The Lower Miocene (Aquitanian to ?lower Burdigalian) type locality of the Wiesbaden Formation in the northern region of the Mainz Basin (abandoned 'Kalkofen Quarry', Wiesbaden, State of Hesse, Germany) is known to reveal a regressive- dominated sequence encompassing marine, brackish to terrestrial sediments. Our documentation of this depositional setting includes a detailed sedimentological description, geochemical study and palynological analysis of the succession. Our new data suggest significant environmental turnovers such as changes in the siliciclastic fraction and variation from arid to warm humid climatic conditions. Based on macroscopic fossil evidence, we suggest the presence of an autochthonous mangal root system- bearing horizon, with a lateral extent of over 200 sq. m in the uppermost limestone bed of the sequence. Consistent with this, our geochemical analyses indicate subtropical climatic conditions within a marginal marine environment just before the silting up of the coastline. The almost monospecific mass occurrence of hydrobiid gastropods within the root horizon, as well as the algal buildups outcropping in the underlying strata, further point towards a marginal marine to brackish environment, probably with episodic hypersaline conditions. Palynological analysis revealed no mangrove pollen but point to warm and humid climatic conditions. This is the first indication that mangal environments may have existed along the Early Miocene coastline of the northwestern Mainz Basin.

Late Jurassic–earliest Cretaceous (Kimmeridgian–earliest Berriasian) marine shelf sediments in northeastern Mexico reveal repeated temperature-related oceanic and biotic turnovers in the northwestern proto-Gulf of Mexico. Our detailed geochemical analysis of four sections crossing the Jurassic-Cretaceous (J/K) boundary is based on chemostratigraphic correlation and repeated mollusk assemblage changes reflecting significant environmental fluctuations, including sea level and marine redox conditions. The present study confirms tectonic tilting and rapid drowning of shallow-water environments in the early Kimmeridgian, associated with the near-synchronous spread of bottom-water anoxia in shelf areas bordering the proto-Gulf of Mexico. Boreal cold-water faunal elements are associated with a sea-level drop in the late Kimmeridgian, while a transient transgressive-regressive phase is interpreted for the shelf transect in the earliest Tithonian. A general transgressional trend is reported for the Tithonian and across the J/K boundary, while the migration into the area of boreal and austral high-latitude faunal elements marks specific intervals. We hypothesize that oscillations in the oceanic current system were responsible for the intermittent establishment of cold-water boreal and austral faunal assemblages in the northwestern proto-Gulf of Mexico.

Our research on Late Jurassic–earliest Cretaceous (Kimmeridgian–earliest Berriasian) marine shelf to bathyal sediments in northeastern Mexico reveals significant repeated oceanic and biotic turnovers in the northwestern Proto-Gulf of Mexico. We here document these environmental changes based on alternating cold and warm water mollusk assemblages, element concentrations and organofacies, as well as associated changes in sea level. We hypothesize that oscillations in the oceanic current system of the Gulf of Mexico were responsible for appearance of cold-water assemblages of Boreal and possibly Austral origins, situated in specific horizons which were previously described as poor in fossil content or even as fossil-free. In addition, these specific horizons show significant changes in element concentrations and organofacies and correlate to relative sea-level changes.

Here, we report on an incomplete human skeleton, soot patches related to anthropogenic fireplaces, and cut marks on the mandible of an extinct peccary, from the submerged Muknal cave southwest of Tulum on the Mexican Yucatán peninsula. The human individual, here named ‘Muknal Grandfather’, was identified as a male based on cranial parameters. The age at the time of death was estimated to be between 40 and 45 years. We propose that the human bones have been brought to the cave during the latest Pleistocene or early Holocene, but not later than 8600 14C yr BP (ca. 9600 cal BP), as a secondary burial of a partial skeleton. The peccary mandible was placed close to the burial site, possibly as part of the same ritual. The Muknal cave therefore served as a place for funeral rituals.

We here report on a type of meter-sized pendant speleothem growing under water in the submerged El Zapote sinkhole (cenote) west of Puerto Morelos on the Mexican Yucatán Peninsula. These conical, mantle-shaped downward expanding and diverging calcareous structures, here termed as Hells Bells, are yet unreported in the scientific literature. They are characterized by bell- or trumpet shaped longitudinal and circular, elliptical or horse-shoe-like horizontal cross-sections. Hells Bells grow downward, based on the downward divergence of the structures and the horizontally laminated internal texture of both blade-shaped spar calcite and microspar laminae. Age dating confirms that Hells Bells are young (<4500yr) and formed in a subaquatic environment. They grow under lightless conditions in a stratified water body, which is characterized by a fresh water body overlying a salt water body with a stagnant transition zone (halocline) of several meters. We hypothesize that the growth of these structures is mediated by specific physical and biogeochemical conditions above and in the halocline. Stagnant hydraulic conditions led to extensive diffusion profiles of several nutrients including calcium originating from the salt water body. Dissolved organic carbon from the fresh water is microbially oxidized in the upper part of the halocline, where a distinct redox zonation was identified from oxic to anoxic conditions. Degradation processes combined with slightly alkaline pH values as well as the diffusive transport of calcium into this zone may induce an increase in calcite oversaturation. Phylogenetic analysis of the community on the surface of the Hells Bells suggests the presence of microorganisms involved in the nitrogen-cycle, from which some potentially have the capability to increase the pH by autotrophic growth and denitrifying activity, thus supporting calcite precipitation. The growth of Hells Bells is strictly dependent on the elevation of the halocline. This offers a wide potential for the use of Hells Bells as archives of paleo-hydrological conditions during the Holocene, e.g. the variation of thickness of the fresh water lens on the Yucatán Peninsula.

ABSTRACTNumerous charcoal accumulations discovered in the submerged Chan Hol cave near Tulum, Quintana Roo, Mexico, have been 14C‐dated revealing ages between 8110 ± 28 14C a BP (9122–8999 cal a BP) and 7177 ± 27 14C a BP (8027–7951 cal a BP). These charcoal concentrations, interpreted here as ancient illumination sites, provide strong evidence that the Chan Hol cave was dry and accessible during that time interval. Humans used the cave for at least 1200 years during the early and middle Holocene, before access was successively interrupted by global sea level rise and flooding of the cave system. Our data thus narrow the gap between an early settlement in the Tulum area reaching from the late Pleistocene (∼13 000 a) to middle Holocene (e.g. 7177 14C a BP), and the Maya Formative period at approximately 3000 a bp. Yet, no evidence has been presented to date for human settlement during the ∼4000‐year interval between 7000 and 3000 a. This is remarkable as settlement in other areas of south‐eastern Mexico (e.g. Chiapas, Tabasco) and in Guatemala was apparently continuous.

Preceramic human skeletal remains preserved in submerged caves near Tulum in the Mexican state of Quintana Roo, Mexico, reveal conflicting results regarding 14C dating. Here we use U-series techniques for dating a stalagmite overgrowing the pelvis of a human skeleton discovered in the submerged Chan Hol cave. The oldest closed system U/Th age comes from around 21 mm above the pelvis defining the terminus ante quem for the pelvis to 11311±370 y BP. However, the skeleton might be considerable older, probably as old as 13 ky BP as indicated by the speleothem stable isotope data. The Chan Hol individual confirms a late Pleistocene settling of Mesoamerica and represents one of the oldest human osteological remains in America.

Here we describe a new genus and species of giant ground sloth, Xibalbaonyx oviceps (Megalonychidae, Xenarthra), from the drowned cave system of the northeastern Yucatán Peninsula. The specimen is Late Pleistocene in age and was discovered in the Zapote sinkhole (cenote) near Puerto Morelos in the Mexican state of Quintana Roo. Xibalbaonyx oviceps differs significantly from all hitherto known Megalonychidae including those from the Greater Antilles and South America. The new taxon suggests a local Caribbean radiation of ground sloths during the Late Pleistocene, which is consistent with the dispersal of the group along a Mexican corridor.

Based on material from the uppermost Tithonian La Caja Formation at Puerto Piñones, northeastern Mexico, the complete ontogenetic development (protoconch to adult) of the ammonite Salinites grossicostatum is outlined by a detailed morphometrical shell analysis. The embryonic stage, consisting of a small ellipsoid protoconch and ammonitella, ends at about 0.6 mm. Four major morphological changes are differentiated throughout ontogeny based on internal features such as reduced septal spacing and siphuncle position. Sexual dimorphism is reflected by shell size, siphuncular diameter, differences in the morphology of the apophysis, and by two distinct general trends in septal spacing. In addition, macroconchs are characterized by septal crowding at different stages, followed by the return to normal septum distances. Our analysis indicates a change in the mode of life after the neanic stage. A change in habitat preference is inferred for adult individuals. While microconchs persisted at Puerto Piñones, large mature macroconchs temporarily migrated to other areas, possibly for egg deposition. Salinites grossicostatum is endemic to the ancient Gulf of Mexico and is there restricted to outer continental shelf environments.

Two unique localities that combine an unusual diversity of avian, pterosaurian, and dinosaur tracks as well as trails of arthropods were recently discovered by us in uppermost Maastrichtian siliciclastic sediments of the Las Encinas Formation in the Mexican state of Coahuila, similar to 40 km north of Saltillo. The trackway assemblages at Amargos and -Rancho San Francisco were produced by at least six different types of birds, while trackways of azhdarchoid pterosaurs are rare. Only a single footprint was produced by a nonavian theropod. A diverse ichnofauna of arthropod traces is also present in a different facies. The tetrapod trackway assemblage was deposited during the very latest Maastrichtian, as indicated by an up to 2.5-mthick unit with abundant smectite spherules attributed to the Chicxulub impact less than 8.5 m stratigraphically up section at Amargos. Sphenodiscus pleurisepta is the last ammonite at Amargos and may have crossed the Cretaceous-Paleogene boundary.

Here we describe the left mandibular ramus of a fossil peccary from the submerged karst cave system in the southeastern Mexican state of Quintana Roo. The specimen, which was discovered in the Muknal cave northwest of Tulúm, is a new genus and species of peccary termed Muknalia minima. The taxon likely dates from the latest Pleistocene and differs significantly from all extant peccaries and their Pleistocene relatives by a concave notch at the caudal edge of the mandibular ramus and prominent ventrally directed angular process. These diagnostic osteological differences suggest that the masticatory apparatus differed from all other peccaries, which may hint to an ecological isolation on the late Pleistocene Yucatán Peninsula.

Based on our taxonomic revision of the ammonite Salinites grossicostatum from the uppermost Tithonian of the La Caja Formation at Puerto Pinones, in the state of Coahuila, northeastern Mexico, we suggest that some specimens described from other Tithonian sites of Cuba and Mexico assigned to S. grossicostatum belong to a new species, here presented as S. finicostatum. Salinites grossicostatum and S. finicostatum sp. nov. are endemic to the ancient Gulf of Mexico and are restricted to outer continental shelf environments.

A coral-rich Berriasian unit locally known as the San Juan Lentil conforms the basal Taraises Formation in the San Juan canyon located half distance between the cities of Saltillo and Monterrey in northeastern Mexico. Here we document the environmental conditions and discuss its regional distribution of this biostrome unit. Calpionellids are intermittently present and indicate a middle to late Berriasian age for the coral-bearing unit that was deposited during an interval of increased oligotrophic conditions.

Five taxa of Kimmeridgian to Tithonian (Upper Jurassic) aptychi are here described from the La Caja Formation of northeastern Mexico. Laevaptychus (Latuslaevaptychus) latus meyrati Trauth, 1931, L. (Hoplisuslaevaptychus) mexicanus (Castillo and Aguilera, 1895), L. (Autharislaevaptychus) favrei Trauth, 1931, Lamellaptychus lamellosus (Parkinson, 1811) and Lam. murocostatus Trauth, 1929 were previously known from the Tethyan Realm. In northeastern Mexico, records of Lamellaptychus are restricted to the upper lower Kimmeridgian-lower upper Tithonian, while Laevaptychus is presently restricted to the uppermost Kimmeridgian-uppermost Tithonian.

Here we present evidence for a semi-sessile early juvenile stage of ammonites. Our hypothesis is based on fossil evidence in early diagenetic limestone concretions discovered in platy limestone deposits of Cenomanian age in the northern state of Coahuila, Mexico. In these locations densely packed post-embryonic shell assemblages were attached to fossilized algal or bacterial mats and preserved in sediments deposited under permanently anoxic bottom conditions. Tiny ammonites, as well as gastropods and byssate pectinid bivalves are abundant and restricted to these mats. They do not occur elsewhere in the sediment. The ammonite hatchlings were apparently unable to escape from mats sinking to the hostile sea floor and must thus have been semi-sessile, similar to the associated gastropods and bivalves.

Here we provide a detailed description of the upper Campanian sediment succession at Las Aguilas, southern Coahuila, northeastern Mexico, including the first absolute age dating for this interval, paleoenvironmental reconstructions and taphonomic observations on the abundant dinosaur remains at the locality. Stratigraphic investigations of the dinosaur-bearing succession at the Las Aguilas vertebrate fossil area near Porvenir de Jalpa reveal a diverse vertebrate assemblage, including dinosaurs, crocodilians and turtles. New findings in adjacent sites include eusuchian crocodylomorphs, four different kinds of turtles, dromaeosaurids, lambeosaurines, pterosaurs and elasmosaurid plesiosaurs. Strontium isotope measurements on fossil oyster shells provide an absolute age of 73 +/- 1 Ma for the lower part of the Las Aguilas section. The locality is thus of late Campanian age. The vertebrate, invertebrate and plant materials as well as the sediment structures observed in a 50 m thick predominantly siliciclastic succession of the Cerro del Pueblo Formation suggest deposition in an extensive delta plain environment. The fades succession indicates a short-termed cyclicity of limnic, brackish and shallow marine environments during the late Campanian-early Maastrichtian Cerro del Pueblo Formation with numerous layers containing dinosaur fossil remains. (C) 2015 Elsevier B.V. All rights reserved.

Ammonites, bivalves and calpionellids of the late Berriasian-early Valanginian from southern Mexico are poorly known; those here described are from the Sabinal Formation at Santa Catarina Ticuá, Oaxaca state. Samples were collected and analyzed bed-by-bed. Ammonite assemblages correlate to the West Mediterranean late Berriasian Subthurmannia boissieri and early Valanginian Thurmanniceras pertransiens and Neocomites neocomiensiformis zones and contain taxa, which are majorly endemic, although a few European species are also identified. The bivalve Arctotis cretacea (Felix, 1891) is common in several horizons throughout the section. Calpionellids are present in the upper part of the Santa Catarina Ticuá section and are indicative of the middle Berriasian Remaniella cadischiana Subzone, the late Berriasian Calpionellopsis Zone (including the Calpionellopsis simplex and Cs. oblonga subzones) and the early Valanginian Calpionellites darderi Subzone. Our data indicate that biogeographic correlation of faunal and environmental changes is possible across the Berriasian–Valanginian boundary between southern Mexico and faunal realms of the southwestern Gulf of Mexico and the western Tethys, and thus throughout the western hemisphere.

Here we present two early Kimmeridgian faunal assemblages composed of the ammonite Idoceras (Idoceras pinonense n. sp. and I. inflatum Burckhardt, 1906), Boreal belemnites Cylindroteuthis cuspidata Sachs and Nalnjaeva, 1964 and Cylindroteuthis ex. gr. jacutica Sachs and Nalnjaeva, 1964, as well as the Boreal bivalve Buchia concentrica (J. de C. Sowerby, 1827). The assemblages were discovered in inner- to outer shelf sediments of the lower La Casita Formation at Puerto Pinones, southern Coahuila, and suggest that some taxa of Idoceras inhabited cold-water environments.