Taxonomic conclusions and significance
CMN 8902 and UALVP 53595 possess derived characters or character combinations that are uniquely shared with
Q. henanensis (
Xu et al. 2011), and are distinct from other named ornithomimid taxa in the Belly River Group, when comparable. Previously noted similarities between CMN 8902 and
S. altus appear to be plesiomorphic or homoplastic within Ornithomimidae. On account of the geographic and temporal separation of this material from
Q. henanensis (Campanian of North America, versus probably Maastrichtian of Asia), it is unlikely that either Canadian specimen belongs to that species. Unfortunately, neither CMN 8902 nor UALVP 53595 is complete enough to determine whether all diagnostic characters of
Q. henanensis listed by
Xu et al. (2011) were present. Furthermore, there are no autapomorphic characters in this material that are absent in
Q. henanensis. Therefore, we consider it most reasonable to refer CMN 8902 and UALVP 54595 to
Qiupalong sp., as the first known North American representatives of this genus, although it is also possible that the discovery of additional material will support the naming of a new genus in the
Qiupalong lineage. Observed differences between
Qiupalong sp. and
Q. henanensis are minor but appear to be closer to the probable plesiomorphic condition for North American ornithomimids in
Qiupalong sp.
A similarity has long been noted between theropod assemblages in the Belly River Group of Alberta and various Upper Cretaceous localities in eastern Asia (
Currie 1992), but relatively few taxa are shared at the generic level. A recent census of Canadian dinosaurs recognized only two dinosaur genera in the Belly River Group that are also present in Asia, the oviraptorosaurs
Avimimus and
Elmisaurus (
Brown et al. 2015). More recently,
Funston et al. (2016) considered the Dinosaur Park Formation elmisaurine material as generically distinct from
Elmisaurus. The recognition of
Qiupalong sp. in the Belly River Group thus adds significantly to the record of theropods with Asian affinities at the generic level in this group.
Qiupalong sp. also represents the sixth ornithomimid taxon reported from the Dinosaur Park Formation. Although it may be suspected that not all of these taxa are distinct (e.g.,
Makovicky et al. 2004), the taxonomic diversity of non-macropredaceous theropods such as ornithomimosaurs and oviraptorosaurs in the Late Cretaceous may have been greater than generally appreciated, with at least three genera of Caenagnathidae present in the Dinosaur Park Formation (
Funston et al. 2015), and seven genera of Oviraptoridae present in the Nanxiong Formation of southern China (
Lü et al. 2016).
Phylogenetic and palaeobiogeographic origins of Qiupalong
The age of
Q. henanensis was initially reported as “late Late Cretaceous” (
Xu et al. 2011).
Jiang et al. (2011) identified continuous deposition across the Cretaceous–Paleogene (K/Pg) boundary (66 Ma) at the top of the Qiupa Formation, which was previously thought to not have a conformable contact with the Paleocene Gaoyugou Formation (
Xu et al. 2011). The exposed section of the Belly River Group in Dinosaur Provincial Park was deposited from approximately 76.5 to 74.8 Ma, in the Campanian stage (
Eberth 2005). Ornithomimid material with diagnostic characters of
Qiupalong may, therefore, occur up to approximately 10 million years earlier in North America than in Asia, although it is still not precisely known how much time is represented between the dinosaur-bearing beds of the Qiupa Formation and the K/Pg boundary.
The phylogenetic analysis by
Xu et al. (2011) recovered
Q. henanensis as the sister taxon of (
S. altus +
O. edmontonicus), based on two derived characters of the pubis: a large acute angle between the pubic shaft and boot (character 45: state 1), and the tip of the anterior extension of the pubic boot extending farther anteriorly than the anterior border of the pubic shaft (character 46: state 1). These characters are potentially correlated, in being related to a rotation of the pubic boot with respect to the shaft.
Xu et al. (2011) scored both characters as unknown in
S. altus, but the derived states can be confirmed in referred specimens of this species (AMNH 5339, UCMZ 1980.1). A single character supported the exclusion of
Q. henanensis from the (
S. altus +
O. edmontonicus) clade: the presence in the latter of a pubic boot with a strongly convex ventrally expanded ventral border (character 35: state 0). Based on the distribution of taxa included in the phylogenetic analysis by
Xu et al. (2011),
Q. henanensis could be inferred to have diverged from the ancestor of the (
S. altus +
O. edmontonicus) clade prior to the migration of the latter into North America from Asia. However, ornithomimid specimens from the Kaiparowits and Hell Creek formations in the United States (
DeCourten and Russell 1985; LACM 47520) show plesiomorphic characters in the pubis that are absent in
Q. henanensis and the Canadian ornithomimids, including a distally recurved pubic shaft (
Xu et al. 2011, character 44: state 0), suggesting that some North American ornithomimids diverged more basally than
Qiupalong. Although the degree of convexity and ventral expansion of the ventral border of the pubic boot was cited to exclude
Q. henanensis from the (
S. altus +
O. edmontonicus) clade, the expression of this character in Canadian ornithomimids is highly variable. This character is most highly developed in AMNH 5201 (
Fig. 4F), referred to
O. edmontonicus (
Eberth et al. 2013) or
Dromiceiomimus brevetertius (
Russell 1972) but is much less developed in the potentially conspecific
O. edmontonicus holotype CMN 8632 (
Fig. 4E), which more closely resembles the condition in
Q. henanensis.
Sues and Averianov (2016) recovered
Q. henanensis as the sister taxon of the clade (
A. planinychus +
O. edmontonicus), with
S. altus as the sister taxon of the former three taxa. The relationship between
Q. henanensis and (
A. planinychus +
O. edmontonicus) was supported by the supposed absence of a pronounced flexor fossa on the ventral surface of the proximal end of the pedal unguals (
Sues and Averianov 2016, character 567: state 0), regarded as occurring in
Q. henanensis and
O. edmontonicus (
Sues and Averianov 2016;
Averianov et al. 2017); the condition in
A. planinychus has not been described. However, a pronounced flexor fossa can be observed in at least some pedal unguals of
O. edmontonicus (CMN 8632, ROM 851), as well as in
O. velox (CMN 12242, cast of YPM 542), so this character does not support a close relationship between
Ornithomimus and
Qiupalong. A sister taxon relationship between
Anserimimus and
Ornithomimus has been previously suggested primarily on the basis of manual characters (
Bronowicz 2011), which are not preserved in
Qiupalong. In the analysis by
Sues and Averianov (2016), the “subequal” length of metatarsals II and IV in these taxa (character 559: state 0) is recovered as providing additional support for the (
A. planinychus +
O. edmontonicus) clade excluding
Qiupalong. However, a comparison of published measurements of ornithomimid metatarsals (
Parks 1933;
Sternberg 1933;
Osmólska et al. 1972;
Russell 1972;
Barsbold 1988;
Xu et al. 2011;
Claessens and Loewen 2015) suggests that the variation in this ratio is not split between two discrete character states, and just as much variation can occur between specimens of a single taxon or even between different authors’ measurements of the same specimen. The metatarsal II/IV ratio derived from measurements of
O. edmontonicus (CMN 8632) by
Claessens and Loewen (2015, appendix 1) is indistinguishable from that of
Q. henanensis, as measured by
Xu et al. (2011, table 1).
A close relationship between
Qiupalong and
Ornithomimus may be supported by the presence of an approximately T-shaped proximal end of the second metatarsal in medial or lateral view (
Claessens and Loewen 2015, figs. 8
c–
d;
Xu et al. 2011, figs. 6
d–
e). The proximal end of the second metatarsal has a simple subtriangular expansion that merges gradually with the posterior border of the metatarsal shaft in
Archaeornithomimus asiaticus (
Smith and Galton 1990, fig. 4
b),
Garudimimus brevipes (
Kobayashi and Barsbold 2005, fig. 15
d)
R. evadens (
McFeeters et al. 2016, fig. 10
d),
S. dongi (
Kobayashi and Lü 2003, fig. 23
b), and
S. altus (
Osborn 1917, fig. 11). In
Q. henanensis (
Xu et al. 2011, fig. 6
d),
Ornithomimus sp. (TMP 1995.110.1), and
O. velox (
Claessens and Loewen 2015, fig. 8
c) the posterior expansion has a more pronounced ventral border distinct from the shaft, and the transition from the proximal expansion to the vertical posterior border of the shaft is abrupt. However, this condition of the second metatarsal is also present in a basal ornithomimosaur foot from the Lower Cretaceous of China (
Shapiro et al. 2003, fig. 1
f). Another character shared by
Q. henanensis and some specimens of
Ornithomimus is the laterally divergent distal end of metatarsal IV, which is separated by a gap from the distal end of metatarsal III (
Claessens and Loewen 2015, figs. 4
f and 11
k;
Xu et al. 2011, fig. 6
a).
Parks (1933) originally noted this character in his diagnosis of “
Struthiomimus ingens” (ROM 852), later synonymized with
O. edmontonicus (
Makovicky et al. 2004), although the type specimen of
O. edmontonicus (CMN 8632) has the distal ends of metatarsals III and IV closely appressed (
Claessens and Loewen 2015, fig. 11
g). The distal end of metatarsal IV is also divergent from metatarsal III in
Q. henanensis (
Xu et al. 2011, fig. 6
a) and
O. velox (
Claessens and Loewen 2015, fig. 4
f).
Claessens and Loewen (2015) considered the relatively short and robust metatarsus to be an autapomorphy of
O. velox, but did not compare it to
Q. henanensis, which has a very similarly proportioned metatarsus. It is possible that
Qiupalong is nested phylogenetically within
Ornithomimus, as the sister taxon of
O. velox. The currently accepted monophyly of
O. velox and
O. edmontonicus is based solely on the relative lengths of the metacarpals (
Claessens and Loewen 2015), which are not preserved in any specimen of
Qiupalong.
The likely greater geological age of the Canadian
Qiupalong sp. material in comparison with
Q. henanensis and the reconsideration of characters bearing on the phylogenetic relationships of
Qiupalong to other North American ornithomimids both support a North American origin for this genus. North American ornithomimids attained a high taxonomic and morphological diversity by the late Campanian (
McFeeters et al. 2016;
Serrano-Brañas et al. 2016). At least some characters previously considered diagnostic of
Q. henanensis (combination of straight pubic shaft and reduced anterior extension of pubic boot, pit between astragalus and calcaneum) evolved prior to the dispersal of
Qiupalong into Asia. A complex palaeobiogeographic history involving multiple dispersals between North America and Asia has been supported for a variety of other Late Cretaceous dinosaur clades, including hadrosaurids (
Prieto-Márquez 2010), neoceratopsians (
Xu et al. 2010), dromaeosaurids (
Evans et al. 2013), and tyrannosaurids (
Brusatte and Carr 2016).
Loewen et al. (2013) proposed a relationship between falling sea levels at the end of the Campanian or the beginning of the Maastrichtian and the dispersal of several dinosaur clades (including tyrannosaurines, centrosaurines, and some hadrosaurid lineages) into Asia from North America, although
Brusatte and Carr (2016) found it equally parsimonious that
Tyrannosaurus dispersed into North America from Asia. The dispersal of a derived ornithomimid,
Qiupalong, into Asia from North America may have occurred during this time as part of the same faunal interchange event and suggests a more complex history of ornithomimid dispersals in both directions across Beringia, comparable to the pattern previously proposed in other dinosaur clades.