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Despite numerous systematic studies, the relationships among many species
within the dog family, Canidae, remain unresolved. Two problems of broad
evolutionary significance are the origins of the taxonomically rich canid
fauna of South America and the development in three species of the
trenchant heel, a unique meat-cutting blade on the lower first molar. The
first problem is of interest because the fossil record provides little
evidence for the origins of divergent South American species such as the
maned wolf and the bush dog. The second issue is problematic because the
trenchant heel, although complex in form, may have evolved independently
to assist in the processing of meat. We attempted to resolve these two
issues and five other specific taxonomic controversies by phylogenetic
analysis of 2,001 base pairs of mitochondrial DNA (mtDNA) sequence data
from 23 canid species. The mtDNA tree topology, coupled with data from the
fossil record, and estimates of rates of DNA sequence divergence suggest
at least three and possibly four North American invasions of South
America. This result implies that an important chapter in the evolution of
modern canids remains to be discovered in the fossil record and that the
South American canid endemism is as much the result of extinction outside
of South America as it is due to speciation within South America. The
origin of the trenchant heel is not well resolved by our data, although
the maximum parsimony tree is weakly consistent with a single origin
followed by multiple losses of the character in several extant species. A
combined analysis of the mtDNA data and published morphological data
provides unexpected support for a monophyletic South American canid clade.
However, the homogeneity partition tests indicate significant
heterogeneity between the two data sets.
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