Physeteroidea Gray, 1821
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publication ID |
https://doi.org/ 10.5194/fr-23-151-2020 |
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persistent identifier |
https://treatment.plazi.org/id/9F6E87DC-E122-B85E-FF4A-FE2263FAF8A9 |
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treatment provided by |
Felipe |
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scientific name |
Physeteroidea Gray, 1821 |
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Superfamily Physeteroidea Gray, 1821
Physeteroidea , indet.
( Figs. 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 )
Material
One incomplete right periotic ( MNUL.Pal.100.755a), one bullar fragment ( MNUL.Pal.100.755b; see also comments in the Introduction).
Locality
Gross Pampau, Schleswig-Holstein, northern Germany.
Age
Miocene mica clay deposits underneath Pleistocene gravel; Bolboforma fragori –subfragoris Zone, upper Langenfeldian, about Serravallian–Tortonian boundary, ca. 10.6–11.8 Ma (see Spiegler and Gürs, 1996).
Description
Only the recovered periotic is described in detail here due to the poor preservational status of the other fragmentary bones. The bullar fragment consists of a lower part of the involucrum presenting the spoonlike depressed tympanic cavity. The inner posterior prominence is also determinable – all other parts are broken away ( Fig. 2 View Figure 2 ).
The current condition of the periotic bone is incomplete but well preserved ( Fig. 3a–h View Figure 3 ). The bone is composed of a large pars cochlearis and a relatively large body and anterior process. A small posterior portion of the body and the posterior process are lost due to a breakage (indicated by crosshatched area in Fig. 3e, f View Figure 3 ). The bone tissue is in general compact and dense, although fragile in thin portions.
Measurements of the periotic are shown in Table 1 and Fig. 4a–g View Figure 4 .
Dorsal view of the periotic ( Fig. 3a, b View Figure 3 ). The large pars cochlearis displays the following shape: the posterior and medial surfaces are flattened; the latter ascends anteriorly; the anterior surface is markedly vaulted. A prominence on the anteromedial edge arises dorsally as the highest point on the dorsal surface.
The internal auditory meatus has a wide ovate shape and is located nearly in the middle of the dorsal surface of the pars cochlearis. It contains, in a funnel-like hollow, the tractus spiralis foraminosus, the foramen singulare, and the area vestibularis inferior. Furthermore, it encloses the small area vestibularis superior and the oval and larger dorsal opening of the facial canal. Both are located in this order laterally to the transverse crest. A septum, the Bill’s bar (see definition in Reiss, 2003; Ritsche, 2018), is mediolaterally tilted and separates the area vestibularis superior and the foramen of the facial canal. Both the transverse crest and the Bill’s bar are distinctly below the outside rim of the meatus.
While the medial rim is somewhat elevated, the lateral does not protrude noticeably from surrounding bone. The elliptic aperture for the endolymphatic duct lies obliquely on the dorsal surface of the pars cochlearis posterior but very close to the internal auditory meatus. It is separated by a thin bony septum from the smaller and more rounded perilymphatic foramen that lies medially.
Lateral to the aperture for the endolymphatic duct is a rounded protuberance, the dorsal tuberosity, delimited anteriorly by the slightly pronounced posterior rim of the internal auditory meatus.
The suprameatal fossa forms an elongated but shallow depression that is wider posteriorly than anteriorly. It extends laterally to the dorsal tuberosity and internal auditory meatus and medially to the dorsal crest. The latter is a pronounced elevation stretched from a point posterolateral to the dorsal tuberosity towards the anterior. At the level of the area vestibularis superior, the slender crest is oriented more medially and reaches almost the anterior incisure.
An elongated prominence extends laterally from a point posterior to the perilymphatic foramen until it joins the dorsal crest at nearly a right angle forming a small peak. The posterior surface of the periotic body is flattened.
In dorsal view, the rugose tegmen tympani is convex and merges anteriorly into the anterior process. The anterior process is elongated, markedly longer than wide, thin, and shows a slightly pronounced keel as the anterior continuation of the dorsal crest. The lateral part of the anterior process forms a diagonal that rises anteriorly and bends in the ventral direction towards the apex, making the anterior portion of the process rounded. The surface of the anterior process is wrinkled. Prominent dorsal and anterodorsal spines ( Muizon, 1988a) are absent, as well as an anteroexternal sulcus.
The pars cochlearis and anterior process meet at nearly a right angle. Two bony elements coalesce to the medial surface of the anterior process. The larger element, the accessory ossicle, is placed more ventrally and has a vaulted shape and an anteriorly pointed edge. The second is a smaller element placed dorsally with an oval but less uniform shape and small protuberances. It covers a large part of the medial surface of the anterior process and a suture between both is visible. Posterior to and at the level of this small element the surface shows a series of grooves that extend ventrally.
Lateral view of the periotic ( Fig. 3d View Figure 3 ). The lateral surface of the tegmen tympani and of the anterior process is slightly rugose and of convex shape. The dorsal margin is delimited by the dorsal crest and its anterior continuation.
I. Montaaeez-Rivera and O. Hampe: An unfamiliar physeteroid periotic ( Cetacea : Odontoceti ) 155
The dorsal tuberosity and the pars cochlearis protrude dorsally, the latter with an anteriorly tilted pyramidal shape exposing partially the internal auditory meatus.
The anterior process is thick at the base and tapers anteriorly. Spines on the anterior process are not pronounced; only a very slight protuberance is present and marks the point from where the process narrows out more rapidly in the anterior direction. The ventral outline of the anterior process is a marked concave curvature that accentuates the ventrally pointed apex. Due to the ventral bend of the apex, the anterior margin of the process is rather truncated. The breakage of the outer lip of the tympanic bulla and its suture to the periotic are ventrally visible.
The ventrolateral tuberosity ( Luo and Gingerich, 1999) also protrudes ventrally, posterior to the base of the anterior process. From this view, it has a subtriangular outline and an erratically rugose surface. Due to the thinness and curvature of the anterior process, its apex and the ventrolateral tuberosity do not lie on the same horizontal level.
Posterior to the ventrolateral tuberosity, a diagonal edge marks the breakage of the posterior process and a part of the caudal tympanic process remains exposed.
The posterior margin of the periotic body is slightly concave.
Ventral view of the periotic ( Fig. 3e, f View Figure 3 ). The pars cochlearis is slightly anteriorly inclined, and its medial surface is flattened, demonstrating a rectangular outline. The ventral surface is the most convex part of the pars cochlearis, of which the midpoint is flattened at the same time.
The fenestra rotunda is large and almost circular in frontal view. A fissure extends dorsally from its dorsomedial margin towards the most lateral point of the perilymphatic foramen.
Lateral to the fenestra rotunda is the origin of the slightly pronounced, keel-like caudal tympanic process that extends posteriorly and sharpens at the point of breakage.
The fenestra ovalis and laterally the ventral opening of the facial canal are situated posteriorly to the level of the midpoint of the pars cochlearis. The long axis of the fenestra ovalis is oriented anteromedially to posterolaterally. The ventral opening of the facial canal is nearly circular and flows into a shallow depression that extends posteromedially towards the also shallow fossa for the stapedius muscle. This is situated posteriorly to the fenestra ovalis and is flanked medially by the caudal tympanic process. The fossa for the stapedius muscle is also affected by the breakage.
On a keel lateral to the ventral opening of the facial canal rises the circular profile of the incudal process ( Luo and Marsh, 1996). Anterior to the incudal process is the mallear fossa, a large circular, shallow depression. The pyramidal ventrolateral tuberosity is elevated laterally between the mallear fossa and incudal process. In this view, its surface and the surface of the periotic body are smooth. A hiatus epitympanicus is not visible due to the breakage posterior to the ventrolateral tuberosity.
I. Montaaeez-Rivera and O. Hampe: An unfamiliar physeteroid periotic ( Cetacea : Odontoceti ) 157
The anterior process is thin and tapers towards its apex that forms the anteroventral spine, which is partially damaged. A groove with a medially elevated rim, possibly for the tensor tympani muscle, extends dorsoventrally between the pars cochlearis and accessory ossicle along the anterior incisure towards the ventral opening of the facial canal. The accessory ossicle is vaulted and lies medially to the broken lip of the tympanic bulla. Both cover the anterior process almost entirely, except for a small anterior part that remains uncovered likely due to the breakage of the tympanic bulla.
The lateral outline of the anterior process rises anteriorly, is in the beginning concave, and then becomes slightly convex. The anteroventral spine reaches about the same horizontal level as the ventral opening of the facial canal.
Medial view of the periotic ( Fig. 3c View Figure 3 ). The pars cochlearis has a somewhat triangular outline ventrally rounded. Its ventral protrusion obscures a portion of the fenestra rotunda, and its dorsal protrusion on the anterior edge has an anteriorly tilted pyramidal shape. The opening of the internal auditory meatus, the aperture for the endolymphatic duct, the perilymphatic foramen, and the dorsal crest are only partially visible in this view.
The posterior margin of the pars cochlearis merges into the body of the periotic bone. This surface forms an obtuse angle with the medial surface of the pars cochlearis.
The length of the anterior process comprises more than one-third of the length of the broken periotic bone. The dorsal outline of the anterior process is convex. The small element coalesced to the medial surface is thin and slightly shorter than the accessory ossicle. These have only a little contact with each other at the anterior incisure. The accessory ossicle displays a trapezoid shape and covers the medial surface of the anterior process almost completely. Lateral to this is the broken area of the fused tympanic bulla.
The anteroventral spine of the anterior process is situated dorsally to the ventral edge of the pars cochlearis and is bent so that the anterior bullar facet is facing ventrally and slightly medially.
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