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The late Miocene Gatun Formation of northern Panama contains a highly diverse and well sampled fossil marine assemblage that occupied a shallow-water embayment close to a purported connection between the Pacific and Atlantic (Caribbean) oceans. However, the diverse chondrichthyan fauna has been poorly documented. Based on recent field discoveries and further analysis of existing collections, the chondrichthyan fauna from this unit comprises at least 26 taxa, of which four species are extinct today. The remaining portion of the total chondrichthyan biodiversity has affinities with modern taxa and is therefore comprised of long-lived species. Based on known records of the modern geographic distribution range of the Gatun chondrichthyans, the fauna has mixed biogeographic affinities suggesting that around 10 million yr ago, a connection likely occurred between the Pacific Ocean and the Caribbean Sea. Given the known habitat preferences for modern chondrichthyans, the Gatun fauna was primarily adapted to shallow waters within the neritic zone. Finally, comparisons of Gatun dental measurements with other faunas suggest that many of the taxa have an abundance of small individuals, in agreement with previous studies that proposed this area as a paleonursery habitat for the species Carcharocles megalodon.
Six species of conulariids, assigned to four genera, were recovered from the type locality of the Cat Head Member of the Red River Formation in southern Manitoba, Canada. These are middle Katian (Late Ordovician) in age. The most abundant conulariid species from this locality, Conularia porcella, is new, and is represented by 21 specimens. Additionally, 28 three-dimensionally preserved micromorphic conulariids, assigned to Eoconularia aff. loculata, were recovered using acetic acid preparation from limestone samples of late Katian (Late Ordovician) age. These samples had been collected from Churchill, northern Manitoba, by the Geological Survey of Canada's J. B. Tyrrell in 1894. These taxa are unusually abundant for conulariids, which are normally represented by only a few specimens from any given locality, and this abundance may be a reflection of the exceptional preservation at these two localities.
To clarify the systematic positions of the important gonyaulacacean genera Operculodinium Wall, 1967 emend. Matsuoka et al., 1997 and Protoceratium Bergh, 1881, we present in detail the tabulation of the Oligocene–Pleistocene, thermophilic, cyst-defined species Operculodinium bahamense Head in Head and Westphal, 1999 emend., and the extant, cosmopolitan, theca-defined species Protoceratium reticulatum (Claparède and Lachmann, 1859) Bütschli, 1885. Both species have a sexiform hyposomal tabulation, and L-type (Protoceratium reticulatum) or modified L-type (Operculodinium bahamense) ventral organization. Protoceratium reticulatum has dextral torsion of the hypotheca, requiring assignation of the genus to the subfamily Cribroperidinioideae Fensome et al., 1993, whereas Operculodinium bahamense has neutral torsion requiring assignation to the subfamily Leptodinioideae Fensome et al., 1993. The stratigraphic range of this subfamily is now extended upwards to the lower Pleistocene. Paradoxically, Protoceratium reticulatum produces a cyst whose morphology is circumscribed by the cyst-defined genus Operculodinium, either implying polyphyletic origins for this genus or that combinations of ventral organization and torsion used to subdivide the family Gonyaulacaceae cannot always be applied rigidly. In detail, Operculodinium bahamense is shown to have an unusual ventral tabulation in which the first apical plate contacts the apical pore complex but not the sulcus. The new term “episert” is proposed to describe this plate relationship, which appears to have evolved independently in several lineages of the suborder Gonyaulacineae.
The first records of the upper Cambrian agnostoid genera Kormagnostella, E. Romanenko, in Romanenko and Romanenko, 1967, and Biciragnostus F. Ergaliev, in Eraliev and Ergaliev, 2001, in Laurentian North America are from a narrow stratigraphic interval in the Steptoean–Sunwaptan boundary interval (Furongian, Jiangshanian) of Nevada and Utah. In Nevada, both genera occur in a condensed bioclastic lag below a major flooding surface, and Kormagnostella also appears in a transgressive interval in Utah. Immigration of these genera is associated with sea level rise, and also with faunal turnover. Biciragnostus is confined to the latest Elvinia Zone, immediately below the onset of a trilobite and agnostoid extinction event at the base of the Irvingella major Zone (basal Sunwaptan). Kormagnostella is present in the latest Elvinia Zone, and has its highest occurrence in the I. major Zone. Stratigraphic data from the Karatau-Naryn Terrane, Kazakhstan indicate that both genera disappear near the local extinction of Irvingella, suggesting that faunal turnover in that region may have been broadly correlative with the more profound extinction in Laurentia. New species are Kormagnostella advena, K. insolita and Biciragnostus viator.
Strophomenid brachiopods have long been interpreted as “snowshoe” strategists, with their flattened concavo-convex valves providing resistance to foundering in very soft sediments. There has been a sharp difference of opinion in whether the shells were oriented with their convex or their concave surface in contact with the sediment. This study, along with independent evidence from sedimentology, ichnology, and morphology, indicates that the strophomenids lived with their shells concave down (convex up). Experiments indicate the force required to push shells into soft cohesive muds is much greater for the convex up than for the convex down orientation. Forces also increase with shell curvature. All measured forces greatly exceed estimates of the downward force exerted by the weight of the shell, indicating that foundering resistance may not have been the key functional requirement. Instead, a convex up orientation would have provided resistance to overturning in currents, in particular if the valves gaped widely. The “snowshoe” may not be the relevant paradigm for the shell morphology of these forms. An alternative is that they functioned more as a tip-resistant base, similar to those of garden umbrellas or stanchions.
The west coast of North America record of the shallow-marine stromboid gastropod genus Rimella Agassiz, 1841 is restudied for the first time in 90 years. This genus comprises a small group of Paleogene gastropods characterized by having an ornamented fusiform shell, a posterior canal ascending the spire, and simple (non-flared) outer lip. Rimella, whose familial ranking has been inconsistent, is placed here in family Rostellariidae Gabb, 1868, subfamily Rimellinae Stewart, 1927. Ectinochilus Cossmann, 1889; Macilentos Clark and Palmer, 1923; Vaderos Clark and Palmer, 1923; and Cowlitzia Clark and Palmer, 1923 are recognized here as junior synonyms of Rimella. Four species are recognized from the west coast of North America: early to middle Eocene Rimella macilenta White, 1889; early Eocene Rimella oregonensis Turner, 1938; middle to late Eocene Rimella supraplicata (Gabb, 1864) new combination, of which Rostellaria canalifer Gabb, 1864, Cowlitizia washingtonensis Clark and Palmer, 1923, and Cowlitzia problematica Hanna, 1927 are recognized here as junior synonyms; and late Eocene Rimella elongata Weaver, 1912.
Rimella was a warm-water gastropod whose earliest known record is of early Paleocene (Danian) age in Pakistan. Other than the west coast of North America, Rimella is found in Eocene strata in western Europe, Turkey, Egypt, Pakistan, southeastern United States, Panama, Peru, and, to a lesser degree, in Trinidad, Columbia, Java, and New Zealand. Global cooling near the end of the Eocene greatly diminished the genus. Its youngest known occurrences are of early Oligocene age in Germany, Italy, England, and Peru.
A new tillodont, Anthraconyx hypsomylus, n. gen. n. sp., is described from the early Eocene Cambay Shale Formation at Vastan Lignite Mine, Gujarat, India. Anthraconyx hypsomylus is the smallest Eocene tillodont and is distinguished by having the most buccally hypsodont cheek teeth of any known esthonychine. The closest dental resemblances are to North American Esthonyx and Azygonyx and European Plesiesthonyx, providing further evidence of affinities between the Vastan local fauna and Euroamerican vertebrate faunas.
The Dinwoody Formation of the western United States represents an important archive of Early Triassic ecosystems in the immediate aftermath of the end-Permian mass extinction. We present a systematic description and a quantitative paleoecological analysis of its benthic faunas in order to reconstruct benthic associations and to explore the temporal and spatial variations of diversity, ecological structure and taxonomic composition throughout the earliest Triassic of the western United States. A total of 15 bivalve species, two gastropod species, and two brachiopod species are recognized in the study area. The paleoecological analysis shows that the oldest Dinwoody communities are characterized by low diversity, low ecological complexity and high dominance of few species. We suggest that this low diversity most likely reflects the consequences of the mass extinction in the first place and not necessarily the persistence of environmental stress. Whereas this diversity pattern persists into younger strata of the Dinwoody Formation in outer shelf environments, an increase in richness, evenness and guild diversity occurred around the Griesbachian–Dienerian boundary in more shallow marine habitats. This incipient recovery towards the end of the Griesbachian is in accordance with observations from other regions and thus probably represents an interregional signal. In contrast to increasing richness within communities (alpha-diversity), beta-diversity remained low during the Griesbachian and Dienerian in the study area. This low beta-diversity reflects a wide environmental and geographical range of taxa during the earliest Triassic, indicating that the increase of within-habitat diversity has not yet led to significant competitive exclusion. We hypothesize that the well-known prevalence of generalized taxa in post-extinction faunas is primarily an effect of reduced competition that allows species to exist through the full range of their fundamental niches, rather than being caused by unusual and uniform environmental stress.
The cephalopods from Union y Progreso represent the first fossil assemblage described from the Parras Shale in Coahuila, Mexico. Pseudoschloenbachia (Pseudoschloenbachia) aff. P. (P.) mexicana (Renz, 1936), P. (P.) mexicana (Renz, 1936), Baculites haresi Reeside, 1927, and Menabites (Delawarella) vanuxemi (Morton, 1830) have a geographically restricted occurrence. Didymoceras juv. sp., Menuites juv. sp., Polyptychoceras juv. sp., Pseudoxybeloceras (Parasolenoceras) juv. sp., and Scaphites sp. ex gr. S. hippocrepis (DeKay, 1828) are represented by juveniles and could not be determined to species level. Desmophyllites diphylloides (Forbes, 1846) is the only long-ranging, cosmopolitan species described from this assemblage. Three new species are described: Eutrephoceras irritilasi n. sp., Hypophylloceras (Neophylloceras) arturoi n. sp., and Tetragonites silencioensis n. sp. The morphotype Baculites n. sp. is also inferred to be distinct. The faunal composition of this assemblage indicates a late early Campanian age. This assemblage shows a high degree of endemism. The causes for this endemism are currently unknown and difficult to assess. Nevertheless, the generic composition of the Union y Progreso ammonite assemblage suggests a short-term early Campanian endemic event.
The geographic population patterns of Lingula anatina across the Indo-West Pacific region are analyzed based on mitochondrial COI and nuclear EF-1α gene sequences. Compared with the remarkable morphological stasis, genetic evidence of extant Lingula species displays deep genetic divergence. Three distinct COI lineages were detected for L. anatina, one of which is from Qinhuangdao (Hebei, China, Bohai Sea), the other two from Beihai (Guangxi, China, Gulf of Tonkin). Individuals from South Japan have a very close relationship with one of the two COI lineages found in Beihai, which is also supported by EF-1α results, suggesting a relatively recent migration between South China Sea and East China Sea. Genetic distances between the three lineages of L. anatina are rather high (8.9%, 8.6%, and 2.7%), and those between L. anatina and L. adamsi is much higher (44.5%), compared to other marine invertebrates. Both tectonic evolution and the repeated Quaternary glaciations have contributed to the complex phylogeographic pattern found in these recent Lingula anatina populations.
Colonial rugose corals ranging in age from Carboniferous to Late Triassic and Early Permian (Cisuralian) fusulinids have been recovered from cobbles in a conglomerate in the Upper Triassic Brisbois Member of the Vester Formation in the Izee terrane in central Oregon. Early Permian (late Sakmarian or early Artinskian) fusulinids typical of those present in the Coyote Butte Limestone in the nearby Grindstone terrane (part of the allochthonous McCloud Belt) include Eoparafusulina, Pseudofusulinella, Chalaroschwagerina, and Schwagerina. The presence of these fusulinid genera and the Pennsylvanian coral Heritschioides?, which is mostly restricted to the McCloud Belt, suggest these particular cobbles were derived from limestone in that belt. The Early Permian fusulinids Changmeia bostwicki new species and Changmeia bigflatensis new species, and the Early Permian corals Yokoyamaella? oregonensis new species and Yokoyamaella? sp. 1, all of which have Tethyan affinities, occur rarely in other cobbles. The presence of definitive fossils from the two different realms in a conglomerate associated with beds containing Late Triassic ammonoids indicates that by Late Triassic time a fragment of a Tethyan terrane was close to or had been amalgamated with a terrane belonging to the McCloud Belt.
A partial skeleton of a pelagornithid bird found in latest Oligocene or earliest Miocene marine strata in Oregon consists of a pelvis fragment, thoracic vertebrae, and leg bones of a single individual. It is the most completely preserved pelagornithid from the late Oligocene/early Miocene, and one of the few bony-toothed birds from this time period in general. The new fossil is from the Nye Mudstone and shows some previously unknown features that contribute to a better understanding of the osteology of pelagornithids. Because Paleogene and late Neogene pelagornithids differ in several osteological features and the temporally intermediate forms are poorly known, it further bridges a gap in our knowledge of character evolution in pelagornithids. The interrelationships within Pelagornithidae are still poorly resolved, but we detail that a clade of Neogene species, which the Oregon pelagornithid is not part of, can be supported by a derived morphology of the femur. To ease description of Neogene pelagornithids, we synonymize Palaeochenoides Shufeldt, 1916 and Tympanonesiotes Hopson, 1964 with Pelagornis Lartet, 1857, and suggest classification of all Neogene pelagornithids in the latter taxon.
Simojovelhyus pocitosense is based on a lower jaw fragment with three molars from the late Oligocene amber mine deposits near the village of Simojovel, Chiapas Province, Mexico. It is the oldest fossil mammal known from Central America. It was described by Ferrusquia-Villafranca in 2006 as a helohyid, a group of primitive artiodactyls known from the Bridgerian and Uintan (older than 49–42 Ma), yet it comes from early Arikareean deposits about 25–27 Ma, suggesting that it was a very late helohyid living more than 10 m.y. after their apparent Uintan extinction. We re-examined the specimen, and compared it to the large collection of recently described peccaries from the Chadronian (Perchoerus minor) and Orellan (Perchoerus nanus) and Bridgerian helohyids (Helohyus sp.). Once the range of variation of characters in helohyids and peccaries is accounted for, Simojovelhyus shows derived similarities to early peccaries, especially in the bunodont molars with inflated cusps and the configuration of cristids and accessory cuspulids, and none of the incipient lophodonty and primitive morphology seen in helohyids. In fact, the only real similarity other than symplesiomorphies between Simojovelhyus and helohyids is its small size, but it is close to the size range of the tiny Chadronian peccary P. minor. Thus, based on both derived tooth characters and its age, it is much more parsimonious to regard Simojovelhyus as a tiny Mexican peccary from the Arikareean, not a very late helohyid. This removes the anomalously late occurrence of helohyids from the mammalian fossil record, and forces a re-examination of our view of mammalian evolution in Central America.
Late Carnian–early Norian corals from the Luning and Osobb formations in west-central Nevada represent an important Late Triassic fauna for understanding the paleoecology and the paleogeography of the eastern Panthalassa region during Late Triassic time. The corals occur in bedded limestone representing biostromes and patch reefs and their composition presages the important global changeover of faunas of the intra-Norian interval. A taxonomic analysis of over 60 specimens reveals a majority of colonial corals ranging from cerioid, astreoid (i.e., cerioid-plocoid lacking walls), meandroid and thamnasterioid types. Surprisingly, remnants of the original aragonite microstructure remain in some specimens, allowing a better comparison with more remote Tethyan corals. In total, 14 genera have been identified from Nevada while two genera remain undetermined. The fauna is composed of species considered typical of both the North American Cordillera and cratonal South America. The following genera and species are new and endemic to the Americas: Khytrastrea silberlingi and K. cuifiamorpha, Flexastrea serialis, Nevadoseris punctata, Areaseris nevadaensis and a new genus Minasteria (with Astrocoenia shastensis Smith, 1927 as type species). Likewise are the new species: Margarogyra silberlingi and Curtoseris dunlapcanyonae. Genera Meandrovolzeia, Margarogyra, Ceriostella, Ampakabastraea, Retiophyllia, Distichomeandra, Curtoseris, Thamnasteria and Astraeomorpha provide important links to the former Tethys province. The revised coral fauna changes previous views of the close taxonomic similarity with the Tethys, instead producing a paleogeographic pattern emphasizing a much greater degree of endemism. This pattern emphasizes the isolation of Nevada from the Tethys and the similarities with some outboard terranes of the Cordillera.