Iberomeryx parvus Gabunia, 1964
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publication ID |
https://doi.org/ 10.26879/629 |
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persistent identifier |
https://treatment.plazi.org/id/CD76E66A-4055-FF8B-FEE1-7745FCB278A7 |
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treatment provided by |
Felipe |
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scientific name |
Iberomeryx parvus Gabunia, 1964 |
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Iberomeryx parvus Gabunia, 1964
Figures 3.1-3.21 View FIGURE 3 , 4.1-4.16 View FIGURE 4
Referred species. I. minor ( Filhol, 1882) ; I. sp. cited in Sudre, 1984).
Referred material. This taxon has been identified in the five localities that yielded ruminant material.
Gözükızıllı 2 (lower member of the Kızılırmak Formation). Rght cubo-navicular ( GK 2-5), right maxilla with D2-M1 ( GK 2-4), lower jaw with erupting right m2 ( GK 2-10), lower jaw with right d3, d4, and the trigonid of m1 ( GK 2-11).
Gözükızıllı 3 (lower member of the Kızılırmak Formation). Left p3 (GK3-1), left m3 (GK3-2), GK3-3, right m2; GK3-4, left P2; GK3-5, right P4; GK3-6, left i1; GK3-7, left i2; GK3 A-8, fragmentary lower jaw preserving left m1; GK3-9, fragmentary right M3; GK3-11, right p3; GK3-12, phalanx media; GK3-13, phalanx proximalis; GK3-14, phalanx media; GK3-15, phalanx media; GK3-16, phalanx media; GK3 A-17, phalanx media; GK3-19, left calcaneum (damaged); GK3-20, distal pulley of right humerus; GK3-21, distal pulley of right humerus; GK3-22, distal pulley of left humerus; GK3-23, right calcaneum (damaged); GK3-24, left calcaneum (damaged); GK3-25, right astragalus (damaged); GK3-46, phalanx proximalis; GK3-27, posterior half of right p4; GK3-28, fragmentary right upper molar; GK3-29, labial half of left lower molar; GK3-30, fragmentary left lower molar preserving M Structure; GK3-31, complete left M2; GK3-32, right edentelous lower jaw; GK3-33, right fragmentary lower jaw preserving m1?; GK3-34, left m2; GK3- 36, right p4; GK3-37, right astragalus; GK3-38, right astragalus (damaged); GK3-39, right astragalus (damaged); GK3-54, proximal part of fused metatarsal III and IV.
Bağdatlı (upper member of the Kızılırmak Formation). BA-10, distal extremity of femur (damaged).
Tepe 641 (upper member of the Kızılırmak Formation). TP641-1, lower jaw preserving the talonid of m1 and the trigonid of m2; TP641-2, left m3; TP641-3, left m2; TP641-4, left m1; TP641-5, left m1; TP641-6, lower jaw preserving right m2; TP641-7, lower jaw preserving right m2; TP641-8, lower jaw preserving heavily worn m1-2; TP641 A-11, lingual part of left M2?; TP641-12, right M2; TP641-13, left M1; TP641-14, right M2?; TP641- 15, left cubonavicular; TP641-16, left cubonavicular; TP641-17, right calcaneum; TP641-18, left calcaneum; TP641-19, TP641-19, left calcaneum (damaged); TP641-20, left calcaneum (damaged); TP641-21, right astragalus (damaged); TP641-22, right astragalus (damaged); TP641-26, distal extremity of left tibia; TP641-27, lower jaw preserving left m3; TP641-28, fragmentary vertebrae; TP641-30, right distal tibia.
Type locality of the Kızılırmak Formation (upper member of the Kızılırmak Formation). KZ-4, distal extremity of a phalanx proximalis; KZ 5, distal extremity of phalanx proximalis; KZ-7, right M1; KZ-8, distal pulley of a metatarsus.
Description and Comparisons
Lower deciduous dentition (based on the unique specimen GK2-11, Figure 3.6-7 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 ). The d3 is anteroposteriorly elongated and transversely narrow as it is in non pecoran ruminants. The protoconid has an anterior crest extending to the anterior conid, which is slightly directed lingually as in Iberomeryx minor . The anterolingual conid is small, and a short crest extends anterolingually. The posterolingual cristid of the protoconid is short. The posterolabial conid is large and its posterior cristid extends posteriorly and turns lingually to form the posterolabial edge of the tooth as in Iberomeryx minor ( Geraads et al., 1987) . There is a thin cingulid on the anterolabial part of the tooth. The d4 is badly damaged and only the posterior lobe is preserved. The hypoconid and entoconid are of the same size. The entostylid is salient and separated from the posteriorly rounded entoconid by a distinct groove. The external postprotocristid is preserved and observed linked to the prehypocristid as it is in all tragulids known so far. The posterior rim of the d4 is damaged and deforms the posthypocristid. There is no ectostylid but a cingular shelf.
Upper deciduous dentition (based on the unique specimen GK2-4, Figure 3.1 View FIGURE 3 ). The D2 is fragmented and missing the antero-lingual part. The tooth is anteroposteriorly elongated and transversely narrow, and it has a strong posterolingual cingulum, and a smaller anterolabial cingulum. Unlike the D2 of Dorcatherium , there is a distinct lingual cone emerging from the lingual cingulum. The paracone (positioned at about midway of the tooth length) has a weak labial rib and strong anterolabial and posterolabial crests. There is a posterolingual cingulum between the paracone and the posterior corner of the tooth. The D3 has a similar configuration of cones and crests, but exhibits a triangular shape in occlusal view due to the larger lingual cone (metaconule) that is positioned at a more anterior level than the paracone. The labial rib of the paracone is more marked than on the D2, and the metacone bears a weak labial rib. The lingual cone (metaconule) has four crests. Its posterior crest fuses with the posterior cingulum. There is a well-marked internal transversal crest, and the anterior crest is split into a short internal crest and a posterior one which fuses with the anterolingual cingulum. The styles are weak, and there is no labial cingulum. The D4 has the configuration of the upper molars of adults, but it has a trapezoidal outline in occlusal view, and slightly more pronounced styles than on the molars. The protocone is sickle-shaped in occlusal view with an anteroposteriorly oriented postprotocrista. The metaconule is crescent-shaped with a premetaconulecrista ending between the paracone and metacone, and a slightly curved postmetaconulecrista joining the postero-labial corner of the tooth. The metastyle is absent. The paracone and metacone are aligned, and only the paracone displays a weak labial rib. The mesostyle forms a small column. There is an anterolingual cingulum surrounding the protocone.
Adult dentition. The lower incisors are tentatively referred to Iberomeryx parvus on the basis of their size, and the spatula-like morphology (especially i1) that is reminiscent to that of Dorcatherium ( Kaup, 1839; Aiglstorfer et al., 2014) and Tragulus . The roots of the teeth are cylindrical and more and less straight ( Figure 3.18 View FIGURE 3 -19). The crown of the first lower incisor ( Figure 3.18 View FIGURE 3 ) is of spade-like shape, almost symmetrical, and lingually concave like in Dorcatherium ( Kaup, 1839) . Its lingual face bears an anterior crest, and the posterior border is bounded by a groove. The second or third incisors are more difficult to differentiate. They are pen-like, lingually concave, clearly assymetrical, and bear a small anterior crest on the lingual face, and a groove on the posterior rim (GK3-7) ( Figure 3.19 View FIGURE 3 ), like in the i1.
The anterior premolars are poorly represented in our material. The p3 is an elongated and narrow tooth. The mesolabial conid (protoconid) is the main cuspid and the anterolabial cristid is bent lingually to join a small anterior conid ( Figure 3.20 View FIGURE 3 ). The posterolabial cristid joins the posterolabial conid that extends posteriorly into a single crest that reaches the posterior border of the premolar. There is small posterior cingulid. This p3 corresponds well to the morphology and proportions of the p3 of Iberomeryx minor .
Overall, the p4 is in accordance with those of Iberomeryx parvus and I. minor with two crests running posteriorly from the apex of the mesolabial conid (protoconid) forming a deep, posterolingually open gulley ( Figure 3.21 View FIGURE 3 ). The p4 of I. parvus is gracile and its anterior conid is more pronounced than on p3. The anterolingual cristid extends anteriorly and turns anterolingually at the level of the anterior conid. There are anterolingual and anterolabial cingulids, and a postero-labial cingulid as in I. parvus . This strong crest corresponds to a wear facet, which is strongly worn in all p4s observed.
Lower molars are brachydont (although tooth crowns are taller than those of Iberomeryx minor ), and the hypoconid and protoconid are crescent-shaped ( Figure 3.11 View FIGURE 3 -17). The trigonid is narrower than the talonid, and the protoconid is taller than the metaconid on unworn teeth. The preprotocristid extends anteriorly, and turns abruptly lingually along the anterior part of the molar, forming a low crest, reaching the lingual margin of the tooth. Because of the absence of a premetacristid, this large anterior fossid shows a broad lingual opening ( Figure 3.12 View FIGURE 3 ). The entoconid is cuspidate, transversely compressed, and slightly anterior to the hypoconid. The posterior face of the hypoconid is distinctly concave; the posthypocristid extends to the lingual margin of the tooth; the cristid obliqua (or prehypocristid) is connected to the external postprotocristid. This crest tends to vanish during early wear of the molars. The M structure on the posterior side of the trigonid is well marked on the m1 and m2 ( Figure 3.11 View FIGURE 3 ). The lingual half of the M structure is formed by the external and internal postmetacristid whereas the labial half of the M structure is formed by the external and internal postprocristid. The internal postmetacristid and the internal postprotocristid are short and fused high to form a cristid that joins the prehypocristid (cristid obliqua). There is a distinct anterior basal cingulid extending anterolabially from the base of the preprotocristid, a strong and high posterior basal cingulid, and a low and poorly expressed ectostylid.
The upper premolars are rare and fragmentary. The only available P2 is an elongate tooth with a thin lingual cingulum from which emerges a tiny cusp, which may be interpreted as an incipient protocone ( Figure 3.9 View FIGURE 3 -10). The labial wall of P2 forms a distinct rib at mid-length of the tooth. The only P4 is triangular in occlusal outline ( Figure 3.8 View FIGURE 3 ), its posterior style is prominent, and its lingual protocone is fairly crescentic on this unworn tooth. The posterolingual crista is taller and more salient than the anterolingual crista, and it connects labially the posterior style.
The upper molars are trapezoidal in occlusal outline because of the enlargement of the labial (stylar) area ( Figure 3.2-4 View FIGURE 3 View FIGURE 4 ). They show a very strong lingual cingulum extending around the base of the protocone, forming a shelf, but there is no trace of protoconule as in Nalameryx . The styles are strong, anteroposteriorly compressed, and salient labially. The paracone has a strong, asymmetrical, and salient labial rib; the labial side of the metacone is flat and not excavated as in N. savagei ; the enamel is smooth.
Postcrania. Fragmentary postcranial material is tentatively attributed to I. parvus , in regard to its size, and because this species is largely dominant in our sample. The postcranial morphology of Oligocene tragulids is almost unknown (with exception of the astragalus, and distal metatarsal, Sudre, 1984), and we based the comparisons with the postcranial data known for the Miocene tragulid Dorcatherium ( Kaup, 1839) , Paleogene traguloids ( Webb and Taylor, 1980; Vislobokova, 2001), and extant tragulids.
The forelimb remains consist of a distal part of a right humerus, and a distal extremity of a metacarpal. The distal epiphysis of the humerus is gracile and resembles overall to that of extent Tragulus . The condylus humeri is trapezoidal, and the lateral diameter of the trochlea is smaller than the medial one ( Figure 4.9 View FIGURE 4 -11). The sagittal crest is well-marked, and the groove between the medial and lateral part of the trochlea is more concave than in pecoran humeri. The medial epicondyle is snoblike and rather extended caudally ( Figure 4.11 View FIGURE 4 ) compared to extant tragulids. The deep olecranon fossa perforates the shaft, forming a supratrochlear foramen as in Hypertragulus and Tragulus . The coronoid fossa is well-marked and oval-shaped. The lateral capitulum is more or less circular in lateral view, and it has a sharp lateral border like in extant tragulids.
The tarsal bones are fairly well represented with cubonaviculars, astragali, and calcanei. Three classes of size can be distinguished among the cubonaviculars and astragali; this is less obvious in calcanei. We consider that the smallest tarsal elements ( Figure 4.1-3 View FIGURE 4 ) might belong to a small species of tragulid, even if there is so far no dental material that would correspond to such a small size.
The cubonaviculars show the same morphology with the exception that the facet for the calcaneum appears to be reduced when the size increases ( Figure 4.1, 4.4, 4.17 View FIGURE 4 ). Unlike most tragulids, none of them display a fusion with the ectocuneiform.
As in all traguloids, the proximal and distal trochleae of the astragalus are not aligned, and the distal trochlea is slightly rotated medially and transversely narrow. The astragalus of Iberomeryx parvus is anteroposteriorly elongated and overall more gracile than it is in Pecoran ruminants. The sustentacular facet is medially bordered by a distinct but weak ridge reducing the transverse development of the facet in plantar view ( Figure 4.5-6 View FIGURE 4 View FIGURE 5 View FIGURE 6 ). The sustentacular facet is concave due to the presence of a longitudinal groove extending anteroposteriorly. The distal trochlea does not show any ridge separating the articular surfaces of the cuboid and the navicular. The astragalo-calcaneal facet is well-developed, and there is a deep fossa for the fibular condyle of the calcaneum ( Figure 4.8 View FIGURE 4 ). The distal astragalar facet is generally well- developed as it is in the primitive Pecora. The distal part of the internal malleolus facet is wide in all the known specimens.
The number of calcanei is more reduced, and the size range may reflect the intraspecific variation. The lateral side of the calcaneum has a long, deep groove. The sustentacular process is rather prominent, and its articular surface for the astragalus is wide and divided into two parts. The fibular condyle has a narrow convex facet for the fibula ( Figure 4.7 View FIGURE 4 -8). When preserved, the astragalo-calcaneal facet is reduced in size compared to pecoran ruminants.
The proximal part of a central right metatarsal shows fused metatarsal III and IV ( Figure 4.12 View FIGURE 4 ). The bone is longitudinally broken, but there is a flattened surface ( Figure 4.12 View FIGURE 4 -13) on the medial part suggesting the presence of a metatarsal II as in I. minor ( Blondel, 1997) . A proximal phalange is also tentatively referred to I. parvus ( Figure 4.14 View FIGURE 4 - 16). The proximal articulation is wide and the dorsal border is robust and high. The distal articulating surface is concave and of rather rounded outline. The plantar edge of the articular surface contains a strong indentation ( Figure 4.16 View FIGURE 4 ), which corresponds to the incomplete keel of the metacarpal head like in tragulids. This indentation extends on between third and half of the length of the articulating surface. The distal pulley is transversely compressed. It is morphologically most similar to those of Archaeomeryx although more gracile.
Discussion. In specimen numbers, Iberomeryx parvus is the most common ruminant taxon in the Kızılırmak Formation. The material recorded is the most extensive available for that species, making it especially valuable for our knowledge of this taxon. The dental and postcranial material described above is clearly referable to tragulids because of the morphology of d3 (anteroposterior elongation and short lingual cristids), d4 (external postprotocristid connected to the prehypocristid), the structure of the p4 with a deep groove posterolingually opened at the rear of the protoconid, and the lower molars showing the characteristic M structure. The morphology of the distal radius is also typical of tragulids. The thorough comparisons with the holotype of I. parvus (lower jaw preserving p4-m2) shows a general similar dental pattern, but the orientation of the prehypocristid is very labial, and it tends to connect the preentocristid, obliterating partially the M structure. The narrowness of the trigonid of molars, the elongated anterolingual preprotocristid, and the lack of premetacristid are typical features of Iberomeryx . It is worth noting that the upper deciduous dentition of the genus is here described for the first time. The D2 is not known for most Oligocene ruminants, and comparisons are necessarily limited. However, the D2 is more reminiscent to that of the extant genus Tragulus than to any Pecora which display a molarized D2 with a wider lingual extension. The D3 is most similar to that of Lophiomeryx chalaniati although the latter does not have a labially ribbed paracone nor the transverse crest linking the paracone and the protocone. The post-cranial material, especially the astragalus, displays the typical traguloid ( Lophiomerycidae and Tragulidae ) morphology, and it is in a size range that fit with the expected size range of the tooth sample ( Tables 1 View TABLE 1 and 2), and it is thus naturally referred to as Iberomeryx .
This genus (also known as Cryptomeryx in the literature) was referred to tragulids by Sudre (1984), and to lophiomerycids by Janis (1987). These two families display, during the Paleogene, a characteristic morphology of the lower molars with a trigonid lingually opened (i.e., the anterior face of the metaconid is devoid of cristid). Recently, Mennecart et al. (2011) provided a systematic review of the Western European species I. minor and convincingly proposed the re-affiliation of Iberomeryx to the Tragulidae based mostly on the presence of the typical M structure on the lower molars; a character that is now considered as an important apomorphic feature of the family although not all tragulids display such a dental structure (e.g., Rössner, 2007). The Paleogene fossil record of tragulids is only documented by four genera, all are rather poorly known. The earliest record of tragulids is from the late Eocene lignite of Krabi (Southern Thailand) with Archaeotragulus krabiensis which bears the typical M structures on its lower molars ( Métais et al., 2001), and the more ambiguous the earliest representative of the family, is known from the late Eocene of Thailand ( Métais et al., 2001). Krabitherium waileki is another enigmatic bunoselenodont form from Krabi that has been tentatively considered as a tragulid (Métais et al., 2007). According to these authors, Krabitherium waileki might be an early precursor of the bunoselenodont linage represented by the Miocene genus Dorcabune and the extant tragulid Hyemoschus (Métais et al., 2007) . Although the distinctive dental features are tenuous, the lower molars of Archaeotragulus differ from those of Iberomeryx in being more brachydont, the cristid obliqua more lingually orientated, the absence of ectostylid, and the pinched and transversely compressed hypoconulid ( Métais et al., 2001). During the Oligocene, the family is known in Western Europe, Georgia, and in the Indian Subcontinent if Nalameryx is considered as a tragulid ( Métais et al., 2009, 2015). The genus Iberomeryx is based on the species I. parvus Gabunia 1964 , which is so far restricted to the late Oligocene of Benara ( Georgia). In Western Europe, the genus is documented by the sole species I. minor ( Filhol, 1882) , which is known in several early Oligocene localities (MP23) ( Mennecart et al., 2011). Among tragulids, the material described above is closest dentally to Iberomeryx and Nalameryx . The lack of protoconule on the upper molars, the high-crowned teeth, and the lesser transverse development on our material are the main morphological features that prevent assignment to Nalameryx . The Turkish material differs from I. minor in having higher crowned molars, reduced labial ribs on the paracone and the metacone, and the morphology of the p3. Moreover, the lower molars of I. minor retain a small protoconulid (=paraconid) which is not present on the lower molars from the Kızılırmak Formation. However, our material is closely comparable to that of Iberomeryx parvus because of the morphology of its lower dentition, especially the p4. I. parvus also shows higher crowned cheek teeth, and square upper molars ( Gabunia, 1964, personal observation), features that also characterise the material described above. Nevertheless, the fossil material from the Kızılırmak Formation differs from I. parvus from Benara in the reduction of the transverse development of its upper and lower molars, its higher crowned cheek teeth, and its slightly smaller size. It is worth noting that the upper molars from TP641 and Kızılırmak Type locality referred to I. parvus tend to show higher labial walls with a concomitant reduction of the labial ribs and the transverse width ( Figure 3.4-5 View FIGURE 3 View FIGURE 4 View FIGURE 5 ). Because of the incomplete material currently available, we prefer to refer the small tragulid from the Kızılırmak Formation to Iberomeryx parvus .
If the material here referred to I. parvus is homogeneous in terms of morphology, it has nevertheless a size range that suggests either a noticeable intraspecific size variation or the presence of several taxa ( Tables 1 View TABLE 1 and 2). The largest astragalus and cubonavicular ( Figure 4.4-6 View FIGURE 4 View FIGURE 5 View FIGURE 6 ) are about twice the size of the smallest astragalus and cubonavicular in our sample ( Figure 4.1-3 View FIGURE 4 ). The estimates of body mass provided from the size of the astragalus ( Martinez and Sudre, 1995) show that such a variation would not fit the size variation of Tragulus kanchil , the smallest extant tragulid ( Table 3). Strikingly, this variation of size is not reflected in the dental material which is associated with the medium- and large-sized tarsal elements of our sample. Also, we cannot rule out that a small species of tragulid only represented by tarsal bones ( Figure 3.1-3 View FIGURE 3 ) is present in our sample. Since the material is limited, we prefer to consider provisionally that the population of Iberomeryx parworn /digested. Abbreviations: prox for proximal.
astragali length prox width distal width
GK3-18 I. sp.
641-23 I. sp.
641-24 I. sp.
641-25 I. sp.
GK3-25 I. parvus
GK3-37 I. parvus
GK3-38 I. parvus
GK3-39 I. parvus
641-21 I. parvus
641-22 I. parvus
BA-2 lophiomerycid indet.
KZ-9 Pecora indet.
16.1
15.9
16.6
15,5*
12*
13.1
TABLE 1. Measurements (in mm) of the dental material of taxa discussed in the text from the different fossil localities of the Kızılırmak. The values in brackets designate the width of the trigonid of lower molars, the non-bracketed values the maximal width. The asterisk designates estimated values when material is slightly broken or heavily worn/digested.
| Specimen | Taxon | Tooth | Length | Width |
|---|---|---|---|---|
| GK2-11 | Iberomeryx parvus | d3 | 4.8 | 1.3 |
| GK2-11 | I. parvus | d4 | 4.7 | 2.3 |
| GK3-6 | I. parvus | i2-3? | 3.2 | 2.5 |
| GK3-7 | I. parvus | i1 | 2.4 | 2.9 |
| GK3-11 | I. parvus | p3 | 3 | 1.2 |
| GK3-36 | I. parvus | p4 | 4.4 | 1.9 |
| GK3-8 | I. parvus | m1 | 5.3 | 2,8 (2,2) |
| 641-5 | I. parvus | m1 | 5.5 | 2,9 (2,6) |
| 641-4 | I. parvus | m1 | 5.4 | 3,2 (2,5) |
| GK3-3 | I. parvus | m1 | 5.6 | 3,1 (2,6) |
| GK3-42 | I. parvus | m2 | 6.1 | 3,4 (2,9) |
| 641-7 | I. parvus | m2 | 6.3 | 3,4 (2,6) |
| 641-3 | I. parvus | m2 | 6.8 | 3,7 (3) |
| GK3-34 | I. parvus | m2 | 7.2 | 4,5 (3,4) |
| GK3-33 | I. parvus | m2 | 6 | 3,5 (2,9) |
| 641-6 | I. parvus | m2 | 7.1 | 4 (3,1) |
| 641-2 | I. parvus | m3 | 7.8 | 3,4 (2,9) |
| GK3-2 | I. parvus | m3 | 7.9 | 3,1 (2,7) |
| GK2-4 | I. parvus | D2 | 5.1 | 2.1 |
| GK2-4 | I. parvus | D3 | 5.2 | 2.8 |
| GK2-4 | I. parvus | D4 | 4.5 | 4.4 |
| GK2-4 | I. parvus | M1 | 5.3 | 5.2 |
| GK3-4 | I. parvus | P2 | 6.3 | 3.7 |
| GK3-5 | I. parvus | P4 | 3.8 | 4.4 |
| KZ-7 | I. parvus | M1 | 5.4 | 5.1 |
| 641-13 | I. parvus | M1 | 5.3 | 5.5 |
| GK3-31 | I. parvus | M2 | 6.4 | 6.8 |
| 641-12 | I. parvus | M2 | 6.3 | 6.2 |
| 641-14 | I. parvus | M2? | 6.7 | 6.4 |
| GK3-35 | I. sp. | p4 | ? | 3.2 |
| 641-9 | lophiomerycid i ndet. | p1? | 7.3 | 2.9 |
| BA-3 | Dremotherium guthi | m1 | 10.1 | 7.9 |
| BA-6 | D. guthi | M2? | 10.4 | ? |
| 641-10 | cf. Palaeohypsodontus sp. | M2? | 9,5* | ? |
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