The earliest known eutherian mammal

The skeleton of a eutherian (placental) mammal has been discovered from the Lower Cretaceous Yixian Formation of northeastern China. We estimate its age to be about 125 million years (Myr), extending the date of the oldest eutherian records with skull and skeleton by about 40 50 Myr. Our analyses place the new fossil at the root of the eutherian tree and among the four other known Early Cretaceous eutherians, and suggest an earlier and greater diversification of stem eutherians that occurred well before the molecular estimate for the diversification of extant placental superorders (104 64 Myr). The new eutherian has limb and foot features that are known only from scansorial (climbing) and arboreal (tree-living) extant mammals, in contrast to the terrestrial or cursorial (running) features of other Cretaceous eutherians. This suggests that the earliest eutherian lineages developed different locomotory adaptations, facilitating their spread to diverse niches in the Cretaceous.     

A Jurassic mammal from South America

The Jurassic period is an important stage in early mammalian evolution, as it saw the first diversification of this group, leading to the stem lineages of monotremes and modern therian mammals. However, the fossil record of Jurassic mammals is extremely poor, particularly in the southern continents. Jurassic mammals from Gondwanaland are so far only known from Tanzania and Madagascar, and from trackway evidence from Argentina. Here we report a Jurassic mammal represented by a dentary, which is the first, to our knowledge, from South America. The tiny fossil from the Middle to Late Jurassic of Patagonia is a representative of the recently termed Australosphenida, a group of mammals from Gondwanaland that evolved tribosphenic molars convergently to the Northern Hemisphere Tribosphenida, and probably gave rise to the monotremes. Together with other mammalian evidence from the Southern Hemisphere, the discovery of this new mammal indicates that the Australosphenida had diversified and were widespread in Gondwanaland well before the end of the Jurassic, and that mammalian faunas from the Southern Hemisphere already showed a marked distinction from their northern counterparts by the Middle to Late Jurassic.     

柞水县兽类调查报告

通过调查结果表明 ,柞水县境内共分布兽类 5 3种 ,隶属 6目、2 0科 .国家一级保护动物 2种 ,国家二级保护动物 8种 .从兽类区系成分看 ,柞水县古北界种类有14种 ,占全县兽类总数的 2 6.42 % ;东洋界种类 2 6种 ,占全县兽类总数的 49.0 6% ;广布种等 13种 ,占全县兽类总数的 2 4.5 3 % .     

A Mesozoic gliding mammal from northeastern China

Gliding flight has independently evolved many times in vertebrates. Direct evidence of gliding is rare in fossil records and is unknown in mammals from the Mesozoic era. Here we report a new Mesozoic mammal from Inner Mongolia, China, that represents a previously unknown group characterized by a highly specialized insectivorous dentition and a sizable patagium (flying membrane) for gliding flight. The patagium is covered with dense hair and supported by an elongated tail and limbs; the latter also bear many features adapted for arboreal life. This discovery extends the earliest record of gliding flight for mammals to at least 70 million years earlier in geological history, and demonstrates that early mammals were diverse in their locomotor strategies and lifestyles; they had experimented with an aerial habit at about the same time as, if not earlier than, when birds endeavoured to exploit the sky.     

A new eutriconodont mammal and evolutionary development in early mammals

Detachment of the three tiny middle ear bones from the reptilian mandible is an important innovation of modern mammals. Here we describe a Mesozoic eutriconodont nested within crown mammals that clearly illustrates this transition: the middle ear bones are connected to the mandible via an ossified Meckel's cartilage. The connected ear and jaw structure is similar to the embryonic pattern in modern monotremes (egg-laying mammals) and placental mammals, but is a paedomorphic feature retained in the adult, unlike in monotreme and placental adults. This suggests that reversal to (or retention of) this premammalian ancestral condition is correlated with different developmental timing (heterochrony) in eutriconodonts. This new eutriconodont adds to the evidence of homoplasy of vertebral characters in the thoraco-lumbar transition and unfused lumbar ribs among early mammals. This is similar to the effect of homeobox gene patterning of vertebrae in modern mammals, making it plausible to extrapolate the effects of Hox gene patterning to account for homoplastic evolution of vertebral characters in early mammals.     

A Chinese triconodont mammal and mosaic evolution of the mammalian skeleton

Here we describe a new triconodont mammal from the Late Jurassic/Early Cretaceous period of Liaoning, China. This new mammal is represented by the best-preserved skeleton known so far for triconodonts which form one of the earliest Mesozoic mammalian groups with high diversity. The postcranial skeleton of this new triconodont shows a mosaic of characters, including a primitive pelvic girdle and hindlimb but a very derived pectoral girdle that is closely comparable to those of derived therians. Given the basal position of this taxon in mammalian phylogeny, its derived pectoral girdle indicates that homoplasies (similarities resulting from independent evolution among unrelated lineages) are as common in the postcranial skeleton as they are in the skull and dentition in the evolution of Mesozoic mammals. Limb structures of the new triconodont indicate that it was probably a ground-dwelling animal.     

Non-marine Jurassic rocks of Thailand: A summary

Non-marine Jurassic rocks are widespread in the northeastern part (Khorat Plateau), and partly in the northern, eastern, and southern parts of Thailand. In the Khorat Plateau, the rocks, more than 1000 m thick, are represented by the Phu Kradung and Phra Wihan Formations of the Khorat Group but are less extensive in the north, east, and south. Reddish brown to grayish purple sandstones, siltstones, claystones, conglomeratic sandstones and conglomerates are the main lithologies; calcrete nodules are also present in claystones only in the Phu Kradung Formation. Deposition occurred mostly in meandering and braided rivers in semi-arid and slightly humid conditions for the Phu Kradung and Phra Wihan Formations, respectively, except for the southern rocks, where lacustrine deposits dominate. Age determinations are based mainly on vertebrates, bivalves and palynomorphs indicating reassignment to the Jurassicpossibly Early Cretaceous.     

Non-marine Jurassic rocks of Thailand: A summary

Non-marine Jurassic rocks are widespread in the northeastern part (Khorat Plateau), and partly in the northern, eastern, and southern parts of Thailand. In the Khorat Plateau, the rocks, more than 1000 m thick, are represented by the Phu Kradung and Phra Wihan Formations of the Khorat Group but are less extensive in the north, east, and south. Reddish brown to grayish purple sandstones, siltstones, claystones, conglomeratic sandstones and conglomerates are the main lithologies; calcrete nodules are also present in claystones only in the Phu Kradung Formation. Deposition occurred mostly in meandering and braided rivers in semi-arid and slightly humid conditions for the Phu Kradung and Phra Wihan Formations, respectively, except for the southern rocks, where lacustrine deposits dominate. Age determinations are based mainly on vertebrates, bivalves and palynomorphs indicating reassignment to the Jurassicpossibly Early Cretaceous.     

Transformation and diversification in early mammal evolution

Evolution of the earliest mammals shows successive episodes of diversification. Lineage-splitting in Mesozoic mammals is coupled with many independent evolutionary experiments and ecological specializations. Classic scenarios of mammalian morphological evolution tend to posit an orderly acquisition of key evolutionary innovations leading to adaptive diversification, but newly discovered fossils show that evolution of such key characters as the middle ear and the tribosphenic teeth is far more labile among Mesozoic mammals. Successive diversifications of Mesozoic mammal groups multiplied the opportunities for many dead-end lineages to iteratively evolve developmental homoplasies and convergent ecological specializations, parallel to those in modern mammal groups.     

Long-period astronomical forcing of mammal turnover

Mammals are among the fastest-radiating groups, being characterized by a mean species lifespan of the order of 2.5 million years (Myr). The basis for this characteristic timescale of origination, extinction and turnover is not well understood. Various studies have invoked climate change to explain mammalian species turnover, but other studies have either challenged or only partly confirmed the climate-turnover hypothesis. Here we use an exceptionally long (24.5-2.5 Myr ago), dense, and well-dated terrestrial record of rodent lineages from central Spain, and show the existence of turnover cycles with periods of 2.4-2.5 and 1.0 Myr. We link these cycles to low-frequency modulations of Milankovitch oscillations, and show that pulses of turnover occur at minima of the 2.37-Myr eccentricity cycle and nodes of the 1.2-Myr obliquity cycle. Because obliquity nodes and eccentricity minima are associated with ice sheet expansion and cooling and affect regional precipitation, we infer that long-period astronomical climate forcing is a major determinant of species turnover in small mammals and probably other groups as well.     

Late Cretaceous relatives of rabbits, rodents, and other extant eutherian mammals.

Extant eutherian mammals and their most recent common ancestor constitute the crown group Placentalia. This taxon, plus all extinct taxa that share a more recent common ancestor with placentals than they do with Metatheria (including marsupials), constitute Eutheria. The oldest well documented eutherian-dominated fauna in the world is Dzharakuduk, Uzbekistan. Among eutherians that it yields is Kulbeckia, an 85-90-Myr-old member of Zalambdalestidae (a family of Late Cretaceous Asian eutherians). This extends Zalambdalestidae back by some 10 million years from sites in the Gobi Desert, Mongolia. A phylogenetic analysis of well described Late Cretaceous eutherians strongly supports Zalambdalestidae, less strongly supports 'Zhelestidae' (a Late Cretaceous clade related to Tertiary ungulates), but does not support Asioryctitheria (a group of Late Cretaceous Asian eutherians). A second analysis incorporating placentals from clades that include rodents (Tribosphenomys), lagomorphs (Mimotona) and archaic ungulates (Protungulatum and Oxyprimus) strongly supports Zalambdalestidae in a clade with Glires (rabbits, rodents and extinct relatives) and less strongly 'Zhelestidae' within a clade that includes archaic ungulates ('condylarths'). This argues that some Late Cretaceous eutherians belong within the crown group Placentalia. The ages of these taxa are in line with molecularly based estimates of 64-104 Myr ago (median 84 Myr ago) for the superordinal diversification of some placentals, but provide no support for a Late Cretaceous diversification of extant placental orders.     

哺乳动物精子发生过程的基因表达

雄性生殖细胞的发育要相继发生有丝分裂、减数分裂和后减数分裂，许多生殖细胞特异的转录本在此过程产生。它们的表达是受发育调节的和有阶段特异的，雄性生殖细胞基因表达的调节是以内、外部相互作用进行的，一个对于生殖细胞高度保守的“内部的”遗传程序决定了构成生殖细胞发育基础的事件的发生顺序，在减数分裂和其它的生殖细胞特有的过程中，内部程序决定了哪一个基因被利用以及何时使它们被表达，内部水平的调节又依赖于“外部的”影响。     

判别正项级数敛散性的一种新方法

本文给出了正项级数敛散性的一种新的比值判别法，这种判别法强于达朗贝尔比值判别法，且使用方便。     

A basal tyrannosauroid dinosaur from the Late Jurassic of China

The tyrannosauroid fossil record is mainly restricted to Cretaceous sediments of Laurasia, although some very fragmentary Jurassic specimens have been referred to this group. Here we report a new basal tyrannosauroid, Guanlong wucaii gen. et sp. nov., from the lower Upper Jurassic of the Junggar Basin, northwestern China. G. wucaii is the oldest known tyrannosauroid and shows several unexpectedly primitive pelvic features. Nevertheless, the limbs of G. wucaii share several features with derived coelurosaurs, and it possesses features shared by other coelurosaurian clades. This unusual combination of character states provides an insight into the poorly known early radiation of the Coelurosauria. Notably, the presumed predatory Guanlong has a large, fragile and highly pneumatic cranial crest that is among the most elaborate known in any non-avian dinosaur and could be comparable to some classical exaggerated ornamental traits among vertebrates.     

Brevetoxicosis: red tides and marine mammal mortalities

Potent marine neurotoxins known as brevetoxins are produced by the 'red tide' dinoflagellate Karenia brevis. They kill large numbers of fish and cause illness in humans who ingest toxic filter-feeding shellfish or inhale toxic aerosols. The toxins are also suspected of having been involved in events in which many manatees and dolphins died, but this has usually not been verified owing to limited confirmation of toxin exposure, unexplained intoxication mechanisms and complicating pathologies. Here we show that fish and seagrass can accumulate high concentrations of brevetoxins and that these have acted as toxin vectors during recent deaths of dolphins and manatees, respectively. Our results challenge claims that the deleterious effects of a brevetoxin on fish (ichthyotoxicity) preclude its accumulation in live fish, and they reveal a new vector mechanism for brevetoxin spread through food webs that poses a threat to upper trophic levels.     

A Middle Jurassic 'sphenosuchian' from China and the origin of the crocodylian skull

The skull of living crocodylians is highly solidified and the jaw closing muscles are enlarged, allowing for prey capture by prolonged crushing between the jaws. Living species are all semi-aquatic, with sprawling limbs and a broad body that moves mainly from side-to-side; however, fossils indicate that they evolved from terrestrial forms. The most cursorial of these fossils are small, gracile forms often grouped together as the Sphenosuchia, with fully erect, slender limbs; their relationships, however, are poorly understood. A new crocodylomorph from deposits in northwestern China of the poorly known Middle Jurassic epoch possesses a skull with several adaptations typical of living crocodylians. Postcranially it is similar to sphenosuchians but with even greater adaptations for cursoriality in the forelimb. Here we show, through phylogenetic analysis, that it is the closest relative of the large group Crocodyliformes, including living crocodylians. Thus, important features of the modern crocodylian skull evolved during a phase when the postcranial skeleton was evolving towards greater cursoriality, rather than towards their current semi-aquatic habitus.