Aporotus recurvirostris du Bus, 1868
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publication ID |
https://doi.org/ 10.5281/zenodo.5376445 |
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persistent identifier |
https://treatment.plazi.org/id/03FED57F-FFC7-9F5D-83FA-FEDAFCFDFBCC |
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treatment provided by |
Marcus |
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scientific name |
Aporotus recurvirostris du Bus, 1868 |
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Aporotus recurvirostris du Bus, 1868
Aporotus recurvirostris du Bus, 1868: 626 .
HOLOTYPE. — IRSNB 3812- M.1887, partial skull (single specimen placed in Aporotus recurvirostris by du Bus [1868], included in the species Mioziphius belgicus by Abel [1905]).
REFERRED SPECIMENS. — Partial rostra IRSNB 3810, IRSNB 3811, IRSNB 3813, IRSNB 3814, IRSNB 3815, IRSNB 3816- M.1888, and IRSNB 3817, found in Antwerp without precise location, and two isolated fragments of rostra IRSNB 8243d and IRSNB 8243g, both found in October 1909 in Kessel, 18 km south-east of Antwerp.
TYPE HORIZON. — There are no data available for most of the specimens. The fragments of premaxillae found in Kessel might originate from the Antwerp Sands, late early to middle Miocene ( Louwye et al. 2000), but this kind of dense fragment is strong enough to undergo one or more phases of reworking ( Glaessner 1947).
TYPE LOCALITY. — Antwerp, Belgium, exact locality uncertain.
DIAGNOSIS. — Species larger than Aporotus dicyrtus , Ziphirostrum marginatum and Choneziphius planirostris , with a size of the skull close to adult Ziphius cavirostris (more than 380 mm in preorbital width). This species differs from Aporotus dicyrtus in: the longer, slightly anterodorsally curved rostrum; more elevated premaxilla on the rostrum forming a high longitudinal crest with a top more posteriorly positioned and a steeper posterior slope; the deeper and wider prenarial basin; the more elevated vertex with transverse premaxillary crests more anteriorly directed and overhanging the premaxillary sac fossae. This species appears to be more derived than A. dicyrtus for most of the given characters.
DESCRIPTION ( FIGS 29 View FIG ; 30 View FIG )
The description is essentially based on the holotype, which is much better preserved than the referred specimens, which only consist in rostrum fragments. The holotype is a large skull including the nearly complete rostrum, the anterior of the cranium, and the anterior of the vertex. The basicranium is lacking, as well as the supraoccipital and the frontals on the vertex and the supraorbital processes. The rostrum has a total length estimated at 570 mm, close to Ziphirostrum marginatum , but it is clearly curving upwards. The cranium is larger and the vertex is higher than for the latter species. Only a few additional measurements could be taken on that skull, because of the absence of a clear contact between the two halves: the width of the rostrum at the base is estimated at 270 mm, and the width of the skull at the level of the preorbital processes at 380 mm. The measurements on the rostral longitudinal premaxillary crests are given below ( Table 5).
Premaxilla
The development of elevated longitudinal premaxillary crests makes the rostrum very high, with a maximum height posteriorly positioned ( Fig. 29C View FIG ). The posterior lowering is abrupt and steep, while the anterior lowering is progressive and accompanied by a narrowing. The right and left crests match very well, although there is no sutural contact between the median surfaces; in fact these surfaces show numerous anastomosed vascular sulci, which indicate the absence of a fused suture ( Fig. 29D View FIG ). The most ventral major sulcus originates at the large premaxillary foramen, located on an elongated depressed surface posteromedian to the crest, at the contact with the premaxillary sac fossa. The lateral surface of the crest is also covered by sulci.
The prenarial basin is wide and deep between the two maxillary crests, but the medial resorption of the premaxillae seems little pronounced (not totally preserved): there is no interruption between the high longitudinal premaxillary crest and the premaxillary sac fossa.
The posterior portion of the premaxillae, including the premaxillary sac fossae and the transverse premaxillary crests, is poorly preserved. The remaining fragments and the underlying maxillae allow a general description of the area: the premaxillary sac fossa is strongly tilted, anteromedially facing (seen on the right side), and the curvature continues on the ascending process of the bone, so that the roughly rectilinear transverse premaxillary crest is anterolaterally directed ( Figs 29A View FIG ; 30A View FIG ).
The Neogene ziphiids Ziphirostrum and Choneziphius ( Cetacea, Odontoceti )
Maxilla
Laterally to the longitudinal crest of the premaxilla, the maxilla is little exposed on the rostrum, widening backwards without distinct horizontal surface. At a level posterior to the end of the premaxillary crest, the lateral margin of the maxilla strongly elevates to form an elongated longitudinal crest, more acute and higher on the right side, with a maximum height just before the antorbital notch. The posterior part of the crest, lowering on the preorbital process, is excavated by a dorsal infraorbital foramen (with a double exit on the right side), and a posteriorly directed foramen is present at the base of the inner slope of the crest, along the suture with the premaxilla. A wide valley separates the maxillary crest from the rostral longitudinal crest of the premaxilla, anterolaterally directed from the prenarial basin.
In lateral view, the curvature of the rostrum is distinct at the level of the lateral suture between maxilla and premaxilla. The maxilla finishes anteriorly at least 60 mm before the apex of the rostrum. The latter is formed only of the premaxilla, laterally hollowed by a deep sulcus anteriorly following a foramen located at the apex of the maxilla. The lateral margin of the maxilla is less dense and more eroded than the premaxilla; instead of an alveolar groove, there is a shallow depression with an irregular surface, lacking alveoli.
The maxilla is thin on the supraorbital process compared to the thick preorbital process of the frontal. A large dorsal infraorbital foramen pierces the supraorbital process of the maxilla near the posterolateral edge, accompanied by a more anterior smaller foramen.
The erect medial plate of the maxilla at the vertex extends medially beyond the level of the lateral margin of the nasal.
Nasal
The nasals, slightly longer than wide, are anteromedially pointed, with a concave posterior margin. The left nasal is shorter and narrower than the right, and the median suture is anterolaterally deflected on the left side. The mesethmoid is lost.
Palatine-vomer-lacrimal-jugal
The median sutures of the rostrum are totally eroded, the palatine is poorly delimited, the pterygoid is lost, and the vomer is preserved as a high keel in front of the choanae. The suture of the lacrimal with the frontal is not completely fused, allowing a good correlation with the morphology of Ziphius . The jugal is lost.
ADDITIONAL SPECIMENS
Several paired (six) and isolated (four) rostral longitudinal premaxillary crests similar to those of the holotype of Aporotus recurvirostris were found at Antwerp and Kessel. Surprisingly, the pairs, always clearly belonging to a same individual ( Fig. 29E, F View FIG ), never show a bony suture, even ventrally. They were thus probably transported with other parts of the rostrum, which were destroyed after deposition and before burial, maybe because of their higher porosity. The right crest is in each case higher than the left (see Table 5), with a difference of 8 to 17%, but not clearly wider. There is no good correlation between the degree of asymmetry and the height of the crest. The maximum elevation is sometimes located somewhat more anteriorly than on the holotype.
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Institut Royal des Sciences Naturelles de Belgique |
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
