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Prosqualodon australis

Osteichthyes - Cetacea

Taxonomy

Prosqualodon australis was named by Lydekker (1894) [specimen number not listed in Lydekker. Kellogg (1923) states that the type specimen i sin the Museo de La Plata, Argentina]. Its type specimen is MLP 5-9, a skull, and it is a 3D body fossil. Its type locality is Cerro Castillo, which is in a Burdigalian/Burdigalian shallow subtidal sandstone in the Gaiman Formation of Argentina.

Synonyms

Prosqualodon davidis was named by Flynn (1923) [The holotype skull is now lost (Mahoney & Ride, 1975; Fitzgerald 2004). UTDG = University of Tasmania Department of Geology]. Its type specimen is UTDG85542-85576, 85578-85603, a partial skeleton (partial skull and skeleton), and it is a 3D body fossil. Its type locality is PL3029 - Upper Bed, Table Cape, which is in an Aquitanian shoreface sandstone/siltstone in the Fossil Bluff Sandstone Formation of Australia.

It was corrected as Prosqualodon davidi by Zittel (1925), Kellogg (1942), Flynn (1948); it was misspelled as Prosqualodon davidi by Flynn (1932), Fordyce (1991), Fitzgerald (2004), Fordyce and Roberts (2009), Geisler et al. (2011), Tanaka et al. (2023); it was synonymized subjectively with Prosqualodon australis by Gaetán et al. (2025).

Synonymy list

Year	Name and author
1894	Prosqualodon australis Lydekker
1898	Prosqualodon australis Trouessart p. 1011
1901	Prosqualodon australis Ameghino p. 80
1904	Prosqualodon australis Trouessart p. 754
1914	Prosqualodon australe Abel p. 220
1923	Prosqualodon davidis Flynn p. 267 figs. Fig. 2
1923	Prosqualodon australis Kellogg p. 7
1925	Prosqualodon australis Zittel p. 86
1925	Prosqualodon davidi Zittel p. 86
1932	Prosqualodon davidi Flynn p. 328
1942	Prosqualodon davidi Kellogg p. 447
1948	Prosqualodon davidi Flynn
1981	Prosqualodon australis Fordyce p. 1041
1982	Prosqualodon australis Sanders et al. p. H120
1991	Prosqualodon davidis Fordyce p. 1180
2004	Prosqualodon davidis Fitzgerald p. 206
2009	Prosqualodon davidis Fordyce and Roberts p. 553
2011	Prosqualodon davidis Geisler et al. p. 5 figs. Table 1
2019	Prosqualodon australis Gaetán et al. p. 4
2023	Prosqualodon davidis Tanaka et al.
2025	Prosqualodon australis Gaetán et al. p. 9

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Rank	Name	Author
kingdom	Animalia	()
—	Bilateria
—	Eubilateria	Ax 1987
—	Deuterostomia
phylum	Chordata	Haeckel 1874
subphylum	Vertebrata
superclass	Gnathostomata
class	Osteichthyes
subclass	Sarcopterygii	()
subclass	Dipnotetrapodomorpha	(Nelson 2006)
subclass	Tetrapodomorpha	()
—	Tetrapoda
—	Reptiliomorpha
—	Anthracosauria
subclass	Amphibiosauria	Kuhn 1967
—	Cotylosauria	()
—	Amniota
subclass	Synapsida
—	Therapsida	()
infraorder	Cynodontia	()
—	Mammaliamorpha

Rank	Name	Author
—	Mammaliaformes
class	Mammalia
—	Cladotheria
—	Zatheria
subclass	Tribosphenida	()
subclass	Theria
—	Eutheria	()
—	Placentalia
—	Boreoeutheria
—	Laurasiatheria
—	Scrotifera
—	Euungulata
—	Artiodactylamorpha
—	Artiodactyla	()
—	Whippomorpha
order	Cetacea
—	Pelagiceti
—	Neoceti
suborder	Odontoceti
genus	Prosqualodon
species	australis

If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.

†Prosqualodon australis Lydekker 1894

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Invalid names: Prosqualodon davidis Flynn 1923 [synonym]

Diagnosis

Reference	Diagnosis
C. M. Gaetán et al. 2019	Prosqualodon australis is a medium- sized odontocete (estimated total body length is 2–3 m long) characterized by the following combination of charac- ters: presence of an antorbital process of the maxilla with a very extended anterior blunt projection, lateral to the an- torbital notch and with a lateral concave margin; a well-de- veloped heterodontia with a rugose tooth enamel forming minute denticles; two dorsal infraorbital foramina; nasals as the highest bone on the vertex and nuchal crest below the frontals. Prosqualodon australis differs from Prosqualo- don davidis in the presence of a ventrally triangular postgle- noid process instead of a squared one, in having a zygomatic process of the squamosal with a flat or almost flat ventral surface and in the more developed antorbital process of the maxilla. It also differs from Prosqualodon davidis and Squalodon calvertensis in the lack of the maxillary intrusion between premaxillae at the narial region. Prosqualodon aus- tralis differs from Squalodon calvertensis in having a more concave posterior sinus, frontals posteriorly wider than nasals, a triangular postorbital process of the frontal, the absence of entocingulum, occipital condyles without pedicels, lacrimal and jugal in the antorbital notch, and in the absence of premaxillary notch. It differs from Otekaikea Tanaka and Fordyce, 2014 in lacking the intra-premaxillary foramen and from Waipatia Fordyce, 1994 in having a ven- trally triangular postglenoid process. Unlike Squalodelphis Dal Piaz, 1917, Prosqualodon australis has a lateral margin of the rostrum concave (anterior to the maxillary flange) instead of straight, premaxillae separated by the mesorostral canal in all rostral extension, and in having a ventrally straight zygomatic process. Prosqualodon australis differs from Notocetus Moreno, 1892, Platanista Wagler, 1830, and Zarhachis Cope, 1868 in the absence of a posterior dorsal infraorbital foramen near the posterior end of the premaxilla, in having a less developed vertex asymmetry, in having occipital condyles without pedicels, frontals posteriorly wider than the nasals and heterodont teeth. With Platanista and Zarhachis differs in lacking rostral asymmetry, in having a zygomatic process ventrally straight instead of convex, and in lacking a longitudinal groove on the posterior apex of the maxilla. It also differs from Platanista in having a well- developed postglenoid process of the squamosal bone, a proportionally wider rostrum, an external occipital crest, contact between maxilla and supraoccipital, in lacking parietals expose at the dorsal surface of the vertex and in lacking contact between orbitosphenoid and lacrimal. Prosqualodon australis differs from Zarhachis in having nodular enamel on the teeth, nasals higher than frontals, a semicircular nuchal crest in posterior view and a smaller tympanosquamosal recess. Prosqualodon australis also differs from Notocetus in having transversally wider premaxillae at the rostrum, in the conical shape of the anterior end of the zygomatic process of the squamosal, in the al- most straight ventral border of the aforementioned process, in having a semicircular nuchal crest (in posterior view), in having an external occipital crest and longer teeth crowns (proportionally).
C. M. Gaetán et al. 2025	Prosqualodon australis is a bre- virostrine, medium-sized odontocete characterized by two autapomorphies: presence of a long, well-devel- oped anterior extension of the antorbital process of the maxilla lateral to the antorbital notch; and the presence in the basicranial region of a large, concave, triangular- shaped parafalciform fossa. Additionally P. australis is characterized by a unique combination of characters: large, heavily heterodont teeth with ornamented enamel forming minute denticles on all its surface; nasals and anteromedial part of frontals in the vertex forming a convexity followed posterolaterally by a subtle concav- ity of the frontals; presence in the basicranial region of a narrow and deep furrow that originates from the peri- otic fossa and is anteromedially blind; ascending pro- cess of the maxilla does not reach the supraoccipital posteriorly; premaxillae extending posterior to the anterior tip of the nasals; nuchal crest below the level of nasals; occipital shield bearing a distinct external sagittal crest; posterior edge of the paroccipital process in transverse line with the posterior edge of occipital condyles; heavily built anterior process of the periotic; promontorial groove associated to an anteroventral tubercle; well-developed dorsal crest. It differs from ‘P.’ hamiltoni in having tooth enamel covered by minute denticles; a supraoccipital less anteriorly extended, reaching the level of the postglenoid process; in lacking an intertemporal constriction; in having a short rostrum; a premaxilla dorsally sharp in the ros- trum; more heavily built orbit processes; a sturdier, anteriorly oriented zygomatic process; and in the pres- ence of the anterior extension of the antorbital process of the maxilla. Differs from Eosqualodon, Squalodon, Ankylorhiza tiedemani, Inticetus vertizi, Phoberodon arctirostris, Notocetus vanbenedeni and Dolgopolis kinchikafiforo in having a brevirostrine rostrum; a more robust orbit and zygomatic processes; and in having a narrower, almost slit-like antorbital notch. It further differs from Eosqualodon and Squalodon in having a temporal fossa less posteriorly extended and less rounded posteriorly; in having an ascending process of the maxillary that does not reaches the supraoccipital; in having a ventrally shorter postglenoid process; in having teeth with no more than three accessory cusps. P. australis further Anatomy and phylogeny of Prosqualodon australis 9 differs from Squalodon in the posterior extension of the premaxilla which does not extend beyond the anterior tip of the nasals. It further differs from A. tiedemani in lacking an exposed interparietal and parietal in dorsal view; as well as in the absence of intertemporal con- striction and foramina in the nasals; in having a latero- medially more expanded supraoccipital bone; in having nasals less anteriorly extended forming a shorter partial posterior roof over the bony nares; in having a premax- illary sac fossa anteroposteriorly shorter and in having 14 upper teeth/alveoli. From I. vertizi it further differs in having a longer pharyngeal crest; in having the meso- rostral canal dorsally open along all the rostrum and in having more delicate accessory cups in the post-canine teeth. It further differs from Phoberodon arctirostris in having frontals more dorsally exposed than the nasals in the vertex; in having cheek teeth with three or fewer accessory denticles; and in the more sculpted tooth enamel, with minute denticles on lingual and labial sur- faces. It further differs from D. kinchikafiforo in the less-developed maxillary crest and in the presence of well-defined dental alveoli on the posterior portion of the rostrum. It further differs from N. vanbenedeni in the lack of the supraorbital crest; and in having large, heterodont teeth. P. australis differs from Crisocetus lydekkeri in the lack of contact between both premaxil- lae just anterior to the external bony nares; in lacking thickened frontals at the level of the orbit; in having a trapezoidal-shaped temporal fossa in lateral view; in the proportionally shorter zygomatic process; and in having a thicker, more robust postorbital process. Unlike any other extinct Patagonian odontocete species, the periotic of P. australis has a well-developed, conspicuous dorsal crest and a more strongly developed caudal tympanic process. The periotic of P. australis also differs from that of N. vanbenedeni and Aondelphis talen, in the presence of a suprameatal fossa; in the less marked anterior bullar facet; in the more laterally placed fovea epitubaria; in having a pyriform internal acoustic meatus; and in the more developed caudal tympanic process.