Primate Taxonomy And The Study Of Euprimate Origins

How does this debate over where to draw the primate-nonprimate boundary relate to the study of primate origins? For most workers a key issue is the identification of those taxa that are important to elucidating the evolutionary relationships of unquestionable Primates (i.e., Euprimates), independent of taxonomy. That is, we need to understand which forms have features that tell us something about the common ancestor of Euprimates, and which more primitive taxa might give us clues about the order in which euprimate features were added through time. Those key taxa are not adapids, omomyids, or other fossil forms whose inclusion in Primates is not debated, no matter which definition is employed. Adapids and omomyids exhibit many features of the cranium, postcranium, and dentition (Silcox, 2001; Szalay et al., 1987; characters listed at "N" on Figure 5) that clearly demonstrate that they have already markedly diverged from the primitive archontan stock. As such, these taxa already postdate all the evolutionary events of interest—that is, the points at which euprimate features were added to some ancestral non-euprimate stock. It is necessary to go at least a node down to study euprimate origins, to forms that give us information on the order, pattern, and adaptive context in which euprimate characters were acquired—that is, to the "protoeupri-mates" indicated on Figure 5. According to my results, these "protoeuprimate" positions are occupied by plesiadapiforms. Therefore, no matter what you call them, plesiadapiforms are the key taxa to this question. Whether you call them primates, proprimates, primatomorphs or something else is irrelevant to that fact.

'Protoeuprimate 2" "Protoeuprimate 1" Euprimates

'Protoeuprimate 2" "Protoeuprimate 1" Euprimates

Figure 5. Hypothetical cladogram indicating the stepwise acquisition of distinctive euprimate features (present at N) through intermediates that possess only some of these traits ("protoeuprimates"). The author's analysis would place plesiadapiforms in the "protoeuprimate" positions, implying that it is these animals that will tell us about the order in which euprimate traits were acquired. Figure modified from a slide shown by D. Gebo at the Anthropoid Origins conference (April, 2001).

Characters at N = petrosal bulla, postorbital bar, reduced snout, nails, postcranial features for leaping arborealism, low-crowned molars with bunodont cusps and broad talonid basins, etc.

Figure 5. Hypothetical cladogram indicating the stepwise acquisition of distinctive euprimate features (present at N) through intermediates that possess only some of these traits ("protoeuprimates"). The author's analysis would place plesiadapiforms in the "protoeuprimate" positions, implying that it is these animals that will tell us about the order in which euprimate traits were acquired. Figure modified from a slide shown by D. Gebo at the Anthropoid Origins conference (April, 2001).

Having said that, one of the inevitable facts about taxonomy is that it directs the way that we formulate questions about evolution. If plesiadapiforms are excluded from the order Primates, studies aiming to consider primate origins may omit them (e.g., Soligo and Martin, in press). This is particularly true if they are relegated to some meaningless wastebasket taxon, which carries with it the implication that they are fundamentally unimportant. This assertion is based in part on my observation that, with the wide popularity of the view that plesi-adapiforms and dermopterans are sister taxa, there is a general feeling that plesi-adapiforms can be safely ignored by anthropologists. This is in spite of the fact that one of the major proponents of this view, Beard, published a cladogram that supported a closer relationships between plesiadapiforms + dermopterans and Primates than between Primates and any other taxon (Beard, 1993a).

A decision on the question of whether or not to include plesiadapiforms in Primates has real practical implications in terms of the way in which we ask questions about euprimate origins. Although it is not absolutely necessary to recognize with taxonomy the fact that plesiadapiforms are the key taxa to the study of euprimate origins, from a practical viewpoint their classification as primates ensures the appropriate focus when asking questions about the origins of the group of central interest to most.

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  • maria
    What ancestor is euprimate?
    8 years ago

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