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The planktivorous mobulid rays are a sister group to, and descended from, rhinopterid and myliobatid rays that possess a dentition showing adaptations consistent with a specialized durophagous diet. Within the Paleocene and Eocene, there are several taxa that display dentitions apparently transitional between these extreme trophic modalities, in particular the genus Burnhamia. The holotype of Burnhamia daviesi was studied through X-ray computed tomography (CT) scanning. Digital renderings of this incomplete but articulated jaw and dentition revealed previously unrecognized characters regarding the jaw cartilages and teeth. In addition, the genus Sulcidens, gen. nov., is erected for articulated dentitions from the Paleocene previously assigned to Myliobatis. Phylogenetic analyses confirm Burnhamia as a sister taxon to the mobulids and the Mobulidae as a sister group to Rhinoptera. Shared dental characters between Burnhamia and Sulcidens likely represent independent origins of planktivory within the rhinopterid-myliobatid clade. The transition from highly specialized durophagous feeding morphologies to the morphology of planktivores is perplexing but was facilitated by a pelagic swimming mode in these rays and, we propose, through subsequent transition from either meiofauna-feeding or pelagic fish-feeding to pelagic planktivory.
The Hippopotamidae have been a major component of the African wetland fauna for the last 7 million years, following the ‘Hippopotamine Event,’ i.e., the sudden emergence in the fossil record of the subfamily Hippopotaminae, including both extant species. The general dearth of African fossiliferous deposits dated between 9.5 Ma and 7.5 Ma concealed until now the evolution that led to the Hippopotamine Event and the subsequent success of these large semiaquatic herbivores. Part of this evolution is unveiled by the hippopotamid dental remains found at Chorora, a late Miocene site of the southern Afar Depression in Ethiopia spanning most of the fossil-depleted time interval. Although fragmentary, these remains represent a new, mid-sized hippopotamid species dated to ca. 8 Ma, as well as a somewhat younger, larger form. A cladistic analysis of a large array of cetartiodactyls indicates that the Chorora taxa were basal to the latest Miocene hippopotamines. The new species displays a mosaic of dental characters that support the attribution of the new species to a new genus within Hippopotaminae. The new fossils also clarify the course of early hippopotamine dental evolution. The Chorora hippopotamids suggest that transition to a marked abundance of hippopotamines with their unique dental pattern in African ecosystems occurred within a relatively short time interval, most probably between 8Ma and 7.5 Ma.
A new genus and species of late Pleistocene megalonychid sloth, Nohochichak xibalbahkah, gen. et sp. nov., is described from Hoyo Negro, a chamber in the Sac Actun cave system, Quintana Roo, Mexico. Phylogenetic analysis indicates that this new sloth is most closely related to Meizonyx salvadorensis from the middle Pleistocene of El Salvador, and that these two genera in turn are the sister clade to Megistonyx and Ahytherium in South America and not the other North American megalonychids, Pliometanastes and Megalonyx. This new sloth indicates that the number of sloth taxa involved in the Great American Biotic Interchange is greater than previously understood, and that a significant part of the Interchange biodiversity, as represented by taxa confined to the semitropical and tropical portions of Central and North America, remains to be discovered.
We describe here an ichthyological and herpetological assemblage that was obtained from washing-screening sediments from the early late Oligocene locality of Lokone, Kenya. This provides original information on the hitherto oldest known fauna from the East African Rift since it started to open from north to south during the Oligocene. The description of the fossil remains allows the identification of crocodiles (crocodylids), squamates (lacertid and Serpentes), turtles (pelomedusoids cf. Erymnochelys group), dipnoan (?Protopterus sp.), and actinopterygian fishes (Polypterus sp., Heterotis sp., Gymnarchus sp., Hydrocynus sp., Sindacharax sp. and other alestids, a claroteid, a cichlid, possibly a Distichodus, and other indeterminate fish). The preservation of this material testifies to a certain level of hydrodynamism, and the ecology of these ectotherm vertebrates suggests that freshwater environment was developed in this area. Moreover, the assemblage corresponds to herpeto- and ichthyofaunas that prefigured the modern African diversity as early as the Oligocene, before the Miocene invasion by Asian fish. It thus testifies to connections between the newly formed hydrographical system in the Turkana Basin with the Lokone main hydrographical system beginning at a very early stage of the Eastern Rift development.
Crocodile-tailed lizards are represented by a single extant species, Shinisaurus crocodilurus, the Chinese crocodile lizard, which until 2006 was completely unknown in the fossil record. These lizards may play an important role in understanding squamate phylogeny, but their biogeographic history remains murky. A new specimen from the middle Eocene of Messel, Germany, is the first record of the clade in the Paleogene of Europe. The specimen comprises an autotomized tail preserved in complete articulation. It retains a number of plesiomorphies with respect to S. crocodilurus, and it also differs from the coeval species Bahndwivici ammoskius, but comparisons with other shinisaurs are necessarily limited. The present specimen documents for the first time in the fossil record the superficially crocodile-like tail for which the extant species is named, indicating aquatic adaptation already by the middle Eocene. It furthermore raises questions about the identification of isolated ‘necrosaur' material from the European Paleogene. Finally, it adds to growing evidence of a taxonomically similar squamate fauna in Europe and North America in the early Paleogene.
As purely sedimentary structures, fossil footprints are all about shape. Correctly interpreting the significance of their surface topography requires understanding the sources of morphological variation. Differences among specimens are most frequently attributed to either taxonomy (trackmaker) or to preservation quality. ‘Well-preserved' tracks are judged more similar to pedal anatomy than ‘poorly preserved' ones, but such broad-brush characterizations confound two separate episodes in a track's history. Current evaluations of track quality fail to distinguish among behavioral, formational, intravolumetric, and postformational sources of variation. On the basis of analogy with body fossils, we recommend restricting assessments of track preservation quality to modifications that take place only after a track is created. Ichnologists need to try to parse the relative influence of factors affecting disparity, but we currently lack an adequate vocabulary to describe the overall shapes and specific features of formational variants.
A recent study hypothesized that Yanoconodon allini (Eutriconodonta: Jeholodentidae) from the Lower Cretaceous Yixian Formation of northeastern China was a terrestrial mammal capable of swimming. However, a detailed description and functional study of the postcranial skeleton of Yanoconodon have not yet been published. Here, we describe and analyze the functional morphology of its postcranial skeleton. Our analyses indicate that Yanoconodon has a combination of adaptive features for diverse locomotor modes. Its humerus has a spindle-shaped head, an indistinct neck, and a broad and shallow intertubercular groove, all of which resemble those of non-therian mammals and premammaliaform cynodonts. The lack of an enlarged olecranon process of the ulna and the lack of styloid processes at the distal ends of the radius and ulna would have limited the digging efficiency of Yanoconodon. The triangular scapula and the pivotal pectoral girdle of Yanoconodon resemble those in extant mammals with some climbing ability. The femur has a spherical head with a very short neck and small greater trochanter. No malleoli are present in the distal ends of the tibia and fibula to constrain the movement of the upper ankle joint in a parasagittal plane. The astragalus is partially superimposed on the calcaneus. The axial skeleton is elongate relative to the short limbs and small skull. These postcranial skeletal features imply that Yanoconodon had a sprawling posture and was a generalized terrestrial mammal, whereas its capability of swimming was inferred from multivariate ecomorphological analysis using extant small-bodied mammals as analogs.
An iniid fossil (Cetacea, Odontoceti) is reported based on a periotic found in the Codore Formation (late Miocene to middle Pliocene) of northwestern Venezuela. The marine sediments where the Codore dolphin was collected have yielded another cetacean and a diverse elasmobranch fauna. Cladistic analysis indicates a close relationship between the Codore dolphin and the extant Amazon River dolphin (Inia geoffrensis); key characteristics include a large cochlear portion that is dorsoventrally compressed and the extremely small size of the posterior process. High-resolution micro-computed tomography scans were used for the description and analysis of the bony labyrinth endocast. Geometric morphometric analysis of the bony labyrinth endocast places the Codore dolphin as intermediate between the La Plata dolphin (Pontoporia blainvillei) and Inia geoffrensis (principal component 1), but distinctive from both extant species (principal component 2). Comparisons of the depositional environment with cladistically informed reconstructions and inferences based on cochlear and vestibular anatomy suggest that the Codore dolphin had the flexibility to enter marine, brackish, and fluvial environments as some extant cetaceans do today (e.g., Pontoporia blainvillei).
The Pleistocene sea lion Proterozetes ulysses belongs to a monophyletic group of North Pacific otariids that includes the living genera Eumetopias and Zalophus. Mandibles of Proterozetes from the Port Orford Formation of Oregon are described and found to be intermediate in morphology and size to the other North Pacific otariids, most resembling Eumetopias. Among other characters, the presence of an oblong lingual prominence on the anterior lingual surface of the mandible links the taxon to Eumetopias, which commonly expresses the same feature. Uniquely among North Pacific otariids, Proterozetes possesses a p1 alveolus distinctly smaller than that of the p2. The presence of a distinct but morphologically intermediate taxon in the eastern North Pacific during the Pleistocene establishes it as a time of increased otariid diversity, in contrast to a suggested decline in other marine mammal clades. The timing of sea lion diversification along the west coast of North America appears to follow diversification in Japan, reinforcing the possibility of an eastward dispersal trend in the North Pacific after the end-Pliocene.
We investigated dental homologies, development, and growth in living and fossil hyracoids and tested if hyracoids and other mammals show correlations between eruption patterns, gestation time, and age at maturity. Unlike living species, fossil hyracoids simultaneously possess replaced P1 and canine teeth. Fossil species also have shorter crowns, an I3/i3, I2, and a hypoconulid on m3. Prenatal specimens of the living Procavia capensis and Heterohyrax brucei show up to three tooth buds posterior to dI1 and anterior to the seven upper cheek teeth that consistently erupt; erupted teeth include an anterior premolar but not a canine. Most lower cheek teeth finish eruption during growth in hyracoids, not after growth as in most other afrotherians. All hyracoids show the m1 at (lower) or near (upper) the beginning of eruption of permanent teeth; M3/m3 is the last permanent tooth to erupt. The living P. capensis erupts most lower antemolar loci before m2. In contrast, fossil hyraxes erupt lower antemolars after m2. Although the early eruption of antemolars correlates with increased gestation time and age at maturity in primates and Tupaia (i.e., ‘Schultz's rule’), and although modern hyraxes resemble some anthropoid primates in exhibiting long gestation and eruption of antemolars at or before molars, eruption patterns do not significantly covary with either life history parameter among afrotherians sampled so far. However, we do observe a shift in eruption timing and crown height in Procavia relative to fossil hyracoids, mirroring observations recently made for other ungulate-grade mammals.
Gomphotherium is a stem taxon of Elephantida that was widespread in Africa, Eurasia, and North America during the Miocene. However, the evolution of this genus is greatly debated because of morphological variation among the species of Gomphotherium. In the present work, we describe a cranium and accompanying material of Gomphotherium from the late middle Miocene Hujialiang Formation of Linxia Basin, China. The new material shows dental similarities to G. subtapiroideum from the middle Miocene of Europe; however, it displays some cranial, mandibular, and dental feature combinations that are distinct from the known species of Gomphotherium. Therefore, a new species, G. tassyi, is established. We further study the phylogeny of Gomphotherium by cladistic analysis and recognize four groups. The most basal ‘G. annectens group’ is a paraphyletic group that includes G. annectens, G. cooperi, G. sylvaticum, and G. hannibali. The African taxa, G. libycum and G. pygmaeus, constitute a monophyletic group that has not been named. The ‘G. angustidens group’ is a monophyletic group that includes G. inopinatum, G. mongoliense, G. connexum, and G. angustidens. In addition, the ‘derived Gomphotherium group,’ which includes G. subtapiroideum, G. tassyi, G. wimani, G. browni, G. productum, and G. steinheimense, was widely distributed in Eurasia and North America during the middle and late Miocene.
The anatomy and phylogenetic relationships of the Las Hoyas gobiosuchid (upper Barremian, La Huérguina Formation, Cuenca, Spain) are discussed on the basis of two fully articulated specimens. Phylogenetic analysis supports the monophyly of Gobiosuchidae, defined by the Las Hoyas taxon, Cassissuchus sanziuami, gen. et sp. nov., as the sister taxon of the Asian clade Gobiosuchus Zaraasuchus. The family Gobiosuchidae is diagnosed by a large number of synapomorphies, such as the presence of extensively sutured palpebrals, ridges on the dorsal surface of the posterolateral region of the squamosal, a longitudinal ridge along the dorsolateral surface of the surangular, appendicular osteoderms, and closure of the supratemporal fenestra. Specimens attributed to Lisboasaurus estesi, a putative gobiosuchid, are evaluated and the taxon regarded as a nomen dubium. Cassissuchus sanziuami provides new evidence on the anatomy of the pectoral and pelvic girdles and the forelimb morphology in Gobiosuchidae. The phylogeny of basal Crocodyliformes supports the nested sequence of three clades: Protosuchidae, Gobiosuchidae, and ((Shantungosuchus Sichuanosuchus) Shartegosuchidae), but their interrelationships are only partially solved. The early evolution of Crocodyliformes is further characterized by the high number of phenotypic specializations, many of which are related to the dermal skeletal overgrowth of the temporal region, palpebrals, and osteoderms.
Renewed research at the early Miocene fossil site of Bukwa in northeastern Uganda has resulted in new fossil finds, including fish, with representatives of two families, Cichlidae and Alestidae. Although the two families were previously briefly reported from Bukwa, we here give a more detailed account of the fishes based on newly collected material. The cichlid material, mainly composed of vertebrae, can be tentatively assigned to one or more species of Pseudocrenilabrinae. The alestid material, comprising a diversity of teeth, likely represents several different species of Alestes, Brycinus, and/or Bryconaethiops. Although the ichthyofaunal diversity of Bukwa is low, the fishes are important for indicating the paleoenvironment and hydrographic connections of Bukwa. The early Miocene was a critical time for African faunas, because it was during this time that the Afro-Arabian and Eurasian plates came into contact with one another, ending the long isolation of Africa, which, along with rifting in East Africa, created new terrestrial and hydrological connections allowing faunal interchanges. Bukwa is one of only a few African early Miocene localities known that sample fish and, based on these fish, the site probably represents an area of interconnected lakes and large rivers, including floodplains.
Gaining a detailed understanding of the geographic and temporal variations between Lancian mammalian faunas within the Western Interior Basin requires specimens to be associated with precise stratigraphic data, but only a few mammal-producing localities are documented in such detail from the Hell Creek Formation of southwestern North Dakota. Recent work at two sites in southwestern North Dakota resulted in the discovery of additional mammal specimens from previously documented localities for which the stratigraphic position is precisely recorded. The most productive site is situated 12.07 m below the K/Pg boundary and produced 18 mammal specimens that are referable to at least six taxa, two of which (the multituberculate Essonodon browni and the marsupialiform Glasbius twitchelli) are first occurrences for North Dakota. Another important specimen (NDGS 1719) was collected as float approximately 1 m below a documented vertebrate locality that is positioned 2.72 m below the K/Pg boundary. This specimen is also referable to G. twitchelli and consists of a right dentary preserving p2-m4, making it the most complete dentary yet referred to that species. Specimen NDGS 1719 is the stratigraphically highest mammal specimen referred to a specific taxon yet reported from the Hell Creek Formation in North Dakota, and its completeness facilitates a detailed description of the dentition of G. twitchelli. These discoveries expand our knowledge of the Lancian fauna from southwestern North Dakota and demonstrate that further work is needed to ensure that our understanding of the Lancian fauna from North Dakota is comprehensive.
The occipital regions of the braincases of two gigantic ctenacanthiform sharks are described from the Finis Shale (Virgilian, Upper Pennsylvanian, ca. 300 Ma) of Texas. Their original braincase lengths are estimated to have been 42.8–68.2 and 33.9–64.8 cm, based on comparison with smaller, more complete ctenacanthiform specimens (e.g., Tamiobatis). In complete ctenacanthiform body fossils (e.g., Goodrichthys), braincase length represents approximately 10% of total body length. This suggests that the Finis Shale sharks attained lengths up to 7 m (as large as modern great white sharks and Cretaceous cardabiodontids) and body weights of 1500–2500 kg. As apex predators, such large sharks probably maintained a high hepatosomatic index and may even have utilized lamnid-like heat exchange retia in critical parts of the body (e.g., brain, eyes, stomach).
Turonian deposits of the Goulmima area, Er-Rachidia Province in southern Morocco, have yielded a diverse marine vertebrate fauna, including chondrichthyans, bony fishes, and large marine reptiles such as plesiosaurians, mosasauroids, and turtles. These fossils are included in ovoid calcareous nodules that are difficult to prepare. Moreover, bones may be partially or totally dissolved, making their study difficult. Using computed tomography, we have reconstructed the entire skull anatomy of SMNS 81783, one of the rare plesiosaurian specimens found in this locality and more generally in Africa. The digital three-dimensional reconstruction of the skull and the mandible offers for the first time the possibility to describe this specimen exhaustively. The new anatomical characters recorded confirm that SMNS 81783 belongs to Elasmosauridae on the basis of (1) slender and triangular skull; (2) beak index equal to 42%; (3) temporal fossa estimated to occupy about 40% of the skull length; (4) long process of the premaxillae extending posteriorly to meet the parietal above the orbit and separating the frontals; and (5) margin of the temporal fenestra lacking obvious contribution from the frontal. A preliminary phylogenetic analysis confirms its elasmosaurid affinity. The relationships between SMNS 81783, Libonectes atlasense, and Libonectes morgani, as well as the presence of stapes and pineal foramen, are discussed.