Duboisia aff. santeng ( Dubois, 1891 )

Nishioka, Yuichiro & Correspondence, Chavalit Vidthayanon, 2018, First occurrence of Duboisia (Bovidae, Artiodactyla, Mammalia) from Thailand, Fossil Record 21 (2), pp. 291-299 : 294-295

publication ID	https://doi.org/ 10.5194/fr-21-291-2018
DOI	https://doi.org/10.5281/zenodo.13751217
persistent identifier	https://treatment.plazi.org/id/03A687C4-F910-FFE0-FF6E-B5E2FD60C73F
treatment provided by	Felipe
scientific name	Duboisia aff. santeng ( Dubois, 1891 )
status

Treatment

Duboisia aff. santeng ( Dubois, 1891)

( Fig. 3 View Figure 3 )

Examined material: PPN 01-000109, a calvarium with right and left horn cores.

Locality: A sandpit at Tha Chang, Nakhon Ratchasima City, north-eastern Thailand.

Age: Younger than the Middle Miocene and older than the Middle Pleistocene.

Measurements: Antero-posterior diameter of the left horn core: 18.5 mm; medio-lateral diameter of the left horn core: 33.6 mm; length of brain case (between bregma and superior nuchal line): 65.1 mm; maximum width of brain case: 68.7 mm; height of the occipital without the foramen magnum: 38.1 mm (see also Table 1 View Table 1 ).

Description: The present specimen is a calvarium with complete right and left horn cores, including the frontal, parietal, temporal and occipital bones. The basioccipital part is broken. The dorsal surface on the fronto-parietal region is flat and faintly depressed. The frontal surface is rugose, with weak precornual ridges extending from the anterior ridge of the horn cores ( Fig. 3g View Figure 3 ). Supraorbital foramina are not found on the preserved parts: that means they are situated further towards the front than the horn pedicels. The postero-dorsal rims of the orbits weakly project outwards. Temporal crests are moderately developed, slightly overhanging along the superior nuchal line on the occipital. The external occipital protuberance is projected posteriorly. The median nuchal line forms a sharp ridge and gently inclines below the centre. The brain case is squared in dorsal view (length/width = 0.95). The height of the occipital without the foramen magnum is low relative to the brain-case width (height/width = 0.55). The mastoid processes project laterally, with shallow squamosal shelves.

The horn cores insert caudolaterally from the orbits, strongly inclined backwards being parallel to the frontal surface at the base, and bend upwards at the middle part. In the antero-dorsal view ( Fig. 3a View Figure 3 ), the horn cores diverge at an angle of 95 ◦ at the base, and curve inwards after the middle part. The horn core is weakly twisted clockwise (right side). Right and left horn cores have a wide interval at the frontal surface (56.0 mm between the medial keels). The cross section of the horn cores has a rounded triangular outline antero-posteriorly compressed ( Fig. 4b View Figure 4 ). There are medial and lateral keels from the base to the top. The anterior surface is convex but does not have a clear keel.

Remarks: Most antelope-sized species of Bovinae were traditionally included in the tribe Boselaphini ( McKenna and Bell, 1997) . However, it is currently accepted that the tribe encompasses only the following crown genera: Boselaphus , Tetracerus , and Duboisia (Bibi, 2009; Bibi et al., 2009). There are some bovines whose taxonomic positions are formally pending. Schlosser (1903) proposed Paraboselaphus ameghinoi , referring to some isolated cheek teeth from China, but his materials and description are insufficient to define an independent taxon based on apomorphies of the genus. Matsumoto (1915) described Proboselaphus from the Pleistocene of Sichuan, China, as a primitive form of living Boselaphus , but the holotype skull of P. watasei has neither cranial nor tooth characteristics of Bovidae , but rather those of Cervidae ( Nishioka et al., 2018a) . According to Pilgrim (1939), Sivaportax from the Neogene Irrawaddy beds of Myanmar is phylogenetically related to Boselaphus , but our recent studies indicated that the former shares horn core morphology with Miocene Tragoportacini or Stem Bovini rather than Boselaphini ( Nishioka et al., 2018b). In this study, we accept that Duboisia is the only extinct genus included in Boselaphini .

Regarding cranial morphology, PPN 01-000109 has the precornual ridges extending from the anterior keels (or ridges) of the horn cores which are a synapomorphy of Boselaphini . Rugosity on the fronto-parietal surface is a symplesiomorphy of Tragoportacini (e.g. Protragocerus , Helicoportax , Tragoportax , and Miotragocerus ) and Boselaphini , but that of PPN 01-000109 is finer than that of the tragoportacin genera. Moreover, PPN 01-000109 has relatively weaker temporal crests on the parietals and an antero-posteriorly shorter brain case than the tragoportacin genera listed above. According to previous studies ( Stremme, 1911; Hooijer, 1958) and our observation, a combination of the following characteristics of the horn cores is diagnostic to distinguish the genus Duboisia from all of the other genera of Bovinae : the lower half inclined backwards; the upper half curved upwards; and the cross section rounded triangular, compressed antero-posteriorly, and with medial and lateral keels. Boselaphus namadicus is known as an extinct form of boselaphins from the older alluvium (Middle Pleistocene) of the Narmada basin, India (Rütimeyer, 1878; Pilgrim, 1939; Chauhan, 2008), and from the Plio-Pleistocene deposits of Sardhok, Pakistan ( Siddiq et al., 2017). The horn core of the holotype ( BMNH 36851) of B. namadicus has equilateral triangular cross section with a sharp anterior keel and is less compressed antero-posteriorly than that of PPN 01- 000109 or the genus Duboisia . In measurements ( Table 1 View Table 1 ), the brain case of PPN 01-000109 is antero-posteriorly shorter than that of Boselaphus tragocamelus and approximately as long as that of Boselaphus namadicus or Tetracerus quadricornis based on dividing length by width. In the occipital height divided by width, PPN 01-000109 is intermediate between Boselaphus and Tetracerus . Based on the qualitative and quantitative comparisons in horn core and brain-case morphology, as mentioned above, PPN 01-000109 is distinguished from Boselaphus and Tetracerus .

The genus Duboisia formally contains two species i.e. D. santeng ( Dubois, 1891) and D.? sartonoi Geraads, 1979 (or D. saatensis Von Koenigswald, 1934 ), although the latter was established based on some isolated teeth. Van den Bergh (1988), in his unpublished master dissertation, suggested that Cervus problematicus Von Koenigswald, 1933 , from Bumiayu, Java, should be combined with the genus Duboisia based on a large skull fragment. Both? D. sartonoi and D. problematicus are likely larger than D. santeng , but these species are still debatable taxonomically ( Rozzi et al., 2013). PPN 01-000109 is almost as large as the specimen MGB.Dbs. of D. santeng from Sangiran ( Table 1 View Table 1 ). The horn cores of PPN 01-000109 are primarily similar to those of D. santeng , in having keels on the medial and lateral sides and cross section compressed antero-posteriorly, but there are some minor differences between PPN 01-000109 and D. santeng ( MGB. SA 290709) from Pucung. Compared to the latter, the former has slender horn cores, curved prominently, and incomplete anterior and medial keels ( Fig. 4 View Figure 4 ). Moreover, precornual ridges of PPN 01-000109 are weaker than those of MGB.SA 290709. These differences of horn cores are possibly due to intraspecific variation. Although a species identification of PPN 01-000109 should be discussed in detail based on additional specimens from Thailand and comparing with a sufficient number of specimens of D. santeng from Java, PPN 01-000109 has a strong affinity with D. santeng .