Dinosaurs came from eggs.
Dinosaur egg . When the first scientifically documented remains of dinosaurs were being described in England during the 1820s , it was presumed that dinosaurs had laid eggs because they were reptiles . In 1859 , the first scientifically documented dinosaur egg fossils were discovered in France by Jean-Jacques Poech , although they were mistaken for giant bird eggs . The first scientifically recognized dinosaur egg fossils were discovered in 1923 by an American Museum of Natural History crew in Mongolia . The oldest known dinosaur eggs and embryos are from Massospondylus , which lived during the Early Jurassic , about 190 million years ago .