They are almost exclusively known from Late Jurassic Chinese deposits, although Ostromia was discovered in Germany and Yixianosaurus (a putative member of the group only known from forelimbs) is believed to hail from the early Cretaceous.

[9][8] Foth and Rauhut (2017) established several diagnostic features present in anchiornithids:[1] In 2015 Chatterjee created Tetrapterygidae in the second edition of his book The Rise of Birds: 225 Million Years of Evolution, where he included Xiaotingia, Aurornis, Anchiornis, and even Microraptor; together they were proposed to be the sister group of the Avialae.

[1] They provided their own definition of Anchiornithidae as "all maniraptoran theropods that are more closely related to Anchiornis huxleyi than to Passer domesticus, Archaeopteryx lithographica, Dromaeosaurus albertensis, Troodon formosus, or Oviraptor philoceratops.

This analysis placed anchiornithids (or as the study calls them, members of "Anchiorninae") either as troodontids or unresolved paravians, depending on whether parsimony or bootstrap analyses are used.

[20] In 2019 with the description of the Late Jurassic genus Hesperornithoides, Hartman et al., using every named Mesozoic maniraptoromorph (with the addition of 28 unnamed specimens), which they scored 700 characters and 501 operational taxonomic units, found that most of the anchiornithids are members of Archaeopterygidae, with only Xiaotingia and Yixianosaurus being classified as a troodontid and a dromaeosaurid respectively, Pedopenna found in many possible positions within the Paraves phylogeny, and Ostromia described too late to include in the analysis.

[6] Below is their phylogeny: Serikornis Caihong Anchiornis Archaeopteryx Eosinopteryx Aurornis The cladogram below shows the results of the phylogenetic analysis by Cau (2020).

[22] A good majority of the known anchiornithid fossils have been recovered from the Tiaojishan Formation in Liaoning, China dating back to 160 million years.

[23][24] The climate during this period of time would have been subtropical to temperate, warm and humid based on the plant life present in the Tiaojishan Formation.

Fujianvenator prodigiosus was discovered in the 148 to 150 million-year-old Zhenghe Biota of southeastern China, which was dominated by aquatic and semi-aquatic fossils such as fish and turtles indicative of a lacustrine swamp environment.