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Eggs and eggshell are generally rare in the Upper Cretaceous rocks of Alberta, despite being relatively abundant nearby in Montana. Palaeontologists and other people have been prospecting the Horseshoe Canyon Formation for more than a 130 years, but eggshell fragments have only just been recovered. The fragments are unornamented with angusticanaliculate pores and three structural layers. Numerous features support their referral to Prismatoolithus levis, and they confirm the presence of a bird-like external layer in this ootaxon. The fragments, which likely belonged to Albertavenator curriei, are from a site with abundant troodontid teeth and perinate material from hadrosaurs, ceratopsians, and theropods. The discovery of eggshell challenges the notion that the Horseshoe Canyon Formation is too heavily sideritized to preserve eggshell. [ABSTRACT FROM AUTHOR]

Troodontid material from the Maastrichtian of North America is extremely rare, beyond isolated teeth from microvertebrate sites. Here we describe troodontid frontals from the early Maastrichtian Horseshoe Canyon Formation (Horsethief Member). The most complete specimen, TMP 1993.105.0001, is notably foreshortened and robust when compared with numerous specimens referred to Troodon from the Dinosaur Park Formation, and exhibits several characteristics that distinguish it from other Late Cretaceous troodontids. Morphometric analyses reinforce shape differences between TMP 1993.105.0001 and other North American troodontids, and show that proportional differences are independent of size. We therefore erect a new taxon, Albertavenator curriei gen. et sp. nov., which is diagnosed by the following autapomorphies: (1) primary supraciliary foramen is truncated anteriorly by the lacrimal contact; (2) superficial (ectocranial) surface of the frontal proportionally shorter than all known troodontids, with a length to width ratio under 1.3; and (3) frontoparietal contact in which an enlarged lappet of the frontal extends medially to extensively overlap the lateral region of the anteromedial process of the parietal. Interestingly, tooth and jaw morphology from the single relatively complete dentary recovered from the Horseshoe Canyon cannot be distinguished from dentaries and teeth from the Dinosaur Park Formation. If the dentary and teeth from the Horsethief Member of the Horseshoe Canyon Formation prove to belong to A. curriei, extensive overlap in tooth morphology between the Dinosaur Park and Horseshoe Canyon formations reinforces the notion that tooth morphotypes do not exhibit strong correspondence to species alpha diversity, and may encompass multiple closely related taxa. [ABSTRACT FROM AUTHOR]

Eighty-nine samples from three boreholes penetrating the Horseshoe Canyon Formation (Late Campanian) in south-central Alberta (Canada) were investigated for megaspore content. The samples were found to contain 49 species belonging to the genera Azolla, Bacutriletes, Costatheca, Dictyothylakos, Echitriletes, Erlansonisporites, Ghoshispora, Glomerisporites, Minerisporites, Molaspora, Monophyllosporites, Paxillitriletes, Spermatites, Striatriletes and Trileites, including one new species of Spermatites (S. reticulatus). Deposits representing low-lying coastal plains with widespread peat swamps, meandering channels and back swamp environments yielded the highest numbers of megaspores. An analysis of characteristics of the 22 species of Costatheca and 18 species and one subspecies of Spermatites leads to the proposal of a system of shape classes. Dichotomous keys to species were prepared. The geographical and stratigraphical distributions of the genera were also reviewed to elucidate their potential use in biostratigraphic and palaeoecological studies. [ABSTRACT FROM AUTHOR]

In connection with the excavation of the Danek Bonebed in 2011, a half-metre long, well preserved right ceratopsian orbital horncore was recovered. The horncore belongs to the taphonomic group of larger, heavier elements from the bonebed. So far, no other ceratopsian elements have been identified from the bonebed. Ceratopsids from the Horseshoe Canyon Formation of southern Alberta include Anchiceratops, Arrhinoceratops, Eotriceratops, and Pachyrhinosaurus. The size, proportions, and gently anterolaterally procurving morphology of the horncore indicates that it is from a chasmosaurine ceratopsid. There is weak morphological information to suggest that it may represent Anchiceratops ornatus, which is the most common chasmosaurine at this stratigraphic level. The base of the specimen has been hollowed out by a sinus system, which in conjunction with its large size indicates it is probably from a mature animal. The rarity of ceratopsian remains in this and other hadrosaur bonebeds suggests horned dinosaurs were excluded from anywhere that was occupied by herds of large numbers of Edmontosaurus. [ABSTRACT FROM AUTHOR]

The Danek Bonebed is a monodominant Edmontosaurus bonebed preserving predominantly disarticulated material from the Upper Campanian Horseshoe Canyon Formation within the city limits of Edmonton, Alberta, Canada. To date, at least six dinosaur taxa have been identified at the site: Albertosaurus sarcophagus, Chasmosaurinae indet., Dromaeosauridae indet., Edmontosaurus regalis, Ornithomimidae indet., and Troodontidae indet. This bonebed has been used as a case study for creating a digital, searchable bonebed map using a geographic information system (GIS) platform. The original quarry maps produced on site are refined when digitized with new anatomical information gathered during preparation of collected specimens. Each specimen is labeled with the known specimen identification, quarry coordinates, and catalogue number. Creating a digital map of the bonebed allows easier interpretation of data and the ability to share maps to compare specific elements within the bonebed. [ABSTRACT FROM AUTHOR]

The Danek Bonebed (Edmonton, Alberta, Canada) is a monodominant Edmontosaurus regalis assemblage of the upper Campanian (Upper Cretaceous) Horseshoe Canyon Formation. Bone histology of humeri and femora are used in this paper to test hypotheses about the growth dynamics and palaeobiology of Edmontosaurus. The high number of elements collected from the Danek Bonebed allow for an expansion of the multi-element histological record for hadrosaurs. Results indicate that Edmontosaurus had a growth trajectory similar to other large-bodied dinosaurs and reached the onset of somatic maturity at about 10-15 years of age; however, even the largest elements to preserve lines of arrested growth do not have external fundamental systems. This timing of the onset of somatic maturity agrees with the estimated body size of Edmontosaurus relative to other dinosaurs for which life-history data are available. Vascularity patterns support the hypothesis that edmontosaurs preserved at the Danek Bonebed were not subject to the same extreme seasonal environmental shifts as congenerics preserved at higher latitudes, further supporting overwintering behaviour in the latter. [ABSTRACT FROM AUTHOR]

For fossil assemblages, quantitative size and shape studies are often complicated by diagenetic distortion. Different vertebrate elements, although subjected to similar burial stresses, exhibit deformations based upon their original shapes; this hypothesis is tested here by quantitatively comparing deformed humeri and femora from the Danek Bonebed (a monodominant Edmontosaurus regalis bonebed from the upper Campanian Horseshoe Canyon Formation in Edmonton, Alberta, Canada) with samples of undeformed humeri and femora from modern and fossil assemblages. Analyses suggest that at the Danek Bonebed a strong relationship exists between element length and circumference despite being distorted by crushing deformation. Major and minor axes of the midshaft cross section, however, were not uniformly distorted. Although their anatomical position did not change, the major axis became longer relative to the minor axis in distorted specimens. A regression based on the undeformed humeri was not able to accurately predict circumference in the Danek humeri. Further study might quantify the deformation of other bones in the Danek Bonebed and could be extended to other assemblages and genera. Caution should be taken when conducting studies in which diagenetic crushing may have altered morphological features of fossil vertebrate remains. [ABSTRACT FROM AUTHOR]

Tyrannosaurid cranial bones - including a maxilla, dentary, and pterygoid - were collected from a monodominant Edmontosaurus bonebed in the Horseshoe Canyon Formation exposed near the city of Edmonton, Alberta, Canada. The maxilla can be identified as Albertosaurus sarcophagus based on the narrow interfenestral strut and relatively deep dental pits along the length of the palatal shelf. Cranial bones are interpreted to have come from a single large individual that was incorporated into the site during, or temporally close to, the formation of the final taphocoenosis. This discovery constitutes the northernmost record of A. sarcophagus, and helps to narrow the geographic gap of latest Cretaceous tyrannosaurs between Alberta and Alaska. The geographic distribution of A. sarcophagus - eclipsed only in areal extent by Tyrannosaurus rex in North America - attests to the adaptability of this species, which endured regional changes in climate that forced extirpation of many ornithischian taxa during deposition of the Horseshoe Canyon Formation. [ABSTRACT FROM AUTHOR]

A significant number of fossil remains of the hadrosaurid Edmontosaurus have been recovered from the Danek Bonebed (Horseshoe Canyon Formation, Upper Cretaceous, Alberta). Bones from theropod dinosaurs are scarce in this hadrosaur-dominated bonebed, but more than 60 tyrannosaurid theropod teeth have been found. The isolated tyrannosaurid teeth include juvenile and adult specimens, although the precise ontogenetic stage has not been determined. The use of multivariate analyses helps determine the variance of the sample and verifies the initial taxonomic affinities given to these teeth, showing their high potential as a useful tool to better discriminate tyrannosaurid teeth. It also provides an insight into the tyrannosaurid intraspecific variability in the Horseshoe Canyon Formation. [ABSTRACT FROM AUTHOR]

The Danek Bonebed (Horsethief Member, Horseshoe Canyon Formation, Late Campanian) is dominated by the remains of at least 12 Edmontosaurus regalis. Skeletal remains of a tyrannosaurid and ceratopsid are also known. The predominantly disarticulated remains were interred on a periodically inundated floodplain and, although the cause of death is unknown, a sudden, catastrophic death explains the demographic spread, faunal diversity, rare greenstick fractures, and homogeneous weathering/abrasion categories of the assemblage. The Danek Bonebed shares a similar taphonomic signature to the Liscomb Bonebed (Prince Creek Formation, Alaska), but it is unique among all other described hadrosaurid bonebeds in the unusually high proportion of bite-marked bones (∼30%), suggesting scavenging played a major role in the reworking of the assemblage. The highest frequency of bite marks is found on small, often unidentifiable (and commonly ignored) bone fragments, underscoring the role that such fragments can play in taphonomic interpretation. Finally, the recognition of E. regalis from central Alberta is an important datum linking contemporaneous occurrences in southern Alberta with slightly older records of this species from the Wapiti Formation in northwestern Alberta. [ABSTRACT FROM AUTHOR]

An ash-rich volcaniclastic sandstone immediately underlying dinosaur-rich material from the Danek Bonebed in the Horseshoe Canyon Formation (HCF), Edmonton, Alberta, Canada, contains accessory zircon, which have been dated employing U-Pb geochronology. Both laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and chemical abrasion isotope dilution thermal ionization mass spectrometry (ID-TIMS) U-Pb analyses have been conducted. The zircon age distributions are complex with U-Pb dates ranging from Precambrian to Cretaceous. We consider the youngest ID-TIMS 206Pb/238U date of 71.923 ± 0.068 Ma as the maximum deposition age of the ash-rich sandstone, placing the overlying Danek bonebed in the early Maastrichtian. This age is compatible with the paleontological assemblage from the Danek Bonebed and the regional stratigraphy. The zircon age distribution also implies that the HCF had a complex provenance of the detritus with some Archean and Proterozoic zircons, a group of Mesozoic, and a large compliment of Cretaceous grains. The results highlight the importance of high precision geochronology in constraining the age of important fossil deposits such as the Danek Bonebed. [ABSTRACT FROM AUTHOR]

Although considerable work has been conducted on the stratigraphy and dinosaur assemblages of the Horseshoe Canyon Formation of southern Alberta, equivalent strata and assemblages in central Alberta remain poorly understood. Data from the Danek Bonebed (Edmonton, Alberta) are beginning to fill this gap. The bonebed occurs 4 m above the #9 Big Island Coal Seam. This stratigraphic position lies just below the middle of the Horseshoe Canyon Formation in the Edmonton region, and also lies below a thick, stratigraphically significant non-coaly interval that is expressed throughout central and southern Alberta. The stratigraphic position of the Danek Bonebed equates best with the uppermost Horsethief Member of the Horseshoe Canyon Formation in the Drumheller region and the upper part of Unit 4 of the Wapiti Formation in the Grande Prairie region. In both Drumheller and Grande Prairie, the correlated position of the bonebed underlies a zone of marine transgression (Drumheller Marine Tongue), which, in turn, includes the Campanian-Maastrichtian boundary. In the context of Geologic Time Scale 2004, we infer a late Campanian age of 71.0-71.3 Ma for the bonebed. The Danek's dinosaurian assemblage is limited taxonomically, but compares well with the Edmontosaurus regalis - Pachyrhinosaurus canadensis fossil assemblage zone in the Drumheller region. We propose that a mega-herbivore faunal assemblage, characterized by Edmontosaurus and Pachyrhinosaurus, extended continuously across the climatically wet coastal plain of latest Campanian southern and central Alberta, and likely extended northwest into the North Slope of Alaska, where it persisted into the early Maastrichtian. [ABSTRACT FROM AUTHOR]

The Upper Cretaceous paralic to nonmarine Horseshoe Canyon Formation (HCFm) of southern Alberta is divided into seven mappable members: Strathmore, Drumheller, Horsethief, Morrin, Tolman, Carbon, and Whitemud (bottom to top). This subdivision, based on combined outcrop and subsurface analyses, reflects lithostratigraphic variations related to changes in sea level (previously recognized) and newly documented changes in climate, volcanism, and orogenesis in an evolving foreland basin. Million-year-scale cycles of orogenesis resulted in changes in sediment supply and rates of subsidence in the basin and are interpreted in the context of a simple, two-phase foreland-basin sequence stratigraphic model: ( i) overthrust loading resulting in reduced rates of sediment supply and subsidence in the most distal portions of the Alberta foredeep (our field area); ( ii) tectonic quiescence leading to increased rates of sediment supply and subsidence during proximal-foredeep rebound. During the first ∼2.5 Ma of its history (Strathmore and Drumheller members), the HCFm was tectonically and climatically 'stable', and depositional style and stratigraphic architecture were influenced by vertical aggradation and modest progradation of shorelines. During the remaining ∼4.5 Ma (Horsethief, Morrin, Tolman, Carbon, and Whitemud members), there were more complex and frequent changes in climate, volcanism, orogenesis, landscape weathering, and soil formation. Understanding this previously unrecognized complexity is critical for correctly assessing hydrocarbon resource distributions and biostratigraphic and taphonomic patterns. [ABSTRACT FROM AUTHOR]

Anchiceratops is a chasmosaurine ceratopsid from the Upper Cretaceous Horseshoe Canyon Formation (HCF) of Alberta. It is distinguished primarily by its unique parietosquamosal frill ornamentation and possibly by the presence of a ventrally flexed olfactory bulb of the brain. Although Anchiceratops is known from at least ten partial skulls, only two of these have been formally described. These skulls are not stratigraphically segregated, but they differ markedly in their proportions (e.g., supraorbital horncore and frill dimensions), causing previous authors to account for this disparity with reference to either interspecific or sexual differences. Both of these hypotheses assume that variation in Anchiceratops is dimorphic; however, this assumption has never been tested with reference to all available material. The present study describes all material from the HCF that can be positively attributed to Anchiceratops, and tests the assumption of dimorphism by subjecting this material to a series of morphometric analyses. We find no compelling evidence for dimorphism in Anchiceratops, although sample size is still too small for convincing statistical support. We conclude that there is a single, variable species of Anchiceratops, A. ornatus. Average sedimentation rates for the HCF suggest that A. ornatus is a particularly long-lived species compared with other ceratopsids (∼1.5-2.0 Ma), and the paleoecological implications of this are discussed. A cladistic analysis that includes the new data presented here indicates that Anchiceratops is more closely related to Chasmosaurus than to Triceratops, in contrast with previous studies. [ABSTRACT FROM AUTHOR]

The type series of Albertosaurus sarcophagus, consisting of a type (CMN 5600) and a paratype (CMN 5601) is inadequately established, since it has not been demonstrated that the specimens represent the same taxon. This problem has arisen because the original diagnostic characters have a wider distribution among Tyrannosauridae or they are in error, and both specimens consist of incomplete and damaged skulls. The type series was studied to test for the presence of diagnostic characters in the type specimen and, if so, to provide a rationale for referring the paratype to the taxon. Of the bones shared between the skulls, only five could be compared. One character, the enlarged posterior pneumatic recess of the palatine, is shared between the two specimens; this condition differs from the situation seen in other tyrannosaurids. This character provided the rationale for assessing the identity of the specimens collected from the Albertosaurus bonebed, from which one palatine was collected that exhibits the diagnostic recess. Isolated cranial bones from the bonebed were compared with those preserved in the type series to evaluate their referral to A. sarcophagus; additional characters shared between the type series and the specimens from the bonebed were identified in the maxilla, lacrimal, and palatine. This evidence supports the hypothesis that A. sarcophagus is the tyrannosaurid preserved in the bonebed. A hypothesis of the principal growth changes in the skull in A. sarcophagus, which includes the type series and bonebed material, is proposed. La série type d'Albertosaurus sarcophagus, qui consiste en un type (CMN 5600) et un paratype (CMN 5601), n'est pas bien établie, puisqu'il n'a pas été démontré que ces spécimens représentent le même taxon. Ce problème est dûau fait que les caractères diagnostiques définis à l'origine ont une distribution élargie au sein des tyrannosauridés ou sont erronés, et que les deux spécimens représentent des crânes endommagés et incomplets. La série type a été étudiée afin de vérifier la présence des caractères diagnostiques dans le spécimen type et, le cas échéant, de justifier l'affectation du paratype au taxon. Des os présents dans les deux spécimens, cinq seulement ont pu être comparés. Un caractère, la grande cavité pneumatique postérieure du palatin, est commun aux deux spécimens; cette condition se distingue de la situation observée chez d'autres tyrannosauridés. Ce caractère a motivé l'évaluation de l'identité des spécimens prélevés du gisement d'ossements d'Albertosaurus, duquel un palatin a été recueilli qui présente la cavité diagnostique. Des os crâniens isolés prélevés du gisement d'ossements ont été comparés à ceux préservés dans la série type afin d'évaluer leur affectation à A. sarcophagus; d'autres caractères communs à la série type et aux spécimens provenant du gisement d'ossements ont été cernés dans l'os maxillaire, l'os lacrymal et le palatin. Ces observations appuient l'hypothèse voulant qu'A. sarcophagus soit le tyrannosauridé préservé dans le gisement d'ossements. Une hypothèse est proposée concernant les principales modifications, durant la croissance, du crâne d'A. sarcophagus, qui inclut la série type et le matériel provenant du gisement d'ossements. [ABSTRACT FROM AUTHOR]

Over the past decade, excavations of a monodominant theropod bonebed from the lower Maastrichtian beds of the Horseshoe Canyon Formation have recovered a minimum number of 26 individuals of the tyrannosaur, Albertosaurus sarcophagus. Examination of skeletal elements from the bonebed revealed a small number of abnormalities from at least two individuals. These include bony spurs (enthesophytes) of unknown origin on three pedal phalanges. Well-healed fracture calluses are present on two rib shafts and a gastralia element. The left dentary of one adult preserves both healed and unhealed parallel bite marks and a perforative lesion attributable to a partially healed, mechanically induced puncture wound. Unfortunately, the limited range in the types and frequencies of pathological changes provides only little information on the distribution of such phenomena but may be suggestive of the overall 'health' of the population. Au cours de la dernière décennie, des excavations d'un gisement d'ossements à théropodes monodominant dans des lits du Maastrichtien inférieur de la Formation de Horseshoe Canyon ont produit un minimum de 26 exemplaires du tyrannosaure Albertosaurus sarcophagus. L'examen d'éléments squelettiques provenant du gisement a révélé un petit nombre d'anomalies chez au moins deux exemplaires, dont des éperons osseux (enthésophytes) d'origine inconnue sur trois phalanges pédieuses. Des cals de fractures bien consolidées sont présents sur deux diaphyses de côte et un élément de gastralium. L'os dentaire gauche d'un adulte conserve des marques de morsure parallèles guéries et non guéries, ainsi qu'une lésion perforante attribuable à une plaie punctiforme d'origine mécanique partiellement guérie. Malheureusement, la gamme limitée des types et des fréquences de modifications pathologiques ne fournit que peu d'information sur la distribution de ces phénomènes, mais pourrait être un indicateur de la « santé » globale de la population. [ABSTRACT FROM AUTHOR]

Horseshoeichthys armaserratus, gen. et sp. nov., (Clupeomorpha: Ellimmichthyiformes: Sorbinichthyidae) is described from the Horseshoe Canyon Formation (Maastrichtian), Albertosaurus bonebed locality, Alberta, Canada. Horseshoeichthys armaserratus is classified as an ellimmichthyiform based on the following characters: the presence of a sixth infraorbital with a sensory canal that leads to the fifth infraorbital, absence of a supraorbital bone, subrectangular predorsal scutes, parietals in contact with each other at the midline, and two supramaxillae. The specimen is classified in the Sorbinichthyidae Family as it has abdominal ribs articulating in pits on the centra, posterior spines on predorsal scutes, and absence of a median spine on predorsal scutes. A new genus and species is proposed based on the presence of (anteriorly) Y-shaped mesethmoid, supraorbital, subrectangular predorsal scutes with coarse, rounded serrae on the posterior margin and a large anterior projection, scales with serrae on the circuli, and two postcleithra. This specimen represents the first freshwater ellimmichthyiform from the Upper Cretaceous of North America and the highest paleolatitude (59°N) occurrence known for the family. Furthermore, the dentary and centra have distinctive morphologies that are matched by specimens in microvertebrate localities from three underlying formations, including the Milk River Formation (Santonian), which indicates at least a 14 million year history for this lineage. Horseshoeichthys armaserratus, gen. et sp. nov., (Clupeomorpha: Ellimmichthyiformes: Sorbinichthyidae), de la localité du gisement d'ossements d'Albertosaurus de la Formation de Horseshoe Canyon (Maastrichtien), en Alberta, au Canada, est décrit. Horseshoeichthys armaserratus est affecté aux ellimmichthyiformes à la lumière des caractères suivants : la présence d'un sixième sous-orbitaire présentant un canal sensoriel qui mène au cinquième sous-orbitaire, l'absence d'un os sus-orbitaire, des plaques osseuses pré-dorsales sub-rectangulaires, des pariétaux en contact les uns avec les autres au niveau de la ligne médiane et deux sus-maxillaires. Le spécimen est affecté aux sorbinichthyidés puisqu'il présente des côtes abdominales s'articulant dans des fosses sur le centrum et des épines postérieures sur les plaques osseuses pré-dorsales, et que ces dernières n'ont pas d'épine médiane. Un nouveau genre et une nouvelle espèce sont proposés à la lumière de la présence d'un mésethmoïde (antérieurement) en forme de Y, d'un sus-orbitaire, de plaques osseuses pré-dorsales sub-rectangulaires présentant des stries arrondies et épaisses sur leur bord libre postérieur et une grande projection antérieure, d'écailles avec des stries sur le circulus et de deux postcleithra. Ce spécimen représente le premier ellimmichthyiforme d'eau douce du Crétacé supérieur de l'Amérique du Nord et l'exemple connu de cette famille provenant de la plus haute paléolatitude (59oN). En outre, le dentaire et le centrum présentent des morphologies particulières semblables à celles de spécimens trouvés dans des localités de microvertébrés de trois formations sous-jacentes, dont la Formation de Milk River (Santonien), ce qui indique une histoire d'au moins 14 millions d'années pour cette lignée. [ABSTRACT FROM AUTHOR]

The Albertosaurus bonebed provides evidence for the mass-mortality of at least 12 Albertosaurus. Albertosaurus, other vertebrates, and trees are concentrated on upper point bar surfaces of a small meandering paleochannel. Throughout the field area, Albertosaurus, other vertebrates, and coalified plants are also preserved patchily in overbank mudstones at the same horizon. Although the bonebed is dominated by Albertosaurus, there are also sparse macrofossil remains of Hypacrosaurus and Albertonykus. The basal lag yields vertebrate microfossils containing at least 19 additional taxa. Freshwater invertebrates are preserved at and below the base of the paleochannel. Large elements are over represented at the site, whereas smaller elements are under represented, suggesting hydraulic sorting. The taphonomic signature of the site suggests that death, disarticulation, and burial took place within one year. We conclude that one or more storms of large intensity downed trees and temporarily drowned the paleolandscape, ultimately killing the tyrannosaurids directly or indirectly. Logs and carcasses were reworked on a point bar during the waning stages of the storm and over subsequent years. Scavenging and breakage of remains by large carnivores was probably inhibited by the mixed log and bone jam. Remains of smaller scavengers (small theropods and snails) are plentiful suggesting these forms were more successful at accessing remains. Juvenile Albertosaurus are under represented at the site suggesting the possibility of age segregation. Because the group of Albertosaurus may have been forced together by rising floodwaters, it is not possible to assess the degree to which the taxon was gregarious from these data alone. Le gisement d'ossements d'Albertosaurus témoigne de la mortalité massive d'au moins douze Albertosaurus. Albertosaurus, d'autres vertébrés et des arbres sont concentrés sur des surfaces supérieures de barre de méandre d'un petit paléochenal méandrique. Dans toute la région, Albertosaurus, d'autres vertébrés et des plantes carbonisées sont également préservés par endroits dans des mudstones de débordement situés au même horizon. Bien que le gisement d'ossements soit dominé par Albertosaurus, il présente également ça et là des restes de macrofossiles d'Hypacrosaurus et d'Albertonykus. Le dépôt de déflation à la base du paléochenal présente des microfossiles de vertébrés d'au moins 19 autres taxons. Des invertébrés d'eau douce sont préservés à la base du paléochenal et sous celle-ci. Les grands éléments sont sur-représentés dans le site, alors que les éléments plus petits sont sous-représentés, ce qui suggère un tri hydraulique. La signature taphonomique du site suggère que la mort, la désarticulation et l'enfouissement ont eu lieu dans la même année. Il est conclu qu'une ou plusieurs tempêtes de forte intensité ont abattu les arbres et provisoirement noyé le paléopaysage, entraînant finalement la mort directe ou indirecte des tyrannosauridés. Les billots et les carcasses ont été remaniés sur une barre de méandre vers la fin de la tempête et au cours des années subséquentes. L'embâcle de billes et d'ossements a probablement empêché la récupération et le bri des restes par des grands carnivores. La présence de nombreux restes de détritivores plus petits (petits théropodes et escargots) donne à penser que ces animaux pouvaient accéder aux restes plus efficacement. Les Albertosaurus juvéniles sont sous-représentés dans le site, ce qui porte à croire à une ségrégation selon l'âge. tant donné que la montée des eaux pourrait avoir provoqué le rassemblement du groupe d'Albertosaurus, il est n'est pas possible d'évaluer le degré de grégarisme de ce taxon à la lumière de ces seules données. [ABSTRACT FROM AUTHOR]

The overall palynology of the upper Horseshoe Canyon Formation to lower Scollard Formation within the Edmonton Group is reviewed providing new insights into biostratigraphic relationships for the interval, including the recognition of unconformities in the stratigraphic package. The palynomorph recovery from the Horseshoe Canyon Formation and overlying units documents a number of significant events that allow the subdivision of the section. The Albertosaurus bonebed occurs within the lower Maastrichtian portion of the Edmonton Group. The bonebed is situated just below the base of the Scollardia trapaformis Palynomorph Zone, an important marker assemblage that has been documented from areas of the Yukon, Northwest Territories, Alberta, and Saskatchewan. This indicates that the bonebed lies at the top of the Mancicorpus vancampoi Zone. The transition between the zones is marked by a colour change in the sediments, the appearance of coals and organic-rich sediments above the transition, a decrease in numbers of vertebrate fossils, and the appearance of new pollen species. It is inferred that the observed changes reflect a climatic switch from dry to wetter conditions. At a large scale, palynomorph assemblages across this transition do not clearly indicate marked differences that can be attributed to the climatic change, with the exception of the appearance of Scollardia trapaformis and Mancicorpus gibbus in the assemblages. On a microscale of a few metres, there are changes in relative abundance of plant groups. Un examen de la palynologie globale de la partie supérieure de la Formation de Horseshoe Canyon à la partie inférieure de la Formation de Scollard, du Groupe d'Edmonton, jette un nouvel éclairage sur les relations biostratigraphiques dans cet intervalle, dont la reconnaissance de discordances stratigraphiques. Les palynomorphes trouvés dans la Formation de Horseshoe Canyon et les unités sus-jacentes documentent un certain nombre d'évènements importants qui permettent de subdiviser cet intervalle. Le lit à ossements d'Albertosaurus se trouve dans la partie maastrichtienne inférieure du Groupe d'Edmonton, juste en dessous de la zone de palynomorphe à Scollardia trapaformis, un important assemblage repère qui a été documenté dans diverses régions du Yukon, des Territoires du Nord-ouest, de l'Alberta et de la Saskatchewan. Cela indique que le lit à ossements se situe au sommet de la zone à Mancicorpus vancampoi. La transition d'une zone à l'autre est marquée par un changement de couleur des sédiments, l'apparition de charbons et de sédiments riches en matière organique au-dessus de la transition, la diminution du nombre de fossiles de vertébrés et l'apparition de nouvelles espèces de pollen. Les changements observés refléteraient le passage d'un climat sec à un climat plus humide. À grande échelle, les assemblages de palynomorphes qui caractérisent cette transition ne révèlent clairement aucune différence marquée pouvant être attribuée à des changements climatiques, à l'exception de l'apparition de Scollardia trapaformis et Mancicorpus gibbus au sein de l'assemblage. À l'échelle de quelques mètres, l'abondance relative de certains groupes de plantes varie. [ABSTRACT FROM AUTHOR]

One century ago, a field party from the American Museum of Natural History discovered a bonebed in the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada. Excavations by that museum, the Royal Tyrrell Museum of Palaeontology, and the University of Alberta have revealed the presence of at least a dozen individuals - represented by articulated partial skeletons, associated skeletons, and disarticulated isolated elements - of Albertosaurus sarcophagus. Tyrannosaurids dominate the bonebed assemblage, which also includes an adult Hypacrosaurus altispinus, two individuals of Albertonykus borealis, and numerous other, predominantly terrestrial, vertebrates. Skeletal morphology, phylogenetic inference, monodominant bonebeds, trackway sites, and ecological inferences support the notion that some non-avian theropods were gregarious animals. And specifically in the Albertosaurus bonebed, associated geologic and taphonomic evidence do not rule out a behavioural component in this catastrophic, mass-death assemblage. Il y a de cela un siècle, une expédition de l'American Museum of Natural History découvrait un lit d'ossements dans la Formation de Horseshoe Canyon du Crétacé supérieur de l'Alberta (Canada). Des fouilles effectuées par du personnel de ce musée, du Royal Tyrrell Museum of Palaeontology et de l'Université de l'Alberta ont révélé la présence d'au moins douze individus d'Albertosaurus sarcophagus, représentés par des squelettes articulés partiels, des squelettes associés et des éléments désarticulés isolés. S'il est dominé par des tyrannosauridés, l'assemblage du lit d'ossements renferme également un spécimen adulte d'Hypacrosaurus altispinus, deux individus d'Albertonykus borealis, ainsi que de nombreux autres vertébrés principalement terrestres. La morphologie des squelettes, l'inférence phylogénétique, des lits d'ossements monodominants, des sites de pistes et des inférences écologiques appuient la thèse voulant que certains théropodes non aviaires aient été des animaux grégaires. En ce qui concerne plus particulièrement le lit d'ossements d'Albertosaurus, les données géologiques et taphonomiques associées appuient la thèse d'une composante comportementale pour expliquer la présence de cet assemblage témoignant d'une mortalité massive catastrophique. [ABSTRACT FROM AUTHOR]

The faunal assemblage from the early Maastrichtian portion of the Horseshoe Canyon Formation is described on the basis of four new vertebrate microfossil localities and remains from the Albertosaurus bonebed. All of the localities sampled were deposited during a cool, dry climate at a palaeolatitude of ~58°N. Thus, these assemblages provide insight into a northern cool-climate assemblage in the early Maastrichtian of western North America. This fauna is characterized by the presence of taxa with more northern affinities, such as Holostean A, champsosaurs, Troodon, and toothed birds. Warm-climate taxa, such as crocodylians, large and diverse turtles, and albanerpetontids are notable in their absence. The Albertosaurus bonebed locality at the top of unit 4 of the Horseshoe Canyon Formation was deposited during the initial stages of a trend to a warmer and wetter climate that is represented in unit 5. The bonebed shares many taxa with the underlying vertebrate microfossil localities. However, a notable difference is the presence of Atrociraptor marshalli from the Albertosaurus bonebed but not the other localities in the upper Horseshoe Canyon Formation. The presence of Atrociraptor may be attributable to this change in climate rather than local ecological conditions. Also, the assemblages are different in the paucity of fish remains in the bonebed, and the relative rarity of shed hadrosaur teeth. The low abundance of aquatic taxa and rarity of shed teeth of hadrosaurs indicate that the locality is largely autochthonous, with little material being transported into the site. L'assemblage faunique de la portion du Maastrichtien précoce de la Formation de Horseshoe Canyon est décrit à la lumière de quatre nouvelles localités de microfossiles de vertébrés et de restes provenant du gisement d'ossements d'Albertosaurus. Toutes les localités échantillonnées témoignent d'un dépôt en climat sec et frais à une paléolatitude d'environ 58°N. Ainsi, ces assemblages offrent une fenêtre sur un assemblage de climat nordique frais du Maastrichtien précoce de l'ouest de l'Amérique du Nord. Cette faune est caractérisée par la présence de taxons présentant des affinités plus nordiques, tels que des holostéens A, des champsosaures, Troodon et des oiseaux à dents. L'absence de taxons de climat chaud, tels que des crocodiliens, diverses tortues dont de grandes espèces et des albanerpetontidés, est notable. Les sédiments de la localité du gisement d'ossements d'Albertosaurus au sommet de l'unité 4 de la Formation de Horseshoe Canyon ont été déposés durant les stades initiaux d'une transition vers le climat plus chaud et plus humide représenté dans l'unité 5. Le gisement d'ossements présente bon nombre des mêmes taxons que les localités à microfossiles de vertébrés sous-jacentes. Toutefois, le fait qu'Atrociraptor marshalli soit présent dans le gisement d'ossements d'Albertosaurus, mais absent des autres localités de la partie supérieure de la Formation de Horseshoe Canyon constitue une différence notable. La présence d'Atrociraptor pourrait être attribuable au changement climatique susmentionné plutôt qu'à des conditions écologiques locales. La paucité de restes de poissons dans le gisement d'ossements et la rareté relative des dents d'hadrosaure tombées distinguent également le gisement d'ossements. La faible abondance de taxons aquatiques et la rareté de dents d'hadrosaure tombées indiquent qu'il s'agit d'une localité principalement autochtone caractérisée par une faible proportion de matériel apporté sur les lieux. [ABSTRACT FROM AUTHOR]

A skeleton of a new ceratopsid dinosaur, Eotriceratops xerinsularis gen. et sp. nov., is described in this paper. It is the first associated vertebrate skeleton found within the upper 20 m of the Horseshoe Canyon Formation. Eotriceratops xerinsularis is a large chasmosaurine that differs from other chasmosaurines in a unique set of features in the premaxilla, nasal horn core, squamosal frill, and epijugal. The most striking of those features includes an extremely tall, non-recessed narial process of the premaxilla; the presence of greatly elongate, spindle-shaped epoccipitals on the squamosal frill; a deep, well-demarcated fossa on the anteroventral surface of the squamosal frill; a sharply conical epijugal with a pronounced proximoposterior process and separate fossa-like facets for the jugal and quadratojugal; and the presence of an obliquely extending vascular trace meeting a transverse vascular trace ventrally on the anterior surface of the nasal horn core. Our phylogenetic analysis suggests that E. xerinsularis is nested within a clade including Triceratops, Diceratops, and Torosaurus, which are all from late Maastrichtian deposits. The upper 20 m of the Horseshoe Canyon Formation comprises a coal-rich interval (Carbon–Thompson coal zone, unit 5), which previously has been assigned to upper Maastrichtian magnetochrons 31n and 30r, and the Mancicorpus gibbus miospore subzone. The ceratopsid specimen was collected from between the Carbon and Thompson coal seams, and thus, is inferred to (1) occur near the top of magnetochron 31n and (2) have an age of 67.6–68.0 Ma. Large chasmosaurine ceratopsids, such as Triceratops and Torosaurus, have not previously been described from the Horseshoe Canyon Formation or from magnetochron 31n or the M. gibbus miospore subzone. Thus, Eotriceratops is distinctly older than any other ceratopsid in the Triceratops group, and the discovery of E. xerinsularis helps fill a biostratigraphic gap between early and late Maastrichtian chasmosaurines. [ABSTRACT FROM AUTHOR]

A fossilized aroid infructescence has been recovered from the Horseshoe Canyon Formation in southern Alberta, Canada. Its stratigraphic position places it near the end of the Campanian Stage of the Late Cretaceous Epoch, at an absolute age of approximately 72 million years before present. It is one of the few Cretaceous aroid fossils known at present, and it represents a new genus of Araceae, here named Albertarum. The infructescence is fertile to the apex, and the flowers must have been bisexual. Flowers bear remains of a long, attenuated style, surrounded by a perigone of six tepals. A fracture reveals ellipsoid seeds with a thick, ribbed testa and traces of a raphe, arranged in groups of three. The gynoecium was probably trilocular with one ovule per locule, and ovules were anatropous, probably with apical–parietal or axile placentation. Bisexual, perigoniate flowers occur in subfamilies Gymnostachydoideae, Orontioideae, Pothoideae, Monsteroideae, and Lasioideae, no genera of which have ribbed seeds, but the infructescence and stylar region of Albertarum resemble those of extant Symplocarpus (Orontioideae). The Horseshoe Canyon Formation was deposited in a delta plain setting, and like Symplocarpus, Albertarum probably grew in a wetland environment. [ABSTRACT FROM AUTHOR]

We describe a new species of nanhsiungchelyid turtle, Basilemys morrinensis, based on a nearly complete shell from the Horsethief Member (lower Maastrichtian) of the Horseshoe Canyon Formation of Alberta. The species is intermediate in age between the Campanian forms B. variolosa and B. gaffneyi and the upper Maastrichtian forms B. sinuosa and B. praeclara. It is also intermediate in its morphology, possessing a unique suite of both plesiomorphic (e.g., divided extragulars) and derived (e.g., square epiplastral beak, pygal wider than long) traits. It is further characterized by an autapomorphic square cervical scale. Phylogenetic analysis assuming parsimony recovers B. morrinensis in a polytomy with B. variolosa and B. gaffneyi, outside the clade formed by the upper Maastrichtian forms B. sinuosa and B. praeclara. The holotype of Basilemys morrinensis provides the first evidence that this genus reached large size (∼1 m long) in the Horseshoe Canyon Formation and was not diminutive as previously thought based on less complete shell material. Although Basilemys is usually regarded as terrestrial in habit based on its skull and limb morphology, we note that the low profile of its shell is a derived feature usually indicative of an aquatic mode of life. This suggests that there is yet much to learn about the life habits of this interesting turtle. https://zoobank.org/urn:lsid:zoobank.org:pub:F1F61F25-C441-4D7D-99B0-D460ABCC7918 SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Mallon, J. C., and D. B. Brinkman. 2018. Basilemys morrinensis, a new species of nanhsiungchelyid turtle from the Horseshoe Canyon Formation (Upper Cretaceous) of Alberta, Canada. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1431922. [ABSTRACT FROM AUTHOR]