The applications and limitations of ontogenetic comparisons for phylogeny reconstruction: the case of the strepsirhine internal carotid artery
Ontogeny and phylogeny together determine organismal form and consequently, the two should be reciprocally illuminating. Ontogeny contributes valuable information for phylogenetic studies, not because it is a window into phylogeny, but because ontogenetic comparisons provide data that is easily incorporated into the framework of systematic investigation. Ontogenetic data allow independent tests of character homology and polarity, increase knowledge of character complexity, and can also provide new characters for phylogenetic analysis. Cheriogaleid and lorisiform primates share a unique condition of the internal carotid artery. A large medial branch of the internal carotid, the ascending pharyngeal artery, bypasses the bulla to enter the cranial cavity through the foramen lacerum. This character has been defined by primate systematists as the primary synapomorphy of a cheirogaleid-lorisiform clade. To test the hypotheses of homology and polarity, the development of the internal carotid artery in a cheirogaleid, Microcebus murinus, was compared with that of a lorisiform, Galago senegalensis senegalensis. The comparison revealed that the ontogeny of this character is nearly identical in these two strepsirhine primates, thus supporting the hypothesis of homology. Also, a new character was identified that, if interpreted as derived, adds further support to the hypothesis that cheirogaleids and lorisiforms constitute a monophyletic clade. The same developmental sequences do not contribute to the determination of polarity for the ascending pharyngeal artery. Consequently, this study cannot distinguish between hypotheses of synapomorphy or symplesiomorphy. Outgroup comparisons, however, strongly support the hypothesis that the ascending pharyngeal artery is a derived character and therefore indicative of cheirogaleid-lorisiform monophyly. © 1992.
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