The Proboscidea from the Middle Miocene Wood Mountain Formation, Saskatchewan

Abstract

Zygolophodon proavus (Palaeomastodontidae) and Gomphotherium osborni (Gomphotheriidae) occur in the Middle Miocene (Barstovian) Wood Mountain Formation, Saskatchewan. Wood Mountain specimens represent the northernmost occurrences of both species.

Partial skull ofZygolophodon(Mammalia, Proboscidea) from the Barstow Formation of California

“…Madden (1980) also considered Zygolophodon to be monotypic, with Z. tapiroides having priority. This interpretation was abandoned by its proponent only 5 years later when Madden and Storer (1985) described a specimen of Z. proavus from Saskatchewan, Canada. In the most recent review of North American Proboscidea, Lambert and Shoshani (1998) only recognize Z. proavus (equals Z. merriami, Z. tapiroides nomen nudum).…”

“…Thus, the point of comparison between RAM 908 and other specimens of the genus is limited to the M3 and only three have been described. All are referred to Z. proavus; one each from the Wood Mountain Formation of Saskatchewan (Madden and Storer, 1985), the Pawnee Creek Formation of Colorado (Frick, 1933), and the Deep River Formation of Montana (Madden, 1980). These occurrences, as well as that of RAM 908 (Barstow Formation of California), are all from Barstovian assemblages (Woodburne, Tedford, and Swisher, 1990;Tedford et al, 2004;Pagnac, 2009).…”

“…Zygolophodon proavus is also represented in the Wood Mountain Formation of Saskatchewan by joined dentaries (SMNH P1665) and a right M3 (NMC 9999) described by Madden and Storer (1985). NMC 9999 appears to be nearly unworn, but damaged, because part of the labial, lingual, and anterior margins of the tooth are missing (Madden and Storer, 1985: fig.1).…”

“…NMC 9999 appears to be nearly unworn, but damaged, because part of the labial, lingual, and anterior margins of the tooth are missing (Madden and Storer, 1985: fig.1). The cusp pattern on the lophs of NMC 9999 is more complex than in RAM 908, F:AM 23337, and AMNH 8137, with mesoconelets present on the first three lophs; small central conules may also be present but this is unclear, because the illustration of NMC 9999 (Madden and Storer, 1985: fig.1) lacks sufficient detail.…”

“…NMC 9999 appears to be nearly unworn, but damaged, because part of the labial, lingual, and anterior margins of the tooth are missing (Madden and Storer, 1985: fig.1). The cusp pattern on the lophs of NMC 9999 is more complex than in RAM 908, F:AM 23337, and AMNH 8137, with mesoconelets present on the first three lophs; small central conules may also be present but this is unclear, because the illustration of NMC 9999 (Madden and Storer, 1985: fig.1) lacks sufficient detail. A major difference between the Wood Mountain Formation M3 and the others is that its fourth loph has four small cusps (Madden and Storer, 1985) and its anteroposterior length is much less than the fourth lophs in RAM 908, F:AM 23337, and AMNH 8137.…”