Whereas the anatomy of birds, domesticated mammals, and humans is described by standardized terminology, the anatomy of most fossil vertebrates is described by nonstandardized terminology. New fossil discoveries increasingly resolve the transitions between these living groups and their fossil outgroups, diminishing morphological differences between them, and vertebrate paleontologists can easily apply more than one system of anatomical terms to such groups. This plurality of systems has led to recent proposals to standardize anatomical terminology for tetrapods, either by applying avian and mammalian anatomical terminology to their respective stem groups (Sauropsida and Synapsida) or by creating an all-encompassing terminology for Tetrapoda from a combination of existing terminologies. The main rationale for implementing standardized anatomical terminology, which requires abandoning competing terminologies, is that it reflects homology and evolutionary descent, eliminates ambiguity, and enhances interdisciplinary communication. The proposed standardized anatomical terminology, however, entails many negative consequences, including reversing character trajectories, misrepresenting complex anatomical transformations and uncertain homologies, and requiring far-reaching terminological conversions. These negative consequences result from increasing the taxonomic scope of standardized anatomical terms that were developed for a specific group, but now: (1) apply to a broader hierarchy of character states; (2) involve additional phylogenetic interpretations or assumptions; and (3) are used for basal, often more generalized conditions. In contrast, traditional non-standardized anatomical terminology, although not strictly phylogenetic, is anatomical ‘lingua franca’ that has been in usage for nearly two centuries and is consistent, ubiquitous, and descriptive.

Fossils are frequently conserved with cyanoacrylate (CA) adhesives, which have never been scientifically assessed for their long-term stability and suitability for this application. The degradation of three types of CA adhesives were studied: an ethyl CA, an ethyl CA with added poly(methyl methacrylate) (PMMA), and a butyl CA, in the presence and absence of five different fossils obtained from various sites. The fossils were characterized by pH, moisture content, porosity, and ash content, as well as by their mineral and elemental composition. Hydrolytic degradation of polymerized CA adhesives was monitored by quantitative determination of formaldehyde, one of the degradation products. Both in the presence and absence of a fossil, butyl CA degraded more slowly than ethyl CA, making it attractive for fossil applications. It was also found that acidic fossil inhibits the degradation of CA adhesives, while neutral or alkaline fossils increase the CA degradation. The CA degradation appears to be correlated to some degree with a fossil's physical and chemical properties, but this requires further study. Further study is also necessary to determine how the observed CA degradation affects the actual fossil/CA bond strength.

New anatomical details are described for the acanthodian Brochoadmones milesi based on nearly complete body fossils from Lochkovian rocks at MOTH, Mackenzie Mountains, Northwest Territories, Canada. The body and caudal peduncle are deep, and a prominent nuchal hump is present before the dorsal fin origin. The caudal fin is correspondingly deep and ventrally, the caudal fin lies close to and is partly joined to the slender anal fin.

A delicate pectoral fin trails the flattened pectoral-fin spine where previously known specimens showed only a fin spine resembling a bivalve shell. Seen for the first time in any vertebrate, each of the six pairs of prepelvic spines supports a small, scale-covered finlet. Both prepelvic spines and scale-covered finlets increase in size posteriorly. The series of paired prepelvic finlets originates ventral to the branchial chamber and anteroventral to the pectoral fin, and extends posteriorly as far as the pelvic fins.

The scales of the body and fins are thin and flat, without obvious evidence of ossified basal tissue or entry point for vascular tissue. The main lateral-line canal passes dorsal to the branchial chamber and terminates at the trailing edge of the caudal fin web. Lateral-line scales are thicker than body scales and show concentric growth zones. Scales from the dorsal midline of the caudal fin are also thicker, showing few superpositional growth zones in the mesodentine of the crown together with what appears to be cellular basal tissue.

The structure and position of the pectoral spine and fin, the extremely thin body scales, the slender anal fin, and the prepelvic finlets are all unique and appear to be autapomorphic features compared to those of other acanthodians. Brochoadmones milesi is derived relative to other fishes traditionally classified in the Climatiiformes. Kathemacanthus rosulentus is removed from the Brochoadmonoidei, leaving only B. milesi in a monotypic suborder.

A partial association of fourteen teeth from a small lamniform shark with uncertain affinities is described. The material comes from the middle? Albian of Peru and represents a new genus and species, Priscusurus adruptodontus. The new taxon is characterized by a tearing-type dentition with comparably small teeth that lack any ornamentation and lateral cusplets. Other diagnostic features include distally inclined cusps in all tooth positions, an asymmetric root, and the lack of a lingual nutritive groove. The most remarkable feature is the very distinctly shaped lingual tooth neck, which differentiates teeth of the new taxon from all known lamniforms. The total body length, which was estimated from the crown height of the tallest preserved anterior tooth and a regression equation for the dentition of the modern sand tiger shark, Carcharias taurus, is only 69 cm. The very rare finds of this taxon and the restricted occurrence may indicate that Priscusurus was probably an endemic element of the shelf areas of western South America.

A new genus and species of fossil moonfish (Teleostei, Lampridiformes, Lamprididae) is reported on the basis of a large, partially articulated skeleton from North Otago, New Zealand. The source horizon is shelf sediments of basal Otekaike Limestone, upper Duntroonian stage, Upper Oligocene (∼26 Ma). The deep-bodied proportions of the fossil, along with features of its caudal and pectoral skeleton, support assignment to a new genus and species, described here as Megalampris keyesi, in the family Lamprididae (moonfish and opah). The fossil is notable for its large size—at an estimated 4 m total length, it is about twice the length recorded for the extant moonfish Lampris guttatus. The new form has a greatly enlarged cleithrum, which is associated with the specialized pectoral swimming characteristic of lampridids, demonstrating that this distinctive locomotory mode, along with impressively large body size, evolved in lampridids at least as early as the Oligocene. This is the first Southern Hemisphere report for a fossil lampridiform.

Description of Rhynchodercetis regio, sp. nov., from Upper Cretaceous (Turonian) sediments of Vallecillo, State of Nuevo León, northeastern Mexico is based on three specimens. Rhynchodercetis regio differs from the other species of Rhynchodercetis in the exclusive combination of characters that includes the proportions of the head with its standard length, the length of the preorbital area, and the presence of an interopercle and a short mandibule. The occurrence of this fish in Mexico expands the known distribution of Rhynchodercetis in North America during the Late Cretaceous, from the Canadian portion of the Interior Sea to Mexico, in the western Tethys area.

The skull of the temnospondyl amphibian Saharastega moradiensis, from the Upper Permian Moradi Formation (Izégouandane Group, Izégouandane Basin) of northwestern Niger, is described in detail. Saharastega moradiensis is the most primitive known temnospondyl from Gondwana and possesses a combination of plesiomorphic and apomorphic character states, which suggest affinities with the Edopoidea, a clade of basal temnospondyls from the Upper Carboniferous and Lower Permian of Euramerica. These include the exclusion of the lacrimal from the orbital margin, the exclusion of the vomers and palatines from the interpterygoid vacuities, and the presence of an intertemporal ossification. Autapomorphies of the new taxon include the presence of narrow and elongated, transversely oriented nostrils; an extensive tongue-and-groove contact between the premaxillae and maxillae; tabulars that possess exceptionally large, laterally and ventrally directed ‘horns’; and an extraordinary ‘occipital plate’ that may be formed, at least in part, by a supraoccipital ossification. A phylogenetic analysis of select Paleozoic temnospondyls indicates that S. moradiensis is the sister taxon to the edopoids, represented in this analysis by Chenoprosopus and Edops. This suggests that S. moradiensis represents a late-surviving member of a clade that is the sister group of the Edopoidea. Members of this clade may have been restricted to equatorial northwest Africa during the Late Carboniferous and Early Permian, an area that was not affected by the extensive glaciation that covered much of southern Pangea.

A reexamination of the holotype of ‘Plesiochelys’ tatsuensis Yeh, 1963, from the Late Jurassic of China, allows us to establish previously unknown characters of this species. A phylogenetic analysis places ‘P.’ tatsuensis on the stem of Trionychia, near the clades Adocidae and Nanhsiungchelyidae. Given the hypothesized phylogenetic position of ‘P.’ tatsuensis, a new genus, Yehguia gen. nov., is erected for this species. The phylogenetic position of Y. tatsuensis pushes the origin of the crown clade Cryptodira into the Late Jurassic. This is remarkable in light of recent studies that moved the origin of crown group turtles (Testudines) from the Triassic to the Late Jurassic. This means that the establishment of basal cryptodiran lineages must have quickly followed the origin of Testudines in the Late Jurassic. The fact that the most ancient fossil Cryptodira is hypothesized to be on the stem of Trionychia is concordant with recent molecular hypotheses that place Trionychia as the most basal extant lineage of Cryptodira. Finally, our results further highlight that the Late Jurassic of China is important for understanding the earliest evolution of cryptodiran turtles.

South America contains a diverse Miocene snake record. Heretofore, the most significant assemblages were from the early and middle Miocene of Patagonia and Colombia. Colubroid vertebrae assignable to the ‘Colubridae’ and Viperidae are here reported from the upper Miocene Cerro Azul Formation at Caleufú, in La Pampa province, central Argentina. The viperid fossil is the oldest record of the family in South America and, together with molecular evidence, it supports the hypothesis of viperids first entering South America prior to the closure of the Isthmus of Panamá. South American viperid specimens also have been recognized from the Pliocene (aff. Bothrops) and Pleistocene of Buenos Aires province, Argentina. The presence of Bothrops during the early–middle Pleistocene near La Plata city suggests that during more humid intervals this genus had a wider distribution than at present. A previous report of a viperid from the late Pleistocene of Bolivia cannot be corroborated.

The cranial osteology of the large ichthyosaur Guizhouichthyosaurus tangae from the Wayao Member of the Falang Formation (Lower Carnian, Upper Triassic) of Guizhou, southwest China, is described, based on a well preserved skull and mandible and additional specimens. It can be diagnosed by a suite of cranial characters that include premaxilla without well-developed processus subnarialis, maxilla reaches far anteriorly and has a very long processus postnarialis, orbit of characteristic shape with concave dorsal and straight posterior and ventral margins, small prefrontal that forms only the anterior third of the dorsal orbital margin, postfrontal meets the supratemporal externally, postorbital forms a large part of the lateral margin of the temporal fenestra internally, deep triangular incisura postjugalis, jugal fails to meet quadratojugal externally, short postorbital skull segment; frontals and parietals form sharp ridges lateral to the area of the foramen parietale; parietals form a low and narrow sagittal crest; teeth thecodontously implanted, blunt, conical and without carinae. New data on the postcranial skeleton are also provided. The available evidence indicates that Guizhouichthyosaurus is an advanced member of the Merriamosauria, but more plesiomorphic than the parvipelvians. The taxonomy of the large ichthyosaurs from the Falang Formation remains largely problematic. It appears probable that only two taxa are valid, Guizhouichthyosaurus tangae and Guanlingsaurus liangae. They differ in the length of the snout, the number of the presacral vertebrae, vertebral proportions, the shape of the humerus and fibula, among other features.

The structure of the braincase and the posterior portion of the palate of the type and only known specimen of Phantomosaurus neubigi (Sander, 1997) from the Upper Muschelkalk (Late Anisian) of Franconia (Southern Germany) is redescribed. P. neubigi is unique among hitherto known ichthyosaurs in numerous features of braincase morphology. These include an anteroposteriorly compressed, elongate and slender processus paroccipitalis, a clear sutural connection between the basioccipital and opisthotic, a foramen metoticum that is completely enclosed by the exoccipital and opisthotic, fusion between exoccipital and opisthotic, the retention of rudimentary postparietals -which are recorded in ichthyosaurs for the first time- and a concave occipital condyle (the latter feature is also known in a limited number of other Triassic ichthyosaurs). These characters of the Phantomosaurus braincase differ from post-Triassic ichthyosaurs, which are characterized by a strong reduction of braincase ossification, particularly with regard to the otic capsule. A short survey of current knowledge on ichthyosaur braincase anatomy as well as comparison to well-known basal amniotes and basal diapsids suggests, that the features shown by Phantomosaurus must largely be regarded as plesiomorphic and that its braincase is the most plesiomorphic ichthyosaur braincase currently known. This leads to a new view on the primitive condition of the ichthyosaur braincase that has to be considered in any further studies on ichthyosaur origins and evolution.

The study of more than 100 skeletal remains of Hispanochampsa muelleri Kälin, 1936, from the Oligocene of El Talladell (Lleida Province, Catalonia, Spain), has been decisive in revealing misinterpretations about its anatomy and phylogenetic position. Hispanochampsa muelleri is shown to be a member of the clade Diplocynodontinae, and is here considered a junior synonym of Diplocynodon. This analysis provides strong evidence for this monophyletic grouping, which is made up of the species Baryphracta deponiae, Diplocynodon darwini, Diplocynodon muelleri, D.tormis, D. ratelii, and D.hantoniensis. All of these species bear ventral osteoderms with paired ossifications, and a deep posterior tip of the iliac blade, which are synapomorphies of Diplocynodontinae. However, the interrelationships of the Diplocynodontinae remain unresolved. D. muelleri shares with D. hantoniensis, D. tormis, and D. ratelii the presence of an enlarged jugal foramen, and the particular dentary occlusion in line with the maxillary tooth row. It is highly likely that the two Spanish species, Diplocynodon muelleri and Diplocynodon tormis, were close relatives.

The thalattosuchian crocodyliform Pelagosaurus typus Bronn, 1841 is fully documented and described from the Upper Lias (Toarcian, Lower Jurassic) of England. The material under study is part of a historical collection made by Charles Moore (1814–1881) at Strawberry Bank (Ilminster, Somerset, England) around 1848. Apomomorphic features of the genus include: sculpturing on almost the entire skull and mandible with extensive sculpturing on the prefrontal, lachrymal, frontal, parietal, temporal arcade and the posterior extent of the mandible; 30 piercing teeth on each side of the upper and lower jaws; small, shallow, egg-shaped antorbital fenestra present within the lachrymal and maxilla; supratemporal fenestrae short anteroposteriorly; paired frontal; anterior margin of internal choana tapers anteriorly between the paired palatines; and presence of a choanal septum on the palatine and pterygoid. Pelagosaurus was a small, exceedingly long-snouted, gracile crocodyliform whose diet probably consisted of small fishes, crustaceans and possibly insects. The small-bodied fish Leptolepis is confirmed as part of its diet as a specimen is found in the rib cage of a small juvenile Pelagosaurus. Laterally placed eyes suggest that this species actively pursued its prey rather than sitting and waiting at the water surface. The phylogenetic position of Pelagosaurus has been debated. Pelagosaurus possesses the majority of teleosaurid apomorphies, including: four premaxillary teeth; small prefrontal; lachrymal visible in dorsal aspect; presence of mandibular fenestrae; dermal armor; and a straight tail; however, these are all plesiomorphic for the Crocodyliformes in general. There also appear to be problems when defining the proposed metriorhynchid features of Pelagosaurus (i.e., broad nasal, large frontal, lateral orbit, sclerotic ring and arrangement of prefrontal-lachrymal). Moreover, characters that have been used in past cladistic analyses are either incorrect or too simplistic. Accordingly, Pelagosaurus is considered to belong to the Thalattosuchia incertae sedis until a more thorough phylogenetic investigation is conducted.

The recent discovery of a dense, paucispecific bonebed from the Early Cretaceous Cedar Mountain Formation, central Utah, has yielded new information on the morphology and evolution of therizinosaurs. Detailed description of the pectoral girdle and forelimb of Falcarius utahensis—the predominant taxon recovered from this site—provides the basis for a species-level, phylogenetic investigation of this enigmatic group. The analysis, consisting of 32 characters arrayed among 13 taxa, supports previous assertions that Falcarius represents the basal-most known member of the clade. The analysis further supports a monophyletic Therizinosauroidea on the basis of seven unambiguous synapomorphies of the pectoral girdle and forelimb. Contrary to previous hypotheses, analysis of the pectoral girdle and forelimb suggests that Therizinosauridae is more appropriately defined as a derived clade including Nothronychus, Erlicosaurus, Neimongosaurus, Therizinosaurus, and Segnosaurus. Equally strong support is recovered for a clade containing these five genera plus “Alectrosaurus” and Erliansaurus. The morphology of primitive therizinosauroids—characterized by Falcarius, Beipiaosaurus, and Alxasaurus—suggests that Early Cretaceous taxa already exhibited the beginnings of a trend toward increased robustness and altered range of motion of the pectoral girdle and forelimb. Derived therizinosaurs exhibit an amplification of these evolutionary trends as well as increased dorsal reach, increased wrist flexibility, and severe reduction in manual digit length. The functional reorganization of the pectoral girdle and forelimb throughout the evolutionary history of therizinosaurs can be reasonably attributed to a shift from obligatory predation to a novel paleoecological role that reached its pinnacle in derived Late Cretaceous members.

The incompletely known sauropod Tornieria africana from the Upper Jurassic (Tithonian) of Tendaguru, Tanzania, has for over 80 years been regarded to represent a Gondwanan species of the North American genus Barosaurus Marsh (Morrison Formation: Kimmeridgian-Tithonian), but this identification has recently been questioned. The holotype and referred specimens are redescribed here, and the characters present are reevaluated in light of current knowledge of sauropod phylogeny. Synapomorphies of the skull (prefrontal with triangular posterior process) and anterior caudal vertebrae (procoelous centra, presence of diapophyseal laminae, and presence of a pleurocoel) indicate that the Tendaguru material represents a member of the Diplodocinae (Diplodocoidea, Diplodocidae) and is therefore very closely related to Barosaurus and Diplodocus. It differs from all other diplodocine genera in several characters, such as robust anterior caudals with pleurocoels located in the upper third of the centrum and ventral excavations, and stout hind limb proportions similar to Apatosaurus (tibia:femur length ratio less than 0.64). In a phylogenetic analysis, the African form consistently emerges as the sister taxon to Barosaurus Diplodocus. Therefore, previous suggestions that Tornieria africana is the available name for this taxon are supported by this analysis. The existence of this form in Gondwana contradicts the idea of Laurentian endemism of the diplodocid clade, and is best explained by a vicariance model of diplodocoid paleobiogeography. This implies an extensive ghost lineage of this group, extending back at least as far as the upper Middle Jurassic.

A new species of Hathliacynidae (Sparassodonta, Metatheria), Acyon myctoderos, from the middle Miocene of Quebrada Honda, Bolivia, is described. This new species is the largest known hathliacynid. Compared to the type species of the genus, A. tricuspidatus, Acyon myctoderos differs in having: (1) longer diastemata among premolars; (2) p2 comparatively more robust, with a better developed posterior cusp and with a sharp anterior crest; (3) lower molars with a more poorly developed anterobasal cingulum; (4) m1–m3 with hypoconulids less salient posteriorly and more vertically oriented; and (5) larger hypoconids at least on the m2. A phylogenetic analysis including nine taxa of Sparassodonta, with Mayulestes as the outgroup, showed that Acyon is more closely related to Cladosictis than to any other hathliacynid.

New discoveries in the latest Eoceneaged Florissant Formation in Florissant Fossil Beds National Monument, Colorado more than double the known diversity of fossil mammals from this rock unit, and provide a window into a diverse micromammal fauna that lived near Lake Florissant. Taxa first recorded here from the Florissant Formation include the lipotyphlans Centetodon magnus and Domnina cf. D. thompsoni, the lagomorph Megalagus brachyodon, and rodents Pelycomys, Eutypomys parvus, Ischyromys cf. I. typus, I. cf. I. doruglassi, and Adjidaumo minimus, all represented by dental material. We also describe isolated teeth of the artiodactyl Leptomeryx and the brontothere Megacerops. The mammalian fauna corroborates the Chadronian (latest Eocene) age of the Florissant Formation determined by others; Megalagus brachyodon suggests an age no older than Middle Chadronian. Several taxa reported here represent geographic range extensions. Eutypomys parvus is extended southeastward from southwestern Montana; ranges of Domnina thompsoni, Megalagus brachyodon, and Ischyromys douglassi are extended southwestward from western Nebraska; and ranges of Pelycomys, Ischyromys typus, and Adjidaumo minimus are extended slightly southwest from northeastern Colorado. Compared to other coeval North American faunas, the Florissant mammalian fauna is most similar to more northern faunas (including those of Montana, Nebraska, Wyoming, Saskatchewan, and NE Colorado). Geographically and faunally, the Florissant fauna appears to straddle the border between the Rocky Mountain and Great Plains Provinces defined by others, and appears consistent with weakened faunal provinciality during the Chadronian.

Two new species of tapiroid perissodactyls referred to Hesperaletes gen. nov. are described from the Uintan of southern California. Hesperaletes has a deeply retracted narial incision, which is an indicator of prehensile proboscis development. This feature also characterizes early Oligocene Protapirus from North America and has been used to diagnose Tapiridae. All late Uintan samples from San Diego County, California, are referred to H. borineyi sp. nov., but anomalous patterns of variability and morphological variation prohibit referral of much smaller early Uintan samples to a single species. Most of the early Uintan samples are referred to H. walshi sp. nov. with the exception of one sample, which is referred to cf. Hesperaletes. North American Protapirus and Hesperaletes show many cranial similarities, and phylogenetic analysis resolves them as members of an unnamed clade, implying that Hesperaletes is a tapirid.

Samples of the new middle Eocene tapiroid Hesperaletes are analyzed to determine the merits of their referral to particular species. Criteria for recognizing species not only include documenting apomorphic morphologies, but also statistically estimating similarity and variability between and within samples. These criteria are consistent with the general lineage species concept that considers species to be segments of population lineages. Statistical comparisons use Student t tests and an analysis of the coefficient of variation in different samples and combinations of pooled samples. Application of these criteria to samples of Hesperaletes leads to confident referral of late Uintan material to a single species, Hesperaletes borineyi, but indicate that early Uintan samples cannot confidently be referred to a single species. Accordingly, most of the early Uintan samples are referred to a second species, Hesperaletes walshi, with the exception of one sample of uncertain taxonomic status. Although several evolutionary scenarios are consistent with these patterns of variability, they are interpreted to be the result of a cladogenetic speciation event.

Miocene land mammals are described from the Gaillard Cut Local Fauna based on a collection made by Stewart and Whitmore in the 1960s from Cucaracha Reach, former Canal Zone, Republic of Panama. In addition to the Order Rodentia described elsewhere, the land mammals represent three other orders (Carnivora [new record], Artiodactyla, Perissodactyla), including the canid Tomarctus brevirostris, indeterminant Amphicyonidae or Hemicyonidae, oreodont Merycochoerus matthewi, protoceratid Paratoceras wardi, horses Anchitherium clarencei and Archaeohippus sp., and rhinocerotids Menoceras barbouri and Floridaceras whitei. Despite its close proximity to South America, all of the taxa in the Gaillard Cut Local Fauna are of distinctly North American faunal affinities. Given their geological context in Panama and biochronology of the Cucaracha mammals as they are known from North America, the age of this assemblage is within an interval from latest Arikareean (Ar4) through early Barstovian (Ba2), between 19.5 and 14 Ma. Field relationships indicate a collection from a narrow stratigraphic zone: there does not appear to be temporal mixing from different land-mammal ages. Depending on the exact absolute age, which has not yet been determined, the Gaillard Cut Local Fauna either contains relictual ‘Hemingfordian’ species that persisted into the Barstovian, or ‘Barstovian’ indicators that originated earlier in Central America than they are known from North America. The predominance of low-crowned herbivores in the Gaillard Cut Local Fauna is interpreted to indicate forested and woodland habitats in the ancient Neotropics.

The endemic insular canid Cynotherium sardous has been known for 1 ½ centuries, yet its phylogenetic position remained unsolved. This was because inherited ancestral characters and acquired adaptations to different ecological pressures could not be separated. In this study the problem is approached again, with the use of morphological features that were either overlooked or could not be explained properly, combined with results from recent major revisions of canid phylogeny. It appears that Xenocyon is the ancestor of Cynotherium, and that this large hypercarnivorous canid, once on the island, faced a rather different menu consisting of small prey only. The subsequent necessary adaptation resulted in a smallsized dog whose dentition remained much the same, whereas its skull lost the typical fortifications seen in the other hypercarnivorous canids; these are considered superfluous for Cynotherium, which had to exchange big and strong prey for small and fast prey.

The skulls and isolated tympanics are described for the earliest whales, pakicetids, from the H-GSP Locality 62 in the Ganda Kas area in Northern Pakistan. Currently three pakicetid genera are known: Pakicetus, Ichthyolestes, and Nalacetus. Ichthyolestes is smaller than the two other genera. Nalacetus and Pakicetus are similar in size, but morphologically different. Pakicetids have a nasal opening at the tip of the rostrum. Their palate retains an incisive foramen. This study reveals three characters of the cranial anatomy useful for systematic analyses. In pakicetids the orbits are orientated dorsally, and there is no supraorbital shield. The dorsal orientation of the orbits is diagnostic for the family, and the lack of supraorbital shield distinguishes pakicetids, ambulocetids, and remingtonocetids from the other Eocene archaeocetes. The intertemporal region of the pakicetid skull is very narrow, a feature that also occurs in many other Eocene cetaceans. The tympanic, which is the most abundant cranial bone (more than 30 specimens) in the pakicetid collections from H-GSP Locality 62, can be used to distinguish the species of pakicetids. In Ichthyolestes, the tympanic bulla is of the same absolute size as in Pakicetus, hence relatively larger, and the tympanic bulla of Nalacetus is larger than either of these. Morphologically, the tympanic bullae differ between the genera, and on the basis of these morphologies it is possible to recognize a fourth species of pakicetid at this locality.

Baguatherium jaureguii gen. et sp. nov. from the early Oligocene of northern Peru is the best known pre-Deseadan pyrothere. It has a relatively wider palate and less oblique lophs on the molariform teeth than Pyrotherium macfaddeni and Pyrotherium romeroi. A conspicuous lingual crest connects the anterior and posterior lophs of molariform teeth. Nares are retracted. Phylogenetic analysis places Baguatherium with Gryphodon and Pyrotherium in an unresolved polytomy. In Proticia and Colombitherium the wear facets of the molariform teeth indicate a mainly grinding masticatory apparatus. In Pyrotherium, Baguatherium, Gryphodon, and to a lesser degree, Propyrotherium, the oblique wear facets generate a cutting surface caused by a greater antero-posterior component to dorsoventral mastication. The cingulae function like stops or buttresses. Considering its brachydont condition, this specialization and the increase in the molariform surface in Baguatherium and Pyrotherium may have improved masticatory efficiency in response to the expansion of open environments during the Oligocene.

Eocardiid rodents from the late early Miocene Pinturas Formation (Ameghino's “Piso Astrapothericu-lense”) of Patagonia are here studied. Three species are recognized: Luantus propheticus Ameghino and Luantus toldensis sp. nov. are recorded exclusively from the Pinturas Formation; Phanomys mixtus Ameghino is also known from the Santa Cruz Formation (Santacrucian SALMA). The dentition of Luantus propheticus has rudiments of accessory prisms in M3 and p4, and the cheek teeth exhibit a bilobated occlusal pattern with interlobular cement and discontinuous enamel covering in senile stages. Luantus toldensis has more hypsodont cheek teeth than L. propheticus, even more developed M3 and p4 accessory prisms, and a bilobated pattern that is attained in earlier stages of wear. Luantus propheticus, L. toldensis, and Phanomys mixtus represent an evolutionary series that leads to the hypselodont pattern of Eocardia; thus, the traditional dichotomy between “Luantinae” and “Eocardiinae” is not supported. Luantus propheticus occurs in the lower and middle sequences of the Pinturas Formation, whereas the more derived species are recorded in localities interpreted as corresponding to the upper sequence. This distribution agrees with that of other faunal components recorded at the Pinturas Formation.