Neohelos tirarensis Stirton, 1967
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publication ID |
https://doi.org/ 10.4202/app.2012.0001 |
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persistent identifier |
https://treatment.plazi.org/id/03D987C9-652E-FFB4-FFA7-FF74B881EC18 |
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treatment provided by |
Felipe |
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scientific name |
Neohelos tirarensis Stirton, 1967 |
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Neohelos tirarensis Stirton, 1967
Fig. 5 View Fig , Table 1.
Holotype: SAMP 13848, portion of a left P3 preserving the parametacone, protocone, and hypocone.
Type locality: Leaf Locality (UCMP Locality V6213), Kutjamarpu LF, Wipajiri Formation, Lake Ngapakaldi, South Australia ( Stirton et al. 1967).
Type horizon: The Kutjamarpu LF is estimated to be Early Miocene in age ( Archer et al. 1997; Megirian et al. 2010) on the basis of close faunal comparisons with local assemblages from Riversleigh.
Referred specimens.—From Leaf Locality, Lake Ngapakaldi, South Australia: AM F87625, RP3; AM F87626, LM2; AR456, M1; AR3340, I3; AR3358, I3; AR3459, RM2; SAM/ UC465, RM1; UCMP 69977, LM1; UCMP 69978, RM2; UCMP 69979, m3. The following material is from the Riversleigh WHA, Queensland. From BC2 Site: QM F36321, LP3; QM F36322, C1; QM F36535, Lm1. From BR Site: QM F40163, LP3; QM F24137, left maxilla with M1–4. From BO Site: QM F40124 (NTM P91166−1), right maxilla, canine alveolus and P3; QM F40125 (NTM P91166−2), edentulous premaxilla; QM F40128 (NTM P91166−3), edentulous premaxilla; QM F40126 (NTM P91166−6), crushed braincase; QM F40127 (NTM P91166−7), Li1; QM F40028, Lm1. From CS Site: QM F40133, LP3; QM F40134, LM3; QM F40135, Rp3; QM F40136, RP3; QM F40137, RP3; QM F56235, Lp3; QM F40138, LM3–4; QM F40139, Lm1; QM F40140, left maxilla with M1–2; QM F40141, Rm1. From CR Site: QM F56236, left partial maxilla with P3 and anterior margin of M1. From Site D: CPC22558, RP3, M2; QM F41043, right dentary with i1, p3, m1–4; QM F41044, left dentary with i1, p3, m1–4. From DT Site: QM F56237, LP3. From Dunsinane Site: QML935, left maxilla with P3–M1–4 (still in matrix but with crowns exposed). From FT Site: QM F23157, partial right maxilla with P3, M1–4. From Inabeyance Site: QM F13088, palate with LP3–M1–3, RM2–4. From JJS Site: QM F40145, RP3; QM F40146, m3. From KCB Site: QM F56137, left partial maxilla with P3–M1; QM F56238, LP3; QM F30383, RM3; QM F30479, Lp3; QM F41200, left partial dentary with p3, m1–2. From MM Site: QM F40147, LM2; QM F40148, Lm3; QM F40149, LM3; QM F40150, LP3; QM F40151, right maxilla with P3, M1–3,M4. From NG Site: QM F40152, Lm3; QM F40153, RM3; QM F40154, Rm3; QM F12449, Rm1. From NP Site: QM F30868, Lm1. From Stick Beak Site: QM F56239, left partial M2, M3–4; QM F40130; right maxilla with P3–M1; QM F40173, right dentary fragment with p3–m1; QM F40131, LP3. From UBO Site: QM F40129 (NTM P91167−1), partial cranium with RP3, M1–4 and LM2–4. From Wang Site: QM F56240, Lm2. From WW Site: QM F40155, right partial dentary with p3, m1–4; QM F40156, RM3; QM F40157, left partial dentary with p3–m1; QM F56135, right partial maxilla with P3, M1–4 (M3 missing buccal protoloph). From WH Site: QM F56241, Rp3.
Revised diagnosis.— Neohelos tirarensis differs from Ne. solus : in having squarer, proportionately broader upper molars; in having a more consistently developed posterobuccal cingulum, mesostyle and transverse parametacone crest on P3; in having a weaker anterobuccal parametacone crest on P3; in having a more continuous lingual cingulum and better developed stylar cusps on M1; in lacking the posterolingual metaconule crest on M1; and in having a lower paracristid and higher protolophid on m1. Neohelos tirarensis differs from Ne. stirtoni : in being generally smaller; having a less bladed, more pyramidal parametacone on P3; and in having an upper canine. Neohelos tirarensis differs from Ne. davidridei : in being smaller and lower crowned; in having a smaller parastyle that is less separated from the base of the parametacone on P3; in lacking the incipiently divided parametacone on P3; in having less overhanging upper molar lophs; and in having a well−developed anterior protoconid crest on p3.
Description of referred material.— P3: Description is based on the additional material QM F56135 ( Fig. 5 View Fig ), QM F56237, QM F56236, QM F56238, and QM F36321, and is compared with both the holotype (SAMP 13848) and AMF87625, an unworn P3 enamel cap from the type locality, originally figured and referred to Ne. tirarensis by Hand et al. (1993) and later described by Murray et al. (2000b).
QM F56238, a left P3 from the KCB Site, is similar in overall size to AMF87625, though narrower anteriorly across the parastyle. The parastyle is taller however, as is the protocone and hypocone. The anterior parametacone crest is less distinct in QM F56238, yet the buccal cingulum is more greatly developed and the mesostyle is distinctly cuspate. It is very similar to the holotype in the development of the protocone and hypocone, but differs in having a more bulbous mesostyle and a less distinct transverse parametacone crest .
QM F56137, a left P3, also from KCB, is slightly larger than the holotype, but similar in the development of the protocone, hypocone and transverse parametacone crest. It differs in having a weaker mesostyle that is more of a swelling of the posterobuccal cingulum than a distinct cusp. It differs from AMF 87625 in being larger and more elongate as a result of a more greatly developed parastyle anteriorly. Its buccal margin is more linear owing to the reduced mesostyle and its retraction towards the posterobuccal cingulum. These same differences distinguish QM F56137 from QM F56238, also from KCB .
QM F56237, a left P3 from DT Site, is less elongate than AMF87625, with a better developed parastyle, protocone and hypocone. The mesostyle exists as a bulbous swelling on the buccal margin opposite the parametacone apex, similar to the condition in the holotype. Consequently, the occlusal outline of QM F56237 is more bulbous posterobuccally than AMF 87625. The anterolingual cingulum is less well developed and does not ascend the anterior base of the protocone as it does in AMF87625 .
QM F56236, a left P3 from CR Site, is unworn and dominated by a very tall central parametacone. The protocone is well developed, whereas the hypocone, although distinct, is a swelling on the posterolingual cingulum, the apex of which is continuous with a posterior crest from the protocone. Consequently, there is minimal separation between the bases of the protocone and hypocone, unlike that seen in the holotype and AMF87625. The parastyle is moderately tall and widely separated from the base of the parametacone which results in a more elongate tooth compared with AMF87625. The anterior parametacone crest is weak and fades out before reaching the valley between the parametacone and parastyle. The transverse link between the protocone and parametacone is well developed, as is the postparametacrista, which descends steeply to meet the parastyle of M1. Unlike in the holotype and
http://dx.doi.org/10.4202/app.2012.0001
AMF87625, a posterobuccal cingulum is absent, as is a mesostyle and, as a consequence, there is little emargination between the anterobuccal and posterobuccal tooth margins. QM F56236 is most similar to AR15119 (QM F40150), a left P3, from MM, referred by Murray et al. (2000b) to Ne. tirarensis .
The premolar of QM F56135 ( Fig. 5 View Fig ), a right partial maxilla from WW Site, is “typically” Ne. tirarensis −like in occlusal outline and cusp development, and is strikingly similar to the holotype. It is also very similar to AMF87625, except that the parastyle and protocone are larger and the base of the hypocone is broader .
QM F36321, an unworn enamel cap from BC2 Site is slightly larger than AMF87625 and higher crowned. The parametacone is taller with a well−developed (albeit shorter) transverse crest. The parastyle is anteroposteriorly more elongate and larger overall. The hypocone is similarly developed to that in AMF87625, and the holotype, however, its apex is continuous with the posterolingual cingulum. A moderately cuspate, bulbous mesostyle lies opposite the parametacone apex and is the terminus of a well−developed posterobuccal cingulum.
Upper molars.—Description of the upper molars is based primarily on QM F56135 ( Fig. 5 View Fig ), a right partial maxilla with P3, M1–4.
M1: The M1 is slightly larger than the paratype UCMP 69977 and most similar in morphology to the M1 of QM F40151, a right maxilla described by Murray et al. (2000b). As in QM F40151, the protoloph is shorter than the metaloph and both the parastyle and metastyle are well developed, resulting in a more trapezoidal outline to the crown. This feature is further emphasized in QM F56135 owing to a larger, more cuspate metastyle that connects the postmetacrista to the posterior cingulum. The anterior, lingual and posterior cingula are moderately developed, while a buccal cingulum is absent. In lateral view, the median transverse valley is broadly V−shaped. There is a large degree of interdental contact between M1 and P3, with the postparametacrista of P3 becoming almost continuous with the parastyle of M1. In QM F56138 which is a smaller tooth overall, the metastyle is weaker and the postmetacrista is lower than in QM F56135.
M2: The M2 of QM F56135 is similar to M1 but larger, with a wider protoloph than metaloph. The parastyle and metastyle are reduced and the postmetacrista is weak and not continuous with the posterior cingulum. It is very similar in size and morphology to AMF87626, a right M2 figured by Hand et al. (1993) and described by Murray et al. (2000b), from the Leaf Locality.
M3: The M3 of QM F56135 is missing the buccal margin of the protoloph, but, overall, appears to be narrower and more elongate than M2. The metastyle is further reduced, as is the metaloph.
M4: Similar to M3, but with the metaloph is further reduced and more crescentic. The parastyle is smaller but distinct, while the metastyle is absent.
Lower dentition.— p3: Additional p3s referred to Ne. tirarensis include: QM F56235, a left p3 (CS); QM F56241, a right p3 (WH); QM F30479, left p3 (KCB); and QM F41200 ( Fig. 5B View Fig ), a left partial dentary with p3, m1–2 (KCB). Comparisons of the lower premolar are made with QM F40135 (AR10641) from CS, which was described (but incorrectly numbered) as AR10841 by Murray et al. (2000b: 20, fig. 17), and QM F40155, a right dentary with p3, m1–4, described by Murray et al. (2000b: 22, fig. 19).
QM F56235 differs from QM F40135 and QM F 40155 in being smaller, and in having: steeper anterior and posterior protocristids; a better developed lingual cingulum and, consequently, a deeper lingual fossa. QM F30479 is also smaller than QM F56235 and QM F40135, and has a more distinct lingual cingulum and deeper lingual fossa. However, the anterior protocristid is less steep and the posterior protocristid is less convex.
QM F56241, a Rp3 from the WH LF, is moderately worn on the protoconid and missing the enamel from the posterolingual tooth corner. It is smaller overall than QM F40155 and slightly less elongate than QM F40135. In differs from QM F 40155 in having a weaker, less anteriorly extensive posterobuccal cingulum, although the latter is more strongly developed than in QM F40135. It differs further from QM F 40135 in having a less steeply sloping anterior protoconid face and weaker anterior protoconid crest.
QM F41200 ( Fig. 5 View Fig ) is the longest recorded Ne. tirarensis p3 (13.4 mm), yet is not as broad as QM F40155 owing to a linear, less bulbous posterobuccal tooth margin. The tooth is extremely worn, so that the height of the protoconid and the relative steepness of the posterior protocristid cannot be determined. The lingual cingulum is well developed and the lingual fossa is deep, but narrow.
m1: The m1 of QM F41200 ( Fig. 5 View Fig ) is less elongate than QM F40155 (16.4 mm versus 17.4 mm), but far broader both anteriorly (12.6 mm versus 10.8 mm) and posteriorly (13.3 mm versus 12.2 mm). The reduced length is the result of a blunt, poorly developed paralophid and a far rounder anterior tooth margin than is the case in QM F40155. Other differences include a wider protolophid and less difference in the width of the protolophid compared with the hypolophid. QM F40028 (a left m1 from BO Site) exhibits the more characteristic well−developed paralophid as seen in QM F40155, yet is proportionately smaller overall; however, it is comparable in size to the Site D specimens QM F41043–44 described by Murray et al. (AR1685– 86 in Murray et al. 2000b: 22, fig. 18).
m2: The m2 of QM F41200 ( Fig. 5 View Fig ) is similar to m1 but wider anteriorly and posteriorly, with broadly rounded lingual and buccal bases of the lophids. The protolophid is wider than the hypolophid and the paralophid is absent. The interlophid valley is broadly V−shaped in occlusal view. It is similar to the m2 of QM F40155, yet with a broader protolophid and more linear, parallel arrangement of the lophids.
m3: QM F30383 is an isolated, unworn right m3 from KCB. It is deemed an M 3 owing to its size, but it is possible that it is a large m2. The tooth is high crowned with a protolophid that is taller than the hypolophid. In lateral view, the crests of the lophids curve posteriorly. There are a weak buccal and lingual cingula positioned low on the crown. The apex of the protoconid is bulbous and a weak, short preprotocristid is present. The anterior cingulum is linear and short. The posterior cingulum is crescentic and elevated on the buccal side of its midline.
Dentary: QM F41200 ( Fig. 5 View Fig ), a partial left dentary from KCB, retains only a short section of the horizontal ramus including the posterior border of the symphysis and the mental foramen. The dentary is deep 63.4 mm (measured below the anterior root of m1) and robust compared with QM F40155 (45 mm deep). The symphysis is unfused, broad (27.6 mm compared with 21.6 mm in QM F40155) and ovate along its posterior border, which extends to a point level with the anterior root of m1. The mental foramen (4 mm diameter) lies 1 mm anterior to the root of p3, and approximately 11 mm ventral to the diastemal crest (however, this area is poorly preserved). The sublingual fossa is shallow and narrow. A shallow, irregular genial pit lies at the posteroventral surface of the symphysis.
Remarks.—Extended descriptions and figures of the following referred material can be found in Murray et al. (2000b: 11−31): AR16492 (QM F40151), QM F13088, CPC22558, AR9947 (QM F40133), AR10726 (QM F40137), AR10362 (QM F40134), AR12120 (QM F40138), AR17291 (QM F40153), NTM P91167−1 (QM F40129), QM F24137, AR10641 (QM F40135), AR16787 (QM F40157), AR10458 (QM F40155), AR1685−6 (QM F41043−44), QM F12449, AR14393 (QM F40146), AR13795 (QM F40130), NTM P91166−2 (QM F40125), NTM P91166−1 (QM F40124), NTM P91166−7 (QM F40127), NTM P91166−6 (QM F40126).
A reanalysis by Black (2010) of the specimens NTM P−91171−2 (left P3 fragment and LM2) and NTM P91171−4 (Rm4), both from 300BR Site, and referred to Ne. tirarensis by Murray et al. (2000a), suggests they should be referred to Ngapakaldia bonythoni . The P3 fragment, regarded by Murray et al. (2000b) to be a LP3 parastyle of Ne. tirarensis is in fact a LP3 protocone of Ng. bonythoni . Further, the M2 and m4 are indistinguishable from Ng. bonythoni material from Riversleigh. Specimens NTM P91171−5 (LI1), NTM P91171−6 (RI3) and NTM P942−1 (M4), also from 300BR Site, have not been examined, and hence are not included in this study.
Geographic and stratigraphic range.— Early Miocene Kutjamarpu LF of the Wipajiri Formation, Lake Ngapakaldi , South Australia ; Late Oligocene Kangaroo Well LF of the Ulta Limestone, Northern Territory ; and numerous Late Oligocene to Middle Miocene deposits ( FZ A–C) of the Riversleigh World Heritage Area , northwestern Queensland, Australia .
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