Sunday, August 25, 2019

[PaleoMammalogy • 2019] Casatia thermophila • A New Monodontidae (Cetacea, Delphinoidea) from the lower Pliocene of Italy Supports A Warm-water Origin for Narwhals and White Whales

Casatia thermophila
Bianucci, Pesci, Collareta & Tinelli, 2019

Illustration: A. Gennari.

A new taxon of monodontid cetacean, Casatia thermophila, gen. et sp. nov., is here described on the basis of a partial skull from lower Pliocene (5.1–4.5 Ma) marginal-marine deposits of Tuscany (central Italy). This new taxon belongs to Monodontidae based on the presence of a medial exposure of the maxillae anterior and lateral to the external bony nares; it mainly differs from all other named monodontids by the presence of a median depression of the premaxillae anterior to the premaxillary sac fossae and by a medial margin of the premaxillary-maxillary suture that does not parallel the anterolateral profile of the external bony nares. Our phylogenetic analysis, the first including all taxa of Monodontidae, recovers Casatia as a crown monodontid, more closely related to Delphinapterus than to Monodon and sister group of an unnamed taxon from the North Sea. The holotype of Casatia represents the first and only fossil monodontid from the Mediterranean Basin. Taking its place beside abundant fossils of strongly thermophilic marine vertebrates, such as the bull shark Carcharhinus leucas, the tiger shark Galeocerdo cuvier, and the extinct sirenian Metaxytherium subapenninumCasatia thermophila represents the strongest evidence supporting the hypothesis that monodontids once thrived in low-latitude, warm-water habitats. On the basis of our phylogenetic reconstruction, early relatives of the extant monodontids might have adapted independently to the high-latitude, cold-water environments they currently master. The definitive disappearance of the Neogene thermophilic monodontids could be attributed to the cooling episode that accompanied the onset of long-term Northern Hemisphere glaciation around 3 Ma.

Life reconstruction of Casatia thermophila, gen. et sp. nov., swimming in the coastal waters off present-day Tuscany in early Pliocene times (5.1–4.5 Ma). Behind the cetacean, two individuals of the sirenian Metaxytherium subapenninum are approaching the shallow sea floor, likely attracted by the presence of abundant seagrasses. The coexistence of monodontids (C. thermophila) and sea cows (M. subapenninum) in the warm marginalmarine waters of the central Mediterranean Basin during the early Pliocene reflects the composition of the fossil vertebrate assemblage from Arcille, where a sirenian specimen was collected from the same horizon as the holotype of C. thermophila.
Illustration: A. Gennari

CETACEA Brisson, 1762
ODONTOCETI Flower, 1867

CASATIA, gen. nov.

Type and Only Known Species— Casatia thermophila, sp. nov.

Etymology— The genus name honors Simone Casati, prominent amateur paleontologist who discovered most of the fossil vertebrates from Arcille (the locality where the holotype of Casatia thermophila was found) and author of several academic and popularizing works on the Pliocene marine vertebrates of Tuscany (Casati, 2007; Bianucci et al., 2009; Cigala-Fulgosi et al., 2009; Oddone et al., 2009; Casati and Oddone, 2011; Collareta et al., 2017, 2018).


Etymology— The species name is from the Greek ‘thermós’ (= hot) and ‘philos’ (= loving), considering the warm-water habits of this extinct cetacean.

Map of the Northern Hemisphere showing the distribution of extant Delphinapterus (pink area) and congeneric Quaternary fossils (pink squares), extant Monodon (blue area) and congeneric Quaternary fossils (blue squares), and the extinct Casatia (arrow) and other Neogene monodontid genera (green squares).

Giovanni Bianucci, Fabio Pesci, Alberto Collareta and Chiara Tinelli. 2019. A New Monodontidae (Cetacea, Delphinoidea) from the lower Pliocene of Italy Supports A Warm-water Origin for Narwhals and White Whales. Journal of Vertebrate Paleontology.  DOI: 10.1080/02724634.2019.1645148