Eocene Rodents, Pruett Formation, Southwest Texas; Their Pertinence to the Origin of the South African Caviomorpha
Abstract
The rodents from three localities in the Pruett Formation of the Buck Hill Volcanic
Group from the Big Bend region of Texas are described. Included are the
paramyids Thishemys plicatus, Microparamys minutus, Lophiparamys sp. indet.,
and at least one indeterminate paramyid; new species, M. boskeyi, of the cylindro- dont genus Mysops and hystricognathous rodent of uncertain familial position,
Prolapsus, new genus. Prolapsus is represented by P. sibilatoris, new species; P.
junctionis, new species; and third, smaller but indeterminate species. The rodents
both individually and collectively strongly support Middle Eocene (Bridgeran)
age for the lower part of the Pruett Formation. Prolapsus is the first fully hystricognathous
rodent to be reported from the Eocene of any part of the world. It is already
too advanced in the characters of the cheek teeth to have been ancestral to
the South American Caviomorpha. The incisor enamel is of the pauciserial type, characteristic of the primitive Eocene rodents, the families Paramyidae and Sciuravidae,
and the mid-Eocene cylindrodont Mysops. Although the incisor enamel and
the cheek teeth show that Prolapsus could not have been caviomorph, it seems
probable that the Caviomorpha were derived from Middle American Eocene ancestors
of the same general stock as Prolapsus. The presence of Prolapsus in North
America is weighty argument against late Eocene trans-Atlantic migration of
rodents. Unknown but probably related forms, from southwest Asia, were presumably
ancestral to the African Phiomorpha.
Department
Description
Contents: Abstract -- List of Illustrations -- List of Tables -- Introduction -- Family Paramyidae -- Family Cylindrodontidae -- Family indet -- Age of the Lower Pruett Formation as indicated by the Rodents -- References Cited