggs
(75,000 kg sauropod) for any of the taxa studied. This estimated
maximum is probably an overestimation due to unrealistic assumptions.
According to most AEN estimations, the dinosaurs studied laid less
than 200 eggs per year. Only some AEN estimates obtained for medium to
large sized sauropods were higher (200-400 eggs). Our results provide
new (testable) hypotheses, especially for reproductive traits that are
insufficiently documented or lacking from the fossil record. This
contributes to the understanding of their evolution.