Afromeryx palustris

Miller, Ellen R., Gunnell, Gregg F., Gawad, Mohammad Abdel, Hamdan, Mohamad, El-Barkooky, Ahmed N., Clementz, Mark T. & Hassan, , 1914, Anthracotheres from Wadi Moghra, early Miocene, Egypt, Journal of Paleontology 88 (5), pp. 967-981: 974-976

publication ID

10.1666/13-122

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http://treatment.plazi.org/id/3B095517-A32D-D953-42FE-4E1DEBB222D8

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scientific name

Afromeryx palustris
status

new species

Afromeryx palustris  new species

Type.-CGM 83751, right dentary with symphysis, alveoli i1- p1, crowns p2-4 (Table 1, Fig. 5B-5D).

Diagnosis.-Differs from A. zelteni  and A. grex  in being much larger (m2 area >70% larger than A. zelteni  , m2 area >25% larger than A. grex  ); further differs from A. grex  in having premolars with weaker pustulate crest development, premolars lacking distinct and elevated premolar cingulids, taller and more sharply tapering p2-3, p2 with better developed anterior crest. All premolar crowns have very finely wrinkled enamel.

Etymology.-"Palustris,'" marshy or swampy, from the Latin ‘‘palus,’’ marsh, in recognition of the anthracothere habitat at Moghra.

Occurrence.-Early Miocene, Wadi Moghra, Egypt.

Material.-DPC 2542, right dentary with symphysis, p3-m1; DPC 4244 right dentary p2-3; DPC 4604, left dentary p4-m3; DPC 12593, right dentary dp4-m1, m2 in crypt.

Description.-The dentary, as in other anthracotheres, has an unfused symphysis. It angles inferioposteriorly and is relatively short, not extending beyond p1. The dentary is deepest just posterior to m3 and has a rounded angle. The dentary tapers gently to the level of m1-p4 and then tapers more dramatically anteriorly.

Incisors and canine: alveoli for three lower incisors are present, and judging from their size these would have been small teeth. The incisors are followed by an alveolus for a relatively small canine, which is separated from the single-rooted and relatively small p1 (see Fig. 5D) by a modest diastema (ranging from 20-30 mm in length).

p2: relatively robust with a tall and tapering protoconid, a convex labial surface, and concave lingual surface. The labial aspect is covered with crenulated enamel that extends lingually around the anterior and posterior surfaces. There is a welldeveloped anterior crest extending from the tip of the protoconid along the anterolingual margin-there are three well-developed accessory cuspules arrayed down the lingual surface of the crest. The posterior portion of the tooth is broken but it is clear that there was no talonid development. A weak and low lingual cingulid is present but it extends only about half the length of the tooth, from the anterior crest posteriorly. Weak antero- and posterolabial cingulids are present.

p3: is generally similar to p2 but differs in several important respects. Both the anterior and posterior surfaces are more extensive with the posterior surface having a strong ridge extending down the crown to reach a relatively well developed cingulid. In addition, the cingulid wraps around the base of the tooth both labially and lingually, but it is not continuous with a similarly developed but less extensive anterior cingulid. As on p2, there is no talonid development but the posterior cingulid on p3 is better developed and forms a weak shelf. A heavy anterior crest extends to the base of the tooth-this crest is weakly cuspate, showing development of bulbous but indistinct cuspules formed along its length. There is no distinct paracristid extending to the protoconid. A slightly weaker and less robust posterior crest extends to the tooth margin. This posterior crest is not cuspate and, while robust, is not as heavy as the anterior crest. A narrow, deep, dorsoventrally elongate and mesiodistally constricted valley extends between the anterior and posterior crests. A weak, low and short lingual cingulid closes the base of this valley. The tooth crown is covered by complex, rugose enamel.

p4: is a more elongate version of p3, differing principally by having a distinct and broad talonid region that extends posteriorly as a flat shelf. The talonid shelf is weakly divided by a vague crest extending down the posterior surface and bifurcating with one branch extending to the talonid and the other terminating at the metaconid. The anterior and posterior lingual crests are slightly less robust than on p3 and are more angled anteriorly and posteriorly, respectively, producing a less deep, but equally extensive, lingual valley (CGM 83751, DPC 2542). However, this development appears variable as other specimens (e.g., DPC 4604) show more closely juxtaposed anterior and posterior crests that turn toward each other dorsally, producing a very narrow and restricted lingual valley. In DPC 2542 there are no cuspules developed on the anterior and posterior crests, while in DPC 4604 and CGM 83751, bulbous cuspules are present. The lingual cingulid is better developed on p4 than the other premolars, and produces a sloping lingual shelf that closes the base of the lingual valley. p4 has no crest connecting the paraconid and protoconid, but there is a weak crest connecting the metaconid to the apex of the protoconid. A much better developed anterior cingulid that forms a low but distinct shelf is present on p4.

Molars: the molars of Afromeryx palustris  are poorly represented but, where known, differ little from a common bunoselenodont anthracothere pattern. Lower first and second molars have trigonids and talonids of equal size and disposition. The cristid obliqua nearly reaches the lingual border producing a deep hypoconid notch that is closed ventrally by a hypocristid. Lingual cusps are aligned along the lingual margin, except for the small hypoconulid that is positioned lingual of center. There are weak pre- and postcristids but these are not labially continuous with the hypocristid. No lingual cingulids are present. The third lower molar appears to be a more robust version of m2, but with a large hypoconulid extension that forms a weakly oblique, single loop that is separated from the talonid by a deep labial valley. Like the premolars, all molars are covered by finely wrinkled enamel.

Remarks.-Material assigned to A. palustris  resembles other species of Afromeryx  in having an unspecialized symphyseal region, a single-rooted p1, and in placement of the mental foramina. At present there are few comparable parts across all species, but the three species of Afromeryx  ( A. zelteni  , A. grex,  A. palustris  ) differ greatly in size, premolar proportions, and elaboration of the premolar series.

To investigate more fully the nature of the relationship between the larger ( A. palustris  ) and smaller ( A. grex  ) specimens from Moghra, we looked at m2 dimensions. Specifically we examined the square root of m2 area in a range of extant male and female artiodactyl species, to test hypotheses about whether the size difference between the m2 of A. palustris  and that of A. grex  was on a par with what might be expected for males and females within a species, two species in a genus, or perhaps between individuals in two different genera.

In general, artiodactyls are not particularly sexually dimorphic in the size of their postcanine dentition. Instead, sexual dimorphism in artiodactyls is primarily manifest in body size differences, elaboration of horns or antlers, and sometimes also in canine size and pelage characteristics (e.g., presence of a dewlap). However, we chose to use m2 dimensions partially because m2 size was one of the few attributes available in both A. palustris  and A. grex  , but also because the postcanine dentition in artiodactyls is morphologically conservative with regard to sexual dimorphism, so that a large degree of difference between males and females in this feature would be a clear result.

Table 3 presents summary statistics involving m2 proportions in 14 artiodactyl species compared with the same proportions in

A. grex  and A. palustris  . The raw data from which these calculations are derived are available as Appendix 1. Table 3 shows the average m2 area square root for males divided by that of females. This ratio is used to approximate the degree of m2 sexual dimorphism present among the extant sample. The values for the extant sample are then compared with the m2 square root ratio of A. palustris  (DPC 4604) versus A. grex  (M 15021). Results show that the ratio of m2 size in A. palustris  to A. grex  is outside what might be expected for males and females in a single artiodactyl species. The ratio for A. palustris  to A. grex  is about 1.17 while members of the extant sample fall within a fairly restricted range of 0.92 to 1.08. The ratio of A. palustris  to A. grex  also exceeds what might be expected for two species in the same genus, as the values for Kobus ellipsiprymnus versus K. kob  were 0.92 to 1.04, and Hippotragus equinus  versus H. niger  ranged from 0.99 to 1.03. In fact, based on the data presented here, the ratio of A. palustris  m2 area to that of A. grex  is even greater than might be expected for members of two different artiodactyl genera. However, we recognize A. palustris  and A. grex  as two species of Afromeryx  on the basis of anterior tooth morphology, and also because the ratio of m2 size in A. palustris  versus A. grex  does not exceed that which might be expected between a large male of one species and a small female of a second species within the same genus. For example, Appendix 1 shows that the m2 ratio of a large male Hippotragus equinus  (NMNH 164790) compared with that of a small female of H. niger  (NMNH 545318) is about 1.2, and a large male Kobus ellipsiprymnus (NMNH 61731) compared with a small female of K. kob  (NMNH 164784) is about 1.54, ratios that are either on a par with or exceed the ratio of 1.17 observed for A. palustris  to A. grex  .