Brief Communications
Comparative analysis of a Stone Age human tooth fragment from Khaiyrgas Cave on the Middle Lena (Yakutia, Russian Federation)
2016 年 124 巻 2 号 p. 135-143
詳細
2016 年 124 巻 2 号 p. 135-143
In 1999, during the excavation of Khaiyrgas Cave on the Middle Lena River in Yakutia (in the Russian Federation), a fragmented human deciduous tooth was discovered in the upper 5th (Paleolithic) horizon, at the contact with the 4th (Mesolithic) horizon. The cave is one of a number of interesting Upper Paleolithic sites on the Lena, located at the border of two cultural regions: Lake Baikal and Yakutia. Previous findings indicate active cultural and perhaps ethnic contacts, in particular with areas of the Lower Angara region and Northern Baikal. In order to determine the morphology and taxonomic position of the tooth, its metric and non-metric parameters were studied. Comparative analysis indicates that the tooth characteristics adhere to the Eastern dental pattern with some archaic traits. This tooth is one of the earliest known human remains in Yakutia, which are crucial for the study of the ancient population of the Upper Palaeolithic and Mesolithic in North-East Asia. Its conformity with the Eastern dental pattern confirms the alleged affiliation of human groups that inhabited the territory of Yakutia in the late Pleistocene/early Holocene to the Mongoloid anthropological type. In addition, the results of comparative analysis suggest the presence of ancient affinities between the Upper Paleolithic populations of North-Eastern and Western Siberia.
The Khaiyrgas Cave site is located 7 km north-west of the village of Macha in the Olekminsky district, Sakha Republic (Yakutia), on the right bank of the Lena river, near the mouth of the river Malyi Patom (59°56′ N, 117°28′ E) (Figure 1, Figure 2). Excavations in the cave were undertaken in 1984, 1985, 1998 and 1999 (Cherosov, 1988; Stepanov et al., 2003). There are two distinct geological strata in the stratigraphy of the cave: a friable Holocene stratum, which includes horizons 1–4, and a late Pleistocene stratum, composed mainly of rubble (horizons 5–7) (Figure 3).
The map of North Eurasia showing the location of Khaiyrgas Cave and the other Upper Paleolithic, Mesolithic and Neolithic sites referred in the text.
Location map of Khaiyrgas Cave.
A profile of Khaiyrgas Cave and a photo of the cave entrance, viewed from the north-eastern side.
In 1999, the fragment of a human tooth crown was discovered in the center of the cave, in the upper 5th horizon (Figure 4). The tooth was found together with fragments of bone needles and pointed tools, plates and chips of quartz, pebble chips, and numerous shards of broken animal bones, including the teeth and bones of Pleistocene horses. In 2007, the AMS Laboratory of the University of Arizona supplied a few dates from the cave’s different cultural horizons, which limit the upper and lower boundaries of the chronological period to which the tooth can be attributed. For the 5th horizon the nearest date is 13150 ± 150 years ago (AA-79780), for the 4th horizon, 8160 ± 80 years ago (AA-79779). In calibrated form (± 2 SD), these dates are 14150–13150 BC and 7460–6840 BC, respectively.
Stratigraphy of square G-11 and the tooth’s location.
Found at the top of the 5th horizon, directly in contact with layer ‘B’ of the 4th horizon, the tooth cannot be unambiguously attributed to the Paleolithic, as the dating provided represents a fairly wide chronological range. However, this does not diminish the significance of the find or the importance of its study. In any case, the tooth crown fragment is the earliest Paleoanthropological discovery ever made on the territory of Yakutia. Determining its morphological features and taxonomic status is essential for studying the genesis of the indigenous North-East Asian population.
This paper’s main objective is to provide a full description of the metric and non-metric traits of this tooth fragment from Khaiyrgas Cave and to compare them with other samples from North Eurasian Upper Paleolithic, Mesolithic and Neolithic sites.
The age of the tooth fragment’s owner was determined according to Ubelaker’s scale (Bass, 1989). Morphological examination was performed using different dental morphology scoring systems, the main two being Zubov’s method (Zubov, 1968, 1974, 2006; Zubov and Khaldeyeva, 1993), traditional for Russian odontology, and the ASUDAS dental anthropology system (University of Arizona) (Turner et al., 1991; Scott and Turner, 1997). In addition, an odontoglyphic technique was used to take into account the variations in the patterns of tooth crown furrows (Zubov, 1974). The list of traits and grades of presence are given in Table 1, and the odontoglyphic terms are explained in the text at first occurrence. A full description of the odontoglyphic system of traits can be found in the supplementary information in the Appendix.
| Presence/absence | ||
|---|---|---|
| Russian Dental System | ASUDAS | |
| Number of cusps | 4–6 | >4, 4, <4 |
| Groove pattern | X, Y, + | X, Y, + |
| Cusp | 7 +/0 | 2–4/0–1a |
| Distal trigonid crest | +/0 | +/0 |
| Deflecting wrinkle | +/0 | 2–3/0–1 |
| Anterior fovea | +/0 | +/0 |
| 2med (II)* | +/0 | No trait |
| 2med (III)** | +/0 | No trait |
| 1med/1prd*** | 1, 2, 3 | No trait |
Some of these permanent teeth traits are of great value for differentiating between the modern variants of Mongoloid and Caucasoid dental complexes in North Eurasia. The most important of these is the distal trigonid crest, which is considered one of the most important markers of the Mongoloid complex for post-Palaeolithic permanent molars (Zubov, 2006; for major geographical distribution in the contemporary groups, see Scott and Turner, 1997). The next important trait is the odontoglyphic variant 2med (II), which is counted as present when the distal groove of the metaconid falls into the fissure which separates the metaconid and protoconid. On the lower first permanent molars this trait is used as a Western marker. The variant 2med (III), opposite to 2med (II), is counted as present when the distal groove of the metaconid falls into the fissure which separates the metaconid and entoconid. It has important value as an Eastern trait (Zubov, 2006) but no data about its distribution have been published; in all existing publications attention has focused on 2med (II). The third important trait is Cusp 6 which occurs more frequently in the Eastern groups. High frequencies of four-cusped molars, especially first molars, are more common for European populations (Zubov and Khaldeyeva, 1993). The other traits listed in Table 1 are used predominantly for diagnosis of local affinities, although types 1–3 of 1med/1prd (mesial grooves of metaconid and protoconid) superposition have more significance. In modern groups, the third type, where 1prd falls into the mesial fissure II closer to the central fovea than 1med, is common for Mongoloid groups (occurring with about 50% frequency) and very rare in the European series (Zubov, 2006).
The dental dimensions used were: mesiodistal crown size (MDcor), defined as the distance between the furthest point on the distal cusp and the opposite point on the mesial surface, parallel to the longitudinal axis of the crown; and the mesiodistal cervical diameter of the tooth (MDcol), the distance between the most protruding mesial and distal points of the cement–enamel junction.
Morphological Description of the Tooth CrownThe find from Khaiyrgas Cave is the crown of a lower left second deciduous molar, approximately three-quarters of which is preserved (Figure 5). The tooth’s deciduous status is confirmed firstly by the small height of the crown, and secondly by a sharp narrowing in the cervical area of the tooth. The lingual side is defined by the position of the highest cusps, the metaconid and entoconid, and on the distal side by the presence of a hypoconulid. The buccal part of the protoconid and hypoconid was destroyed postmortem. The roots of the tooth underwent an almost complete resorption due to age-related changes; fragments of them, no longer than 0.7 mm, remain only in the cervical region. The condition of the roots, the considerable abrasion of the crown partially leveling the cusp relief, and the presence of a large (4 mm × 3 mm) contact facet on the distal interproximal surface, formed as a result of long interaction of the second deciduous molar with the first permanent one, allows the age of the tooth’s owner to be determined as 9–10 years old. Mesial interproximal facet is also present.
Human tooth from Khaiyrgas Cave. Top left, lingual view; top middle, buccal view; top right, distal view; bottom left, basal view; bottom middle, occlusal view; bottom right, mesial view.
The shape of the tooth crown is close to oval (Figure 5). The crown consists of six cusps arranged in two rows, buccal and lingual (Table 2). In the lingual region, the metaconid and entoconid are reliably identified. Judging by the size of the distolingual part of the tooth and the position of the fissures, limiting the hypoconulid, despite the strong erosion in the vicinity of their confluence, there had also been an additional sixth cusp. The protoconid, hypoconid, and hypoconulid are present on the buccal side. The crown fissure pattern is Y; its structure lacks the central cusp, the middle trigonid crest, and the anterior fovea. The distal trigonid crest is present, formed by the middle segment of the metaconid and the distal one of the protoconid. The presence or absence of a metaconid-deflecting wrinkle is hard to judge because of abrasion, and the cingulum structure and the presence of a protostylid are uncertain due to the postmortem damage of the tooth’s buccal part. The surviving elements of the odontoglyphic pattern comprise of the cuspdividing fissures II (between metaconid and protoconid), III (between metaconid and entoconid) and IV (between hypoconid and entoconid), fragments of the fissures V and VI, limited hypoconulid, mesial grooves of metaconid (1med), protoconid (1prd), and entoconid (2end), and elements of distal groove of metaconid (2med) and additional groove, paralleled with this one (2′med). 2end falls into fissure III, 2med also falls into fissure III. 1med and 1prd simultaneously fall into fissure II, with their contact points forming a type 1 superposition. The mesiodistal diameter of the crown is as large as about 11.2 mm. This is considerably larger than the world average of 10.2 mm (Zubov and Khaldeyeva, 1993). Spots of dental calculus occur on the crown’s cervical part; other pathological changes are absent.
| Shape m2 | Protostylid | Cusp 7 | Distal trigonid crest | Deflecting wrinkle | 1med/1prd | 2med | fa | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| R | L | R | L | R | L | R | L | R | L | R | L | R | L | R | L | ||
| Listvenka | Upper Palaeolithic | Y5 | − | 0 | − | 0 | − | 0 | − | 0 | − | − | − | III | − | + | − |
| Malta 1 | Y6 | Y6 | + | + | + | + | 0 | 0 | 0 | 0 | 1 | 1 | III | III | + | + | |
| Malta 2 | Y5 | Y5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 1 | Fc | II | + | + | |
| Kostenki 15 (Gorodtsovskaya site) | Y5 | Y5? | 0 | 0 | 0 | 0 | + | + | + | 0 | 2 | 2 | III | Fc | − | + | |
| Kostenki 14 | − | 5 | − | − | − | 0 | − | − | − | 0? | − | 1 | − | fc? | − | + | |
| Khaiyrgas | − − | Y6 | − | − | − | 0 | − | + | − | − | − | 1 | − | III | − | 0 | |
| Kamenka 2, skeleton 1 | Mesolithic and Neolithic | X6 | X6 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | − | − | III | fc? | 0 | − |
| Kamenka 2, skeleton 2 | Y6 | 6+ | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | − | 2 | III | III | + | + | |
| Kamenka 2, skeleton 3 | − | Y6 | − | + | − | 0 | − | + | − | 0 | − | 1 | − | II | − | + | |
| Vilyui Highway | Y5 | − | − | − | − | − | − | − | − | − | − | − | − | − | − | − | |
| Verkholensk (Serovo stage), MAE No. 6020-35 | Y5 | Y5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | + | − | − | − | − | + | + | |
| Verkholensk (Serovo stage), MAE No. 6020-27 | Y5 | Y5 | − | − | 0 | 0 | − | + | − | 0 | − | − | − | − | 0 | 0 | |
| Verkholensk (Serovo stage), MAE No. 6020-29 | Y5 | Y | P | P | 0 | 0 | 0 | 0 | 0 | 0 | − | − | − | − | 0 | 0 | |
| Verkholensk (Glazkovo stage), MAE No. 6020-19 | Y6 | Y6 | P | P | 0 | 0 | 0 | 0 | 0 | + | − | − | − | − | 0 | 0 | |
| Kretuonas 1C, kv. H99 | Y5 | − | 0 | − | 0 | − | 0 | − | 0, 5 | − | 2 | − | III | − | 0 | − | |
The diagnostic value of traits measured in deciduous teeth, and their correlation with the parameters of the permanent teeth, are poorly studied. Accordingly, any conclusions about the taxonomic affiliation of the findings from Khaiyrgas Cave and the directions of the biological affinities of the investigated tooth’s owner are to be made only after an analysis of the geographical distribution of the tooth’s registered features over Eurasia (Table 2). The range of materials to base such analysis upon is small at the moment. For the Russian Upper Palaeolithic, it includes a few samples of deciduous teeth from such Siberian sites as Malta in the Irkutsk region, Listvenka in the Krasnoyarsk region (Shpakova and Derevyanko, 2000), Kostenki 14, Kostenki 15 (Gorodtsovskaya site) in the Voronezh region (Zubova, unpublished data), and Sungir 3 near Vladimir city in the European part of Russia (Zubov, 2000). The Mesolithic and Neolithic findings from Siberia include lower second deciduous molars from the sites of Ymyiakhtakh Neolithic culture Kamenka 2 (Shpakova, 2001a, b; Zubova, unpublished data) and Vilyui Highway (Dyakonov et al., 2003) in Yakutia, the Verkholensk Neolithic burial site at the riverhead of the Lena, and the Vengerovo 2 Neolithic burial site in the Novosibirsk region. European findings include Mesolithic findings from Zamostje 2 in the Moscow region of Russia, and Donkalnis and Kretuonas in Lithuania (Zubova, unpublished data). These findings’ main characteristics are presented in Table 2.
Table 2 shows that only the presence or absence of a sixth cusp on lower second deciduous molars itself follows a distinct geographic gradient. This feature has only been recorded on findings from the Circum-Baikal region and Yakutia (Khaiyrgas, Malta, Kamenka 2, and Glazkovo-time graves at the Verkholensk burial site). It corresponds to the gradient of the frequencies observed on the permanent teeth in modern Eurasian groups. While the sixth cusp on the permanent lower first molars is not of independent value for the dental differentiation of Mongoloid and Caucasoid groups, given that there are numerous modern Mongoloid populations with a low occurrence of the trait, e.g. Kazakhs and Uzbeks, the highest level of the trait is nevertheless observed in Mongolia, China (Tibet), Japan, and in the indigenous people of Chukotka. In the populations of the western part of Eurasia, usually only low frequencies occur (Zubov and Khaldeyeva, 1989). In the Neolithic groups from the different parts of North Eurasia the sixth cusp on the lower first permanent molars presents more frequently in the East than in the West. In the Western Siberian Neolithic its occurrence varies from 21.4% to 50% (Zubova and Chikisheva, 2015a). In the Baikal region the frequency of the trait varies from 26.7% (Waters-Rist et al., 2015, Table 1) to about 50% (Zubova, unpublished data). In the Upper Paleolithic findings from Siberia, it was present in two out of three cases (Zubova and Chikisheva, 2015b). In the East European Mesolithic–Neolithic groups, Cusp 6 on the permanent molars is rarer (0–20%) (Zubova, 2014, unpublished data). In the Upper Paleolithic samples from West and East Europe it also occurs infrequently (6.1–7.8%) (Manni et al., 2007) and it is absent in findings from the European part of Russia (Zubov, 2000; Zubova and Chikisheva, 2015b).
As for the distal trigonid crest, its status with respect to the deciduous molars appears less unambiguous. On the permanent lower first molars it presents in contemporary populations at frequencies of 0–45% on average, with the highest levels being evident in modern Mongols (42%) and Chukchi (35.3%) (Zubov and Khaldeyeva, 1993). High frequencies are also found in Koreans, Ainu, and in some groups of the indigenous peoples of North America (Zubov and Khaldeyeva, 1989). In Western groups, the distal trigonid crest is rare or completely absent. In Neolithic times, however, the distribution of this trait in Asia differed from the modern distribution. The highest frequency was found in Western Siberia, where almost half of Neolithic permanent lower first molars have the distal trigonid crest, if it can be observed (Zubova and Chikisheva, 2015a). In the Baikal region the trait’s presence is lower, and in the series of the Yakutian Neolithic Ymyiakhtakh culture it is completely absent (Zubova, unpublished data). In the Upper Paleolithic samples from Western Siberia, the distal trigonid crest is also absent (Zubova and Chikisheva, 2015b), and for northeast Asia we have no information.
On the deciduous lower second molars discussed in this article three of four cases of distal trigonid crest presence were located in the territory of Yakutia and the Circum-Baikal region (Khaiyrgas; Kamenka 2, skeleton 3; Verkholensk MAE 6020-27), but it should be noted that in the case of individual 3 from the Kamenka burial this feature is observed on the enamel–dentine surface of a non-mineralized matrix, as a part of a fully formed complex of the trigonid crests, which includes, in addition to the distal crest, the mesial marginal ridge and the middle trigonid crest (epicristid). Accordingly, it is firstly impossible to state with absolute confidence that the distal trigonid crest would be distinct in the external topography of the enamel; and secondly, this complex described by Korenhof (1982) is commonly considered not as part of the Mongoloid complex, but rather as an archaic feature, especially in the case of Paleolithic specimens (Khaldeyeva et al., 2010).
The fourth case of distal trigonid crest presence was witnessed on the lower molars of a child buried at the Gorodtsovskaya site (Kostenki 15), in the European part of Russia. This may either indicate a very ancient migration of Asian groups into Europe, or relate the distal trigonid crest of upper Palaeolithic deciduous molars to a pool of traits marking those undifferentiated complexes that pre-date the formation of the modern system of population differentiation on Eurasian territory.
The 2med (II/III) trait on the deciduous molars also does not present a group-defining value, whereas in the case of permanent first molars it has been traditionally used as an important marker differentiating populations of Western and Eastern parts of Eurasia. The 2med (II) variant is traditionally considered a Western marker with highest frequencies in modern Western Europeans (33.3–44%), Russians (24.3–65.4%), Estonians (33.3–51.6%), Lithuanians (25.6–69.1%), and lowest frequencies in the indigenous peoples of the Russian Far East (10–17.6%), Kalmyks (9.0%), Koreans (11.4%), Nganasans (8.8%), and Buryats (12.3%) (Zubov and Khaldeyeva, 1989).
We have scant information about the distribution of these two traits in ancient groups because of strong attrition of the enamel surface. The few observations are for Western Siberian Neolithic specimens (Zubova and Chikisheva, 2015a). In all of the Neolithic permanent lower first molars from Yakutia, 2med (II) was absent and 2med (III) was present. Among the Upper Paleolithic teeth from Western Siberia, 2med (II) was observed on the permanent teeth from the Malta site (Irkutsk region), and 2med (III) was present in the sample from Listvenka and Afontova Gora II (Krasnoyarsk region) (Zubova and Chikisheva, 2015b).
In the case of the compared findings of deciduous teeth, however, the 2med (II) variant was encountered in both cases on the territory of Siberia—in the Kamenka 2 burial and in one of the children buried at the Malta site. The 2med (III) variant, considered a sign of the Eastern pattern in permanent teeth in modern populations, was found on the second deciduous molars of upper Paleolithic–Neolithic eras both in Siberia and in European Russia, as well as in Lithuania.
When comparing odontometric data available for lower second deciduous molars (Table 3), it was found that the mesiodistal diameter of the examined tooth crown was noticeably larger than other findings from the territory of Yakutia. The mesiodistal size is closer to that of the West Siberian finds from Neolithic burials at Vengerovo 2 site and from the Paleolithic site of Listvenka. They are characterized by a relatively large crown size and tend to relate to the South Siberian odontological complex, which formed during an era at least as late as the upper Paleolithic and is characterized by a very conservative morphogenesis model (Zubova and Chikisheva, 2015b). This may indicate the Khaiyrgas Cave finding’s greater archaism compared with the parameters of the Neolithic population, but may also be an instance of individual variability.
| Mesiodistal crown diameter | Mesiodistal cervical diameter | ||
|---|---|---|---|
| Khaiyrgas | Upper Paleolithic | 11.2 | 7.9 |
| Listvenka* | 10.9 | — | |
| Malta 1* | 10 | — | |
| Malta 2* | 10.7 | — | |
| Sungir 3** | 9.1 | — | |
| Kostenki 15 (Gorodtsovskaya site) | 10.72 | — | |
| Kostenki 14 | 11 | 8.7 | |
| Donkalnis, grave 5 | Mesolithic and Neolithic | 10.8 | — |
| Kretuonas 1C, kv. H99 | 9.5 | — | |
| Zamostje 2, specimen 14 | 10.2 | — | |
| Vilyui Highway*** | 10.5 | — | |
| Kamenka 2, skull 1 | 10.1 | 8 | |
| Kamenka 2, skull 2 | 10.4 | 8.4 | |
| Vengerovo 2, Complex 2, grave 1, skeleton 7 | 11.5 | — | |
| Vengerovo 2, object 3 | 11.5 | — | |
| Vengerovo 2, Complex 2, grave 1, skeleton 4 | 9.8 | — |
Diagnosing the exact taxonomic position of the second lower deciduous molar from Khaiyrgas Cave is unfortunately not possible within the existing odontological taxonomy. Based on the presence of the sixth cusp and a distal trigonid crest in the complex of its morphological parameters, however, the findings can be assumed to belong to the Eastern dental pattern (without specifying more closely its particular odontological type or complex). The findings demonstrate the closest similarity to deciduous teeth from the children’s burial Kamenka 2 in the central Kolyma, which belong to the Neolithic Ymyiakhtakh culture of the middle–late second millennium BC (Kashin, 2001). This offers evidence of long-term preservation of genetic continuity among the indigenous population of Yakutia. The tooth from Khaiyrgas Cave differs from Neolithic finds from Yakutia in terms of a larger mesiodistal diameter which makes the tooth closer to the Western Siberian Upper Paleolithic and Neolithic teeth from Listvenka and Vengerovo-2 site.
The research project was supported by Russian Science Foundation, Grant No.14-50-00036 (for A.V. Zubova and A.D. Stepanov) and by D.I. Mendeleev Fund, Tomsk State University, for 2015–2016 (for Y.V. Kuzmin).
There are three types of fissures on the occlusal surface of teeth (Zubov, 1974). First-order cusp-dividing fissures are the most ancient in origin. They divide the main cusps of the crown from each other and are designated by Roman numerals I–IV on the upper molars, or I–VI on the lower ones. Second-order fissures are located on the surface of the crown’s main cusps, and are designated by Arabic numerals 1 and 2. They confine the axial ridges of each cusp, differentiating the cusp into three segments (crests). In papers by other authors, these segments are referred to as mesial, central, and distal (Carlsen, 1987; Bailey et al., 2011). Third-order fissures are divided into two categories. The first one includes additional grooves separating the main segments of each cusp into two parts longitudinally, running parallel to the fissures 1 and 2, and designated by numbers 1′ and 2′, respectively. The second category includes the additional grooves of the main cusps’ axial ridges. They are designated by numbers 3 and 4 (Zubov and Khaldeyeva, 1989; Zubov, 2006). The locations of the crown’s main cusps for lower molars are as follows (according to Zubov, 2006: fig. 26c, d).
Cusp-dividing furrows| 1med: | a groove separating the central and mesial segments of the metaconid. |
| 2med: | a groove separating the central and distal segments of the metaconid. |
| 1′med: | an additional third-order groove parallel to 1med. Falls into fissure II, and divides the mesial segment of the metaconid into two parts in the lingual direction. |
| 2′med: | an additional third-order groove parallel to 2med. Usually falls into fissure III or central fovea, and divides the distal segment of the metaconid into two parts in the lingual direction. |
| 3med: | an additional third-order groove parallel to 1med and 2med. Falls into fissure II, and divides the central segment of the metaconid into two parts in the lingual direction. |
| 4med: | an additional third-order groove, falls into 2med and divides the central segment of the metaconid into two parts in the mesiodistal or mesiodistolingual direction. |
| 1prd: | a groove separating the central and mesial segments of the protoconid. |
| 2prd: | a groove separating the central and distal segments of the protoconid. |
| 1′prd: | an additional third-order groove parallel to 1prd. Falls into fissure II, and divides the mesial segment of the protoconid into two parts in the buccal direction. |
| 2′prd: | an additional third-order groove parallel to 2prd. Usually falls into fissure I or central fovea, and divides the distal segment of the protoconid into two parts in the buccal direction. |
| 3prd: | an additional third-order groove parallel to 1prd and 2prd. Falls into fissure II, and divides the central segment of the protoconid into two parts in the buccal direction. |
| 4prd: | an additional third-order groove, falls into 2prd and divides the central segment of the protoconid into two parts in the mesiodistal or mesiodistobuccal direction. |
| 1hyd: | a groove separating the central and distal segments of the hypoconid. |
| 2hyd: | a groove separating the central and mesial segments of the hypoconid. |
| 2′hyd: | an additional third-order groove parallel to 2hyd. Falls into fissure I, and divides the mesial segment of the protoconid into two parts in the buccal direction. |
| 3hyd: | an additional third-order groove parallel to 1hyd and 2hyd. Falls into the central fovea, and divides the central segment of the hypoconid into two parts in the distobuccal direction. |
| 4hyd: | an additional third-order groove, falls into 1hyd and divides the central segment of the hypoconid into two parts in the mesiodistal direction. |
| 1hld: | a groove separating the central and mesial segments of the hypoconulid. |
| 2hld: | a groove separating the central and distal segments of the hypoconulid. |
| 1end: | a groove separating the central and distal segments of the entoconid. |
| 2end: | a groove separating the central and mesial segments of the entoconid. |
| 2′end: | an additional third-order groove parallel to 2end. Falls into fissure III, and divides the mesial segment of the entoconid into two parts in the mesiobuccal–distolingual direction. |
| 3end: | an additional third-order groove parallel to 1hyd and 2hyd. Falls into the central fovea, or fissure IV and divides the central segment of the entoconid into two parts in the lingual direction. |
| 4end: | an additional third-order groove, falls into 1end and divides the central segment of the entoconid into two parts in the mesiodistal direction. |
