Variation of orbital features in adapine skulls

doi:10.1006/jhev.1993.1050

Journal of Human Evolution

Volume 25, Issue 4, October 1993, Pages 287-317

https://doi.org/10.1006/jhev.1993.1050 Get rights and content

Abstract

Variations of orbital features (orbital diameter, frontation, convergence, and interorbital breadth) in Adapis and Leptadapis are compared to those of living primate species. Adapis shows more variation in orbital diameter and orbital frontation than do living primate species, whereas Leptadapis shows greater variation in convergence, and particularly much greater variation in interorbital breadth than do living primates. Variation in orbital features does prove that the samples are heterogeneous, but does not allow separation into specific groups. However, interorbital breadth is the only feature which allows the Leptadapis sample to be separated into two groups which probably represent two distinct Leptadapis lineages.

When allometric effects are taken into account, Leptadapis has relatively larger orbits, weaker frontation and weaker orbital convergence than Adapis . Since these features distinguish different genera, and even different families in living species, these marked differences support the retention of two separate genera for Adapis and Leptadapis. Adapis has an unusually small orbit size for a primate. Since all living primate species have relatively much larger orbits, Adapis is likely to have reduced its orbits from an adapine ancestor. Adapines have less frontation than living lemuriform species (their eyes were oriented more upwardly), but have greater convergence than living lemuroids (lemurids and indriids). This high convergence, an advanced feature, shows that they were very visually oriented animals. Skulls of Adapis (and some Leptadapis) also have smaller interorbital breadths than living lemuroid species.

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Cited by (15)

Primates and Plesiadapiformes from Cos (Eocene; Quercy, France)
2021, Geobios
Citation Excerpt :
Paleontological studies of Quercy fossils are ongoing and still providing new insights on plants, insects, lower vertebrates, birds and mammals. Concerning primates, more recent contributions have focused on well-dated dental material (Godinot, 1984a, 1985, 1988a, 2003), adapine crania from the Old Quercy Collections (Lanèque, 1992, 1993), and postcranials (Dagosto, 1983; Godinot and Dagosto, 1983; Godinot, 1992; Bacon and Godinot, 1998). The systematics of large adapines were revised (Godinot and Couette, 2008) and adapine locomotion continues to be discussed (Boyer et al., 2013; Marigό et al., 2019).
A new fauna has been collected from a fissure filling named Cos in the Quercy region, southwestern France. It includes four primate species and a plesiadapiform. The cercamoniine adapiform Protoadapis andrei Godinot and Vidalenc, nov. sp., is represented by material that adds to our knowledge of the genus Protoadapis for the upper canine, upper molars and other morphological details. It appears more primitive than P. brachyrhynchus from the Old Quercy Collections. The other cercamoniine Pronycticebus cosensis Godinot and Vidalenc, nov. sp., offers insight on intraspecific variations and other details of the genus. Both species suggest a bushy evolution within these genera. Two teeth document the presence of a third cercamoniine, Anchomomys sp. indet. The new microchoerid Quercyloris eloisae Godinot and Vidalenc, nov. gen., nov. sp., has very primitive characters and seems to document a primitive member of the Pseudoloris clade. A poorly documented paromomyid plesiadapiform is distinct enough to be named Arcius moniquae Godinot and Vidalenc, nov. sp. It represents the first discovery of a plesiadapiform in the Quercy fossil record and makes a link with paromomyids surviving until the late Lutetian European Mammal Paleogene MP 13 reference level. The primates indicate a broad age interval between MP 10 (late Ypresian) and MP 12 (mid-Lutetian). The identification of the same species of Pronycticebus and of the new genus in the Vielase fauna suggests more precisely the MP 10–MP 11 (late Ypresian–early Lutetian) time interval.
Systematic and locomotor diversification of the Adapis group (Primates, Adapiformes) in the late Eocene of the Quercy (Southwest France), revealed by humeral remains
2019, Journal of Human Evolution
Citation Excerpt :
Indeed, exchanging “Adapis parisiensis” for “Adapis group” would be better in future phylogenetic analyses using postcranial characters in order to illustrate that A. parisiensis is most probably a compilation of different closely related species or even closely related genera. In fact, that several species of Adapis are recognized through cranial characters has been known for a long time (Stehlin, 1912; Lanèque, 1992, 1993). The primate humeri attributed to Adapis parisiensis in the Quercy collections show a great morphological diversity, with variance in some features of the distal articulation exceeding that found in living species, confirming the hypothesis that several species must be represented within the sample, as has been proposed in previous studies of the femora and tibiae.
Twenty humeral specimens from the old and new Quercy collections attributed to the fossil primates Adapis and Palaeolemur are described and analysed together. We provide a qualitative and quantitative analysis of the different humeri, revealing that high variability is present within the “Adapis group” sample. Six different morphotypes are identified, confirming that what has often been called “Adapis parisiensis” is a mix of different species that present different locomotor adaptations. Such a relatively high level of locomotor diversity is unique in the Paleogene primate fossil record.
The humeral proportions of Adapis overlap with different groups of extant strepsirrhines and platyrrhines depending on the specimen, so the popular view of Adapis as a loris-like slow climbing primate does not apply to the whole sample presented here. Moreover, different humeral features traditionally associated with “Adapis parisiensis”, such as the absence of a zona conoidea and a reduced brachioradialis flange, are variable depending on the sample studied. In addition, results of our analyses show that adapine and omomyid humeral morphology overlap extensively, leading us to question the accuracy of taxonomic attributions based on morphology of isolated humeri at localities where omomyids and adapines of similar size coexist.
Finally, assuming our different morphotypes represent different species within two genera, we propose a phylogenetic hypothesis relating these morphotypes, which inhabited a small geographic area.
Visual influences on primate encephalization
2006, Journal of Human Evolution
Primates differ from most other mammals in having relatively large brains. As a result, numerous comparative studies have attempted to identify the selective variables influencing primate encephalization. However, none have examined the effect of the total amount of visual input on relative brain size. According to Jerison's principle of proper mass, functional areas of the brain devoted primarily to processing visual information should exhibit increases in size when the amount of visual input to those areas increases. As a result, the total amount of visual input to the brain could exert a large influence on encephalization because visual areas comprise a large proportion of total brain mass in primates. The goal of this analysis is to test the expectation of a direct relationship between visual input and encephalization using optic foramen size and optic nerve size as proxies for total visual input. Data were collected for a large comparative sample of primates and carnivorans, and three primary analyses were undertaken. First, the relationship between relative proxies for visual input and relative endocranial volume were examined using partial correlations and phylogenetic comparative methods. Second, to examine the generality of the results derived for extant primates, a parallel series of partial correlation and comparative analyses were undertaken using data for carnivorans. Third, data for various Eocene and Oligocene primates were compared with those for living primates in order to determine whether the fossil taxa demonstrate a similar relationship between relative brain size and visual input. All three analyses confirm the expectations of proper mass and favor the conclusion that the amount of visual input has been a major influence on the evolution of relative brain size in both primates and carnivorans. Furthermore, this study suggests that differences in visual input may partly explain (1) the high encephalization of primates relative to the primitive eutherian condition, (2) the high encephalization of extant anthropoids relative to other primates, and (3) the very low encephalization of Eocene adapiforms.
Taxonomic status of purported primate frontal bones from the Eocene Pondaung Formation of Myanmar
2005, Journal of Human Evolution
Citation Excerpt :
In NMMP 19, interorbital breadth is narrower than postorbital breadth, as is typical of primates with relatively little postorbital constriction (e.g., Smilodectes, Galago, Eulemur, Loris). The opposite condition describes primates having severe postorbital constriction, such as Leptadapis and Adapis (Lanèque, 1993). On this basis, NMMP 19 appears to exhibit relatively minor postorbital constriction, but the endocranial morphology of the specimen complicates this assessment.
Two isolated cranial fragments from the late middle Eocene Pondaung Formation of central Myanmar have previously been interpreted as frontal bones of the amphipithecid primate Amphipithecus mogaungensis. Aside from a few maxillary fragments, these specimens provide the only potential source of information currently available regarding the cranial anatomy of Amphipithecidae. Were this taxonomic attribution correct, these specimens would indicate that amphipithecids retained numerous primitive skull features, including the absence of a postorbital septum, the retention of a voluminous olfactory chamber, and strong separation between the forebrain and the orbital fossa. However, several anatomical details observable on these specimens are incompatible with their attribution to any primate and strongly suggest that they cannot be ascribed to Mammalia. Particularly problematic in this regard are the extreme thickness of the dermal bone, the odd structure of the alleged “frontal trigon,” and the mediolateral orientation and uniquely robust construction of the descending process of the frontal bone (which partially segregates the orbital and temporal fossae). Because these isolated elements can no longer be attributed to Amphipithecus, the anatomical, phylogenetic, and behavioral inferences regarding amphipithecid paleobiology that have been drawn from these specimens can no longer be sustained.
Quantitative morphology of Eocene primates compared to living primates: Examples of current studies
1997, Geobios
Après un bref historique des recherches en morphologie quantitative des primates, deux exemples sontdonnés dans des thématiques en cours d'étude. Chez les Adapis éocènes, la hauteur du museau montre des variations excédant celles des espèces actuelles. Une étude allométrique permet de mettre en évidence deux groupes corcespondant à deux états du caractère, un groupe à museau bas et un groupe à museau modérément élevé. Concernant la main des primates, une première étude de robustesse fait ressortir que les strepsirhiniens ont un métacarpien du pouce plus robuste que les simiiformes, ce qui suggère une différence de fonctionnement entre les deux groupes. En conclusion sont données des orientations de recherches futures.
After a short historical account of the studies in primate quantitative morphology, two examples from our current research are given. The height of the muzzle in Eocene Adapis shows variations which exceed those found in living species. An allometric study allowed the recognition of two groups having two different states for this character, a group with a low muzzle, and a group with a moderately high muzzle. Concerning primate hands, a preliminary study of robusticity shows that the metacarpal of the thumb is more robust in strepsirhines than in simiiforms, which suggests a difference in function. In conclusion we give orientations for future research.
Eocene Paleoecology of Adapis parisiensis (Primate, Adapidae): From Inner Ear to Lifestyle
2017, Anatomical Record

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Regular ArticleVariation of orbital features in adapine skulls

Abstract

Regular Article
Variation of orbital features in adapine skulls