PBDB Taxon

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Chilcacetus

Mammalia - Cetacea

Taxonomy

Chilcacetus was named by Lambert et al. (2015). Its type is Chilcacetus cavirhinus. It was considered monophyletic by Lambert et al. (2015).

It was assigned to Odontoceti by Lambert et al. (2015).

Species

C. cavirhinus (type species)

Year	Name and author
2015	Chilcacetus Lambert et al. p. 81 figs. Figs. 1-12

Diagnosis

Reference	Diagnosis
O. Lambert et al. 2015	Chilcacetus cavirhinus n. gen., n. sp. is a long- snouted homodont odontocete (ratio between rostrum length and condylobasal length > 0.70) differing from all other odontocetes in the presence of a cavity between nasals and mesethmoid on the posterior wall of the bony nares. It differs from members of other long-snouted homodont extinct families (Allodelphinidae, Eoplatanistidae, Eurhinodelphinidae, and Platanistidae) in the absence of a deep lateral groove along the rostrum and in the absence of ankylosis for the symphysis of the mandibles. It further differs from Eurhinodelphinidae in lacking an extended edentulous anterior premaxillary portion of the rostrum, in the nasals partly overhanging the bony nares, in the more anteriorly elongated zygomatic process of the squamosal (ratio between the height of the process and the length of the process ≥ 1.10), in the cranium distinctly longer than wide, in the lesser transverse widening of the supraoccipital shield (ratio between the maximum width of the supraoccipital at the lateral corners of the nuchal crest and the postorbital width < 0.70), in the posterior margin of the postorbital process being vertical, in the top of the temporal fossa being nearly as high as the nuchal crest, in the palatines being separated anteromedially for a long distance at rostrum base, and in the longer and more laterally directed posterior process of the periotic. It differs from Eoplatanistidae in the premaxillary foramen roughly at the level of the antorbital notch, in the thinner and flatter antorbital process, in the acute anterior margin of the nasal partly overhanging the bony nares, in the transversely concave and less anteriorly projected anterodorsal portion of the supraoccipital shield, in the deep anterior bullar facet of the periotic, in the elongated posterior process of the periotic, and in bearing a conspicuous median furrow on the tympanic bulla. It differs from Argyrocetus patagonicus in the reduced widening of the premaxillae at the rostrum base, in lacking a wide dorsal opening of the mesorostral groove, in the premaxillary foramen roughly at the level of the antorbital notch, in the angle formed by the basioccipital crests in ventral view < 50°, in the top of the temporal fossa being nearly as high as the nuchal crest, and in the absence of ankylosis for the symphysis of the mandibles. It differs from ‘Argyrocetus’ bakersfieldensis in lack- ing a deep lateral groove on the rostrum, in lacking a deep sulcus anterior to the main dorsal infraorbital foramen at rostrum base, and in the palatines being separated anteromedially for a long distance at rostrum base. It differs from ‘Argyrocetus’ joaquinensis in the dorsal opening of the mesorostral groove anterior to the ros- trum base narrower than the premaxilla, in the presence of more than one dorsal infraorbital foramen at rostrum base, in lacking a deep sulcus anterior to the main dorsal infraorbital foramen at rostrum base, in the proportionally shorter and wider nasal, in the nasal partly overhanging the bony nares, in the wide exposure of the frontal on the vertex, in the posterior margin of the postorbital process being vertical, in the palatines separated anteromedially for a longer distance at rostrum base, in the significantly shorter hamular process of the pterygoid, and in the ventral margin of the postglenoid process of the squamosal being approximately at the same level as the ventral margin of the exoccipital in lateral view. It differs from Macrodelphinus in its smaller size, in the premaxillary portion of the rostrum making less than 10 per cent of its total length, in the premaxillary foramen roughly at the level of the antorbital notch, in the nasal proportionally longer compared to the frontal on the vertex, in the palatines separated anteromedially for a long distance at rostrum base. It differs from Papahu Aguirre-Fernández & Fordyce, 2014 in the rostrum being proportionally dorsoventrally thicker in its proximal part, in the single premaxillary foramen roughly at the level of the antorbital notch, in the dorsal exposure of the premaxilla wider than the exposure of the maxilla at rostrum base, in the proportionally wider ascending process of the premaxilla, in the anterodorsal elevation of the dorsal surface of the nasal, in the posterolateral projection of the nasal, in the elongate postorbital process of the frontal, in the long and deeper anterior bulla facet of the periotic, in the posterior elevation of the dorsal margin of the mandible being progressive. It differs from Platanistidae and Squalodelphinidae in that its cranium is as long as wide, in lacking a deep medial depression in the dorsal surface of the premaxillae at rostrum base, in the posterior dorsal infraorbital foramen being lateral to the lateral margin of the premaxillary sac fossa, in the nasal rising anterodorsally and partly overhanging the bony nares, in the strong reduction of the lateral lamina of the pterygoid, in the absence of an extension of the pterygoid sinus in the orbit roof; in the zygomatic process of the squamosal not being dorsoventrally inflated, in the proportionally longer posterior process of the periotic, in lacking an individualized anterior spine on the tympanic, and in the lower involucrum of the tympanic in medial view, cut by an indentation at mid-length. It further differs from Platanistidae in lacking a dorsal crest on the antorbital process. It differs from Allodelphinidae in lacking a deep medial depression in the dorsal surface of the premaxillae at rostrum base, in the cranium as long as wide, in the proportionally wider vertex, in the strong reduction of the lateral lamina of the pterygoid, in the anteriorly long zygomatic process of the squamosal, and in the top of the temporal fossa being nearly as high as the nuchal crest.