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A newly discovered fossil of an extinct whale from Peru indicates that the animal’s skeleton was unexpectedly enormous. This finding challenges our understanding of body-size evolution.

Abstract The origin and early evolution of Cetacea (whales, dolphins, and porpoises) is one of the best examples of macroevolution as documented by fossils. Early whales are divided into six families that differ greatly in their habitats, which varied from land to freshwater, coastal waters, and fully marine. Early cetaceans lived in the Eocene (55-37 million years ago), and they show an enormous morphological diversity. Toward the end of the Eocene the modern cetacean body plan originated, and this body plan remained more or less the same in the subsequent evolution. It is possible that some aspects of this body plan are rooted in constraints that are dictated by cetacean embryol ogic development and controlled by genes that affect many organ systems at once. It may be possible to use a study of patterns of correlations among morphological traits to test hypotheses of developmental links among organ systems.

Continued excavation at the type locality of Ambulocetus natans led to the recovery of a majority of the axial skeleton of the holotype of this early Eocene cetacean, including both innominates, the sacrum, and most of the thoracic cage and thoracolumbar vertebral column. Additional appendicular, caudal, and cranial materials were also recovered, resulting in a specimen that is now approximately 80 percent complete. This new material allows refined interpretations of its functional morphology. Ambulocetus has a longer thoracolumbar column than that reported for later remingtonocetid and protocetid genera, suggesting that previous estimates of spinal length derived from models of mesonychid ancestry may be inaccurate. Ambulocetus also possesses a co-ossified ecto-mesocuneiform, a character found in some early and middle Eocene artiodactyls, but not mesonychids. New postcranial material provides further evidence of a systemic shift to aquatic locomotion.

Four new ungulate species described here from the early middle Eocene Uzuncarsidere Formation, near Ankara, Turkey present a phylogenetic and biogeographic puzzle. The four species, known from jaws, teeth, and skull and postcranial fragments, share a suite of diagnostic dental features (selenolophodont molars, all lower molars lacking hypoconulids, premolars with metacones small or absent, and narrow, short premolar talonids) and are included in a single new genus, Hilalia. Hilalia saribeya, H. selanneae, H. sezerorum, and H. robusta are distinguished from each other by size and details of premolar morphology. Cladistic analysis indicates that although Hilalia shares a common ancestor with perissodactyls, hyracoids and some “condylarths” to the exclusion of artiodactyls, its position relative to those taxa is unresolved—the calcaneum lacks derived features of artiodactyl, perissodactyl or hyracoid calcanea, some features of Hilalia's molar morphology are convergent with features in some hyracoids, perissodactyls, and selenolophodont “condylarths”, and Hilalia has more primitive premolars than most members of those groups. The affinities of some other members of the Uzuncarsidere mammal fauna, including an embrithopod, marsupials, and a possible proboscidean, have suggested that central Anatolia may have served as a biogeographic crossroads for mammalian dispersal among Asia, Africa, and Europe during the early Paleogene. However, the absence of convincing links between Hilalia and any of the increasingly well-known Paleogene ungulates of Asia, Indo-Pakistan, and Africa, or those of Europe and North America suggests that our understanding of early Paleogene ungulate evolution and biogeography is far from complete.

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 IndoPakistan. 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.

The cranial anatomy of Megalohyrax eoceanus Andrews, 1903, a pliohyracid (Hyracoidea, Mammalia) from Oligocene levels of the Jebel Qatrani Formation of the Fayum Depression in Egypt, is described. Megalohyrax is the largest of the Fayum hyracoids, its skull is 391 mm long and the specimen described here is probably the best-preserved pliohyacid skull known. Megalohyrax has a strong lambdoid crest, a primitive alisphenoid canal, a notch for the minor palatine neurovascular group, orbits which are not anteriorly displaced, and a broad contact between the maxilla and frontal. In all of these features, Megalohyrax differs from modern hyracoids. Contrary to previous suggestions, the dental formula of Megalohyrax is 3.1.4.3, not similar to early sirenians (which have 5 premolars). Basi-occipital morphology suggests that Megalohyrax may have had a eustachian sac.

A new early-to-middle Eocene cetacean from the Kala Chitta Hills of northern Pakistan is described: Attockicetus praecursornew genus and species. It is based on fragmentary cranial material, including a rostral fragment, P3–M3, endocast, and ectotympanic. Attockicetusis the first remingtonocetid from northern Pakistan, and the oldest member of its family. Attockicetus praecursoris smaller than the species of the other remingtonocetid genera, Remingtonocetus, Andrewsiphius, and Dalanistes. It is also more primitive in the retention of large protocones on the upper molars and the anterior position of the orbit. Known material for Attockicetusis fragmentary, but the taxon is important because it extends the geographic and temporal range of remingtonocetids, is one of the few remingtonocetids in which toothcrowns are preserved, and because it is probably the most plesiomorphic remingtonocetid.

We investigate the role of the ancestral ungulates Phenacodontidae in the evolution of Perissodactyla, Hyracoidea, Proboscidea, Sirenia, and Desmostylia on the basis of parsimony analysis of dental, cranial, and postcranial data. The monophyletic order Phenacodonta (Phenacodontidae and Meniscotheriidae) is the sistergroup to the mirorder Pantomesaxonia (consisting of the five mammalian orders mentioned), and these two clades are united as superorder Paenungulata. The relationships of taxa within Pantomesaxonia remain unresolved. Important characters of the ancestor of Pantomesaxonia include partially molarized premolars and a cursorial limb skeleton.

Prorastomus sirenoides is both the oldest and the most primitive sirenian known; it is the only unquestioned sirenian recorded from beds of probable early Eocene age. The unique holotype skull from Jamaica is here redescribed, new material from middle Eocene beds in Jamaica is referred to this species, and two atlases from the late Eocene of Florida are referred to the family Prorastomidae. Although Prorastomus appears to have some autapomorphies that exclude it from the direct ancestry of other sirenians, it is the best available approximation to a structural ancestor of the Sirenia. Therefore, Prorastomus is more appropriate than any Recent species as a representative of the order in analyzing the relationships of sirenians to other mammals. Sirenians are cladistically related to some other primitive ungulates as follows: (Arctocyon (Phenacodus (Moeritherium, Sirenia))). The 3.1.5.3 dental formula of Prorastomus and other Eocene sirenians may be a synapomorphy of the order and a reversal of the loss of P5 and M3 postulated by McKenna (1975) to have occurred in early eutherians; or it may be simply a retention of the primitive eutherian formula. Prorastomus was probably an amphibious but mainly aquatic quadruped that inhabited coastal rivers and embayments. It was probably a selective browser on floating and emergent aquatic plants and, to a minor degree, on seagrasses.

The evolutionary steps leading up to the origin of cetaceans involved pervasive changes in the masticatory apparatus, the ear, and limb morphology. These changes bear heavily on the phylogenetic relationships of Cetacea, and are investigated here on the basis of two of its earliest members:Pakicetus andAmbulocetus. A phylogenetic analysis of cetaceans, five groups of mesonychians, and five other groups of ungulates indicates thatPakicetus is the sister group to all other cetaceans, and that Cete (mesonychians and Cetacea) is a monophyletic group.

We describe pads on the thumb of five vespertilionoid bats based on microanatomy and scanning microscopy and make inferences about their function. The pad of Thyroptera adheres by means of suction, and that of Tylonycteris uses dry adhesion. The pad of Glischropus has no true adhesive function and probably functions using friction. Topography of the pad of Pipistrellus nanus could interlock with substrate features, but the pad may have a minor function as a suction device. Glueing is most likely involved in the adhesion of Myzopoda to its substrate.