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OREODONTS OF THE TICK CANYON FORMATION,
SOUTHERN CALIFORNIA

BY DAVID P. WHISTLER

In 1940, Richard H. Jahns reviewed the stratigraphy of
the nonmarine Mint Canyon Formation in the eastern part of
the Ventura Basin and separated from it a new formation and
fauna. Previous to this work, a controversy existed as to
the age of the Mint Canyon Formation, for it contained
vertebrates considered indicative of both the Miocene and
Pliocene (Kew, 1924, Maxson, 1930, and Stirton, 1933). As a
partial solut,ion to this controversy, Jahns demonstrated the
presence of an erosional unconformity low in the nonmarine
sequence which indicated a shift in source area. He
redefined the beds below the unconformity as the Tick Canyon
Formation (Jahns, 1940, pp. 163-66).
Additional fossils discovered in the Tick Canyon
Formation since Maxson's work, and certain of the forms
described by Maxson, comprise the Tick Canyon fauna. Only
two specimens described by Maxson are from the Tick Canyon
Formation, UCMP 30046, the type of Miolabis californicus
and UCMP 23852, a dentary fragment of a Parahippus. Neither
of these permitted a definitive age determination. The
additional fauna described by Jahns indicates an Arikareean
mammalian age (early Miocene), and there is a noteworthy
temporal hiatus between the Tick Canyon fauna and the over-
lying Mint Canyon fauna. In addition, faunas comprising
three mammalian ages, late Barstovian, and earlier and late
Clarendonian, are now recognized from the Mint Canyon
Formation, but this is not the principal concern of this
paper.
Several reviews of individual taxa from the Tick Canyon
fauna describe either new genera or species (Dawson, 1958,
Reeder, 1960). All the described taxa were originally
restricted to the Tick Canyon Formation. Unpublished records
of these taxa now occur in other California localities.
The composite Tick Canyon fauna as presently known is
as follows: a heteromyid rodent, Trogomys rupinimenthae
Reeder, 1960, a rabbit, Archaeolagus acaricolus Dawson,
1958, two oreodonts, Merychyus (Merychyus) calaminthus Jahns,
1940, and Merychyus (Merychyus) jahnsi (this paper), a camel,

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