A new longirostrine dyrosaurid (Crocodylomorpha,Mesoeucrocodylia) from the Paleocene of north‐eastern Colombia: biogeographic and behavioural implications for New‐World Dyrosauridae

Abstract: Fossils of dyrosaurid crocodyliforms are limited in South America, with only three previously diagnosed taxa including the short‐snouted Cerrejonisuchus improcerus from the Paleocene Cerrejón Formation of north‐eastern Colombia. Here we describe a second dyrosaurid from the Cerrejón Formation, Acherontisuchus guajiraensis gen. et sp. nov., based on three partial mandibles, maxillary fragments, teeth, and referred postcrania. The mandible has a reduced seventh alveolus and laterally depressed retroarticular process, both diagnostic characteristics of Dyrosauridae. Acherontisuchus guajiraensis is distinct among known dyrosaurids in having a unique combination of craniomandibular characteristics, and postcranial morphology that suggests it may have occupied a more placid, fluvial habitat than most known Old‐World dyrosaurids. Results from a cladistic analysis of Dyrosauridae, using 82 primarily cranial and mandibular characters, support an unresolved relationship between A. guajiraensis and a combination of New‐ and Old‐World dyrosaurids including Hyposaurus rogersii, Congosaurus bequaerti, Atlantosuchus coupatezi, Guarinisuchus munizi, Rhabdognathus keiniensis and Rhabdognathus aslerensis. Our results are consistent with an African origin for Dyrosauridae with multiple dispersals into the New World during the Late Cretaceous and a transition from marine habitats in ancestral taxa to more fluvial habitats in more derived taxa.     

New data on the Dyrosauridae (Crocodylomorpha) from the Paleocene of Togo

Following our fieldwork in Paleogene deposits of Togo, we herein report cranial as well as postcranial elements belonging to the family Dyrosauridae. This assemblage is dated to the Late Paleocene (Thanetian) from two quarries in southern Togo. The specimens include a partial skull presenting two large supratemporal fossae and a massive occipital condyle; long and slender isolated teeth; amphicoelous vertebrae including several articulated ones; and two osteoderms devoid of carina. The morphology of the partial skull reveals similarities with some African longirostrine forms such as Rhabdognathus spp., although this attribution cannot be confirmed. Longirostrine forms, known in the late Paleocene and early Eocene of the Iullemmeden basin (Nigeria, Niger, Mali, Algeria) and in the phosphates of Morocco and Tunisia, is only represented in Thanetian levels in Togo. Different palaeoenvironmental settings seem to have characterized the various African basins during the lower Eocene, with consequences for the geographic distribution of dyrosaurids. These dyrosaurid remains confirm the presence of the family in Togo during the Paleocene and underline the fossiliferous potential of the coastal sedimentary basin in Togo and in the bay of Benin.     

DNA evidence for a Paleocene origin of the Alcidae (Aves: Charadriiformes) in the Pacific and multiple dispersals across northern oceans

The Alcidae is a group of marine, wing-propelled diving birds known as auks that are distributed along the coasts of the northern oceans. It has been suggested that auks originated in the Pacific coastal shores as early as the Miocene, and dispersed to the Atlantic either through the Arctic coasts of Eurasia and North America (northern dispersal route), or through upwelling zones in the coastal areas of California to Florida (southern dispersal route), before the closure of the Isthmus of Panama in the Pliocene. These hypotheses have not been tested formally because proposed phylogenies failed to recover fully bifurcating, well-supported phylogenetic relationships among and within genera. We therefore constructed a large data set of mitochondrial and nuclear DNA sequences for 21 of the 23 species of extant auks. We also included sequences from two other extant and one extinct species retrieved from GenBank. Our analyses recovered a well-supported phylogenetic hypothesis among and within genera. Aethia is the only genus for which we could not obtain strong support for species relationships, probably due to incomplete lineage sorting. By applying a Bayesian method of molecular dating that allows for rate variation across lineages and genes, we showed that auks became an independent lineage in the Early Paleocene and radiated gradually from the Early Eocene to the Quaternary. Reconstruction of ancestral areas strongly suggests that auks originated in the Pacific during the Paleocene. The southern dispersal route seems to have favored the subsequent colonization of the northern Atlantic Ocean during the Eocene and Oligocene. The northern route across the Arctic Ocean was probably only used more recently after the opening of the Norwegian Sea in the Middle Miocene and the opening of the Bering Strait in the Late Miocene. We postulate that the ancestors of auks lived in a warmer world than that currently occupied by auks, and became gradually adapted to feeding in cool marine currents with high biomass productivity. Hence, warmer tropical waters are now a barrier for the dispersal of auks into the Southern Hemisphere, as it is for penguins in the opposite direction.     

On the early biogeographical history of the African placentals

The Paleocene Adrar Mgorn local fauna recently discovered in the Ouarzazate basin (Morocco) along with several significant Eocene North African faunas, has yielded the oldest known placental mammals of Africa. Contrary to those from the Eocene which are basically endemic, the Adrar Mgorn placentals display affinities with taxa from North‐Tethyan continents and indicate active faunal interchanges between Africa and Europe (and perhaps Asia) during the Cretaceous/Paleogene times. On biogeographical grounds, two dispersal events are suggested as a working hypothesis. The oldest one, exemplified by the presence of paleoryctid and adapisoriculid “insectivores”; in the Moroccan locality, possibly took place by the K/T boundary. The second dispersal event exemplified by the discovery of an omomyid primate and possible hyaenodontid creodonts may have been contemporaneous with the Paleocene/Eocene boundary during which a marine regression is also known.     

A new species of Dyrosaurus (Crocodylomorpha, Dyrosauridae) from the early Eocene of Morocco: phylogenetic implications

A new dyrosaurid is described from the Ypresian of the phosphatic deposits of the Oulad Abdoun Basin of Morocco. It is based on numerous cranial and postcranial remains, allowing an almost complete reconstruction. This new Dyrosaurus species, Dyrosaurus maghribensis sp. nov. , is currently only known from Morocco. It differs from D. phosphaticus , present in contemporaneous levels of Algeria and Tunisia, by several autapomorpies, including a smooth dorsal margin of the parietal and widely opened choanae. A phylogenetic analysis, using 47 taxa and 234 morphological characters, shows the dyrosaurids as the sister taxon of pholidosaurids, which include Elosuchus , Sarcosuchus , Terminonaris and Pholidosaurus , and the thalattosuchians. Goniopholididae is a non-monophyletic group; however, if dyrosaurids are not included in the analysis, the result differs and the goniopholidids form a distinct clade. If Thalattosuchia is excluded, both Goniopholididae and Pholidosauridae become paraphyletic assemblages. Thus, phylogenetic problems remain with respect to longirostrine clade, and more attention should be paid to resolving their evolutionary relationships amongst the crocodyliforms.  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 148 , 603–656.     

内蒙古苏崩地点的古新世软食中兽(哺乳纲,中兽目):古新世-始新世界线附近“东方伊甸园”扩散模式的新证据(英文)

记述了发现于内蒙古苏崩晚古新世格沙头期的中兽类软食中兽Hapalodectes属的一个新种。这是软食中兽在中国古新世地层中的首次发现,也是亚洲格沙头期的第二种软食中兽。已有的系统学和生物地层学证据支持软食中兽属和软食中兽科(Hapalodectidae)亚洲起源的观点。软食中兽显然是在古新世-始新世极热事件(PETM)期间通过白令陆桥扩散到北美大陆的,因而符合"东方伊甸园"学说中的生物地理格局。软食中兽有限的(即非欧洲的)地理分布使得我们可以重建该属生物地理学历史。如同软食中兽一样的"东方伊甸园"式的扩散模式,可以看作是大的环境变化事件导致多个支系产生相似的系统学和生物地理学分布格局的生物地理扩散机制。严格地检查了所谓的在古新世-始新世界线上或其附近的与"东方伊甸园"模式相矛盾的大陆间哺乳动物扩散事例,结果发现这些例子都是不可靠的。"东方伊甸园"生物地理学说充分解释了PETM时期哺乳动物群更替以及劳亚古陆哺乳动物地理分布格局的成因。     

A comprehensive phylogeny of extinct and extant Rhizomyinae (Rodentia): evidence for multiple intercontinental dispersals

The subfamily Rhizomyinae is known from the Late Oligocene up to the present. Today this group comprises six species, which live in southern Asia and eastern Africa. Despite the current moderate diversity of the rhizomyines, they had a greater diversification and wider distribution in the past: from Asia, their land of origin, to Africa, which they entered during the Early Miocene. So far 33 fossil species can be referred to this group. A cladistic analysis involving fossil and living species has been carried out. Prokanisamys spp. turned out to be the most basal taxa of the ingroup. This analysis calls into question the monophyly of several genera, and allows the proposal of a phylogenetic definition of the tribes Tachyoryctini and Rhizomyini. It also provides information about the origin of the African rhizomyines and allows inferring multiple dispersal phenomena from Asia to Africa in Early and Late Miocene times.     

Limited Dispersal, Deleterious Mutations and the Evolution of Sex

This study presents a mathematical model that allows for some offspring to be dispersed at random, while others stay close to their mothers. A single genetic locus is assumed to control fertility, and this locus is subject to the occurrence of deleterious mutations. It is shown that, at equilibrium, the frequency of deleterious mutations in the population is inversely related to the rate of dispersal. This is because dispersal of offspring leads to enhanced competition among adults. The results also show that sexual reproduction can lead to a decrease in the equilibrium frequency of deleterious mutations. The reason for this relationship is that sex involves the dispersal of genetic material, and thus, like the dispersal of offspring, sex enhances competition among adults. The model is described using the example of a hermaphroditic plant population. However, the results should apply to animal populations as well.     

The long‐term history of dispersal among lizards in the early Eocene: new evidence from a microvertebrate assemblage in the Bighorn Basin of Wyoming,USA

Abstract: Early Eocene mammal faunas of North America were transformed by intercontinental dispersal at the Paleocene–Eocene boundary, but lizard faunas from the earliest Eocene of the same area were dominated by immigrants from within the continent. A new lizard assemblage from the middle early Eocene of Wyoming sheds light on the longer‐term history of dispersal in relation to climate change. The assemblage consists of three iguanid species (including two new species possibly closely related to living Anolis), Scincoideus, ‘Palaeoxantusia’, four anguids, two species of an undescribed new anguimorph clade, Provaranosaurus and a varanoid (cf. Saniwa). Most North American glyptosaurin glyptosaurines are now referred to Glyptosaurus, and Glyptosaurus hillsi is given a new diagnosis. Scincoideus is otherwise known only from the mid‐Paleocene of Belgium, and the specimens described here are the first to document intercontinental dispersal to North America among lizards in the early Eocene. Like in mammals, some immigrant lizard lineages first appearing in the Bighorn Basin in the earliest Eocene persisted in the area long after the Paleocene–Eocene thermal maximum, but other immigrants appear to have been restricted to the Paleocene–Eocene thermal maximum.     

The Cenozoic Brachiopods of the Carnarvon Basin, Western Australia

The Paleocene-Miocene deposits of the Carnarvon Basin of Western Australia contain a rich fauna of brachiopods, but only two species, Tegulorhynchia boongeroodaensis Westralicrania allani , both from the Paleocene, have previously been described.One new genus, Giraliathyris , and eight new species are described herein. They are Giraliathyris mcnamari, G. kaitrinae, G. jubileensis, Liothyrella longorum, Victorithyris decapello, V. cardabiaensis, V. blakeorum, V. tulkiensis, Diedrothyris cf. johnstoniana Paraldingia timi . A Terebratulina species and two species of indeterminate genera are also described. Basiliola (Rhynchonellida) and Cancellothyris (Terebratulida) are recorded for the first time from the upper Paleocene of Australia. These, together with Victorithyris Diedrothyris Liothyrella and Paraldingia , represent the oldest records of these genera. It is suggested that their early occurrence, together with those known from the Antarctic Peninsula, indicates a southern origin for this fauna and a high latitude, southern circum-Indo-Atlantic faunal province is proposed. Subsequently the brachiopod fauna spread northwards towards lower latitudes and west to east around southern Australia, before and during the development of the circum-polar current during the Oligocene.     

A new blunt-snouted dyrosaurid,Anthracosuchus balrogus gen. et sp. nov. (Crocodylomorpha,Mesoeucrocodylia), from the Palaeocene of Colombia

A new exceptionally brevirostrine dyrosaurid is described from the middle Palaeocene (58–60 million years ago) Cerrejón Formation, northeastern Colombia, based on four partial skulls and associated postcrania. This taxon is unique among dyrosaurids not only in skull shape, but also in having orbital tuberosities, and osteoderms that are dorsoventrally thick and unpitted, a trait otherwise unknown in Crocodylomorpha. Results from a cladistic analysis of Dyrosauridae suggest that the new taxon, together with Cretaceous–Palaeocene Chenanisuchus lateroculi from Africa and Cerrejonisuchus improcerus also from the Cerrejón Formation, are the most basal members of the family. Results from a biogeographic analysis indicate at least three independent dispersals of dyrosaurids from Africa to the New World occurred in the Late Cretaceous or early Palaeocene. Widely set orbits in the new taxon indicate a deviation from surface-based predation, characteristic of other dyrosaurids, to sub-surface predation, as in modern Gavialis. Tooth impressions found on turtle shells recovered from the same locality match well with teeth of the new taxon indicating possible predation.http://www.zoobank.org/urn:lsid:zoobank.org:pub:AB2B24A5-27CC-4D3F-B580-F11F17851CE6     

Benthic foraminiferal assemblages between two major extinction events: the Paleocene El Kef section,Tunisia

The development of benthic foraminiferal assemblages from the Paleocene outcrops of the El Haria Formation near El Kef, Tunisia is discussed qualitatively and quantitatively. The aim of the study is to reconstruct the paleoenvironmental evolution between the K/Pg boundary interval and the late Paleocene event, and to compare this evolution with results from other sites along the southern Tethyan margin. Eighty-four samples, covering virtually the entire Paleocene, provide a dataset that allows detailed qualitative and multivariate analysis. The benthic foraminiferal faunas indicate a complex pattern of environmental changes during the Paleocene, marked by the succession of different benthic associations. Following the K/Pg boundary event, community restoration was characterized by the gradual build-up of faunal diversity. Decreasing dominance and the entry of taxa common to normal marine, outer neritic to upper bathyal environments indicate the completion of the ecosystem restoration in Zone Plb. A highly diverse benthic foraminiferal assemblage persisted throughout the remainder of the early Paleocene into the earliest late Paleocene. At the P3a-P3b zonal transition relative sea-level lowering is evidenced by the sudden disappearance or decreasing abundance of deeper-water taxa (e.g. Anomalinoides affinis, A. susanaensis, Gavelinella beccariiformis). Neritic deposition continued into Zone P4, when trophic levels at the seafloor increased as indicated by the entry and increasing dominance of species such as Anomalinoides cf. aegyptiacus, Bulimina midwayensis, and B. strobila, which we consider to be sensitive to eutrophication. The combined effect of shallowing and the subsequent eutrophication led to the establishment of assemblages similar to late Paleocene benthic foraminiferal assemblages from Egyptian sections, some of which record the latest Paleocene extinction event. These assemblages were interpreted to be indicative of a middle neritic, highly eutrophic environment. Enhanced vertical fluxes of organic matter along the southern Tethyan margin may have resulted from intensified upwelling. This eventually led to oxygen deficiency at the seafloor. It appears that oxygen-deficient, high-productivity shelves were a common feature of the southern Tethyan margin during the latest Paleocene.     

First report of the giant snake Gigantophis (Madtsoiidae) from the Paleocene of Pakistan: Paleobiogeographic implications

We report here the discovery of madtsoiid snake remains from the early Paleocene Khadro Formation (Ranikot Group, Sindh, Southern Pakistan). These specimens consist of vertebrae and are referred to Gigantophis. This is the first report of Gigantophis from outside of Africa. The problem of the generic distinction between Gigantophis and Madtsoia is stressed. The specimens from Pakistan slightly differ from the single species (G. garstini) referred to the genus Gigantophis, but the available material does not allow further considerations and the fossil is referred to as Gigantophis sp. However, Gigantophis sp. from the Khadro Formation is more closely related to G. garstini, that is known only from the middle and late Eocene of northern Africa, than to any other species, thus suggesting dispersal between these two areas during the Paleocene or earlier. These results are consistent with the hypothesis of intermittent dispersals between the Indo-Pakistan Plate and Africa suggested by other fossil evidences.     

New dyrosaurid crocodylomorph and evidences for faunal turnover at the K-P transition in Brazil

The discovery of a new dyrosaurid crocodylomorph from the well-dated Palaeocene deposits of northeastern Brazil sheds new light on the evolutionary history of this extinct group of marine crocodylomorphs that have survived the Cretaceous-Palaeogene (K-P) extinction crisis. Guarinisuchus munizi, the most complete member of this group collected in South America so far, is closely related to the African forms, and this fact suggests that dyrosaurids had crossed the Atlantic Ocean before the K-P boundary and dispersed from there to North America and other parts of South America. This discovery also suggests that on the coast of northeastern Brazil, dyrosaurids replaced the pre-existing Late Cretaceous fauna of diversified mosasaurs, a group of marine lizards, after the K-P extinction event, becoming the main predators, together with sharks, in shallow marine Palaeocene environments. More detailed stratigraphic records and detailed dating of the deposits with dyrosaurids are necessary to correlate this particular pattern found in the ancient northeastern Brazilian coast within the evolution of the group, especially in Africa.     

New Ichnotaxa of Mammal and Reptile Tracks from the Upper Paleocene of Alberta

Only two vertebrate trackways are known from the Paleocene of western Canada and are among the few Paleocene vertebrate trackways known worldwide.

A natural cast trackway consisting of five prints (three pes, two manus) on a fallen block was found along the Red Deer River, near the town of Red Deer, Alberta, in 1927. The discoverers, Ralph Rutherford and Loris Russell, identified the strata the track block had fallen from as belonging to the Paskapoo Formation (upper Paleocene: middle Tiffanian). The trackway was attributed to a mammalian track-maker in two subsequent publications. However, the prints are more characteristic of a reptilian (crocodylian) track-maker.

A natural cast track-bearing block was discovered on Signal Hill in the city of Calgary during the preparation of a new residential subdivision in 1990. The large track-bearing block was found in a rock pile but is suspected to have originated from strata belonging to the Porcupine Hills Formation (Upper Paleocene: late Torrejonian), which was being excavated at the time. This large slab contains twelve prints (six pes, six manus) and is associated with extensive mud cracks. The mammalian affinity of the trackmaker was recognized by researchers from the Royal Tyrrell Museum of Palaeontology.     

Die Tricks der Stinkenden Nieswurz

The tricks of stinking hellebore The stinking hellebore (Helleborus foetidus) uses ingenious tricks in order to attract pollinators and to achieve the dispersal of its seeds. Yeasts metabolise sugar available in nectar und thereby warm it up to attract bees and bumble bees in cold, early spring. This remarkable heating system allows the flowers to already attract pollinators at a time, when competition by other flower species is still low and visits by pollinators are often limited by low temperatures. Early flowering in turn allows seed set in late spring and early summer. The seeds have a fleshy structure attached, an elaiosome that contains lipids, sugars and vitamins. This makes them highly attractive to ants during a season when high-quality foods are still in short supply and leads to dispersal of the seeds (myrmecochory). The elaiosome also contains a fatty acid that acts as an olfactory attractant. But what attracts ants, is also attractive for other seed predators such as mice. Long-term survival of seeds (and thus germination) therefore greatly depends on the detachment of the elaiosome from the seed by the ants. There is much more than meets the eye with respect of stinking hellebore pollination and seed dispersal. It is an example of the highly complex interdependencies between plants, their blossoms, different animal species as well as yeasts and bacteria.     

Early Cenozoic Differentiation of Polar Marine Faunas

The widespread assumption that the origin of polar marine faunas is linked to the onset of major global cooling in the Late Eocene – Early Oligocene is being increasingly challenged. The Antarctic fossil record in particular is suggesting that some modern Southern Ocean taxa may have Early Eocene or even Paleocene origins, i.e. well within the Early Cenozoic greenhouse world. A global analysis of one of the largest marine clades at the present day, the Neogastropoda, indicates that not only is there a decrease in the number of species from the tropics to the poles but also a decrease in the evenness of their distribution. A small number of neogastropod families with predominantly generalist trophic strategies at both poles points to the key role of seasonality in structuring the highest latitude marine assemblages. A distinct latitudinal gradient in seasonality is temperature-invariant and would have operated through periods of global warmth such as the Early Cenozoic. To test this concept a second global analysis was undertaken of earliest Cenozoic (Paleocene) neogastropods and this does indeed show a certain degree of faunal differentiation at both poles. The Buccinidae, s.l. is especially well developed at this time, and this is a major generalist taxon at the present day. There is an element of asymmetry associated with this development of Paleocene polar faunas in that those in the south are more strongly differentiated than their northern counterparts; this can in turn be linked to the already substantial isolation of the southern high latitudes. The key role of seasonality in the formation of polar marine faunas has implications for contemporary ecosystem structure and stability.     

Herpetofaunas from the Upper Paleocene and Lower Eocene of Morocco

Two Upper Paleocene and one Lower Eocene localities from Morocco (Ouarzazate basin) have yielded terrestrial assemblages that stand among the rare herpetofaunas from the Paleogene of the African Plate. The collections include one of the rare frogs and the only lizards known from the Paleogene of Africa. One of the two Upper Paleocene localities, Adrar Mgorn 1, has produced an indeterminate anuran and the most diverse assemblage of squamates from the Mesozoic and Cenozoic of Africa. It has yielded the earliest known scolecophidian snake and the earliest Gekkonidae, amphisbaenians, Tropidophiidae, and perhaps Boidae from Africa. Moreover, a specimen represents either the last sphenodontian or the earliest acrodontan lizard from this continent. One of the amphisbaenians represents a very distinct new taxon, Todrasaurus gheerbranti gen. and sp. nov. Indeterminate scincomorphans, lacertilians, Madtsoidae, and Aniliidae are also present. The fauna from the Lower Eocene is less diverse than that from the Upper Paleocene, but some taxa are common to both levels. Contrary to nearly all other Paleogene herpetofaunas from the African Plate, these Paleocene and Eocene assemblages include taxa that were terrestrial, not aquatic.