Secondarily flightless birds or Cretaceous non-avian theropods?

Area of Science:

• Paleontology and Evolutionary Biology
• Reproductive Strategies in Dinosaurs and Birds

Background:

• Recent studies indicate paternal egg care in Cretaceous non-avian theropods (troodontids, oviraptorids), similar to extant Paleognathic birds.
• These theropods exhibited large clutches with large eggs, contrasting with biparental care and smaller clutches of most extant birds.
• Varricchio et al. proposed paternal care preceded bird origins, classifying these dinosaurs as pre-avian.

Purpose of the Study:

• To re-evaluate the evolutionary context of egg care in troodontids and oviraptorids.
• To investigate the relationship between secondary flightlessness and reproductive behaviors in avian evolution.
• To propose a new theory on the evolution of avian reproductive strategies based on relict behaviors.

Main Methods:

• Review and synthesis of paleontological evidence for troodontid and oviraptorid morphology and behavior.
• Comparative analysis of reproductive strategies between non-avian theropods, Paleognathic birds, and other extant birds.
• Examination of conserved vertebrate brain evolution and relict avian reproductive behaviors.

Main Results:

• Abundant paleontological evidence suggests troodontids and oviraptorids were secondarily flightless birds, not pre-avian.
• Secondary flightlessness in these dinosaurs, like ratites, may favor paternal care of large clutches.
• Independent findings indicate a likely evolutionary sequence of maternal, followed by biparental, egg care in early bird ancestors.

Conclusions:

• Troodontids and oviraptorids were likely secondarily flightless birds, strengthening the link between flightlessness and paternal care.
• Paternal egg care was likely not primitive in avian evolution.
• Relict avian reproductive behaviors provide crucial insights into the evolution of maternal and biparental care in early birds.