Laura MacLatchy

Developments in Primatology: Progress and Prospects

While it may be unusual to pick up an edited science volume devoted to fossil mammals from Egypt and living primates from North Carolina, it is a true reflection of the remarkable research trajectory of a unique individual. Elwyn Simons: A Search for Origins is an amalgam of anecdote, admiration, and scientific research by, about, and inspired by its titular character. Consequently, this personal book deserves a review that comments on the scholarship within as well as on the aspects of it that pay unabashed tribute to the gentleman whose 75th birthday festschrift occasioned its publication. Throughout, I will refer to Professor Simons as “Elwyn” as this is how he is best known. The book has three distinct sections. The first is a collection of reflections about Elwyn by colleagues and supporters (including his wife, Friderun AnkelSimons) as well as two essays (by Bernard Wood and Elwyn Simons himself) on Elwyn’s major mentor, Sir Wilfred Le Gros Clark. An essay by Elwyn’s former student, David Pilbeam, is a delightful musing on the many paleontological greats in Elwyn’s sphere. More delightful still is Elwyn’s own commentary on Le Gros Clark, which I intended to skim, but read in total. This essay ends by recounting a wistful comment that Le Gros once made to Elwyn: that younger colleagues were fortunate because they would live to see more new discoveries of fossils. One can’t help but conclude that this is how Elwyn, an intrepid fossil finder, now views the many who follow in his footsteps. The second section deals with Elwyn’s paleontological contributions and his role in inspiring such investigation world-wide. Most notable is Elwyn’s five decade-long research program in the Eocene and Oligocene beds of the Fayum, Egypt, where critical stages of primate evolution, including early anthropoid and strepsirrhine diversification, are chronicled as nowhere else on earth. A chapter co-written by Elwyn, the editors of the book, and his long-time field manager Prithijit Chatrath, is a compendium of field photos taken almost yearly from 1961–2006. It’s a nostalgic look at the scores of researchers and students who have worked and trained with Elwyn. The photos show men in turbans, men in ties, men in khakis, or shirtless in shorts, and, from 1977, a smattering of women. Some individuals make multiple appearances, notably the indomitable Mr. Chatrath, John Fleagle, and Tom Bown, and serve as testimony to the many successful long-term collaborations Elwyn has sustained during his career. Paleontological articles on the Fayum include Eric Seiffert and colleagues’ overview of the geology, environment, and age of Birket Qarun Locality 2, an J Mammal Evol (2010) 17:69–70 DOI 10.1007/s10914-009-9114-1

Specimen size and porosity can introduce error into μCT-based tissue mineral density measurements

The accurate measurement of tissue mineral density, rho(m), in specimens of unequal size or quantities of bone mineral using polychromatic microCT systems is important, since studies often compare samples with a range of sizes and bone densities. We assessed the influence of object size on microCT measurements of rho(m) using (1) hydroxyapatite rods (HA), (2) precision-manufactured aluminum foams (AL) simulating trabecular bone structure, and (3) bovine cortical bone cubes (BCt). Two beam-hardening correction (BHC) algorithms, determined using a 200 and 1200 mg/cm(3) HA wedge phantom, were used to calculate rho(m) of the HA and BCt. The 200 mg/cm(3) and an aluminum BHC algorithm were used to calculate the linear attenuation coefficients of the AL foams. Equivalent rho(m) measurements of 500, 1000, and 1500 mg HA/cm(3) rods decreased (r(2)>0.96, p<0.05 for all) as HA rod diameter increased in the 200 mg/cm(3) BHC data. Errors averaged 8.2% across these samples and reached as high as 29.5%. Regression analyses suggested no size effects in the 1200 mg/cm(3) BHC data but differences between successive sizes still reached as high as 13%. The linear attenuation coefficients of the AL foams increased up to approximately 6% with increasing volume fractions (r(2)>0.81, p<0.05 for all) but the strength of the size-related error was also BHC dependent. Equivalent rho(m) values were inversely correlated with BCt cube size (r(2)>0.92, p<0.05). Use of the 1200 mg/cm(3) BHC ameliorated the size-related artifact compared to the 200 mg/cm(3) BHC but errors with this BHC were still significant and ranged between 5% and 12%. These results demonstrate that object size, structure, and BHC algorithm can influence microCT measurements of rho(m). Measurements of rho(m) of specimens of unequal size or quantities of bone mineral must be interpreted with caution unless appropriate steps are taken to minimize these potential artifacts.

Tchad: Découverte d'une faune de mammifères du pliocène inférieur

Abstract In Northern Chad, the site of Kolle in the Djourab erg has yielded a vertebrate fauna including 21 species, 14 of which are Mammals. This fauna provides evidence of a mosaic of environments: fresh-water, woodlands, grasslands. In spite of possible taphonomic or collecting bias, and of some endemicity, this fauna allows us to propose an age in the range 5-4 My.

Early Miocene hippopotamids (Cetartiodactyla) constrain the phylogenetic and spatiotemporal settings of hippopotamid origin

The affinities of the Hippopotamidae are at the core of the phylogeny of Cetartiodactyla (even-toed mammals: cetaceans, ruminants, camels, suoids, and hippos). Molecular phylogenies support Cetacea as sister group of the Hippopotamidae, implying a long ghost lineage between the earliest cetaceans (∼53 Ma) and the earliest hippopotamids (∼16 Ma). Morphological studies have proposed two different sister taxa for hippopotamids: suoids (notably palaeochoerids) or anthracotheriids. Evaluating these phylogenetic hypotheses requires substantiating the poorly known early history of the Hippopotamidae. Here, we undertake an original morphological phylogenetic analysis including several “suiform” families and previously unexamined early Miocene taxa to test previous conflicting hypotheses. According to our results, Morotochoerus ugandensis and Kulutherium rusingensis, until now regarded as the sole African palaeochoerid and the sole African bunodont anthracotheriid, respectively, are unambiguously included within the Hippopotamidae. They are the earliest known hippopotamids and set the family fossil record back to the early Miocene (∼21 Ma). The analysis reveals that hippopotamids displayed an unsuspected taxonomic and body size diversity and remained restricted to Africa during most of their history, until the latest Miocene. Our results also confirm the deep nesting of Hippopotamidae within the paraphyletic Anthracotheriidae; this finding allows us to reconstruct the sequence of dental innovations that links advanced selenodont anthracotheriids to hippopotamids, previously a source of major disagreements on hippopotamid origins. The analysis demonstrates a close relationship between Eocene choeropotamids and anthracotheriids, a relationship that potentially fills the evolutionary gap between earliest hippopotamids and cetaceans implied by molecular analyses.

Locomotor and postural development of wild chimpanzees

Chimpanzees are our closest living relatives and their positional repertoire likely includes elements shared with our common ancestor. Currently, limitations exist in our ability to correlate locomotor anatomy with behavioral function in the wild. Here we provide a detailed description of developmental changes in chimpanzee locomotion and posture. Fieldwork was conducted on wild chimpanzees at Ngogo, Kibale National Park, Uganda. The large size of the Ngogo chimpanzee community permitted cross-sectional analysis of locomotor and postural changes across many individuals. Chimpanzee positional behavior proceeds developmentally through a number of distinct stages, each characterized by its own loading regime. Infants principally used their upper limbs while moving; the loading environment changed to more hindlimb dominated locomotion as infants aged. Infants displayed more diversity in their forms of positional behavior than members of any other age-sex class, engaging in behaviors not habitually exhibited by adults. While the most common locomotor mode for infants was torso-orthograde suspensory locomotion, a large shift toward quadrupedal locomotion during infancy occurred at three years of age, when rates of this behavior increased. Overall, the most dramatic transition in positional behavior occurred during juvenility (at approximately five years), with the advent of complete independent locomotion. Juveniles decreased the amount of time they spent clinging and in torso-orthograde suspensory locomotion and increased their time spent sitting and walking and running quadrupedally compared with younger individuals. Juvenility marked the age at which quadrupedal walking became the most frequent locomotor behavior, but quadrupedal walking did not encompass the majority of locomotor time until individuals reached adolescence. Relative to all younger individuals, adolescent chimpanzees (10-13 years) experienced a further increase in the amount of time they walked quadrupedally. Locomotor behavior did not reach adult form until adolescence, closer to the time of epiphyseal fusion than previously thought. These findings provide new data to make predictions about how behavioral transitions influence skeletal change.

Reconstruction of Hip Joint Function in Extant and Fossil Primates

The strepsirhines engage in a variety of locomotor behaviors, including vertical clinging and leaping, active arboreal quadrupedalism and deliberate climbing and suspension. In each of these locomotor modes, hip abduction plays a role in enabling an animal to move in the complex, three-dimensional arboreal realm (Figure 1). For instance, hip abduction characterizes clinging postures prior to leap take-off in galagos, indriids and Lepilemur (Anemone, 1990; Demes et al., 1996; Demes, pers. com.). Abducted hip postures also occur among above-branch quadrupeds such as cheirogaleids and many lemurids who primarily walk, run and leap, but who also climb and engage in hindlimb suspension (Oxnard et al., 1990), both of which require moderate hip abduction. In turn, lorisids, such as the potto, frequently use highly abducted hip postures and even on the ground progress slowly with limbs abducted (Walker, 1969, 1979; Oxnard et al., 1990). Since hip abduction is such an important and variable component of hindlimb locomotion in extant small-bodied primates, the ability to reconstruct this behavior in small-bodied fossil primates should prove useful in determining their overall locomotor profile.

Long bone cross-sectional properties reflect changes in locomotor behavior in developing chimpanzees

OBJECTIVES Recent studies indicate that the locomotor behavior of wild chimpanzees changes during development. Before transitioning to quadrupedal knuckle-walking in adulthood, young chimpanzees engage in a significant amount of upper limb loading suspensory behavior. We investigated whether these dramatic changes in locomotion influence the strength and shape of chimpanzee long bones. MATERIALS AND METHODS We examined changes in chimpanzee arboreal locomotion over the course of development using behavioral data collected on wild chimpanzees. We measured the midshaft geometric properties of femora and humeri of wild-caught individuals housed in museum collections using micro computed tomographic scans. RESULTS Chimpanzees spent less time moving arboreally as they aged. Femoral/humeral strength ratios also increased with age, as predicted by the changing loading environment during development. Additional analyses revealed that femoral shape, but not humeral shape, varied across chimpanzee age classes. Adult femora were more elliptical compared with those of infants. This change in adult femora is consistent with the observation that adult chimpanzees spend most of their time moving terrestrially and consequently experience a less variable loading environment than do infants. DISCUSSION Taken together, these findings contribute to our understanding of how ontogenetic changes in function affect form. As similar changes may have characterized the behavioral and skeletal ontogeny of extinct hominoids including hominins, these findings furnish a potential means to make inferences about the behavior of fossil taxa based on the structural properties of their bones.

Lumbar Vertebral Body Bone Microstructural Scaling in Small to Medium-Sized Strepsirhines

Bone mass, architecture, and tissue mineral density contribute to bone strength. As body mass (BM) increases any one or combination of these properties could change to maintain structural integrity. To better understand the structural origins of vertebral fragility and gain insight into the mechanisms that govern bone adaptation, we conducted an integrative analysis of bone mass and microarchitecture in the last lumbar vertebral body from nine strepsirhine species, ranging in size from 42 g (Microcebus rufus) to 2,440 g (Eulemur macaco). Bone mass and architecture were assessed via µCT for the whole body and spherical volumes of interest (VOI). Allometric equations were estimated and compared with predictions for geometric scaling, assuming axial compression as the dominant loading regime. Bone mass, microarchitectural, and vertebral body geometric variables predominantly scaled isometrically. Among structural variables, the degree of anisotropy (Tb.DA) was the only parameter independent of BM and other trabecular architectural variables. Tb.DA was related to positional behavior. Orthograde primates had higher average Tb.DA (1.60) and more craniocaudally oriented trabeculae while lorisines had the lowest Tb.DA (1.25), as well as variably oriented trabeculae. Finally, lorisines had the highest ratio of trabecular bone volume to cortical shell volume (∼3x) and while there appears to be flexibility in this ratio, the total bone volume (trabecular + cortical) scales isometrically (BM1.23, r2 = 0.93) and appears tightly constrained. The common pattern of isometry in our measurements leaves open the question of how vertebral bodies in strepsirhine species compensate for increased BM. Anat Rec, 2013.

Dentognathic remains of an Afropithecus individual from Kalodirr, Kenya.

We describe here the well-preserved dentognathic remains of an Afropithecus individual from the early Miocene site of Kalodirr in northern Kenya. The specimen includes a nearly complete dentition in which most of the crowns are undamaged and unworn. The new information gleaned from this specimen adds to our knowledge of this genus in several ways. Afropithecus exhibits an atypical pattern of canine dimorphism, and is probably more easily sexed by the pattern of variation in its upper premolars. Both phenomena are likely related to the modification of its antemolar dentition for the purpose of sclerocarp harvesting. The new fossils clarify the role in this adaptation of the premolars, which appear specialized for initiating and propagating cracks in large food items bearing protective coats. Comparison with other Miocene apes suggests that the closest known relative of Afropithecus is Nacholapithecus, to which Equatorius is more distantly related. Morotopithecus shares some primitive traits with Afropithecus, but lacks the derived features shared by the latter and Nacholapithecus.

A New Lorisid Humerus from the Early Miocene of Uganda

An early Miocene (18–20 mya) distal humerus from Napak, Uganda, is the only element of the forelimb to be allocated to African Lorisinae. Its loris-like features distinguish it from other East African material that more closely resembles galagids. Tracing the evolution of the lorisoid body has been a difficult task due to the lack of good fossil material. Here, we add a single specimen to this poor record. This humerus helps to document the beginning of extant lorisid locomotor specialization and function.