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Geographical position of Ullujaya and Zamaca (Pisco Basin, southern coast of Peru) (a, b) and related composite stratigraphic sections (c, d) showing the distribution of fossil platanistoids in the Chilcatay Fm, including the specimens with known stratigraphical position described in this paper. Red silhouette indicates holotype. Absolute datings ( 40 Ar/ 39 Ar on ash layers) constraining the age of the fossil platanistoids are also reported along the sections.

Geographical position of Ullujaya and Zamaca (Pisco Basin, southern coast of Peru) (a, b) and related composite stratigraphic sections (c, d) showing the distribution of fossil platanistoids in the Chilcatay Fm, including the specimens with known stratigraphical position described in this paper. Red silhouette indicates holotype. Absolute datings ( 40 Ar/ 39 Ar on ash layers) constraining the age of the fossil platanistoids are also reported along the sections.

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Several aspects of the fascinating evolutionary history of toothed and baleen whales (Cetacea) are still to be clarified due to the fragmentation and discontinuity (in space and time) of the fossil record. Here we open a window on the past, describing a part of the extraordinary cetacean fossil assemblage deposited in a restricted interval of time...

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... than 180 partial skeletons of cetaceans, together with remains of other vertebrates, have been discovered in these two localities and most of these fossils are marked on two published geological maps [20][21][22]. Furthermore, all the fossils reported in the maps have been included in detailed stratigraphic columns accompanied by a precisely defined geochronological and biostratigraphic framework (ca 19-18 Ma) for the deposition of the entire sequence of fossil-bearing marine sediments (Figure 1). ...
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... using an allostratigraphic approach, Di Celma et al. [21,22] subdivided the Chilcatay strata exposed in the vertebrate-bearing fossil localities of Ullujaya and Zamaca into two distinctive sediment wedges, informally designated Ct1 and Ct2 in ascending stratigraphic order, separated by a major intraformational unconformity (Figure 1). In the Zamaca area the base of Ct1 rests with an angular unconformity on the Otuma Formation. ...
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... locality. Zamaca locality, Western Ica Valley, Ica Region, Southern Peru (Figure 1a,b). Geographic coordinates: 14°37'1.65" ...
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... horizon. The holotype of Ensidelphis riveroi MUSM 3898 was collected in the Chilcatay Fm exposed at Zamaca locality, and more precisely at 10.7 m above the contact with the underlying Otuma Formation, near the top of the Ct1c facies association of the Ct1 allomember [21,22] (Figure 1d). The age of the Ct1c facies association is constricted between 19.25 ± 0.08 Ma and 19.00 ± 0.28 Ma (early Burdigalian) on the basis of two volcanic ash layer samples dated by 40 Ar/ 39 Ar [89]. ...
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... and teeth are not preserved. Zamaca locality, Western Ica Valley, Ica Region, Peru (Figure 1a,b). Geographic coordinates: 14°37'28.77" ...
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... specimen was reported in the Zamaca fossil map of Di Celma et al. [22] with the field number ZM 128 and provisionally referred to "Platanistoidea indet." From the Chilcatay Fm, 38.1 m above the contact with the underlying Otuma Formation, in the Ct1a facies association of the Ct1 allomember [21,22] (Figure 1d). The age of this portion of the Ct1a facies association can be constricted between 19.00 ± 0.25 Ma and 18.08 ± 0.07 Ma (early Burdigalian) on the basis of two volcanic ash layer samples dated by 40 Ar/ 39 Ar [89]. ...
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... long hamular fossa of the pterygoid sinus extending anteriorly on the palatal surface of the rostrum, the cranium distinctly shorter than wide, and the anterior portion of the zygomatic process of the squamosal tightly appressed to the postorbital process of the frontal are all derived characters allowing us to refer MUSM 3899 to the Platanistoidea superfamily ( Figure 10). In particular, MUSM 3899 belongs to the Platanidelphidi clade in having: (1) Asymmetry of the premaxillae on the rostrum at some distance anterior to the premaxillary foramina, with the right premaxilla being distinctly narrower than the left in dorsal view; (2) posterior dorsal infraorbital foramen along the vertex more medial than the lateralmost margin of the premaxilla in the cranium; (3) deep fossa in the frontal on the orbit roof, at the level of the frontal groove, presumably for an orbital lobe of the pterygoid sinus; (4) vertex distinctly shifted to the left compared to the sagittal plane of the skull; (5) palatine not exposed anterior to the pterygoid; (6) dorsoventrally thick zygomatic process of the squamosal; and (7) straight ventral edge of the zygomatic process in lateral view. ...
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... locality. MUSM 487 was collected several years ago from layers of the Chilcatay Fm in the Zamaca-Ullujaya area, western Ica Valley, Ica Region, southern Peru (Figure 1a,b). Approximate geographic coordinates: 14°36' S, 75°38' W. ...
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... rostrum of Furcacetus has a peculiar sinusoidal shape in lateral view (Figure 13a-d): from its base, it curves upward until about 50 mm from the apex, where it curves downward until its anterior end. The 50 mm downward-bent anterior portion of the rostrum is formed by the premaxillae only and hosted procumbent incisors (Figure 13e,f). ...
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... rostrum of Furcacetus has a peculiar sinusoidal shape in lateral view (Figure 13a-d): from its base, it curves upward until about 50 mm from the apex, where it curves downward until its anterior end. The 50 mm downward-bent anterior portion of the rostrum is formed by the premaxillae only and hosted procumbent incisors (Figure 13e,f). Among other squalodelphinids, we also observed a curved (but not sinusoidal) rostrum in the cranium MUSM 1403 of Huaridelphis raimondii (but not in the holotype) and in the crania MUSM 1395 and MUSM 3897 of Notocetus vanbenedeni (but not in the holotype and the other referred specimens). ...
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... rostrum of Furcacetus is dorsoventrally compressed in its anterior and posterior portions, whereas it becomes more laterally compressed towards mid-length. A deep transverse concavity, involving both the maxillae and the premaxillae, occurs on the dorsal surface of the cranium around the base of the rostrum (Figures 11,13c). This concavity is laterally overhung by the elevated antorbital regions, which, as in all Platanidelphidi, are distinctly higher than the dorsal margin of the rostrum base in lateral view. ...
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... The anterior portion of the rostrum is formed by the premaxilla alone for 50 mm (Figure 11), a condition also observed in all squalodelphinids having the apex of the rostrum preserved (Dilophodelphis, Huaridelphis, Notocetus, and Squalodelphis), and in Ensidelphis. Partially related to this feature, in dorsal view the lateral premaxilla-maxilla suture is laterally bent and the premaxilla widens transversely towards the apex of the rostrum. ...
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... outlined above, this anterior premaxillary portion of the rostrum is curved downward, dorsoventrally compressed, and bears three alveoli on each side ( Figure 13). ...
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... ventral view (Figure 12), on the rostrum the premaxilla-maxilla suture runs obliquely from the posterior margin of the third incisor to a medial point located 138 mm anterior to the right antorbital notch. Consequently, the premaxillae display a narrow and elongated ventral exposure between the palatal processes of the maxillae. ...
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... The rostral portions of the maxillae are not well preserved, with some missing parts, especially for the left maxilla (Figure 11). However, it is clearly discernible that the transverse width of the dorsal exposure of the maxilla remains narrow for the entire length of the rostrum. ...
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... the maxilla displays a limited anterolateral extension above the preorbital process of the frontal, although the maxilla-frontal suture it is not clearly discernible on the right side of the cranium and the left side is incompletely preserved. Above the orbit, the right maxilla exhibits a longitudinal bulge posterolateral to the antorbital notch (Figure 13c). A similar bulge is present in other squalodelphinids, but less marked, except in Dilophodelphis (thickening significantly greater than in Furcacetus) and Squalodelphis (thickening similar to Furcacetus). ...
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... ventral view (Figure 12), the palatal surface of the rostrum is mainly formed by the maxillae. It is flat along its anterior two thirds, becoming weakly transversely convex towards the base of the rostrum. ...
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... and cribriform plate. The nasal septum separating the asymmetrical nares is well ossified and elevated (Figure 11). Its posterodorsal margin (medial portion of the cribriform plate) is in contact with the right nasal. ...
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... the right nasal is preserved. In dorsal view (Figure 11), it is weakly inflated, rectangular, with a main axis that is obliquely oriented in respect to the frontal plane of the skull. Similar features are observed in Huaridelphis, Macrosqualodelphis, and Notocetus. ...
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... features are observed in Huaridelphis, Macrosqualodelphis, and Notocetus. In lateral view (Figure 13a,b), the nasal of Furcacetus appears to slope anteriorly (at least in its anterior portion) as in Huaridelphis, but not in Macrosqualodelphis and Notocetus, having the dorsal surface of the nasal roughly horizontal. The lost left nasal was probably smaller than the right, judging by the size and the shape of the depressed area between the right nasal and the medial margin of the posterior portion of the left premaxilla. ...
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... At the vertex, the lateral margin of the right frontal is longitudinally more elongated than the left (Figure 11), a condition shared with Dilophodelphis, Huaridelphis, Notocetus, and Squalodelphis. The medial suture between the frontals at the vertex is not discernible. ...
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... medial suture between the frontals at the vertex is not discernible. In lateral view (Figure 13a,b), the dorsal surface of the frontals at the vertex appears horizontal, as in Notocetus, but not in Huaridelphis and Macrosqualodelphis, both having frontals anteroventrally sloping. ...
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... postorbital process of the frontal of Furcacetus is robust and trapezoidal in lateral view, similar to that of Notocetus. The medial portion of the ventral surface of the frontal of Furcacetus is excavated in the orbit region by a deep and obliquely oriented fossa (Figure 12). A similar fossa, probably corresponding to an extension of the pterygoid sinus in the orbit region, has been observed in all other Platanidelphidi. ...
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... supraoccipital is poorly preserved. The eroded nuchal crest is roughly straight in dorsal view (Figure 11). The supraoccipital slopes posteriorly from the vertex with its posterodorsal surface drawing, in lateral view, an angle of ca 50° with the horizontal plane ( Figure 13a,b). ...
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... eroded nuchal crest is roughly straight in dorsal view (Figure 11). The supraoccipital slopes posteriorly from the vertex with its posterodorsal surface drawing, in lateral view, an angle of ca 50° with the horizontal plane ( Figure 13a,b). A similar inclination of the supraoccipital is observed in Notocetus, whereas Huaridelphis and Macrosqualodelphis display a lower inclination and Squalodelphis an almost vertical supraoccipital. ...
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... The palatines are not discernible on the ventral surface of the skull (Figure 12). Their anterior portions are probably fully covered by the pterygoids, as generally observed in other Platanidelphidi. ...
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... On the posterior palatal surface of the rostrum (Figure 12), the right and left pterygoids are medially sutured and each is excavated by a pterygoid sinus fossa extending about 30 mm anterior to the right antorbital notch. An elongated hamular fossa of the pterygoid sinus, extending anterior to the rostrum base, is a derived feature shared by all platanistoids. ...
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... is no trace of the jugals and lacrimals. Nevertheless, the ventral surface of the well-preserved preorbital process of the right frontal is marked by a deep oblique groove that represents the suture for the missing lacrimal ( Figure 12). This suture indicates that the lacrimal was anteroposteriorly narrow along the lateral wall of the antorbital notch, as in all other platanistoids. ...
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... In lateral view (Figure 13a,b), the zygomatic process of the squamosal is robust and displays a convex dorsal margin, two features shared with all Platanidelphidi. More specifically, the dorsal margin of the zygomatic process of Furcacetus is more similar to that of Medocinia, contrasting with those, more regularly arched, of other squalodelphinids. ...
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... In lateral view (Figure 13a,b), the parietal is widely exposed in the temporal fossa. There is no trace of the peculiar temporal swelling observed in Ensidelphis. ...
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... The whole left exoccipital is lost and the right paroccipital process is badly preserved (Figure 13 c). A shallow dorsal condyloid fossa is visible dorsolateral to the broken right occipital condyle. ...
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... The basioccipital is damaged, but the right basioccipital crest is partially preserved (Figure 12). The angle between right and left basioccipital crests in ventral view is estimated to about 40°. ...
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... The vomer is exposed in ventral view (Figure 12), posterior and medial to each choana, and on the palatal surface of the rostrum, between the maxillae, for a tract extending from roughly 100 to 150 mm anterior to the right antorbital notch. ...
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... The incomplete right periotic is preserved in articulation with the corresponding squamosal ( Figure 12). The posterior process is lost and the pars cochlearis is damaged. ...
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... estimated tooth count for each upper quadrant is 25 (Figure 12). Excluding the longirostrine platanistoids, all having smaller and more numerous teeth, the tooth count of Furcacetus is slightly higher than in Notocetus (18−23), significantly higher than in Squalodelphis (15), and lower than in Araeodelphis (ca 50), Dilophodelphis (ca 35), and Huaridelphis (28−30). ...
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... ratio between the maximum transverse width for alveoli at rostrum mid-length and the estimated BZW is 0.025, a value similar to Huaridelphis (0.026) and smaller than in Macrosqualodelphis (0.042) and Notocetus (0.040). Judging by the marked oblique orientation of the axis of the three roots embedded in the premaxillae, the incisors (premaxillary teeth) were anterolaterally procumbent (Figure 13e,f), a condition absent in all other Platanistoidea s.s. and more similar to Waipatia and squalodontids. The maximum diameter of the root of these incisors is 7 mm. ...
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... maximum diameter of the root of these incisors is 7 mm. The posteriormost preserved tooth, located about 100 mm anterior to the right antorbital notch, displays a small proximal portion of crown (Figure 13g,h). In particular, only the lateral surface of the crown is well preserved, showing cusp-like cingular nodules and enamel ornamented with longitudinal striations. ...
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... maximum diameter of the root and crown of this tooth is 6.0 and 6.5 mm, respectively. About 70 mm anterior to this tooth, along the upper alveolar groove, another tooth has a root with a diameter of 6.0 mm and a crown without accessory denticles (Figure 13a,b). ...
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... referred specimens, localities, and ages. MUSM 3896 (Figures 14a-e, 15a,b), an almost complete skull including the cranium (only the jugals are missing, the dorsal surface of the vertex is covered by a concretion, and the dorsal surface of the rostrum at mid-length is damaged), fused mandibles in articulation with the cranium, articulated ear bones, and presumably all upper and lower teeth in their respective alveoli. Zamaca locality, western Ica Valley, Ica Region, Peru. ...
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... 3897 ( Figures. 14f-k, 15c-f), a cranium with eroded vertex, lacking jugals and ear bones, and without teeth in situ; incomplete mandibles fused, but not articulated to the cranium and with two teeth inside alveoli; and 4 detached teeth, all belonging to the same animal. Zamaca locality, Western Ica Valley, Ica Region, Peru. Geographic coordinates: 14°37'18.05" S, ...
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... 1484 (Figures 16 and 17) consists of the left tympanic bulla, the incomplete fused mandibles, one tooth, the atlas, the right and left humeri, the left radius and the left ulna of a single individual. Other bones of the same animal, including some vertebrae and ribs are still in the field (Figure 8h-i in [20]); the cranium is not preserved. ...
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... new Zamaca material confirms that Notocetus was a squalodelphinid with a powerful feeding apparatus characterized by robust mandibles, large, interlocking, and moderately heterodont teeth, and anteroposteriorly elongated temporal fossa and zygomatic process of the squamosal. These characters are particularly evident in MUSM 3896 (Figure 14a-e), the only skull of the species that preserves the complete mandibles firmly articulated to the cranium (and probably all the teeth and ear bones in place). For these features Notocetus is found to be intermediate between the slightly smaller Furcacetus and the significantly larger Macrosqualodelphis. ...
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... these features Notocetus is found to be intermediate between the slightly smaller Furcacetus and the significantly larger Macrosqualodelphis. On the ventral surface of the tympanic bulla of MUSM 3896, the wide and deep median furrow extends clearly on the anterior spine (Figure 14e). Such an anterior extension of the median furrow is present in N. vanbenedeni AMNH 29026 from Argentina and is considered a synapomorphy of the family Squalodelphinidae. ...
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... an anterior extension of the median furrow is present in N. vanbenedeni AMNH 29026 from Argentina and is considered a synapomorphy of the family Squalodelphinidae. By contrast, the median furrow of the well-preserved tympanic bulla of MUSM 1484 apparently does not extend anteriorly along the anterior spine (Figure 16a-d). However, some longitudinal striations on the ventral surface of the anterior spine could represent spongy bone filling the anterior portion of the median furrow, suggesting that this character could be subject to intraspecific variation, possibly due to ontogenesis. ...
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... The preservation of a complete set of teeth implanted in their alveoli in MUSM 3896 ( Figure 15a,b), together with the four detached teeth of MUSM 3897 (Figure 15c-f; Table 4), is relevant since, to date, teeth of Notocetus were only known in the fragmentary specimen AMNH 29026 [92]. The Peruvian teeth confirm the observations made by Muizon [92] on AMNH 29026: the two posterior teeth embedded in the left mandible of MUSM 3896 have a low triangular crown with two-three small posterior accessory denticles and cusp-like cingular nodules on the lateral surface; moving to the anterior portion of the mandibles and rostrum of MUSM 3896, tooth crowns become gradually higher, forming a conical point, slightly recurved posteriorly, and lacking the posterior denticles; their enamel is ornamented only by thin longitudinal striations. ...
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... The preservation of a complete set of teeth implanted in their alveoli in MUSM 3896 ( Figure 15a,b), together with the four detached teeth of MUSM 3897 (Figure 15c-f; Table 4), is relevant since, to date, teeth of Notocetus were only known in the fragmentary specimen AMNH 29026 [92]. The Peruvian teeth confirm the observations made by Muizon [92] on AMNH 29026: the two posterior teeth embedded in the left mandible of MUSM 3896 have a low triangular crown with two-three small posterior accessory denticles and cusp-like cingular nodules on the lateral surface; moving to the anterior portion of the mandibles and rostrum of MUSM 3896, tooth crowns become gradually higher, forming a conical point, slightly recurved posteriorly, and lacking the posterior denticles; their enamel is ornamented only by thin longitudinal striations. ...
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... same tooth has a peculiar swelling on the posterior surface of the root. The only preserved tooth of MUSM 1484 (Figure 16h) fully overlaps in size and shape with the described anterior teeth of N. vanbendeni [92]. This tooth is fusiform, weakly curved, and its crown is conical, weakly mesiodistally compressed, and bearing a posterior carina. ...
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... enamel is ornamented by thin anastomosed longitudinal grooves and ridges, more marked on the labial surface of the crown, where an ectocingulum is also visible. As in the mandibles of the Argentinian specimens, in MUSM 3896 (Figure 14a,c,d), MUSM 3897 ( Figure 14g,i,k), and MUSM 1484 (Figure 16e-g) the mandibular symphysis is fused, the symphyseal portion is markedly dorsoventrally flattened, and, as in Huaridelphis and Squalodelphis, lacking the pair of lateral grooves observed in members of the families Allodelphinidae and Platanistidae, and in the basal Platanidelphidi Ensidelphis. The symphyseal portion of the complete mandibles of MUSM 3896 represents 40% of the total mandibular length, measured parallel to the sagittal plane, a value close to Squalodelphis (42%), the only other squalodelphinid for which complete mandibles are known. ...
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... enamel is ornamented by thin anastomosed longitudinal grooves and ridges, more marked on the labial surface of the crown, where an ectocingulum is also visible. As in the mandibles of the Argentinian specimens, in MUSM 3896 (Figure 14a,c,d), MUSM 3897 ( Figure 14g,i,k), and MUSM 1484 (Figure 16e-g) the mandibular symphysis is fused, the symphyseal portion is markedly dorsoventrally flattened, and, as in Huaridelphis and Squalodelphis, lacking the pair of lateral grooves observed in members of the families Allodelphinidae and Platanistidae, and in the basal Platanidelphidi Ensidelphis. The symphyseal portion of the complete mandibles of MUSM 3896 represents 40% of the total mandibular length, measured parallel to the sagittal plane, a value close to Squalodelphis (42%), the only other squalodelphinid for which complete mandibles are known. ...
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... enamel is ornamented by thin anastomosed longitudinal grooves and ridges, more marked on the labial surface of the crown, where an ectocingulum is also visible. As in the mandibles of the Argentinian specimens, in MUSM 3896 (Figure 14a,c,d), MUSM 3897 ( Figure 14g,i,k), and MUSM 1484 (Figure 16e-g) the mandibular symphysis is fused, the symphyseal portion is markedly dorsoventrally flattened, and, as in Huaridelphis and Squalodelphis, lacking the pair of lateral grooves observed in members of the families Allodelphinidae and Platanistidae, and in the basal Platanidelphidi Ensidelphis. The symphyseal portion of the complete mandibles of MUSM 3896 represents 40% of the total mandibular length, measured parallel to the sagittal plane, a value close to Squalodelphis (42%), the only other squalodelphinid for which complete mandibles are known. ...
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... angle between the two mandibles equals 38° in both MUSM 3896 and MUSM 3897, similar to Squalodelphis but significantly smaller than in all platanistids (> 50°). Embrasure pits are observed between and lateral to the alveoli on the mandibles of MUSM 3897 (Figure 14g) and MUSM 1484 (Figure 16f-g). In lateral view, posterior to the alveolar row, the robust ramus (preserved in MUSM 3896 and MUSM 3897) raises posterodorsally and the coronoid process is significantly elevated. ...
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... angle between the two mandibles equals 38° in both MUSM 3896 and MUSM 3897, similar to Squalodelphis but significantly smaller than in all platanistids (> 50°). Embrasure pits are observed between and lateral to the alveoli on the mandibles of MUSM 3897 (Figure 14g) and MUSM 1484 (Figure 16f-g). In lateral view, posterior to the alveolar row, the robust ramus (preserved in MUSM 3896 and MUSM 3897) raises posterodorsally and the coronoid process is significantly elevated. ...
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... almost complete atlas of MUSM 1484 (Figure 16i,j) is close in shape to the atlas of the specimen of N. vanbenedeni AMNH 9485, described by True [125], in the extreme reduction of the ventral transverse processes, the neural arch being proportionally lower, and the roughly circular neural canal. ...
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... humerus, radius, and ulna, preserved in MUSM 1484 ( Figure 17; Table 5), are here described in detail because up to now these bones were unknown in Notocetus vanbenedeni. Among other squalodelphinids the forelimb was described only in Macrosqualodelphis ukupachai, whereas among other platanistoids these bones are known in the extant Platanista gangetica and in the allodelphinids Allodelphis pratti, A. woodburnei, Goedertius oregonensis, and Zarhinocetus errabundus ( [121], Figure 39). ...
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... other squalodelphinids the forelimb was described only in Macrosqualodelphis ukupachai, whereas among other platanistoids these bones are known in the extant Platanista gangetica and in the allodelphinids Allodelphis pratti, A. woodburnei, Goedertius oregonensis, and Zarhinocetus errabundus ( [121], Figure 39). Comparisons ( Figure 18; Table 6) were made also with the few other archaic odontocetes having some of these bones preserved (Awamokoa tokarahi, Kelloggia barbara, Otekaikea huata, Schizodelphis sp., Squalodon bellunensis, S. calvertensis, and with derived archaeocetes (e.g., Cynthiacetus peruvianus). Humerus. ...
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... The humerus of MUSM 1484 ( Figure 17) is similar in shape but smaller than in Macrosqualodelphis ukupachai; among platanistoids it shares only with M. ukupachai the large, hemispherical and posterolaterally protruding head, the lesser tubercle being higher than the head, the salient and distally elongated deltopectoral crest, and the large and deep fossa for insertion of M. infraspinatus. In particular, the large, hemispherical and posterolaterally protruding head may be a diagnostic character of squalodelphinids since it was not observed in the humerus of any other cetacean, whereas the lesser tubercle being higher than the head is also observed in Kelloggia barbara [130]. ...
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... The radius of MUSM 1484 (Figure 17c) is a mediolaterally flat bone that distally widens anteroposteriorly, more so than in M. ukupachai but to a lesser degree than in P. gangetica. The proximodistal length of the radius of MUSM 1484 is significantly smaller than the proximodistal length of the humerus, with a ratio (C/A in Table 6) = 0.69, lower than in M. ukupachai (0.77), but higher than in P. gangetica (0.50-0.56), whereas in the allodelphinid Ninjadelphis ujiharai the two bones almost have the same length (C/A = 0.96).The ratio between the anteroposterior width at mid-length and the proximodistal length (D/C) is relatively high (0.51), if compared to N. ujiharai (0.24) and some archaic odontocetes, whereas it is similar to M. ukupachai (0.49) and lower than in P. gangetica (0.68-0.74). ...
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... The ulna of MUSM 1484 (Figure 17c), is proximodistally shorter than the radius and, as in M. ukupachai and P. gangetica, at its mid-length it is anteroposteriorly narrower than the radius. Like the radius, it is mediolaterally flattened and the ratio between its anteroposterior width at mid-length and its proximodistal length (F/E in Table 6) has a value (0.51) higher than in allodelphinids and other archaic odontocetes, but lower than in P. gangetica (0.72-0.87) (ratio not computable for the ulna of M. ukupachai due to its incompleteness). ...
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... Notocetus sp. Figure 19 Referred specimen, locality, and age. MUSM 1485 consists of a right isolated tympanic bulla. ...
Context 60
... MUSM 1484 described above this tympanic bulla is similar in size and shape to those referred to Notocetus vanbenedeni. The median furrow (Figure 19b) is only moderately deep, but it extends anteriorly on the preserved portion of the broken anterior spine, a feature that, as outlined above, has been observed in all squalodelphinid tympanic bullae (Phocageneus, Notocetus, and Squalodelphis). Here also, as in the other squalodelphinids, the inner and outer posterior prominences have approximately the same posterior extent. ...
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... cladistic analysis produced 12 equally parsimonious trees, with tree length = 98, consistency index (CI) = 0.60, and retention index (RI) = 0.83. The strict consensus tree, the bootstrap values, and the Adams consensus tree are presented in Figure 21. ...

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Nowadays, the requiem sharks comprise one of the most diverse and widespread families of selachians, i.e., Carcharhinidae. Among the carcharhinids, the genus Carcharhinus has the largest number of living species, namely, at least 35. Known from fossils as old as the Cretaceous, the requiem sharks did not significantly radiate before the Eocene (when Carcharhinus also appeared), and their diversification mainly occurred in Neogene times. Here, we describe a new species of requiem shark, Carcharhinus dicelmai sp. nov., based on fossil teeth from Lower Miocene (18.4–18.1 Ma) strata of the Chilcatay Formation of the East Pisco Basin (southern Peru). Upper teeth of C. dicelmai sp. nov. are typically provided with a slender, smooth-edged cusp; a marked coronal twist; and a distal heel that bears 1–5 coarse, angularly lobate serrae that become more prominent toward the base of the cusp. The dentition of C. dicelmai sp. nov. appears less akin to that of most other carcharhines to the cutting-clutching type, and seemingly testifies to the development of more predominantly clutching adaptations. A carcharhinid tooth from the Burdigalian to lower Langhian Cantaure Formation of Venezuela is reassigned to C. dicelmai sp. nov., suggesting a trans-Panamanian distribution for this extinct shark species.
... Squalodelphinidae are archaic longirostrine platanistoid dolphins known mostly from the early and middle Miocene of Europe, North America, and South America (Dal Piaz, 1917;Lambert et al., 2014;Nelson and Uhen, 2018). Though many archaic odontocetes in various stem and crown groups have been allied with Platanista within the Platanistoidea, Squalodelphinidae seem to be the only other family consistently forming a sister taxon relationship with the Platanistidae (Geisler et al., 2011;Lambert et al., 2014;Tanaka and Fordyce, 2015;Boersma and Pyenson, 2016;Albright et al., 2018;Bianucci et al., 2020). Squalodelphinids share maxillary crests and long rostra with the Platanistidae, though the crests are dense, massive, and dorsally convex (Lambert et al., 2014) rather than being large flanges flanking the melon (e.g., Platanista, Zarhachis). ...
Article
A diverse but fragmentary assemblage of fossil cetaceans is reported from the Oligocene-Miocene Belgrade Formation of North Carolina. This assemblage preserves many odontocetes including four xenorophids (Albertocetus, Echovenator sp., cf. Cotylocara, and Xenorophus sp.), a possible waipatiid (cf. Waipatiidae), a giant agorophiid-grade dolphin (Ankylorhiza), a shark-toothed dolphin (cf. Squalodon), longirostrine “swordfish” dolphins (Eurhinodelphinidae), a longirostrine eoplatanistid dolphin (cf. Eoplatanista), a longirostrine squalodelphinid dolphin, a possible early delphinidan (Kentriodontidae), as well as an eomysticetid baleen whale (Eomysticetus sp.) and sirenian fragments. Most of these taxa are characteristic of or unique to Oligocene deposits (Xenorophidae, cf. Waipatiidae, Ankylorhiza, Eomysticetus) whereas others are more typical of early or middle Miocene deposits (cf. Eoplatanista, Eurhinodelphinidae, cf. Squalodon, Squalodelphinidae, Kentriodontidae). The Belgrade Formation at Belgrade Quarry is dated to 25.95-21.12 Ma, approximating the Oligocene-Miocene transition. The transitional composition of the Belgrade cetacean assemblage suggests gradual changes between Oligocene to Miocene cetacean faunas, to be verified by the discovery of more complete remains from the poorly sampled earliest Miocene (Aquitanian).
... Lydekker 1893;True 1910;Dal Piaz 1917;Cabrera 1926;Kellogg 1928;Simpson 1945;de Muizon 1987). Recently, new putative records of the species from the early Miocene of Peru were described (Bianucci et al. , 2020. Even though Notocetus vanbenedeni has been included in different morphological phylogenetic matrices (e.g. ...
... We acknowledge this is not an exhaustive list of possible platanistoids to include, but we have included as many taxa as possible to capture the diversity of the group. Finally, based on preliminary differences observed, we included Peruvian specimens MUSM 1395 ) and MUSM 3896, 3897 and 1484 (Bianucci et al. 2020) assigned to Notocetus vanbenedeni, to test their phylogenetic relationship with the Patagonian specimens analysed here. The list of characters and coding modifications is provided in Supplemental material S3. ...
... In ventral view, the main feature is the deep, straight and long median furrow, extending almost the entire length of the tympanic bulla, as in Squalodelphis fabianii. However, it does not extend onto the anterior spine as Bianucci et al. (2020) reported in Peruvian Notocetus vanbenedeni MUSM 3896. Platanista gangetica and Zarhinocetus errabundus have a medially convex furrow. ...
Article
Platanistoidea remains one of the most evolutionarily intriguing lineages of toothed whales (Odontoceti). The clade comprises mostly extinct species from the late Oligocene–early Miocene onward and a single extant riverine genus (Platanista). There is an ongoing debate as to the membership of Platanistoidea and the causes of their near extinction. In Patagonia (Argentina), the most abundant platanistoid recorded in the lower Miocene Gaiman Formation is Notocetus vanbenedeni, first described by Moreno in 1892 based on two individuals. The goal of the present contribution is to conduct an updated anatomical, palaeobiological and phylogenetic analyses of Notocetus vanbenedeni and hence contribute to an understanding of the evolutionary history of the Platanistoidea. Our analyses, including at least 26 individuals (12 undescribed), show that Notocetus vanbenedeni is a valid platanistoid taxon, recovered as part of a new clade. Among its most outstanding features, this taxon has an elevated dorsal tubercular supraorbital crest formed mainly by the frontal, the precursor of the pneumatized crest of the extant Platanista. Notocetus vanbenedeni also shows initial stages of the plesiomorphic bony connection between the earbones and skull as in Platanista, although the functional implications for hearing remain elusive. The nasal sac system, pterygoid sinus system and morphology of the earbones suggest that this species was able to hear high-frequency sounds and echolocate underwater, similar to extant odontocetes. Thus, Notocetus vanbenedeni presents a mosaic of features that suggest an intermediate platanistoid morphotype. Anatomical differences and phylogenetic analyses suggest that Peruvian specimens could not be referred to this species. The feeding apparatus of Notocetus vanbenedeni makes it the only combination suction-feeder recorded in the early Miocene of Patagonia and among the smallest odontocetes. Finally, the abundant records of Notocetus vanbenedeni in an inner shelf environment with freshwater influence suggest a possible early preference for such protected habitats.
... As redefined by Bianucci et al. (2020), the superfamily Platanistoidea (including Allodelphinidae, Platanistidae and Squalodelphinidae, but not Squalodontidae and Waipatiidae) is a monophyletic group of nearly homodont odontocetes that had its greatest radiation in late Oligocene-Early Miocene times and is nowadays represented only by the South Asian freshwater dolphins (Platanista gangetica [Lebeck, 1801] and Platanista minor Owen, 1853;Braulik et al., 2021). Platanistoids are odontocetes with singlerooted teeth characterised by the combination of several morphological characters, some of which are peculiar of this clade (synapomorphies) and mainly concern the ear bones, while others are shared with other odontocetes, e.g., the elongated hamular fossa of the pterygoid sinus extending anteriorly on the palatal surface of the rostrum (also present in Ziphiidae). ...
... The high diversity of this clade during the Early Miocene is demonstrated by the odontocete assemblage of the Chilcatay Formation as known from strata exposed at Ulluyaja, Zamaca and south of Cerro Colorado. Indeed, three new genera and species of squalodelphinids (Furcacetus flexirostrum Bianucci et al., 2020, Huaridelphis raimondii Lambert et al., 2014band Macrosqualodelphis ukupachai Bianucci et al., 2018a and a new genus and species of platanistoid basal to the clade formed by the squalodelphinids and the platanistids (Ensidelphis riveroi Bianucci et al., 2020) have been described from these localities; in addition, the squalodelphinid Notocetus vanbenedeni Moreno, 1893, a platanistid close to Araeodelphis natator Kellogg, 1957 and another unnamed platanistoid have also been reported (Lambert et al., 2014b;Bianucci et al., 2015Bianucci et al., , 2018aBianucci et al., , 2020. The high diversity of platanistoids of the Chilcatay Formation (Figs 18, 19) correlates with a high disparity in the size and shape of the skulls. ...
... The high diversity of this clade during the Early Miocene is demonstrated by the odontocete assemblage of the Chilcatay Formation as known from strata exposed at Ulluyaja, Zamaca and south of Cerro Colorado. Indeed, three new genera and species of squalodelphinids (Furcacetus flexirostrum Bianucci et al., 2020, Huaridelphis raimondii Lambert et al., 2014band Macrosqualodelphis ukupachai Bianucci et al., 2018a and a new genus and species of platanistoid basal to the clade formed by the squalodelphinids and the platanistids (Ensidelphis riveroi Bianucci et al., 2020) have been described from these localities; in addition, the squalodelphinid Notocetus vanbenedeni Moreno, 1893, a platanistid close to Araeodelphis natator Kellogg, 1957 and another unnamed platanistoid have also been reported (Lambert et al., 2014b;Bianucci et al., 2015Bianucci et al., , 2018aBianucci et al., , 2020. The high diversity of platanistoids of the Chilcatay Formation (Figs 18, 19) correlates with a high disparity in the size and shape of the skulls. ...
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The East Pisco Basin is one of the forearc basins that formed during the Cenozoic along the coast of Peru due to the subduction of the Farrallon-Nazca plate beneath the South American plate. The sedimentary fi ll of this basin is extensively exposed along the coastal Ica Desert, and includes a succession of Eocene to Pliocene marine sediments that account for a ~50-myr-long history of semi-continuous deposition. These rocks are characterized by an outstanding fossil content that remarkably contributed to our understanding of the evolutionary history of the main groups of Cenozoic marine vertebrates. In the Ica desert, the most common and signifi cant vertebrate remains belong to cetaceans. Knowledge on the fossil cetaceans of the East Pisco Basin has grown dramatically in the last fi fteen years thanks to several international research projects involving, among many others, the authors of the present article. These research eff orts have led to the discovery of several hundred fossil skeletons, the most signifi cant of which have been collected, prepared and partly published. Furthermore, interdisciplinary studies were also conducted in order to provide a high resolution chronostratigraphic framework for this fossil record. Remarkable cetacean specimens (42.6 Ma) Yumaque strata are home to the quadrupedal protocetid archaeocete Peregocetus pacifi cus, which documents the fi rst arrival of cetaceans in the Pacifi c Ocean. Geologically younger (36.4 Ma) Yumaque deposits have yielded the holotype skeleton of Mystacodon selenesis, the oldest mysticete ever found. This ancestor of the modern baleen whales had a skull provided with a complete dentition and retained hindlimbs, albeit reduced in size. In the Otuma Formation, a nine-m-long basilosaurid (Cynthiacetus peruvianus) has been discovered. The Chilcatay Formation records the fi rst great radiation of the odontocetes, represented by Inticetidae (Inticetus vertizi), basal Platanidelphidi (Ensidelphis riveroi), Squalodelphinidae (Furcacetus fl exirostrum, Huaridelphis raimondii, Macrosqualodelphis ukupachai and Notocetus vanbenedeni), Platanistidae (aff. Araeodelphis), Physeteroidea (Rhaphicetus valenciae and cf. Diaphorocetus), Chilcacetus cavirhinus, indeterminate Eurinodelphinidae, and Kentriodontidae (Kentriodon). Overall, this roughly coeval assemblage displays a considerable disparity in terms of skull shape and body size that is possibly related to the development of diff erent trophic strategies, ranging e.g., from suction to raptorial feeding. In the Pisco Formation, starting from P0, the baleen-bearing whales (Chaeomysticeti) represent the most frequent cetacean fossils (only a few mysticetes are known from the Chilcatay strata). Two chaeomysticete lineages are found in the Pisco Formation: Cetotheriidae (from Tiucetus rosae in P0 to Piscobalaena nana in P2) and Balaenopteroidea (from Pelocetus in P0 to several undescribed species of Balaenopteridae in P2, testifying to a progressive trend toward gigantism). Odontocetes are rare in P0, the "kentriodontid" Incacetus broggii being the only species described from these strata, but they become more abundant and diverse in P1 and P2. In P1, the commonest toothed whale is Messapicetus gregarius, a member of Ziphiidae featuring an extremely elongated rostrum and a complete set of functional teeth. Another ziphiid from P1 is Chimuziphius coloradensis, known only from the fragmentary holotype cranium. The P1 strata also record the appearance of the crown Delphinida, with the superfamily Inioidea being represented by two small pontoporiids (Brachydelphis mazeasi and Samaydelphis chacaltanae) and one iniid (Brujadelphis ankylorostris). Moreover, P1 is also home to the stem physeteroid Livyitan melvillei; featuring a three-m-long skull and teeth reaching 36 cm in length, L. melvillei was one of the largest raptorial predators and, possibly, the biggest tetrapod bite ever found. Acrophyseter is another macroraptorial sperm whale, distinctly smaller than L. melvillei, known from both P1 and P2. Even smaller in size are the kogiids Platyscaphokogia landinii and Scaphokogia cochlearis, both of which are known from the upper strata of P2. The same allomember is also home to the ziphiids Chavinziphius maxillocristatus and Nazcacetus urbinai, the "kentriodontids" Atocetus iquensis and Belenodelphis peruanus, and undescribed members of Phocoenidae.
... Those include members of the following extinct clades: Allodelphinidae (in the North Pacific; Kimura and Barnes 2016), Eurhinodelphinidae (further characterized by the edentulous anterior part of the rostrum being markedly longer than the mandible; Kellogg 1925), Pomatodelphininae (a platanistid subfamily whose members are characterized by a dorsoventrally flattened rostrum; Barnes 2006), the non-platanistid Platanidelphidi as represented by Ensidelphis , and the Eoplatanistidae (Muizon 1988a) (Fig. 1). While the fossil record of Ensidelphis and Eoplatanistidae is for now restricted to the early Miocene of Peru and the Mediterranean, respectively (Bianucci and Landini 2002;Bianucci et al. 2020), Allodelphinidae, Eurhinodelphinidae, and Pomatodelphininae display a broader temporal and, to some extent, geographic distribution. Still, the diversity of hyper-longirostrine dolphins underwent a major drop before the late Miocene: no allodelphinid is currently known to have persisted beyond the Serravallian-Tortonian boundary (Kimura and Barnes 2016); only one pomatodelphinine survived to the Tortonian along the Atlantic Coastal Plain (USA) (unpublished data); and one eurhinodelphinid has been tentatively recovered from the early late Miocene of the North Sea Basin (Lambert 2005b). ...
... Distribution of hyper-longirostry within a composite phylogenetic tree of crown odontocetes supplemented with schematic drawings of the dorsal view of the skull from a well-known species for each clade in which hyper-longirostry is documented. Relationships between extant odontocete families based on McGowen et al. (2020) and relationships of extinct clades (including debated relationships of Eurhinodelphinidae + Eoplatanistidae; different hypotheses indicated with dashed lines) based on Muizon (1991), Lambert (2005a), Geisler et al. (2011), Tanaka et al. (2017, and Bianucci et al. (2020). Line drawings of Eoplatanista, Parapontoporia, Zarhinocetus, and Xiphiacetus modified from Marx et al. (2016); line drawing of Ensidelphis modified from Bianucci et al. (2020). ...
... Relationships between extant odontocete families based on McGowen et al. (2020) and relationships of extinct clades (including debated relationships of Eurhinodelphinidae + Eoplatanistidae; different hypotheses indicated with dashed lines) based on Muizon (1991), Lambert (2005a), Geisler et al. (2011), Tanaka et al. (2017, and Bianucci et al. (2020). Line drawings of Eoplatanista, Parapontoporia, Zarhinocetus, and Xiphiacetus modified from Marx et al. (2016); line drawing of Ensidelphis modified from Bianucci et al. (2020). All skulls scaled at the same condylobasal length Goolaerts et al. 2020) of the new finds of fossil remains of Eurhinodelphinidae in the upper Miocene (middle Tortonian) Diest Formation in Belgium (North Sea Basin). ...
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Hyper-longirostry, the character of having extremely elongated rostra, emerged in the early and middle Miocene among several different clades of echolocating toothed whales (odontocetes) followed by a rapid decline near the end of the middle Miocene, and postdated by a much lower number of occurrences in the late Miocene and Pliocene and a complete absence among extant odontocetes. New finds of unreworked fossils of Xiphiacetus cristatus (Eurhinodelphinidae) in the middle Tortonian Diest Formation in Belgium (9.54–8.8 Ma) allow for the documentation of the survival of a hyper-longirostrine dolphin into the early late Miocene. An extensive dataset of the rostral index (calculated as the ratio between rostral length and condylobasal length) of Neogene and extant odontocetes is compiled and presented here, which facilitates discussion of evolutionary trends of rostrum proportions during a time period spanning 23 million years. Of interest, the iterative survival into the late Miocene of a single different species of hyper-longirostrine dolphins in a number of paleogeographic regions (North Sea Basin, Atlantic Coastal Plain, and probably the southeastern Pacific) is noted, whereas hyper-longirostrine morphologies only seem to re-appear by the late Messinian in the Northeastern Pacific. A correlation between this pattern and a decrease in habitat size for coastal to estuarine dolphins linked to a major sea level drop is tentatively proposed; such a process may also have played a role in the ecological shift in several dolphin families to freshwater habitats.
... The Eocene-Miocene deposits of the East Pisco Basin, southern Peru, feature exceptionally common and remarkably well-preserved marine vertebrate remains that make them a true Fossil Lagerstätte (Bosio et al., 2021a,b;Esperante et al., 2015;Gariboldi et al., 2015). Fossils from the East Pisco Basin include marine mammals, seabirds, marine reptiles, and fishes (Bianucci et al., , 2016c(Bianucci et al., , 2020Clarke et al., 2007;Clarke et al., 2010;Collareta et al., 2015Collareta et al., , 2017Collareta et al., , 2020aCollareta et al., , 2020bde Muizon et al., 2019;Gioncada et al., 2016Gioncada et al., , 2018Lambert et al., 2015Lambert et al., , 2018Lambert et al., , 2017Lambert et al., , 2019Lambert et al., , 2020aLambert et al., , 2020bLandini et al., 2017aLandini et al., , 2017bLandini et al., , 2019Marx et al., 2017). ...
Article
The Eocene sediment successions of the East Pisco Basin (southern Peru) host an exceptionally rich and well-preserved assemblage of vertebrate fossils. However, due to the dearth of geochronological and biostratigraphic controls as well as of stratigraphic correlations, our understanding of these rocks and their fossil content remains elusive. This paper provides a comprehensive calcareous nannofossil, diatom, and silicoflagellate biostratigraphic framework for the Eocene strata exposed at four localities along the Ica River Valley, permitting a robust chronological calibration of the marine vertebrate fauna entombed therein and a better definition of important appearance/ extinction events. The Paracas Formation, deposited directly on top of the Proterozoic and Paleozoic rocks of the crystalline basement, is formed by a siliciclastic-bioclastic gravel-sized deposit (Los Choros member) and calcareous-terrigenous siltstone (Yumaque member) that was deposited from the Lutetian (47.8–41.2 Ma) through the Bartonian (41.2–37.7 Ma) to the early Priabonian (37.7–33.9 Ma). The unconformably overlying Otuma Formation consists of a basal sand, followed by calcareous siltstone intercalated by diatomite layers towards the top. In the study area, the Otuma Formation is Priabonian in age and is truncated at the top by an unconformity at the base of the overlying Miocene Chilcatay Formation. Due to the angular nature of the unconformity, the upper Otuma strata reach the Oligocene elsewhere. Average sedimentation rates range from 17 to 24 m/My in the Yumaque member of the Paracas Formation and increase to 147–170 m/My in the Otuma Formation. The microfossil assemblages witness a coastal setting with warm-temperate conditions for the Paracas Formation that become slightly cooler (though still temperate) in the upper Otuma Formation. Diatomaceous layers in the upper Otuma Formation indicate an overall increase in nutrient availability, which could reflect the global reorganization of ocean currents at the Eocene-Oligocene transition. However, the taxonomic composition of the diatom assemblage suggests seasonal rather than persistent upwelling conditions.
... One living riverine species, P. gangetica, warrants special attention. This species is the sole extant representative of an otherwise diverse fossil group, the Platanistoidea (sensu de Muizon 1987), whose contents and phylogenetic relationships are still debated (e.g., Fordyce and de Muizon 2001;Boersma et al. 2017;Tanaka and Fordyce 2017 and references therein;Viglino et al. 2018aViglino et al. ,b, 2020Gaetán et al. 2019;Bianucci et al. 2020). The earliest fossil record of this group comes from the late Oligocene, reaching a peak in diversity by the early Miocene and a marked decrease by the middle-late Miocene (e.g., de Muizon 1987;Fordyce and de Muizon 2001). ...
... For the purposes of this study, we have defined the clade Platanistoidea as including the genera Waipatia, Otekaikea, Awamokoa, Zarhachis, Notocetus, Aondelphis, and Platanista (Viglino et al. 2018a,b). These genera represent families that are usually recovered within this clade: Waipatiidae, Squalodelphinidae, and Platanistidae (for details on specimens used, see Table 1) (but note that some authors recovered waipatiids as stem Odontoceti; e.g., Lambert et al. 2018;Bianucci et al. 2020). For further details on the still-debated systematic and phylogenetic aspects of Platanistoidea, see, for example, Fordyce (1994), Lambert et al. (2014), Fordyce (2015, 2017), Boersma and Pyenson (2016), Boersma et al. (2017), Viglino et al. (2018aViglino et al. ( ,b, 2020, Gaetán et al. (2019), and Bianucci et al. (2020), as well as references therein. ...
... These genera represent families that are usually recovered within this clade: Waipatiidae, Squalodelphinidae, and Platanistidae (for details on specimens used, see Table 1) (but note that some authors recovered waipatiids as stem Odontoceti; e.g., Lambert et al. 2018;Bianucci et al. 2020). For further details on the still-debated systematic and phylogenetic aspects of Platanistoidea, see, for example, Fordyce (1994), Lambert et al. (2014), Fordyce (2015, 2017), Boersma and Pyenson (2016), Boersma et al. (2017), Viglino et al. (2018aViglino et al. ( ,b, 2020, Gaetán et al. (2019), and Bianucci et al. (2020), as well as references therein. The sample also included representatives of two putative platanistoids, Squalodon calvertensis and Prosqualodon australis (for details on the phylogenetic position of these taxa, please see de Muizon [1994] and Gaetán et al. [2019]). ...
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The inner ear of the two higher clades of modern cetaceans (Neoceti) is highly adapted for hearing infrasonic (mysticetes) or ultrasonic (odontocetes) frequencies. Within odontocetes, Platanistoidea comprises a single extant riverine representative, Platanista gangetica, and a diversity of mainly extinct marine species from the late Oligocene onward. Recent studies drawing on features including the disparate tympanoperiotic have not yet provided a consensus phylogenetic hypothesis for platanistoids. Further, cochlear morphology and evolutionary patterns have never been reported. Here, we describe for the first time the inner ear morphology of late Oligocene-early Miocene extinct marine platanistoids and their evolutionary patterns. We initially hypothesized that extinct marine platanistoids lacked a specialized inner ear like P. gangetica and thus, their morphology and inferred hearing abilities were more similar to those of pelagic odontocetes. Our results reveal there is no "typical" platanistoid cochlear type, as the group displays a disparate range of cochlear anatomies, but all are consistent with high-frequency hearing. Stem odontocete Prosqualodon australis and platanistoid Otekaikea huata present a tympanal recess in their cochlea, of yet uncertain function in the hearing mechanism in cetaceans. The more basal morphology of Aondelphis talen indicates it had lower high-frequency hearing than other platanistoids. Finally, Platanista has the most derived cochlear morphology, adding to evidence that it is an outlier within the group and consistent with a >9-Myr-long separation from its sister genus Zarhachis. The evolution of a singular sound production morphology within Platanistidae may have facilitated the survival of Platanista to the present day.
... Basal odontocetes with double-rooted cheek teeth (e.g., Inticetus), platanistoids (e.g., Huaridelphis, Macrosqualodelphis), and archaic delphinidans (e.g., Incacetus, Atocetus, 'Kentriodontidae') experienced a demise at ~ 10 Ma or much earlier within the EPB (Colbert 1944;Muizon 1988;Lambert et al. 2017;Bianucci et al. 2018Bianucci et al. , 2020. Some platanistoids and 'kentriodontids', however, did survive longer in isolated marine and freshwater settings (Ichishima et al. 1994;Marx et al. 2017), as the South Asian river dolphin Platanista, the only extant representative of the platanistoids (Barnes et al. 2006). ...
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The highly productive waters of the Humboldt Current System (HCS) host a particular temperate ecosystem within the tropics, whose history is still largely unknown. The Pisco Formation, deposited during Mio-Pliocene times in the Peruvian continental margin has yielded an outstanding collection of coastal-marine fossils, providing an opportunity to understand the genesis of the HCS ecosystem. We present a comprehensive review, completed with new results, that integrates geological and paleontological data from the last 10 My, especially focusing on the southern East Pisco Basin (Sacaco area). We discuss the depositional settings of the Pisco Formation and integrate new U/Pb radiometric ages into the chronostratigraphic framework of the Sacaco sub-basin. The last preserved Pisco sediments at Sacaco were deposited ~ 4.5 Ma, while the overlying Caracoles Formation accumulated from ~ 2.7 Ma onwards. We identified a Pliocene angular unconformity encompassing 1.7 My between these formations, associated with a regional phase of uplift. Local and regional paleoenvironmental indicators suggest that shallow settings influenced by the offshore upwelling of ventilated and warm waters prevailed until the early Pliocene. We present an extensive synthesis of the late Miocene–Pleistocene vertebrate fossil record, which allows for an ecological characterization of the coastal-marine communities, an assessment of biodiversity trends, and changes in coastal-marine lineages in relation to modern HCS faunas. Our synthesis shows that: (i) typical endemic coastal Pisco vertebrates persisted up to ~ 4.5 Ma, (ii) first modern HCS toothed cetaceans appear at ~ 7–6 Ma, coinciding with a decline in genus diversity, and (iii) a vertebrate community closer to the current HCS was only reached after 2.7 Ma. The genesis of the Peruvian coastal ecosystem seems to be driven by a combination of stepwise transformations of the coastal geomorphology related to local tectonic pulses and by a global cooling trend leading to the modern oceanic circulation system.
... During the middle-to-late Miocene the odontocete diversity worldwide included a wide array of sperm whales (Lambert et al. 2017a;Benites-Palomino et al. 2020), beaked whales (Bianucci et al. 2016), stem delphinidans (Peredo et al. 2018;Kimura and Hasegawa 2019), and several longirostrine taxa belonging to Eurhinodelphinidae and Platanistoidea (Bianucci et al. 2020). Most of these groups have been found in multiple localities across the world, especially in the case of stem delphinidans. ...
... The middle-to-late Miocene fossil record of cetaceans indicates, that along with the global temperature drop by the end of the middle Miocene Climatic Optimum, Odontoceti diversity also entered a phase of change where marine platanistoids (Bianucci et al. 2020) and some lineages of early odontocetes disappeared, being replaced by a more modern community that included the earliest relatives of crown delphinoids, but also a fair diversity of other groups as sperm whales (Lambert et al. 2017a;Benites-Palomino et al. 2020;Collareta et al. 2020), inioids (Lambert et al. 2017b and beaked whales (Bianucci et al. 2016). The fossil record indicates that the earliest representatives of crown Delphinida coexisted along with early diverging forms, thus sharing world oceans for at least a couple of millions of years. ...
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The dense Miocene record of cetaceans is known from localities along the coasts of all continents, mostly in the northern Atlantic or the eastern Pacific regions, but Antarctica. Fossils from the Caribbean region are few and include of a couple of findings from Panama and Venezuela. Here, we report a partly complete skull from the Caujarao Formation (middle Miocene), Falcon State, Caribbean region of Venezuela. Our phylogenetic analyses indicate that the Caujarao specimen is a 'stem delphinidan' , a group that includes several taxa of early diverging odontocetes whose phylogenetic affinities remain a matter of debate. The fossil record has shown that this group of stem delphinidans was taxonomically diverse, but displayed a somewhat homogeneous cranial patterning, with most of the variations being found within the mandible or tympanoperiotic characters. As other stem delphinidans the Caujarao odon-tocete displays an enlarged temporal fossa and a fairly symmetrical cranium. Because the skull is missing several key diagnostic characters due to the preservation state of the specimen, a more precise taxonomic identification is not possible. Despite this, the finding of this specimen highlights the importance of the fossil record from the Neogene of Venezuela, and the importance of the area to understand cetacean evolution in the proto-Caribbean.