A new genus and five new species of fossil cichlid fishes (Perciformes: Labroidei) are described from Mahenge, Tanzania. These cichlids represent the oldest confirmed fossils of the family, dating from the middle of the Eocene. The specimens share many lepidological characters, and, from comparison with other members of the family, are identified as being a monophyletic group. Therefore, they are described as belonging to a single genus, Mahengechromis gen. nov., named for the type locality. Detailed anatomical study of the well-preserved specimens allows five species to be identified, M. plethos, M. rotundus, M. brachycranium , M. ellipticus, and M. curvifrons spp. nov. These species are distinguished on the basis of osteological characters, including the shape of the frontal bones, hyomandibulae and opercular bones. The species are believed to be endemic to the type locality, which, along with monophyly of the species, indicates that these fishes formed a species flock. This suggests that the capacity for cichlids to form species flocks arose early in the family's history. / Previously published phylogenetic analyses of the family Cichlidae have included few characters that can be used to incorporate fossil material. Osteological features that may be useful for determining relationships are identified and used in a phylogenetic analysis of the family. The results of this analysis are compared with the results of previous analyses to determine the usefulness of the characters. This comparison indicates that most osteological characters are homoplastic among cichlids, although some of the characters may prove to be phylogenetically useful. Although phylogenetic analysis of osteologic characters does not result in a well-resolved phylogeny, the most parsimonious placement of the fossil cichlids from Mahenge is in a relatively basal position among the African lineages, as the sister group to the hemichromine cichlids from West Africa. / The biogeographic relationships of members of the Cichlidae are examined based on information from the fossil record and the interrelationships of the lineages within the family. Two suggestions have been made for the age of the family; either the cichlids originated in the Early Cretaceous or they evolved near the end of the Mesozoic. The later time of origin would have required a trans-Atlantic dispersal. Based on the distribution of Recent and fossil cichlids, the latter hypothesis is accepted. A reconstruction of the dispersal patterns and possible means of dispersal are evaluated.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.37794 |
| Date | January 2000 |
| Creators | Murray, Alison M. |
| Contributors | Carroll, Robert L. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Biology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001802256, proquestno: NQ70109, Theses scanned by UMI/ProQuest. |
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