Stratigraphy of the Early Paleogene Muthaymimah Formation exposed on the western flank of the Northern Oman Mountains

Sixty-one species belonging to 32 foraminiferal genera are reported from the Paleocene to Early Eocene Muthaymimah Formation at different localities in the western flank of the Northern Oman Mountains of the United Arab Emirates (UAE) and Oman. Several of the discovered species provide precise ages for the Paleocene series (Bolivinoides curtus and Neoflabellina jarvisi). A prominent conglomerate bed marks the K–T boundary between the Late Cretaceous Simsima Formation and Muthaymimah Formation in the study area. Occurrences of planktonic foraminiferal Morozovella inconstans (Subbotina, 1947) and Morozovella trinidadensis (Bolli, 1957) of Early Paleocene age (P1–P2 zones) are recorded for the first time in some locations in the study area.

http://zoobank.org/2266E0F1-0C0F-428F-B18C-F8347F0CEE07     

Fossil moonseeds from the Paleogene of West Gondwana (Patagonia,Argentina)

Premise of the Study

The fossil record is critical for testing biogeographic hypotheses. Menispermaceae (moonseeds) are a widespread family with a rich fossil record and alternative hypotheses related to their origin and diversification. The family is well‐represented in Cenozoic deposits of the northern hemisphere, but the record in the southern hemisphere is sparse. Filling in the southern record of moonseeds will improve our ability to evaluate alternative biogeographic hypotheses.

Methods

Fossils were collected from the Salamanca (early Paleocene, Danian) and the Huitrera (early Eocene, Ypresian) formations in Chubut Province, Argentina. We photographed them using light microscopy, epifluorescence, and scanning electron microscopy and compared the fossils with similar extant and fossil Menispermaceae using herbarium specimens and published literature.

Key Results

We describe fossil leaves and endocarps attributed to Menispermaceae from Argentinean Patagonia. The leaves are identified to the family, and the endocarps are further identified to the tribe Cissampelideae. The Salamancan endocarp is assigned to the extant genus Stephania. These fossils significantly expand the known range of Menispermaceae in South America, and they include the oldest (ca. 64 Ma) unequivocal evidence of the family worldwide.

Conclusions

Our findings highlight the importance of West Gondwana in the evolution of Menispermaceae during the Paleogene. Currently, the fossil record does not discern between a Laurasian or Gondwanan origin; however, it does demonstrate that Menispermaceae grew well outside the tropics by the early Paleocene. The endocarps’ affinity with Cissampelideae suggests that diversification of the family was well underway by the earliest Paleocene.     

The molecular evolution of acrosin in placental mammals

Acrosin is thought to fulfill several different roles in fertilization including that of a serine protease and in secondary zona pellucida (ZP) binding. However, acrosin's importance as a fertilization protein has been questioned. Especially since it was discovered that acrosin knockout mice are fertile. In this study, we explored the sites involved in serine protease activity and secondary binding. We also assessed conservation in functional sites across species and examined whether amino acid changes present in the human population have the potential to affect fertility. In addition, since many mammalian reproduction proteins have been found to evolve rapidly, we tested for positive selection. Sequences from 43 mammals from all 19 placental orders, which included a total of 828 nucleotides from acrosin exons 2, 3, 4, and a portion of exon 5, were obtained. We found that all sites of the serine catalytic triad as well as three other sites linked to catalytic activity were completely conserved. Five of six sites proposed to play a role in secondary binding were 100% conserved as basic residues. These results support an evolutionary conserved role for acrosin as a serine protease and secondary binding protein across placental mammals. We found statistically significant support for positive selection within acrosin, but no single amino acid site reached the significance level of P > 0.95 for inclusion within the category omega > 1. Based upon two amino acid mutation scoring systems, three out of seven human residue changing single nucleotide polymorphisms (SNPs) were found to be potentially protein-altering mutations.     

美国怀俄明州大角盆地北部Polecat台地古新世动物群演化（英文）

怀俄明州大角盆地北部的Polecat台地和麦卡洛峰的重要发现对了解北美古新世哺乳动物生物地层以及古新世-始新世极热事件中陆生动物群更替模式和原因具有重要意义。1910年,普林斯顿大学和美国自然历史博物馆的古生物学者指出,古新世的哺乳动物与始新世的明显不同,这使得古新世是一个不同于始新世的时期的观点很快被接受。80年之后,密歇根大学和卡耐基研究院的古生物学者指出,陆相古新统-始新统界线可以用动物群的快速更替和小型化作为标志,并伴随着一次重要的碳同位素漂移,这使得古新世-始新世极热事件(PETM)作为真正的全球性温室升温事件得到了公认。1950年,投身古生物事业的年轻学者周明镇被介绍到怀俄明参加古新世哺乳动物野外工作。在那里,他积累了专业知识和经验,并促成了对中国古新统进行的类似考察。现在的挑战是如何将北美和亚洲大陆相似的古新世历史拼合在一起。     

我国部分地区E1^3—E2^1孢粉属种演变的古气候意义

通过对我国部分地区古新世晚期一始新世早期孢粉植物群演化发展规律的分析研究,结合国内外地层学研究的新进展,提出我国古新世晚期气候以暖湿为特征,且暖期的结束与始新世/古新世界限相吻合或接近,因此可以本次暖期的结束作为古新世的顶界。     

The first species of Hapalodectes (Mesonychia,Mammalia) from the middle Paleocene of China (Qianshan Basin,Anhui Province) sheds light on the initial radiation of hapalodectids

A lower jaw of the mesonychian Hapalodectes is reported from Nongshanian sediments (Upper Doumu Formation; middle Paleocene) of the Qianshan Basin (Anhui Province, China). The fragmentary mandible is only the third specimen of Hapalodectidae discovered in Paleocene deposits, and the first in south east China; it is moreover the oldest, the two other specimens having been found in Gashatan (late Paleocene) localities. The premolars and molars of the new fossil are morphologically similar to Hapalodectes dux (late Paleocene of Mongolia), which has been considered to be the most primitive hapalodectid, but their relative proportions recall H. paleocenus and the Eocene Hapalodectes species. As a result, the fossil described herein appears to be different from the other previously described species of Hapalodectes in being morphologically intermediate between H. dux and the other Hapalodectes species, notably the Bumbanian Hapalodectes hetangensis and H. huanghaiensis from China; it is thus identified as a new species, Hapalodectes lopatini (possibly a male individual). Its discovery is important because it sheds light on the initial radiation of hapalodectids. The presence of one primitive hapalodectid in Mongolia previously suggested the Mongolian Plateau as the centre of origination of this carnivorous family, but the discovery of H. lopatini in older sediments from south‐east China challenges this hypothesis. In the earliest Eocene, Hapalodectes dispersed from Asia to North America; this event being part of the ‘East of Eden’ dispersals. This event resulted in the geographical separation of two distinct Hapalodectes groups, in North America and south‐eastern China respectively.     

Diversity of Menispermaceae from the Paleocene and Eocene of South China

We present here the earliest known Asian fossil records of the Menispermaceae based on fossil fruits from Paleocene and Eocene localities in South China. A new genus and species, Paleoorbicarpum parvum sp. nov., and two new species of Stephania Loureiro, S. ornamenta sp. nov. and S. geniculata sp. nov., are recognized from Paleocene deposits of the Sanshui Basin, Guangdong, and a new occurrence of the widespread Eocene species Stephania auriformis (Hollick) Han & Manchester is recognized from the Maoming Basin, Guangdong. The Paleocene Stephania specimens described here represent the earliest fossil endocarp record of the Menispermaceae in eastern Asia. This discovery shows that the moonseed family had arrived in tropical and humid South China by at least the middle Paleocene, which provides important evidence for the origin and phytogeographic history of the family.     

Correlation between the Paleocene/Eocene boundary and the Ilerdian at Campo, Spain

The Ilerdian is a well-established Tethyan marine stage, which corresponds to an important phase in the evolution of larger foraminifera not represented in the type-area of the classical Northwest-European stages. This biostratigraphic restudy of its parastratotype in the Campo Section (northeastern Spain) based on planktic foraminifera, calcareous nannofossils, dinoflagellate cysts and the distribution of the stable isotopes ∂¹³C and ∂¹⁸O is an attempt to correlate the Paleocene/Eocene boundary based on a characteristic carbon isotope excursion (CIE) marking the onset of the Initial Eocene Thermal Maximum (IETM) and the Ilerdian stage. The base of this ∂¹³C excursion has been chosen as the criterion for the recent proposal of the Global Stratotype Section and Point (GSSP) of the base of the Eocene (= base of the Ypresian) in the Dababiya Section (Egypt) to which an age of 54.9 Ma has been attributed. This level is also characterized by a marked extinction among the deep-water benthic foraminifera (Benthic Foraminifera Extinction Event, BFEE), a flood of representatives of the planktic foraminiferal genus Acarinina and the acme of dinoflagellate cysts of the genus Apectodinium. In the Campo Section, detailed biozonations (planktic foraminifera, calcareous nannofossils, dinoflagellate cysts) are recognized in the Lower and Middle Ilerdian. The correlation with the Ypresian stratotype is based on dinoflagellate cysts and calcareous nannofossils. The base of the Ilerdian is poor in planktic microfossils and its precise correlation with the redefined Paleocene/Eocene boundary remains uncertain.     

Origin of the Eocene planktonic foraminifer Hantkenina by gradual evolution

Hantkenina is a distinctive planktonic foraminiferal genus characterized by the presence of tubulospines (robust hollow projections) on each adult chamber, from Middle and Upper Eocene marine sediments worldwide. Here we illustrate its evolutionary origin using c. 150 specimens from 30 stratigraphic intervals in two sediment cores from Tanzania. The specimens, which span an estimated time interval of 300 ka, show four intermediate steps in the evolution of the tubulospines that amount to a complete intergradation from Clavigerinella caucasica, which does not possess them, to Hantkenina mexicana, which does. Stable isotope analyses indicate that the transitional forms evolved in a deep planktonic habitat not occupied at that time by other species of planktonic foraminifera. We discuss the morphogenetic constraints involved in the evolutionary transition and propose an ecological/adaptive model for the selective pressures that resulted in the evolution of tubulospines. We compare our record with similar, recently described assemblages from Austria and Italy, and we update the biostratigraphy and systematic taxonomy of the key morphospecies involved in the transition.     

Origin and evolution of a placental-specific microRNA family in the human genome

Background  

MicroRNAs (miRNAs) are a class of short regulatory RNAs encoded in the genome of DNA viruses, some single cell organisms, plants and animals. With the rapid development of technology, more and more miRNAs are being discovered. However, the origin and evolution of most miRNAs remain obscure. Here we report the origin and evolution dynamics of a human miRNA family.     

Origin and evolution of the grazing guild in new world terrestrial mammals

Although vertebrate herbivory has existed on land for about 300 million years, the grazingadaptation, principally developed in mammals, did not appear until the middle Cenozoic about 30 million years ago. Paleontological evidence indicates that grazing mammals diversified at the time of the spread of grasslands. Recently revised fossil calibrations reveal that the grazing mammal guild originated during the early Miocene in South America about 10-15 million years earlier than it did during the late Miocene in the northern hemisphere. Carbon isotopic analyses of extinct grazers' teeth reveal that this guild originated predominantly in C(3) terrestrial ecosystems. The present-day distribution of C(3) and C(4) grasslands evolved on the global ecological landscape since the late Miocene, after about 7 million years ago.     

Origin and evolution of laminin gene family diversity

Laminins are a family of multidomain glycoproteins that are important contributors to the structure of metazoan extracellular matrices. To investigate the origin and evolution of the laminin family, we characterized the full complement of laminin-related genes in the genome of the sponge, Amphimedon queenslandica. As a representative of the Demospongiae, a group consistently placed within the earliest diverging branch of animals by molecular phylogenies, Amphimedon is uniquely placed to provide insight into early steps in the evolution of metazoan gene families. Five Amphimedon laminin-related genes possess the conserved molecular features, and most of the domains found in bilaterian laminins, but all display domain architectures distinct from those of the canonical laminin chain types known from model bilaterians. This finding prompted us to perform a comparative genomic analysis of laminins and related genes from a choanoflagellate and diverse metazoans and to conduct phylogenetic analyses using the conserved Laminin N-terminal domain in order to explore the relationships between genes with distinct architectures. Laminin-like genes appear to have originated in the holozoan lineage (choanoflagellates + metazoans + several other unicellular opisthokont taxa), with several laminin domains originating later and appearing only in metazoan (animal) or eumetazoan (placozoans + ctenophores + cnidarians + bilaterians) laminins. Typical bilaterian α, β, and γ laminin chain forms arose in the eumetazoan stem and another chain type that is conserved in Amphimedon, the cnidarian, Nematostella vectensis, and the echinoderm, Strongylocentrotus purpuratus, appears to have been lost independently from the placozoan, Trichoplax adhaerens, and from multiple bilaterians. Phylogenetic analysis did not clearly reconstruct relationships between the distinct laminin chain types (with the exception of the α chains) but did reveal how several members of the netrin family were generated independently from within the laminin family by duplication and domain shuffling and by domain loss. Together, our results suggest that gene duplication and loss and domain shuffling and loss all played a role in the evolution of the laminin family and contributed to the generation of lineage-specific diversity in the laminin gene complements of extant metazoans.     

Joint reconstruction of divergence times and life-history evolution in placental mammals using a phylogenetic covariance model

Violation of the molecular clock has been amply documented, and is now routinely taken into account by molecular dating methods. Comparative analyses have revealed a systematic component in rate variation, relating it to the evolution of life-history traits, such as body size or generation time. Life-history evolution can be reconstructed using Brownian models. However, the resulting estimates are typically uncertain, and potentially sensitive to the underlying assumptions. As a way of obtaining more accurate ancestral trait and divergence time reconstructions, correlations between life-history traits and substitution rates could be used as an additional source of information. In this direction, a Bayesian framework for jointly reconstructing rates, traits, and dates was previously introduced. Here, we apply this model to a 17 protein-coding gene alignment for 73 placental taxa. Our analysis indicates that the coupling between molecules and life history can lead to a reevaluation of ancestral life-history profiles, in particular for groups displaying convergent evolution in body size. However, reconstructions are sensitive to fossil calibrations and to the Brownian assumption. Altogether, our analysis suggests that further integrating inference of rates and traits might be particularly useful for neontological macroevolutionary comparative studies.     

The recent and Paleogene craniid brachiopod,Valdiviathyris quenstedti Helmcke, 1940

Recent and fossil (mid‐Cenozoic) specimens of the brachiopod Valdiviathyris quenstedti Helmcke, 1940 are described from New Zealand. The unusual median processes of this genus are shown to be the attachment sites of the brachial protractor muscles. Valdiviathyris is compared with Ancistrocrania, Neoancistrocrania and Novocrania and is considered to be a valid separate genus in the family Craniidae.     

The evolution of the type I interferon gene family in mammals

A phylogenetic analysis of mammalian type I interferon (IFN) genes showed: (1) that the three main subfamilies of these genes in mammals (IFN-, IFN-, and IFN-) diverged after the divergence of birds and mammals but before radiation of the eutherian orders and (2) that IFN- diverged first. Although apparent cases of interlocus recombination among mouse IFN- genes were identified, the hypothesis that coding regions of IFN- genes have been homogenized within species by interlocus recombination was not supported. Flanking regions as well as coding regions of IFN- were more similar within human and mouse than between these species; and reconstruction of the pattern of nucleotide substitution in IFN- coding regions of four mammalian species by the maximum parsimony method suggested that parallel substitutions have occurred far more frequently between species than within species. Therefore, it seems likely that IFN- genes have duplicated independently within different eutherian orders. In general, type I IFN genes are subject to purifying selection, which in the case of IFN- and IFN- is strongest in the putative receptor-binding domains. However, analysis of the pattern of nucleotide substitution among IFN- genes suggested that positive Darwinian selection may have acted in some cases to diversify members of this subfamily at the amino acid level.