An unusual microsite from the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada

ABSTRACT

The Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada, is among the best-studied paleoecosystems in North America. However, its microvertebrate paleocommunity structure is relatively poorly known, partly because it lacks the abundant microsites of other Upper Cretaceous deposits of Alberta. An unusual microsite (FTS-2) from the Horsethief Member of the Horseshoe Canyon Formation is described that produces abundant anuran and troodontid material, alongside perinatal material from ornithischians and tyrannosaurs. Anuran specimens representing a minimum of two separate taxa and a metatherian molar suggest that these components of the fauna were more diverse than currently recognized. The assemblage is similar to three other North American sites that produce abundant troodontid teeth alongside perinatal dinosaurs. However, environmental and taphonomic conditions of these sites vary, supporting the notion of mixed biotic and abiotic factors driving the association of troodontids alongside perinates. In part, this may stem from similar nesting preferences between troodontids and other dinosaurs, as material collected from all three sites suggests proximity to troodontid nesting sites. Sites such as FTS-2 are important for revealing the rare and small components of paleoecosystems, and hold promise for revealing interactions between these parts of the fauna.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

ACKNOWLEDGEMENTS

FTS-2 was found and reported to the TMP by Eric Felber in 1995 (at that time referred to as “1st Site”). The specimens in this paper were collected during the 2016–18 seasons of the Horseshoe Canyon Formation Expedition, supported by the time and effort of volunteers and the generosity of the Dinosaur Research Institute. We thank J. Gardner (TMP) and C. Scott (TMP) for assistance identifying some material and some very informative conversations. We thank D. Brinkman (TMP) for assistance with screen-washing the material. We also thank J. Gardner, C. Redman, and D. Eberth for their insightful comments in review of a previous incarnation of this manuscript. S.A.W. is funded by an Australian Government Research Training Program Scholarship. G.F.F. is funded by a Banting Postdoctoral Fellowship, and fieldwork was funded by Vanier Canada, NSERC, Alberta Innovates, the Alberta Lottery Fund, the Alberta Historical Resources Foundation, and the Dinosaur Research Institute. P.J.C. is funded by NSERC [Grant # RGPIN-2017-04715].

DATA AVAILABILITY STATEMENT

All specimens are accessioned into the University of Alberta Vertebrate Palaeontology collections (UALVP) which is a public resource. Raw data for all elements CT scanned for this study are publicly available on Morphosource under the following IDs:

1. Hadrosaurid perinate (UALVP 59600)—000581951

2. Anuran maxilla (UALVP 59596.8)—000581886

3. Anuran ilium (UALVP 59596.6)—000581947

4. Anuran cranial elements, unornamented (UALVP 59596.5)—000581927

5. Anuran cranial elements, ornamented (UALVP 59596.4)—000581935

6. Pediomyid molars (UALVP 59597)—000581943