Continuous replacement of teeth throughout their lifetimes is a well known phenomenon in modern sharks. The mechanism involves the continuous generation of embryonic teeth internally on the inner surface of the jaws, and their subsequent displacement on a moving mat of connective tissue in “assembly-line” fashion. The fully-formed teeth erupt from the gum at the outer jaw margin, are functional for a short time, and are shed as the next tooth in the series takes its place.

This study reports a specimen of a Devonian cladodont shark, Ctenacanthus, in which the dentition was not shed at the jaw margin, but instead migrated beneath the skin on the outside of the head. A survey of additional specimens demonstrates that tooth retention was present in cladoselachians as well, and may have been a feature of cladodont sharks in general.

Tooth retention in the cladodonts (the top-level predacious sharks of their day) seems to have been a problem that had to be overcome before the development of the modern cutting and gouging mechanism. It is suggested that the reorganization of the blood supply to the teeth, coupled with a sharp jaw margin, may have provided the mechanism for tooth loss and the eventual development of rapid tooth replacement.

Problems arise when relationships of the early members of new classes of organisms are being discussed. Our concern about this problem arises from the recent work on Diabolepis, which some workers have regarded as the sister group of the Dipnoi. The main morphological work on this genus by Chang (1995), has set out the main features of the skull of the genus. She has analyzed the relationships without cladistic analysis, but other workers have cladistically analyzed the data. In this paper we criticise many of the observations on morphology discussed by Chang, and contest many of the synapomorphies used by workers who do the cladistic analysis. Broad conclusions concerning the development of sarcopterygian fishes and more detailed results such as the evolution of the dental plates of dipnoans, have been falsely drawn because of this.

Extensive and well preserved sauropod material belonging to more than twelve individuals were recovered from the Early Jurassic Kota Formation of India. The sauropod Kotasaurus yamanpalliensis is characterized by simple dorsal vertebrae and a low iliac blade. Detailed osteological description of Kotasaurus is presented. The characters that distinguish Kotasaurus from the primitive sauropods are provided. It is considered to be one of the earliest sauropods and has some primitive features. The character analysis revealed that Kotasaurus is a basal sauropod in addition to Vulcanodon, Shunosaurus, Barapasaurus, and Omeisaurus.

A plesiosaur specimen from the Lower Lias (Lower Jurassic) of England displays lesions of the vertebral end-plate in 24 of the 27 preserved centra. A single Schmorl's node is visible towards the ventral margin of the anterior end-plate in each of eight vertebrae. The herniated intervertebral discs have penetrated the cortex of the adjacent vertebral bodies, forming the typical mushroom-shaped cavities of Schmorl's nodes. BRSUG 26539 represents the first fossil, reptile or marine organism to be diagnosed with Schmorl's nodes, a disease most commonly associated with the human spine and a bipedal stance. Compressive stresses arising from bending loads within the ‘archer's bow’ system of the plesiosaur trunk region are concentrated towards the ventral margin of the vertebral end-plate and may explain the location of Schmorl's nodes in the posteriormost cervical vertebrae. Degeneration of the vertebral column due to old age, a congenital weakness in the vertebral end-plates, or bending moments and torsional loadings induced by the weight of the head and long neck are possible explanations for the development of Schmorl's nodes in this plesiosaur. Osteoporosis is an unlikely cause of the disease in this specimen due to the pachyostotic nature of plesiosaur vertebrae.

The osteology of the Eocene lizard Eolacerta robusta from Messel and Geiseltal is redescribed. Contrary to former opinions, Eolacerta does not possess body osteoderms, the pubis is typically lizard-like, the astragalus and calcaneum are fused, and the first cervical rib is distinctly curved posterolaterally. The suggestion that Eolacerta belongs to the modern family Lacertidae cannot be corroborated due to its many plesiomorphies and character incongruences, a view which is also supported by phylogenetic analysis. At present, Eolacerta cannot be assigned to any modern lizard family and is classified as Scleroglossa incertae sedis.

New crania, dentitions, and postcrania of the fossil pinniped, Proneotherium repenningi are described from the early to middle Miocene-age Astoria Formation of Lincoln County, Oregon. This sample includes specimens of four adult individuals; all probably males. The skull of Proneotherium repenningi shares many generalized features with basal pinnipeds (e.g., species of Enaliarctos) including its overall elongation, low profile, low sagittal crest, well developed lambdoidal crests, slender zygomatic arches, small orbits, slightly arched palate, dental formulae, and distinct embrasure pit. Proneotherium, however, differs from species of Enaliarctos in possession of a continuous and horizontal crest connecting the mastoid and paroccipital processes and in having a less secodont dentition. The molariform premolar dentition of Proneotherium is noteworthy and can be interpreted as representing the initial stage in a morphologic series that extends through Neotherium to Imagotaria. This morphologic series reflects a functional change from a shearing dentition to more of a piercing dentition and from a dentition capable of processing food (i.e., chewing) to a dentition that serves primarily to seize and hold prey. The hindlimb anatomy of Proneotherium provides important information concerning the evolution of aquatic adaptations and clearly shows that many pinniped innovations (short and broad femur, long and slender tibia, and elongated metatarsals I and V [relative to metatarsal III]) evolved very early.

Evaluation of available specimens of Proneotherium supports recognition of a single species, Proneotherium repenningi. A cladistic analysis utilizing 24 cranial, dental and postcranial characters supports monophyly of the genus Proneotherium and suggests a close sister group relationship with another basal walrus, Prototaria. The parsimony analysis also confirms the monophyly of the Odobenidae, which is here defined as the clade containing the most recent common ancestor of Proneotherium and Odobenus and all of its descendants including Prototaria, Neotherium, Imagotaria, the dusignathines, and the odobenines.

The Pliocene Ringold Formation of eastern Washington has yielded important new materials of tremarctine bears of the anagenetic Plionarctos lineage. The genus is reviewed in light of this new material and observations made on other described specimens. One of these was previously described from the medial Hemphillian Rattlesnake Formation of Oregon and is recognized as a tremarctine bear, thus extending the earliest record of the group into the early part of the late Miocene. The late Hemphillian P. edensis, the genotypic species, is rediagnosed, although no new material is added to its hypodym. A new species from the early Blancan White Bluffs sites, P. harroldorum, appears to have been derived from P. edensis. Referred Plionarctos sp. from the medial Blancan Taunton Locality has some dental features that are more derived and approach those of the Pleistocene Tremarctos floridanus. Plionarctos forms a paraphyletic stem-group for the Tremarctinae. Species of this genus can be traced successively into the Pliocene where they form the stock from which the Pleistocene and Recent species of Tremarctos, Arctodus, and Pararctotherium arose.

This study examined the dietary adaptations of 38 species of small-bodied omomyoid primates known from North America and Europe. Two parameters were examined to investigate the dietary proclivities of these early primates: body mass and relative molar shearing crest development. Body mass was estimated from dental dimensions. Based upon size distributions of modern mammals of known diets, species with estimated masses of under 500 g were categorized as faunivores/frugivores. In order to partition this dietary grouping more precisely into faunivory and frugivory, measurements reflecting shearing crest development were compared to an extant prosimian base line. Based on these data it appears that the majority of the taxa sampled from this early primate radiation were primarily frugivorous.

The Australopithecus-bearing sites of Koro Toro in central Chad yielded at least 9 species of bovids (Ruminantia: Bovidae). They all belong to genera found in North and/or East Africa, but three new species are named. Kobus korotorensis, sp. nov. is quite distinct from East African species, and is probably an early offshoot from primitive Reduncines. Kobus tchadensis, sp. nov. is more like some East African forms. Parmularius pachyceras, sp. nov. should rather be compared with a North African species. This relative endemism hinders precise biochronological correlation, but the best fit is in the range 2.7–3.4 Ma. The lack of Tragelaphines, and an abundance of Reduncines, Alcelaphines and Antilopines definitely points towards an open environment, that was drier than most East African sites of this age.

We present a summary of the Eocene mammal faunas of Indo-Pakistan based on study of the known faunas and new collections. New taxa described here are the carpolestid Parvocristes oligocollis, the plesiadapid Jattadectes mamikheli (both new families for the subcontinent), the hyaenodontid Paratritemnodon jandewalensis, the arctocyonid Karakia longidens, the raoellid Khirtharia aurea, and the helaletid Jhagirilophus chorgalensis. Based on the faunal evidence and considering the geological setting, we also evaluate the uniformity of the Eocene faunas from northern Indo-Pakistan. Tentatively, we propose that three chronologically distinct faunas occur in Northern Indo-Pakistan. These are, from oldest to youngest, (1) the Banda Daud Shah Fauna, (2) the Ganda Kas Fauna, and (3) the Kalakot Fauna. Although there are broad similarities between these faunas and Eocene faunas of the Northern Hemisphere, the Indian subcontinent retained a highly distinctive fauna in that period.

An extended and revised mammal succession of 99 fossil localities from the Upper Miocene sediments of the Teruel–Alfambra region (NE Spain) is presented. An updated biozonation is proposed. The biostratigraphic justification for the correlation of the magnetic polarity patterns of the La Gloria, El Bunker, Masada Ruea, Masada del Valle and Masía de la Roma sections to the Geomagnetic Polarity Time Scale (GPTS) is discussed.

A comparison with Late Miocene faunas from elsewhere in Europe demonstrates that faunal resemblance across the continent is very low. As illustrated by an analysis of the “Progonomys event,” local appearances of genera may be strongly diachronous and even species should not a priori be assumed to be isochronous at resolutions higher than several hundred thousands of years. These observations have implications for European continental stratigraphy and chronology: (1) The usefulness of the European mammal-based Stages/Ages can be doubted because their biostratigraphic significance is mainly local, and because more and more direct calibrations of mammal faunas to the numerical time scale are becoming established; (2) The European Mammal Neogene (MN) system, currently defined as a series of 16 time-ordered faunas, should not be divided into sub-units, because this weakens its power for cross-continental faunal correlation. In addition, the use of MN “boundaries” is erroneous and misleading, both from a philosophic and technical point of view.