Ihlengesi changoensis Bianucci & Sielfeld & Olguin & Guzmán 2023, sp. nov.
Creators: name: Bianucci, Giovanni
name: Sielfeld, Walter
name: Olguin, Nicole A.
name: Guzmán, Guillermo
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Cetacea
Hyperoodontidae
Ihlengesi
Ihlengesi changoensis

description: Ihlengesi changoensis sp. nov.
Figs. 2–5, Table 1.
Zoobank LSID: urn:lsid:zoobank.org:act: 503E74DA-918C-4125-B419- C4A084E9F317
Etymology: From “Changos”, the indigenous people and fishermen, who originally inhabited the coast of Northern Chile.
Holotype: MUAP(MM)-068, a partial cranium including the complete rostrum, the medial facial area (premaxillary sac fossae and vertex) and part of both supraorbital regions.
Type locality: Off the port of Pisagua (19°35’50”S; 70°12’48’’W), Northern Chile, at a depth of 1000 m (Fig. 1), collected by Dany Manzo in May 2022.
Type horizon: Iquique Basin, Plio-Pleistocene (Gonzáles et al. 2023).
Diagnosis.— Ihlengesi changoensis sp. nov. differs from Ihlengesi saldanhae in the following characters: more elongated premaxillary sac fossa and consequently premaxillary foramen more anteriorly located (ratio between the longitudinal distance between the right premaxillary foramen and the rostrum base and the width of rostrum base equals 0.10 contra 0.32 in I. saldanhae); dorsal margin of each premaxillary crest sloping markedly ventrolaterally and generating an acute dorsal profile of the vertex in anterior view (rounded profile in I. saldanhae); less anterolateral extension of the right nasal forming part of the premaxillary crest; lateral margins of the nasals not anteriorly diverging but weakly convex; nasofrontal suture not convex posteriorly but anteriorly pointed.
Description.—Judging from the size of the cranium (Table 1), Ihlengesi changoensis was a small ziphiid which, like Ihlengesi saldanhae, did not reach 4 m in length. Indeed, by roughly estimating the postorbital width of the cranium to 250 mm and applying the aforementioned equation proposed by Bianucci et al. (2008), the body length results to be 3.5 m, a value close to that estimated for I. saldanhae (3.1 m). Therefore, based on these estimations, species of Ihlengesi were smaller than all extant ziphiids with the exception of the pygmy beaked whale Mesoplodon peruvianus (maximum body length 3.72 m; Reyes et al. 1991).
The complete rostrum is moderately elongated and, similarly to the paratype of Ihlengesi saldanhae (SAM PQ 69673), shows a strong lateral compression generating a narrow dorsal profile and a transverse section with a height significantly greater than its width (Figs. 2, 5). Due to its narrow dorsal shape, the rostrum of Ihlengesi changoensis clearly differs from Khoikhoicetus spp. Indeed, the rostrum of this latter genus is significantly transversely wider than in I. changoensis, a feature particularly marked in Khoikhoicetus kergueleni having a triangular outline of the rostrum in dorsal view (Lambert et al. 2018).
The medial margins of the premaxillae on the rostrum never contact medially and the mesorostral groove is filled by the pachyosteoscleorotic vomer along its whole rostral portion (Fig. 2A 1), a feature that, at least in the extant ziphiids, is only observed in adult males (Bianucci et al. 2016b). The vomer greatly inflates towards the posterior portion of the rostrum as in the holotype of Ihlengesi saldanhae (SAM PQ 2792). A median longitudinal suture between the lateral walls of the vomer in the rostrum base area is visible as in all hyperoodontines.
In ventral view the rostrum does not show a distinct alveolar groove whereas a clear maxilla-palatine suture extends about 12 cm anterior to the antorbital notch (Fig. 2A 3).
Medial to the narrow antorbital notch, a distinct maxillary tubercle is visible. The position the suture between the maxilla and the missing lacrimojugal complex, well visible in the ventral surface of the left side of the neurocranium, supports that this tip, apparently laterally located to the rostrum base, is actually the maxillary tubercle. Indeed, this suture is located well lateral to the lateral margin of the rostrum, leaving exposed ventrally a wide portion of the maxilla that anteriorly bears what we interpret as maxillary tubercle. The presence of a well-defined maxillary tubercle separated from the lateral margin of the rostrum by a distinct prominental notch is a feature shared by most hyperoodontines including Ihlengesi saldanhae but absent in Khoikhoicetus spp.
The prominental notch of the Ihlengesi changoensis holotype is transversely wide, U-shaped and shallow as in the paratype of I. saldanhae, whereas in the I. saldanhae holotype this notch is V-shaped and transversely shorter, suggesting that this character is subject to intraspecific variation (Fig. 3).
The dorsal surface of the preorbital area is roughly flat without a distinctive maxillary crest, as in I. saldanhae, while in most of the other crown Ziphiidae, including Khoikhoicetus, the maxillary crest is present and generally elevated to form a peculiar dome.
Both the right and the left maxilla are pierced by a single dorsal infraorbital foramen near the prominental notch, 13- and 7-mm posterior to the rostrum base, respectively. Similar dorsal infraorbital foramina are observed in Ihlengesi saldanhae but more posteriorly located in I. saldanhae paratype.
The right and the left premaxillary foramina are distinctly posterior to the rostrum base (5 mm) but less than in Ihlengesi saldanhae as well quantified by the ratio between the longitudinal distance between the right premaxillary foramen and the rostrum base and the width of rostrum base, being this ratio equal to 0.10 in I. changoensis against 0.34– 0.32 in I. saldanhae. This significant difference in the position of the premaxillary foramina is related to the greater anteroposterior extension of the premaxillary sac fossae in I. changoensis compared to I. saldanhae. Indeed, the premaxillary sac fossae of I. saldanhae are unusually short so that this feature was previously considered an apomorphy of the Ihlengesi (Bianucci et al. 2007). Interestingly, in I. saldanhae the premaxillary foramina are distinctly posterior to the dorsal infraorbital foramina, an unusual condition in beaked whales. The premaxillary foramina of I. changoensis are posteriorly located to the dorsal infraorbital foramina but to a lesser degree than I. saldanhae. Regardless the position of the foramina with respect to the rostrum base, in all hyperoodontines, except some species of Mesoplodon (e.g., Mesoplodon grayi von Haast, 1876), the premaxillary foramina are always roughly at the same level or weakly anterior to the maxillary foramina.
The weakly concave premaxillary sac fossae of I. changoensis are distinctly asymmetrical as in I. saldanhae, being the right fossa transversally wider than the left fossa ratio between the widths of the left and right premaxillary fossae = 0.78).
The ascending process of the premaxilla rises towards the vertex with its posterodorsal portion partly overhanging the bony nares (Fig. 2A 2). Therefore, with the cranium in lateral view, the anterior profile of this portion of the ascending process of the premaxilla is clearly concave in Ihlengesi changoensis as in I. saldanhae, not straight and vertical as in Khoikhoicetus spp.
The vertex is moderately elevated as in Ihlengesi saldanhae and Khoikhoicetus spp. (ratio between the vertical distance between the dorsal margin of the maxilla at the rostrum base and the top of the vertex and the width of the premaxillary sac fossae between 0.70 and 1.0). All other hyperoodontines have a higher vertex (ratio> 1.0).
The ascending process of the premaxilla displays a strong constriction between premaxillary sac fossa and premaxillary crest (ratio between the minimal width of ascending process of the right premaxilla and the width of right premaxillary crest = 0.56).
As in Ihlengesi saldanhae and Khoikhoicetus agulhasis, the posterolaterally directed premaxillary crests are transversally narrower than in the other hyperoodontines (ratio between the transverse width of the premaxillary crests and the width of premaxillary sac fossae = ca. 1.0), whereas the distance between the premaxillary crests is greater than in Mesoplodon and Hyperoodon (ratio between the minimum distance between the right and left premaxillary crests and the width of the premaxillary sac fossae = 0.3).
The dorsal margin of each premaxillary crest slopes markedly ventrolaterally generating an acute dorsal profile of the vertex in anterior view, similarly to species of Mesoplodon, Hyperoodon, Khoikhoicetus but not Ihlengesi saldanhae, this latter having premaxillary crests with a rounded dorsolateral profile (Fig. 4).
The elongated nasals (ratio between the length of medial suture of nasals on vertex and the maximum width of nasals = 1.1) show a deep anteromedial excavation on their joined dorsal surface as in the other hyperoodontines but Indopacetus pacificus (Longman, 1926). Due to a significant anterolateral expansion of the nasals forming part of the premaxillary crests, a deep notch is visible on the dorsal margin of each nasal, a feature not discernible in Ihlengesi saldanhae holotype due to the bad preservation of the vertex. The inclusion of the nasals in the premaxillary crests is significant, although less for the right than for the left nasal, a condition shared with Khoikhoicetus spp. rather than with I. saldanhae having a greater anterolateral expansion of the right nasal.
The lateral margins of the nasals are weakly convex as in Khoikhoicetus spp., not anteriorly diverging as in Ihlengesi saldanhae. The nasofrontal suture is anteriorly pointed as in Khoikhoicetus spp., not convex posteriorly as in I. saldanhae.
Remarks.—All characters listed in the diagnosis separating Ihlengesi changoensis from Ihlengesi saldanhae are shared with Khoikhoicetus spp. Indeed Khoikhoicetus is a hyperoodontine with a cranium roughly similar to Ihlengesi (i.e., for the size and for the moderate elevation of the vertex). Nevertheless Khoikhoicetus does not show many of the character above listed of the genus Ihlengesi (i.e., rostrum narrow in dorsal view, presence of a distinct maxillary tubercle and a wide and shallow prominental notch anteromedial to the antorbital notch; premaxillary foramen distinctly posterior to the antorbital notch, roughly flat dorsal surface of the preorbital area without distinct maxillary crest; ascending process of the premaxilla in lateral view concave with posterodorsal portion partly overhanging the bony nares) and therefore we consider reliable the appurtenance of the new Chilean species to Ihlengesi rather than Khoikhoicetus, being also supported by the phylogenetic analysis.
Stratigraphic and geographic range.— Type locality and horizon only.
description: Published as part of Bianucci, Giovanni, Sielfeld, Walter, Olguin, Nicole A. & Guzmán, Guillermo, 2023, A new diminutive fossil ziphiid from the deep-sea floor off northern Chile and some remarks on the body size evolution and palaeobiogeography of the beaked whales, pp. 477-491 in Acta Palaeontologica Polonica 68 (3) on pages 480-484, DOI: 10.4202/app.01076.2023, http://zenodo.org/record/12198764