Physeteroidea indet
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publication ID |
https://doi.org/ 10.4202/app.00763.2020 |
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DOI |
https://doi.org/10.5281/zenodo.11093007 |
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persistent identifier |
https://treatment.plazi.org/id/091887AB-FFDB-F41A-4739-FB64C68FEBB9 |
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treatment provided by |
Felipe |
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scientific name |
Physeteroidea indet |
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Figs. 2–4 View Fig View Fig View Fig .
1980 Preaulophyseter gualichensis, Caviglia and Jorge 1980: 363– 368 , pls. I, II.
Material.—MLP 76-IX-5-1, a left periotic and two isolated fragmentary teeth, from near Puesto Echávez, 38 km north of San Antonio Oeste city within the Gran Bajo del Gualicho depression, Río Negro province, Argentina; Gran Bajo del Gualicho Formation; Miocene ( Caviglia and Jorge 1980); MLP 76-IX-2-3 and MLP 76-IX-2-4, isolated right periotics, MLP 52-X-2-8, an isolated right periotic, and MLP 76-IX-2- 7, a fragmentary periotic, from Patagonia, without a precise geographic provenance, Argentina; Miocene ( Caviglia and Jorge 1980). MPEF-PV-605, an isolated right periotic and MPEF-PV-651, an isolated right periotic, from Bryn Gwyn (= Loma Blanca); MPEF-PV-6098, an isolated left periotic from Cerro Castillo; MLP 80-VIII-30-133 (right -a and left -b), two isolated periotics from Gaiman, Lower Valley of Chubut River; all Chubut province, Argentina; Gaiman Formation; lower Miocene.
Description.— Teeth: The two isolated teeth of MLP 76-IX-5-1 are broken and eroded. They are conical with an oval transverse section, and a thin layer of crenulated enamel on their crowns. Given that these teeth are isolated, we could neither determine their anteroposterior position along the toothrow nor their location on the skull (lower versus upper jaw). The better-preserved tooth ( Fig. 2 View Fig : I) is long (150 mm) and slender (maximum diameter about 21 mm). There is a shallow crest in both mesial and distal margins of the crown, being more conspicuous on the lingual side ( Fig. 2A View Fig 4 View Fig ). Over this side, and ventral to the crest, there is a dorsoventrally long and shallow occlusal facet, extending for 47 mm on the crown and the root. The occlusal facet runs along the longitudinal axis of the tooth, being obliquely oriented in its proximal region. The presence of this occlusal facet reinforces the hypothesis that both the crown and part of the root were erupted above the gums in most physeteroids (e.g., Bianucci and Landini 2006). Besides, the presence of a long occlusal facet allows us to infer that both upper and lower teeth were present in this specimen. The crown is short, about one fourth of the total length 31 mm), and there is a shallow cingulum at the base, which is clearer on the labial side. The long (83 mm) and fusiform root displays cement rings in the proximal region. The pulp cavity is obscured by sediment and occupies one third of the total length of the tooth (38 mm). In both teeth, some oblique layers of dentine (Growth Layer Groups, GLGs) are observed along break surfaces.
Periotics: MLP 76-IX-5-1 includes a left periotic almost completely preserved ( Fig. 3 View Fig ). The fenestra rotunda, fenestra ovalis, some parts of the ventral surface of the periotic, as well as the fossa for the stapedial muscle are obscured by sediment. In dorsal view ( Fig. 3A View Fig 1 View Fig ), the circular aperture for the cochlear aqueduct is smaller than the anteroposteriorly compressed aperture for the vestibular aqueduct, and these two openings are not anteroposteriorly aligned. The lateromedially pyriform internal acoustic meatus (IAM) has a well-developed transverse crest and a tear drop-shaped foramen singulare. The IAM also has a large and tear drop-shaped spiral cribriform tract. The proximal opening of the facial canal is a large foramen that is also tear drop-shaped, with its rounded part posteriorly oriented. Some prominences lateral to the IAM give the periotic an irregular dorsolateral surface. In ventral view ( Fig. 3A 3 View Fig ), the pars cochlearis is mediolaterally wide with a well-defined convex medial surface; it is weakly tilted towards the anterior process. The oval-shaped accessory ossicle is large ( Table 1 View Table 1 ), and, as in most other physeteroid periotics, together with part of the outer lip of the tympanic bulla it is fused with the anterior process of the periotic, leaving visible only a small and circular part of the anterior bullar facet. The mallear fossa is deep and circular, whereas the fenestra ovalis is oval. The conspicuous lateral tuberosity is anterior to the wide and deep epitympanic hiatus. Posteriorly, the posterior bullar facet is ventrally concave and has grooves and fracture lines. In medial and dorsal views, there is a circular prominence on the anterior process dorsal to the accessory ossicle. The facial sulcus is wide and deep. In medial view ( Fig. 3A View Fig 5 View Fig ), the pars cochlearis is subcircular. The fenestra rotunda has a dorsoventrally oval outline, and it is connected with the aperture for the cochlear aqueduct by a shallow groove. The anterior process of the periotic is small and pointed. In lateral view ( Fig. 3A View Fig 7), the body of the periotic is perpendicular to the posterior process, resulting in an L-shaped profile of the periotic. The posterior process has a deep groove at the posteroventral apex.
The periotics MLP 76-IX-2-3 and MLP 76-IX-2-4 have the same general characteristics as MLP 76-IX-5-1. When comparing all the periotics, MLP 76-IX-2-3 is smaller, while MLP 76-IX-2-4 and MLP 76-IX-5-1 are similar in size ( Table 1 View Table 1 ). In MLP 76-IX-2-3, the posterior process is broken and the accessory ossicle is missing, making the oval fovea epitubaria visible. In medial view, the periotic has a triangular outline due to the erosion of the dorsal region of the pars cochlearis. In ventral view, the pars cochlearis of MLP 76-IX-2-3 and MLP 76-IX-2-4 ( Fig. 3C View Fig ) is shorter than in MLP 76-IX-5-1, and leaning towards the anterior process more than in MLP 76-IX-5-1. Finally, the fenestra rotunda of MLP 76-IX-2-3 and MLP 76-IX-2-4 is D-shaped, whereas it is oval in MLP 76-IX-5-1.
MPEF-PV-605 ( Fig. 4A View Fig ) corresponds to an almost complete right periotic with a certain degree of erosion and of similar size than MLP 76-IX-2-3 ( Table 1 View Table 1 ). The general morphology is in concordance with MLP 76-IX-5-1, so we only provide here the main differences. In medial view, the pars cochlearis has a D-shape profile, with a straight dorsal and a convex ventral margin. The D-shaped fenestra rotunda is positioned on the posterior margin of the pars cochlearis. In ventral view, the fenestra ovalis is circular whereas the fossa incudis is oval. The posterior bullar facet is laterally oriented, concave and has grooves and ridges. The pars cochlearis leans towards the anterior process. In dorsal view, the circular aperture for the cochlear aqueduct is larger than the anteroposteriorly compressed aperture for the vestibular aqueduct. The spiral cribriform tract is large and circular, medial to the oval proximal opening of the facial canal. The foramen singulare is small and mediolaterally narrow, and the transverse crest is less conspicuous than in MLP 76-IX-5-1.
The anterior process and the ventral part of the pars cochlearis of the right periotic MPEF-PV-651 ( Fig. 4B View Fig ) are highly eroded, so the margins of the fovea epitubaria are lost. The pars cochlearis’ profile, fenestra rotunda, aperture for the vestibular and cochlear aqueducts are similar to MPEF-PV-605. In ventral view, the fenestra ovalis has broken edges.
The left periotic MPEF-PV-6098 ( Fig. 4C View Fig ) has a size similar to MLP 76-IX-5-1. Even though it is eroded, most of the features are visible. In dorsal view, the apertures for the cochlear and vestibular aqueducts have approximately the same size. In ventral view, the fovea epitubaria is visible and oval-shaped. The anterior bullar facet is rounded due to erosion. The posterior bullar facet is laterally bended and has crests and grooves as in MPEF-PV-605. In medial view, the pars cochlearis is oval and the fenestra rotunda is D-shaped.
The two periotics MLP 80-VIII-30-133a and b ( Fig. 4D, E View Fig ) have an eroded and rounded surface. The better-preserved (MLP 80-VIII-30-133a) individual ( Fig. 4D View Fig ) lacks the posterior process. In medial view, the pars cochlearis is anteroposteriorly oval, and the fenestra rotunda has a D-shape profile as in MPEF-PV-605, MPEF-PV-6098, and MPEF-PV-651. In dorsal view, the aperture for the vestibular aqueduct is larger than the aperture for cochlear aqueduct, as in MLP 76-IX-5-1. The other left periotic (MLP 80-VIII-30-133b) is poorly preserved ( Fig. 4E View Fig ), lacking most of the pars cochlearis. The posterior process is reduced to a thin process, and the margins of the anterior process are rounded due to erosion. Both processes are at a right angle, resulting in an L-shaped profile of the periotic. Posterior to the anterior process is a prominent lateral tuberosity.
MLP 52-X-2-8 is an eroded and fragmentary right periotic ( Fig. 4F View Fig ), with the anterior process missing. In medial view, the fenestra rotunda is D-shaped and the pars cochlearis is oval as in the previous specimens. In dorsal view, the aperture for the vestibular aqueduct is anteroposteriorly compressed and larger than the aperture for the cochlear aqueduct, as in MLP 76-IX-5-1.
MLP 76-IX-2-7 is represented by an eroded portion of pars cochlearis, in which the spiral cribriform tract and the medial edge of the foramen singulare are preserved. The spiral cribriform tract is circular and delimited by conspicuous edges.
The periotics analyzed above present the diagnostic characters of Physeteroidea described in the previous section. Cozzuol (1993: 22) referred MPEF-PV-605 to “ Aulophyseter ” rionegrensis, the only Patagonian physeteroid species that is currently known with associated ear bones. However, we cannot confidently assign any of these isolated periotics to any known or new taxa, and therefore they are here identified as Physeteroidea indet. (see Discussion).
The morphology of the periotics and teeth referred to Preaulophyseter by Caviglia and Jorge (1980) is consistent with that of Physeteroidea. The physeteroid periotic is characterized by a large accessory ossicle often fused with the anterior process of the periotic, contact surface between posterior process of tympanic bulla and periotic with keels and grooves, a pointed anterior process, posteroventrally recurved posterior process at a right angle with the body of periotic, anteriorly inclined pars cochlearis, a thick superior process, concave posterior bullar facet, and a volcano-shaped IAM ( Kasuya 1973; Luo and Marsh 1996). However, there are no characteristics that differentiate these specimens from other known non kogiid-physeteroid species. The observed minor differences could possibly be explained by intraspecific (including ontogenetic variation and sexual dimorphism, although the latter has not yet been demonstrated at the level of ear bones in physeteroids; e.g., de Buffrenil et al. 2004; Lancaster et al. 2015) or interspecific variations (e.g., Kasuya 1973; Oelschläger 1986; Gutstein et al. 2014). Therefore, we assign MLP 76-IX-5-1, MLP 76-IX-2-3 and MLP 76-IX-2-4 as Physeteroidea indet. (see Discussion).
The main differences observed between the periotics described above are related to: (i) size; (ii) shape of the pars cochlearis; and (iii) size of the apertures for the cochlear and vestibular aqueducts. Below, we provide detailed comparisons between the specimens analyzed in this contribution and with other non-kogiid physeteroid species.
The periotic MLP 76-IX-5-1 ( Fig. 5A View Fig ) differs from that of “ Aulophyseter ” rionegrensis in being larger, mediolaterally wide, with a more circular pars cochlearis that is less inclined towards the anterior process. It further differs in having an oval fenestra rotunda. “ A. ” rionegrensis ( Fig. 5B View Fig ) and MLP 76-IX-2-3 differ only in the size of the pars cochlearis in medial view. Both MLP 76-IX-2-4 and MLP 52-X-2-8 differ from “ A. ” rionegrensis in being larger. On the other hand, there are no significant differences between “ A. ” rionegrensis, MPEF-PV-605 and MLP 80-VIII-30- 133a and b. MPEF-PV-651 differs from “ A. ” rionegrensis in having a higher pars cochlearis in ventral view, whilst MPEF-PV-6098 differs in being larger and in having a small prominence along the posteromedial outline on the pars cochlearis, above the fenestra rotunda. The periotic of Acrophyseter deinodon ( Lambert et al. 2016; Fig. 5C View Fig ) differs from all remaining physeteroids in having a quadrangular pars cochlearis in medial view. However, as in MLP-76-IX-5-1, A. deinodon has an oval-shaped fenestra rotunda, whereas in the other studied specimens it is D-shaped. MLP-76-IX-5-1 differs from Zygophyseter varolai ( Bianucci and Landini 2006; Fig. 5D View Fig ) in having a smaller pars cochlearis. Zygophyseter differs from all other studied specimens in having a rectangular fovea epitubaria. MLP-76-IX-5-1 differs from Aulophyseter morricei ( Kellogg 1927; Fig. 5E View Fig ) in having a higher pars cochlearis in ventral view, whilst this genus differs from the other specimens analyzed here in having more circular IAM and apertures for cochlear and vestibular aqueducts. Orycterocetus crocodilinus ( Kellogg 1965; Fig. 5F View Fig ) differs from all the specimens analyzed here in having a larger and circular spiral cribriform tract. In ventral view, O. crocodilinus presents the same small prominence along the posteromedial outline as MPEF-PV 6098. Finally, the main difference between Physeter ( Fig. 5G View Fig ) and the physeteroid periotics studied here is the acute angle formed by the posterior process and the body of the periotic in the former, whereas our specimens display a right angle.
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