Dromaeosaurids (aug 27, 143000000 BC – aug 26, 66000000 BC)

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Since the 1960s, the dromaeosaurids and troodontids have often been classified together in a group or clade named the Deinonychosauria, initially based primarily on the presence of a retractable second toe with sickle claw (now also known to be present in some primitive birds). The name Deinonychosauria was coined by Ned Colbert and Dale Russell in 1969, and defined as a clade (all theropods closer to dromaeosaurids than to birds) by Jaques Gauthier in 1986. Through the early 2000s, consensus among paleontologists was that dromaeosaurids were most closely related to the troodontids, and together with the troodontids, with deinonychosaurians in turn the sister taxon to avialans, and therefore the closest relatives of avialan birds.[72] In 2012, Turner et al. conducted a phylogenetic analysis (using a dataset of 474 characters scored for 111 taxa) which found Deinonychosauria to be monophyletic.[73] However, several more recent studies have cast doubt on the hypothesis that dromaeosaurids and troodontids were more closely related to each other than either was to birds. A more robust 2013 study by Godefroit et al. (using a dataset of 1,500 characters scored for 358 taxa) found that troodontids were possibly more closely related to birds than to dromaeosaurids; forcing troodontids to remain in a monophyletic Deinonychosauria required four extra steps in the analysis, making this result less likely but not implausible.[74][75] Because Deinonychosauria was originally defined as all animals closer to dromaeosaurids than to birds without specific reference to troodontids, Deinonychosauria is a synonym of Dromaeosauridae if Troodontidae is closer to birds.

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