Parvavorodon gheerbranti Solé, Lhuillier, Adaci, Bensalah, Mahboubi, and Tabuce, 2014b
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https://doi.org/ 10.26879/598 |
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https://treatment.plazi.org/id/FE3F87A4-FFF8-DC24-E889-831CFB34FE26 |
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Felipe |
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Parvavorodon gheerbranti Solé, Lhuillier, Adaci, Bensalah, Mahboubi, and Tabuce, 2014b |
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Parvavorodon gheerbranti Solé, Lhuillier, Adaci, Bensalah, Mahboubi, and Tabuce, 2014b
Figures 3-5 View FIGURE 3 View FIGURE 4 View FIGURE 5 , Table 3
Referred specimen. CBI-1-555, left P3; CBI-1- 556, left M1or2; CBI-1-557, left p2; CBI-1-558, right m1; CBI-1-559, left m3; CBI-1-613, left dentary bearing dp4, m1, alveoli of dp3 and m2, and distal alveolus of dp2?.
Measurements. Table 3.
Description. The P3 exhibits a simple morphology ( Figure 3.1-2 View FIGURE 3 ): the only known specimen is worn, which prevents from identifying the parastyle, but this latter was certainly weak. The metastyle is large but low. We identify the tooth as a P3 due to the enlargement of its base in the lingual side. This corresponds to the usual position of the protocone on P3 and P4; the latter is, however, more individualized and slightly more mesially located on P4 than on P3.
On the unique upper molar discovered ( Figure 3.3-4 View FIGURE 3 View FIGURE 4 ), the paracone is less developed than the metacone and appears mesiodistally narrower. The parastyle is broken but it was certainly large based on the surface of breakage – the tooth thus could represent a M2. Despite its breakage, the postmetacrista is elongated. The protofossa is short and narrow despite the presence of the paraconule and metaconule. The stylar shelf is strongly reduced. No cingulum is visible.
The dentary is narrow – its depth only slightly exceeds the length of the m1 ( Table 2). A mental foramen is present below the dp3 (see below for the determination of this locus); it corresponds to the most distal one of the two mental foramina, which are generally observed in Hyaenodonta . There is no diastema between dp2, dp3, and dp4.
The most mesial tooth preserved (dp4) on the dentary is characterized by a very low trigonid that is elongated mesiodistally. This feature is characteristic of the dp 4 in Hyaenodonta . Indeed, the paraconid occupies a mesial position. It is slightly lower than the metaconid and protoconid. The protoconid is roughly at the same elevation than the paraconid. The metaconid is clearly more distally located than the protoconid. The talonid is – as the trigonid – elongated mesiodistally. The postfossid is narrow. The hypoconid, hypoconulid, and entoconid are distinguishable in occlusal view ( Figure 4.3-4 View FIGURE 4 ). The entoconid appears less individualized than the two other talonid cusps. A strong precingulid is visible.
On the fragmentary dentary ( Figure 4 View FIGURE 4 ), the presence of two foramina can be observed in occlusal view (black arrows on Figure 4.2 View FIGURE 4 ). The most distal foramen is located between the roots of dp4; the second foramen is visible between the two alveoli that are mesial to the dp4. These foramina seem to be related to the eruption of the permanent teeth. This has been indeed observed in Hyaenodon (K.A. Bastl, personal commun., 2015). The presence of a foramen suggests that the two alveoli located mesially to the dp4 correspond to that of a dp3.
We made CT-scan reconstructions of CBI- 1- 613 in order to determine whether germs were present or not. No germ is visible neither below dp4 nor below dp3 ( Fig. 5 View FIGURE 5 ). As shown by Bastl et al. (2011) and Bastl et al. (2014), there isn't necessarily a germ visible for p3 and p4, when a fully erupted m2 is present. This absence of germs below these deciduous teeth (while m2 is present) was actually similarly observed for the mandible NMHW2009z0082/0002 referred as Hyaenodon sp. ( Bastl et al., 2011, figure 1): the mandible shows p1, dp4, m1, and the alveoli of dc, dp2, dp3, and m2, while the X-ray only reveals the germs of p2 and the canine. Based on this data (i.e., absence of germ and presence of a foramen in occlusal view), one can could conclude that p3 had not started to erupt on that specimen and that dp3 was present when the individual died. The presence of an m2 associated with a dp3 and dp4 agrees with stage 2 (North American Hyaenodon ) and stages 3-4 (European Hyaenodon ) of the tooth eruption sequence established by Bastl et al. (2011) for the hyaenodontine Hyaenodon . The distal root situated mesially to those of the latter tooth may correspond either to that of dp2 or to that of p2. NHMUK M 4498 ( Hyaenodon exiguus ) and NHMUK M 84866 ( Hyaenodon filholi ) showed that the germs of p3 and p4 are present when the germ of p2 is developed or when p2 is erupting. If we assume that the early stages of the tooth eruption sequence are somewhat similar in hyaenodonts, we could hypothesize that a dp2 must have been present in CBI-1-613. Whether the p2 is present or not, it is certain that CBI-1-613 represents a very young hyainailourine individual.
CBI-1-557 ( Figure 3.5-7 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 ) is identified as a p2 and CBI-1-555 as a p3. As in hyaenodonts, CBI-1- 557 (p2) is smaller and asymmetric in lateral view compared to CBI-1-555 (p3). The p2 has a simple crown morphology with a small paraconid, which remains as high as the talonid. The talonid is short and low, and bears only one cusp (hypoconid?) at its distal end.
The m1, preserved on the dentary CBI-1-613 ( Figure 4 View FIGURE 4 ), is larger than dp4, but its morphology is virtually similar. The paraconid is well located mesially – the paracristid is thus long and secant – and is larger than the metaconid. The metaconid is less distally located than on dp4. The apex of the protoconid is broken, which prevents estimating its height. The talonid cusps are heavily worn; however, the postfossid is narrow as on dp4. A large precingulid is present. Because the isolated molar CBI-1-558 ( Figure 3.8 View FIGURE 3 -10) is morphologically similar to the CBI-1-613 (m1), we identify the former tooth as a m1.
The second isolated lower molar (CBI-1-559) is characterized by a high paraconid, which is mesiolingually located, a low and reduced metaconid, and a narrow and mesiodistally elongated talonid ( Figure 3.11 View FIGURE 3 -13). Only a precingulid is visible. The talonid is worn, which prevents from determining the exact position of the talonid cusps. The presence of a narrower postfossid (but with a wide talonid), a paraconid more lingually located, and a trigonid more opened than on the m1/m 2 specimens described from the Gour Lazib and Chambi, suggest that the CBI-1-559 molar is a m3. These differences in the trigonid and talonid morphologies between the m1-m2 and m3 are notably exemplified by the holotype of the contemporaneous hyaenodont Furodon crocheti ( Solé et al., 2014b) .
Discussion. The small hyainailourine Parvavorodon was originally described based on two identical lower molars from the Gour Lazib ( Solé et al., 2014b). These two molars differ from those of Furodon in being smaller in size despite the fact that they display similar derived secant features (e.g., elongation of the paracristid).
Because the fossils described from Chambi are similar in size and morphology with the two small molars from the Gour Lazib, we refer them to Parvavorodon gheerbranti . This new material from the Eocene of Tunisia testifies to (1) the presence of this small hyaenodont in the late Ypresian (or early Lutetian) of Maghreb, and (2) the secant morphology of its dentition.
The new fossils are also important because they allow recognizing five new dental loci for the species: dp4, P3, p2, M2 (or M1), and m3. Moreover, we describe the first dentary element known for this genus: it corresponds to the oldest dentary element known thus far for a juvenile of Hyaenodonta in Africa. The position of the unique mental foramen present on the dentary is particularly interesting inasmuch as it represents an important feature for discussing the subfamilial classification of Parvavorodon : the distal foramen is actually located below the p 3 in hyainailourines, while it is generally located close to or below the roots of p 4 in koholiines ( Solé et al., 2009). Because the position of the distal mental foramen corresponds to the first case, the dentary CBI-1-613 supports the hyainailourine status of Parvavorodon .
As indicated above, in Parvavorodon , the differences observed between the m1-m2 and m3 are similar to those observed in Furodon . This indicates that the two taxa are probably closely related.
Age and locality. Late Ypresian or early Lutetian; Chambi CBI-1 ( Tunisia).
Hyainailourinae indet.
Figure 6 View FIGURE 6
Referred specimen. UON 84-359, left P3.
Measurements. L = 4.6 mm; W = 3.6 mm.
Description. The tooth is three-rooted. The paracone is prominent. There is no parastyle. Unfortunately the distal part of the tooth is broken, which prevents from observing the morphology of the metastyle. The lingual root bears a small cusp (? protocone). The enamel is crenulated. The cingula are developed around the tooth.
Discussion. The small size of the lingual cusp and absence of a parastyle indicate that UON 84-359 is not a P4. However, this tooth is three-rooted and bears a small lingual cusp, two characters which allow identifying it as a P3.
The presence of a third root on P3 is often observed in hyainailourines – and in some limnocyonines ( Morlo and Gunnell, 2005). For instance, it has been observed in the following Eocene-Oligocene taxa: Pterodon africanus Andrews, 1903 , Pterodon syrtos Holroyd, 1999 , Paroxyaena Martin, 1906 , and Parapterodon Lange-Badré, 1979 . The presence of this root is related to the development of the lingual cusp, which is analogous to the protocone of P4. This structure is notably well-developed in Paroxyaena ( Lange-Badré, 1979) . It is worth noting that the development of the cingula is found in the European Paroxyaena , but the P3s of the latter are much larger than UON 84-359. As a result, we tentatively refer UON 84-359 to the Hyainailourinae . However, because the taxon of Bir el Ater is only documented by this tooth, we referred it as Hyainailourinae indet. pending additional material.
Age and locality. Latest Bartonian or earliest Priabonian; Bir el Ater ( Algeria).
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