THE PARATAXONOMIC IMPLICATIONS OF A SOUTH ASIAN RATITE RECORD: EGGSHELL MORPHOLOGY AND FAUNAL SEQUENCE

Eggshell fragments attributed to the ratite birds cf. Struthio (ostrich) and cf. Aepyornis (a now extinct form) have been recovered from numerous Neogene localities in Africa and Eurasia. A robust Quaternary ratite (cf. Struthio) record, including rare skeletal material, also occurs throughout much of Eurasia, and within the current range of extant Struthio, etc. in Africa. Eggshell material presents an opportunity for phylogenetic interpretation, as this material is formed under genetic control much like the skeletal material traditionally used in such studies. Evolved characters, such as eggshell thickness, mineral composition, crystal structure (layer) morphology, and pore density and geometry, can be used to characterize the record of these ratites to the genus level.

We have recognized a parataxonomic sequence, based upon several distinct morphologic characteristics, from extensive spatially and temporally documented ratite eggshell material from the Neogene Siwalik Group of Pakistan and India (constrained by magnetic polarity stratigraphy and radiometric [fission-track, zircon] dating). A phylogenetic analysis of the evolutionary characters seen in these eggshells was performed in order to create an evolutionary tree for the closely related cf. Struthio and cf. Aepyornis lineages, as well as the problematic form, Struthiolithus.

These data enable us to recognize first- and last-appearances within this newly defined parataxonomy of Siwalik morphospecies and their possible African counterparts. This has facilitated constraints on the faunal dispersal through the Levant corridor during the Neogene and Quaternary. This analysis provides additional support for the existence of the two well-known clades of ratites, cf. Struthio and cf. Aepyornis, to be present in Eurasia during the late Neogene and Quaternary. Additionally, it considers the problematic group Struthiolithus to be ancestral to both Struthio and Aepyornis. Several episodes of ratite introduction into Eurasia from Africa are postulated, one circa 10 mya, based upon the first-appearances of three distinct morphospecies, and later introductions circa 5.3 mya, 3.3 mya, and 1.5 mya, based upon the first-appearances of three additional morphospecies.