The delphinids (Odontoceti: Delphinidae) comprise the most diverse extant cetacean family. Delphinids are mostly known as fossils from Pliocene deposits of the Emilia Romagna, Piedmont, and Tuscany regions of Italy. Many of the Italian delphinid remains belong to Hemisyntrachelus, an extinct genus that appears to be crucial for reconstructing the evolutionary history of this highly derived odontocete clade. Hemisyntrachelus is a delphinid whose size and shape are intermediate between those of the extant bottlenose dolphin (Tursiops truncatus) and killer whale (Orcinus orca). These morphological affinities are supported by recent phylogenetic analyses that suggest a basal position within the Orcininae for Hemysintrachelus. Although only two Hemisyntrachelus species – namely, H. cortesii (Fisher, 1829) and H. pisanus Bianucci, 1996 - are currently recognized from the Pliocene of Italy, an unexpectedly high intrageneric disparity is being revealed by our ongoing studies of the Italian Hemisyntrachelus fossil record. Indeed, the data we have collected in recent years seem to reevaluate the pioneering studies carried out in the second half of the 19th century, when a plethora of species and subspecies were described based on several specimens from Italy. Our integrated studies follow several approaches: 1) the analysis of the intraspecific skeletal morphological variability in extant delphinids using statistically significant samples in order to identify robust characters for diagnosis and phylogeny; 2) the implementation with new taxa and characters of a large matrix to obtain a better resolution of the delphinid phylogeny; 3) the acquisition of 3D skeleton models for geometric morphometrics analyses; and 4) the morphofunctional analyses of skull and postcranium for reconstructing trophic strategies and swimming styles. Our preliminary results suggest that Hemisyntrachelus is probably a paraphyletic genus that includes several species and constitutes an evolutionary grade towards the killer whale ecomorph.
DISPARITY VS DIVERSITY WITHIN THE HEMISYNTRACHELUS LINEAGE (CETACEA, DELPHINIDAE): A REVIEW OF THE ITALIAN PLIOCENE RECORD
Giovanni BIANUCCI
Primo
;Alberto COLLARETA;Marco MERELLA;Giorgio CARNEVALE;
2023-01-01
Abstract
The delphinids (Odontoceti: Delphinidae) comprise the most diverse extant cetacean family. Delphinids are mostly known as fossils from Pliocene deposits of the Emilia Romagna, Piedmont, and Tuscany regions of Italy. Many of the Italian delphinid remains belong to Hemisyntrachelus, an extinct genus that appears to be crucial for reconstructing the evolutionary history of this highly derived odontocete clade. Hemisyntrachelus is a delphinid whose size and shape are intermediate between those of the extant bottlenose dolphin (Tursiops truncatus) and killer whale (Orcinus orca). These morphological affinities are supported by recent phylogenetic analyses that suggest a basal position within the Orcininae for Hemysintrachelus. Although only two Hemisyntrachelus species – namely, H. cortesii (Fisher, 1829) and H. pisanus Bianucci, 1996 - are currently recognized from the Pliocene of Italy, an unexpectedly high intrageneric disparity is being revealed by our ongoing studies of the Italian Hemisyntrachelus fossil record. Indeed, the data we have collected in recent years seem to reevaluate the pioneering studies carried out in the second half of the 19th century, when a plethora of species and subspecies were described based on several specimens from Italy. Our integrated studies follow several approaches: 1) the analysis of the intraspecific skeletal morphological variability in extant delphinids using statistically significant samples in order to identify robust characters for diagnosis and phylogeny; 2) the implementation with new taxa and characters of a large matrix to obtain a better resolution of the delphinid phylogeny; 3) the acquisition of 3D skeleton models for geometric morphometrics analyses; and 4) the morphofunctional analyses of skull and postcranium for reconstructing trophic strategies and swimming styles. Our preliminary results suggest that Hemisyntrachelus is probably a paraphyletic genus that includes several species and constitutes an evolutionary grade towards the killer whale ecomorph.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
