Nannocetus Explained

Nannocetus is an extinct baleen whale belonging to the family Cetotheriidae.^{[1] [2]}

Description

Nannocetus is a diminutive mysticete measuring 13abbr=offNaNabbr=off long. It is characterized by the ventral orientation (in posterior view) of the postglenoid process; postglenoid process twisted medially (in ventral view) relative to the anteroposterior axis of the skull; equal projection of the ventral and dorsal lobes of the tympanic than the dorsal lobe; deeper notch separating the two lobes of the tympanic; reniform morphology of the tympanic in ventral view; lip of the tympanic slightly inflated; sub-rectilinear medial edge of the involucrum with a step in its anterior third; anterior process of the petrosal sub-triangular; thin crista transversa of the petrosal; and pars cochlearis hemispherical.^[3]

Taxonomy and classification

The holotype is UCMP 26502. It was collected from the Late Miocene (Messinian) Towsley Formation of Humphreys, Los Angeles County, California.^[4] It has been traditionally assigned to Cetotheriidae since its description, a classification that still stands and has been vindicated by recent cladistic analyses of 'cetothere' relationships.^{[5] [6]}

Notes and References

1. M. D. Uhen, R. E. Fordyce, and L. G. Barnes. 2008. Mysticeti. In C. M. Janis, K. M. Scott, and L. L. Jacobs (eds.), Evolution of Tertiary Mammals of North America II:607-628
2. L. G. Barnes. 1977. Outline of eastern North Pacific fossil cetacean assemblages. Systematic Zoology 25(4):321-343
3. V. Bouetel and C. Muizon. 2006. The anatomy and relationships of Piscobalaena nanna (Cetacea, Mysticeti), a Cetotheriidae s.s. from the early Pliocene of Peru. Geodiversitas 28(2):319-395
4. R. Kellogg. 1929. A new cetothere from southern California. University of California Publications in Geological Sciences 18(15):449-457
5. M. C. McKenna and S. K. Bell. 1997. Classification of Mammals Above the Species Level 1-640
6. M. Bisconti, O. Lambert, and M. Bosselaers. 2013. Taxonomic revision of Isocetus depauwi (Mammalia, Cetacea, Mysticeti) and the phylogenetic relationships of archaic 'cetothere' mysticetes. Palaeontology 56(1):95-127