Michelangelo Bisconti

Morphology and postnatal growth trajectory of rorqual petrosal

Abstract Petrosals of two species of Balaenopteridae are described. The ontogenetic changes of the petrosal features are also presented. It is suggested that the ontogenetic variation of them must be consi dered when using the petrosal features for phylogenetic inference.

A new balaenopterid whale from the late Miocene of the Stirone River, northern Italy (Mammalia, Cetacea, Mysticeti)

ABSTRACT The new genus and species Plesiobalaenoptera quarantellii is established and compared to other living and fossil mysticete taxa. The new taxon belongs to the family Balaenopteridae (rorqual and humpback whales) and represents the oldest balaenopterid taxon of the Mediterranean basin coming from Tortonian sediments of the Stirone River, northern Italy (11–7 Ma). Plesiobalaenoptera quarantellii has a wide rostrum, dentary with postcoronoid fossa, periotic with triangular anterior process and raised central portion, tympanic bulla with ventral keel, and high Eustachian opening. From a phylogenetic view, it is closely related to the Late Miocene Parabalaenoptera baulinensis of California, a taxon used to establish the subfamily Parabalaenopterinae. Both Plesiobalaenoptera and Parabalaenoptera are sister taxa of the clade that includes Megaptera, Balaenoptera, and other crown balaenopterids. The presence of the postcoronoid fossa in the dentary of Plesiobalaenoptera quarantellii suggests that the intermittent ram feeding as performed by living balaenopterids was not fully developed in this extinct species.

Titanocetus, a new baleen whale from the middle Miocene of northern Italy (Mammalia, Cetacea, Mysticeti)

Abstract The Italian fossil baleen whale Aulocetus sammarinensis Capellini, 1901, represents a new genus, Titanocetus. The holotype skull of Titanocetus sammarinensis has a long ascending process of the maxilla, a wide and flat rostrum, a triangular interorbital region of the frontal, an anteriorly extended apex of the zygomatic process of the squamosal, and an anteriorly rounded, concave supraoccipital. Features primitive for mysticetes include strong bulging of the squamosal and parietal into the temporal fossa, a lambdoidal crest posterior to the occipital condyles, and a marked intertemporal constriction involving the parietals. Archaeocete-like features are the round anterior process of the supraoccipital and nasals that are transversely constricted anteriorly. These and other features suggest that Titanocetus sammarinensis represents an early-diverging baleen-bearing mysticete probably related to Cetotherium-like taxa.

Late Pliocene fossils of Ecuador and evolution of the Panamic bioprovince after closure of Central American Isthmus

Studies carried on in the last several years allow us to date the Canoa Formation as Late Pliocene. The rich paleontological record (foraminifers, mollusks, and otoliths) allowed us to outline a first articulate picture of the biogeographic relationships in the tropical eastern Pacific during the Plio-Pleistocene. The mollusk fauna shows a Panamic connotation, as the majority (88.7%) of the extant species are present between the Gulf of California and the coasts of Ecuador or northern Peru. Benthic foraminifers assemblages indicate a temperate character with a certain affinity with the Mexican Pacific microfauna. More than 7000 otoliths have been found in the Canoa Formation that are attributed to 105 taxa of 46 fish families. Only 65% of the fossil association is living today along the Ecuadorian coasts, while the association as a whole shows closer relationships with the extant Californian fish community (about 80%). In particular, a conspicuous group of fishes (15 taxa) today spread in the boreal East Pacific (from Oregonian to Californian Province or limited only to the Californian area) has been recorded in the Canoa Formation. We named these taxa “Californian guests.” After the rising of the Central American Isthmus, climatic variations may have caused changes in the pattern of surface currents and (or) activated coastal upwelling cells, supporting the diffusion of a part of the boreal biota toward more southern areas. At the present state of knowledge, both proximal causes seem to be compatible with the data presented.