Ramphastosula aguirrei, Stucchi & Varas-Malca & Urbina-Schmitt, 2016
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publication ID |
https://doi.org/ 10.4202/app.00170.2015 |
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publication LSID |
lsid:zoobank.org:pub:12E70E13-D7F9-43BB-A388-6A93FF0E4A52 |
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persistent identifier |
https://treatment.plazi.org/id/51F31FFF-4D44-45B6-A221-07A128E4A5F3 |
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taxon LSID |
lsid:zoobank.org:act:51F31FFF-4D44-45B6-A221-07A128E4A5F3 |
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treatment provided by |
Felipe |
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scientific name |
Ramphastosula aguirrei |
| status |
sp. nov. |
Ramphastosula aguirrei sp. nov.
Fig. 4 View Fig .
ZooBank LSID: urn:lsid:zoobank.org:act:51F31FFF-4D44-45B6-A221-07A128E4A5F3
Etymology: In honor to Walter Aguirre (MUSM, Peru), for his substantial work as a fossil preparator of the vertebrate paleontological collection of the MUSM.
Holotype: MUSM 665 ; almost complete, well-preserved skull with partial jugal bars, and lacking lacrimals and the right quadrate.
Type locality: MUSM 665 was collected from the Sacaco Sur (Sud-Sacaco or SAS) locality (Pisco Formation, Peru) which is dated to 6.59– 5.93 Ma ( Ehret et al. 2012) ( Fig. 1B View Fig ). There are two areas (sublocalities) recognized there: Poza Roja (red hole) and Poza Negra (black hole). The first refers to the type locality described in Muizon and DeVries (1985), where R. ramirezi was recovered. The second corresponds to underlying beds (18 m lower in the stratigraphic column of Leonard Brand, unpublished material) being older than the former one and where R. aguirrei was recovered.
Type horizon: Sacaco Sur was formally dated as Pliocene age ( Muizon and DeVries 1985), but new radiometric data suggests a Late Miocene age, (Messinian; see Ehret et al. 2012).
Diagnosis.—Height of the rostrum at its mid-length is 2/3 the height of the nasofrontal hinge, and its entire dorsal edge is slightly convex.
Measurements.—See SOM 1.
Description.— Rostrum: R. aguirrei has a robust and large rostrum, slightly larger than that of R. ramirezi . In lateral view, the lateral sulci ( Fig. 4A View Fig 1 View Fig , A 3 View Fig ) are oriented parallel to the culmen due to the ossification of primary nasal apertures. These sulci divide the rostrum rather equally into dorsal and ventral parts as in R. ramirezi , but in Sula , Morus , and Papasula the dorsal part comprises 1/3 of the rostrum see Fig. 4A View Fig 1 View Fig ). Interestingly, we note that in S. figueroae this division is closer to the condition in Ramphastosula although this could be the product of lateromedial deformation. Furthermore, the height of the rostrum at its mid-length equals 2/3 the maximum height (at the level of the nasofrontal hinge). In S. variegata and generally among living sulids, this height equals 1/2 the maximum height, and in R. ramirezi the height at the mid-length of its rostrum is higher than the level of the nasofrontal hinge. Some individuals of the living species S. leucogaster and S. dactylatra show a slender protuberance in the posterior part of the rostrum (see Stucchi 2013: fig. 4). The rostrum is projected downward with respect to the horizontal plane since the nasofrontal hinge towards the tip in R. aguirrei and Sula spp. , whereas R. ramirezi shows an upward angle until the mid-length of the rostrum where it begins to descend. In R. aguirrei the tip of the rostrum is ventrally curved in almost 40% of its maximum height from approximately its mid-length.
In dorsal view ( Fig. 4A View Fig 3 View Fig ), R. aguirrei as well as Sula and Papasula exhibit a rough surface across its length. Ventrally Fig. 4A 4 View Fig ), the rostrum has the typical schizognathous condition of the family. Palatines are separated in their cranial extremes and fused in the caudal extreme as in other sulids.
Neurocranium: The only noticeable difference between R. aguirrei and R. ramirezi in the braincase is located at its dorsal surface. From the nasofrontal hinge to the mid-length of the orbitals the frontals of R. aguirrei are lower than those of R. ramirezi with respect of the horizontal plane. Posterior to the mid-length of orbitals, the braincase is slightly inclined upward in R. aguirrei whereas that of R. ramirezi remains flat.
Remarks.—The morphology of Ramphastosula suggests closer affinities to Sula than to Morus or Papasula . Both Sula and Ramphastosula have a roughened maxilla surface in its posterior-most part, and both have reduced and bifurcated postorbital processes. Conversely, Morus has a smooth maxilla surface, but shows the same condition of the postorbital processes. Papasula shows long, sharp and ventrally-inclined postorbital processes but retains the roughened maxilla surface (Stucchi 2003; Stucchi and Urbina 2004). In this respect, the primitive condition of both characters is present in Papasula (according to Smith 2010).
The skull of R. aguirrei has an intermediate morphology between other sulids and R. ramirezi . Interestingly, the rostrum of R. aguirrei is more similar to that of Sula rather than R. ramirezi . Taking all this into account, along with the previously observed morphological stability in the cranium of sulids (Stucchi 2003), allows us to suggest that the specimens from Poza Negra and Poza Roja represent different species.
Stratigraphic and geographic range.—Messinian, Pisco depositional sequence, Pisco Formation, Southwestern Peru.
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