Late Triassic (Late Norian) gastropods from the Wallowa Terrane (Idaho,USA)

A diverse Late Triassic (Late Norian) gastropod fauna is described from the Mission Creek Limestone of the Wallowa terrane (Idaho, USA). Sample standardization by rarefaction analysis indicates that the fauna is even more diverse than the Late Triassic gastropod fauna from the Pucara Formation (Peru) which represents the most diverse gastropod fauna from South America. The gastropod fauna consists of 66 species; several genera are reported for the first time from North America. A high percentage of the species are highly ornamented and several have distinct siphonal canals. This suggests that the appearance of truly Mesozoic elements among the gastropods began before the Mesozoic Marine Revolution in other clades. The fauna is dominated by high-spired strongly ornamented procerithiids, a group more characteristic for the Jurassic. Comparison of the present fauna and the Iranian Nayband Formation gastropod fauna show that the procerithiids underwent a first global radiation in the Late Triassic. The high number of new species in this fauna suggests that sampling of Late Triassic gastropod faunas is still incomplete and hinders palaeobiogeographic considerations. Previous suggesions that gastropod faunas from the Wallowa and Wrangellia terranes resemble each other and are distinct from those of Alexander, Chulitna, and Farewell terranes are basically corroborated. The gastropod fauna of the Mission Creek Limestone differs considerably from that of the western and central Tethys but shares several taxa with the Late Triassic gastropod fauna of the Pucara Formation in Peru. Thus, the Hispanic corridor was probably not present in the Norian but opened only in the Early Jurassic. The subfamily Andangulariinae is introduced and placed in the Zygopleuridae. The generaSpiniomphalus, Nodoconus, Gudrunella, Blodgettella, Idahospira, andSiphonilda and the subgenusCryptaulax (Wallowax) are introduced. 27 species are erected. A lectotype is designated forCryptaulax rhabdocolpoides Haas, 1953.      

苏皖地区早志留世坟头组腹足类

记述苏皖地区坟头组腹足类１１属１２种,其中Ｕｍｂｏｎｅｌｌｉｎａ ｃｆ．ｇｌｏｂｕｌｏｓａ Ｙｕ,Ｒａｐｈｉｓｔｏｍｉｎａ ｒｈｏｍｂｉｓｔｏｍａ Ｙｕ,Ｔｒｏｃｈｏｎｅｍａ ｃｆ．ｆｒａｇｉｌｅ Ｕｌｒｉｃｈ ｅｔ Ｓｃｏｆｉｅｌｄ常见于西南地区早志留世秀山组、上翁项群及石牛栏组。坟头组上段所产的三叶虫Ｃｏｒｏｎｃｅｐｈａｌｕｓ,Ｋａｉｌｉａ;头足类Ｓｉｃｈｕａｎｏｃｅｒａｓ;腕足类Ｓａｌｏｐｉ     

Early Carboniferous radiolarians from north-west Thailand: palaeogeographical implications

Moderately well-preserved radiolarian assemblages are described from bedded cherts south of Mae Hong Son, north-west Thailand. Twenty species and subspecies are identified, including one new species ( Archocyrtium sashidai Feng sp. nov.). The assemblages belong to the middle Early Carboniferous Albaillella indensis and Eostylodictya rota zones. The new data suggest that there was a pelagic basin between the Shan-Thai terrane and Gondwana during the Early Carboniferous. This implies, contrary to previous interpretations, that the Shan-Thai terrane had already rifted apart from Gondwana during the Early Carboniferous.     

Recent advances in New Caledonian biogeography

The biota of New Caledonia is one of the most unusual in the world. It displays high diversity and endemism, many peculiar absences, and far‐flung biogeographic affinities. For example, New Caledonia is the only place on Earth with both main clades of flowering plants – the endemic Amborella and ‘all the rest’, and it also has the highest concentration of diversity in conifers. The discovery of Amborella's phylogenetic position led to a surge of interest in New Caledonian biogeography, and new studies are appearing at a rapid rate. This paper reviews work on the topic (mainly molecular studies) published since 2013. One current debate is focused on whether any biota survived the marine transgressions of the Paleocene and Eocene. Total submersion would imply that the entire fauna was derived by long‐distance dispersal from continental areas since the Eocene, but only if no other islands (now submerged) were emergent. A review of the literature suggests there is little actual evidence in geology for complete submersion. An alternative explanation for New Caledonia's diversity is that the archipelago acted as a refugium, and that the biota avoided the extinctions that occurred in Australia. However, this is contradicted by the many groups that are anomalously absent or depauperate in New Caledonia, although represented there by a sister group. The anomalous absences, together with the unusual levels of endemism, can both be explained by vicariance at breaks in and around New Caledonia. New Caledonia has always been situated at or near a plate boundary, and its complex geological history includes the addition of new terranes (by accretion), orogeny, and rifting. New Caledonia comprises ‘basement’ terranes that were part of Gondwana, as well as island arc and forearc terranes that accreted to the basement after it separated from Gondwana. The regional tectonic history helps explain the regional biogeography, as well as distribution patterns within New Caledonia. These include endemics on the basement terranes (for example, the basal angiosperm, Amborella), disjunctions at the West Caledonian fault zone, and great biotic differences between Grande Terre and the Loyalty Islands.     

Silurian trace fossils in carbonate turbidites from the Alexander arc of southeastern Alaska

Early to Late Silurian (Llandovery‐Ludlow) body and trace fossils from the Heceta Formation of southeastern Alaska are preserved in the oldest widespread carbonates in the Alexander terrane. These fossils represent the earliest benthos to inhabit diverse shallow and deep subtidal environments in the region and are important indicators of early stages in benthic community development within the evolving Alexander arc. The ichnofossils are particularly significant because they add to a small but growing body of knowledge about trace fossils in deep‐water carbonates of Paleozoic age.

Carbonate turbidites that originated along a deep marine slope within the arc yield a low‐diversity suite of trace fossils consisting of five distinct biogenic forms. Simple burrows (Planolites, two forms), ramifying tunnels (Chondrites), and tiny cylindrical burrows (?Chondrites) represent the feeding activities (fodinichnia) of pre‐turbidite animals that burrowed in the lime mud before the influx of coarser sediment deposited by turbidity currents. These trace fossils are associated locally with cross‐cutting burrows created as domichnia (Palaeophycus). Rarer hypichnial burrows and endichnial traces were created by post‐turbidite animals that fed soon after the deposition of coarse detritus from turbidity flows.

Trace fossils in these deposits reflect much lower diversity levels than in Paleozoic siliciclastic turbidites. This difference may represent unfavorable environmental conditions for infaunas, differential preservation, or significant paleogeographic isolation of the Alexander terrane during the Silurian. Greater utilization of trace fossils in terrane analysis may help to resolve this issue and provide new data for reconstructing the paleogeography of circum‐Pacific terranes.     

Panbiogeography of Nothofagus (Nothofagaceae): analysis of the main species massings

Aim The aim of this paper is to analyse the biogeography of Nothofagus and its subgenera in the light of molecular phylogenies and revisions of fossil taxa. Location Cooler parts of the South Pacific: Australia, Tasmania, New Zealand, montane New Guinea and New Caledonia, and southern South America. Methods Panbiogeographical analysis is used. This involves comparative study of the geographic distributions of the Nothofagus taxa and other organisms in the region, and correlation of the main patterns with historical geology. Results The four subgenera of Nothofagus have their main massings of extant species in the same localities as the main massings of all (fossil plus extant) species. These main massings are vicariant, with subgen. Lophozonia most diverse in southern South America (north of Chiloé I.), subgen. Fuscospora in New Zealand, subgen. Nothofagus in southern South America (south of Valdivia), and subgen. Brassospora in New Guinea and New Caledonia. The main massings of subgen. Brassospora and of the clade subgen. Brassospora/subgen. Nothofagus (New Guinea–New Caledonia–southern South America) conform to standard biogeographical patterns. Main conclusions The vicariant main massings of the four subgenera are compatible with largely allopatric differentiation and no substantial dispersal since at least the Upper Cretaceous (Upper Campanian), by which time the fossil record shows that the four subgenera had evolved. The New Guinea–New Caledonia distribution of subgenus Brassospora is equivalent to its total main massing through geological time and is explained by different respective relationships of different component terranes of the two countries. Global vicariance at family level suggests that Nothofagaceae/Nothofagus evolved largely as the South Pacific/Antarctic vicariant in the breakup of a world‐wide Fagales ancestor.     

New Caledonian biogeography: a reply to Murienne

This note replies to criticisms raised by Murienne (Journal of Biogeography, 2010, doi: 10.1111/j.1365‐2699.2010.02321.x ). Herein it is argued that assuming distributions in New Caledonia are caused by current environmental factors overlooks the possible importance of regional tectonic history for the biogeography.     

The Galápagos Islands: biogeographic patterns and geology

In the traditional biogeographic model, the Galápagos Islands appeared a few million years ago in a sea where no other islands existed and were colonized from areas outside the region. However, recent work has shown that the Galápagos hotspot is 139 million years old (Early Cretaceous), and so groups are likely to have survived at the hotspot by dispersal of populations onto new islands from older ones. This process of metapopulation dynamics means that species can persist indefinitely in an oceanic region, as long as new islands are being produced. Metapopulations can also undergo vicariance into two metapopulations, for example at active island arcs that are rifted by transform faults. We reviewed the geographic relationships of Galápagos groups and found 10 biogeographic patterns that are shared by at least two groups. Each of the patterns coincides spatially with a major tectonic structure; these structures include: the East Pacific Rise; west Pacific and American subduction zones; large igneous plateaus in the Pacific; Alisitos terrane (Baja California), Guerrero terrane (western Mexico); rifting of North and South America; formation of the Caribbean Plateau by the Galápagos hotspot, and its eastward movement; accretion of Galápagos hotspot tracks; Andean uplift; and displacement on the Romeral fault system. All these geological features were active in the Cretaceous, suggesting that geological change at that time caused vicariance in widespread ancestors. The present distributions are explicable if ancestors survived as metapopulations occupying both the Galápagos hotspot and other regions before differentiating, more or less in situ.