Richard F. Kay

Cranial morphology and adaptations of Palaechthon nacimienti and other paromomyidae (Plesiadapoidea, ? primates), with a description of a new genus and species

The Middle Paleocene paromomyid Palaechthon nacimienti has the most primitive cranial anatomy known for any plesiadapoid. In relative size and functional morphology, its molars resemble those of primates and tree shrews known to feed largely on insects. Its orbits were small, laterally directed, and widely separated, and the relative size of its infraorbital foramen shows that it had well-developed facial vibrissae resembling those of extant erinaceids. Its anterior dentition was probably also hedgehog-like. These features suggest that it was a predominantly terrestrial insect-eater, guided largely by tactile, auditory and olfactory sensation in its pursuit of prey. Adaptations to living in trees and feeding on plants probably developed in parallel in more than one lineage descended from the ancestral plesiadapoids. A new genus and species of paromomyid, Talpohenach torrejonius, is erected for material originally identified as Palaechthon.

The phyletic relationships of extant and fossil Pitheciinae (Platyrrhini, Anthropoidea)

A phylogenetic assessment of Pitheciinae ( sensu Hershkovitz, 1977) is undertaken. Among the three living genera of pitheciines, Chiropotes and Cacajao share a more recent common ancestor than either does with Pithecia . Evidence for the position of pitheciines within the platyrrhine clade is weak and contradictory owing partly to the amount of parallelism within and among various platyrrhine subfamilies. Rosenbergers (1979, 1984) hypothesis that Aotus and/or Callicebus are closely related to pitheciines is not supported by a review of the cranial, dental and postcranial evidence. The evidence is weak that Alouatta and the atelines are the sister group of pitheciines as argued by Ford (1986) . An alternative view is advanced that pitheciines are an early offshoot of the platyrrhine clade. The relationships of some fossil forms to living pitheciines are considered. Cebupithecia from the Miocene of Colombia is definitely pitheciine based especially on the dentition (rounded, chisel-shaped canines) but also on postcranial evidence. However, it lacks some of the dental specializations shared by living pitheciines; therefore it is most likely a sister group of living pitheciines. Argentine Miocene Soriacebus is not a pitheciine but is convergently specialized for a diet similar to living pitheciines. Colombian Miocene Mohanamico hershkovitzi (a senior synonym of Aotus dindensis ) is possibly a very primitive pitheciine and an unlikely sister taxon to Callimico .

Osteological evidence for the evolution of activity pattern and visual acuity in primates

Examination of orbit size and optic foramen size in living primates reveals two adaptive phenomena. First, as noted by many authors, orbit size is strongly correlated with activity pattern. Comparisons of large samples of extant primates consistently reveal that nocturnal species exhibit proportionately larger orbits than diurnal species. Furthermore, nocturnal haplorhines (Tarsius and Aotus) have considerably larger orbits than similar-sized nocturnal strepsirrhines. Orbital hypertrophy in Tarsius and Aotus accommodates the enormously enlarged eyes of these taxa. This extreme ocular hypertrophy seen in extant nocturnal haplorhines is an adaptation for both enhanced visual acuity and sensitivity in conditions of low light intensity. Second, the relative size of the optic foramen is highly correlated with the degree of retinal summation and inferred visual acuity. Diurnal haplorhines exhibit proportionately larger optic foramina, less central retinal summation, and much higher visual acuity than do all other primates. Diurnal strepsirrhines exhibit a more subtle but significant parallel enlargement of the optic foramen and a decrease in retinal summation relative to the condition seen in nocturnal primates. These twin osteological variables of orbit size and optic foramen size may be used to draw inferences regarding the activity pattern, retinal anatomy, and visual acuity of fossil primates. Our measurements demonstrate that the omomyiforms Microchoerus, Necrolemur, Shoshonius, and Tetonius, adapiform Pronycticebus, and the possible lorisiform Plesiopithecus were likely nocturnal on the basis of orbit diameter. The adapiforms Leptadapis, Adapis, and Notharctus, the phylogenetically enigmatic Rooneyia, the early anthropoids Proteopithecus, Catopithecus, and Aegyptopithecus, and early platyrrhine Dolichocebus were likely diurnal. The activity pattern of the platyrrhine Tremacebus is obscure. Plesiopithecus, Pronycticebus, Microchoerus, and Necrolemur probably had eyes that were very similar to those of extant nocturnal primates, with a high degree of retinal summation and rod-dominated retinae. Leptadapis and Rooneyia likely had eyes similar to those of extant diurnal strepsirrhines, with moderate degrees of retinal summation, a larger cone:rod ratio than in nocturnal primates, and, more speculatively, well-developed areae centrales similar to those of diurnal strepsirrhines. Adapis exhibited uncharacteristically high degrees of retinal summation for a small-eyed (likely diurnal) primate. None of the adapiform or omomyiform taxa for which we were able to obtain optic foramen dimensions exhibited the extremely high visual acuity characteristic of extant diurnal haplorhines.

The ecology of oligocene African anthropoidea

African anthropoids are first recorded in Early Oligocene deposits of the Fayum Province, Egypt. Six genera and nine species are recognized. Estimated body weights for these taxa are based on the regression equation log10(B) = 2.86log10(L) + 1.37, whereB is the bodyweight in grams, and Lis the M2length in millimeters. The equation is derived from 106 species of living primates. Fayum species range in body weight from about 600 g (Apidium moustafai)to about 6000 g (Aegyptopithecus zeuxis).A similar range of body weight is found among extant Cebidae. The Fayum primates are larger than any extant insectivorous primates;this fact probably rules out a predominantly insectivorous diet. Extant frugivorous hominoids can be separated from folivorous hominoids on the basis of molar morphology. Folivorous apes (gorilla and siamang) have proportionately more shearing on their molars than do frugivorous species. Based on the hominoid analogy, the molar morphology of the Fayum species is consistent with a frugivorous diet. Parapithecus grangeristands apart from other Fayum species in having better developed molar shearing, possibly indicating that it had more fiber in its diet. Terrestrial species of Old World monkeys tend to have significantly higher molar crowns than do more arboreal species. This difference may relate to an increased amount of grit in the diet of the more terrestrial species, selecting for greater resistance to wear. Oligocene primates have molar crown heights consistent with a primarily arboreal mode of existence. However, the particularly high molar crowns of Parapithecus grangerisuggest that this species may have foraged on the ground to a considerable degree. Other evidence is advanced suggesting that Apidiummay have had a diurnal activity pattern.

A Comparative Test of Adaptive Explanations for Hypsodonty in Ungulates and Rodents

Hypsodonty has long been recognized as an adaptation for grazing: grazing is suggested to increase tooth wear due to endogenous (e.g., fiber, silica) and/or exogenous (e.g., dust, grit) properties of ingested food. However, it is unknown whether tooth crown height is correlated with the mastication of high fiber or silica in grasses, the ingestion of external abrasives, or both. Furthermore, comparative studies of hypsodonty have not explicitly taken into account phylogenetic biases due to shared ancestry in tooth morphology and/or feeding behavior. This study highlights the relationship between molar crown height and feeding habits in African ungulates and South American rodents when phylogenetic effects are controlled. Among ungulates, high hypsodonty indices are significantly associated with specific plant and foraging height preferences, while habitat and climate show no correlation with tooth crown height. For rodents, grass-eating species are significantly more hypsodont than frugivorous or folivorous species, and arboreal rodents are less hypsodont than terrestrial species. These results as well as those of a posteriori analyses controlling for aspects of the behavioral ecology (e.g., grass-eating, substrate preference) of the sample species confirm the role of both diet and grit in shaping the evolution of cheek tooth crown height in herbivorous mammals.

The phyletic position of the Parapithecidae

Abstract The Parapithecidae are a group of primitive anthropoid primates known only from the early Oligocene Jebel Qatrani Formation of Fayum, Egypt. Since the initial discovery of the group early in the century, their phyletic position relative to other higher primates has been ambiguous and the subject of considerable debate. Various authors have considered the parapithecids as the sister taxon of (1) Old World monkeys, (2) all other Old World anthropoids; (3) platyrrhines; or (4) all other higher primates. Although there are anatomical features that can be advanced to support each of these views, parapithecids lack a number of anatomical features that characterize all other anthropoids and are best considered the most primitive higher primates. Such a phyletic position for parapithecids involves fewer evolutionary parallelisms and reversals in anthropoid evolution than does any other phylogeny. This suggests that the origin of anthropoids from prosimians was most probably in Africa.

Reconstructing behavior in the primate fossil record

1. Preface J.M. Plavcan, et al. 2. Adaptation and behavior in the primate fossil record C.F. Ross, et al. 3. Functional morphology and in vivo bone strain patterns in the craniofacial region of primates: beware of biomechanical stories about fossil bones W.L. Hylander, K.R. Johnson. 4. On the interface between ontogeny and function M.J. Ravosa, C.J. Vinyard. 5. Dental ontogeny and life-history strategies: the case of the giant extinct indroids of Madagascar L.R. Godfrey, et al. 6. A comparative approach to reconstructing the socioecology of extinct primates C.L. Nunn, C.P. van Schaik. 7. The use of paleocommunity and taphonomic studies in reconstructing primate behavior K.E. Reed. 8. Reconstructing diets of fossil primates P. Ungar. 9. Reconstructing social behavior from dimorphism in the fossil record J.M. Plavcan. 10. The adaptations of Branisella boliviana, the earliest South American monkey R.F. Kay, et al. 11. Ecomorphology and behavior of giant extinct lemurs from Madagascar W.L. Jungers, et al. 12. Conclusions: reconstructing behavior in the fossil record J.M. Plavcan, et al.

The Evolution of High Visual Acuity in the Anthropoidea

Most definitions of the order primates make some reference to the importance of vision relative to the other special senses (Le Gros Clark, 1959; Martin, 1990; Napier and Napier, 1967). This characterization is particularly fitting for haplorhine primates, in which vision is unquestionably the dominant sensory modality. Anthropoids and tarsiers differ from strepsirrhines in exhibiting a derived reduction of the olfactory apparatus (Baron et al., 1983; Cave, 1973) and an elaboration of the visual sense to a degree that is unique among mammals (Rodieck, 1973; Walls, 1942). Visual adaptations, however, are divergent within the haplorhine suborder. While the tarsier visual system is primarily specialized for enhanced sensitivity in the context of nocturnal visual predation (Castenholz, 1984s), most living anthropoids are adapted for extremely acute diurnal vision.

Anthropoid origins : a phylogenetic analysis

Living Anthropoidea—the group that includes monkeys, apes, and humans—has long been recognized as a monophyletic group among primates diagnosed by a suite of features of the skull, dentition, and postcranium. Likewise it is agreed that there are two monophyletic groups of living anthropoids—the Central and South American Platyrrhini (New World monkeys) and African and Eurasian Catarrhini (Old World monkeys, “apes,” and humans). As well, most paleontologists and neontologists agree that Tarsius is the closest living relative of anthropoids and that strepsirrhines, lemurs and lorises, are more distantly related (but see Eizirik et al., this volume for a different view). Paleontologists also generally accept the following “facts”: The oldest Tarsius relatives occur in the Asian middle Eocene. The oldest undisputed fossil record of anthropoids is from the late Eocene localities in Afro-Arabia. Platyrrhines first appear in the late Oligocene in South America and the catarrhine record is acknowledged by all to include Propliopithecidae from the early Oligocene of Egypt and Oman.

Sivapithecus simonsi, a new species of miocene hominoid, with comments on the phylogenetic status of the ramapithecinae

The Ramapithecinae are an extinct, mainly Miocene group of hominoids, whose relationship to modern taxa is disputed. Some regard them as hominids, while others view them as ancestral toPongo,or even as the group ancestral to both hominids and extant apes. In this paper a systematic revision of Ramapithecinae is undertaken. Sivapithecus sivalensis andRamapithecus punjabicus are considered the same species, with the former name having priority. A new Indian species,Sivapithecus simonsi,is recognized. Ramapithecine anatomy is reviewed and compared with that of gracileAustralopithecus, early and middle MioceneProconsul andDryopithecus, and living pongidsPan, Gorilla, andPongo.Ramapithecines are shown to be much more primitive or “ape-like” than some have argued. Anatomical data are evaluated cladistically with several results. Parallel evolution in the jaws, teeth, and facial structure of hominoids appears to be the rule rather than the exception. Bearing this in mind, nevertheless, from the available evidence of anatomy, ramapithecines are cladistically hominids.