Complete Skull Research Articles

A new South American archaic ungulate and new insight for the early diversification of the South American native ungulates

ABSTRACT Palaeogene South American faunas include enigmatic ungulates that cannot be classified unequivocally within any of the main South American (SA) Native Ungulates clades (Litopterna, Notoungulata, Astrapotheria, Pyrotheria and Xenungulata) because they retain plesiomorphic features, resembling Laurasian ‘archaic ungulates’ traditionally classified within the order ‘Condylarthra’. Most SA ‘condylarths’ are known by partial dental series and isolated teeth and unassociated postcranial remains, hampering comparisons with better-known ungulates. Here, we describe a nearly complete skull and associated mandible of an SA ‘condylarth’, Talquinodus puertai gen. et sp. nov., preserving most of the dentition and basicranium, derived from middle Eocene rocks of the Sarmiento Formation at Central Patagonia. Talquinodus shows a combination of plesiomorphic traits (complete dentition with bunolophodont cheek teeth, ring like ectotympanic, retention of stapedial system, etc.), combined with some autapomorphies, as the reduction of the m3 talonid. Our phylogenetic analyses support consistently that Talquinodus belongs to the SA radiation of Euungulata along with Litopterna, Notoungulata and Astrapotheria. However, the internal relationships could not be resolved unambiguously: Talquinodus could be a didolodontid related to the origin of Litopterna, or could be part of a separate radiation of South American archaic ungulates, along Depaulacoutoia, Lamegoia and Escribania, with no descendants in post-Eocene faunas.

A new species of black drum (Acanthuriformes: Sciaenidae: Pogonias Lacépède, 1802) from the Upper Miocene of Argentina

Pogonias blettleri sp. nov., a new species of black drum (Acanthuriformes, Sciaenidae) from the marine Upper Miocene Paraná Formation, which crops out in the Province of Entre Ríos, Argentina, is described. The holotype specimen comprises a large and nearly complete skull articulated with the anterior vertebral column and associated with fragmentary remains of the pectoral and pelvic girdles, as well as a complete pectoral fin. Morphological and phylogenetic analyses including several Western Atlantic sciaenid taxa confirm the assignment of the fossil specimen to the genus Pogonias Lacépède, 1802, as the sister taxon to the clade of Pogonias cromis + Pogonias courbina. The erection of a new species is based on the presence of a combination of primitive and derived characters, such as: the sub-triangular dorsal outline of the anterior neurocranium, with the lateral borders of frontals delimiting an isosceles triangle; the cavernous frontals with wide bridge-like bony struts; a conspicuous dorsal protuberance of frontals; a crescent-shaped preoperculum, with a smooth posterior margin and a strongly thickened anteroventral edge; and a robust and craniocaudally wide hyomandibula, with a strongly ossified anterior expansion. The palaeoenvironmental reconstruction of the upper levels of the Paraná Formation suggests that P. blettleri sp. nov. inhabited brackish and shallow waters in estuarine environments, particularly in areas near large river run-offs. The known palaeontological content from this unit includes potential prey of the black drum, suggesting that P. blettleri sp. nov. likely fed on annelids, crabs, molluscs, and small fish, similar to its extant counterparts. https://zoobank.org/urn:lsid:zoobank.org:pub:3AA77DDD-4FDA-4CFD-AC7F-476F432B950B

Morphological peculiarity of the fossil bison (<i>Bison priscus</i>) from Yakutia

The steppe bison (Bison priscus) is one of the most widespread and numerous representatives of the mammoth fauna. However, the features of the extinction of steppe bison at the end of the Pleistocene and their replacement by modern forms of the American bison (Bison bison) and European bison (Bison bonasus) have not yet been fully studied. Thus, complete skulls of fossil steppe bison are of great interest for studies on taxonomy and kinship relations in the genus Bison. This article presents the results of a study of the finely preserved skull of a fossil bison found in the Verkhoyansk district (Yakutia). This skull was compared by its morphological and osteometric features with other bison skulls, which were found at different times and locations in Upper Pleistocene deposits, as well as with the skulls of modern American bison Bison bison from the collection of the Zoological Museum of the Lomonosov Moscow State University. Standard morphometric indicators of bison skulls and horns were obtained using the Skinner and Kaisen measurement methods. Analysis showed that skulls of Bison priscus from Late Pleistocene sediments of Yakutia, according to most parameters, correspond to the maximum size of modern American bison Bison bison or even larger than the latter. The horns of bison from the Late Pleistocene are 1.5–2 times larger in size than the horns of modern bison and are comparable to those of the Middle Pleistocene long-horned bison B. p. crassicornis Richardson (=longicornis). The disproportion in the size of the skull and horns of the Late Pleistocene bison is due to their habitat in the open landscapes of the Arctic steppe. The morphological uniqueness of the steppe bison of the Late Pleistocene in Yakutia has prospects for further research, because it deserves to be identified as an independent taxon (subspecies), which is relevant for regional paleontology and stratigraphy.

A large new Middle Jurassic ichthyosaur shows the importance of body size evolution in the origin of the Ophthalmosauria

The Middle Jurassic is an important time period for the evolutionary history of marine reptiles as it represented a transitional phase for many clades. Notably, in ichthyosaurs, many early parvipelvian taxa went extinct. The Middle Jurassic saw the emergence of the derived Ophthalmosauria, ultimately becoming the dominant ichthyosaurian clade by the end of the epoch. Even though this is an important period in the evolutionary history of Ophthalmosauria, our understanding remains limited in terms of morphology and taxonomy due to the scarcity of vertebrate-bearing strata. Here we present a large new ichthyosaur from the Bajocian of Switzerland, represented by an almost complete skull with 3D-preserved bones, the (inter)clavicles and a large portion of the postcranial skeleton. After CT- and surface scanning, we reconstructed the 3D in vivo morphology. Our morphological observations and phylogenetic analyses show that the new taxon named Argovisaurus martafernandezi is nested at the base of the Ophthalmosauria. The holotype and only known specimen of Argovisaurus likely represents an adult individual. Bajocian members of the Ophthalmosauria (Mollesaurus and Argovisaurus) were large-bodied animals, a trait typically associated with the more derived Platypterygiinae. This hints at the importance of a large body size early in ophthalmosaurian evolution.LSID: urn:lsid:zoobank.org:act:C3312628-1544-4B87-BBE3-B12346A30BE3LSID: urn:lsid:zoobank.org:act:23C2BD71-8CF0-4D99-848A-0D631518415B

A new sphenodontian (Diapsida: Lepidosauria) from the Upper Triassic (Norian) of Germany and its implications for the mode of sphenodontian evolution

The Arnstadt Formation of Saxony-Anhalt, Germany has yielded some of Germany’s most substantial finds of Late Triassic tetrapods, including the sauropodomorph Plateosaurus and the stem-turtle Proganochelys quenstedti. Here, we describe an almost complete skull of a new sphenodontian taxon from this formation (Norian, 227–208 Ma), making it the oldest known articulated sphenodontian skull from Europe and one of the oldest in the world. The material is represented by the dermal skull roof and by the complete maxilla and temporal region, as well as parts of the palate, braincase, and lower jaw. A phylogenetic assessment recovers it as a basal sphenodontian closely related to Planocephalosaurus robinsonae and to Eusphenodontia, making it the earliest-diverging sphenodontian known with an articulated skull. Its cranial anatomy is generally similar to the well-known Diphydontosaurus avonis from the Rhaetian of England, showing that this successful phenotype was already established in the clade around 10 myr earlier than assumed. An analysis of evolutionary change rates recovers high rates of evolution in basal sphenodontians, with decreasing rates throughout the evolution of the group. However, contrary to previous studies, reversals in this trend were identified, indicating additional peaks of evolutionary change. These results improve our understanding of the early sphenodontian diversity in Europe, providing critical information on evolutionary trends throughout the history of the clade and sparking renewed interest in its evolution.

A new Crocodyloidea from the middle Eocene of Zamora (Duero Basin, Spain).

The eusuchian crocodyliforms recorded in the Eocene levels of the Spanish Duero Basin belong to three lineages: Planocraniidae, with the species Duerosuchus piscator; Alligatoroidea, represented by several specimens of the genus Diplocynodon; and Crocodyloidea, which includes several specimens traditionally attributed to Asiatosuchus. The genus Asiatosuchus, established in 1940 based on a middle Eocene species from Mongolia, has subsequently served as a wastebasket taxon for Paleogene remains belonging to several species, not only from Asia but also belonging to the European and North American records. Many of these species are known by highly fragmentary remains, sharing the presence of characters such as a flat and triangular skull, and long symphyses in the lower jaw, recognized as characteristic for the crocodyloids. In addition to isolated cranial remains, among the material traditionally attributed to Asiatosuchus at the Duero Basin stands out a nearly complete skull and a left mandible, from the middle Eocene area of Casaseca de Campeán (Zamora Province). The present study analyses in detail these specimens, previously reported during the 1980s, but analyzed in a very preliminary way. They are included for the first time in a phylogenetic analysis to establish the systematic position of this Spanish form. The results confirm that it corresponds to a new species of basal crocodyloid, defined here as Asiatosuchus oenotriensis sp. nov.

Craniodental ontogenetic variation in the leontiniid coquenia bondi Deraco, Powell, & López, 2008 (Notoungulata, Toxodontia) from the Eocene of Northwestern Argentina

ABSTRACT Craniodental ontogenetic analyses on notoungulates are scarce. Several well-preserved specimens of the Eocene species Coquenia bondi allow for the first ontogenetic study in a Palaeogene leontiniid notoungulate. We studied five almost complete skulls of C. bondi representing three different ontogenetic stages. Cranial ontogeny indicates negative allometry for most of the variables related to the brain and sense organs, with thicker postorbital constriction and braincase breadth in juveniles. The rostrum grows isometrically in length, with positive allometry in height and negative in anterior width. Isometry is recovered for the palatal length and the upper postcanine length, both variables correlated with the longitudinal growth of the splanchnocranium. Other ontogenetic difference is the stouter and sigmoid zygomatic arch in adults, with its posterior root shifted dorsally accompanying the modification of the basicranial angle. Cranial growth of C. bondi is similar to that of Nesodon imbricatus, sharing four coefficients with close values. Molar eruption sequence is anteroposterior, whereas the deciduous premolars are substituted posteroanteriorly. In the juvenile, dentine in M2 is already exposed on the occlusal surface before wear, but the enamel covers the entire crown in m2 of the advanced juvenile.

The postcranial skeleton of Teyujagua paradoxa (Reptilia: Archosauromorpha) from the early Triassic of South America.

Teyujagua paradoxa is a remarkable early archosauromorph from the Lower Triassic Sanga do Cabral Formation, Brazil. The species was originally described from an almost complete skull and a few associated cervical vertebrae, and no further postcranial elements were known at that time. Additional fieldwork in the Sanga do Cabral Formation, however, was successful in recovering a fairly complete postcranial skeleton attributable to the holotype. Here, we describe this new postcranial material, which is composed of cervical, dorsal, sacral and caudal vertebrae, limbs, pectoral and pelvic girdles, ribs, and gastralia. The description of its postcranial skeleton makes T. paradoxa one of the best-known early-diverging archosauromorphs. The cladistic analysis performed after the scoring of postcranial data recovered T. paradoxa in the same position initially described, close to the node that defines the Archosauriformes. Teyujagua paradoxa shares morphological features with representatives of early-diverging archosauromorphs and archosauriforms, with certain traits demonstrating a mosaic of plesiomorphic and apomorphic character states. We also performed partitioned morphospace and disparity analysis to elucidate the morphological disparity and evolutionary patterns among archosauromorphs. Teyujagua paradoxa occupies a notable position, suggesting an intermediate morphology between early archosauromorphs and proterosuchids. Disparity estimates highlighted Pseudosuchia and Avemetatarsalia as having the highest median disparity, reflecting their diverse cranial and postcranial morphologies, respectively. These findings offer valuable insights into archosauromorph macroevolution and adaptation.

New Cretaceous neosuchians (Crocodylomorpha) from Thailand bridge the evolutionary history of atoposaurids and paralligatorids

Abstract The origin of modern crocodylians is rooted in the Cretaceous, but their evolutionary history is obscure because the relationships of outgroups and transitional forms are poorly resolved. Here, we describe a new form, Varanosuchus sakonnakhonensis gen. nov., sp. nov., from the Early Cretaceous of Thailand that fills an evolutionary gap between Paralligatoridae and Atoposauridae, two derived neosuchian lineages with previously unsettled phylogenetic relationships. Three individuals, including a complete skull and associated postcranial remains, allow for a detailed description and phylogenetic analysis. The new taxon is distinguished from all other crocodylomorphs by an association of features, including a narrow altirostral morphology, a dorsal part of the postorbital with an anterolaterally facing edge, a depression on the posterolateral surface of the maxilla, and fully pterygoid-bound choanae. A phylogenetic analysis confirms the monophyly and taxonomic content of Atoposauridae and Paralligatoridae, and we underline the difficulty in reaching a robust definition of Eusuchia. Furthermore, we put forward further arguments related to the putative terrestrial ecology with semi-aquatic affinities of atoposaurids based on their altirostral snout morphology and osteoderm ornamentation.

Early Miocene Aprotodon (Perissodactyla, Rhinocerotidae) from Northern China

ABSTRACT The genus Aprotodon is a special group of rhinoceroses, which has a very long survival time frame but a relatively limited distribution in Asia. Herein, we report on a well-preserved and complete skull found in the lower layers of the Zhang’enbao Formation from the Early Miocene age in Tongxin County, China. The morphology of the new specimen is different from all the known species of Aprotodon in its smaller size, with both sides of the parietal crest fused and forming a sagittal crest, the V-shaped anterior edge of the posterior nares positioned at the level of M2, the weak supraorbital tuberosity, the developed and multiple crista on premolars, and the reduced lingual cingulum, forming a pillar around the entrance of the medisinus on molars. Based on these, we refer the Tongxin specimen to a new species, A. qiui sp. nov. Phylogenetic analysis reveals that A. qiui sp. nov. and other members of Aprotodon are in a stable monophyletic clade. A. qiui sp. nov. is the sister taxon to A. lanzhouensis.

Sparse convolutional neural network for high-resolution skull shape completion and shape super-resolution

Traditional convolutional neural network (CNN) methods rely on dense tensors, which makes them suboptimal for spatially sparse data. In this paper, we propose a CNN model based on sparse tensors for efficient processing of high-resolution shapes represented as binary voxel occupancy grids. In contrast to a dense CNN that takes the entire voxel grid as input, a sparse CNN processes only on the non-empty voxels, thus reducing the memory and computation overhead caused by the sparse input data. We evaluate our method on two clinically relevant skull reconstruction tasks: (1) given a defective skull, reconstruct the complete skull (i.e., skull shape completion), and (2) given a coarse skull, reconstruct a high-resolution skull with fine geometric details (shape super-resolution). Our method outperforms its dense CNN-based counterparts in the skull reconstruction task quantitatively and qualitatively, while requiring substantially less memory for training and inference. We observed that, on the 3D skull data, the overall memory consumption of the sparse CNN grows approximately linearly during inference with respect to the image resolutions. During training, the memory usage remains clearly below increases in image resolution—an times 8 increase in voxel number leads to less than times 4 increase in memory requirements. Our study demonstrates the effectiveness of using a sparse CNN for skull reconstruction tasks, and our findings can be applied to other spatially sparse problems. We prove this by additional experimental results on other sparse medical datasets, like the aorta and the heart. Project page at https://github.com/Jianningli/SparseCNN.

Morphometric evaluation of the orbital region for sex determination in a Saudi Arabian population using 3DCT images.

In forensic anthropology, the analysis of variations in the orbitometric features plays a crucial role in identifying the sex of a skull detached from its skeleton. Therefore, it is essential to create population-specific values to maximize the accuracy rate of sex estimation. The objective of this study was to evaluate the orbital region morphometrically for sex determination in a Saudi Arabian population using CT scan images. This study included 456 CT images (228 males and 228 females; age range, 18-58years). Six orbital measurements and the orbital index of both sides were evaluated to determine sexual dimorphism and laterality using an independent t-test. Sex was estimated using discriminant function analysis. Based on the orbital index, the orbit was classified into megasemes, mesosemes, and microsemes. All the measurements were significantly greater in males than females, but the orbital index showed no significant sexual dimorphism. No significant asymmetry was found in all orbital dimensions. The univariate discriminant function of the orbital measurements showed an accuracy rate between 83.8 and 70%. The multivariate analysis classified the orbital dimensions into male (93%) and female (92.1%) to the highest level of accuracy. In Saudis, the megaseme category was the most prevalent form of orbit. The right orbit height (83.8%), left orbit height (80.7%), right orbit width (79.4%), and left orbit height (79.4%) were the most reliable variables that could be used in sex determination. According to multivariate analysis, the overall accuracy rate for determining sex was 92.1%. While the present study data may not be used alone for sexing a complete skull, there must be various occasions in which this new standard will contribute to determining sex in forensic contexts.

Wadi Al-Hitan or ‘Valley of Whales’ – an Eocene World Heritage Site in the Western Desert of Egypt

Abstract Wadi Al-Hitan is a UNESCO World Heritage Site in the Western Desert of Egypt famous for the fossils it has produced, including some of the most complete skulls and skeletons of Eocene whales known anywhere in the world. Most are from the early part of the late Eocene epoch of Earth history and lived in the Tethys Sea some 38 to 36 million years before present. Basilosaurus isis and Dorudon atrox are the most abundant and best known of the archaic whales. Sea cow skeletons are present as well, as are bones or teeth of a bird, crocodiles, turtles, bony fishes, and a diversity of sharks and rays. The fossils are preserved in sedimentary strata that accumulated as sea level rose and fell, producing a succession of nearshore marine environments. Rocks exposed at the surface, now dissected by erosion, enable study of stratigraphic sequences and their architecture. Taken together, the fossil-and-strata geoheritage of Wadi Al-Hitan has exceptional value for science and for public education.

Reidentification of the holotype specimen of Trilophosaurus buettneri Case, 1928 (Archosauromorpha, Trilophosauridae) from the Upper Triassic of Crosby County, Texas, U.S.A.

ABSTRACT The Late Triassic archosauromorph Trilophosaurus buettneri is known from many sites in the Dockum Group and Chinle Formation of Texas and Arizona, spanning nearly 10 Ma from the Otischalkian to the Adamanian estimated holochrons. The holotype specimen, UMMP 2338, was described as a small fragment of a lower jaw in 1928 by E.C. Case. However, at the time no other specimens of the taxon were known. The present availability of several nearly complete skulls, mandibles, and postcranial skeletons referred to T. buettneri allows for reexamination of the anatomical context of the holotype. Here, we provide high-resolution photographs and 3D models of UMMP 2338 to justify our reidentification of the holotypic specimen of T. buettneri as an incomplete maxilla, which may have important implications for future work on trilophosaurid archosauromorphs.

Redescription of the soft-shell turtle Rafetus bohemicus (Testudines, Trionychidae) from the Early Miocene of Czechia.

The taxonomy of the soft-shell turtle Rafetus bohemicus (Liebus, 1930), family Trionychidae, subfamily Trionychinae, is revised based on new and previously mentioned material (including the type material) from the Early Miocene (Burdigalian, MN 3) sites of the Most Basin, Czechia. Given that the diagnosis was so far based only on plastral elements, here we focused on the cranial material and combined our study with previously published data on postcranial elements. 3D models of the skulls derived from CT scans allow us to provide the first complete skull description of R. bohemicus, including several new cranial diagnostic characters of the species. Our results not only enable the distinction of the trionychid genera Trionyx and Rafetus, both recorded from Central Europe during the Early Miocene, but further allow us to provide an emended diagnosis for R. bohemicus. We confirm the conclusions of a previous study according to which Trionyx pontanus, T. preschenensis, T. aspidiformis, and T. elongatus are nomina dubia. R. bohemicus from Břešt'any (MN 3) represents the oldest record of this genus in Europe as well as the oldest occurrence of the genus.

Partial skeleton from the Paleocene of New Zealand illuminates the early evolutionary history of the Phaethontiformes (tropicbirds)

We describe a new stem group representative of the Phaethontiformes (tropicbirds) from the Paleocene Waipara Greensand in New Zealand. The fossil consists of a partial skeleton with a nearly complete skull and represents the first unambiguous record of the Phaethontiformes from the Paleocene of the Southern Hemisphere. Clymenoptilon novaezealandicum gen. et sp. nov. has a proportionally shorter pelvis than Prophaethon shrubsolei from the early Eocene London Clay and appears to have been less adapted to foraging in an aquatic environment at or below sea-level. It is furthermore distinguished from P. shrubsolei and Lithoptila abdounensis from the late Paleocene/early Eocene of Morocco in a proportionally smaller foramen magnum of the skull. Together with other plesiomorphic features, this suggests that C. novaezealandicum is the sister taxon of a clade including Lithoptila, Prophaethon and crown group Phaethontiformes, and as one of the oldest stem group phaethontiforms the new species may indicate a Southern Hemispheric centre of origin of tropicbirds. After a recently described bony-toothed bird, C. novaezealandicum is the second seabird species from the Waipara Greensand to show affinities to taxa from the early Paleogene of the Northern Hemisphere. The wide early Paleogene distribution of the Phaethontiformes stands in sharp contrast to the geographic restriction of coeval diving seabirds, and different factors appear to have limited the dispersal of aquatic and pelagic seabird taxa in the early Paleogene. Gerald Mayr [Gerald.Mayr@senckenberg.de], Senckenberg Research Institute and Natural History Museum Frankfurt, Ornithological Section, Senckenberganlage 25, D-60325 Frankfurt am Main, Germany; Vanesa L. De Pietri [vanesa.depietri@canterbury.ac.nz], University of Canterbury, School of Earth and Environment, Private Bag 4800, Christchurch 8140, New Zealand; Al Mannering [alman@slingshot.co.nz], Canterbury Museum, Rolleston Avenue, Christchurch 8050, New Zealand; Leigh Love [lvlove@xtra.co.nz], PO Box 49, Waipara 7483, New Zealand; Erica Crouch [e.crouch@gns.cri.nz], GNS Science, 1 Fairway Drive, Lower Hutt 5040, New Zealand; Catherine Reid [catherine.reid@canterbury.ac.nz], University of Canterbury, School of Earth and Environment, Private Bag 4800, Christchurch 8140, New Zealand; R. Paul Scofield [pscofield@canterburymuseum.com], Canterbury Museum, Rolleston Avenue, Christchurch 8050, New Zealand, and University of Canterbury, School of Earth and Environment, Private Bag 4800, Christchurch 8140, New Zealand.

A new dolphin with tusk-like teeth from the late Oligocene of New Zealand indicates evolution of novel feeding strategies.

All extant toothed whales (Cetacea, Odontoceti) are aquatic mammals with homodont dentitions. Fossil evidence from the late Oligocene suggests a greater diversity of tooth forms among odontocetes, including heterodont species with a variety of tooth shapes and orientations. A new fossil dolphin from the late Oligocene of New Zealand, Nihohae matakoi gen. et sp. nov., consisting of a near complete skull, earbones, dentition and some postcranial material, represents this diverse dentition. Several preserved teeth are horizontally procumbent, including all incisors and canines. These tusk-like teeth suggest adaptive advantages for horizontally procumbent teeth in basal dolphins. Phylogenetic analysis places Nihohae among the poorly constrained basal waipatiid group, many with similarly procumbent teeth. Features of N. matakoi such as its dorsoventrally flattened and long rostrum, long mandibular symphysis, unfused cervical vertebrae, lack of attritional or occlusal wear on the teeth and thin enamel cover suggest the rostrum and horizontally procumbent teeth were used to injure and stun prey though swift lateral head movements, a feeding mode that did not persist in extant odontocetes.

Neanderthal bones collected by hyena at Grotta Guattari, central Italy, 66–65 ka: U/Th chronology and paleoenvironmental setting

After eight decades since its discovery in 1939, new investigations have been undertaken at Grotta Guattari (Latium, central Italy), a coastal cave by the Tyrrhenian Sea coast and one of the iconic sites of the Italian prehistory, as it yielded an almost complete skull and other remains of Neanderthals. The new excavations of the innermost and untouched cave deposits resulted in an outstanding amount of mammal bones, 40 out of which attributable to Neanderthal, including new large portions of cranial remains. Preliminary taphonomic hints and the collected stratigraphic evidence strongly indicate that the impressive accumulation of the large mammal bones was the work of spotted hyena, in a period in which human frequentation was really sporadic or even completely absent. The new acquired U/Th chronology of Grotta Guattari speleothems provided new constraints for reconstructing the sedimentary and paleoenvironmental history of the archaeological successions and human remains. The accumulation of terrestrial sediments started at ∼112 ka, immediately after the end of the Last Interglacial sea-level highstand (∼116 ka). However, the hyena frequentation, and thus the bone accumulations, occurred several thousands of years after and lasted for a very short time interval, precisely between slightly before 66 ka and 65 ka. The cave became abandoned by hyena after ∼65 ka and before ∼59 ka, because of the cave obstruction and/or the altered environmental conditions related to the Heinrich Event 6 (∼64–60 ka). The regional paleoclimatic records indicate severe conditions during the short interval of the hyena frequentation. In contrast, though providing evidence of open and arid environments, the faunal assemblage and the pollen from Grotta Guattari reveal that the local conditions were less severe, likely because of the mitigating effect of the Tyrrhenian Sea. In the framework of the Italian findings, Grotta Guattari results the richest and better chronologically constrained site of Neanderthal remains, posing it as one of the rare sites of the European prehistory that allows putting into the context an extraordinary large sample of the population of Neanderthals, and of other large mammals, in a very narrow and precisely dated temporal interval of the early Pleniglacial.

First postcranial remains of the Late Cretaceous gondwanatherian mammal Vintana sertichi

Postcranial remains of gondwanatherian mammals were previously known by only a single specimen, an essentially complete skull and postcranial skeleton constituting the holotype and only known specimen of Adalatherium hui (UA 9001), from the uppermost Cretaceous (Maastrichtian) Anembalemba Member of the Maevarano Formation, Mahajanga Basin, northwestern Madagascar. Here we report the discovery of a caudal vertebra (DMNH EPV.141354) that we provisionally refer to a much larger gondwanatherian, Vintana sertichi, also from the Maevarano Formation. V. sertichi, the largest known mammal from the Mesozoic of Gondwana, was previously represented only by a cranium from the Lac Kinkony Member, which represents a nearshore, peritidal paleoenvironment, but the caudal vertebra was recovered from the underlying Anembalemba Member, which represents an earlier, more fully terrestrial fluvial/floodplain paleoenvironment. The presence of V. sertichi in the latter rock unit therefore expands the age (making it more fully contemporaneous with A. hui) and the known paleoenvironmental range for the species. Comparing various metrics of vertebral body proportions suggests that (1) gondwanatherians are unique among Mesozoic mammals in possessing mid-caudal vertebral centra that are anteroposteriorly short; and (2) the tail of V. sertichi was relatively wider and shorter than that of A. hui.

Tusked walruses (Carnivora: Odobenidae) from the Miocene–Pliocene Purisima Formation of Santa Cruz, California (U.S.A.): a new species of the toothless walrus Valenictus and the oldest records of Odobeninae and Odobenini

ABSTRACT Currently limited to cold climates near the Arctic circle, living walruses are the sole survivors of a previously much more diverse clade that occupied coastal waters throughout the northern hemisphere during the Mio–Pliocene. Though pinniped faunas have the highest diversity of walruses in the Miocene, the Purisima Formation of California records a moderately diverse assemblage of four walrus species. We report new specimens of tusked walruses (Odobeninae) including the oldest known members of Odobeninae, and Odobenini, and fossils of the specialized toothless odobenine walrus Valenictus Mitchell, 1961. Among these is the new species Valenictus sheperdi sp. nov., represented by a complete skull and referred post-crania from lower Pliocene strata within the Purisima Formation (5.33–4.89 Ma). Additionally, we report a geochronologically younger skull of Valenictus chulavistensis Deméré, 1994 from further up section (4.89–3.59 Ma). Expanded phylogenetic analysis recovers Odobeninae including Ontocetus Leidy, 1859 as the earliest diverging lineage in the Odobenini, and places a monophyletic Valenictus as the sister taxon to Pliopedia, Kellogg, 1921 which is included in a phylogeny for the first time; Odobenus is sister to the Valenictus + Pliopedia clade. Discovery of an isolated metacarpal near the base of the formation provides the oldest known well-dated evidence of odobenines. A diverse assemblage of molluskivores characterized the Neogene eastern North Pacific and their extinction around the Pliocene–Pleistocene boundary coincided with tectonically driven paleogeographic changes on the Pacific coast. The loss of temperate walruses may have provided opportunities for both new molluskivores and the otariid and phocid pinnipeds that make up present North Pacific pinniped communities.