Frederick S. Szalay

Locomotor Adaptations as Reflected on the Humerus of Paleogene Primates

Examination of Paleogene distal humeri and a survey of homologous articulations in living primates allows some anatomical correlation with elbow mechanics and the occurrence of these during specific locomotor behaviors in living species. Claw climbing is postulated to be the ancestral primate locomotor mode from which the ancestral euprimate (strepsirhines and haplorhines) evolved a grasp leaping locomotor pattern. This pattern, which depends on a powerful grasp either during climbing or when landing after a jump, is still the most pervasive form of primate locomotion. Morphological evidence of Paleogene humeri suggest that vertical clinging and leaping behavior derived from grasp leaping at least six times independently.

Phylogenetic Relationships and a Classification of the Eutherian Mammalia

It is remarkable that the enormous increase in the fossil evidence, new facts from the study of living mammals, and the promising rise of molecular studies have in fact had less than the usually declared effect in modifying a number of basic ideas on methods of phylogenetic inference which have been in practice since the beginning of this century. Similarly, one finds that many of the early (late 19th and early 20th century) hypotheses of relationships are being “rediscovered” or have remained unfalsified when evidence already known to these workers is rediscovered. Growth in the data base and the increasing number of students addressing themselves to phylogenetic problems nevertheless have resulted in an enormous increase in the literature and many very sound phylogenetic and morphological studies.

Evolution of hallucial grasping in the primates

Abstract Homology of the adaptive solutions of grasping, like other attributes of the postcranial skeleton, have long been assumed for marsupials, early eutherians, and euprimates. Evidence is presented which contradicts this view. The origin of grasping is documented and discussed in the order Primates, the semiorder Euprimates, the suborders Strepsirhini and Haplorhini, and the semisuborder Anthropoidea. Grasping may have been primitive in the cohort Archonta, but the euprimate grasp appears to be related not only to climbing but to a saltatory, graspleaping, locomotor mode of the common ancestor. The origin of anthropoid modifications involves a reduced emphasis on the pedal grasp. The “prehallux” hypothesis for the explanation of the sesamoid in the entocuneiform-hallucial articulation of anthropoids cannot be corroborated by either topographical, developmental, or functional evidence.

Evolution and Diversification of the Archonta in an Arboreal Milieu

This paper attempts to analyze three distinct but closely interrelated biological problems pertinent to the animals included within the Archonta. The tree shrews and relatives (Scandentia), the colugos (Dermoptera), and the archaic primates will be examined, primarily their tarsus, to pose and answer questions about their evolutionary history.

The Mongolian Late Cretaceous Asiatherium, and the early phylogeny and paleobiogeography of Metatheria

ABSTRACT The skull and skeleton of the Mongolian Late Cretaceous (Barungoyotian) marsupial Asiatherium are described, illustrated, and compared to various therian taxa. The study supports the distinctness of Asiatherium from deltatheroidans and eutherians, and the metatherian status (sensu stricto) of asiatheriids, based primarily on the dental formula, but also on cranial, dental, and postcranial characters. Its postcanine dental formula (three premolars and four molars), found only in dentally primitive living marsupials, is shown to be a derived condition within the Theria (tribosphenic mammals, sensu stricto). In addition, the closely twinned hypoconulid and entoconid, correlated with a (relative) hypertrophy of the metacone, an alisphenoid component to the bulla (possibly an independently derived trait), oval (not elliptical) fenestra vestibuli, and an elliptical fenestra cochleae, along with other unmistakenly marsupial-like (and therian as well as pre-therian) postcranial taxonomic properties, all ...

Rodent and Lagomorph Morphotype Adaptations, Origins, and Relationships: Some Postcranial Attributes Analyzed

The literature on postcranials, whether descriptive or analytical, paleontological or neontological, is amazingly scanty for the largest of the mammalian orders, the Rodentia. Although some excellent descriptions can be found on fossils (see especially Wood, 1937, 1962; Emry and Thorington, 1982), and equally important contributions have been made to comparative myology of the postcranium (e. g., Hildebrand, 1978; Woods, this volume, and references therein), this evidence has not been utilized convincingly to attempt an understanding of the origins and relationships, and the early postcranial adaptations of the order. My aim in this paper is to concentrate on these two closely interrelated goals of evolutionary analysis, primarily for the Rodentia, but with some definite observations on the Lagomorpha, sensu lato, as well.

Cranioskeletal Morphology of Archontans, and Diagnoses of Chiroptera, Volitantia, and Archonta

The seemingly intractable problem of the earliest adaptations and the nature of relationships of the mixodectids, microsyopids, plesiadapiforms, tupaiids, euprimates, colugos, and bats has been in the forefront of mammalian system-atics for quite some time. The literature of the past two decades that has specifically focused on parts, or the whole, of this problem is briefly reviewed below, and a number of the specific character evolution hypotheses are examined. After a general neglect of the issues related to the Archonta, perhaps because of Simpson’s (1945) influential views, there has been a resurgence of interest in the 1970s. Many contributions, on a considerably expanded data base, have grappled with the problems of adaptation and phylogenetic relationships. Beard (1989, 1993, this volume) in particular has clearly and firmly stated his several hypotheses of various character polarities, and of the tax-onomic concepts of Primatomorpha and Eudermoptera, all based on carefully analyzed postcranial evidence. In these works he has rejected, more by implication than strong arguments, the Archonta. His hypotheses are important not only because of the greatly increased postcranial evidence that was analyzed in sophisticated functional-adaptive detail, but also because within their confines the recency of relationships of colugos, plesiadapiforms, euprimates, and bats, in that order, was seemingly supported by a number of apparently well-tested synapomorphies.

The foot of Oreopithecus: an evolutionary assessment

A nearly complete composite foot of Oreopithecus bambolii is described and analyzed both mechanically and comparatively. Unlike the probable primitive anthropoid and catarrhine conditions in which the tarsus was considerably elongated, as in monkeys, for efficient leaping, this region is dramatically foreshortened in the Tuscan catarrhine. The phyletic reduction in the length of the tarsus exceeds that seen in the Miocene sample of Proconsul footbones. Although the foot of Oreopithecus is most similar in its inferred mechanical abilities to living chimps, the details of morphology and subtle but distinct morphological solutions to expedite virtually identical function (mechanics) strongly contradicts the hypothesis that the similarities are homologous to the shared pedal similarities observed in the living apes. The known pedal morphology of parapithecids, monkeys and hominoids is discussed in order to place Oreopithecus in a meaningful phylogenetic and functional perspective. Oreopithecus, with its decidedly advanced catarrhine pedal complex for climbing behavior, shows several modifications, namely: general robusticity of the tarsals and metatarsals; an exceptionally short load arm on the lever system of the calcaneus; strong flexor fibularis; pronounced plantar process on the calcaneal tuber; lack of tight upper ankle joint constraints; mediolateral as opposed to dorsoplantar movements favored by the astragalar head. These form-function attributes of the foot are different from those correlated with habitual pedal hanging in Pongo. The small astragalar head and the relatively undeviated long neck in the Asian ape are in revealing contrast to the conditions in Oreopithecus, although the 1958 skeleton, an adult male, was probably as large as a fully developed female orang, in the 30–35 kg, or heavier, size range.

CRANIODENTAL FUNCTIONAL MORPHOLOGY AND TAXONOMY OF DERMOPTERANS

Abstract Craniodental form and function were evaluated in the 2 extant, parapatric species of dermopterans (Dermoptera: Cynocephalidae). The level of morphological distinction between the 2 taxa was such that were they known as fossils; most taxonomists would not contest their genus-level distinction as indicative of adaptive differentiation. In fact, these taxa exemplify the widely employed but implicit morphological distance-based standards used for delineating mammalian genera in the paleontological literature. Appropriate names for these 2 taxa are Cynocephalus volans for the Philippine flying lemur and Galeopterus variegatus for the heterogeneous populations of the Sundaic flying lemurs. Cynocephalus probably has a hypertrophied version of the ancestral cynocephalid molar complex and modified incisor and canine morphology. The hypertrophied metaconules of cynocephalids occlude with an expanded paracristid and a cusplike shelf, the distocuspid. Cynocephalus also has a broader rostrum, a greater degree of postorbital constriction, and enhanced ectocranial ridges associated with a more robust masticatory musculature than Galeopterus. Cynocephalus appears adapted to a diet that requires a greater degree of shearing by the anterior dentition and crushing by the molariform dentition. These anterior shearing teeth (I3, C1, P3, c1, p3) are larger and more bladelike than those of Galeopterus, and the bite force is more anteriorly directed. Angle of the mandible is ventrally expanded in Cynocephalus, facilitating enhanced chewing force for the postcanine dentition while maintaining orientation of the temporalis muscle. Dwarfed forms of Galeopterus are found on many of the smaller islands of the Sunda Shelf and in central Laos. They are not morphologically distinguishable from larger members of this species, other than in size, and do not warrant specific distinction. However, it may be desirable to designate 4 subspecies of G. variegatus: G. v. variegatus from Java, G. v. temminckii from Sumatra, G. v. borneanus from Borneo, and G. v. peninsulae from the Malay Peninsula and mainland Southeast Asia. Separate species rank for each of the dwarfed populations should not be recognized. Phylogenetic relationships of Dermoptera are discussed in light of the morphological differences of the 2 genera.

The Tarsal Complex of Afro-Malagasy Tenrecoidea: A Search for Phylogenetically Meaningful Characters

Morphological characters should be assessed in an ecological and evolutionary framework before their use in phylogenetic analyses. We have attempted such an assessment for the tarsal complex of the Tenrecoidea. The 30+/− extant species of these small mammals live in a diverse range of microhabitats. They exhibit markedly different positional behaviors, encompassing four basic locomotor repertoires: terrestrial running and walking, scansorial climbing, digging, and swimming. Articular surfaces from the upper, middle, and lower ankle joints in 10 Malagasy tenrecid, 1 potamogalid, 1 solenodontid, and 1 macroscelidid species were compared. The results were tested against published data on the correlation between function and morphology in other therian locomotor specialists. Descriptive accounts, supported by quantitative analyses, demonstrate significant differences in many aspects of tarsal morphology that may be explained by function-based hypotheses within the context of the tenrecoid heritage. Three closely related tenrecines (Hemicentetes, Setifer, and Echinops) show divergences in form that are consistent with their respective semifossorial, terrestrial, and scansorial/arboreal modes of locomotion. In addition to functional–adaptive considerations, we propose several synapomorphies for the tenrecine and oryzorictine clades that appear to corroborate their monophyly. There are apparent convergences between the habitual diggers from different subfamilies (Hemicentetes and Oryzorictes), and there are adaptive differences within subfamilies (e.g. arboreal Echinops vs. terrestrial Setifer). The few likenesses between Potamogale and Limnogale cannot be supported as homologies, and the proposal of a recent phylogenetic affiliation between them is therefore rejected here. Manifest differences in tarsal form between Geogale and the oryzorictines support recognition of the subfamily Geogalinae. As expected, the tarsal complex of Solenodon is fundamentally unlike that of the tenrecoids. Finally, the similarities in detail between Macroscelididae and Potamogalidae reflect the stabilization of UAJ during plantarflexion, and therefore such attributes are rejected as synapomorphies. Traits with clear species-specific adaptations are a potential interference in cladistic analyses and cannot be meaningfully used without ecology-based character assessment. While this practice may ultimately reduce the size of a database, it will nonetheless result in taxonomic properties with lasting value against which phylogenetic hypotheses may be tested with confidence.