A Middle Jurassic mammal from Madagascar
Article Abstract:
Middle Jurassic sediments in northwest Madagascar have yielded three lower teeth in a jaw fragment from the earliest tribosphenic mammal discovered so far. This mammal is from the youngest of a series of early Mesozoic vertebrate faunas found in the Isalo 'Group' of western Madagascar. This find significantly extends the known range of the Tribosphenida, but is consistent with predicted ages for the earliest members of the clade on the basis of the age of its closest known relatives. However, the discovery goes against other molecular analyzes indicating significantly more ancient divergences between major mammalian clades than indicated by the fossil record.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1999
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Discovery of tetraploidy in a mammal
Article Abstract:
Genetic evidence shows that the red viscacha rat, Tympanoctomys barrerae (Octodontidae), is tetraploid. This rat has the largest chromosome complement in mammals with a single XY sex-chromosome system. There is little information about meiotic chromosome pairing in T. barrerae, but there is evidence that segregation takes place normally. It appears that T. barrerae has a genome of 16.8 pg, twice the DNA content of its closest relatives and of most other mammals. The disomic condition of the X chromosome in female T. barrerae is either adequate or perhaps the only way for the tetraploid to escape arrested gonodal development.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1999
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The oldest coelurosaurian
Article Abstract:
The discovery of a therizinosaur from the Early Jurassic Lower Lufeng Formation of Yunnan, China is reported, extending the age range by a further 94 million years. It is the oldest record of a coelurosaurian theropod, contradicting the theory of the non-avian Coelurosauria occurring too late in the fossil record to be related to birds. The discovery suggests that the major clades of the group must have already diverged by the Late Jurassic.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1998
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