The anatomical observations published elsewhere (Rossie, 2005, 2006) are distilled here into seven sinus characters. Many of the more interesting anatomical discoveries made in these works are not represented here because they constitute autapomorphies of a single genus (e.g., the sphenoidal fossae of Leontopithecus). The product may seem an almost insignificant number of characters, but it is my intention to produce character data of high quality, not quantity, having been subjected to thorough “pre-congruence” homology testing (Rieppel and Kearney, 2002).
To preserve the distinction between my primary hypotheses of homology and my final postcongruence assessment, I will present the former now, before proceeding to the congruence test. It is at this juncture that one must translate their primary hypotheses of homology into a character matrix amenable to the congruence test. To characterize the decisions made in character delineation and coding in a cladistic analysis as nontrivial would be a gross understatement (Pleijel, 1995; Wilkinson, 1995; Hawkins et al., 1997; Strong and Lipscomb, 1999; Wiens, 2001; Rieppel and Kearney, 2002). Decisions made during this process essentially determine the outcome of the analysis (Cartmill, 1982). As Stevens (1984) stressed, one of the most important properties of a homology is the taxonomic level at which it constitutes a synapomorphy. This level is a property of taxonomic distribution that can emerge only once the characters are mapped onto a phylogeny, but it is constrained by the manner in which character states are delineated. If anatomies are excessively atomized, they have no chance of emerging as high-level synapomorphies. For this reason, I see no justification for proliferating states for a given character on the basis of variations in shape or size that have no apparent relationship with the underlying developmental processes responsible for their genesis. Such a practice would not only produce the mistaken impression of synapomorphies at lower taxonomic levels (or worse, only autapomorphies), it would also prevent the detection of the real higher-level synapomorphy.
How can this be avoided? Ideally, the criterion for delimiting character states would be Wagner's (1989a, b) criterion for identifying “individualized” structures or potential homologs, which are, after all, character states. On this basis, most sinuses would be coded as simply present or absent, although the various forms of the cupular sinus would warrant some subdivision, not simply because they differ in their final adult form, but rather because they appear to be produced by a second set of diverticula that, although in direct continuity with the cupular sinus proper, possesses a morphogenetic potential of their own. A similar argument would be made for the anterior ethmoid sinuses, which can be expressed as lamellar cells or as frontal sinuses or both. According to the developmental data described elsewhere (Rossie, 2003, 2006), I would recognize the following fully individualized potential homologs or character states. Brief definitions of the structures are provided here (see Rossie, 2006 for more detailed discussion):
lateral recess (not recessus lateralis);
The recessus lateralis
is an internal concavity of the lateral wall of the fetal nasal capsule. It is a product of the pars intermedia
being overlapped posteriorly by the pars posterior
and anteriorly by the pars anterior.
When this recess (or the cartilaginous elements that circumscribe it) ossifies without the occurrence of any secondary pneumatization, the resulting concavity in the middle meatus is called a lateral recess (Maier, 2000
; Rossie, 2006
). The misuse of this term in the literature lead Rae and Koppe (2003) to advocate its abandonment, but as defined here and elsewhere (Rossie, 2003
), it remains a useful term if applied consistently.
A maxillary sinus is an excavation of the bones surrounding the recessus lateralis
produced by secondary pneumatization. It therefore opens into the nasal cavity via an ostium in the middle meatus (Cave, 1967
; Maier, 2000
; Rossie, 2006
cupular recess (not recessus cupularis);
Like the lateral recess, the cupular recess is produced by ossification of the cartilaginous recessus cupularis
). The latter structure is the posterior portion of the nasal capsule, consisting of the pars posterior
or lamina antorbitalis
, and is floored by the lamina transversalisposterior
cupular sinus (a.k.a. sphenoid sinus);
The cupular sinus is an excavation of the bones surrounding the recessus cupularis
produced by secondary pneumatization. In humans and some apes it pneumatizes mainly the sphenoid bone, and opens into the nasal cavity via ostia in the anterior portion of the sphenoid bone (Cave & Haines, 1940
). For this reason it has been termed the sphenoid sinus in most literature. However, in other primates its ostia may be found in the ethmoid or frontal bone simply because these are the membranous bones that happen to overgrow the underlying cartilaginous recess (Rossie, 2006
). This illustrates the danger in using the site of the ostium as the ultimate guide to sinus homology, since it is only a proxy for the identification of the cartilaginous recess from which pneumatization emanates. Accordingly, I find it more informative to name the sinus after the true arbiter of homology—the recess.
These are bilateral diverticula that develop from the roof of the cupular sinus and invade the supraorbital portion of the frontal bone in some primates (Hershkovitz, 1977
; Rossie, 2006
). Their development begins late, after pneumatization of the sphenoid body (Rossie, 2006
anterior ethmoid sinuses;
The superior portion of the recessus lateralis
is termed the recessus frontalis
). In some primates (e.g, African apes, Aotus
), sinuses develop from this space and invade mainly the ethmoid bone (Cave & Haines, 1940
; Rossie, 2006
). These sinuses are separated from the posterior ethmoid sinuses by the base of the first ethmoturbinal, which is the ossification of the anterior edge of the pars posterior
(Moss-Salentijn, 1991; Rossie, 2006
). In other words, the anterior ethmoid sinuses develop from within the recessus lateralis
, whereas the posterior ethmoid sinuses do not.
In some primates (e.g., Saguinus
, African apes and humans), one or more of the anterior ethmoid sinuses expands superiorly to invade the interorbital and supraorbital portions of the frontal bone (Cave & Haines, 1940
; Rossie, 2006
). This is called a frontal sinus (Paulli, 1900). This expansion occurs late in postnatal development, after the ethmoid sinuses are nearly full-sized (Cave & Haines, 1940).
posterior ethmoid sinuses;
These small sinuses develop from the spaces between the 1st
, and 3rd
ethmoturbinals on the lateral wall of the pars posterior
(Moss-Salentijn, 1991; Rossie, 2006
). The homology and individualization of ethmoid sinuses is a complex problem that is discussed in greater detail elsewhere (Rossie, 2006
These character states are conditions that, if found in two taxa, would be assumed homologous unless refuted by the congruence test. To summarize the “precongruence” hypotheses of homology between platyrrhines and catarrhines that were articulated in the work of Rossie (2006), I assume that these eight features are homologous among all anthropoids in which they are found because no aspect of their ontogeny has been found that contradicts this. Note that this list of homologs will not correspond in number with the character states that are ultimately constructed to portray them (see below), which will include several states that represent the absence of these structures.
Conspicuously absent from this list of characters is the ethmoid labyrinth. The proliferation and hypertrophy of anterior and posterior ethmoid sinuses that produces the catarrhine ethmoid labyrinth is difficult to portray in terms of an individualized character, being a modification of two separate characters (anterior and posterior ethmoid sinuses), and may best be considered an emergent property. However, its distribution within catarrhines is still of interest and will be investigated, particularly because of its occurrence in Proconsul, and possibly Aegyptopithecus (Rossie et al., 2002; Rossie, 2005).
Before one can proceed to the congruence test, these primary hypotheses of homology must be translated into a character matrix, and here one encounters a problem. Some of the characters above are mutually exclusive (e.g., maxillary sinus, lateral recess) and are easily portrayed as alternative states of a character, but others are logically dependant upon one another (e.g., cupular sinus, cupulofrontal sinus). The methods for coding logically dependent characters are a source of considerable debate at present (see Maddison, 1993; Pleijel, 1995; Wilkinson, 1995; Hawkins et al., 1997; Lee and Bryant, 1999; Strong and Lipscomb, 1999), and there appears to be little consensus beyond the conclusion that none actually solve the problem, and different methods are justifiable for different purposes. There are basically two justifiable methods, which will be summarized here.
In the first, dubbed “composite coding” (Wilkinson, 1995), all dependent conditions are coded as states of one compound character (Maddison, 1993). In Maddison's (1993) example of tail presence and tail color, tail colors are coded as part of states of the character “tails” in which “tail absent” is also a state. In the case of the cupular sinus, there would be one character with the states: 0, absent; 1, present; 2, present with cupulofrontal extension. The advantage of this method is that every taxon can be scored for one of these three states, so there will be no missing or inapplicable data. This is not the case in the second method, “reductive coding” (Wilkinson, 1995), in which the character would be divided into two characters:
Cupular sinus: 0, absent: 1, present.
Cupulofrontal sinus: 0, absent; 1, present.
The advantage of such a division is to preserve the transformational independence of the cupulofrontal extensions and the cupular sinus so that each can be a synapomorphy at a different taxonomic level (e.g., Wilkinson, 1995; Lee and Bryant, 1999). In other words, composite coding robs the character data of one of its potential synapomorphies, and reductive coding restores it. In essence, the homology of the cupular sinus itself becomes ambiguous in the composite character (Lee and Bryant, 1999). In Maddison's (1993) example, the presence of a tail is no longer a synapomorphy of a clade if that clade includes taxa with different tail colors because the two will be coded with different states (e.g., tail present and blue, tail present and red). Maddison (1993) has proposed that the full phylogenetic signal could be recovered by either differential weighting or ordering of states in the composite character, but these procedures are not always justifiable (Lee and Bryant, 1999), and in the present case they are not even desirable. For these reasons, I will follow Hawkins et al. (1997) in scoring the independent part (e.g., cupular sinus) as present or absent and the logically dependent conditions (e.g., cupulofrontal extensions) as states of a separate character.
The only drawback to this reductive coding method is that taxa that lack a cupular sinus must also be coded for the presence or absence of a cupulofrontal extension—the “inapplicable data” problem alluded to earlier. There are three options here: they can be coded as “absent,” “?,” or “9.” To code them as “absent” produces a potential synapomorphy that has no evidentiary basis (Maddison, 1993). That is, the absence of cupulofrontal extensions is not observable in the taxa that lack cupular sinuses. Coding them as “?” is problematic because current parsimony algorithms read this as uncertainty, not inapplicability, and will infer a state for them based on the states of other taxa (Maddison, 1993). Maddison (1993) described two problems that can result from such coding. The first problem, assignment of impossible states to ancestral nodes, only occurs when the entity (tail in his case) evolves convergently in two separate clades. This happens because the tailless stem taxa of each clade are coded as “?” for tail color and are reconstructed by PAUP or MacClade according to the distribution of the tail colors in the tailed clades. This results in stem taxa being coded as lacking a tail, but as having a tail color.
However, if the tailless taxa are instead coded as “9” for tail color (e.g., Novacek, 1992) the ancestral nodes would be reconstructed as “9” for tail color, which the investigator knows to mean “inapplicable data.” The only remaining problem is that “9” could become a potential synapomorphy of false clades, but as Maddison notes this will not be the case if the “9”s are confined to paraphyletic or monophyletic groups, in which case they will only falsely bolster true clades. Because the essential problem is intractable with currently available algorithms (Hawkins et al., 1997), this solution seems the lesser of several evils.
Character optimization was performed by comparing the length of competing trees using MacClade version 4.03 (Maddison and Maddison, 2001). The platyrrhine data were traced on trees composed of only the 10 genera for which data was collected. While this precludes analysis of a few lower-level relationships, it is an honest portrayal of the data at hand. In the absence of first-hand data on the six missing genera, nothing can be said about relationships among Alouatta, Lagothrix, Ateles, and Brachyteles, which are viewed differently by various researchers (e.g., Kay, 1990; Rosenberger, 1992). Similarly, relationships among Callimico, Saguinus, and Leontopithecus can be assessed, but the position of Callithrix and Cebuella relative to them cannot. Not all previously proposed platyrrhine phylogenies were evaluated here. Instead, a subset was chosen to represent the alternative placements of taxa currently entertained by systematists (Figs. 1 and 2). The trees of Ford (1986), Horovitz (1999), Schneider et al. (1996), von Dornum and Ruvolo (1999), Rosenberger (1992, 2002), and MacPhee and Horovitz (2002) were pruned of the six genera not included here, and the cladogram of Kay (1990) was modified in an attempt to reflect his more recent view of the position of Callicebus (Kay, 1994; Meldrum and Kay, 1997). Some of these trees include polytomies involving the genus Aotus. In these cases, the polytomies were treated as “hard” so that tree length would not be underestimated (Maddison and Maddison, 1992).
Figure 2. Four of the eight hypotheses of platyrrhine phylogeny used for character optimization: (a) MacPhee and Horovitz (2002), (b) von Dornum and Ruvolo (1999), (c) Schneider et al. (1996), (d) Horovitz (1999).
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The only fossil catarrhines that were included in the character optimization were those that preserve more than maxillary sinus morphology. This excluded all of the East African small-bodied “apes,” as well as several other phylogenetically significant genera such as Equatorius, Kenyapithecus, Nacholapithecus, Rangwapithecus, and Nyanzapithecus. The conclusions drawn here may require revision when better material is known for these taxa. There are no published phylogenetic hypotheses available that encompass all of the catarrhine taxa included here. As a result, character optimization was performed on a set of three cladograms that are based largely on that of Begun et al. (1997), later modified by Begun (2002) to include Ankarapithecus (Fig. 3a). For the purpose of this baseline phylogeny, cercopithecoids were placed in a conservative position between Aegyptopithecus and Proconsul. Proconsul, Afropithecus, and Morotopithecus are placed as stem hominoids because they lack many of the postcranial synapomorphies of crown hominoids, particularly in the shoulder joint and thorax (Harrison, 1982, 1987, 2002; Ward et al., 1993; Pilbeam, 1996; Gebo et al., 1997; Walker, 1997; Ward, 1997a). Morotopithecus is placed above Afropithecus because of orthograde features in its lumbar vertebra and scapula (Gebo et al., 1997). Aegyptopithecus is placed as the sister taxon to crown catarrhines because of its retention of an entepicondylar foramen and an annular ectotympanic (Fleagle, 1984; Harrison, 1987).
Figure 3. Three hypotheses of catarrhine phylogeny used for character optimization: (a) “Begun” tree, (b) “Andrews” tree, (c) “Harrison” tree. See text for explanations of topology.
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This baseline tree was then modified to reflect the views of Harrison (e.g., 1987, 2002) and Andrews (1992, 1996; Andrews and Bernor, 1999) so that they could also be evaluated (Fig. 3b,c). Unfortunately, this requires certain inferences that may not reflect the precise views of those authors. For example, Ankarapithecus was not discussed by Andrews (1992, 1996) in his most inclusive systematic reviews, but was considered a sister taxon or junior synonym of Sivapithecus elsewhere (Andrews and Tekkaya, 1980; Andrews and Bernor, 1999). The “Andrews” tree also requires inferential placement of Oreopithecus, from which Andrews sensibly abstains from in his recent work. Because he recently referred it to “Hominidae indet” (Andrews, 1992), it seems safe to place it as a stem hominid above his Afropithecini (or Afropithecinae in Andrews, 1996) on the basis of its postcranial anatomy. It is not positioned as a sister to Dryopithecus because he specifically rejects such a scenario (Andrews, 1992). Construction of the “Harrison” tree requires only inference in the placement of Ankarapithecus, because all other taxa are included in either Harrison (2002) or Harrison and Rook (1997). Here again, it is placed as a stem pongine following Begun (2002).