戈壁锯齿象(Serridentinus gobiensis Osborn & Granger, 1932)和同心中新乳齿象(Miomastodon tongxinensis Chen, 1978)再研究：关于粗壮型轭齿象(Zygolophodon)的讨论

doi:10.19615/j.cnki.1000-3118.200310

摘要/Abstract

摘要：

中国北方中中新世的乳齿象类戈壁锯齿象(Serridentinus gobiensis Osborn & Granger, 1932)和同心中新乳齿象(Miomastodon tongxinensis Chen, 1978)后来被改为戈壁轭齿象(Zygolophodon gobiensis)。然而,由于它们的臼齿形态介于典型的丘型齿(嵌齿象类)和轭型齿(玛姆象类)之间,它们的系统演化位置一直存在争议。将戈壁锯齿象和同心中新乳齿象的颊齿和下颌与欧亚大陆及北美的类群进行了广泛比较,比较对象包括欧亚的苏黎士轭齿象(Z. turicensis)、亚似貘嵌齿象(Gomphotherium subtapiroideum)、塔氏嵌齿象(G. tassyi), 及北美的麦氏中新乳齿象(Mio. merriami)和进步嵌齿象(G. productum)。结果表明,戈壁锯齿象和同心中新乳齿象与北美的麦氏中新乳齿象具有一些共同特征,包括臼齿比苏黎士轭齿象略显丘型化(例如,釉质层较厚,主齿柱新月嵴较粗,齿谷侧视釉质柱高度达到齿谷一半,以及副齿柱横向较窄以致于整体轮廓较窄), 并且下门齿截面的背腹径大于内外径,使得下门齿截面呈竖立的椭圆形。而在苏黎士轭齿象和进步嵌齿象中,下门齿截面的背腹径小于内外径,使得下门齿截面呈平躺的椭圆形。因此,有必要恢复中新乳齿象属(Miomastodon Osborn, 1922), 它包括那些曾被归为轭齿象属,但牙齿相对丘型化的那一类(即所谓“粗壮型苏黎士轭齿象类群”), 并且下门齿截面呈竖立的椭圆形可以作为中新乳齿象属各种的共衍征。此外,亚似貘嵌齿象和塔氏嵌齿象的臼齿也呈现介于丘型齿和轭型齿的形态,但两者的下颌比中新乳齿象更伸长,下门齿截面呈梨形。中新乳齿象以及亚似貘嵌齿象和塔氏嵌齿象的存在模糊了嵌齿象科和玛姆象科的界线,表明嵌齿象科和玛姆象科的演化历史是深度相关的,并非截然分开。这一点已在胶原蛋白序列分析南方乳齿象(Notiomastodon)、玛姆象(Mammut)和现生象的工作中所揭示,需要进一步的研究。

关键词: 华北, 中中新世, 长鼻类, 嵌齿象科, 玛姆象科

Abstract:

The elephantimorph proboscideans, Serridentinus gobiensis Osborn & Granger, 1932, and Miomastodon tongxinensis Chen, 1978, from the Middle Miocene of northern China, were revised as Zygolophodon gobiensis (Osborn & Granger, 1932). However, their phylogenetic positions are still being debated because of their intermediate morphology between the typical bunodont (Gomphotheriidae) and zygodont (Mammutidae) elephantimorphs. In the present paper, we compare their dental and mandibular morphology with that of the Eurasian Z. turicensis, Gomphotherium subtapiroideum, and G. tassyi, as well as the North American Mio. merriami and G. productum. It appears that S. gobiensis and Mio. tongxinensis share with Mio. merriami the slightly more bunodont molar morphology than that of Z. turicensis, e.g., the thicker enamel, thicker pretrite crescentoids, higher interlophid enamel pillars in buccal view, and the narrower contour majorly caused by the narrower posttrite half loph(id)s. S. gobiensis and Mio. merriami also possess an “erected oval cross-sectioned mandibular tusk”, in which the cross-section is mediolaterally compressed (dorsoventral diameter being larger than the mediolateral one). Whereas, in Z. turicensis and G. productum, the mandibular tusk is “laid oval cross-sectioned”, in which the cross-section is dorsoventrally compressed (dorsoventral diameter is smaller than the mediolateral one). Therefore, it is reasonable to revive the genus Miomastodon Osborn, 1922, which contains the species that were previously attributed to Zygolophodon, but they have relatively bunodont molar morphology (i.e., the robust type of the Z. turicensis group). The mandibular tusk with erected oval cross-section seems to be a synapomorphy of Miomastodon species. Furthermore, the molar morphology of G. subtapiroideum and G. tassyi also exhibits intermediate status between the typical bunodonts and zygodonts. However, the mandibular symphysis of G. subtapiroideum and G. tassyi is stronger than that of Miomastodon, and the mandibular tusk is pyriform cross-sectioned. The validity of Miomastodon and G. subtapiroideum/tassyi obscures the boundary between the Gomphotheriidae and Mammutidae, and suggests that the evolutions of the Gomphotheriidae and Mammutidae are deeply involved in with each other, rather than straightforwardly detached. This phenomenon has been revealed by a collagen sequence analysis among Notiomastodon, Mammut, and extant elephants, which should be further studied.

Key words: North China, Middle Miocene, proboscidean, Gomphotheriidae, Mammutidae

中图分类号:

Q915.878

王世骐, 张晓晓, 李春晓. 戈壁锯齿象(Serridentinus gobiensis Osborn & Granger, 1932)和同心中新乳齿象(Miomastodon tongxinensis Chen, 1978)再研究：关于粗壮型轭齿象(Zygolophodon)的讨论. 古脊椎动物学报, 2020, 58(2): 134-158.

WANG Shi-Qi, ZHANG Xiao-Xiao, LI Chun-Xiao. Reappraisal of Serridentinus gobiensis Osborn & Granger and Miomastodon tongxinensis Chen: the validity of Miomastodon. Vertebrata Palasiatica, 2020, 58(2): 134-158.

图/表 9

Fig. 1 Terminology and measurements of mastodont molars A. right M3 of Sinomastodon praeintermedius, denoting the terminology of tooth crown; B. molar crown measurements; C. molar height measurements; D, E. the development of pretrite accessory elements in a typical zygodont molar, Zygolophodon turicensis, only pretrite crescentoids present (D), and in a typical bunodont molar, Gomphotherium connexum, only pretrite central conule present in the lophid 2 (E);F, G. the cross-sections of lower tusks, showing the “erected oval cross-sectioned mandibular tusk” in Miomastodon merriami, in which Ddv > Dml (F), and the “laid oval cross-sectioned” in Gomphotherium productum, in which Ddv < Dml (G). Note that the discrimination of the pretrite accessory elements in the panels A, D, E: green color, pretrite crescentoids; blue color, pretrite central conules. Panels F and G were modified from Frick (1933). Abbreviations: L. length; L1+2. length of the first two loph(id)s; H. height;Hpo. height of the posttrite side; Hpr. height of the pretrite side; W. width;W1, 2, …, 5. width of the 1st, 2nd, …, 5th loph(id); Wpo2. width of the second posttrite half loph(id)

Fig. 2 Type mandible of Miomastodon gobiensis, AMNH 26461, from the Zhunwuguer locality, Tunggur region, Nei Mongol, in dorsal (A), lateral (B), and rostral (C) views, and the contour of the cross-section of mandibular tusks, in rostral view (D)

Table 1 Mandibular and tusk measurements of Miomastodon gobiensis* (mm)

maximum length		1190
symphyseal length		338.41
alveolar distance (from the most salient point of the retromolar trigonum to the symphyseal border of the corpus)		424.1
ventral length measured from the gonion (angulus mandibular) to the tip of the symphysis		965
width of corpus measured at the root of the ramus		148.52
width of corpus measured at the anterioralveolus (or the grinding tooth if the alveolus is entirely resorbed)		62.01
anterior symphyseal width		113.75
maximum symphyseal width in the anterior part of the symphysis		118.09
minimum symphyseal width in the posterior part of the symphysis		69.88×2
maximum width of rostral trough in the anterior part of the symphysis		80.17
minimum width of rostral trough in the posterior part of the symphysis		82.76
rostral height measured at the symphyseal border (measurement taken perpendicular to the ventral border of the symphyseal rostrum)		146.84
rostral height measured at the tip of rostrum (measurement as above)		70.13
maximum mandibular height measured at the condyle perpendicular to the ventral border of the corpus		467.97
maximum depth of ramus		317.14
depth between gonion and coronoid processes		364.98
height between gonion and condyle		329.08
mid-alveolar length measured on the buccal side between the anterior alveolus (or grinding tooth if the alveolus is resorbed) and the root of the ramus		321.73
exposed length of mandibular tusk	left	134.25
	right	131.5
width of mandibular tusk at the alveolu	left	38.26
	right	39.74
height of mandibular tusk at the alveolus	left	45.60
	right	47.32
length of wear facet of mandibular tusk	left	35.33
	right	48.31

Table 2 Cheek tooth measurements of Miomastodon* (mm)

	Miomastodon gobiensis			Miomastodon tongxinensis
specimen	AMNH 26461		AMNH 24676	IVPP V 5584	IVPP V 5585
locus	right m2	right m3	right m3	right m3	right M3
L	136.8	203.31	158.3	152.0	137.5
W1	75.19	91.29	74.65	69.0	81
W2	78.2	ca.98	77.61	73.4	82
W3	87.52		75.51	67.6	66.5
W4			63.34	51.5	44
Hpo	51.55+	68	42.89+	48.5+	48.5+

Fig. 3 Cheek teeth of Miomastodon gobiensis and Mio. tongxinensis A-C. Mio. gobiensis, AMNH 26461, right m2 and m3 of the type specimen, from the Zhunwuguer locality, Tunggur region, Nei Mongol, China, the ramus has been removed in the 3D digital model, in occlusal (A), buccal (B), and lingual (C) views; D-F. Mio. tongxinensis, from Tongxin region, Ningxia, China: IVPP V 5584, the type right m3, in occlusal view (D), V 5585, the referred right M3, in occlusal view (E), and the occlusion of V 5584 and V 5585, in buccal view (F), indicating that they belong to the same individual+Note: green color, pretrite crescentoids; blue color, pretrite central conules

Fig. 4 Molars of the comparative species of the relevant taxa A-C. Miomastodon merriami, AMNH 14471 (type cast), the right m3, from Thousand Creek Formation, Nevada, USA, in occlusal (A), buccal (B), and lingual (C) views; D, E. Mio. metachinjiensis, AMNH 19414 (type specimen), the right m2 and m3, from Chinji Bungalow, Pakistan, in occlusal (D) and lingual (E) views; F-H. Zygolophodon turicensis, NMB OSM1288 (type cast), the left m2, from Elgg, Kanton Zürich, Switzerland, in occlusal (F), buccal (G), and lingual (H) views; I-K. Z. chinjiensis, AMNH 19447 (type specimen), the right M3, from Chinji Bungalow, Pakistan, in occlusal (I), lingual (J), and buccal (K) views; L-N. Gomphotherium productum, AMNH 14383 (type cast), the left m3, from Santa Fé, New Mexico, USA, in occlusal (L), buccal (M), and lingual (N) views; O-Q. G. subtapiroideum, SNSB-BSPG 1959 II 11381, the right m3, from Sandelzhausen, Germany, in occlusal (O), buccal (P), and lingual (Q) views; R-T. G. tassyi, HMV 1945, the right m3, from Linxia Basin, China, in occlusal (R), buccal (S), and lingual (T) views+Note: green color, pretrite crescentoids; blue color, pretrite central conules

Fig. 5 Scatter plots of bunodont and zygodont cheek teeth and mandibular tusks of the relevant taxa A. m3 length vs. width (W/L); B. normalized maximal width (W/L1+2) vs. normalized posttrite width of lophid 2 (Wpo2/W2) for lower molars; C. cross-sectional mediolateral diameter (Dml) vs. dorsoventral (Ddv) diameter of mandibular tusk; D. mandibular measurements, the relative mandibular length (Ls/Lt) vs. the relative mandibular width (Ws/Lt). The raw data see Tables S1-S3

Fig. 6 Mandibles of Gomphotherium productum and G. tassyi, in comparison with Miomastodon gobiensis A, B. AMNH 14383, the type mandible cast of G. productum, from Santa Fé, New Mexico, USA, in lateral (A) and dorsal (B) views; C, D. IVPP V 22781, unpublished mandible of G. tassyi, from the Heijiagou locality, Zhongning region, in dorsal (C) and lateral (D) views

Table 3 Comparison of mandible and dentition among selected species of Zygolophodon, Miomastodon, and Gomphotherium

Taxa	Zygolophodon turicensis	Miomastodon merriami	Miomastodon gobiensis	Gomphotherium productum complex	Gomphotherium subtapiroideum/tassyi
elongation of mandibular symphysis	moderately elongated	weakly elongated	moderately elongated	moderately elongated	moderately elongated
inclination of mandibular symphysis	slightly ventrally inclined	slightly ventrally inclined	slightly ventrally inclined	strongly ventrally inclined	strongly ventrally inclined
posterior mental foramina	?	present	absent	present	present
cross-section of mandibular tusk	laid oval	erected oval	erected oval	laid oval to circular	pyriform
protrusion of mandibular tusk	short	short	short	short	long
enamel thickness	thin	thick	thick	thick	thick
mesiodistal distance of interlophids	wide	moderate	moderate	narrow	moderate
pretrite central conules	absent	absent or small	small and singular	large and serrate	small, singular or subdivided
posttrite half lophids	strongly subdivided	moderately subdivided	moderately subdivided	weakly subdivided or undivided	weakly subdivided or undivided
posttrite main cuspid and mesoconelet	separation clear or unclear	separation unclear	separation unclear	separation clear	separation clear
alternative position and chevron	absent	absent	present	absent	absent

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