A recently discovered site in southern Mississippi considered early Arikareean based on identified mammals represents the first of this age from the Gulf Coastal Plain outside of Florida. The Jones Branch Local Fauna was recovered from deltaic/estuarine deposits low in the Catahoula Formation resting unconformably on marl/clay beds of the subjacent, upper Rupelian (lower Oligocene), marine Paynes Hammock Formation. In addition to well-preserved plant material plus reptiles, amphibians, and fishes, the mammals are represented primarily by species previously known almost exclusively from the Great Plains, the northern Rocky Mountains (Montana), and/or John Day region, Oregon, with only a few apparently endemic to the Gulf Coastal Plain. Genera representative of the former include the proscalopid Mesoscalops, the sciurid Hesperopetes, the aplodontiid Downsimus, the putative early castoroid Eutypomys, the castorid Microtheriomys, the eomyids Apeomys and Leptodontomys, the florentiamyid Kirkomys, the mustelids Corumictis and Promartes, the tapir Protapirus, the leptochoerid Leptochoerus, the anthracothere Elomeryx, and the hornless ruminants Hypertragulus and ?Leptomeryx. Mesoscalops, Downsimus, and Apeomys are represented by new species. Additionally, a new genus and species of lagomorph is described, Oligolagus welleri, as is a new genus and new species of eomyid, Paraktioeomys palmeri. Known from both regions is the marsupial Herpetotherium, an apatemyid provisionally referred to Sinclairella, and the borophagine Phlaocyon. Gulf Coastal Plain endemics include the protoceratid Prosynthetoceras orthrionanus and apparently Oligolagus n. gen. and Paraktioeomys n. gen. The geographically broadly distributed horse Miohippus, rhinoceros Diceratherium, and giant entelodont Daeodon are also present. Marine mammals are represented by the dugong Crenatosiren olseni and the odontocete Agorophius pygmaeus. Additionally noted are two taxa from stratigraphically lower formations that are not part of the Jones Branch LF. These include a large species of the entelodont Archaeotherium and the anthracothere Elomeryx armatus, both of which were previously unknown along the Gulf Coastal Plain. The long recognized biotic disparity between the Midcontinent and Gulf Coastal Plain by the early Miocene was not yet strongly apparent during the early to middle Oligocene.UUID: http://zoobank.org/c1b57f31-4ed1-42fb-bf31-c803e2e61cfd

Isolated elasmobranch and teleost teeth, jaws, otoliths, scales, vertebrae, and fin spines were recovered from the upper Oligocene (Chattian) Catahoula Formation in Wayne County, Mississippi, USA. A total of 13 551 specimens were examined and 12 340 of these were identified at least to the ordinal level. These remains represent 49 unequivocal fish taxa, viz. 29 elasmobranchs and 20 teleosts. The 3614 elasmobranch remains indicate that Carcharhiniformes is the most diverse group of Elasmobranchii, with 12 taxa belonging to five families. Orectolobiformes and Lamniformes are represented by far fewer taxa (three and four, respectively). Carcharhinus acuarius (Probst, 1879) constitutes 49% of the total number of shark teeth in our sample. Ten batoids have been identified within Myliobatiformes (seven taxa) and Rhinopristiformes (three taxa). Partial teeth of durophagous myliobatids (three genera) are the most abundant batoid remains, constituting 41% of the total number of ray fossils. However, teeth of Dasyatidae and Rhynchobatus cf. pristinus (Probst, 1877) are abundant and represent 36.5% and 15.4%, respectively, of the specimens identified. Herein, we erect five new elasmobranch taxa, including Galeocerdo platycuspidatum sp. nov., Hemipristis intermedia sp. nov., Hypanus? heterodontus sp. nov., “Sphyrna” gracile sp. nov., and “Sphyrna” robustum sp. nov. The Catahoula Formation sample includes over 9935 teleost fossils, which constitutes 73% of the total fish sample. Nine bony fish taxa are represented solely by teeth, jaw elements, or fin spines. Although otoliths are much less common than the other identifiable remains (409 versus roughly 8430, respectively), they allowed us to identify four taxa not known from other skeletal remains. Albulidae, Sciaenidae, and Sparidae are represented by isolated teeth, jaw elements, and otoliths, but we could not ascertain whether the various teeth and jaw elements are conspecific with the otolith-based species we identified. The remains of Sciaenidae (teeth, jaw elements, otoliths) dominate the Catahoula Formation bony fish assemblage, constituting 70% of the teleost specimens identified at least to the ordinal level. Our sample includes the first Oligocene occurrence of Tetraodontidae in the Western Hemisphere. The vertebrate assemblage within the Catahoula Formation at the study site indicates an estuarine depositional environment, which is consistent with previous interpretations based on lithology. At the study site the Catahoula Formation disconformably overlies the Paynes Hammock Limestone, and we believe the disconformable contact locally represents the Rupelian (early Oligocene)/Chattian (late Oligocene) boundary. The fish fauna described herein is therefore of Chattian age.

The extent to which the Cretaceous-Paleogene (K-Pg) extinction event impacted decapod crustaceans has yet to be tested rigorously due to a lack of studies at the outcrop scale. We comprehensively describe an early but not earliest Danian assemblage from Mussel Creek, central Alabama, United States, based on collecting of decapod carapaces and appendage remains at the roadcut part of this site since 2010. The specimens were recovered chiefly from silty, micaceous mudstones of the Pine Barren Member within the Clayton Formation, c. 8 m above the K-Pg boundary. Microfossil analysis indicates that the decapods originate from the lower middle part of the NP2 nannofossil zone, c. 600-700 ka after the K-Pg boundary. Based on 354 identifiable specimens, we recognize eight species: 1) four Brachyura: Alahexapus martini (Feldmann, Schweitzer & Portell, 2014) n. comb., Costacopluma nicksabani n. sp., Raninoides danicus n. sp., and an indeterminate representative of Palaeoxanthopsidae Schweitzer, 2003; 2) three Axiidea: Alphacheles zeta (Rathbun, 1936) n. comb., Ctenocheles sp., and Eucalliaxiopsis alabamensis (Rathbun, 1935a) n. comb.; and 3) one Paguroidea: "Paguristes" johnsoni Rathbun, 1935a. Two new genera are described: Alahexapus n. gen. and Alphacheles n. gen. The assemblage is dominated by specimens of C. nicksabani n. sp. (52% of identifiable specimens) and E. alabamensis n. comb. (31%). Three specimens of C. nicksabani n. sp. preserve rare gonopods. A rarefaction analysis indicates that (nearly) all species were collected. This assemblage represents the most diverse early Danian decapod assemblage from North America thus far, and provides a basis for further study of decapods across the K-Pg boundary.

This study provides the first focused investigation of rudist bivalves from the Upper Cretaceous of the Gulf Coastal Plain (GCP) in the southern US and previously undescribed specimens from the Flor de Alba Limestone Member of the Pozas Formation in Puerto Rico. Identified rudists from the GCP comprise the Monopleuridae, including Gyropleura, as well as Radiolitidae, including Biradiolites cardenasensi, Durania maxima, Guanacastea jamaicensis, Radiolites acutocostata, and Sauvagesia. Integrating rudist occurrences within well-established GCP biostratigraphy allows for extension of upper ranges of D. maxima and R. acutocostata into the late Campanian, and extension of the lower ranges of B. cardenasensis and G. jamaicensis into the early Campanian. Identified rudists from Puerto Rico comprise the Hippuritidae and include Barrettia monilifera, which supports the age of the Flor de Alba Limestone Member of the Pozas Formation as middle Campanian. Combined taxonomic, biostratigraphic, and paleobiogeographic analyses indicate there is no rudist fauna endemic to the GCP, and the region marks the northeastern range of the Caribbean genera Biradiolites, Durania, Guanacastea, Gyropleura, Radiolites, and Sauvagesia during the Campanian and Maastrichtian. The new occurrences help inform future updates of Late Cretaceous sea surface-current reconstructions for the Caribbean and Western Interior Seaway, USA.

Reconstructing the evolution, diversity, and paleobiogeography of North America’s Late Cretaceous dinosaur assemblages require spatiotemporally contiguous data; however, there remains a spatial and temporal disparity in dinosaur data on the continent. The rarity of vertebrate-bearing sedimentary deposits representing Turonian–Santonian ecosystems, and the relatively sparse record of dinosaurs from the eastern portion of the continent, present persistent challenges for studies of North American dinosaur evolution. Here we describe an assemblage of ornithomimosaurian materials from the Santonian Eutaw Formation of Mississippi. Morphological data coupled with osteohistological growth markers suggest the presence of two taxa of different body sizes, including one of the largest ornithomimosaurians known worldwide. The regression predicts a femoral circumference and a body mass of the Eutaw individuals similar to or greater than that of large-bodied ornithomimosaurs, Beishanlong grandis , and Gallimimus bullatus . The paleoosteohistology of MMNS VP-6332 demonstrates that the individual was at least ten years of age (similar to B . grandis [~375 kg, 13–14 years old at death]). Additional pedal elements share some intriguing features with ornithomimosaurs, yet suggest a larger-body size closer to Deinocheirus mirificus . The presence of a large-bodied ornithomimosaur in this region during this time is consistent with the relatively recent discoveries of early-diverging, large-bodied ornithomimosaurs from mid-Cretaceous strata of Laurasia ( Arkansaurus fridayi and B . grandis ). The smaller Eutaw taxon is represented by a tibia preserving seven growth cycles, with osteohistological indicators of decreasing growth, yet belongs to an individual approaching somatic maturity, suggesting the co-existence of medium- and large-bodied ornithomimosaur taxa during the Late Cretaceous Santonian of North America. The Eutaw ornithomimosaur materials provide key information on the diversity and distribution of North American ornithomimosaurs and Appalachian dinosaurs and fit with broader evidence of multiple cohabiting species of ornithomimosaurian dinosaurs in Late Cretaceous ecosystems of Laurasia.

Paleopathological diagnoses provide key information on the macroevolutionary origin of disease as well as behavioral and physiological inferences that are inaccessible via direct observation of extinct organisms. Here we describe the external gross morphology and internal architecture of a pathologic right second metatarsal (MMNS VP-6332) of a large-bodied ornithomimid (~432 kg) from the Santonian (Upper Cretaceous) Eutaw Formation in Mississippi, using a combination of X-ray computed microtomography (microCT) and petrographic histological analyses. X-ray microCT imaging and histopathologic features are consistent with multiple complete, oblique to comminuted, minimally displaced mid-diaphyseal cortical fractures that produce a "butterfly" fragment fracture pattern, and secondary osteomyelitis with a bone fistula formation. We interpret this as evidence of blunt force trauma to the foot that could have resulted from intra- or interspecific competition or predator-prey interaction, and probably impaired the function of the metatarsal as a weight-bearing element until the animal's death. Of particular interest is the apparent decoupling of endosteal and periosteal pathological bone deposition in MMNS VP-6332, which produces transverse sections exhibiting homogenously thick endosteal pathological bone in the absence of localized periosteal reactive bone. These distribution and depositional patterns are used as criteria for ruling out a pathological origin in favor of a reproductive one for unusual endosteal bone in fossil specimens. On the basis of MMNS VP-6332, we suggest caution in their use to substantiate a medullary bone identification in extinct archosaurians.

Upper Cretaceous marine sequences in the Gulf Coastal Plain (USA) span the Cretaceous–Paleogene (K–Pg) transition, allowing for detailed studies of one of the most severe extinction events of the Phanerozoic. To improve the temporal resolution of the stratigraphic record that represents environmental change leading up to the K–Pg boundary, we constructed a high-resolution chemostratigraphy and cyclostratigraphy of upper Maastrichtian shallow marine deposits located in the state of Mississippi (USA). Upper Maastrichtian strata in this area consist of alternating decimeter scale chalk and marl rhythmites deposited in a hemipelagic setting. New geochemical proxy records were used to test whether rhythmic sedimentation was driven by Milankovitch cycles. Stable isotopes (δ13Ccarb, δ18Ocarb), carbonate content (wt% CaCO3), and elemental concentrations (Ti, K, Fe) integrated with microfossil and ammonite biostratigraphy reveal astronomical forcing in the studied record. Spectral estimation suggests that rhythmic bedding was associated with climate change driven by precession (~20 kyr). Obliquity signals are also apparent in our analysis, and short eccentricity (~100 kyr) is inferred from amplitude modulation of precession. Studied sections were correlated at the precession scale with the recently tuned K–Pg succession near Morello, Italy which is stratigraphically equivalent to the well-characterized K–Pg sites in Gubbio, Italy (Bottaccione, Contessa Highway). Additionally, carbon isotope records from the study area exhibit large scale trends throughout the latest Maastrichtian, similar to those observed in the Morello and Bottaccione sections. Thus, we show that Milankovitch-scale climatic signals and low-amplitude carbon isotope shifts (<0.5‰) of the late Maastrichtian of the Gulf Coastal Plain are well-preserved and can be correlated globally.