Aristonectes quiriquinensis, sp. nov., a new highly derived elasmosaurid from the upper Maastrichtian of central Chile

This paper describes a new species of elasmosaurid plesiosaur, Aristonectes quiriquinensis, sp. nov., based on a partial skeleton recovered from upper Maastrichtian beds of the Quiriquina Formation of central Chile. The material described here consists of two skeletons, one collected near the village of Cocholgue, and a second juvenile specimen from Quiriquina Island. Prior to these finds, Aristonectes was viewed as a monospecific genus, including only the enigmatic Aristonectes parvidens, the holotype of which consists of an incomplete skull and incomplete postcranium. Other material referred to the genus includes an incomplete juvenile skull and other postcranial material from the upper Maastrichtian of Antarctica, as well as a partial skull from the Quiriquina Formation of central Chile. The relationships of Aristonectes have been controversial, with competing theories assigning the genus to Cryptoclididae, Elasmosauridae, and Aristonectidae; however, there is a developing consensus that Aristonectes is a derived elasmosaurid, and this paper gives strong evidence for this view. Comparison of the specimen here studied with the holotype of A. parvidens demonstrates that A. quiriquinensis is a distinct species. The completeness of the adult skeleton allows the first confident size estimates for adult Aristonectes. It is a large plesiosaurian with a relatively large skull with numerous homodont teeth, a moderately long and laterally compressed neck, and relatively narrow trunk, with slender and elongate forelimbs. The two specimens are restricted to the upper Maastrichtian of central Chile, posing questions concerning the austral circumpolar distribution of different elasmosaurids towards the end of the Cretaceous.Fil: Otero, Rodrigo A.. Universidad de Chile; ChileFil: Soto Acuña, Sergio. Museo Nacional de Historia Natural de Santiago; Chile. Universidad de Chile; ChileFil: O'Keefe, Frank Robin. Marshall University; Estados UnidosFil: O'gorman, Jose Patricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; ArgentinaFil: Stinnesbeck, Wolfgang. Heidelberg University; AlemaniaFil: Suárez, Mario E.. Museo Nacional de Historia Natural de Santiago; Chile. Universidad de Chile; ChileFil: Rubilar-Rogers, David. Museo Nacional de Historia Natural de Santiago; Chile. Universidad de Chile; ChileFil: Salazar, Christian. Museo Nacional de Historia Natural de Santiago; Chile. Universidad de Chile; ChileFil: Quinzio Sinn, Luis Arturo. Universidad de Concepción; Chil

The first non-aristonectine elasmosaurid (Sauropterygia; Plesiosauria) cranial material from Antarctica : New data on the evolution of the elasmosaurid basicranium and palate

Elasmosaurids are a monophyletic group of cosmopolitan plesiosaurs with extremely long necks. Although abundant elasmosaurid material has been collected from the Upper Cretaceous of Antarctica, skull material is extremely rare. Here, new elasmosaurid cranial material from the lower Maastrichtian levels of the Cape Lamb Member (Snow Hill Island Formation) on Vega Island, Antarctica is described. The studied specimen (MLP 15-I-7-6) is a non-aristonectine elasmosaurid but shows a palate morphology characterized by the absence of a posterior interpterygoid symphysis and a posterior plate-like extension of the pterygoids, features previously associated with the aristonectine palatal structure. The specimen MLP 15-I-7-6 thus provides an indication that these palatal features are also present in non-aristonectine Weddellian elasmosaurids, and makes available additional evidence of the close phylogenetical relationship between the aristonectines and some Weddellian non-aristonectine elasmosaurids.Museo de La Plat

Ecological Controls on the Campanian Distribution of Hesperornis (Aves: Hesperornithiformes) in the Western Interior Seaway

The epicontinental Western Interior Seaway (WIS) of Late Cretaceous North America provided a unique marine habitat for cephalopods, fish, marine reptiles, and the foot-propelled diving seabird Hesperornis. While several predator-prey relationships among Hesperornis or other hesperornithiforms and other WIS animals have been hypothesized based on gut contents, bite marks, and coprolites/colonites, ecological relationships have not been quantitatively tested. Paleontological species distribution modeling (SDM) studies have focused on extinct non-marine taxa and marine invertebrates, with only two marine vertebrate studies of extant taxa. Here, two SDM methods were used to test the influence of vertebrate faunas, sedimentary rock type, paleogeography, and outcrop area on Hesperornis occurrences: generalized linear models (GLMs) and occupancy models (an extension of standard GLMs). Results of both model types indicate a decreased probability of Hesperornis presence at elasmosaur-occupied sites and an increased probability of Hesperornis presence with higher paleolatitudes. The negative association between elasmosaurs and Hesperornis in all highest-ranked models, coupled with evidence of similar diets, may indicate food resource competition, but the geographic distributions of both taxa may instead reflect different habitat preferences. The positive impact of paleolatitude may reflect seasonal migrations resulting in large breeding congregations at higher paleolatitudes (based on probable immature specimens), preference for specific environmental conditions or feeding areas (e.g., along oceanographic fronts or upwelling zones), or migration mortality. While Spearman’s correlation test did not identify a western, middle, or eastern WIS preference for Hesperornis, the inclusion of this regional covariate with paleolatitude in the highest-ranked occupancy models may indicate an interaction effect between these two covariates that favored higher Hesperornis abundance in South Dakota and Manitoba along probable mixing zones or fronts. Taxa hypothesized by previous authors to have had ecological interactions with hesperornithiforms were not supported by the models as major factors in the Hesperornis distribution. These include Tylosaurus and polycotylid plesiosaurs, hypothesized feeders on Hesperornis, Enchodus, a teleost consumed by the smaller hesperornithiform Fumicollis, and Squalicorax, an opportunistic shark that consumed hesperornithiforms. This study represents the first paleogeographic model for Hesperornis occurrences and the first GLM and occupancy modeling applications to extinct marine vertebrates. These models examine previous hypotheses and provide novel interpretations for hesperornithiform ecology

A new elasmosaurid (Sauropterygia: plesiosauria) from the Bearpaw Formation (late Cretaceous, Maastrichtian) of Montana and the evolution of neck length in elasmosauridae

Thesis (M.S.) University of Alaska Fairbanks, 2015Plesiosauria is a diverse clade of marine reptiles that have been studied since the early 19th century. However, phylogenetic relationships within the group have been contentious due to limited taxon sampling and a misunderstanding of how ontogeny, interspecific and intraspecific variation affect character states. This is particularly true for elasmosaurids, a clade of long-necked plesiosaurians known from the Cretaceous. In 2010, a new, nearly complete skeleton, MOR 3072, was collected from the Late Cretaceous (Campanian-Maastrichtian) Bearpaw Shale of northeast Montana, and it provides morphological information rarely observed within Elasmosauridae. MOR 3072 consists of a complete skull, the anterior 23 cervical vertebrae, a partial dorsal and caudal vertebral column, incomplete pectoral and pelvic girdles, elements of both fore- and hindlimbs, ribs, and gastralia. Here, I present a detailed description of the specimen and conduct the most complete phylogenetic analysis of Elasmosauridae to date. A new taxon is recognized on the basis of the following suite of autapomorphies and unique character combinations: a chordate bilobed external naris, a squared-off posteroventral margin of maxilla, the presence of a maxilla-squamosal contact, a deep anteroposterior-oriented cleft in the articular posterior to the glenoid, a reduced number of cervical vertebrae, proximal caudal vertebrae that are wider than dorsoventrally tall, and small facets for forelimb and hindlimb preaxial accessory ossicles. A phylogenetic analysis places MOR 3072 as the sister taxon to the long-necked, Western Interior elasmosaurids Hydralmosaurus serpentinus + Styxosaurus snowii. Being early Maastrichtian in age, MOR 3072 is the stratigraphically youngest elasmosaurid yet known from the Western Interior Seaway. It is also one of the smallest adult elasmosaurids ever recovered (4.5-5 m) and exhibits a reduced neck length due to a reduction in both the number of cervical vertebrae and centrum length, which is convergent with another clade of Maastrichtian elasmosaurids, Aristonectinae

Revision of the Genus Styxosaurus and Relationships of the Late Cretaceous Elasmosaurids (Sauropterygia: Plesiosauria) of the Western Interior Seaway

Growing evidence indicates that elasmosaurid plesiosaurs from the Late Cretaceous Western Interior Seaway are members of a single clade, the Styxosaurinae. The styxosaurines are reported to be mostly Campanian in age, and taxa within the clade obtain the longest necks, by number of cervical vertebrae, of any known vertebrate. The styxosaurines are morphologically diverse and include taxa that exhibit a secondary reduction in neck length. Given the evolutionary plasticity of postcranial characters in plesiosaurs in general, and neck length in elasmosaurs, scrutiny of cranial osteology is pertinent to advancing understanding of Western Interior Seaway elasmosaurids. This study finds that an elasmosaurid specimen (UNSM 50132) from the Cenomanian of Nebraska is remarkably similar in cranial morphology to the Campanian Styxosaurus snowii (KUVP 1301). The phylogenetic affinity of UNSM 50132 was tested with a cladistic analysis with 94 Operational Taxonomic Units (OTU) and 270 anatomical characters, utilizing the Serratos et al. (2017) character matrix with changes and additions. The analysis supports five unambiguous synapomorphies for the genus Styxosaurus: (1) dorsomedian ridge of premaxilla located posteriorly (19.1); (2) dorsal portion of squamosal reflected anteriorly in lateral view (61.1); (3) posteromedian ridge on the supraoccipital (77.1); (4) a sharp ridge or keel located adjacent to the mandibular symphysis (114.1); (5) a retroarticular process that is shorter in anteroposterior length than the glenoid (116.0). Five additional ambiguous synapomorphies that support the monophyly of Styxosaurus include: lateral expansion of the maxilla that supports caniniform teeth, anisodont dentition, anterior embayment of the squamosal arch, an elongate posteromedian process of the premaxilla, a rugose boss on the ectopterygoid, parietals that form a sagittal crest that rises above the cranial roof, and elongate anterior to middle cervical centra. 67% of 100 bootstrap replicates support the monophyly of UNSM 50132, Styxosaurus snowii, Styxosaurus browni, and Styxosaurus sp. (SDSM 451). UNSM 50132 was previously referred to the genus Thalassomedon, a taxon considered to be outside of the Styxosaurinae. The recommended referral of UNSM 50132 to the genus Styxosaurus pushes back the earliest occurrence of Styxosaurinae in the Western Interior Seaway by over ten million years. Maximum parsimony analysis suggests that all Western Interior Seaway elasmosaurids belong to a single clade, including the genera Libonectes and Thalassomedon. Libonectes and Thalassomedon have been previously recovered as outgroup taxa to a clade composed of the sister relationship of Western Interior Seaway elasmosaurids and Aristonectinae. This study provides additional context for furthering understanding of the origins of Elasmosauridae in the Early Cretaceous

Plesiosaurs (Diapsida, sauropterygia) from Late Cretaceous (Late Campanian- Early maastrichtian) marginal marine environments from north Patagonia

Fil: O`Gorman, Jose Patricio. División Paleontología Vertebrados. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; Argentin

Revised Vertebral Count in the Longest-Necked Vertebrate Elasmosaurus platyurus Cope 1868, and Clarification of the Cervical-Dorsal Transition in Plesiosauria

Elasmosaurid plesiosaurians are renowned for their immensely long necks, and indeed, possessed the highest number of cervical vertebrae for any known vertebrate. Historically, the largest count has been attributed to the iconic Elasmosaurus platyurus from the Late Cretaceous of Kansas, but estimates for the total neck series in this taxon have varied between published reports. Accurately determining the number of vertebral centra vis-à-vis the maximum length of the neck in plesiosaurians has significant implications for phylogenetic character designations, as well as the inconsistent terminology applied to some osteological structures. With these issues in mind, we reassessed the holotype of E. platyurus as a model for standardizing the debated cervical-dorsal transition in plesiosaurians, and during this procedure, documented a lost cervical centrum. Our revision also advocates retention of the term pectorals to describe the usually three or more distinctive vertebrae close to the cranial margin of the forelimb girdle that bear a functional rib facet transected by the neurocentral suture, and thus conjointly formed by both the parapophysis on the centrum body and diapophysis from the neural arch (irrespective of rib length). This morphology is unambiguously distinguishable from standard cervicals, in which the functional rib facet is borne exclusively on the centrum, and dorsals in which the rib articulation is situated above the neurocentral suture and functionally borne only by the transverse process of the neural arch. Given these easily distinguishable definitions, the maximum number of neck vertebrae preserved in E. platyurus is 72; this is only three vertebrae shorter than the recently described Albertonectes, which together with E. platyurus constitute the longest necked animals ever to have lived

The cranial anatomy and relationships of Cardiocorax mukulu (Plesiosauria: Elasmosauridae) from Bentiaba, Angola

We report a new specimen of the plesiosaur Cardiocorax mukulu that includes the most complete plesiosaur skull from sub-Saharan Africa. The well-preserved three-dimensional nature of the skull offers rare insight into the cranial anatomy of elasmosaurid plesiosaurians. The new specimen of Cardiocorax mukulu was recovered from Bentiaba, Namibe Province in Angola, approximately three meters above the holotype. The new specimen also includes an atlas-axis complex, seventeen postaxial cervical vertebrae, partial ribs, a femur, and limb elements. It is identified as Cardiocorax mukulu based on an apomorphy shared with the holotype where the cervical neural spine is approximately as long anteroposteriorly as the centrum and exhibits a sinusoidal anterior margin. The new specimen is nearly identical to the holotype and previously referred material in all other aspects. Cardiocorax mukulu is returned in an early-branching or intermediate position in Elasmosauridae in four out of the six of our phylogenetic analyses. Cardiocorax mukulu lacks the elongated cervical vertebrae that is characteristic of the extremely long-necked elasmosaurines, and the broad skull with and a high number of maxillary teeth (28-40) which is characteristic of Aristonectinae. Currently, the most parsimonious explanation concerning elasmosaurid evolutionary relationships, is that Cardiocorax mukulu represents an older lineage of elasmosaurids in the Maastrichtian.publishersversionpublishe

Plesiosaurios (Diapsida, Sauropterygia) del Cretácico tardío (Campaniano tardío-Maastrichtiano temprano) de ambientes marino-marginales del norte de Patagonia

During the late Campanian and early Maastrichtian, Northern Patagonia suffered the first stage of the Atlantic marine ingression that reached the Neuquén Basin. The Allen and La Colonia formations show the early stages of this change, and were deposited in a complex association of marginal marine environments, including coastal and marine deposits (i.e., flood plains, estuaries and lagoons). The plesiosaurs from the Allen and La Colonia formations included at least three species, each with a distinctive morphotype, representing a high diversity in the Late Cretaceous. The only species that preserved cranial material, Sulcusuchus erraini Gasparini and Spalleti, is a strange polycotylid characterized by the presence of deep grooves in the rostrum and mandible. The other two species correspond to aristonectine and non-aristonectine elasmosaurids. The former are distinguished by relatively large skulls and a high number of teeth compared to other elasmosaurids, whereas the non-aristonectine elasmosaurids are characterized by their relatively small body sizes, despite being adult specimens.Durante el Campaniano tardío y el Maastrichtiano temprano el norte de la Patagonia sufrió la primera etapa de la ingresión marina atlántica, que alcanzó la Cuenca Neuquina. Las formaciones Allen y La Colonia evidencian las primeras etapas de este cambio, habiéndose depositado en una asociación de ambientes irregulares que incluyen depósitos marino-marginales (es decir de llanuras mareales, estuarios y lagunas costeras). Los plesiosaurios de las formaciones Allen y La Colonia incluyen al menos tres especies, cada una con un morfotipo distintivo, lo que representa una alta diversidad hacia fines del Cretácico. La única especie con material craneano preservado es Sulcusuchus erraini Gasparini y Spalleti, un extraño policotílido caracterizado por la presencia de profundos surcos en el rostro y la mandíbula. Las otras dos especies corresponden a elasmosáuridos aristonectinos, caracterizados por tener cráneos relativamente grandes y elevado número de dientes comparados con otros elasmosáuridos y a elasmosáuridos no aristonectinos, que se destacan por su relativo pequeño tamaño, a pesar de tratarse de ejemplares adultos.Facultad de Ciencias Naturales y Muse