A Hadrosaurid (Dinosauria: Ornithischia) from the Late Cretaceous (Campanian) Kanguk Formation of Axel Heiberg Island, Nunavut, Canada, and Its Ecological and Geographical Implications

A hadrosaurid vertebra was recovered during a palynological survey of the Upper Cretaceous Kanguk Formation in the eastern Canadian Arctic. This vertebra represents the farthest north record of any non-avian dinosaur to date. Although highly abraded, the fossil nonetheless represents an interesting biogeographic data point. During the Campanian, when this vertebra was deposited, the eastern Canadian Arctic was likely isolated both from western North America by the Western Interior Seaway and from more southern regions of eastern North America by the Hudson Seaway. This fossil suggests that large-bodied hadrosaurid dinosaurs may have inhabited a large polar insular landmass during the Late Cretaceous, where they would have lived year-round, unable to migrate to more southern regions during winters. It is possible that the resident herbivorous dinosaurs could have fed on non-deciduous conifers, as well as other woody twigs and stems, during the long, dark winter months when most deciduous plant species had lost their leaves.La vertèbre d’un hadrosauridé a été retrouvée pendant l’étude palynologique de la formation Kanguk remontant au Crétacé supérieur, dans l’est de l’Arctique canadien. Il s’agit de la vertèbre appartenant à un dinosaure non avien qui a été recueillie la plus au nord jusqu’à maintenant. Même si ce fossile est fortement abrasé, il n’en reste pas moins qu’il représente un point de donnée biogéographique intéressant. Pendant le Campanien, lorsque cette vertèbre a été déposée, l’est de l’Arctique canadien était vraisemblablement isolé de l’ouest de l’Amérique du Nord par la mer intérieure occidentale, et des régions plus au sud de l’est de l’Amérique du Nord par le bras de mer Hudson. Ce fossile suggère que de gros dinosaures hadrosauridés auraient pu habiter une grande masse terrestre insulaire polaire pendant le Crétacé tardif, où ils auraient évolué à l’année, étant incapables de migrer vers les régions plus au sud pendant l’hiver. Il est possible que les dinosaures herbivores résidents se soient nourris de conifères non décidus ainsi que d’autres tiges ou brindilles ligneuses pendant les longs mois sombres de l’hiver, lorsque la plupart des espèces végétales décidues avaient perdu leurs feuilles.

The dinosaur tracks of Tyrants Aisle: An Upper Cretaceous ichnofauna from Unit 4 of the Wapiti Formation (upper Campanian), Alberta, Canada

The Wapiti Formation of northwest Alberta and northeast British Columbia, Canada, preserves an Upper Cretaceous terrestrial vertebrate fauna that is latitudinally situated between those documented further north in Alaska and those from southern Alberta and the contiguous U.S.A. Therefore, the Wapiti Formation is important for identifying broad patterns in vertebrate ecology, diversity, and distribution across Laramidia during the latest Cretaceous. Tracksites are especially useful as they provide a range of palaeoecological, palaeoenvironmental, and behavioural data that are complementary to the skeletal record. Here, we describe the Tyrants Aisle locality, the largest in-situ tracksite known from the Wapiti Formation. The site occurs in the lower part of Unit 4 of the formation (~72.5 Ma, upper Campanian), exposed along the southern bank of the Redwillow River. More than 100 tracks are documented across at least three distinct track-bearing layers, which were deposited on an alluvial floodplain. Hadrosaurid tracks are most abundant, and are referable to Hadrosauropodus based on track width exceeding track length, broad digits, and rounded or bilobed heel margins. We suggest the hadrosaurid trackmaker was Edmontosaurus regalis based on stratigraphic context. Tyrannosaurids, probable troodontids, possible ornithomimids, and possible azhdarchid pterosaurs represent minor but notable elements of the ichnofauna, as the latter is unknown from skeletal remains within the Wapiti Formation, and all others are poorly represented. Possible social behaviour is inferred for some of the hadrosaurid and small theropod-like trackmakers based on trackway alignment, suitable spacing and consistent preservation. On a broad taxonomic level (i.e., family or above), ichnofaunal compositions indicate that hadrosaurids were palaeoecologically dominant across Laramidia during the late Campanian within both high-and low-latitude deposits, although the role of depositional environment requires further testing

Small Theropod Teeth from the Late Cretaceous of the San Juan Basin, Northwestern New Mexico and Their Implications for Understanding Latest Cretaceous Dinosaur Evolution

Studying the evolution and biogeographic distribution of dinosaurs during the latest Cretaceous is critical for better understanding the end-Cretaceous extinction event that killed off all non-avian dinosaurs. Western North America contains among the best records of Late Cretaceous terrestrial vertebrates in the world, but is biased against small-bodied dinosaurs. Isolated teeth are the primary evidence for understanding the diversity and evolution of small-bodied theropod dinosaurs during the Late Cretaceous, but few such specimens have been well documented from outside of the northern Rockies, making it difficult to assess Late Cretaceous dinosaur diversity and biogeographic patterns. We describe small theropod teeth from the San Juan Basin of northwestern New Mexico. These specimens were collected from strata spanning Santonian - Maastrichtian. We grouped isolated theropod teeth into several morphotypes, which we assigned to higher-level theropod clades based on possession of phylogenetic synapomorphies. We then used principal components analysis and discriminant function analyses to gauge whether the San Juan Basin teeth overlap with, or are quantitatively distinct from, similar tooth morphotypes from other geographic areas. The San Juan Basin contains a diverse record of small theropods. Late Campanian assemblages differ from approximately coeval assemblages of the northern Rockies in being less diverse with only rare representatives of troodontids and a Dromaeosaurus-like taxon. We also provide evidence that erect and recurved morphs of a Richardoestesia-like taxon represent a single heterodont species. A late Maastrichtian assemblage is dominated by a distinct troodontid. The differences between northern and southern faunas based on isolated theropod teeth provide evidence for provinciality in the late Campanian and the late Maastrichtian of North America. However, there is no indication that major components of small-bodied theropod diversity were lost during the Maastrichtian in New Mexico. The same pattern seen in northern faunas, which may provide evidence for an abrupt dinosaur extinction

Palaeomacroecology: large scale patterns in species diversity through the fossil record

Palaeomacroecology is the study of large scale patterns of species diversity in the fossil record, encompassing a variety of subtopics. This thesis also addresses a variety of these subtopics, making it difficult to define under one heading.The first portion of the thesis deals with a new package of software tools for the analysis of large scale datasets, with a specific focus towards palaeoecology and palaeogeography. These software tools have been combined into a package called fossil that has been released on the Comprehensive R Archive Network (CRAN), and is already being used by other palaeoecologists. While the majority of these tools had a basis in previous statistical methods, I have also independently developed a clustering algorithm for use with biogeographic datasets. This clustering algorithm is relational, non-Euclidean and non-hierarchical and as such is called Non-Euclidean Relational Clustering (NERC). NERC eliminates several of the assumptions common to most other clustering methods that are often violated by biogeographic data.The next portion of my thesis describes a new Triassic aged flora from Axel Heiberg Island in Nunavut. Macroecological studies typically use large databases compiled from individual samples; therefore, these individual samples represent the foundation on which macroecological analyses rest, and collection and description of new fossil bearing sites is vital to the advancement of palaeomacroecology.Chapter 5 is an analysis of the provinciality and beta diversity of dinosaurs in the Late Cretaceous of North America. This analysis found that contrary to previous studies, dinosaur genera were widespread across the continent and not restricted to small geographic ranges. Chapter 6 is the final culmination of my thesis, and where I see palaeomacroecology headed in the future. It is an analysis of how latitudinal diversity gradients in plants have changed through time. The analysis assesses the impact of changing climate in creating and sustaining the latitudinal diversity gradient, and lends support to the idea that temperatures are important drivers of the gradient.The final chapter is a summary of where palaeomacroecology has been, and where its future work might be best focused. While the field of palaeontology is vital to our understanding of large scale, especially temporally, patterns of species diversity, the field of palaeontology has an opportunity to advance our understanding at an even more rapid pace provided we ask the appropriate questions of our data.La palaeomacroecology est l'etude des modeles a grande echelle de la diversite des especes dans les archives fossiles, et inclue une variete de sous-themes. Cette these adresse aussi une variete de ces sous-themes, ce qui en fait diffucult de definir sous une seule rubrique. La premiere partie de la these discute d'un nouvel ensemble d'outils logiciels pour l'analyse des ensembles de donnees a grande echelle, avec une attention particuliere a la paleoecologie et la paleogeographie. Ces outils logiciels ont ete combines dans un paquet appele fossil qui a ete publie sur le reseau Comprehensive R Archive Network (CRAN), et est deja utilise par d'autres palaeoecologists. Bien que la majorite de ces outils avait une base en preious methodes statistiques, j'ai aussi developpe independamment un algorithm de regroupement pour une utilisation avec des bases de donnees biogeographiques. Cet algorithme de regroupement est relationnelle, non-euclidienne et non-hierarchique et en tant que telle est appele Non-Euclidean Relational Clustering (NERC). NERC elimine plusieurs des hypotheses communes a la plupart des autres methodes de classification, et qui sont souvent violees par des donnees biogeographiques.La partie suivante de ma these decrit une nouvelle flore du Trias a l'ile Axel Heiberg, au Nunavut. Les etudes macroecologiques utilisent generalement de grandes bases de donnees compilees a partir des echantillons individuels et, par consequent, ces echantillons individuels representent le fondement del'analyse macroecologique, et la collecte et la description des nouveaux sites fossiliferes est indispensable a l'avancement de la palaeomacroecologie.Le Chapitre 5 est une analyse du provincialisme et de la diversite beta des dinosaures aux Cretace superieur en Amerique du Nord. Contrairement aux etudes precedentes, cette analyse a revele que les genres de dinosaures ont ete beaucoup plus repondus a travers le continent et ne se limitement pas a de petites aires geographiques. Le Chapitre 6 est l'aboutissement final de ma these, ou je vois dans quelle direction se dirige a la palaeomacroecologie. Il s'agit d'une analyse de la facon dont les gradients de diversite des plantes ont change au fil du temps. L'analyse evalue le role des changements climatiques dans la creation et le maintien du gradient latitudinal de diversite, et soutient l'idee que les temperatures sont d'importants moteurs de ce gradient.Le dernier chapitre resume l'evolution palaeomacroecologie dans quelle direction les travaux futurs devraient etre orientes. Bien que le domaine de la paleontologie sait vital pour notre comprehension des modeles de la diversite des especes a grande echelle, en particulier celle temporelle, le domaine de la paleontologie a une occasion de faire progresser notre comprehension a un rythme encore plus rapide, a condition de poser les bonnes questions

A comparison of clustering methods for biogeography with fossil datasets

Cluster analysis is one of the most commonly used methods in palaeoecological studies, particularly in studies investigating biogeographic patterns. Although a number of different clustering methods are widely used, the approach and underlying assumptions of many of these methods are quite different. For example, methods may be hierarchical or non-hierarchical in their approaches, and may use Euclidean distance or non-Euclidean indices to cluster the data. In order to assess the effectiveness of the different clustering methods as compared to one another, a simulation was designed that could assess each method over a range of both cluster distinctiveness and sampling intensity. Additionally, a non-hierarchical, non-Euclidean, iterative clustering method implemented in the R Statistical Language is described. This method, Non-Euclidean Relational Clustering (NERC), creates distinct clusters by dividing the data set in order to maximize the average similarity within each cluster, identifying clusters in which each data point is on average more similar to those within its own group than to those in any other group. While all the methods performed well with clearly differentiated and well-sampled datasets, when data are less than ideal the linkage methods perform poorly compared to non-Euclidean based k-means and the NERC method. Based on this analysis, Unweighted Pair Group Method with Arithmetic Mean and neighbor joining methods are less reliable with incomplete datasets like those found in palaeobiological analyses, and the k-means and NERC methods should be used in their place

Data from: The fragmentation of Pangaea and Mesozoic terrestrial vertebrate biodiversity

During the Mesozoic (242–66 million years ago), terrestrial regions underwent a massive shift in their size, position and connectivity. At the beginning of the era, the land masses were joined into a single supercontinent called Pangaea. However, by the end of the Mesozoic, terrestrial regions had become highly fragmented, both owing to the drifting apart of the continental plates and the extremely high sea levels that flooded and divided many regions. How terrestrial biodiversity was affected by this fragmentation and large-scale flooding of the Earth's landmasses is uncertain. Based on a model using the species–area relationship (SAR), terrestrial vertebrate biodiversity would be expected to nearly double through the Mesozoic owing to continental fragmentation, despite a decrease of 24% in total terrestrial area. Previous studies of Mesozoic vertebrates have generally found increases in terrestrial diversity towards the end of the era, although these increases are often attributed to intrinsic or climatic factors. Instead, continental fragmentation over this time may largely explain any observed increase in terrestrial biodiversity. This study demonstrates the importance that non-intrinsic effects can have on the taxonomic success of a group, and the importance of geography to understanding past biodiversity

Date/Publication 2012-03-30 07:54:11

Description A set of analytical tools useful in analysing ecological and geographical data sets, both ancient and modern. The package includes functions for estimating species richness (Chao 1 and 2, ACE, ICE, Jacknife), shared species/beta diversity, species area curves and geographic distances and areas

Supplementary_materials_S2

Complete R code for all analyses and figures used in the paper