Partial crania of two fossil species of koala (family Phascolarctidae) from Oligo-Miocene deposits in the Riversleigh World Heritage Area, one referable to Litokoala kutjamarpensis and another to Nimiokoala greystanesi, are described. Comparison with the extant koala Phascolarctos cinereus and other diprotodontian marsupials reveals a high degree of similarity in basicranial morphology between fossil and modern phascolarctids but substantial differences in the architecture of the masticatory system. Key specialisations present in Phascolarctos but absent in both Litokoala and Nimiokoala include forward displacement of the palate, enlargement of the occlusal surface of the molar teeth, thickening of the maxillae above the toothrow with resultant lowering of the occlusal plane of the cheekteeth relative to the glenoid fossa, and a decrease in the size of the pterygoid fossae. These extreme aspects of the cranial morphology of Phacolarctos probably reflect its dependence on eucalypt leaves, a nutrient-poor food resource that became increasingly abundant in the Australian environment through the Neogene. Derived similarities in basicranial structure, notably the large size of the auditory bulla, between the fossil and modern phascolarctids raises the possibility that two distinctive behavioural characteristics of the modern koala, sedentism and vociferousness, may have developed relatively early during phascolarctid evolution.

Fossil remains of clupeomorph fishes are commonly found in Cretaceous and Tertiary deposits from the northeastern Brazil. The taxonomic diversity is relatively high and include tellimmichthyiforms, early clupeiforms, and advanced clupeoids. However, well-preserved specimens are very scarce so that very little is known about affinities of most taxa. Recently, new localities containing clupeomorphs have been discovered and prospected in Alagoas State, in Northeastern Brazil. From them, Atol Quarry, in which Barremian shales from the Coqueiro Seco Formation crop out, has demonstrated to be meaningful by having a diverse fish assemblage. It contains holosteans, coelacanths, gonorynchiforms, and enchodontids besides clupeomorphs. Most of fishes correspond to new taxa. In this paper, an early clupeiform fish, †Pseudoellimma gallae gen. et sp. nov., is described from those shales. The fish shows many informative characters and revealed to be advanced in comparison with other early and relatively well-known clupeomorphs such as † Spratticeps and † Santanaclupea. Although lacking pleurostyle, it shares with clupeoids derived features such as accessory anterior foramen of temporal canal, hidden post-orbital branch of supraorbital canal on frontal, longitudinal and parallel ridges sculpturing the skull roof, and reduced first ural centrum. If so, many derived features found in advanced extant clupeoids appeared early in the history of clupeiform fishes. Furthermore the present study indicates divergence between Clupeoidei and Denticipitoidei lineages older than Barremian age.

Pseudodalatiids, a chondrichthyan family of uncertain phylogenetic affinities, have been hitherto exclusively known from the tooth-based species Pseudodalatias barnstonensis (Sykes, 1971), which has a stratigraphic range restricted to the Upper Triassic of Europe. Pseudodalatias presents a characteristic dentition which allows it to hold and cut its prey, showing a neoselachian design, but lacking the triple-layered enameloid microstructure of neoselachian teeth. The discovery of Pseudodalatias henarejensis nov. sp. in the Ladinian of Spain extends the stratigraphical range and the palaeogeographical distribution of this family. This new species also demonstrates that a cutting-clutching dentition evolved progressively in the family Pseudodalatidiidae. Pseudodalatiids are likely to represent stem-batoids or stemneoselachians rather than aberrant hybodonts.

New anatomical data are presented for the vertebrae and osteoderms of Dissorophus multicinctus Cope, 1895 and a previously unexamined specimen of Cacops aspidephorus Williston, 1910a from the Early Permian of Texas. The transverse axis of the zygapophyses of vertebrae in Cacops without osteoderms is closer to the horizontal plane than vertebrae with osteoderms. Ontogenetic fusion of internal osteoderms in Cacops to their respective neural spines begins with the anterior vertebrae and proceeds posteriorly. Midventral flanges appear on the external osteoderms after formation of the internal and external series, but prior to fusion of internal osteoderms to vertebrae. The midventral flange initially has a low round shape, but later assumes an adult blade-like morphology. Zygapophyses in Dissorophus are closer to the midline than in Cacops. Their transverse axis is at an angle of approximately 45° to the horizontal plane and the parasagittal axis is approximately 25° to the horizontal plane throughout the presacrals. A flange on each of the four internal osteoderms of Dissorophus immediately posterior to the enlarged first osteoderm inserts into a deep notch along the anterior, dorsal, and posterior sides of the neural spine. These flanges largely immobilized the vertebrae. Flanges of more posterior internal osteoderms in Dissorophus insert between neural spines. A pronounced anterior inclination of these posterior flanges and close proximity of neighboring internal osteoderms suggests either contact or a small gap between a flange and the next anterior internal osteoderm. Interosteodermal ligaments likely bound the osteoderms and limited lateral flexion.

The Lifua Member of the Manda Beds of Tanzania (Middle Triassic: ?latest Anisian) has yielded an exceptionally important assemblage of early archosaurs, including numerous well-preserved specimens. However, the majority of this material has not been described formally, frustrating attempts to incorporate it into studies on early archosaur diversity and evolution. We describe an anterior dorsal vertebra from the Lifua Member as the holotype of a new taxon, Hypselorhachis mirabilis. Hypselorhachis is characterised by the possession of an elongate neural spine that is at least 5.5 times the height of the centrum, and can be diagnosed on the basis of a single autapomorphy relating to the morphology of the prezygapophysis. Hypselorhachis is similar to other early Middle Triassic archosaurs with elongate neural spines, including Arizonasaurus, Ctenosauriscus, and Lotosaurus. It is possible that these taxa form a clade, Ctenosauriscidae, but further anatomical and phylogenetic work is required before this can be confirmed.

A new basal sauropodomorph dinosaur, Massospondylus kaalae sp. nov., is named on the basis of a partial skull from the upper Elliot Formation (Lower Jurassic) of the Herschel District, South Africa. It can be distinguished from Massospondylus carinatus by a combination of character states relating to the proportions of the premaxilla, the presence of a strong ridge on the dorsolateral surface of the lacrimal, and the morphology of the braincase. The description of Massospondylus kaalae further increases sauropodomorph diversity in the previously depauperate upper Elliot fauna.

Rapetosaurus krausei is a titanosaur sauropod from the Upper Cretaceous Maevarano Formation of northwestern Madagascar and is among the most complete titanosaurs ever discovered. To date, over 15 localities in a 10 km² field area have yielded hundreds of titanosaur bones, including associated and articulated specimens of Rapetosaurus. A juvenile skeleton is of particular significance because it was found directly associated with a well-preserved partial skull. The juvenile postcranial skeleton only lacks only the axis, atlas, representative elements from the proximal caudal series, carpals, and tarsals. The Rapetosaurus axial column consists of at least 17 cervical, 10 dorsal, six sacral, and 17 caudal vertebrae. Appendicular skeletal anatomy documents unique aspects of the titanosaur skeleton, and the association of large osteoderms with other, adult specimens confirms the lithostrotian status of Rapetosaurus. These new skeletal data have proven significant for phylogenetic resolution within Titanosauria, particularly because Rapetosaurus can be coded for 83% of over 400 characters for titanosaurs.

Long bone histology has often been used to study growth, life history, and physiology of several dinosaurs but only little is known about life and growth parameters of Stegosaurus. This work provides the first extensive study of the long bone histology of Stegosaurus. We sampled several long bones and scapulae of four almost complete skeletons of Stegosaurus from the Late Jurassic Morrison Formation in Wyoming/USA, which are housed in the Sauriermuseum Aathal near Zurich in Switzerland. Long bone histology of Stegosaurus contains longitudinal primary osteons in a matrix that consists of a combination of both woven bone and parallel-fibered bone in varying proportions. In the inner cortex, fibrolamellar bone dominates, indicating fast growth. Toward the outer cortex, parallel-fibered bone dominates the tissue, indicating a gradual slow-down in growth. Three histologic ontogenetic stages were established. In the subadult stage, growth is still fast, whereas it decreases in adult stage I, and ceases in adult stage II. Comparing the ontogenetic stages to the body size of the specimens, two groups were recognized. This grouping may reflect intraspecific variability, sexual dimorphism, or taxonomic differences. Among dinosaurs, mainly showing true fibrolamellar bone, the long bone histology of Stegosaurus is most similar to that of the small basal thyreophoran Scutellosaurus. Accelerated growth led to the larger body size of the derived thyreophoran Stegosaurus compared to the small Scutellosaurus. Differences to the bone histology of other dinosaurs suggest that Stegosaurus grew more slowly and possibly had a lower metabolic rate than other dinosaurs of its size.

An articulated skeleton of a hadrosauroid dinosaur, Tethyshadros insularis n. gen., n. sp., was recovered from the Liburnian Formation (uppermost Cretaceous) of Villaggio del Pescatore in the Trieste Province of northeastern Italy. One of the most complete dinosaur fossil ever found, it shows for the first time the entire morphology of a hadrosauroid phylogenetically close to, but outside the North American and Asiatic hadrosaurids. It lived on an island developed on a carbonate platform in the Tethys Ocean and the small size of the specimens suggests that it may be an insular dwarf. The skeleton has many peculiarities including cursorial adaptations, and a mix of derived and primitive features. European hadrosauroids probably did not evolve by vicariance nor did they colonize the European Archipelago from North America, but rather came from Asia by island hopping.

The holotype of Dyoplosaurus acutosquameus Parks, 1924 (=Euoplocephalus tutus Lambe, 1910), represents one of the most complete ankylosaurid specimens collected to date. It consists of a partial skull roof, four mandible fragments with two teeth in situ, portions of postcranial armor (some in situ), skin impressions, articulated post-thoracic vertebrae, ten partial thoracic ribs, a partial left ilium, both ischia, and tail club, and associated right radius, left metacarpal IV, femur, tibia, fibula, and pes. We provide a detailed redescription of this material as well as comparisons with other ankylosaurid specimens referred to E. tutus. The synonymy of the genus with Euoplocephalus is not supported, and Dyoplosaurus is a valid taxon. It is possible that the fragmentary nature of the holotype of Euoplocephalus leads to the inference that the diversity of Late Cretaceous North American ankylosaurids is lower than it actually is. As such, it might be necessary to look beyond traditional cranial characters in order to accurately appraise the number and nature of various ankylosaurid taxa.

A Triceratops, NSM PV 20379, excavated from the Upper Cretaceous Hell Creek Formation, Bowman County, North Dakota, USA, confirms the articulation of the right forearm. Detailed study of the forelimb anatomy presented here indicates the manus is in a semi-supinated orientation. This reconstruction is based upon the following morphology: the row of the metacarpals was arranged in an ‘L’-shape in proximal view, as is the distal articular surface of the forearm is in articulation; the second digit is directed parallel to the rotational plane of the elbow joint, reinforced by neighboring digits I and III, and these three inner digits are articulated with the broad articular surface of the radius. Arrangement and directions of robust inner digits seem to be suitably arranged for a powerful stroke exerted by the elbow joint extension. Cerapods, including ceratopsians and ornithopods, share following morphology of the manus: long and robust metacarpals II and III, ungual phalanges on digits I to III, reduced digits IV and V, and a divergent metacarpal V. A laterally oriented manus with reduced outer digits is present in the basal bipedal group of the Cerapoda. Although reversal to a quadrupedal stance and a evolution to a large, heavy body occurred independently in many lineages of Cerapoda, the basic features of the manus were retained throughout Neoceratopsia.

The systematics of Galliformes for the period from Pliocene to early Pleistocene is complex, and little progress has been made toward understanding the relationships among the different groups within it. One step has to be to purge taxonomic mistakes progressively accumulated in a systematics clearly inflated with synonymous nominations. But successes of prior attempts have been uneven. This article is intended to be a piece in this discussion and thorough review that must continue. All the fossil bones of galliform birds from Pliocene and early Pleistocene of the Iberian peninsula are reported in this paper. Eight taxa—three of them are new species—appear in two Pliocene and five early Pleistocene fossil localities. Most of these species did not cross the early / middle Pleistocene boundary. Eurasia, and particularly Europe, shelter for the moment the oldest records of some nowadays largely distributed genera of galliforms. Some of these records take place in the span of time considered in this article. The current partition of the Iberian peninsula between Alectoris and Perdix is already patent in the early Pleistocene. Forest-type taxa not present or rare from the middle Pleistocene onwards occurs in the early Pleistocene. The oldest record of the genus Bonasa is likewise reported.

The dicynodont Colobodectes cluveri was described from a single specimen in 2003. Although the holotype possessed a distinctive combination of primitive, derived, and autapomorphic characters, incompleteness left some aspects of its morphology, such as whether it possessed postfrontal bones, uncertain. Similarly, the holotype was collected near the boundary between the Ecca and Beaufort groups of the Karoo Basin, but the presence of one specimen did not allow a stratigraphic range to be delineated, nor could it be determined whether C. cluveri possessed any biostratigraphic utility. During an ongoing investigation of Tapinocephalus Assemblage Zone dicynodont diversity and biostratigraphy, we identified four new specimens of C. cluveri ranging in size from small juveniles to a large adult. These specimens confirm many aspects of the holotype's distinctive morphology, including the absence of postfrontals, paired premaxillae and vomers, and a low foramen magnum. They also offer insights into ontogentic changes in morphology in C. cluveri. Particularly noteworthy is the fact that small individuals lacked erupted tusks, mid-sized individuals such as the holotype possessed small, newly-erupted tusks, and large adults possessed robust tusks. Finally, all C. cluveri specimens occur in a narrow interval just above the Ecca-Beaufort contact in the northwestern and western portions of the Karoo Basin. This suggests that the species may be a useful marker for the lowermost Beaufort in areas where the Eodicynodon zone is not preserved, and it fits well with basin development models that reconstruct the Ecca-Beaufort contact as a northeasterly prograding paleo-shoreline.

The postcranial skeleton of Kingoria is well-described, and previous authors noted the taxon's divergent pectoral, pelvic, and femoral morphologies. Yet, humeral morphology of Kingoria has remained enigmatic because of poor preservation and the absence of published descriptions. Here we describe new, nearly complete humeri of Kingoria collected from the Upper Permian Usili Formation, Ruhuhu Basin, Tanzania. These specimens demonstrate that the humeral morphology of K. nowacki is much more conservative than that of its pelvis or femur. There is evidence of increased importance for long-axis rotation of the humerus in K. nowacki, and the trochlea and the capitellum are partially separated, but these morphologies are not taken to the extremes observed in cistecephalid dicynodonts. Surprisingly, the new Tanzanian humeri differ from South African specimens: the best-preserved South African specimen is more gracile, with different humeral head and deltopectoral crest morphologies. We use these differences, along with new observations on skull morphology, tusk frequency, pelvic and fibular morphology, and body size to revise the taxonomy of Kingoria. Kingoria is shown to be a junior synonym of Dicynodontoides Broom, 1940, and two species are recognized: D. recurvidens from South Africa and D. nowacki from Tanzania. Finally, we review the stratigraphic and geographic ranges of Dicynodontoides, and document new occurrences in the Pristerognathus and Tropidostoma assemblage zones of the Karoo Basin, as well as its presence in the Chiweta Beds of Malawi.

The braincase and endocranial cavity of a specimen of a nonmammalian eucynodont Chiniquodon is described and illustrated, and a tentative reconstruction of the gross anatomy of the brain offered. Salient features are the well-developed impression for the olfactory lobes, the extreme narrowness of the region available for the telencephalon, and the evidence for a large cerebellum. A two-step theory for the origin of the mammalian brain is proposed. The first step is represented by the nonmammalian cynodont level and consisted of enlargement of the cerebellum and possibly midbrain structures. This stage is associated with the evolution of more sophisticated neuromuscular control of the mandibular and locomotory apparatuses. The second step was the evolution of the mammalian six-layered neocortex, and did not occur until the origin of the mammals themselves. This stage was an integral part of a complex set of allometric changes associated with miniaturization. The origin of the neocortex was correlated with sensitivity to higher frequency sound, and a greater area of olfactory epithelium, both expected to result from miniaturization, and also with the availability of increased space within the cranial cavity expected as the adductor jaw musculature was relatively reduced in mass. Overall, neocortical function was associated with the high energy nocturnal foraging activity generally believed to have appertained in the first mammals, and also sophisticated social communication.

Relatively few studies of cranial endocasts document intraspecific variation. Here, discrete morphological and morphometric variation from a sample of more than 150 natural cranial endocasts from a single Eocene locality, Reeves Bonebed (hereafter ‘RBB’) from West Texas are documented. The first description of a digital endocast of an oreodont, Bathygenys reevesi, is given to provide comparative data for other oreodont endocasts. The RBB endocasts were originally assigned to B. reevesi, but virtually none has diagnostic craniodental material still attached, and isolated endocasts of other cetartiodactyl species are known from this locality. Consequently, an attempt was made to identify apomorphies on the RBB sample to diagnose specimens to the lowest possible taxonomic level. The RBB endocasts were diagnosed as oreodonts based on the presence of large, rounded casts of the tuberculum olfactorium, but no specimen can be diagnosed to a particular species. The range for most linear measurements for the RBB sample overlapped with measures from multiple species of oreodonts from RBB. A coefficient of variation analysis of linear measurements suggests that the RBB sample represents more than one species. Therefore, endocasts from RBB that lack associated craniodental material cannot be definitively assigned to a species, and the original assumption that all are B. reevesi is not supported. This illustrates the necessity of applying apomorphy-based identifications for isolated specimens, including endocasts. In addition, this study reveals some gaps in data from cetartiodactyl brains, which need to be filled for future studies on brain evolution in this clade.

This paper provides the first detailed description of the only known postcranial skeletal elements of “Miacis” uintensis. The morphology of the skeleton differs markedly from previously described “miacids” (a paraphyletic assemblage of early fossil carnivoramorphans), invalidating the notion that all “miacids” were very similar in their postcranial morphology and locomotor styles. The majority of the differences indicate an animal less well adapted to an arboreal lifestyle than has been inferred for other early “miacid” carnivoramorphans. A phylogenetic analysis clearly nests “Miacis” uintensis within the paraphyletic array of taxa previously referred to as the “Miacidae,” in a position closer to the crown clade Carnivora than is Vulpavus, a “miacid” whose postcranium has been previously described. When compared with the early canid Hesperocyon, this specimen shares many features thought to relate to the acquisition of a more terrestrial mode of life. This result indicates that, in contrast to prior models suggesting arboreality for all “miacids,” at least one independent ‘descent from the trees’ occurred much earlier within the array of stem carnivoramorphan taxa.

A remarkably well-preserved primitive horned brontothere skull from the Wiggins Formation of western Wyoming is described. Noteworthy characters of this specimen include an extensive system of large paranasal sinuses, a distinct vomerine plate, and a confluence of the anterior lacerate foramen and foramen rotundum. A nearly complete endocranial cast allows for a description of the brain and many of the cranial nerves. Perhaps the most important structures described are the large openings on the basicranium, here dubbed “sphenoidal apertures,” which may be unique among the Brontotheriidae. Among North American brontothere taxa, the skull is closest in morphology to the holotype of Protitanotherium emarginatum Hatcher, but has some important differences that make assignment to that genus and species uncertain. If reference to the genus Protitanotherium is correct, then the name P. australis (Wilson) may apply, although this may be a junior synonym of P. superbum Osborn. Given the uncertainties, the specimen is identified only as cf. Protitanotherium for the purposes of the present paper. Regardless of which name should be applied, characters displayed by the specimen suggest that it is the primitive sister genus to all other diplacodont brontotheres.

The first diagnostic sirenian material from Madagascar and, more broadly, the first diagnostic pre-Pleistocene Cenozoic mammal material recovered from the island is reported. Eotheroides lambondrano is a new species of sirenian collected from middle Eocene nearshore marine deposits in the Mahajanga Basin of northwestern Madagascar. The recovered material consists of a nearly complete adult skull (including the first complete rostrum known for Eotheroides) and several portions of pachyosteosclerotic ribs. Diagnostic features of E. lambondrano include: primitive upper dental formula of 3.1.5.3, relatively large occlusal area of M2 and M3, long and narrow nasals, weak rostral deflection compared to other Eocene Dugongidae, well developed supraorbital processes, short infraorbital canal, anteroposteriorly short zygomatic-orbital bridge of maxilla, and a palate that is narrow anteriorly, creating a strongly bellshaped maxillary dental arcade. The cranium of E. lambondrano is similar to that of E. aegyptiacum from the middle Eocene of Egypt in aspects of both morphology and size but the upper molars of E. lambondrano are considerably longer and wider and it has longer, narrower nasals. The age and relatively primitive morphology of E. lambondrano suggests that it may represent the ancestral form from which more northerly species were derived.

Our understanding of South American megatheriine ground sloths was traditionally based largely on abundant material from Brazil and Argentina, mainly because megatheriine remains from elsewhere in South America were scant and poorly preserved. In recent years, however, the recovery and description of remains from northwestern South America has led to the recognition of several new taxa and the validation of species originally based on sparse remains. Falling in the latter group is Megatherium (Pseudomegatherium) tarijense Gervais and Ameghino, 1880, which is based on a complete but eroded calcaneum from Pleistocene deposits of the Tanja Valley of southern Bolivia. Most authors of the past century viewed this species as poorly defined and probably synonymous with Megatherium (Megatherium) americanum. This uncertainty is attributable to both the poor nature of the remains of M. (P.) tarijense and the presence of M. (M.) americanum in the Bolivian Pleistocene. Well preserved and nearly complete remains of several individuals indicate that M. (P.) tarijense is indeed valid. This material includes abundant remains from the Tarija Basin (Bolivia) housed in the Field Museum of Natural History (USA) and the Museo Nacional de Paleontología y Arqueología de Tarija (Bolivia) and also from the Peruvian Andes (Yantac), housed in the Universidad Nacional de Ingeniería de Lima. M. (P.) tarijense differs from M. (M.) americanum mainly in its smaller size; shorter, less robust premaxillae; shallower mandibular ramus; reduced size of the humeral deltopectoral crest; less torsion of the femoral diaphysis; unreduced patellar trochlea; and relatively shorter, stockier calcaneum.

A new specimen of a sparassocynid didelphoid, consisting of a single skull, is described and analyzed. The specimen comes from the middle section of the Aisol Formation cropping out in Mendoza Province (Argentina) and constitutes the first marsupial hitherto described for the unit. The entire Aisol Formation was originally regarded as middle Miocene based on the fossil content. The discovery of new specimens, however, suggests that the stratigraphic level where the marsupial was found may have been deposited during the late Miocene (not older than Huayquerian times). The specimen studied here is identified as belonging to a new genus, Hesperocynus, of the family Sparassocynidae, Didelphoidea. A new combination is proposed for the already known species, H. dolgopolae (Reig 1958), previously recognized as a species of Thylatheridium Reig 1952. The new specimen from the Aisol Formation is assigned to the hypodigm of this taxon. The genus Hesperocynus encompasses small-sized carnivorous feeders as evidenced by their dental specializations and palate morphology; however, this taxon is more generalized than species of Sparassocynus, the other genus of the family. Sparassocynids have traditionally been considered the closest relatives of living didelphids. If this hypothesis is correct, then the sparassocynid clade has a long ghost lineage that covers at least 10 million years (as evidenced by the oldest known sparassocynid and didelphid remains). Sparassocynids and other didelphoids probably radiated after the global cooling event that occurred after the Eocene-Oligocene boundary.

Two eobaatarid multituberculate genera including three species from the Lower Cretaceous (Aptian-Albian) Shahai and Fuxin formations in Liaoning Province, northeastern China are described here: Sinobaatar xiei sp. nov., S. fuxinensis sp. nov., and Liaobaatar changi gen. et sp. nov. Sinobaatar xiei is characterized by ml with cusp formula 3:2 (labial:lingual), P4 with cusp formula 2:4, blade-like P5 with three cusps anteroposteriorly arranged, M1 with cusp formula 4:4, and M2 with cusp formula 3:4. P1 to P3 of S. xiei lack distinct posterior cingulum. Sinobaatar fuxinensis has a more distinct posterior cingulum on P1 to P3, and its M2 has cusp formula 3:3. Sinobaatar xiei is within the size range of most other eobaatarids, and S. fuxinensis is slightly larger than S. xiei. Liaobaatar changi is clearly larger than other eobaatarids. The ratio of p4 length and height of L. changi and S. xiei (L./S.) are 1.9 and 1.7, respectively. Liaobaatar changi is also characterized by ml with cusp formula 3:3. A specimen of S. fuxinensis indicates that tooth replacement in eobaatarids occurred in the typical backward sequence seen in Late Cretaceous-Tertiary multituberculates.

Two new species of fossil cetaceans (Pakicetus calcis and Pakicetus chittas) are described from a new locality in the Kuldana Formation (Lutetian, middle Eocene) of the Kala Chitta Hills in Northern Pakistan. Additional dentitions of the pakicetid Nalacetus ratimitus, the remingtonocetid Attockicetus, and additional dental material of the holotype of Ambulocetus natans are also described. Dental morphology of Nalacetus is intermediate between pakicetids and ambulocetids, as indicated by the presence of an ambulocetid-like P4, but pakicetid-like molars. Premolars of the specimen tentatively described as Attockicetus imply that some pakicetids and remingtonocetids were coeval. Furthermore, the new pakicetid dentitions described here are the most complete to date and further our understanding of pakicetid dental diversity.

An extraordinarily well-preserved skull of the Uintan brontothere genus Metarhinus, supplemented by a second, less complete specimen, permits a detailed description of the cranial anatomy, including aspects that have never before been described. Of particular interest is the structure of the nasal cavity and internal nares, which may be virtually unique among mammals. The normal air passageway, connecting the nasal cavity to the internal nares, is effectively blocked except for tiny apertures and the functional air passageway re-directed over the top of the vomer, which, itself, has an unusual morphology. The functional significance of so unusual a feature is uncertain, but may have to do with the supposed amphibious habits of this genus, or perhaps, was an adaptation enhancing olfaction. The brain of Metarhinus is found to be typical of early brontotheres, being of small size and consisting of a rectilinear succession of parts: forebrain, midbrain, and hindbrain. The cerebrum is small in size and the cerebellum proportionately large.