Minute theropod eggs and embryo from the Lower Cretaceous of Thailand and the dinosaur-bird transition

Naturwissenschaften. 2005 Oct;92(10):477-82. doi: 10.1007/s00114-005-0022-9. Epub 2005 Oct 28.


We report on very small fossil eggs from the Lower Cretaceous of Thailand, one of them containing a theropod embryo, which display a remarkable mosaic of characters. While the surficial ornamentation is typical of non-avian saurischian dinosaurs, the three-layered prismatic structure of the eggshell is currently known only in extant and fossil eggs associated with birds. These eggs, about the size of a goldfinch's, mirror at the reproductive level the retention of small body size that was paramount in the transition from non-avian theropods to birds. The egg-layer may have been a small feathered theropod similar to those recently found in China.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Birds / anatomy & histology*
  • Birds / embryology
  • China
  • Dinosaurs / anatomy & histology*
  • Dinosaurs / embryology
  • Embryo, Nonmammalian
  • Female
  • Fossils*
  • Microscopy, Electron, Scanning
  • Ovum / ultrastructure
  • Paleontology*
  • Thailand