Vertebrate Microfossil Research Articles

Paleoecology and sedimentology of a vertebrate microfossil assemblage from the easternmost Dinosaur Park Formation (Late Cretaceous, Upper Campanian,) Saskatchewan, Canada: Reconstructing diversity in a coastal ecosystem

A ~42 m section of Late Cretaceous Upper Campanian sediments in Saskatchewan Landing Provincial Park, southwestern Saskatchewan, Canada, represents the easternmost outcrop of the Dinosaur Park Formation in the Western Interior Basin. Herein we document a new microvertebrate locality from the upper part of this formation that shows high diversity in a mixed coastal and marine assemblage. Palynology, ichnology, sedimentology, and vertebrate palaeontology are integrated to determine paleoenvironmental and paleoecological conditions in the region. The site is interpreted as having been deposited under marginal-marine conditions near a shoreline undergoing transgression by the encroaching Bearpaw Sea. Though well studied and sampled in Alberta, the Dinosaur Park Formation is poorly exposed with little known associated vertebrate assemblages in Saskatchewan. These discoveries from the new microvertebrate site offer new insights into Late Cretaceous ecosystems near paleocoastlines, allowing for future studies of spatial diversity patterns relative to Albertan faunas. Herein is also presented the first published occurrences of several Late Campanian vertebrate taxa in Saskatchewan.

A new hybodont shark (Chondrichthyes, Elasmobranchii) from the Upper Triassic Tiki Formation of India with remarks on its dental histology and biostratigraphy

AbstractA new lonchidiid genus,Pristrisodus, from the Upper Triassic Tiki Formation of India is described based on multiple, well-preserved, isolated teeth. Comparative analysis resulted in synonymizingParvodus tikiensisandLissodus duffini,which are known from the same horizon and resulted in a new taxon,Pristrisodus tikiensisn. comb. These teeth are elongated with mesiodistal length greater than or equal to twice the labiolingual width and have a high principal cusp, lateral cusplets, a distinct ridge near the crown-root junction labially and higher up on the crown lingually, weak ornamentation, and linear depression along the crown-root junction. Five morphotypes based on overall shape, robustness and crown height are determined. The teeth show a gradual monognathic heterodonty. The anterolateral teeth (morphotypes I−II) have high, pyramidal principal cusp with two or three small but pointed cusplets, and triangular labial and lingual protuberance. The posterolateral teeth (morphotypes III−IV) have four incipient cusplets, relatively low principal cusp, bilobed/rounded, hanging labial and incipient lingual protuberances. Morphotype V comprises anterior teeth that are broad, triangular and robust, and have rounded/blunt principal cusp, one cusplet, and low, hanging labial peg. Multivariate analyses corroborate the qualitative assessment of the Indian hybodonts. Dental histology ofPristrisodusn. gen., shows that it is distinctly different from other lonchidiid genera. The assemblage of freshwater sharks, along with other vertebrate microfossils of the Tiki Formation, shows similarity with that of the lower Tecovas Formation of the Chinle Group, USA. The euryhaline nature resulted in the adaptation of the hybodonts to freshwater systems in India during the Carnian.

Erratum: Non-marine fishes of the late Santonian Milk River Formation of Alberta, Canada – evidence from vertebrate microfossil localities

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Non-marine fish of the late Santonian Milk River Formation of Alberta, Canada – evidence from vertebrate microfossil localities

The diversity of fishes from the late Santonian Milk River Formation is investigated using a combined taxonomic/morphotype approach. Twenty-one taxa are present, including four elasmobranchs, seven basal actinopterygians, and of ten teleosts. The Milk River fish assemblage is more similar to assemblages from southern Utah than it is to the late Campanian assemblage of Alberta in the presence of the elasmobranch Lonchidion and a member of amiid subfamily Vidalamiinae, the relatively high abundance of the ostariophysan teleost U3/BvD, and the absence of sturgeon, Holostean A, Holostean B, and Coriops. This similarity is hypothesized to be the result of a northern shift in the distribution of these taxa during times of high global temperature, resulting in the presence of a “southern” faunal assemblage in Alberta during the late Santonian. In the relative abundance patterns of major groups of fish, the Milk River Formation assemblage is similar to late Campanian assemblages and different from those of late Maastrichtian in that amiids and lepsisoteids are of relatively low abundance. The abundance of acanthomorph teleosts in the Milk River Formation is similar to that of contemporaneous assemblages from Utah, which supports a pattern of increasing abundance of acanthomorphs from their first occurrence in non-marine vertebrate assemblages of the Western Interior in the Coniacian through to the end of the Cretaceous.

Techniques for Systematic Collection and Processing of Vertebrate Microfossils from their Host Mudrocks: A Case Study from the Upper Triassic Tiki Formation of India

ABSTRACT Vertebrate microfossils are valuable entities for the reconstruction of ancient ecosystems but difficult to find without using microscopes, resulting in a collection bias towards the macrofossils, which are easily visible to the naked eyes. The current study gives a comprehensive description of the protocols applied for systematic exploration and extraction of vertebrate microfossils. Initial assessment of the microsites for fossil-richness is carried out by spot sampling using coning and quartering, which is a technique applied for the first time. Subsequently, lithologs are prepared to ascertain the microfossil-bearing stratum, bulk samples are collected, screened by wet and dry sieving methods and residues examined under a microscope for extraction of vertebrate microfossils. These well-designed procedures are systematically applied for collection of vertebrate microfossils from the Upper Triassic Tiki Formation of the Rewa basin. More than 8000 kg of Tiki mudrocks collected as bulk samples, have yielded a rich and diverse array of vertebrate microfossils. The fauna incorporates different types of fresh water sharks, bony fishes, small temnospondyls, and varied r eptiles such as the archosauriforms, lepidosauromorphs, and cynodonts. These findings highlight the efficiency of the proposed methodology.

Isotaphonomy in concept and practice: an exploration of vertebrate microfossil bonebeds in the Upper Cretaceous (Campanian) Judith River Formation, north-central Montana

AbstractVertebrate microfossil bonebeds (VMBs)—localized concentrations of small resilient vertebrate hard parts—are commonly studied to recover otherwise rarely found small-bodied taxa, and to document relative taxonomic abundance and species richness in ancient vertebrate communities. Analyses of taphonomic comparability among VMBs have often found significant differences in size and shape distributions, and thus considered them to be non-isotaphonomic. Such outcomes of “strict” statistical tests of isotaphonomy suggest discouraging limits on the potential for broad, comparative paleoecological reconstruction using VMBs. Yet it is not surprising that sensitive statistical tests highlight variations among VMB sites, especially given the general lack of clarity with regard to the definition of “strict” isotaphonomic comparability. We rigorously sampled and compared six VMB localities representing two distinct paleoenvironments (channel and pond/lake) of the Upper Cretaceous Judith River Formation to evaluate biases related to sampling strategies and depositional context. Few defining distinctions in bioclast size and shape are evident in surface collections, and most site-to-site comparisons of sieved collections are indistinguishable (p≤0.003). These results provide a strong case for taphonomic equivalence among the majority of Judith River VMBs, and bode well for future studies of paleoecology, particularly in relation to investigations of faunal membership and community structure in Late Cretaceous wetland ecosystems. The taphonomic comparability of pond/lake and channel-hosted VMBs in the Judith River Formation is also consistent with a formative model that contends that channel-hosted VMBs were reworked from pre-existing pond/lake assemblages, and thus share taphonomic history.

Late Cretaceous (Maastrichtian) Chondrichthyes and Osteichthyes from northeastern Iberia

Intensive sampling for vertebrate microfossils has yielded abundant fish remains in the Maastrichtian units of the Tremp Formation (southern Pyrenees, Catalonia, Spain). Samples were taken from eight new sites representing different palaeoenvironments including coastal wetlands and floodplains, in order to assess the fish diversity and to gain a better understanding of the last dinosaur-dominated ecosystems of northeastern Spain. The results suggest that a diverse ichthyofauna inhabited these transitional to inland fluvial settings throughout the Maastrichtian, comprising both marine and freshwater taxa. Three different chondrichthyans, eight basal neopterygians and at least seven teleostean species were found, the latter being more diverse than in other Maastrichtian localities in Europe. Fossil evidence from the studied late Maastrichtian assemblages suggests that teleosteans were present in all the trophic guilds. In addition, the oldest records for osteoglossids and perciforms in Europe, as well as for cypriniforms worldwide, are reported here. The findings from the southern Pyrenees also reveal ichthyofaunal turnover during the Late Cretaceous, with ‘holosteans’ being replaced by teleosteans. Moreover, Maastrichtian ichthyofaunas from the southern Pyrenees show Asian and North American biogeographical affinities.

Assessing the fidelity of marine vertebrate microfossil δ18O signatures and their potential for palaeo-ecological and -climatic reconstructions

Conodont biogenic apatite has become a preferred analytical target for oxygen isotope studies investigating ocean temperature and palaeoclimate changes in the Palaeozoic. Despite the growing application in geochemically-based palaeoenvironmental reconstructions, the paucity or absence of conodont fossils in certain facies necessitates greater flexibility in selection of robust oxygen-bearing compounds for analysis. Vertebrate microfossils (teeth, dermal denticles, spines) offer a potential substitute for conodonts from the middle Palaeozoic. Vertebrate bioapatite is particularly advantageous given a fossil record extending to the present with representatives across freshwater to fully marine environments, thus widening the scope of oxygen isotope studies on bioapatite. However, significant tissue heterogeneity within vertebrates and differential susceptibility of these tissues to diagenetic alteration have been raised as potential problems affecting the reliability of the oxygen isotope ratios as palaeoclimatic proxies. Well-preserved vertebrate microfossils and co-occurring conodont fossils from the Upper Devonian and Lower Carboniferous of the Lennard Shelf, Canning Basin, Western Australia, were analysed using bulk (gas isotope ratio mass spectrometry, GIRMS) and in-situ (secondary ion mass spectrometry, SIMS) methodologies, with the latter technique allowing investigation of specific tissues within vertebrate elements. The δ18Oconodont results may be interpreted in terms of palaeolatitudinally and environmentally sensible palaeo-salinity and -temperature and provide a baseline standard for comparison against vertebrate microfossil δ18O values. Despite an absence of obvious diagenetic modification, GIRMS of vertebrate denticles yielded δ18O values depleted in 18O by 2–4‰ relative to co-occurring conodonts. SIMS analysis of dentine tissues exhibited significant heterogeneity, while hypermineralised tissues in both scales and teeth produced δ18O values comparable with those of associated conodonts. The susceptibility of permeable phosphatic fossil tissues to microbial activity, fluid interaction and introduction of mineral precipitates post-formation is demonstrated in the dentine of vertebrate microfossils, which showed significant heterogeneity and consistent depletion in 18O relative to conodonts. The hypermineralised tissues present in both teeth and scales appear resistant to many diagenetic processes and indicate potential for palaeoclimatic reconstructions and palaeoecological investigations.

Species Discrimination of Co-Occurring Small Fossil Mammals: A Case Study of the Cretaceous-Paleogene Multituberculate Genus Mesodma

The mammalian fossil record is largely composed of isolated teeth and tooth-bearing elements. In vertebrate microfossil assemblages with closely related, co-occurring species of mammals, it can be difficult to identify isolated teeth to species level because morphological differences among species may be slight and based on a single tooth position. Here we investigate the utility of the allegedly diagnostic lower fourth premolar (p4) for species-level identification in the genus Mesodma (Multituberculata, Neoplagiaulacidae). We conducted linear and geometric morphometrics on 86 p4s representing four Cretaceous-Paleogene (K-Pg) species of Mesodma that are common in deposits of the western interior of North America. Although Mesodma has been extensively discussed in the literature, these four species overlap considerably in p4 size and shape, making species-level identifications challenging. Using linear measurements, landmarks, and semilandmarks, we quantified p4 size and shape to understand morphological variation across the genus and uncover practical sources of morphological differentiation among the species represented here. Our results indicate (1) size is more important than shape for identifying p4s of Mesodma species; p4 shape varies across the genus, but cannot be used alone to identify isolated p4s to species; (2) M. garfieldensis and M. thompsoni cannot be distinguished from each other using p4 size or shape; we therefore subsume M. garfieldensis within M. thompsoni; and (3) M. formosa increased in size across the K-Pg boundary. In light of these results, we recommend that taxonomic diagnoses relying on isolated teeth incorporate quantitative analyses of morphology whenever possible to increase the accuracy of species-level identifications and paleofaunal studies that employ them.

New articulated osteoglossomorph from Late Cretaceous freshwater deposits (Maastrichtian, Scollard Formation) of Alberta, Canada

ABSTRACTArticulated fishes are rare in Late Cretaceous non-marine deposits of the Western Interior; fishes are more often represented by disarticulated elements in vertebrate microfossil localities. A new Maastrichtian locality of the Scollard Formation in central Alberta, Canada, has been named Pisces Point to reflect the diversity of articulated fishes that are now being recovered from this site. Material collected from the Pisces Point locality includes a percopsiform, a semionotiform, at least one esociform, and at least two osteoglossomorphs. One of these is described here as a new genus and species, †Wilsonichthys aridinsulensis. A phylogenetic analysis shows this new taxon to be the sister group of most other Osteoglossiformes. The new articulated material allows us to identify some of the microfossil remains previously collected from other Late Cretaceous sites as belonging to the same or a similar taxon.http://zoobank.org/urn:lsid:zoobank.org:pub:C35449C0-5711-4618-9084-177ADA83FEE7Citation for this article: Murray, A. M., M. G. Newbrey, A. G. Neuman, and D. B. Brinkman. 2016. New articulated osteoglossomorph from Late Cretaceous freshwater deposits (Maastrichtian, Scollard Formation) of Alberta, Canada. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1120737.

New insights into Europe’s most diverse Late Cretaceous anuran assemblage from the Maastrichtian of western Romania

Uppermost Cretaceous (Maastrichtian) continental deposits in the Transylvanian region of western Romania contain a diverse and important assemblage of fossil vertebrates, including lissamphibians. Bones of anurans (frogs) and albanerpetontids are abundantly represented at multiple vertebrate microfossil localities in the region, but there continues to be no evidence for urodeles (salamanders) at any locality. Using previously reported and new collections of isolated bones, here we provide an up-to-date and comprehensive account of the anuran component of the Romanian assemblage, with particular emphasis on new specimens exhibiting features that are informative for differentiating species and resolving their higher level affinities. We recognise at least five species belonging to two or three families of moderately primitive (i.e. non-neobatrachian), crown-clade anurans: the alytids Paralatonia transylvanica, cf. Bakonybatrachus sp. and cf. Eodiscoglossus sp.; the bombinatorid Hatzegobatrachus grigorescui; and an indeterminate, possible pelobatid. Ilia previously reported as cf. Paradiscoglossus (a monotypic alytid genus reliably known only from the Maastrichtian of western North America) are here referred to Paralatonia. Also present are indeterminate alytids and at least two potentially distinctive, but indeterminate, taxa of uncertain family affinities. New specimens allow Hatzegobatrachus, formerly regarded as incertae sedis, to be assigned to Bombinatoridae as the geologically oldest member of that family. The Romanian Maastrichtian anuran assemblage is the most diverse yet documented for the European Late Cretaceous. It contains a mix of endemic taxa (Paralatonia and Hatzegobatrachus), a relict taxon (cf. Eodiscoglossus sp.), and one taxon (cf. Bakonybatrachus) possibly resulting from a pre-Maastrichtian dispersal from present-day Hungary. Compared to contemporaneous and older (Santonian–Campanian) anuran assemblages elsewhere in Europe, the Romanian assemblage is similar in containing alytids and a pelobatid-like taxon, but differs in having more alytid taxa (n = 3) and a bombinatorid, and in lacking the palaeobatrachids seen in the Campanian–Maastrichtian of Western Europe and the probable ranoid Hungarobatrachus reported from the Santonian of Hungary.

Vertebrate paleontology of the Cloverly Formation (Lower Cretaceous), II: Paleoecology

ABSTRACTVertebrate microfossil assemblages in terrestrial formations are a promising source of data on the structure of fossil metacommunities. However, the degree to which these deposits capture true, metacommunity-level samples is unknown. Individual deposits may be biased in ways that limit their utility for intra- and inter-formation comparisons. This study describes the composition of ten vertebrate microfossil assemblages collected from the Lower Cretaceous Cloverly Formation in Montana and Wyoming, U.S.A., and evaluates whether the assemblages are sufficiently similar to suggest the presence of a single Cloverly metacommunity, or ‘paleocommunity type.’ The assemblages appear to be biased by factors related to the preferential incorporation and preservation of different taxa and skeletal element types, which compound with decreasing locality sample size. Less productive localities lack whole taxonomic groups, especially small, fully terrestrial vertebrates. Only the two vertebrate microfossil bonebeds approach the known formation richness. High individual tooth counts overrepresent particular species, especially the crocodylians. Despite these biases, the multiple assemblages nevertheless yield statistically similar taxon abundance rank orders, suggesting the presence of a single, formation-wide paleo-metacommunity, which bears resemblance to a viable metacommunity. The aggregate assemblage exhibits an ‘Eltonian pyramid’ trophic hierarchy for both terrestrial and aquatic taxa. Comparing the multiple assemblages synoptically also reveals possible landscape-scale abundance patterns for particular species. Taken together, microvertebrate assemblages offer insight into regional paleo-metacommunities and provide samples for inter-formational comparisons at this level.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Carrano, M. T., M. P. J. Oreska, and R. Lockwood. 2016. Vertebrate paleontology of the Cloverly Formation (Lower Cretaceous), II: Paleoecology. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1071265.

A vertebrate microsite from a marine-terrestrial transition in the Foremost Formation (Campanian) of Alberta, Canada, and the use of faunal assemblage data as a paleoenvironmental indicator

Vertebrate microfossil assemblages contain abundant fossil material of small and large bodied animals recruited from the local paleocommunity that can provide important information for reconstructing regional paleoecology. The Foremost Formation is the oldest unit of the Belly River Group, and records the transition from the fully marine shales of the Pakowki Formation to the non-marine strata of the relatively well-sampled Oldman and Dinosaur Park formations. Although the Foremost Formation has relatively limited exposure and vertebrate fossil material is not abundant, it does contain some important early records of major vertebrate clades from Laramidia (e.g. ceratopsids, pachycephalosaurids).Here we document a new microfossil locality from the upper part of the formation that shows a transitional assemblage containing an abundance of terrestrial forms such as dinosaurs and other sauropsids, while still showing considerable marine influence. The proportion of marine taxa at this site is reduced relative to most sites known from the Foremost Formation, though much higher than more terrestrial sites of the overlying Oldman Formation. In addition to filling a gap in our understanding of this paleoenvironmental transition, this new site preserves two particularly significant specimens: a large, complete, cephalic spine of the hybodont shark Hybodus, and jaw fragments from the ratfish Elasmodus. This represents the first known complete cephalic spine of a hybodont shark from the Cretaceous of Alberta. The ratfish jaw fragments represent the first published record of this group from the Foremost Formation, further increasing our knowledge of chondrichthyan diversity in the Western Interior Seaway. Comparisons of this site to other microsites from the Campanian of Alberta demonstrate the utility of certain key groups, such as lissamphibians and chondrichthyans, in determining paleoenvironments from Mesozoic and Cenozoic vertebrate microsite assemblage data.

Geological setting of vertebrate microfossil localities across the Cretaceous–Paleogene boundary in southwestern Saskatchewan, Canada

The Frenchman and Ravenscrag formations of southwestern Saskatchewan, Canada, record an apparently continuous sequence of nonmarine clastic sediments across the Cretaceous–Paleogene (K–Pg) boundary. Extensive exposures of these fossil-rich sediments occur in the Frenchman River Valley, near the towns of Ravenscrag, Eastend, and Shaunavon, and have been a focus of study since the 1970s. Despite this long history of investigation, a comprehensive account of the geographic and stratigraphic positions of many of the significant fossil localities has yet to be published. Given this state of affairs, the goals of this paper are to (i) document the geographic locations, stratigraphic positions, and lithologies of 11 key vertebrate microfossil localities, including several new localities that have been recently discovered, and (ii) provide an update on the status of these fossil localities, the majority of which have not been sampled in the last 20 years. Four fossil localities are known from the lower Paleocene Ravenscrag Formation, all of which are Puercan in age: Rav W-1 (Pu2), French Fry (Pu1), Croc Pot (?Pu2), and Pine Cree (?Pu2). With the exception of Rav W-1, which has since been lost as a consequence of quarry reclamation, all of the Ravenscrag Formation localities remain accessible and continue to be productive. Seven vertebrate microfossil localities from the upper Maastrichtian Frenchman Formation are reported here, all of which are Lancian in age: Long Fall, Fr-1, By Gar Gap, Hairpin, Wounded Knee, Wounded C, and Gryde. With the exception of Long Fall and Wounded Knee, which have been lost through reclamation or construction, all of the Frenchman Formation localities are accessible and remain productive.

An edentulous frog (Lissamphibia; Anura) from the Upper Cretaceous (Campanian) Dinosaur Park Formation of southeastern Alberta, Canada

The frog Tyrrellbatrachus brinkmani, gen. et sp. nov., is described on the basis of seven incomplete maxillae from vertebrate microfossil localities in the Upper Cretaceous (Campanian) Dinosaur Park Formation, in the Dinosaur Provincial Park area, southeastern Alberta, Canada. The maxillae are distinctive in a unique suite of features related to size, shape, and proportions of the bone, texture of the labial surface, form of the surface for inferred contact with the squamosal, form of the lamina horizontalis and the processus pterygoideus, relative depth of the crista dentalis, and in being edentulous (i.e., lacking teeth). The higher level affinities of Tyrrellbatrachus are uncertain, although certain features exclude it from several known families; for example, the presence of a processus pterygoideus excludes it from Gobiatidae (Late Cretaceous, Asia), whereas the presence of a crista dentalis and of a relatively unreduced pars facialis exclude it from Pipidae (Cretaceous–Recent, Africa and South America). The lack of teeth in Tyrrellbatrachus is notable because although tooth loss is widespread among extant anurans and has arisen independently multiple times, it has rarely been documented among Mesozoic anurans. Comparisons with the only other edentulous anuran from the Mesozoic of the Northern Hemisphere, namely Theatonius (late Campanian – late Maastrichtian, western USA), reveal no compelling similarities to support a close relationship between the two genera. Those taxa represent an early (Campanian) instance of independent tooth loss in anurans and, potentially, the oldest record of tooth loss in nonpipid anurans.

Vertebrate microfossils from the Upper Freshwater Molasse in the Swiss Molasse Basin: Implications for the evolution of the North Alpine Foreland Basin during the Miocene Climate Optimum

Abstract The older part of the Upper Freshwater Molasse (OSM) in the Swiss and South German Molasse Basin records the extended warm period known as the Miocene Climate Optimum. However, dating and global correlation of fossils and palaeoclimatic data from OSM sediments remains challenging, because sections are often incomplete and biostratigraphic data sometimes ambiguous. Here we present the rare case of a fossiliferous OSM section that can be securely dated to the late Early Miocene and early Middle Miocene ( c . 16.1–15.7 Ma). Vertebrate microfossils have been recovered from three levels in superposition. Fish teeth document primary freshwater fishes (Cyprinidae, Channidae), but otoliths found in the middle level indicate dominance of euryhaline fishes (Cyprinodontiformes, Gobiiformes). The herpetofaunal assemblages largely consist of taxa that were widely distributed in Central Europe during the Miocene Climate Optimum and fragments of turtle eggshells assignable to the Oofamily Testudoolithidae Hirsch, 1996. The small-mammal fauna is dominated by the cricetid Megacricetodon bavaricus Fahlbusch, 1964. The fossil biota implies that the lowermost level (late Early Miocene, c . 16.1 Ma) represents a palaeo-soil that formed under humid conditions, while the levels above it (early Middle Miocene, c . 15.7–15.8 Ma) record a warm freshwater pond subject to evaporation (middle level), and mean annual temperature ≥ 17 °C in the vicinity of a river with an open hinterland (upper level). Our results, together with previous data, suggest that the palaeoclimate of the North Alpine Foreland Basin of Switzerland and Southwest Germany was humid during the late Early Miocene and earliest Middle Miocene, and that the Middle Miocene onset of seasonality and low mean annual precipitation occurred by c . 15.7–15.8 Ma. We conclude that global climate change and the 100-kyr orbital eccentricity minimum at 15.75 Ma may have triggered the decrease in humidity in the North Alpine Foreland Basin.

Mammalian femora across the Cretaceous–Paleogene boundary in eastern Montana

Our understanding of latest Cretaceous and earliest Paleogene mammalian evolution is based almost entirely on the dental fossil record. Mammalian postcranial fossils are rare and mostly found as isolated elements in latest Cretaceous and earliest Paleogene vertebrate microfossil assemblages of North America. Although placing these fossils in a tooth-based taxonomic framework is difficult, they can provide insight into locomotor diversity and habitat preference to complement diet reconstructions and diversity estimates from dental fossils. Here, we describe 64 femora of mammals recovered from latest Cretaceous (Lancian) and earliest Paleogene (Puercan) localities in eastern Montana. We sorted these based on morphology and size (morphotypes). In some cases, morphotypes were tentatively assigned to dentally based taxa that are known from these strata.Although our resulting femoral dataset is small relative to the study area's dental dataset, we show several key findings. First, there is a greater morphological diversity of multituberculate femora than previously recognized, especially in the latest Cretaceous sample. In contrast, metatherians, which have a high relative abundance in Lancian Hell Creek Formation dental assemblages, are absent from our postcranial samples; eutherian femora are only present in the Puercan assemblages. Second, we record a minor decrease in morphotype richness across the K–Pg boundary that is associated with an increase in mean specimen size, due to the appearance of a few significantly larger-bodied, immigrant taxa. Among the eutherians, there are two specimens of larger-bodied early Puercan archaic ungulates, a very large specimen of a middle/late Puercan taeniodont, pantodont, or triisodontid, as well as a specimen possibly attributed to a “plesiadapiform” archaic primate. Third, preliminary functional morphologic analyses of the more complete specimens suggest that locomotor diversity increased from mainly arboreal or terrestrial/saltatorial multituberculates in the latest Cretaceous to include a fossorial multituberculate and potentially an arboreal eutherian in the early Paleocene. These patterns parallel those previously reported from a dental dataset and indicate that postcranial data are valuable as an independent means to test hypotheses of taxonomic and ecomorphological diversity across the K–Pg boundary.

Vertebrate paleontology of the Cloverly Formation (Lower Cretaceous), I: faunal composition, biogeographic relationships, and sampling

ABSTRACT The vertebrate fauna of the Cloverly Formation has been studied for more than 75 years, but remains poorly sampled and incompletely understood. We undertook an extensive survey of the formation that resulted in the discovery of several new, highly productive vertebrate microfossil bonebeds (VMBs). Comprehensive sampling of these and other sites has nearly doubled the known vertebrate diversity of the Cloverly Formation. In addition to the comparatively well-known dinosaurs, this augmented faunal list includes hybodontoid sharks, numerous bony fishes, three lissamphibian lineages, lizards, multiple crocodylians, and several new mammal occurrences. The known Cloverly vertebrate fauna now more closely resembles those of other late Early Cretaceous formations in North America, indicating broad similarities across wide geographic areas at this time. In addition, this work underscores the important role VMBs can play in areas previously studied primarily through surface prospecting and quarrying, especially for assessing paleoecology and species diversity.

Multivariate Analyses of Small Theropod Dinosaur Teeth and Implications for Paleoecological Turnover through Time

Isolated small theropod teeth are abundant in vertebrate microfossil assemblages, and are frequently used in studies of species diversity in ancient ecosystems. However, determining the taxonomic affinities of these teeth is problematic due to an absence of associated diagnostic skeletal material. Species such as Dromaeosaurus albertensis, Richardoestesia gilmorei, and Saurornitholestes langstoni are known from skeletal remains that have been recovered exclusively from the Dinosaur Park Formation (Campanian). It is therefore likely that teeth from different formations widely disparate in age or geographic position are not referable to these species. Tooth taxa without any associated skeletal material, such as Paronychodon lacustris and Richardoestesia isosceles, have also been identified from multiple localities of disparate ages throughout the Late Cretaceous. To address this problem, a dataset of measurements of 1183 small theropod teeth (the most specimen-rich theropod tooth dataset ever constructed) from North America ranging in age from Santonian through Maastrichtian were analyzed using multivariate statistical methods: canonical variate analysis, pairwise discriminant function analysis, and multivariate analysis of variance. The results indicate that teeth referred to the same taxon from different formations are often quantitatively distinct. In contrast, isolated teeth found in time equivalent formations are not quantitatively distinguishable from each other. These results support the hypothesis that small theropod taxa, like other dinosaurs in the Late Cretaceous, tend to be exclusive to discrete host formations. The methods outlined have great potential for future studies of isolated teeth worldwide, and may be the most useful non-destructive technique known of extracting the most data possible from isolated and fragmentary specimens. The ability to accurately assess species diversity and turnover through time based on isolated teeth will help illuminate patterns of evolution and extinction in these groups and potentially others in greater detail than has previously been thought possible without more complete skeletal material.

Theropod teeth from the upper Maastrichtian Hell Creek Formation “Sue” Quarry: New morphotypes and faunal comparisons

Isolated teeth from vertebrate microfossil localities often provide unique information on the biodiversity of ancient ecosystems that might otherwise remain unrecognized. Microfossil sampling is a particularly valuable tool for documenting taxa that are poorly represented in macrofossil surveys due to small body size, fragile skeletal structure, or relatively low ecosystem abundance. Because biodiversity patterns in the late Maastrichtian of North American are the primary data for a broad array of studies regarding non-avian dinosaur extinction in the terminal Cretaceous, intensive sampling on multiple scales is critical to understanding the nature of this event. We address theropod biodiversity in the Maastrichtian by examining teeth collected from the Hell Creek Formation locality that yielded FMNH PR 2081 (the Tyrannosaurus rex specimen “Sue”). Eight morphotypes (three previously undocumented) are identified in the sample, representing Tyrannosauridae, Dromaeosauridae, Troodontidae, and Avialae. Notice...