Lophocetus was the first fossil odontocete to be described from North America. The type species,
L. calvertensis, was originally described as
Delphinus calvertensis by the American naturalist
Richard Harlan in 1842 on the basis of
USNM 16314, a skull from the
St. Marys Formation of Maryland.
Edward Drinker Cope subsequently recognized it as distinct from extant oceanic dolphins and considered it congeneric with the
franciscana (as
Pontoporia calvertensis), before renaming it as a distinct genus,
Lophocetus. The phylogenetic analysis of
Brujadelphis recovered
Lophocetus as polyphyletic, with
L. calvertensis and
L. repenningi forming a clade with taxa assigned to Pithanodelphininae and
Tagicetus, and
L. pappus falling as the sister taxon of
Lipotidae. If
"Lophocetus" pappus is a relative of the
baiji, it would fill a gap in the early evolutionary history of the baiji because the oldest unambiguous extinct relative of the baiji,
Parapontoporia, hails from younger marine deposits. However, a strict consensus phylogenetic analysis of the pontoporiid
Scaldiporia recovers
"Lophocetus" pappus outside the clade formed by Inioidea+Lipotidae and Delphinoidea, while recovering
Lophocetus as a relative of beaked whales and
Squaloziphius.
Reassigned species In 1955,
Remington Kellogg described a new species of
Lophocetus,
L. pappus, on the basis of the skull
USNM 15985 from the
Langhian-age Plum Point Member of the
Calvert Formation. In 1978, however, Lawrence Barnes of the Los Angeles Museum of Natural History referred this species to the similarly Langhian-age genus
Liolithax based on similarities in the earbone morphology, as
Liolithax pappus. The new subfamily Lophocetinae was erected to accommodate
Liolithax and
Lophocetus, and Barnes also named
Lophocetus repenningi on the basis of the skull
USNM 23886 from the Tortonian-age
Santa Margarita Formation of Santa Barbara, California. The assignment of
Lophocetus pappus to
Liolithax by Barnes (1978) was followed by several authors, including Ichishima et al. (1995), Dawson (1996), and Uhen et al. (2008), although Whitmore and Kaltenbach (2008) did not. However, in a couple of abstracts published in 2000 and 2008, Barnes and colleagues recognized
Lophocetus pappus as a new genus of lophocetine distinct from
Liolithax after the discovery of a skull from Middle Miocene marine deposits in Baja California Sur showed that
Liolithax was a kentriodontine rather than a lophocetine and different from
L. pappus in its smaller tooth diameter, smaller size, and more elongated rostrum. Godfrey and Lambert (2023) confirmed the generic distinctness of
"L." pappus from
Liolithax and erected the new genus
Miminiacetus for it. ==References==