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Abstract:
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Lepidosirenidae is a clade of freshwater lungfishes that comprise the South American Lepidosiren paradoxa and four African species of the genus Protopterus . These two genera have been geographically separated since the Early Cretaceous break -up of Gondwana , but they share similar biology and skeletal morphology . The lepidosirenid species traditionally were distinguished by a combination of features such as head -to -body ratios , the number of pairs of vertebral ribs , and the presence or absence of external gills , but there are no published discrete skeletal characteristics and no published comparative studies including all extant species .
I used High Resolution X -Ray Computed Tomography (CT ) , X -Ray photography , and alcohol -preserved , cleared -and -stained , and dry skeletal specimens from museum collections to describe the skeletal morphology of all species of lepidosirenid lungfishes in a comparative context . I digitally disarticulated the bones in each CT scan to compile a comprehensive comparative atlas of the cranial and pectoral elements of all extant lungfish . I discovered that the anocleithrum in Lepidosiren paradoxa , which was previously thought to be lacking , is actually present . I also identified skeletal differences between species in the frontoparietal , parasphenoid , supraorbital , and suboperculum . I incorporated those characters into the first morphological phylogenetic analysis to determine the interrelationships of the lepidosirenids . I also used previously published molecular sequence data from the ribosomal RNA gene 16s to run combined morphological and molecular phylogenetic analyses . To generate phylogenetic hypotheses using different types of data and different methods of determining phylogeny , I employed the maximum parsimony , maximum likelihood , and Bayesian inference methods .
Lepidosirenidae is monophyletic in almost all analyses , Protopterus is monophyletic in each analysis , and Protopterus annectens and Protopterus aethiopicus are sister taxa in every analysis . The phylogenetic positions of Protopterus dolloi and Protopterus amphibius are incongruent in many of the analyses , which indicates that further examination of the skeletal variation and addition of molecular sequences of different genes is needed . Based on the comparative morphological atlas and the phylogenetic analyses , questions of lepidosirenid biogeography , morphological variation within lungfish , and better identification of lungfish fossils can now be investigated in a more rigorous context . |