Some recent mainly Mesozoic papers:
Sahonachelys mailakavava gen. et sp. nov.
The Maevarano Formation in northwestern Madagascar has yielded a series of exceptional fossils over the course of the last three decades that provide important insights into the evolution of insular ecosystems during the latest Cretaceous (Maastrichtian). We here describe a new genus and species of pelomedusoid turtle from this formation, Sahonachelys mailakavava, based on a nearly complete skeleton. A phylogenetic analysis suggests close affinities of Sahonachelys mailakavava with the coeval Madagascan Sokatra antitra. These two taxa are the only known representatives of the newly recognized clade Sahonachelyidae, which is sister to the speciose clade formed by Bothremydidae and Podocnemidoidae. A close relationship with coeval Indian turtles of the clade Kurmademydini is notably absent. A functional assessment suggests that Sahonachelys mailakavava was a specialized suction feeder that preyed upon small-bodied invertebrates and vertebrates. This is a unique feeding strategy among crown pelomedusoids that is convergent upon that documented in numerous other clades of turtles and that highlights the distinct evolutionary pathways taken by Madagascan vertebrates.
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Highlights
Footprints from Puesto Vera (Patagonia, Argentina) are reported for the first time.
Dicynodontipus ichnofauna from Los Menucos Complex is late Lopingian-Early Triassic in age.
Therapsid footprints occurred in an upland setting dominated by intense volcanism.
Abstract
The Los Menucos Complex (North Patagonian Massif, RÃo Negro province, Argentina) has been long regarded as Late Triassic in age. A Dicynodontipus-dominated record is historically known from this complex and particularly from the Puesto Tscherig locality. Here we report the Puesto Vera site, where a new track-bearing horizon was discovered within a 73-m-thick volcano-sedimentary succession. Footprints from this site are morphologically similar to those from Puesto Tscherig and resemble footprints classically referred to the ichnogenus Dicynodontipus, thus we assigned the new material to Dicynodontipus isp. The new ichnological material is age constrained to a time interval between the Changhsingian (Lopingian, Permian) and the Olenekian (Early Triassic), on the basis of recently obtained UâPb radiometric datings from two ignimbrites, respectively at the base and top of the Puesto Vera stratigraphic section. Interestingly, the Dicynodontipus record from the Los Menucos Complex is older than previously supposed. The inherent chronostratigraphy is consistent with the temporal occurrence of the ichnotaxon, which to date has a global distribution spanning from the Wuchiapingian (Lopingian, Permian) of northern Italy to the early Middle Triassic of Germany. Taking into account the most recent datings as well as previous literature about the geology and paleontology of Los Menucos, the new age-constrained finding turns out to encompass the Permian-Triassic transition and mirror a tetrapod fauna dwelling in a mid-latitude, highland paleoenvironment of southwestern Gondwana.
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Turbidites have been regarded as an important sedimentary infilling component in both oceans and lakes, but limited studies have been performed on the mechanisms governing the initiation and development of lacustrine turbidite systems. The present study offers unique insight into the controls and potential extent of ancient lacustrine turbidite systems by an investigation of the Triassic Ordos Lake, where a large turbidite system had been traced across >25 653 km2. This article shows by comparison that the Triassic Ordos Lake turbidite system is larger than all known modern and ancient lacustrine counterparts. The exceptionally large intracontinental sag basin provided a relatively unconfined environment for the development of the turbidite system, explaining its vast extent. Extraordinary flood events formed during the Carnian Pluvial Episode facilitated continuous sediment supply into the turbidite system, supporting its accumulation. Lacustrine floodârelated turbidity currents travelled as sedimentâladen turbulent flows, showing an increase in the proportion of suspendedâload deposits and a decrease in the proportion of bedâload deposits downstream from the river mouth. Five architectural elements have been revealed, reflecting a distinctive assemblage of erosional bedforms and depositional bedforms in channelâlobe systems, and their recognition criteria were established. This study changes the traditional understanding of lacustrine turbidite systems, generally interpreted as having smaller sizes, and demonstrates likewise in the lacustrine realm, that extreme flood events can generate a worldâclass deepâwater turbidite system, which can even be comparable with its submarine counterparts. This study also confirms that the combination of lowâgradient slopes and a longâlived, mixed load, prograding fluvial feeder system can produce exceptionally largeâscale deepâlake floodârelated turbidites. Furthermore, it also has implications for the prediction of facies and reservoir quality in ancient lacustrine turbidite systems.
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Some of the West Antarctica crustal blocks as the Antarctic Peninsula and Thurston Island were by the Late Cretaceous more geographically related to South America's southern tip than to the rest of Gondwanan portions.
Regarding South America's southernmost portion, the Gondwanan Episode happened in a paleogeographical unit assembled by the Antarctic Peninsula crustal block + Magallanes Region and Patagonia from the Late Cretaceous (Campanian/Maastrichtian) to the Early Paleogene (Late Paleocene-Early Eocene).
Recent discoveries of vertebrates from the Late Cretaceous of southern South America and Antarctic Peninsula have played a key role in formulating and testing a biogeographic hypothesis of the West Weddellian province.
Abstract
The Mesozoic plate tectonic and paleogeographic history of the final break up of West Gondwana had a profound effect on the distribution of terrestrial vertebrates in South America. As the supercontinent fragmented into a series of large landmasses (South America, Antarctica, Australia, New Zealand, the Indian subcontinent, and Madagascar), particularly during the Late Jurassic and Cretaceous, its terrestrial vertebrates became progressively isolated, evolving into unique faunal assemblages. The episodic nature of South American mammalian Cenozoic faunas became apparent in its modern formulation after George Gaylord Simpson's seminal works on this topic. Two aspects add complexity to this generally accepted scheme: first, the fact that South America is not (and was not) a biogeographic unit, as the Neotropical Region does not include its southernmost tip (the Andean Region, including Patagonia and the southern Andes). Second, and intimately linked with the first one, that South America was not an island continent during the Late Cretaceous and the beginning of the Cenozoic, being its southernmost portion closely linked with West Antarctica up to the late Paleocene at least. Here we stress on this second aspect; we summarize a series of recent, detailed paleogeographical analyses of the continental breakup between Patagonia (including the Magallanes Region) and the Antarctic Peninsula crustal block, beginning with the opening of the Atlantic Ocean in the Early Cretaceous and running up to the Early Paleogene with the expansion of the Scotia Basin. In second place, we comment on the implications of these distinct paleogeographic and paleobiogeographic scenarios (before and after their geographic and faunistic isolation) for the evolution of South American terrestrial mammalian faunas. Summarizing, (1) we recognize a West Weddellian terrestrial biogeographic unit with the assemblage of the southern part of South America (Patagonia and the Magallanes Region) and the Antarctic Peninsula (and probably Thurston Island) crustal block of West Antarctica, spanning from the Late Cretaceous (Campanian) through the Early Paleogene (Paleocene); (2) we suggest that the Antarctic Peninsula acted as a double "Noah's Ark" regarding, first, the probable migration of some non-therian lineages into southern South America; later, the migration of metatherians to Australasia.
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