FOSSIL RECORD AND THE EVOLUTIONARY HISTORY OF INIODEA - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 200

The type species, Brachydelphis mazeasi was found at Cerro la Bruja level. The holotype
is an almost complete cranium with both periotics and partial tympanics. Referred material
includes incomplete cranial and skeletal material, including postcranial elements, and
additional bones of the auditory region. The age of the Cerro La Bruja level, based on dates
from volcanic tuffs and macroinvertebrates, was estimated to be approximately 12 million
years.
Additional fossils referred to Brachydelphis were recovered from another site of the same
formation, the younger level El Jahuay (calculated to be 9 Ma). Muizon (1984) described 4
periotics and a partial tympanic from this level, all which he recognized distinct enough from
B. mazeasi to not consider them as conspecific but not enough to support the erection of a
new species, so he referred to them as Brachydelphis sp.
Specimens referred to B . mazeasi, cf Brachydelphis' new form and cf Brachydelphis
indeterminate were reported from the late Miocene Bahia Inglesa Formation (Gutstein et al.,
in press).
In the systematic discussion accompanying the type description, Muizon (1984:127)
listed a suite of characters justifying the placement of Brachydelphis in the pontoporiid
lineage. However, Brachydelphis possesses unique characters that Muizon used to erect the
subfamily Brachydelphinae, to reflect its distinction from the other members of the
Pontoporiidae - the living Pontoporia, and the fossil genera Pontistes and Pliopontos,
described below. Brachydelphis , as is was originally described by Muizon (1984), has a very
short rostrum, distinct among both living and fossil river dolphins, which are most often
characterized by very long rostra. As it was supposed to be the earliest pontoporiid, it is
significant that Brachydelphis possesses an asymmetrical cranial vertex. Pontoporia is the
only living odontocete with a symmetrical cranial vertex, a character which the reconstructed
skulls of Pliopontos and Pontistes also exhibited (Muizon, 1988a).
Protophocaena minima Abel, 1905
Lambert & Post (2005) reported the record of the first European Pontoporiidae, based on
a restudy and reinterpretation of Protophocaena minima which Abel, 1905, originally
identified as a Phocoenidae. They included this species in the subfamily Brachydelphinae,
basically because of the asymmetrical vertex. A brief discussion of the biogeographic
implications of those records is presented in their paper.
Stenasodelphis russellae Godfrey and Barnes, 2008
Godfrey and Barnes described a new genus and species of Pontoporiidae, Stenasodelphis
russellae, from the late Miocene St. Marys Formation, in Maryland, USA. The fragmentary
material resemble Brachydelphis in some aspects, particularly the asymmetry of the skull
vertex. Despite that the authors did not refer this species to any of the subfamilies formally
named, I see it as probably belonging to the Brachydelphidae.