The oldest Cretaceous North American sauropod dinosaur

Sauropod dinosaurs have been found in sediments dating to most of the Cretaceous Period on all major Mesozoic landmasses, but this record is spatiotemporally uneven, even in relatively well-explored North American sediments. Within the 80 million-year-span of the Cretaceous, no definitive sauropod occurrences are known in North America from two ca. 20–25 million-year-long gaps, one from approximately the Berriasian–Barremian and the other from the mid-Cenomanian–late Campanian. Herein, we present an undescribed specimen that was collected in the middle part of the twentieth century that expands the known spatiotemporal distribution of Early Cretaceous North American sauropods, partially filling the earlier gap. The material is from the Berriasian–Valanginian-aged (ca. 139 Ma) Chilson Member of the Lakota Formation of South Dakota and appears to represent the only non-titanosauriform from the Cretaceous of North America or Asia. It closely resembles Camarasaurus and may represent a form closely related to that genus that persisted across the Jurassic–Cretaceous boundary.     

<Emphasis Type="Italic">Protungulatum</Emphasis>, Confirmed Cretaceous Occurrence of an Otherwise Paleocene Eutherian (Placental?) Mammal

Neither pre-Cenozoic crown eutherian mammals (placentals) nor archaic ungulates (“condylarths”) are known with certainty based on the fossil record. Herein we report a new species of the Paleocene archaic ungulate (“condylarth”) Protungulatum from undisputed Late Cretaceous aged rocks in Montana USA based on an isolated last upper premolar, indicating rare representatives of these common early Tertiary mammals appeared in North America a minimum of 300 k  years before the extinction of non-avian dinosaurs. The other 1200 mammal specimens from the locality are characteristic Late Cretaceous taxa. This discovery overturns the current hypothesis that archaic ungulates did not appear in North America until after the Cretaceous/Tertiary (K/T) boundary and also suggests that other reports of North American Late Cretaceous archaic ungulates may be correct. Recent studies, including ours, cannot determine whether Protungulatum does or does not belong to the crown clade Placentalia.     

Bite traces on dicynodont bones and the early evolution of large terrestrial predators

Nied?wiedzki, G., Gorzelak, P. & Sulej, T. 2010: Bite traces on dicynodont bones and the early evolution of large terrestrial predators. Lethaia, Vol. 44, pp. 87–92. Dicynodont (Synapsida: Anomodontia) bones from the Late Triassic (late Norian/early Rhaetian) of Poland yield characteristic tooth marks that can be attributed to three ichnotaxa (Linichnus serratus, Knethichnus parallelum and Nihilichnus nihilicus). The general shape and dimension of these traces perfectly match the dental morphology of a co‐occurring carnivorous dinosaur. It is therefore concluded that early carnivorous dinosaurs were feeding on dicynodonts. This discovery constitutes one of the oldest evidence of dinosaur predator–prey interaction. It is suggested that an evolutionary increase in the size of dicynodonts across the Late Triassic may have been driven by selection pressure to reach a size refuge from early dinosaur predators. □Bite traces, dicynodonts, dinosaurs, predation, Triassic.     

Rongements sélectifs des os par les porcs-épics et autres rongeurs : cas de la grotte Tianyuan, un site avec des restes humains fossiles récemment découvert près de Zhoukoudian (Choukoutien)

The Tianyuan cave near Zhoukoudian is among the most special localities in North China for its many porcupine gnawing marks on the bones, as is often the case acknowledged only in South China. But porcupines did not gnaw all the bones, that is gnawing is selective. Skulls, mandibles, tooth roots and long bones are frequently gnawed. The short bones are almost free from gnawing. The selection indicates that, for porcupines, bone gnawing is not only a necessity for attrition of incisors, but also a process of extracting nutrients from the marrow. Additionally, the porcupine gnawing marks can also be employed to determine the provenance of the fossils that were discovered by the local people before the systematic excavation. Those bearing porcupine tooth marks only appear in the upper assemblage. The other significance of the gnawing marks is to infer the habitant of the cave. The bones from the human fossil bearing layer have few tooth marks, which may represent a period of human occupation of the cave. In the upper assemblage, the gnawing marks appear frequently, it may indicate that porcupine and other rodents lived in the cave during this time span.     

A diagnosis of crocodile feeding traces on larger mammal bone, with fossil examples from the Plio-Pleistocene Olduvai Basin, Tanzania

Neotaphonomic studies have determined the patterns of bone damage created by larger mammalian carnivores when consuming mammalian carcasses. Typically, mammalian carnivores gnaw and break bones to various degrees in order to access marrow, grease, and brain tissue. In contrast, crocodiles attempt to swallow whole parts of mammal carcasses, inflicting in the process tooth marks and other feeding traces on some of the bones they are unable to ingest. Although crocodiles are major predators of larger mammals along the margins of protected tropical rivers and lakes, their feeding traces on bone have received little systematic attention in neotaphonomic research. We present diagnostic characteristics of Crocodylus niloticus damage to uningested mammal bones resulting from a series of controlled observations of captive crocodile feeding. The resulting bone assemblages are composed of primarily complete elements from articulating units, some of which bear an extremely high density of shallow to deep, transversely to obliquely oriented tooth scores over often large areas of the bone, along with shallow to deep pits and punctures. Some of the tooth marks (bisected pits and punctures, hook scores) have a distinctive morphology we have not observed to be produced by mammalian carnivores. The assemblages are also characterized by the retention of both low- and high-density bone portions, an absence of gross gnawing, and minimal fragmentation. Together, the damage characteristics associated with feeding by crocodiles are highly distinctive from those produced by mammalian carnivores. Modern surface bone assemblages along the Grumeti River in Tanzania's Serengeti National Park contain a mixture of specimens bearing damage characteristic of crocodiles and mammalian carnivores. Comparison of Plio-Pleistocene fossil bones from Olduvai Gorge, Tanzania, to bones damaged by captive and free-ranging Nile crocodiles reveals direct evidence of fossil crocodilian feeding from larger mammal bones associated with Oldowan stone artifacts.     

Cannibalism in Tyrannosaurus rex

Background

Tyrannosaurus rex was one of the largest terrestrial carnivores of all time, and consequently its ecology and diet have been the focus of much discussion. However, there is little direct evidence of diet or feeding habits in this species.

Methodology/Principal Findings

Examination of museum collections has revealed four specimens of Tyrannosaurus rex that bear tooth marks made by large, carnivorous dinosaurs. Because Tyrannosaurus is the only large carnivore known from the Late Maastrichtian of western North America, we infer that Tyrannosaurus made these tooth marks.

Conclusions/Significance

The marks are interpreted as feeding traces and these fossils therefore record instances of cannibalism. Given that this behavior has a low preservation potential, cannibalism seems to have been a surprisingly common behavior in Tyrannosaurus, and this behavior may have been relatively common in carnivorous dinosaurs.     

New Remains of the Multituberculate Mammal <Emphasis Type="Italic">Barbatodon</Emphasis> from the Upper Cretaceous of the Hațeg Basin (Romania)

The so-called “Ha?eg Island” (Transylvania, Romania) is well known for its rich and peculiar Late Cretaceous vertebrate assemblages, including dwarf dinosaurs, first reported at the end of the 19th century. Besides dinosaurs, other important members of the “Ha?eg Island” terrestrial ecosystems were the multituberculate mammals. Late Cretaceous (Maastrichtian) multituberculates are extremely rare in Europe, being known exclusively from the “Ha?eg Island.” Two genera are reported from this area: Kogaionon, with the single species K. ungureanui, and Barbatodon, with two species: B. transylvanicus and B. oardaensis. Both genera belong to the European endemic family Kogaionidae. We report herein new remains of B. transylvanicus from the Maastrichtian locality of Pui (Hunedoara District) in the Ha?eg Basin, including the most complete dentaries found to date with complete cheek teeth rows. Intraspecific variability of this species in dentary shape, tooth morphology, and size difference is highlighted.     

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 co-eval 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.     

Cretaceous small scavengers: feeding traces in tetrapod bones from Patagonia, Argentina

Ecological relationships among fossil vertebrate groups are interpreted based on evidence of modification features and paleopathologies on fossil bones. Here we describe an ichnological assemblage composed of trace fossils on reptile bones, mainly sphenodontids, crocodyliforms and maniraptoran theropods. They all come from La Buitrera, an early Late Cretaceous locality in the Candeleros Formation of northwestern Patagonia, Argentina. This locality is significant because of the abundance of small to medium-sized vertebrates. The abundant ichnological record includes traces on bones, most of them attributable to tetrapods. These latter traces include tooth marks that provde evidence of feeding activities made during the sub-aerial exposure of tetrapod carcasses. Other traces are attributable to arthropods or roots. The totality of evidence provides an uncommon insight into paleoecological aspects of a Late Cretaceous southern ecosystem.     

Evolutionary analysis of the middle and inner ear of Late Jurassic multituberculates

We describe three previously unreported specimens of petrosal bones of paulchoffatiid multituberculate mammals, collected from strata of Late Jurassic age in the Guimarota lignite mine of Leiria, west-central Portugal. The new fossils allow correction, supplementation, and confirmation of anatomical details, thus refining knowledge of general adaptation in the ear region among Jurassic multituberculates. Virtually all observed characters in the paulchoffatiid otic region are primitive relative to homologous features seen among Late Cretaceous and younger representatives of the Multituberculata; we recognize few unique otic specializations in paulchoffatiids that would preclude ancestry to later multituberculates. The plesiomorphic nature of paulchoffatiid ear regions provides no evidence in support of the hypothesis of a special, sister-group relationship between multituberculates and Late Cretaceous/Cenozoic marsupials plus placentals. Used in isolation, objective evidence derived from paulchoffatiid ear regions is consistent with interpretation of multituberculate divergence from other mammals predating the stem to living monotremes and postdating the stem to extinct morganucodontids. More broadly based comparative studies among Mesozoic mammals, however, suggest that independent acquisition of similarly advanced mammalian features was a pervasive theme among evolutionary histories of early mammals, probably including multituberculates. Although the phylogenetic position of multituberculates relative to other mammalian groups has yet to be unequivocally resolved, we suggest that a very early divergence of the group remains a distinct possibility.     

Difficulties in assigning trace makers from theropodan bite marks: an example from a young diplodocoid sauropod

Bite marks on the bones of dinosaurs are relatively rare for non‐tyrannosaur dominated faunas, and few have been described in detail. Here, we describe a femur of a young diplodocoid sauropod in the Carnegie Quarry (Late Jurassic Morrison Formation) at Dinosaur National Monument that shows extensive bite marks to the proximal part of the bone. This is the only record of bite marks from this extensive quarry of over 1500 vertebrate elements, making this a most unusual find. Identification of the tracemaker is difficult as multiple large theropods are known from the quarry. Furthermore, we show that subtly different actions of feeding can potentially result in very different spacing of bite marks making matches to tooth patterns in the jaws of potential bite makers very uncertain. Although identification is uncertain, the tracemaker is clearly not a tyrannosaurid, but the selective scrape feeding pattern seen here is similar to the of tyrannosaurid theropods. This technique may be more widely distributed among large carnivorous theropods than previously realized.     

Armored dinosaurs(Ornithischia: Ankylosauria)) from the Middle and Upper Jurassic of England

Hitherto the earliest positive record of ankylosaurs(armored dinosaurs) has been from beds well up in the Lower Cretaceous; in fact, however, specimens referable to the ankylosaurian family Nodosauridae are present in the Middle and Upper Jurassic of England: from the Middle Callovian [partial mandible Sarcolestes leedsiLydekker]], the Upper Oxfordian [femur Cryptodraco eumerus (Seeley)), maxilla Priodontognathus phillipsii (Seeley))], and the Upper Tithonian [caudal vertebra, tooth]. The Tithonian tooth and those of Priodontognathus are large and similar to those of the nodosaurids Priconodon and Sauropelta (Lower Cretaceous, U.S.A.). The incomplete mandible of Sarcolestes is similar to that of Sauropelta with a dermal scute fused to the lateral surface, and a tooth row extending to the anterior end of the jaw; an unusual feature is the caniniform first tooth. The quadrupedal ankylosaurs and stegosaurs probably represent separate evolutionary lines that extend back at least into the Lower Jurassic, and both lines probably evolved from ornithopod dinosaurs that were bipedal. Nodosaurid ankylosaurs occur in Europe from the Middle Jurassic to Late Cretaceous and probably reached North America via a filter route in the early Cretaceous.     

A tyrannosauroid dinosaur from the Upper Jurassic of Portugal

Fragmentary theropod remains from the Upper Jurassic (Kimmeridgian) of Guimarota, Portugal, represent a new taxon of theropod dinosaurs, Aviatyrannis jurassica gen. et sp. nov. Together with Stokesosaurus from the Morrison Formation of North America, Aviatyrannis represents the oldest known tyrannosauroid, indicating that tyrannosauroid origins may be found in the Middle–Late Jurassic of Europe/North America. Furthermore, current evidence suggests that early tyrannosaurs were rather small animals, which is in general accordance with their origin amongst the generally rather small coelurosaurs.     

Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic heterodontosaurid from North America

The extremes of dinosaur body size have long fascinated scientists. The smallest (<1 m length) known dinosaurs are carnivorous saurischian theropods, and similarly diminutive herbivorous or omnivorous ornithischians (the other major group of dinosaurs) are unknown. We report a new ornithischian dinosaur, Fruitadens haagarorum, from the Late Jurassic of western North America that rivals the smallest theropods in size. The largest specimens of Fruitadens represent young adults in their fifth year of development and are estimated at just 65–75 cm in total body length and 0.5–0.75 kg body mass. They are thus the smallest known ornithischians. Fruitadens is a late-surviving member of the basal dinosaur clade Heterodontosauridae, and is the first member of this clade to be described from North America. The craniodental anatomy and diminutive body size of Fruitadens suggest that this taxon was an ecological generalist with an omnivorous diet, thus providing new insights into morphological and palaeoecological diversity within Dinosauria. Late-surviving (Late Jurassic and Early Cretaceous) heterodontosaurids are smaller and less ecologically specialized than Early (Late Triassic and Early Jurassic) heterodontosaurids, and this ecological generalization may account in part for the remarkable 100-million-year-long longevity of the clade.     

A New European Marsupial Indicates a Late Cretaceous High-Latitude Transatlantic Dispersal Route

The first record of an undoubted opossum-like marsupial from the Mesozoic of Europe indicates an invasion from North America at the end of Late Cretaceous (Maastrichtian). The new 66.1 million-year-old marsupial, Maastrichtidelphys meurismeti n. gen., n. sp., represented by a right upper molar, comes from the type Maastrichtian of The Netherlands. The Maastricht marsupial exhibits affinities with earlier (early Maastrichtian) North American herpetotheriids providing definitive evidence of a high-latitude North Atlantic dispersal route between North America and Europe during the latest Cretaceous. Previously, the first major interchange for marsupials was thought to have occurred nearly 10 million years later in the Eocene. The occurrence of this new marsupial in Europe implies that at some time during the latest Cretaceous, sea level and climatic conditions must have been sufficiently favorable to allow for such a high-latitude dispersal. The fragmentary remains of hadrosaurid and theropod dinosaurs, as well as boid snakes from northwestern Europe which have affinities with North American taxa help substantiate assumptions made by the occurrence of the herpetotheriid marsupial in Maastricht.     

Additional dinosaur teeth from the Cenomanian (Late Cretaceous) of Charentes,southwestern France

Some isolated teeth of theropod and sauropod dinosaurs from the Cenomanian (Late Cretaceous) of Charentes are described. Two new teeth of Troodontidae confirm the presence of this theropod family, previously based on a single specimen. New dental morphotypes are recognized within Dromaeosauridae and Brachiosauridae in comparison with those already known from Charentes. Lastly, a very small tooth is tentatively assigned to an embryonic or neonatal sauropod. The palaeobiogeographical history of European hadrosauroids is briefly discussed. This history was probably more complex than it appears, involving exchanges with both North America and Asia as early as the mid-Cretaceous (Albian–Cenomanian).     

A second hadrosauroid dinosaur from the early Late Cretaceous of Zuoyun,Shanxi Province,China

A second basal hadrosauroid dinosaur, Zuoyunlong huangi gen. et sp. nov., is reported from the early Late Cretaceous Zhumapu Formation in Zuoyun County, Shanxi Province, northern China. Zuoyunlong preserves a partial right ilium and ischium and is unique in having a very short postacetabular process 50% as long as the iliac central plate. Our cladistic analysis recovers Zuoyunlong as the most basal Late Cretaceous hadrosauroid, with a sister taxon relationship with Probactrosaurus from the late Early Cretaceous of Inner Mongolia. Including Zuoyunlong, four Cenomanian basal hadrosauroids have been recorded, and the two taxa in North America (Eolambia and Protohadros) represent the earliest known hadrosauroids outside of Asia. In the light of the proposed phylogenetic topology and biogeographic data, the discovery of Zuoyunlong indicates that the first dispersal of hadrosauroids from Asia to North America probably happened around the boundary between the Early and Late Cretaceous.     

The origin and early evolution of metatherian mammals: the Cretaceous record

Metatherians, which comprise marsupials and their closest fossil relatives, were one of the most dominant clades of mammals during the Cretaceous and are the most diverse clade of living mammals after Placentalia. Our understanding of this group has increased greatly over the past 20 years, with the discovery of new specimens and the application of new analytical tools. Here we provide a review of the phylogenetic relationships of metatherians with respect to other mammals, discuss the taxonomic definition and diagnosis of Metatheria, outline the Cretaceous history of major metatherian clades, describe the paleobiology, biogeography, and macroevolution of Cretaceous metatherians, and provide a physical and climatic background of Cretaceous metatherian faunas. Metatherians are a clade of boreosphendian mammals that must have originated by the Late Jurassic, but the first unequivocal metatherian fossil is from the Early Cretaceous of Asia. Metatherians have the distinctive tightly interlocking occlusal molar pattern of tribosphenic mammals, but differ from Eutheria in their dental formula and tooth replacement pattern, which may be related to the metatherian reproductive process which includes an extended period of lactation followed by birth of extremely altricial young. Metatherians were widespread over Laurasia during the Cretaceous, with members present in Asia, Europe, and North America by the early Late Cretaceous. In particular, they were taxonomically and morphologically diverse and relatively abundant in the Late Cretaceous of western North America, where they have been used to examine patterns of biogeography, macroevolution, diversification, and extinction through the Late Cretaceous and across the Cretaceous-Paleogene (K-Pg) boundary. Metatherian diversification patterns suggest that they were not strongly affected by a Cretaceous Terrestrial Revolution, but they clearly underwent a severe extinction across the K-Pg boundary.     

“South American” Marsupials from the Late Cretaceous of North America and the Origin of Marsupial Cohorts

Newly described marsupial specimens of Judithian (late Campanian) and Lancian (Maastrichtian) age in the western interior of North America (Wyoming to Alberta) have dental morphologies consistent with those expected in comparably aged sediments in South America (yet to be found). Three new Lancian species are referable to the didelphimorphian Herpetotheriidae, which suggests that the ameridelphian radiation was well under way by this time. The presence of a polydolopimorphian from Lancian deposits with a relatively plesiomorphic dental morphology and an additional polydolopimorphian taxon from Judithian deposits with a more derived molar form indicate that this lineage of typically South American marsupials was diversifying in the Late Cretaceous of North America. This study indicates that typical South American lineages (e.g. didelphimorphians and polydolopimorphians) are not the result of North American peradectian progenitors dispersing into South America at the end of the Cretaceous (Lancian), or at the beginning of the Paleocene (Puercan), and giving rise to the ameridelphian marsupials. Instead, these lineages, and predictably others as well, had their origins in North America (probably in more southerly latitudes) and then dispersed into South America by the end of the Cretaceous. Geophysical evidence concerning the connections between North and South America in the Late Cretaceous is summarized as to the potential for overland mammalian dispersal between these places at those times. Paleoclimatic reconstructions are considered, as is the dispersal history of hadrosaurine dinosaurs and boid snakes, as to their contribution to an appraisal of mammalian dispersals in the Late Cretaceous. In addition, we present a revision of the South American component of the Marsupialia. One major outcome of this process is that the Polydolopimorphia is placed as Supercohort Marsupialia incertae sedis because no characteristics currently known from this clade securely place it within one of the three named marsupial cohorts.     

On the earliest record of Cretaceous tyrannosauroids in western North America: implications for an Early Cretaceous Laurasian interchange event

The sudden appearance of Asian dinosaur clades within Lower Cretaceous strata of western North America has long been recognised as a biotic dispersion event related to initial establishment of a Beringian land bridge. To date, uncertainty exists regarding the timing of the Early Cretaceous Laurasian interchange event (EKLInE) and the pattern of associated biotic dispersal. Here, we report a tyrannosauroid premaxillary tooth (FMNH PR 2750) from the Cloverly Formation, Wyoming, USA, that pushes back the earliest Cretaceous record of the clade in North America. Although fragmentary, the tooth is consistent with mounting evidence for a pre-108 Ma initiation of EKLInE and earliest Albian emplacement of Beringia. Previous authors have considered the Aptian/Albian of western North America a depauperate dinosaur fauna, characterised by regional extinction and diversity decline. Documentation of Albian tyrannosauroids in the region indicates a more dynamic ecosystem than previously appreciated and marks an early start to faunal mixing between immigrant and endemic dinosaur clades. Finally, we find that the enamel microstructure of FMNH PR 2750 conforms to the morphotype of tyrannosaurids, yet exhibits poor columnar differentiation. This morphology bolsters prior interpretations on the phylogenetic utility of enamel microstructure and suggests a trend of increasing enamel complexity within Tyrannosauroidea.