An Intermediate Incubation Period and Primitive Brooding in a Theropod Dinosaur

Area of Science:

• Paleontology
• Developmental Biology
• Evolutionary Biology

Background:

• Non-avian dinosaurs like oviraptorosaurs and troodontids share reproductive traits with birds, but incubation strategies remain debated.
• Understanding dinosaur incubation provides insights into their life history and the evolution of avian reproduction.

Purpose of the Study:

• To estimate the incubation period of the troodontid dinosaur, Troodon formosus.
• To compare estimated incubation periods with modern avian and reptilian analogues.

Main Methods:

• Utilized synchrotron scanning and histologic thin sections to examine a near-term embryonic Troodon formosus tooth.
• Counted daily (von Ebner) growth lines in the tooth to determine embryonic age.
• Applied crocodilian dental development timing to extrapolate total incubation period from tooth age.

Main Results:

• A Troodon formosus embryonic tooth preserved 31 intact daily growth lines.
• Estimated tooth age was 39 days, suggesting a total incubation period of 74 days.
• This 74-day incubation period falls between predicted avian and reptilian values for the estimated egg mass.

Conclusions:

• Accelerated incubation in Troodon formosus supports brooding behavior and reliance on elevated temperatures.
• Reproductive strategies of oviraptorosaurs and troodontids suggest adaptations for higher incubation temperatures.
• Buried Troodon clutches may have necessitated longer incubation compared to exposed avian eggs, despite evidence for brooding.