On the phylogenetic relationships of Vincelestes neuquenianus

This short review paper compares the lower jaw and lower dentition of the small Mesozoic mammal Vincelestes neuquenianus with some other Laurasian and Gondwanan taxa. On this basis a set of 90 characters recognised by recent authors was assembled and used to construct a cladogram. The topology suggests that the early Cretaceous mammal from Patagonia, Vincelestes, is nested within a clade comprising ‘other Gondwanan mammals’, separated from Laurasian taxa. In general, because there is a lack of Mesozoic mammal skulls from Gondwana, meaning that the skull of Vincelestes can only be compared with cranial material from Laurasia, an incomplete understanding of relationships has resulted in earlier studies. The prototribosphenic condition of Vincelestes is supported by the cladistic analysis presented here and permits a number of interesting speculations because it is of later age than Jurassic tribosphenic mammals from Gondwana. It is proposed that the tribosphenic condition may have developed first amongst taxa on Pangea, before the separation of Laurasia and Gondwana.     

Resolving the relationships of Paleocene placental mammals

The ‘Age of Mammals’ began in the Paleocene epoch, the 10 million year interval immediately following the Cretaceous–Palaeogene mass extinction. The apparently rapid shift in mammalian ecomorphs from small, largely insectivorous forms to many small‐to‐large‐bodied, diverse taxa has driven a hypothesis that the end‐Cretaceous heralded an adaptive radiation in placental mammal evolution. However, the affinities of most Paleocene mammals have remained unresolved, despite significant advances in understanding the relationships of the extant orders, hindering efforts to reconstruct robustly the origin and early evolution of placental mammals. Here we present the largest cladistic analysis of Paleocene placentals to date, from a data matrix including 177 taxa (130 of which are Palaeogene) and 680 morphological characters. We improve the resolution of the relationships of several enigmatic Paleocene clades, including families of ‘condylarths’. Protungulatum is resolved as a stem eutherian, meaning that no crown‐placental mammal unambiguously pre‐dates the Cretaceous–Palaeogene boundary. Our results support an Atlantogenata–Boreoeutheria split at the root of crown Placentalia, the presence of phenacodontids as closest relatives of Perissodactyla, the validity of Euungulata, and the placement of Arctocyonidae close to Carnivora. Periptychidae and Pantodonta are resolved as sister taxa, Leptictida and Cimolestidae are found to be stem eutherians, and Hyopsodontidae is highly polyphyletic. The inclusion of Paleocene taxa in a placental phylogeny alters interpretations of relationships and key events in mammalian evolutionary history. Paleocene mammals are an essential source of data for understanding fully the biotic dynamics associated with the end‐Cretaceous mass extinction. The relationships presented here mark a critical first step towards accurate reconstruction of this important interval in the evolution of the modern fauna.     

Molecular dating and biogeography of the early placental mammal radiation

The timing and phylogenetic hierarchy of early placental mammal divergences was determined based on combined DNA sequence analysis of 18 gene segments (9779 bp) from 64 species. Using rooted and unrooted phylogenies derived from distinct theoretical approaches, strong support for the divergence of four principal clades of eutherian mammals was achieved. Minimum divergence dates of the earliest nodes in the placental mammal phylogeny were estimated with a quartet-based maximum-likelihood method that accommodates rate variation among lineages using conservative fossil calibrations from nine different nodes in the eutherian tree. These minimum estimates resolve the earliest placental mammal divergence nodes at periods between 64 and 104 million years ago, in essentially every case predating the Cretaceous-Tertiary (K-T) boundary. The pattern and timing of these divergences allow a geographic interpretation of the primary branching events in eutherian history, likely originating in the southern supercontinent Gondwanaland coincident with its breakup into Africa and South America 95-105 million years ago. We propose an integrated genomic, paleontological, and biogeographic hypothesis to account for these earliest splits on the placental mammal family tree and address current discrepancies between fossil and molecular evidence.     

Dentition and Jaw of Kokopellia juddi, a Primitive Marsupial or Near-Marsupial from the Medial Cretaceous of Utah

We add to the knowledge of the dentition and lower jaw of the primitive marsupial or near marsupial, Kokopellia juddi, based on newly collected materials from the medial Cretaceous (Albian–Cenomanian) of central Utah. The dental formula, i4 c1 p3 m4, is primitive for (or with respect to) Marsupialia, as are a number of features of the dentary and dentition: presence of a labial mandibular foramen, ?an inflected angle, ?and a trace of the meckelian groove; lack of “staggering” of the lower incisor series; lack of “twinning” between entoconid and hypoconulid on lower molars; incompletely lingual position of lower molar paraconid; upper molar protocone relatively small and mesiodistally narrow; and conules placed about halfway between the protocone and the paracone–metacone. Other than the stylocone, cusps are lacking from the stylar shelf; we argue that this represents the primitive marsupial condition based on the economy of character change and the stratigraphic record of marsupials in the Cretaceous of North America. Recent discoveries of early marsupials, eutherians, and therians of metatherian–eutherian grade provide data indicating that some derived features of the dentary and dentition (e.g., loss of coronoid, meckelian groove, and labial mandibular foramen; acquisition of strong, “winged” conules, double rank postvallum/prevallid shearing, and stylar cusp D) probably arose independently, in some cases more than once, among the major groups of tribosphenic mammals. In turn, this suggests that a common ancestor for marsupials and placentals was more primitive than has generally been appreciated.     

Monotremes as Pretribosphenic Mammals

An abundance of evidence points to the conclusion that monotremes are phyletically allied with pretribosphenic, rather than with tribosphenic, mammals. Monotremes do not have a tribosphenic dentition. Character analyses that apply tribosphenic cusp terminology to monotreme dentitions are implicitly limited thereby. A review of the molar dentition of living and fossil monotremes suggests that upper molars are composed of a strongly developed pretribosphenic paracone and metacone and a series of stylar cusps attached to them in a bicrescentic, or dilambdodont, fashion. The lower molars are composed of a trigonid, with a pretribosphenic protoconid, paraconid, and metaconid, and distal metacristid. The paraconid of m1 is reduced or lost. The talonid is composed of the pretribosphenic hypoconid, hypoconulid, and cristid obliqua. There is no evidence for a tribosphenic entoconid, nor for a talonid basin. There was no tribosphenic protocone. Monotremes are not related to other taxa included in Australosphenida. The dentition of Cretaceous taxa, such as Teinolophos and Steropodon, apparently still functioned by orthal mechanisms, whereas by the medial Paleocene (Monotrematum) and later (Obdurodon), monotremes appear to have accommodated a diet of soft-bodied organisms that left little trace of a mastication regime that had changed to apical wear via propalinal motion. Monotremes appear to be modern representatives of a Mesozoic radiation of pretribosphenic mammals centered largely in Gondwana, where they still reside today.     

Relationships of the dog-like marsupials, deltatheroidans and early tribosphenic mammals

A cladistic analysis of the major groups of early metatherian mammals shows that the Deltatheroida and South American dog-like Borhyaenoidea are closely related and are placed in a new supercohort Deltatheralia. while all other metatherians are placed in the supercohort Marsupialia. A reassessment of Early Cretaceous mammals with tribosphenic molars shows that metatherians and eutherians apparently evolved independently from a peramuran-like ancestor, and an entoconid. distinctly basined talonid and large protocone were acquired separately in each group. Consequently. the Tribosphenida ( sensu McKenna) is apparently paraphyletic. Aegialodontia are regarded as structurally ancestral to Metatheria but not Eutheria. The known fossil record supports the view that differentation of the stocks which gave rise to metatherians and eutherians apparently occurred in Late Jurassic or Early Cretaceous time.     

Micro‐computed tomography reveals a diversity of Peramuran mammals from the Purbeck Group (Berriasian) of England

Abstract:  The known sample of the important pretribosphenic mammal Peramus tenuirostris, housed in the Natural History Museum (London, UK), was imaged using micro‐computed tomography (CT). Substantial morphological diversity was discovered, prompting establishment (and resurrection) of additional taxa from within the existing hypodigm of Peramus tenuirostris: Peramus dubius comb. nov., Kouriogenys minor gen. nov. and Peramuroides tenuiscus gen. et sp. nov. The Peramura are revised; this group is restricted to taxa with clear evidence of a fully functional upper molar embrasure for the dominant lower molar talonid cusp (hypoconid), either through development of wear facet 4 or through differentiation of a distinct hypoconulid. The Peramura are the most likely sister taxon to the Tribosphenida (including living marsupials and placentals) and represent a distinct molar morphotype, transitional between primitive lineages characterized by dominant orthal shear (e.g. dryolestoids) and those with modern, multi‐functional tribospheny. A very large masseteric foramen is identified in peramurans, but this feature appears to be autapomorphic and of uncertain function.     

Decouverte dans le Paleocene du Maroc des plus anciens mammiferes eutheriens dáfique

A microvertebrate locality was discovered in the Southern part of the Ourzazate Basin (Morocco). The classical stratigraphic data as well as new elements given by Selacians allow us to date it form Lower Paleocene. Characid fishes, the oldest known to day, and an eutherian mammal fauna are associated with these Selacians. The mammal fauna includes Palaeoryctids, showing close affinities with the North American Upper Cretaceous genus Batodon, three forms which can be attributed to small carnivores, and still undetermined teeth. This fauna brings concrete elements to the problem of the african primitive mammal peopling and to the paleobiogeographical relationships of this continent.     

Paleobiogeography of Africa: How distinct from Gondwana and Laurasia?

Although Africa was south of the Tethys Sea and originally belonged to the Gondwana, its paleobiogeographical history appears to have been distinct from those of both Gondwana and Laurasia as early as the earliest Cretaceous, perhaps the Late Jurassic. This history has been more complex than the classical one reconstructed in the context of a dual world (Gondwana vs. Laurasia). Geological and paleobiogeographical data show that Africa was isolated from the Mid-Cretaceous (Albian-Aptian) to Early Miocene, i.e., for ca. 75 million years. The isolation of Africa was broken intermittently by discontinuous filter routes that linked it to some other Gondwanan continents (Madagascar, South America, and perhaps India), but mainly to Laurasia. Interchanges with Gondwana were rare and mainly “out-of-Africa” dispersals, whereas interchanges with Laurasia were numerous and bidirectional, although mainly from Laurasia to Africa. Despite these intermittent connections, isolation resulted in remarkable absences, poor diversity, and emergence of endemic taxa in Africa. Mammals suggest that an African faunal province might have appeared by Late Jurassic or earliest Cretaceous times, i.e., before the opening of the South Atlantic. During isolation, Africa was inhabited by vicariant West Gondwanan taxa (i.e., taxa inherited from the former South American-African block) that represent the African autochthonous forms, and by immigrants that entered Africa owing to filter routes. Nearly all, or all immigrants were of Laurasian origin. Trans-Tethyan dispersals between Africa and Laurasia were relatively frequent during the Cretaceous and Paleogene and are documented as early as the earliest Cretaceous or perhaps Late Jurassic, i.e., perhaps by the time of completion of the Tethys between Gondwana and Laurasia. They were permitted by the Mediterranean Tethyan Sill, a discontinuous route that connected Africa to Laurasia and was controlled by sea-level changes. Interchanges first took place between southwestern Europe and Africa, but by the Middle Eocene a second, eastern route — the Iranian route — involved southeastern Europe and southwestern Asia. The Iranian route was apparently the filtering precursor of the definitive connection between Africa and Eurasia. The relationships and successive immigrations of mammal (mostly placental) clades in Africa allow the recognition of five to seven phases of trans-Tethyan dispersals between Africa and Laurasia that range from the Late Cretaceous to the Eocene-Oligocene transition. These Dispersal Phases involve dispersals toward Laurasia and/or toward Africa (immigrations). The immigrations in Africa gave rise to faunal assemblages, the African Faunal Strata (AFSs). All successful and typical African radiations have arisen from these AFSs. We recognize four to six AFSs, each characterized by a faunal association. Even major, old African clades such as Paenungulata or the still controversial Afrotheria, which belong to the oldest known AFS involving placentals, ultimately originated from a Laurasian stem group. Africa was an important center of origin of various placental clades. Their success in Africa is probably related to peculiar African conditions (endemicity, weak competition). Although strongly marked by endemicity, the African placental fauna did not suffer extinctions of major clades when Africa contacted Eurasia. The present geographic configuration began to take shape as early as the Mid-Cretaceous. At that time, the last connections between Africa and other Gondwanan continents began to disappear, whereas Africa was already connected to Eurasia by a comparatively effective route of interchange.     

A new Early Cretaceous eutherian mammal from the Sasayama Group,Hyogo, Japan

We here describe a new Early Cretaceous (early Albian) eutherian mammal, Sasayamamylos kawaii gen. et sp. nov., from the ‘Lower Formation’ of the Sasayama Group, Hyogo Prefecture, Japan. Sasayamamylos kawaii is characterized by a robust dentary, a distinct angle on the ventral margin of the dentary at the posterior end of the mandibular symphysis, a lower dental formula of 3–4 : 1 : 4 : 3, a robust lower canine, a non-molariform lower ultimate premolar, and a secondarily reduced entoconid on the molars. To date, S. kawaii is the earliest known eutherian mammal possessing only four premolars, which demonstrates that the reduction in the premolar count in eutherians started in the late Early Cretaceous. The occurrence of S. kawaii implies that the relatively rapid diversification of eutherians in the mid-Cretaceous had already started by the early Albian.     

<Emphasis Type="Italic">Protungulatum</Emphasis>, Confirmed Cretaceous Occurrence of an Otherwise Paleocene Eutherian (Placental?) Mammal

Neither pre-Cenozoic crown eutherian mammals (placentals) nor archaic ungulates (“condylarths”) are known with certainty based on the fossil record. Herein we report a new species of the Paleocene archaic ungulate (“condylarth”) Protungulatum from undisputed Late Cretaceous aged rocks in Montana USA based on an isolated last upper premolar, indicating rare representatives of these common early Tertiary mammals appeared in North America a minimum of 300 k  years before the extinction of non-avian dinosaurs. The other 1200 mammal specimens from the locality are characteristic Late Cretaceous taxa. This discovery overturns the current hypothesis that archaic ungulates did not appear in North America until after the Cretaceous/Tertiary (K/T) boundary and also suggests that other reports of North American Late Cretaceous archaic ungulates may be correct. Recent studies, including ours, cannot determine whether Protungulatum does or does not belong to the crown clade Placentalia.     

Osseous inner ear structures and hearing in early marsupials and placentals

Based on the internal anatomy of petrosal bones as shown in radiographs and scanning electron microscopy, the inner ear structures of Late Cretaceous marsupials and placentals (about 65 Myr ago) from the Bug Creek Anthills locality of Montana, USA, are described. The inner ears of Late Cretaceous marsupials and placentals are similar to each other in having the following tribosphenic therian synapomorphies: a fully coiled cochlea, primary and secondary osseous spiral laminae, the perilymphatic recess merging with the scala tympani of the cochlea, an aqueductus cochleae, a true fenestra cochleae, a radial pattern of the cochlear nerve and an elongate basilar membrane extending to the region between the fenestra vestibuli and fenestra cochleae. The inner ear structures of living therians differ from those of their Late Cretaceous relatives mainly in having a greater number of spiral turns of the cochlea and a longer basilar membrane. Functionally, a coiled cochlea not only permits the development of an elongate basilar membrane within a restricted space in the skull but also allows a centralized nerve system to innervate the elongate basilar membrane. Qualitative and quantitative analyses show that, with a typical therian inner ear, Late Cretaceous marsupials and placentals were probably capable of high-frequency hearing.     

A New Stem Placental Mammal from the Early Cretaceous of Mongolia

A new taxon of stem placentals, Hovurlestes noyon gen. et sp. nov. from the Early Cretaceous of Mongolia (Höovör locality) is described. The new taxon differs from members of the genus Prokennalestes from Höovör in the single-rooted canine and the presence of cusp e, which is an enhancing interlocking between anterior molars (m1 and m2). Hovurlestes noyon gen. et sp. nov. is one of the rarest mammal taxa from Höovör, which expands morphological diversity of the earliest Eutheria.     

长白山自然保护区兽类道路交通致死的初步分析

2007 ～ 2009 年,按月对吉林长白山自然保护区环保护区的2 条要道所造成兽类交通死亡状况以及车流量 和车速等因素进行了调查。结果表明:(1)保护区道路交通致死的兽类种类达14种,占保护区种类的27% ,以棕背鼠平、花鼠和大林姬鼠等为优势种类;(2)道路交通所造成的动物个体死亡为2. 57 ± 0.53 头/10km,其中夜行性种类的致死率很高,达69.8% ;(3) 动物死亡主要发生在车流量为1 ～ 40 辆/ h 的区间,占69.4% ,尤以30 ～ 40 辆/ h 区间的致死率最高;(4)动物致死率与每月的车流量显著相关,主要集中在5 ～ 10 月,以9 月的致死率最高。通过对兽类活动时间和生态习性分析,兽类交通致死主要发生在凌晨、傍晚或夜间时段。这可能与夜间车辆照明对动物产生视觉障碍有较大关系,加上车速快和车流量大,极易造成晨昏或夜间活动的动物的大量死亡。因此,建议在保护区路段上合理控制夜间车辆行驶时间,并对车流量和车速予以限制,从而有效减少动物道路交通致死。     

Evolutionary explosions and the phylogenetic fuse

A literal reading of the fossil record indicates that the early Cambrian (c. 545 million years ago) and early Tertiary (c. 65 million years ago) were characterized by enormously accelerated periods of morphological evolution marking the appearance of the animal phyla, and modern bird and placental mammal orders, respectively. Recently, the evidence for these evolutionary `explosions' has been questioned by cladistic and biogeographic studies which reveal that periods of diversification before these events are missing from the fossil record. Furthermore, molecular evidence indicates that prolonged periods of evolutionary innovation and cladogenesis lit the fuse long before the `explosions' apparent in the fossil record.     

Molecular Evidence for the Major Clades of Placental Mammals

Higher-level relationships among placental mammals, as well as the historical biogeography of this group against the backdrop of continental fragmentation and reassembly, remain poorly understood. Here, we analyze two independent molecular data sets that represent all placental orders. The first data set includes six genes (A2AB, IRBP, vWF, 12S rRNA, tRNA valine, 16S rRNA; total = 5.71 kb) for 26 placental taxa and two marsupials; the second data set includes 2.95 kb of exon 11 of the BRCA1 gene for 51 placental taxa and four marsupials. We also analyzed a concatenation of these data sets (8.66 kb) for 26 placentals and one marsupial. Unrooted and rooted analyses were performed with parsimony, distance methods, maximum likelihood, and a Bayesian approach. Unrooted analyses provide convincing support for a fundamental separation of placental orders into groups with southern and northern hemispheric origins according to the current fossil record. On rooted trees, one or both of these groups are monophyletic depending on the position of the root. Maximum likelihood and Bayesian analyses with the BRCA1 and combined 8.66 kb data sets provide strong support for the monophyly of the northern hemisphere group (Boreoeutheria). Boreoeutheria is divided into Laurasiatheria (Carnivora + Cetartiodactyla + Chiroptera + Eulipotyphla + Perissodactyla + Pholidota) and Euarchonta (Dermoptera + Primates + Scandentia) + Glires (Lagomorpha + Rodentia). The southern hemisphere group is either monophyletic or paraphyletic, depending on the method of analysis used. Within this group, Afrotheria (Proboscidea + Sirenia + Hyracoidea + Tubulidentata + Macroscelidea + Afrosoricida) is monophyletic. A unique nine base-pair deletion in exon 11 of the BRCA1 gene also supports Afrotheria monophyly. Given molecular dates that suggest that the southern hemisphere group and Boreoeutheria diverged in the Early Cretaceous, a single trans-hemispheric dispersal event may have been of fundamental importance in the early history of crown-group Eutheria. Parallel adaptive radiations have subsequently occurred in the four major groups: Laurasiatheria, Euarchonta + Glires, Afrotheria, and Xenarthra.     

A eutherian mammal from the Early Cretaceous of Russia and biostratigraphy of the Asian Early Cretaceous vertebrate assemblages

Prokennalestes abramovi n.sp. is described based on M2 from the upper Barremian-middle Aptian (Early Cretaceous) Mogoito locality in Transbaikalia, Russia. It differs from the Mongolian species of Prokennalestes (Khoboor, early Albian) by a combination of one primitive character (steeper and shorter lingual slopes of the paracone and metacone), one more derived character (larger size), and some characters of uncertain polarity (small preparastyle, lack of labial cuspules along the ectoflexus). P. abramovi n.sp. is the oldest eutherian mammal so far described, and its discovery extends the known geological range of Eutheria by 10-15 Ma. The Tsagantsabian land-vertebrate biochron can be defined by a dominance of sinemyid turtles; the Khukhtekian by a dominance of macrobaenids.     

A Late Pliocene occurrence of the Thick-billed Murre (Alcidae: Uria lomvia) on St. George Island, Pribilofs, Alaska

An associated partial skeleton from the Late Pliocene (3.0–2.6 million years) of St. George Island, Pribilofs, Alaska, is identified as the modern Thick-billed Murre (Uria lomvia). This is the oldest occurrence of either modern species of Uria and probably the oldest Cenozoic bird yet known from Alaska. A split between the two modern species of >3 million years is in accordance with divergence times derived from DNA sequences.     

Evolution and function of the upper molar talon and its dietary implications in microbats

The evolution of mammalian molars has been marked by transitions representing significant changes in shape and function. One such transition is the addition and elaboration of the talon, the distolingual region of the ancestral tribosphenic upper molar of therian mammals and some extinct relatives. This study uses suborder Microchiroptera as a case study to explore the adaptive implications of the expansion of the talon on the tribosphenic molar, specifically focusing on the talon's role in the compression and shear of food during breakdown. Three‐dimensional computer renderings of casts of the upper left first molars were created for microbat species of a variety of dietary categories (frugivore, etc.) and physical properties of food (hard and soft). Relief Index (RFI) was measured to estimate the topography and function of the whole tooth and of the talon and trigon (the remaining primitive tribosphenic region) individually, in order to examine 1) how the shape of the whole tooth, trigon, and talon reflects the compromise between their crushing and shearing functions, 2) how whole tooth, trigon, and talon function differs according to diet, and 3) how the presence of the talon affects overall molar function. Results suggest that RFI of both the whole tooth and the trigon varies according to dietary groups, with frugivores having greater crushing function when compared with the other groups. The talon, however, consistently has low RFI (a flatter topography), and its presence lowers the RFI of the whole tooth across all dietary categories, suggesting that the talon is primarily functioning in crushing during food breakdown. The potential benefits of a crushing talon for microbats of various dietary groups are discussed. J. Morphol. 276:1368–1376, 2015. © 2015 Wiley Periodicals, Inc.     

New mammal remains from the Late Cretaceous Bostobe Formation (Northeast Aral Sea Region,Kazakhstan)

Four recently collected mammal specimens from the Upper Cretaceous (Santonian–?Campanian) Bostobe Formation in the northeastern Aral Sea Region, Kazakhstan are attributed to Asioryctitheria indet. (an edentulous dentary fragment) and the zhelestid Parazhelestes sp. cf. P. mynbulakensis (a maxillary fragment with a double-rooted canine, an M1, and a dentary fragment including m3). These new records double the known mammal fauna from this formation, which previously included the zhelestid Zhalmouzia bazhanovi and Zhelestidae indet. The taxonomic and ecological structure of the mammal assemblage from the Bostobe Formation can, on present evidence, be considered close to the other eutherian dominated Late Cretaceous mammal assemblages of Central Asia. This region is important in particular in the search for Late Cretaceous ancestors of crown-group eutherian mammal clades (Placentalia).