Herbert H. Covert

Primates: cladistic diagnosis and relationships

Abstract The morphological evidence for the phylogenetic relationships of euprimates, archaic primates, and related eutherian orders is reviewed following the methods of Hennigian phylogenetic systematics. Euprimates, the group including living primates and their closest common ancestor, is diagnosed by a suite of shared derived characters of the cranium and posteranium exhibiting relatively unique distributions among Eutheria. Plesiadapiformes, the group of archaic primates generally held to be the sister group to Euprimates, is not demonstrably monophyletic (with or without Microsyopidae). The Superorder Archonta (primates, tree shrews, bats, and colugos) is the only higher-level grouping including Euprimates that is based on uniquely derived morphological characters. Hypotheses of relationships within Archonta ally Euprimates with either tree shrews or some plesiadapiforms (paromomyids and plesiadapids), but the eurprimate-tree shrew clade receives more support from the distribution of derived characters among the taxa studied. Because the higher-level affinities of Euprimates are not well resolved, we advocate equating the Order Primates with the taxon Euprimates.

Anatomy and Behaviour of Extinct Primates

The fossil record of primates provides our only direct evidence of the course of evolution leading to the present diversity of primate species, and about the nature of extinct forms which died without issue. Three goals of palaeoprimatological research are identifiable: (1) to identify and name extinct species and to determine their geographical and temporal distribution; (2) to analyze the associations among the species and reconstruct a picture of their phylogeny; and (3) finally, to clarify in functional and adaptive terms the observed morphology and morphological trends among the species and groups of species. Aspects of this last goal are the subject of this paper, where we outline a possible approach to the assessment of the morphology of species which allows their adaptations to be reconstructed. We can thereby provide a series of adaptive models based on living primates which can form the basis for interpreting the morphology of extinct primates.

It’s Tough Out There: Variation in the Toughness of Ingested Leaves and Feeding Behavior Among Four Colobinae in Vietnam

Colobines are similar in their exploitation of a high percentage of leaf matter. However, this observation obfuscates interesting differences among genera of Southeast Asian colobines in morphology and behavior that may be reflected in the degree to which they rely on mastication or gut volume and gut retention time when ingesting and digesting leaves. We detail the use of a laboratory-based method to measure the mechanical properties of foods selected and processed by 4 captive species of Southeast Asian Colobinae —Pygathrix nemaeus, Pygathrix cinerea, Trachypithecus delacouri, and Trachypithecus laotum hatinhensis— at the Endangered Primate Rescue Center (EPRC), Vietnam. We also detail a field method that quantifies chewing rates and chewing behavior via a consumer-grade video camera and laptop computer. Observations in the captive setting permit a degree of experimental control that is not possible in the wild, and the location of the EPRC in the primates’ habitat country permitted us to provide leaves that they encounter and eat in the wild. We collected toughness data with a portable tester designed by Lucas et al. The average toughness of selected leaves does not differ among the taxa, nor does the length of time spent chewing foods. However, there are differences in feeding rate, with Trachypithecus spp. chewing foods twice as fast as Pygathrix spp. Our findings suggest that Trachypithecus spp. emphasize comminution of food by mastication, while Pygathrix spp. emphasize the comminution of leaf matter in the stomach. The hypothesis is supported by data on molar size, gut mass, and gut morphology. We provide new insights into dietary variation among primate species and detail methods that are typically conducted only in a laboratory setting. We augment the findings with additional data on activity, feeding rates, and tooth morphology.

Ankle and foot morphology of Cantius mckennai: adaptations and phylogenetic implications

Abstract The morphology of the ankle and foot of the early North American adapid Cantius mckennai is described. Significant euprimate traits include a rotated medial malleolus on the tibia, a posterior trochlear shelf on the talus, distal elongation of the calcaneus, a prominent process on the calcaneal articular facet of the cuboid, a large concavoconvex facet for the hallucial metatarsal on the medial cuneiform, a large concavoconvex facet for the medial cuneiform on the hallucial metatarsal, and dorsoplantarly flattened distal phalanges. Functional analysis of the preserved elements suggest that this animal had a mobile ankle, a transverse tarsal joint that allowed a great deal of inversion, an opposable big toe, and grasping digits. Such functional attributes strongly suggest an arboreal lifestyle for Cantius mckennai . The presence of a large posterior trochlear shelf on the talus and a strongly rotated medial malleolus are argued to be important indicators of the strepsirhine affinities of adapid primates.

Unexpected locomotor behaviour: brachiation by an Old World monkey ( Pygathrix nemaeus ) from Vietnam

More than 70 h of positional behaviour data were collected on the red-shanked douc langur Pygathrix nemaeus, Delacour’s langur Trachypithecus delacouri, Hatinh langur Trachypithecus laotum, and the white-cheeked crested gibbon Hylobates leucogenys in January and February of 2001 at the Endangered Primate Rescue Center of Cuc Phuong National Park, Ninh Binh Province, Vietnam. Equal amounts of instantaneous and continuous bout data were collected for each of the four species. All animals were housed in enclosures of 10 × 5 × 3.5 m with similar substrates, and lived in small, species-appropriate social groups. The positional behaviour of white-cheeked crested gibbons was as expected with > 80% of locomotor bouts and 60% of postures being suspensory in nature. The positional behaviour of the Delacour’s and Hatinh langurs was similar to that reported in the literature for other Asian colobines with > 90% of the locomotor bouts being quadrupedal walking, running, and bounding on tops of arboreal supports. Postures were dominated by sitting in and sitting out with forelimb suspension associated with < 10% of these behaviours. The positional behaviour of the red-shanked douc langur is intermediate in nature between the Delacour’s and Hatinh langur and the white-cheeked crested gibbon. Locomotion is nearly evenly divided between arm-swinging (46%) and quadrupedal walking and running bouts (54%). Forelimb suspensory postures were three times more frequent for the red-shanked douc langur than they were for the Delacour’s langur.

New body mass estimates for Omomys carteri, a middle Eocene primate from North America

We report new body mass estimates for the North American Eocene primate Omomys carteri. These estimates are based on postcranial measurements and a variety of analytical methods, including bivariate regression, multiple regression, and principal components analysis (PCA). All body mass estimation equations show high coefficients of determination (R2), and some equations exhibit low prediction errors in accuracy tests involving extant species of body size similar to O. carteri. Equations derived from PCA-summarized data and multiple regression generally perform better than those based on single variables. The consensus of estimates and their statistics suggests a body mass range of 170-290 g. This range is similar to previous estimates for this species based on first molar area (Gingerich, J Hum Evol 10:345-374, 1981; Conroy, Int J Primatol 8:115-137, 1987).

Recently Recovered Specimens of North American Eocene Omomyids and Adapids and Their Bearing on Debates about Anthropoid Origins

Most recent reviews of primate evolution recognize that modern primates can be divided into two monophyletic suborders, the Strepsirhini (lemuriforms and lorisiforms) and the Haplorhini (tarsiers, monkeys, apes, and humans). It is also accepted by most researchers that the radiation of modern primate taxa dates to at least the beginning of the Eocene. The earliest occurring animals that appear to be seeded within this radiation belong to the families Adapidae and Omomyidae, the Eocene euprimates (Hoffstetter, 1974; Szalay and Del-son, 1979; Covert, 1986; MacPhee and Cartmill, 1986; Martin, 1986; Wible and Covert, 1987; and Szalay et al., 1987).

Comparisons of Suspensory Behaviors Among Pygathrix cinerea, P. nemaeus, and Nomascus leucogenys in Cuc Phuong National Park, Vietnam

In our study at the Endangered Primate Rescue Center of Cuc Phuong National Park, Vietnam, we aimed first to assemble a positional behavioral profile of captive gray-shanked (Pygathrix cinerea) and red-shanked (P. nemaeus) doucs that relates to the use of forelimb suspensory postures and arm-swinging locomotion. The profile is of interest because researchers have documented that red-shanked doucs more frequently use suspensory postures and locomotions than other colobines do. We confirmed that red-shanked doucs commonly use suspensory positional behaviors and also that gray-shanked doucs use suspensory behaviors at similar or even higher frequencies than those of red-shanked doucs. Our second goal was to assemble a preliminary kinematic profile of suspensory locomotion in Pygathrix within the context of the arm-swinging locomotion exhibited by northern white-cheeked gibbons, Nomascus leucogenys. Mean forelimb angles at initial contact and release of arm-swinging behaviors were remarkably consistent among gibbons and doucs despite the fact that gibbons typically used more continuous brachiation. Doucs also exhibit a greater range of forelimb angles than gibbons do. In addition, trunk orientation tends to be less vertical at initial contact for doucs than for gibbons, perhaps owing to the frequent use of quadrupedal sequences directly before or after forelimb suspension. Our behavioral and kinematic analyses add to the emerging realization that Pygathrix is capable of, and frequently expresses, a range of suspensory positional behaviors, including brachiation.

Locomotor Adaptations of Eocene Primates: Adaptive Diversity Among the Earliest Prosimians

Since the initial discovery of Eocene primates well over a century ago it has been widely recognized that these animals more closely resemble the prosimians than any other group of living creatures. This fact, along with the realization by evolutionary biologists that form — function — adaptive role relationships among extant creatures provide the basis for making inferences about the adaptations of extinct creatures, indicates that to understand the adaptations of the Eocene primates we must have a firm understanding of the adaptations of extant prosimians. For much of this century our ability to make suggestions about the adaptations of Eocene primates was hampered by the lack of skeletal material for the vast majority of these taxa and the lack of field observations on extant prosimian primates. This has changed dramatically during the past 35 years. Samples of post-cranial remains of Eocene primates have improved significantly and there is now a tremendous amount of information on the ecology of the extant prosimians so that we are now able to offer a range of informed suggestions about the behavior of these earliest primates. Extensive reviews of the ecology and behavior of the extant prosimians can be found in Martin et al. (1974), Charles-Dominique et al. (1980), Fleagle (1988), and this volume. Recent reviews of some of this fossil material can be found in Covert (1986), Fleagle (1988), Gebo (1988), Gebo et al. (1991), Conroy (1990), and Dagosto (1993).

Fossil mammals from the Late Miocene of Vietnam

Very little is known about the evolutionary history of mammals in Southeast Asia, where Myanmar (Burma) and Thailand provide the vast majority of evidence for mammalian evolution in the region predating the late Pleistocene. Recent work in Eocene deposits in Thailand has yielded a range of mammalian remains including an early dermopteran (Ducrocq et al., 1992), anthracotheres (Ducrocq, 1994, 1997), suids (Ducrocq et al., 1998), and early anthropoid primates (Chaimanee et al., 1997; Ducrocq, 1998; Jaeger et al., 1998). This research team has also recovered a number of mammalian taxa from Miocene deposits in Thailand including a hominoid, a rodent, two suids, and a tragulid (Su teethorn et al., 1990; Ducrocq et al., 1997). The Pondaung Formation of Burma includes a late Eocene mammalian fauna that has been rec