Extant Prosimians Research Articles

Oldest evidence for grooming claws in euprimates

Euprimates are unusual among mammals in having fingers and toes with flat nails. While it seems clear that the ancestral stock from which euprimates evolved had claw-bearing digits, the available fossil record has not yet contributed a detailed understanding of the transition from claws to nails. This study helps clarify the evolutionary history of the second pedal digit with fossils representing the distal phalanx of digit two (dpII), and has broader implications for other digits. Among extant primates, the keratinized structure on the pedal dpII widely varies in form. Extant strepsirrhines and tarsiers have narrow, distally tapering, dorsally inclined nails (termed a ‘grooming claws’ for their use in autogrooming), while extant anthropoids have more typical nails that are wider and lack distal tapering or dorsal inclination. At least two fossil primate species thought to be stem members of the Strepsirrhini appear to have had grooming claws, yet reconstructions of the ancestral euprimate condition based on direct evidence from the fossil record are ambiguous due to inadequate fossil evidence for the earliest haplorhines. Seven recently discovered, isolated distal phalanges from four early Eocene localities in Wyoming (USA) closely resemble those of the pedal dpII in extant prosimians. On the basis of faunal associations, size, and morphology, these specimens are recognized as the grooming phalanges of five genera of haplorhine primates, including one of the oldest known euprimates (∼56 Ma), Teilhardina brandti. Both the phylogenetic distribution and antiquity of primate grooming phalanges now strongly suggest that ancestral euprimates had grooming claws, that these structures were modified from a primitive claw rather than a flat nail, and that the evolutionary loss of ‘grooming claws’ represents an apomorphy for crown anthropoids.

Reconstructing Locomotor Behaviors: Cross‐sectional Property Analysis Brings More to the Story of How Earliest Euprimates Moved

As a group, modern primates demonstrate an impressive degree of ecological and behavioral flexibility. It is likely that the earliest euprimates were similarly diverse in how they moved through their environments. Attempts to reconstruct the locomotor behaviors of Eocene primates have relied heavily on comparing the external morphologies of fossilized limb bones with those of extant taxa. Though broadly informative, the application of this method may be limited by the phylogenetic constraints associated with bone length and articular surface size and shape. Alternatively, the internal structure of a long bone's diaphysis is functionally plastic during life, responding to changes in loading behaviors. Therefore, diaphyseal cross‐sectional shape analyses may provide a more accurate account of how that individual actually moved. We apply this technique to a sample of ~54.5 million year old euprimates from Vastan Lignite Mine, India. This sample of fossils falls within 2 clades of Eocene euprimates, Omomyidae and Adapoidea, and represents at least 3 described genera.Our unpaired fossil sample of 6 femora (2 Asiadapis, 2 Marcgodinotius, 2 Vastanomys) and 4 humeri (2 probable Marcgodinotius, 2 unidentified euprimates) was compared with 20 species of extant prosimians (< 1 kilogram), spanning 3 locomotor classifications (leapers, slow climbers, and non‐specialists). Vastan specimens were scanned using a Nikon XT H 225 ST micro x‐ray computed tomography (CT) scanner. From these scans, diaphyseal cross‐sectional geometric properties were calculated at 50% of femoral length and 40% of humeral length (from distal end) using MomentMacro for ImageJ, which calculates polar second moment of area (J), second moments of area about the coronal (Ix) and sagittal (Iy) planes, cortical area (CA), and total subperiosteal area (TA). Each fossil was compared to the distributions of the prosimian locomotor groups for each of the cross‐sectional properties, as well as bone length and proximal articular surface areas (estimated from linear measurements).Results of structural analyses include an unusual mosaic of locomotor indicators. The relative thickness of bone cortices (CA/TA) is high in all humeri, which is best matched among modern slow climbers. Humeri are moderately long relative to humeral head articular surface area, similar to extant slow climbers and non‐specialists. Cross‐sectional shape (Ix/Iy) of femora is variable, with the adapoids (Asiadapis and Marcgodinotius) mostly grouping with leapers and non‐specialists, while the omomyids (Vastanomys) group with slow climbers, in contrast to inferences based on some other aspects of femoral articular morphology. Femoral length relative to bending rigidity (J) or femoral head surface area is moderate to high, primarily overlapping with extant leapers and non‐specialists. These results illustrate a combination of features not found in modern prosimians and may demonstrate a unique generalist regime of movement in our earliest antecedents.Support or Funding InformationNational Geographic and Leakey FoundationThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Comparative functional morphology of the primate peroneal process

The first metatarsal of living Primates is characterized by a well-developed peroneal process, which appears proportionally larger in prosimians than in anthropoids. A large peroneal process has been hypothesized to: 1) reflect powerful hallucal grasping, 2) act as a buttress to reduce strain from loads acting on the entocuneiform-first metatarsal joint during landing and grasping after a leap, and/or 3) correlate with differences in physiological abduction of the hallux. In this study, we address the latter two hypotheses by comparing the morphology of the peroneal process in 143 specimens representing 37 species of extant prosimians, platyrrhine anthropoids, and tupaiids (tree shrews) that engage in different locomotor behaviors. In particular, we compare taxa that vary in leaping frequency and hallucal abduction. Linear and angular measurements on the first metatarsal were obtained to evaluate differences in relative peroneal process thickness and length, first metatarsal abduction angle, and overall first metatarsal shape. Leaping frequency was significantly correlated only with relative peroneal process thickness within extant lorisoids. Relative process length was positively correlated with the angle of hallucal abduction within prosimians; this angle is significantly greater in prosimians than anthropoids. Multivariate analyses of metatarsal shape effectively separate species along phylogenetic lines, but not by locomotor behaviors. The hypothesis that the peroneal process on the first metatarsal reduces the loads on the entocuneiform-first metatarsal joint during landing after a leap is in part supported by data from extant lorisoids (i.e., slow quadrupedal lorises vs. leaping galagos). A peroneal process of greater length within prosimians may serve to increase the lever arm for the peroneus longus muscle in order to prevent hyper-abduction, followed by inversion in locomotor situations where the animal's weight is born on a highly divergent/abducted hallux.

New early Eocene anaptomorphine primate (Omomyidae) from the Washakie Basin, Wyoming, with comments on the phylogeny and paleobiology of anaptomorphines

Recent paleontological collecting in the Washakie Basin, southcentral Wyoming, has resulted in the recovery of over 100 specimens of omomyid primates from the lower Eocene Wasatch Formation. Much of what is known about anaptomorphine omomyids is based upon work in the Bighorn and Wind River Basins of Wyoming. This new sample documents greater taxonomic diversity of omomyids during the early Eocene and contributes to our understanding of the phylogeny and adaptations of some of these earliest North American primates. A new middle Wasatchian (Lysitean) anaptomorphine, Anemorhysis savagei, n. sp., is structurally intermediate between Teilhardina americana and other species of Anemorhysis and may be a sister group of other Anemorhysis and Trogolemur. Body size estimates for Anemorhysis, Tetonoides, Trogolemur, and Teilhardina americana indicate that these animals were extremely small, probably less than 50 grams. Analysis of relative shearing potential of lower molars of these taxa indicates that some were primarily insectivorous, some primarily frugivorous, and some may have been more mixed feeders. Anaptomorphines did not develop the extremes of molar specialization for frugivory or insectivory seen in extant prosimians. Incisor enlargement does not appear to be associated with specialization in either fruits or insects but may have been an adaptation for specialized grooming or food manipulation.

Long bone cross-sectional dimensions, locomotor adaptations and body size in prosimian primates

The cross-sectional geometry of primate long bones appears to be closely related to body size and locomotor behavior. This study investigates this aspect of skeletal design in the humerus and femur of living prosimian primates, a group characterized by a diversity of locomotor modes and a wide range of body sizes. The geometrical variables were collected from biplanar radiographs using formulae for hollow ellipses to approximate cortical area, wall thickness, second and polar moments of area, and section modulus. Indices of strength in static compression and bending were also derived from these data, limb length and body mass. For prosimians as a group, all cross-sectional geometrical properties scale in a positive allometric fashion with body mass (although some of the humeral values have confidence limits that include isometry). Despite positive allometry, measures of strength in static loading decrease as a function of body size and imply that alterations in body posture and locomotion are necessary in order to maintain stress/strain similarity. Within prosimians, leapers tend to have more robust femora (with elongated anteroposterior axes) than non-saltatory species of the same size; no such distinctions exist for the humerus (but Daubentonia exhibits an unusually strong humerus). Slow climbing lorisines, although exposed to only moderate locomotor forces, are not at the low end of absolute and relative bone strength variation. Prosimians less than 1·2 kg exhibit considerable variation in cross-sectional geometry, a finding that could complicate attempts to use such data to reconstruct body size in small-bodied fossil prosimians. Measures of wall thickness (K-values) appear to be of limited utility in the functional analysis of skeletal design in extant prosimians. Compound indices of relative strength—although useful in functional allometric analyses—do not reliably differentiate among either locomotor or taxonomic groups. Functional differences among taxa are more obvious in geometrical properties when body size is used as a covariate.

Locomotor diversity in prosimian primates.

An understanding of prosimian movement is basic to many anatomical and paleontological studies in that these studies attempt to correlate movement with anatomy and therefore infer movement in fossil primates. Duke University has a large and diverse collection of prosimian primates, which are housed in cages and enclosures large enough for movement studies. Extant prosimians move in many different ways, and none are so specialized that only one mode of travel is used. The most general locomotor patterns are observed for the cheirogaleids, and thus theirs may best resemble the locomotor patterns of the ancestral euprimate.

Dentition ofSivaladapis nagrii (Adapidae) from the late Miocene of India

Two genera and three species of adapid primates are known from the middle and late Miocene of India and Pakistan. Most fossil specimens are fragmentary, but the best-known species, Sivaladapis nagrii,is now represented by enough specimens to permit composite reconstruction of much of the dentition. The incisors of Sivaladapishave spatulate crowns, and the canines are large, projecting teeth. Premolars and molars exhibit complex occlusion involving simultaneous approximation of pointed leading cusps on upper and lower molars, with linear trailing lophs. The premolar eruption sequence in Sivaladapisappears to be P2-P4-P3, as in most extant prosimians. Symphyseal fusion of the mandibular rami occurred early in ontogeny, before the eruption of any of the anterior permanent teeth. We interpret Sivaladapisto have been a specialized arboreal folivore that became extinct near the end of the Miocene, when the distribution of forests was increasingly restricted and colobine monkeys first invaded South Asia.

The functional significance of skeletal allometry in Megaladapis in comparison to living prosimians

AbstractSlow vertical climbing and clinging are the dominant positional behaviors of the most convincing reconstruction of the primary spatial niche of Megaladapis, a giant extinct prosimian from Madagascar. The vertical support model of Cartmill ('74) predicts that clawless mammals should exhibit relatively elongated forelimbs in expanded size ranges. The allometric corollaries of this model are tested on closely related interspecific samples of Megaladapis and selected extant prosimians. Megaladapis and indriids (vertical leapers and clingers) conform to the structural predictions of the model, and are clearly distinguished from the more pronograde lemurids and cheirogaleids. Extreme hindlimb reduction (negative allometry) is coupled with moderate forelimb elongation (positive allometry) in Megaladapis. These body proportions effectively optimize pedal friction during vertical climbing and minimize the moment of body weight pulling the animal away from the trunk. Positive forelimb allometry occurs in the indriids, while isometry obtains for the hindlimb. The adaptive significance of these morphological strategies are discussed, as are possible selective mechanisms which effect the extreme hindlimb reduction in Megaladapis. Body weight estimates are also presented for Megaladapis edwardsi and Megaladapis grandidieri (50–100 kg and 40–75 kg, respectively).