Sinosauropteryx
"Sinosauropteryx" was a small theropod with an unusually long tail and short arms. The longest known specimen reaches up to in length, with an estimated weight of It was a close relative of the similar but older genus "Compsognathus", both genera belonging to the family Compsognathidae. Only one species of "Sinosauropteryx" has been named: "S. prima", meaning "first" in reference to its status as the first feathered non-avialian dinosaur species discovered. Three specimens have been described. The third specimen previously assigned to this genus represents either a second, as-yet unnamed species or a distinct, related genus.
Spinosaurus
François Therrien and Donald Henderson, in a 2007 paper using scaling based on skull length, challenged previous estimates of the size of "Spinosaurus", finding the length too great and the weight too small. Based on estimated skull lengths of , their estimates include a body length of and a body mass of . The lower estimates for "Spinosaurus" would imply that the animal was shorter and lighter than "Carcharodontosaurus" and "Giganotosaurus". The Therrien and Henderson study has been criticized for the choice of theropods used for comparison (e.g., most of the theropods used to set the initial equations were tyrannosaurids and carnosaurs, which have a different build than spinosaurids), and for the assumption that the "Spinosaurus" skull could be as little as in length. Improvement of the precision of size estimates for "Spinosaurus" requires the discovery of more complete remains as available for some other dinosaurs, especially the limb bones of "Spinosaurus" which are "hitherto unknown".