[1] The type specimen of Citipes has a convoluted taxonomic history, and has been previously assigned to the genera Ornithomimus,[2] Macrophalangia,[3] Elmisaurus,[4] Chirostenotes,[5] and Leptorhynchos[6] before being given its own genus in 2020.

[1] The material which would eventually be named Citipes was discovered in 1926 during one of the University of Toronto's expeditions to the Sand Creek area of the Red Deer River.

Longrich and colleagues distinguished L. elegans from the type species, L. gaddisi, by the presence of a strongly upturned beak tip and a chin that is square-shaped in lateral view.

[6] In 2020, Gregory Funston conducted a review of all caenagnathid material known from the Dinosaur Park Formation in order to determine their actual diversity in that depositional environment.

[1] Most of the caenagnathid material from the Dinosaur Park Formation was assigned to one of these three genera based on size and diagnoses were amended from the apomorphies of those specimens.

In his review of Dinosaur Park caenagnathids, Gregory Funston concluded that it had a substantially smaller adult size than the contemporaneous genera Caenagnathus and Chirostenotes.

[12] In his comprehensive re-description of the caenagnathids from the Dinosaur Park Formation, Gregory Funston provides amended diagnoses for all three named genera in his analysis.

[7] In their re-assignment, Longrich and colleagues distinguished L. elegans from the genera to which it was assigned previously (Elmisaurus and Chirostenotes) due to its small size, which they believed was not reflective of its ontogenetic age because of the fusion of the tarsal elements.

[6] During his comprehensive analysis in 2020, Gregory Funston referred two partial hip specimens to Citipes, however this assignment is somewhat uncertain because of the lack of overlapping material with the type series.

[1] The first systematic phylogenetic analysis to include ROM 781 was the one conducted by Nicholas Longrich, Ken Barnes, Scott Clark, and Larry Millar in their paper describing the genus Leptorhynchos in 2013.

The authors remark that they referred ROM 781 to Leptorhynchos because of the similar size of the two species, but noted that they may belong to separate genera, pending further research.

However, the authors note that the shape of the beak in modern birds is an important diagnostic trait, as well as in some dinosaurs like Triceratops and Edmontosaurus, so they argue that it is not unreasonable to assume that this may be sufficient in naming new genera or species.

(BMNH 2033 from Hell Creek) In his review of caenagnathids from the Dinosaur Park Formation, Funston conducted a phylogenetic analysis of oviraptorosauria.

Namely, that elmisaurinae was not a natural monophyletic clade; Funston found several traditionally "elmisaurine" genera, such as Chirostenotes and Apatoraptor to be more widely distributed throughout the trees in his analysis, rather than grouping together as a single radiation of Laramidian caenagnathids.

The controversial Asian genera Nomingia and Anomalipes were also recovered as caenagnathids in his analysis, suggesting that the group persisted in Asia even after the diversification of oviraptoridae.

[1] Microvenator Gigantoraptor Anomalipes Chirostenotes Hagryphus Nomingia Citipes Elmisaurus Caenagnathasia Epichirostenotes Anzu Caenagnathus In a study of the pelvic morphology of all caenagnathid material from the Dinosaur Park Formation in 2019, Matthew Rhodes and colleagues categorize every specimen into one of three categories.

The morph which they believe belongs to a new taxon,[14] later named Citipes,[1] is described as the "small, robust morphotype" and is distinct from all other caenagnathid pelves in the formation.

[14] Rhodes and colleagues suggested that these morphological distinctions in the hip bones of caenagnathids were unlikely to be the result of ontogeny because the level of coossification between the ilia and sacra is similar in very differently-sized specimens.

Gregory Funston and colleagues conducted a histological study of caenagnathid dentaries (the most common remains found in Dinosaur Park) and noticed that the mandibular symphysis becomes fully ossified relatively early in caeagnathid growth, and it is thus a poor indicator of the precise age of a specimen.

The fracture extends along the surface between the pubic and ischiatic peduncles, and has resulted in a significant swelling of the ilium, which can be clearly seen from above and slightly obscures the brevis fossa.

Taphonomic breakage of the fossil has also revealed trabecular bone in the specimen, which suggests that the animal survived for at least a short time after it received the injury that caused this fracture.

Caenagnathid remains have not been recovered as often as those of other coelurosaurs, but this is partially accounted for by their relatively small size and lack of teeth, which may present a sampling bias.

[1] While caenagnathid remains are relatively uncommon, they are widely dispersed across Dinosaur Provincial Park, with no clear pattern of which genera are found at specific localities.

Citipes is believed to have been more adapted for cursoriality due to the coossification of its metatarsals and expanded attachment sites for leg muscles along the iliac crest.

[1] In 2023, François Therrien and colleagues described TMP 2009.12.14 — an exceptionally preserved juvenile specimen of Gorgosaurus, which contained remains from at least two Citipes individuals.

The legs of the Citipes individuals were flexed and contorted into a very compact shape, which suggests that they were inside the stomach of the Gorgosaurus, rather than being preserved alongside it or washed together post-mortem.

Histology of the Citipes bones showed a complete lack of growth marks, leading Therrien and colleagues to suggest that these individuals were within their first year of life when they were eaten by the Gorgosaurus.

The upper portion, which was deposited in overbank and floodplain environments, consists primarily of massive to laminated, organic-rich mudstones with abundant root traces, and thin beds of bentonite.

[22] These geological features are interpreted as a low-relief setting of rivers and floodplains that became more swampy and influenced by marine conditions over time as the Western Interior Seaway transgressed westward.

The freshwater systems of the region would have also supported a great variety of fish species including carpet sharks, stingrays, gar, sturgeons, and paddlefish.