Cranial circulation of the pen-tailed tree shrewPtilocercus lowii and relationships of Scandentia

The major cranial arteries and veins are described for a 30-mm crown-rump length fetus of the pen-tailed tree shrewPtilocercus lowii, and comparisons are made with cranial vessels reported in the tree shrewTupaia and with the vascular pattern reconstructed for primitive eutherians.Ptilocercus shares a number of derived features of the cranial circulation withTupaia, which, therefore, represent synapomorphies of tree shrews (Tupaiidae, Scandentia). Included are (1) the enclosure of the intratympanic portion of the internal carotid artery in a bony canal that is floored proximally and distally by the entotympanic and by the petrosal in between, (2) the enclosure of the intratympanic portion of the stapedial artery by the petrosal in a canal on the promontorium and within the epitympanic crest beneath the tympanic roof, (3) the absence of an exit for the arteria diploëtica magna, (4) an alisphenoid canal, (5) a maxillary artery that passes medial to the mandibular nerve beneath foramen ovale, and (6) a laryngeopharyngeal artery. Some of these derived features, however, are also found in certain other eutherians (e.g., numbers 2, 3, and 6 in Euprimates) and, therefore, may be used in future studies to assess the higher-level affinities of Scandentia.     

Ontogeny and cranial morphology of the tympanic region of the Tupaiidae, with special reference to Ptilocercus

The structure of the tympanic region of the skull of Ptilocercus lowii was studied in an embryo of 30 mm crown-rump length and in 5 osteocrania. As in Tupaia, the anterior wall of the bulla of Ptilocercus is not completed by a tympanic process of the alisphenoid, contrary to earlier reports. Ptilocercus resembles Tupaia in the following derived characters. The ventral wall of the tympanic cavity is formed by a rostral entotympanic and by a caudal tympanic process of the petrosal. The entotympanic develops in primary connection with the tubal cartilage. The tympanic aperture of the auditory tube is bordered by the entotympanic. The ring-shaped tympanicum is covered by the entotympanicum and is aphaneric. The musculus tensor tympani is lacking. Among mammals, these characters can be regarded as synapomorphic for the Tupaiidae, that is, to have been present in the common ancestor of the two subfamilies. From the evidence of the tympanic region, the Tupaiidae, therefore, form a monophyletic group. Besides these synapomorphies, there are remarkable differences between Ptilocercus and Tupaia in the structure of the bulla. In Ptilocercus the bulla is smaller and less pneumatized than in Tupaia. An anterior intrabullar septum, present in Tupaia, is lacking in Ptilocercus. The epitympanic wing of the alisphenoid is smaller in Ptilocercus than in Tupaia. A lateral prefacial commissure of the tegmen tympani is present in Ptilocercus, but absent in Tupaia. The caudal tympanic process of the petrosal is larger in Ptilocercus than in Tupaia. These characters are autapomorphic for the Ptilocercinae and for the Tupaiinae, respectively. They demonstrate that the auditory bulla of Ptilocercus and that of Tupaia have evolved independently to a considerable extent. An early phylogenetic separation of their respective ancestors seems likely. The tympanic region of the skull provides no evidence for close relationships of the tree shrews to the primates or to any other eutherians. The classification of the Tupaiidae in a separate order, Scandentia, is supported.     

The angular process of Monodelphis domestica (Didelphidae, Marsupialia) and its relation to the middle ear: an ontogenetic and evolutionary morphologic study

In most marsupials, the angular process is inflected medially. By using an ontogenetic series of Monodelphis domestica, the development of this characteristic structure has been described. In contrast with the eutherian mammals, in marsupials there is retained a close connection between the dentale and the tympanicum and goniale; it is well known that these 2 elements of the middle ear are derived from the angulare and prearticulare of the reptilian lower jaw. At the neonatal stage, the dentale and tympanicum are both relatively vertically orientated; during the following 2 weeks, they take an increasingly oblique position, which is primarily caused by the rapid growth of the braincase. Only after the eruption of the first teeth, the ascending ramus of the dentale takes a more and more vertical position, whereas the angular process remains with its tip near the medioventral floor of the tympanic bulla. The bulla shows at this place a rectangular fenestra which is covered by a membrane of loose connective tissue; the tip of the angular process, which is always free of muscular insertions, maintains contacts with this fenestra throughout life. During juvenile and adult life stages, the process becomes somewhat removed from the fenestra for obvious reasons, but at a gape of about 40 to 50 degrees it inevitably must touch the "inferior tympanic membrane" and possibly also the tympanic ring. It is speculated that the relationship between the angular process and the tympanic bulla represents a specific form-function complex for sound transmission, which may be a modified retention from archaic mammalian conditions. Further details of the ontogenetic development of the tympanic region have been described which may be of some relevance for the evolutionary morphology of mammals: The tympanic process of the petrosal, which fixes the posterior end of the tympanic ring, is formed by 'Zuwachsknochen' (additional bone) but not by cartilage. The styloid process remains cartilaginous throughout life: its free tip ends in the lateral wall of the tympanic cavity and it is closely connected with the collum mallei and the posterior end of the tympanicum; it guides the chorda tympani and may therefore be homologous with the cartilage of Spence. The cartilage of Paauw is interpreted in terms of functional morphology. A model of evolutionary transformation of the dentale-tympanicum complex in mesozoic mammals in outlined on the basis of the ontogenetic findings in Monodelphis and other didelphid and dasyurid marsupials.     

The petrosal of Omomys carteri and the evolution of the primate basicranium

The first omomyine petrosals, those of Omomys carteri, are described. Omomys probably had a tympanic bulla and canals for the intratympanic carotid circulation derived from the petrosal bone. The stapedial and promontory canals were complete, large and subequal. The posterior carotid foramen entered the bulla posteromedially. The intratympanic portion of the facial nerve was fully enclosed in bone, the stapedius fossa is extrabullar and the parotic fissure is patent. The mastoid was pneumatized from the epitympanic recess and a supracochlear cavity may have been present. The Omomys petrosals exhibit a generic omomyiform morphology, exhibiting no features that can be interpreted as autapomorphies and only one feature shared with adapiforms. The monophyly of Omomyiformes is based on other cranial characters, dental and postcranial characters assessed elsewhere. The similarity of the Shanghuang petrosal to the petrosals of omomyiforms, as well as the ambiguous evidence of its association, suggest that an omomyiform affinity for that petrosal cannot be ruled out.     

Reexamination of the morphological evidence for the cohort Epitheria (Mammalia,Eutheria)

Novacek and co-workers recognized a monophyletic clade Epitheria, comprising all eutherians except edentates and the extinct palaeoryctoids, on the basis of two synapomorphies: a stirrupshaped stapes and a foramen ovale enclosed within the alisphenoid. To evaluate this phylogenetic hypothesis, we reexamined the distributions of stapedial morphologies and positions of the foramen ovale across Recent and extinct mammals and nonmammalian cynodonts. The states and distributions of the stapes and forament ovale characters used by Novacek and coworkers were modified by recognizing two stapedial characters (one relating to shape of the crura, the other to the nature of the foramen) and a single, multistate foramen ovale character (within, behind, and lateral to the alisphenoid). The taxon-character matrix used by Novacek (1989, 1992b), substituting our amended stapedial and foramen ovale characters and adding several previously unscored extinct taxa and three new characters, was subjected to a series of PAUP manipulations. Identified among the most parsimonious trees were three major topologies for the base of Eutheria: (1) a polytomy including an Edentata/Ungulata clade, (2) a polytomy with Edentata and Ungulata as separate clades, and (3) Edentata and (when included) Palaeoryctoidea as the successive outgroups to a monophyletic Epitheria. We conclude that topology 2 best reflects the current state of knowledge. An edentate/ungulate clade is supported by three characters (from the mastoid region and subarcuate fossa); however, other morphological studies require modification of the distributions of these characters in xenarthrans and bassal ungulates, thereby eliminating support for this clade. In nearly all manipulations, obtaining a monophyletic Epitheria required that one or two steps be added to the most parsimonious trees. When a monophyletic Epitheria was obtained, it was supported by a triangular stapes and, in some trees, the reappearance of a stapedial artery (lost earlier at the level of Recent therians) and a transpromontorial internal carotid artery. In the most parsimonious trees, a foramen ovale within the alisphenoid was an equivocal synapomorphy of Recent therians or cutherians, and a stapes with strongly convex crura (our state closest to the stirrup-shaped state of Novacek and co-workers) appeared independently within various eutherian lineages. The reduction or loss of the stapedial foramen was identified as an independent event in monotremes and within marsupials and various eutherian lineages.To whom correspondence should be addressed.     

Cranial anatomy of the Paleocene plesiadapiform Carpolestes simpsoni (Mammalia, Primates) using ultra high-resolution X-ray computed tomography, and the relationships of plesiadapiforms to Euprimates

Central to issues surrounding the origin of euprimates, affinities of Paleocene Carpolestidae have been controversial. Carpolestids have been classified as plesiadapoid primates, tarsiiform euprimates, dermopterans, or the sister taxon of euprimates to the exclusion of other plesiadapiforms, based exclusively on dental or postcranial data. Newly discovered crania of Carpolestes simpsoni from the latest Paleocene of the Clarks Fork Basin, Wyoming, are the first described for the family Carpolestidae. The two best preserved skulls were studied using ultra high-resolution X-ray computed tomography. Comparison of these specimens to those of other stem primates (Plesiadapiformes) demonstrates that the diversity of cranial morphology in this group is greater than previously thought. Carpolestes differs from euprimates and is similar to other plesiadapiforms (Ignacius and Plesiadapis) in lacking a postorbital bar and having a relatively long rostrum. Carpolestes is similar to fossil euprimates and Plesiadapis in having a bullar morphology consistent with a petrosal origin, and differs from Ignacius, in which the bulla is composed of the entotympanic. Carpolestes differs from primitive euprimates and all other known plesiadapiforms in possessing a two-chambered auditory bulla, similar to that of modern Tarsius. However, Carpolestes had an internal carotid artery (ICA) that took a transpromontorial route from a posteromedially positioned posterior carotid foramen (pcf), unlike Tarsius, in which this artery takes a perbullar route from an anterolaterally positioned pcf. Carpolestes has clear grooves on the promontorium for both the promontorial and stapedial arteries, indicating that it had an unreduced internal carotid circulation, similar to that of early euprimates. Carpolestes differs from primitive euprimates and some specimens of Ignacius in not having bony tubes surrounding the branches of the ICA. Cladistic analysis of cranial data fails to support a close relationship of Carpolestidae to either tarsiiform euprimates or extant Dermoptera, but suggests a close relationship between Carpolestidae, Plesiadapidae, and Euprimates.     

A Reexamination of Proposed Morphology-Based Synapomorphies for the Families of Dasyuromorphia (Marsupialia). I. Dasyuridae

The validity of eight morphological features previously advanced as synapomorphic for Dasyuridae is investigated in the light of new fossil and molecular data. Results indicate that one of these features (alisphenoid–periotic enclosure of the foramen ovale) is common to outgroups for Dasyuromorphia. Another feature (loss of intestinal cecum) is a likely synapomorphy for Dasyuromorphia. Two features (development of a hypoconulid notch, enlargement of stylar cusp D) may represent shared–derived characters within Dasyuromorphia but not at the family level for Dasyuridae (i.e., probably unite Dasyuridae–Thylacinidae). Another two features (loss of posterolateral palatine foramina, reduction of P₃) are also apomorphic within Dasyuromorphia but unite specialized clades within Dasyuridae. Only two previously treated features are probable synapomorphies for the family (enlargement of the alisphenoid tympanic wing and development of a distinct periotic hypotympanic sinus). An additional feature is identified as a dasyurid synapomorphy (presence of a distinct tubal foramen). Of all putative synapomorphies proposed to date, only the presence of a periotic hypotympanic sinus and tubal foramen are unique for Dasyuridae among dasyuromorphians. Results suggest considerable homoplasy for basicranial features within Dasyuromorphia. Independent acquisition for alisphenoid enclosure of the foramen ovale, development of secondary foramina ovale and loss of posterolateral palatal foramina has occurred in derived thylacinid and dasyurid clades. Convergence is also indicated for hypertrophy of the alisphenoid tympanic wing shown for dasyurids and myrmecobiids, and the development of a squamosal epitympanic sinus in Thylacinidae, Dasyuridae, and Myrmecobiidae. The finding of plesiomorphy for alisphenoid–periotic enclosure of the foramen ovale within Dasyuromorphia undermines the strongest morphology-based synapomorphy uniting a monophyletic Dasyuridae–Myrmecobiidae. Phylogenetic placement for some plesiomorphic fossil dasyuromorphians, known only from dental material, within Dasyuridae is currently untenable, with no dental synapomorphies uniting the family. The value of identifying morphoclines within clades known from robust phylogenetic data for consideration in character analysis is stressed, as is the importance of form–function and ontogenetic data.     

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.     

Significance of primate petrosal from Middle Eocene fissure-fillings at Shanghuang, Jiangsu Province, People's Republic of China

An isolated petrosal bone belonging to a diminutive primate is reported from Middle Eocene fissure-fills near Shanghuang (southern Jiangsu Province, People's Republic of China), the type locality of several newly described primates (Eosimias sinensis, a basal anthropoid; Adapoides troglodytes, a basal adapinan; Tarsius eocaenus, a congener of extant tarsiers; and Macrotarsius macrorhysis, the first Asian representative of an otherwise exclusively North American genus). Because of its fragmentary condition and unique combination of characters, the Shanghuang petrosal cannot be assigned unambiguously to any of the Shanghuang primate taxa known from dental remains. However, the possibility that the petrosal represents either an adapid or a tarsiid can be dismissed because it lacks defining basicranial apomorphines of these groups. By contrast, the element does present arterial features consistent with its being haplorhine. Deciding between the likeliest candidates for its allocation—Omomyidae and Eosimiidae—is difficult, in part because it is not known what (or even whether) basicranial characters can be used to distinguish these clades. If the Shanghuang petrosal is that of an cosimiid, as both direct and indirect evidence appears to indicate, the following implications emerge: (1) as long suspected on other grounds, anthropoids share a closer evolutionary history with Omomyidae (and Tarsiiformes) than they do with Adapidae (and Strepsirhini); (2) the specialised basicranial anatomy of extant anthropoids and their immediate cladistic relatives is derived from a primitive precursor whose otic morphology was like that of omomyids in most known respects; (3) the evolution of the defining dental and basicranial apomorphies of extant Anthropoidea has been distinctly mosaic in pattern.     

Patterns of evolutionary transformation in the petrosal bone and some basicranial features in marsupial mammals, with special reference to didelphids

Twelve petrosal and four nonpetrosal characters were coded for representatives of all 15 extant genera of Didelphidae and for 16 additional genera of marsupials representing all extant orders. Three basal metatherians were used as outgroup comparison. Histological sections of a subset of the data were examined. An intermediate position of the hiatus Fallopii supports the monophyly of Didelphidae. Several basicranial regions support different clades within the Didelphidae that recent molecular work has identified, including a sister group relationship of Caluromys and Caluromysiops , the monophyly of large opossums, a Lestodelphys-Thylamys clade, and a Lestodelphys-Thylamys-Gracilinanus-Marmosops clade. Glironia lacks petrosal and jaw synapomorphies of Caluromys and Caluromysiops. The transverse canal, a synapomorphy of the crown-group Marsupialia, opens as a single foramen anterior to the carotid foramen in most marsupials or as numerous foramina in the pterygoid fossa in diprotodontians. It is either intramural (most marsupials) or simply endocranial (most diprotodontians excluding koalas and wombats). Loss of a deep sulcus in the anterior pole of the promontorium for the internal carotid artery and a rostral tympanic process of the petrosal also characterize the groundplan of the crown group Marsupialia. Pouch-young wombats show a groove in the anterior pole of the petrosal for the internal carotid artery. The absence of a prootic canal foramen in the tympanic side of the petrosal of adults supports the monophyly of Australidelphia. Some pouch-young marsupials possess a prootic canal that is later lost in ontogeny. A rather flat promontorium and a crest running medio-distally in the middle of the promontorium characterize Macropodidae.     

Additional data on early Paleocene metatherians (Mammalia) from Punta Peligro (Salamanca Formation, Argentina): comments based on petrosal morphology

Metatherian remains from Punta Peligro (Chubut Province, Argentina; Salamanca Formation, early Paleocene) are scarce, but at present, there are at least four different taxa known by dental remains. We describe here an incomplete petrosal showing metatherian affinities. Among the dentally known taxa from the same stratigraphic levels, the overall size of the petrosal fits that predicted for Derorhynchus , which in turn was assigned to the order Didelphimorphia. The features of the petrosal we describe do not correspond with the morphology observed among didelphoid marsupials, the only members of Didelphimorphia with well known basicrania, suggesting that if the association of petrosal and dental remains is correct, then referral of Derorhynchus to the Didelphimorphia has to be revised. The taxonomic content of this group of marsupials, as presently interpreted, represents a paraphyletic or polyphyletic grouping of metatherians.     

Eutherian mammals from the Early Cretaceous of Mongolia

A collection of eutherian mammals consisting of 39 specimens (teeth and jaw fragments) from the ?Aptian or Albian Khoboor Beds in the Gobi Desert, Mongolia, is described. It contains 3 taxa: Prokenna1estes gen.n., assigned to the Otlestidae Nessov, new rank, with 2 shrew size species; P. trofimovi sp.n. and P. minor sp.n.; a heavily worn larger lower molar which will be described elsewhere. It cannot be excluded that P. trofimovi and P. minor are only sexual morphs within the same species. Prokennalestes and Bobolestes Nessov are possibly the oldest known eutherian mammals, but Prokennalestes is morphologically more primitive than Bobolestes. It has a labial mandibular foramen, 5 premolars and 3 molars, 3 cusps in parastylur region, paracone larger than metacone, unwinged conules, no pre- and posteingula, and lower molars with a 3-cusped talonid, which is narrower than the trigonid, Otlestes and Kennalestes may be derived with little modification from Prokennalestes. Prokennalestes gen.n. is congeneric with Prokennalestes Trofimov and Prozalambdalestes Trofimov, which are both nomina nuda.     

<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.     

The nocturnal bottleneck and the evolution of activity patterns in mammals

In 1942, Walls described the concept of a ‘nocturnal bottleneck’ in placental mammals, where these species could survive only by avoiding daytime activity during times in which dinosaurs were the dominant taxon. Walls based this concept of a longer episode of nocturnality in early eutherian mammals by comparing the visual systems of reptiles, birds and all three extant taxa of the mammalian lineage, namely the monotremes, marsupials (now included in the metatherians) and placentals (included in the eutherians). This review describes the status of what has become known as the nocturnal bottleneck hypothesis, giving an overview of the chronobiological patterns of activity. We review the ecological plausibility that the activity patterns of (early) eutherian mammals were restricted to the night, based on arguments relating to endothermia, energy balance, foraging and predation, taking into account recent palaeontological information. We also assess genes, relating to light detection (visual and non-visual systems) and the photolyase DNA protection system that were lost in the eutherian mammalian lineage. Our conclusion presently is that arguments in favour of the nocturnal bottleneck hypothesis in eutherians prevail.