Origin of whales from early artiodactyls: hands and feet of Eocene Protocetidae from Pakistan.

Partial skeletons of two new fossil whales, Artiocetus clavis and Rodhocetus balochistanensis, are among the oldest known protocetid archaeocetes. These came from early Lutetian age (47 million years ago) strata in eastern Balochistan Province, Pakistan. Both have an astragalus and cuboid in the ankle with characteristics diagnostic of artiodactyls; R. balochistanensis has virtually complete fore- and hind limbs. The new skeletons are important in augmenting the diversity of early Protocetidae, clarifying that Cetacea evolved from early Artiodactyla rather than Mesonychia and showing how early protocetids swam.

Primate postcrania from the late middle Eocene of Myanmar.

Fossil primates have been known from the late middle to late Eocene Pondaung Formation of Myanmar since the description of Pondaungia cotteri in 1927. Three additional primate taxa, Amphipithecus mogaungensis, Bahinia pondaungensis and Myanmarpithecus yarshensis, were subsequently described. These primates are represented mostly by fragmentary dental and cranial remains. Here we describe the first primate postcrania from Myanmar, including a complete left humerus, a fragmentary right humerus, parts of left and right ulnae, and the distal half of a left calcaneum, all representing one individual. We assign this specimen to a large species of Pondaungia based on body size and the known geographic distribution and diversity of Myanmar primates. Body weight estimates of Pondaungia range from 4,000 to 9,000 g, based on humeral length, humeral midshaft diameter, and tooth area by using extant primate regressions. The humerus and ulna indicate that Pondaungia was capable of a wide variety of forelimb movements, with great mobility at the shoulder joint. Morphology of the distal calcaneus indicates that the hind feet were mobile at the transverse tarsal joint. Postcrania of Pondaungia present a mosaic of features, some shared in common with notharctine and adapine adapiforms, some shared with extant lorises and cebids, some shared with fossil anthropoids, and some unique. Overall, Pondaungia humeral and calcaneal morphology is most consistent with that of other known adapiforms. It does not support the inclusion of Pondaungia in Anthropoidea.

Rates of evolution on the time scale of the evolutionary process.

A generational time scale, involving change from one generation to the next, is the time scale of evolution by natural selection. Microevolutionary and macroevolutionary patterns reflect this process on longer time scales. Rates of evolution are most efficiently expressed in haldane units, H, in standard deviations per generation, indexed by the log of the time interval. Rates from replicated selection experiments and simulations have rate-interval [RI] and log rate-log interval [LRI] scaling relations enabling directional, stationary, and random time series to be distinguished. Empirical microevolutionary and macroevolutionary data exhibit stationary scaling, but point to generational rates of evolution (H0) conservatively on the order of 0.2 standard deviations per generation on the time scale of the evolutionary process. This paradox of long-term stationary scaling and short-term high rates of change can be explained by considering the shape of an heuristic time-form evolutionary lattice. Cenozoic mammals occupy a lattice that is about four orders of magnitude longer in time than it has ever been wide in form. The evolutionary process is dynamic but operates within relatively narrow morphological constraints compared to the time available for change.

Arithmetic or geometric normality of biological variation: an empirical test of theory.

Variation of biological populations is required for evolution by natural selection, and variance is a fundamental component in quantitative characterization of evolutionary differences and rates of change. Biological variation is widely understood to be normally distributed because of a general theoretical law of error. The law of error has two forms, and resulting normality may be arithmetic-where equivalent positive and negative deviations from expectation differ by equal amounts, or normality may be geometric-where equivalent deviations differ by equal proportions. Which law of error applies in biology can only be determined empirically, and this is surprisingly difficult. A new likelihood approach is developed here using data from anthropometric surveys of humans in two states in India: Maharashtra and Uttar Pradesh. Each state sample is large, but more importantly, each includes a large number of smaller subsamples. Likelihood support is additive, and subsamples are advantageous because (1) they are more homogeneous, (2) they yield probabilities and support scores in every case, and (3) significance can be evaluated first by tracing signs of the subsample support scores and then by comparing subsample support sums. Sign traces that fluctuate randomly show arithmetic and geometric normality to be indistinguishable. Two of 14 measurement variables studied here have subsample support sign traces differing from random, and one is significant in having a subsample support sum falling outside a 95% prediction interval for the 12 fluctuating traces: geometric normality is favored by a factor of ca. 10(60). Six of 14 index variables have support sign traces differing from random, and all are significant in having subsample support sums falling outside a 95 % prediction interval for the 8 fluctuating traces: geometric normality is favored by factors of 10(8) or more. Arithmetic and geometric normality cannot be distinguished for 21 of 28 variables studied here, but whenever alternatives are distinguishable geometric normality is consistently and strongly favored. This means that the applicable law of errors is proportional. In practical terms, arithmetic measurements must be transformed using logarithms to represent both the geometric normality of biological variation and the relative functional significance of measurements appropriately.

A new Eocene archaeocete (Mammalia, Cetacea) from India and the time of origin of whales.

Himalayacetus subathuensis is a new pakicetid archaeocete from the Subathu Formation of northern India. The type dentary has a small mandibular canal indicating a lack of auditory specializations seen in more advanced cetaceans, and it has Pakicetus-like molar teeth suggesting that it fed on fish. Himalayacetus is significant because it is the oldest archaeocete known and because it was found in marine strata associated with a marine fauna. Himalayacetus extends the fossil record of whales about 3.5 million years back in geological time, to the middle part of the early Eocene [ approximately 53.5 million years ago (Ma)]. Oxygen in the tooth-enamel phosphate has an isotopic composition intermediate between values reported for freshwater and marine archaeocetes, indicating that Himalayacetus probably spent some time in both environments. When the temporal range of Archaeoceti is calibrated radiometrically, comparison of likelihoods constrains the time of origin of Archaeoceti and hence Cetacea to about 54-55 Ma (beginning of the Eocene), whereas their divergence from extant Artiodactyla may have been as early as 64-65 Ma (beginning of the Cenozoic).

Hind limbs of eocene basilosaurus: evidence of feet in whales.

New specimens of middle Eocene Basilosaurus isis from Egypt include the first functional pelvic limb and foot bones known in Cetacea. These are important in corroborating the intermediate evolutionary position of archaeocetes between generalized Paleocene land mammals that used hind limbs in locomotion and Oligocene-to- Recent whales that lack functional pelvic limbs. The foot is paraxonic, consistent with derivation from mesonychid Condylarthra. Hind limbs of Basilosaurus are interpreted as copulatory guides.

Temporal scaling of molecular evolution in primates and other mammals.

Molecular clocks are routinely tested for linearity using a relative rate test and routinely calibrated against the geological time scale using a single or average paleontologically determined time of divergence between living taxa. The relative rate test is a test of parallel rate equality, not a test of rate constancy. Temporal scaling provides a test of rates, where scaling coefficients of 1.0 (isochrony) represent stochastic rate constancy. The fossil record of primates and other mammals is now known in sufficient detail to provide several independent divergence times for major taxonomic groups. Molecular difference should scale negatively or isochronically (scaling coefficients less than 1.0) with divergence time: where two or more divergence times are available, molecular difference appears to scale positively (scaling coefficient greater than 1.0). A minimum of four divergence times are required for adequate statistical power in testing the linear model: scaling is significantly nonlinear and positive in six of 11 published investigations meeting this criterion. All groups studied show some slowdown in rates of molecular change over Cenozoic time. The break from constant or increasing rates during the Mesozoic to decreasing rates during the Cenozoic appears to coincide with extraordinary diversification of placental mammals at the beginning of this era. High rates of selectively neutral molecular change may be concentrated in such discrete events of evolutionary diversification.

Rates of evolution: effects of time and temporal scaling.

Rates of morphological evolution documented in laboratory selection experiments, historical colonization events, and the fossil record are inversely related to the interval of time over which they are measured. This inverse relationship is an artifact of comparing a narrow range of morphological variation over a wide range of time intervals, and it is also a product of time averaging. Rates measured over different intervals of time must be scaled against interval length before they can be compared.

Origin of whales in epicontinental remnant seas: new evidence from the early eocene of pakistan.

Pakicetus inachus from the early Eocene of Pakistan is the oldest and most primitive cetacean known. The dentition of Pakicetus resembles that of carnivorous mesonychid land mammals as well as middle Eocene cetaceans. The otic region of the cranium lacks characteristic specializations of whales necessary for efficient directional hearing under water. Pakicetus occurs with a land-mammal fauna in fluvial sediments bordering epicontinental Eocene remnants of the eastern Tethys seaway. Discovery of Pakicetus strengthens earlier inferences that whales originated from terrestrial carnivorous mammals and suggests that whales made a gradual transition from land to sea in the early Eocene, spending progressively more time feeding on planktivorous fishes in shallow, highly productive seas and embayments associated with tectonic closure of eastern Tethys.

New Palaeogene primate basicrania and the definition of the order Primates.

The anatomy of the posterior basicranium has been repeatedly invoked in systematic definitions of Primates. One widely cited definition of the order claims that 'all undoubted primates' are distinguished from other mammals by two basicranial specializations: (1) absence of a major vascular foramen on the medial side of the auditory region, and (2) development of the auditory bulla from the petrosal bone. As we show here, specialization (1) does not apply to the paromomyid Ignacius, and is of uncertain incidence in other unquestioned members of suborder Plesiadapiformes (archaic primates from the early Cenozoic of Europe and North America). Specialization (2) cannot be demonstrated without ontogenetic evidence, and all relevant plesiadapiform fossils are adult. In fact, the only plesiadapiform with an arterial pattern remotely resembling that of early primates of modern aspect (or 'euprimates') is the microsyopid Cynodontomys, but it is often regarded as non-primate because it lacks a petrosal bulla. Although plesiadapiforms resemble euprimates in traits of the cheek teeth and postcranium, some other (presumably non-primate) groups possess these traits as well. Since the order Primates is not clearly definable by unique specializations, the best grounds for regarding plesiadapiforms as euprimate antecedents are stratigraphic and phenetic. This fact may be best expressed by systematic arrangements that emphasize adaptive grades rather than unsubstantiated clades.

Allometric scaling in the dentition of primates and prediction of body weight from tooth size in fossils.

Tooth size varies exponentially with body weight in primates. Logarithmic transformation of tooth crown area and body weight yields a linear model of slope 0.67 as an isometric (geometric) baseline for study of dental allometry. This model is compared with that predicted by metabolic scaling (slope = 0.75). Tarsius and other insectivores have larger teeth for their body size than generalized primates do and they are not included in this analysis. Among generalized primates, tooth size is highly correlated with body size. Correlations of upper and lower cheek teeth with body size range from 0.90-0.97, depending on tooth position. Central cheek teeth (P44 and M11) have allometric coefficients ranging from 0.57-0.65, falling well below geometric scaling. Anterior and posterior cheek teeth scale at or above metabolic scaling. Considered individually or as a group, upper cheek teeth scale allometrically with lower coefficients than corresponding lower cheek teeth; the reverse is true for incisors. The sum of crown areas for all upper cheek teeth scales significantly below geometric scaling, while the sum of crown areas for all lower cheek teeth approximates geometric scaling. Tooth size can be used to predict the body weight of generalized fossil primates. This is illustrated for Aegyptopithecus and other Eocene, Oligocene, and miocene primates. Regressions based on tooth size in generalized primates yield reasonable estimates of body weight, but much remains to be learned about tooth size and body size scaling in more restricted systematic groups and dietary guilds.

A new species of Niptomomys (Microsyopidae) from the early eocene of Wyoming.

A new, relatively large species of Niptomomys is described from the late Wasatchian of the Bighorn Basin of Wyoming. The importance of a stratigraphic approach to problems of species-level phylogeny is stressed, and then applied to an investigation of the evolutionary history of Niptomomys. The new Niptomomys species may have evolved gradually from early Wasatchian Niptomomys doreenae in the Bighorn Basin and vicinity, or it may have evolved elsewhere and replaced the earlier form relatively rapidly. The available evidence is not yet sufficient to distinguish between these two alternatives.

Supernumerary molars in Anthropoidea, Adapidae, and Archaeolemur: implications for primate dental homologies.

The model of primate dental homologies and development recently proposed by Schwartz ('75, '78) is re-evaluated in view of documented exceptions to his account of postcanine supernumerary teeth in both anthropoids and prosimians. Schwartz concluded that catarrhines and living indriids retain only two true molars in each dental quadrant. As many as six molars on one side of the jaw can develop in rare instances in catarrhines, and supernumerary molars are also known for a wide range of other primates, including Cebidae, Adapidae, and subfossil Indriidae. Polydontia cannot be explained exclusively by atavistic development. More convincing explanations regard supernumerary teeth as the result of excessive growth of the dental lamina or localized twinning of tooth buds during early development. Conventional dental formulae of catarrhines and indriids including three permanent molars remain the most plausible.

The human mandible: lever, link, or both?

Hylander ('78) recently published important new data on bite force in humans, and showed that the human mandible cannot function purely as a link during incisal biting. He concluded instead that the mandible acts as a lever. Reexamination of Hylander's data suggests that the mandible cannot function purely as a lever either, and in fact it probably functions simultaneously as both lever and link during incisal biting.