| Anthropoid paranasal sinus anatomy provides a frequently used source of discrete morphological traits for phylogenetic analysis. However, little consensus exists over the polarity of character transformations within catarrhines. For example, ethmofrontal sinuses are thought by some to be a derived condition in African apes and humans, whereas others consider their absence from Sivapithecus and Pongo to be a derived similarity. Such uncertainties stem from two lacunae: (1) an incomplete knowledge of sinus anatomy in undoubted stem catarrhines, and (2) an inadequate documentation of sinus anatomy in New World monkeys, the living sister taxon of the Catarrhini.; In order to fully illuminate the phylogenetic significance of paranasal sinus anatomy in anthropoids, the present study employed computed tomography (CT) to reveal the paranasal anatomy of a large sample of extant platyrrhines, as well as the stem catarrhine Aegyptopithecus. Because the determination of sinus identity and homology requires developmental information, the platyrrhine sample consists of an ontogenetic series for each of ten genera: Cebus, Alouatta, Lagothrix, Cacajao, Aotus, Saimiri, Callicebus, Callimico, Saguinus, and Leontopithecus. Aside from Callimico, each series contained five specimens. These 47 skulls, plus one skull each of Lemur, Loris, and Hylobates were scanned at the High Resolution X-ray CT facility at the University of Texas, Austin. The two faces of Aegyptopithecus were scanned at the Duke University Medical Center.; Among the phylogenetically significant results are the following. Anterior and posterior ethmoid sinuses are a primitive condition in anthropoids, rather than a synapomorphy of African apes and humans as previously thought. The hypertrophy of these sinuses into an inflated ethmoid lateral mass, or labyrinth, is a potential synapomorphy of stem and crown catarrhines. The loss of these sinuses in Pongo and Sivapithecus represents a synapomorphy, as does the loss of all sinuses in cercopithecoids, despite the reacquisition of a maxillary sinus by Macaca. Within platyrrhines, the loss of the posterior ethmoid sinuses and the second ethmoturbinal are potential synapomorphies of an atelid clade comprising Atelinae and Pitheciinae (including Callicebus), but excluding Aotus. |
