Campanian Assemblages Research Articles

A systematic reappraisal and quantitative study of the nonmarine teleost fishes from the late Maastrichtian of the Western Interior of North America: evidence from vertebrate microfossil localities1

The diversity and distribution of nonmarine teleost fishes in the Western Interior of North America during the late Maastrichtian is documented based on isolated elements from vertebrate microfossil localities in the Hell Creek Formation of Montana, the Lance Formation of Wyoming, and the Scollard Formation of Alberta. A minimum of 20 taxa are recognized based on >1900 abdominal centra and tooth-bearing elements. These include two elopomorphs, six osteoglossomorphs, three ostariophysans, one esocid, six acanthomorphs, and two taxa of unknown relationships. These assemblages differ from late Campanian assemblages in the absence of the Clupeomorpha and the presence of the Perciformes. Within the Hell Creek Formation, we record patterns in the relative abundances of the most abundant taxa leading up to the Cretaceous–Paleogene (K–Pg) boundary. Most notably, acanthomorphs increased in abundance upsection, whereas a group of osteoglossomorphs, represented by Coriops and (or) Lopadichthys, concurrently decreased in abundance. Conversely, some teleosts exhibited more stable or slightly fluctuating relative abundances throughout the formation (Wilsonichthyidae, Esocidae). These late Maastrichtian teleost assemblages are of higher diversity than an early Eocene assemblage from Wyoming preserved under similar taphonomic conditions. This pattern suggests either that lower Cenozoic deposits in the Western Interior are insufficiently sampled or that the K–Pg mass extinction event adversely affected nonmarine teleosts.

Albanerpetontids (Lissamphibia, Albanerpetontidae) from the Aguja Formation (lower Campanian) of West Texas, USA

The Lowerverse local fauna of West Texas, USA, preserves a rare, early Campanian assemblage of microvertebrates from Laramidia. The recovery of 137 fragmentary specimens reveals that albanerpetontids were locally abundant here and also widespread throughout much of the Western Interior of North America by early Campanian time. Both gracile- and robust-snouted species are represented within the assemblage. Among these, the occurrence of Albanerpeton nexuosum is consistent with its occurrence in paracontemporaneous deposits elsewhere in the Western Interior. The referral of two specimens to Albanerpeton sp., cf. Albanerpeton galaktion, strongly suggests that this long-lived taxon was far more widespread during the early Campanian than previously known and its likely occurrence in West Texas represents a significant geotemporal range extension for the species. However, Albanerpeton gracile is seemingly restricted to Judithian “age” deposits in North America and was not identified at Lowerverse. The Lowerverse assemblage supports the current paradigm involving the occurrence of these three named albanerpetontids during middle Campanian – Maastrichtian time in the Western Interior of North America.

New taxa among a remarkably diverse assemblage of fossil squamates from the Aguja Formation (lower Campanian) of West Texas

A diverse microfauna from the lower shale of the Aguja Formation of West Texas records a rare, early Campanian assemblage of fossil squamates from North America. This assemblage is comprised of scincomorph, anguimorph, and ophidian taxa and is the most inclusive of its kind thus far described from the southern faunal province of Laramidia. Among numerous taxa described herein, three (Hypostylos lehmani gen. et sp. nov., Bothriagenys flectomendax sp. nov., and Hydrargysaurus gladius gen. et sp. nov) pertain to new scincomorphs which dominate the assemblage; however, subordinate anguimorphs are also well-represented. Snakes are represented by a single taxon, aff. Coniophis; a species seemingly ubiquitous throughout most Campanian strata in the southern Western Interior. Comparison among squamate assemblages from similar coastal facies in the upper shale of the Aguja Formation as well as the paracontemporaneous Wahweap and Kaiparowits formations of southern Utah reveals patterns of biogeographic segregation among some lizard species and the presence of two distinct communities. These two ‘southern’ squamate faunas are likely the result of variables involving climate and eustacy which facilitated diversity as well as the development of sub-provincial quarters of endemism during early-middle Campanian time.

ENSAMBLES DE MICROFÓSILES (FORAMINÍFEROS Y NANOFÓSILES CALCÁREOS) CRETÁCICOS DEL SUBSUELO DE LA CUENCA DE MAGALLANES, ISLA DE TIERRA DEL FUEGO, CHILE

Foraminifera and calcareous nannofossils were studied in washed drill-cuttings of three wells from the Chilean sector of the Magallanes Basin. This contribution aims to identify, characterize and illustrate microfossil assemblages throughout the Cretaceous sedimentary record to integrate foraminiferal and the nannofossil data and improve further biostratigraphic studies in the basin. The analyzed Cretaceous succession in these wells corresponds to five discrete foraminiferal and nannofossil assemblages, which were recognized and are described here. The Valanginian–Hauterivian assemblage is characterized by a low diversity of benthic foraminifera typical of this age, like Lenticulina nodosa and Astacolus gibber, and nannofossil markers Lithraphidites bollii and Eiffellithus striatus; then, the Aptian–Albian begins with a predominance of radiolarians and transitions into a highly diverse assemblage comprising mainly gavelinellid benthics as well as abundant planktic foraminifera, which include Muricohedbergella delrioensis and M. portsdownensis, and diverse calcareous nannofossils with the marker Sollasites falklandensis. The Cenomanian can be distinguished by the presence of the nannofossil Corollithion kennedyi and also abundant planktic foraminifers; whilst the Coniacian–Campanian assemblage is characterized by planktic foraminifera like Costellagerina bulbosa, C. pilula, and Planoheterohelix reussi, as well as a diverse benthos and the nannofossil species Reinhardtites anthophorus, Eiffellithus eximius, and Eprolithus floralis. Finally, the Maastrichtian assemblage is characterized by mainly agglutinated foraminifera and few poorly preserved nannofossils. A detailed systematic list of both foraminiferal and nannofossil species is presented, intended to serve as a catalogue that will help to identify the different Cretaceous assemblages of the basin in future studies.

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.

The impact of the Maastrichtian cooling on the marine nutrient regime—Evidence from midlatitudinal calcareous nannofossils

AbstractThe latest Campanian‐earliest Maastrichtian interval is well known as a period of intense climate cooling. This cooling caused a distinctive bipolar biogeographic distribution of calcareous nannofossil assemblages: High‐latitude settings were dominated by newly evolving endemic taxa, former cosmopolitan species disappeared at the same time, and equatorial communities experienced an invasion of cool water taxa. The impact of this cooling on northern midlatitude assemblages is, however, less well known. In order to overcome this gap we studied the Kronsmoor section (northwest Germany). This section provides a continuous upper Campanian—lower Maastrichtian succession with moderately to well preserved nannofossils. Uppermost Campanian assemblages are dominated by Prediscosphaera cretacea; other common taxa include Prediscosphaera stoveri, Watznaueria barnesiae, and Micula staurophora. The lower Maastrichtian is characterized by lower numbers of P. cretacea and frequent Kamptnerius magnificus, Arkhangelskiella cymbiformis, and Cribrosphaerella ehrenbergii. These changes reflect, in part, the Campanian‐Maastrichtian boundary cooling since some successful taxa (e.g., K. magnificus) are related to cool surface waters. Other shifts in the nannofossil communities were perhaps the result of a changing nutrient regime. Stronger latitudinal gradients may have increased wind velocities and thus the eolian input of ferruginous dust required by N‐fixing bacteria. The enhanced high‐latitude deep water formation probably changed the bottom water environment in disfavor of denitrificating organisms. A decline of chemical weathering and fluviatile transport may have reduced the amount of bioavailable phosphate. These processes led to an increased nitrate and a decreased phosphate content shifting the nutrient regime from nitrate toward phosphate limitation.

Planktonic foraminiferal biostratigraphy and quantitative analysis during the Campanian-Maastrichtian transition at the Oued Necham section (Kalâat Senan, central Tunisia)

The Oued Necham (ON) section (Kalâat Senan, central Tunisia) provides a well-exposed outcrop of a Campanian-Maastrichtian series that consists essentially of chalky limestones (i.e. the Abiod Formation) grading progressively to a marly unit (i.e. the El Haria Formation). The transitional Abiod-El Haria succession comprises a rich hemipelagic-pelagic fauna in the study area, but ammonites (e.g., Pachydiscus neubergicus, the Campanian/Maastrichtian (C/M) boundary index taxon) are scarce to absent, thus preventing the recognition of the standard zones defined for the Tethyan realm. However, the rich planktonic foraminiferal taxa of the El Haria Formation allow us to establish an accurate biostratigraphical scheme. Accordingly, this work presents a high-resolution planktonic foraminiferal biostratigraphy that is characterised by distinct bioevents associated with the reported C/M boundary (i.e. lowest occurrences (LOs) of Rugoglobigerina scotti and Contusotruncana contusa) at the Global Stratotype Section and Point (GSSP) of the Tercis-les-Bains section, south-western France. Based on these zonal markers, the rugoglobigerinids and multiserial heterohelicids are used to define a subzonal scheme spanning the standard Gansserina gansseri Zone, including the Rugoglobigerina rotundata Subzone indicative of the late Campanian and the Rugoglobigerina scotti Subzone and the Planoglobulina acervulinoides Subzone, respectively, indicative of the early Maastrichtian. The abundance of foraminiferal assemblages allowed us to carry out high-resolution quantitative analyses that document a significant climate cooling during the early Maastrichtian intermittent with short-term warming episodes. Thus, opportunist taxa (r strategists, mostly heterohelicids) thrived during the earliest Maastrichtian cooling event, whereas specialist taxa (k strategists, mostly double-keeled) that had dominated the late Campanian assemblages declined gradually without any extinction. Opportunist and specialist taxa fluctuated in opposite phases throughout the early Maastrichtian (LO of Rugoglobigerina scotti ? LO of Abathomphalus mayaroensis), suggesting essentially variations in water temperature. Since surface dwellers dominated the assemblages, they imply continuous sea surface optimal conditions of nutrient supply and water connectivity induced from upwelling currents.

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.

First occurrence of a tyrannosaurid dinosaur from the Mesaverde Group (Neslen Formation) of Utah: Implications for upper Campanian Laramidian biogeography

Although upper Campanian dinosaur assemblages are well-known from Alberta, Montana, southern Utah, and New Mexico, specimens from Wyoming and central and eastern Utah are very rare. This area constitutes a biogeographic break between northern and southern biogeographic provinces, so any specimens from this region are critical to understanding the origin, evolution, and limits of upper Campanian biogeographic zones on the west margin of the Western Interior Seaway. We report the discovery of a theropod dinosaur partial hindlimb from the Book Cliffs area northeast of Green River, Utah. The specimen was recovered from the Palisade coal zone in the Neslen Formation (Mesaverde Group), which is dated to the mid-Campanian based on ammonite biostratigraphy and radioisotopic age constraints. The specimen, comprising a partial fibula, the distal half of metatarsal II, a complete metatarsal IV, and a partial metatarsal V, can be assigned to Tyrannosauridae based on a number of synapomorphies, including a bipartite iliofibularis tubercle on the fibula and a teardrop shaped articular surface for metatarsal III on the medial surface of the distal portion of metatarsal IV. This is the first unambiguous tyrannosaurid dinosaur reported from the Mesaverde Group and represents an important biogeographic record situated between northern and southern upper Campanian vertebrate assemblages. Specifically, we identify morphological evidence on the pes that separates northern (Montana and Alberta) and southern (southern Utah and New Mexico) tyrannosaurid dinosaurs, and suggests that the Book Cliffs specimen belongs to the northern group. This implies that either the biogeographic boundary between the northern and southern Campanian assemblages lies somewhere between central and southern Utah or that the Book Cliffs taxon represents a northern emigrant in the southern assemblage.

Dinocyst biostratigraphy of Santonian-Maastrichtian formations of the Western Gulf Coastal Plain, southern United States

This palynological investigation of Santonian-Maastrichtian formations of Texas, U.S.A. consists of an examination of 82 outcrop samples from 19 stratigraphic sections exposed in 9 countries in a north-south trend from about Dallas to Kinney. The Austin Chalk Formation, the Taylor Group, and the lower Navarro Group are examined for palynological data. Most of the samples are rich in dinocysts assemblages. In a total assemblage of 163 palynomorphs species in 95 genera, 111 dinocyst species of 60 genera, 6 acritarch species of 5 genera, and 46 spore pollen species of 33 genera are recognized and their stratigraphic distribution documented. Systematic descriptions and illustrations of all dinocysts and acritarch taxa are given. Spore-pollen taxa occur sporadically in the studied sections and thus are only listed, illustrated and their occurrences noted in the text.
 The stratigraphic distribution of dinocysts species indicating the Santonian age can be recognized by the presence of Chatangiella granulifera, C. robusta, C. spectabilis, Phelodinium gaduatum and Spinidinium lanturnum. The characteristic species of Campanian assemblage are Cannosphaeropsis hyperacantha, C. utinensis, Ceratiopsis subquadra, Chattangiella armata, C. williamsii, Diconodinium martianum, Dinogymnium denticulatum, D. enclaense, D. nelsonense, Impagidinium cristatum, I. microarmum, Rottnestia borusstca, Triblastula utinensis and Xenascus gochtii.
 The appearance of the following dinocysts species viz., Andalusiella acicornula, Areoligera senonensis, Ceratiopsis navarriana, Glaphyrocysta retiintexia, Lejeunecysta decorinassa, L. byalina, Litosphaeridium fenestreconum, Palaeocystodinium australinum, Phelodinium tricuspe and Thalassiphora bononiensis in the Maastrichtian is significant.
 Pollen occurrences indicate that the land area, west of the Senonian epeiric sea, was terrigenous source in the Santonian and the Late Maastrichtian whereas the land on the east of the eperic sea was the source in the Campanian.