New Fossil Suid Specimens from the Terminal Miocene Hominoid Locality of Shuitangba, Zhaotong, Yunnan Province, China

Home , Hippopotamodon, Microstonyx, Propotamochoerus, Suinae

Journal of Mammalian Evolution (2019) 26:557–571 https://doi.org/10.1007/s10914-018-9431-3

ORIGINAL PAPER

Sukuan Hou1,2,3 & Denise F. Su2 & Jay Kelley4 & Tao Deng1,3 & Nina G. Jablonski5 & Lawrence J. Flynn6 & Xueping Ji7,8 & Jiayong Cao9 & Xin Yang 10

Published online: 14 March 2018 # Springer Science+Business Media, LLC, part of Springer Nature 2018, corrected publication April/2018

Abstract Fossil suid specimens recovered from the latest Miocene site of Shuitangba, Zhaotong Basin, Yunnan Province, provide new information on the classification and relationship of Chinese Miocene Suinae. Most of the recovered specimens are referred to a relatively advanced and large species of Suinae, Propotamochoerus hyotherioides, based on dental dimensions and morphology. Detailed morphological comparisons were made between the Shuitangba Pr. hyotherioides and other Asian Miocene suines. From these comparisons, we suggest that Pr. hyotherioides from Shuitangba and northern China may be relatively derived compared to the specimens from Lufeng and Yuanmou, southern China and that Pr. hyotherioides and Pr. wui represent separate branches of the genus in China. Furthermore, Microstonyx differs from Pr. hyotherioides in p4/P4 and m3/M3 characters. Molarochoerus is suggested to represent a relatively derived taxon due to the uniquely molarized upper and lower fourth premolars. Miochoerus youngi is suggested to have a closer relationship to Sus and Microstonyx than to Propotamochoerus due to its small size and p4 morphology. Hippopotamodon ultimus, Potamochoerus chinhsienense, Dicoryphochoerus medius, and D. binxianensis exhibit complex morphologies that variously resemble Propotamochoerus, Microstonyx,andSus and are suggested to be possible transitional forms between Propotamochoerus, Microstonyx,andSus. However, the resolution of their classification requires further analysis when more material is recovered.

Keywords Propotamochoerus . Suinae . Classification . Terminal Miocene . Shuitangba

Abbreviations DTa Width of the First Lobe of a Cheek Tooth DAP Length of Premolar and Molar DTp Width of the Second Lobe of a Cheek Tooth DLL Labio-Lingual Diameter DTpp Width of the Third Lobe of the Third Molar and the DMD Mesio-Distal Diameter Deciduous Fourth Lower Premolar DT Maximum Width of a Cheek Tooth HHeight

* Sukuan Hou 5 Department of Anthropology, The Pennsylvania State University, [email protected] University Park, PA 16802, USA

6 Peabody Museum of Archaeology and Ethnology, Harvard 1 Key Laboratory of Vertebrate Evolution and Human Origins of University, Cambridge, MA 02138, USA Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 7 Yunnan Institute of Cultural Relics and Archaeology, Beijing 100044, China Kunming, Yunnan 650118, China 2 Department of Paleobotany and Paleoecology, Cleveland Museum of 8 Natural History, Cleveland, OH 44106, USA Key Laboratory for Paleobiology, Yunnan University, Kunming, Yunnan 650091, China 3 Department of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China 9 Zhaotong Institute of Cultural Relics, Zhaotong, Yunnan 657000, 4 Institute of Human Origins and School of Human Evolution and China Social Change, Arizona State University, Tempe, AZ 85287-4101, USA 10 Zhaoyang Museum, Zhaotong, Yunnan 657000, China 558 J Mammal Evol (2019) 26:557–571

Introduction relationship of these enigmatic Miocene taxa from China. Here, we describe those fossil Suinae specimens Fossil Suidae are common in the late Miocene faunas of recovered from Shuitangba between 2007 and 2015 China. However, their classification and relationships are (Figs. 2, 3, 4, 5, 6, 7, 8,and9,Tables1, 2,and 3)and highly controversial. Among the late Miocene fossil suids, compare them with those from other Miocene sites in the medium- to large-sized Suinae, which have a China. Almost all the new fossils resemble Dicoryphochoerus-type p4, where the protoconid and the Propotamochoerus hyotherioides from Lufeng, Yunnan metaconid are separated, the metaconid is posterolingual to Province (van der Made and Han 1994), and northern the protoconid, and the talonid is lower than the main cen- China (Pearson 1928), except for one isolated M3 (ZT- tral cusps (Schlosser 1903;Pearson1928;Li1963;Chang 2009-03-511; Fig. 5i) and three incisors (LI1 [ZT-2007-02- 1974;Liuetal.1978;Tangetal.1985;Dong1987;Han 024; Fig. 2d], LDI1 [ZT-2015-2418; Fig. 2e], and RI3 [ZT- 1987; van der Made and Han 1994;Chen1997;Pickford 2015-1820; Fig. 2f]). The M3 (DAP = 22.3, DT = 16.8; see and Liu 2001; Zhang et al. 2002;LiuandPan2003;Liuand below Abstract for Abbreviations) has a very weak talon, Ji 2004;Liuetal.2004; Pan et al. 2006;DongandZhang which makes it resemble an M2. However, its hypoconule 2014), may be the most complicated and controversial is proportionally large compared to that of M2 and compa- group in terms of their classification. Schmidt-Kittler rable to the hypoconule of M3; the talon, though very weak, (1971) established Dicoryphochoerini in addition to the is still proportionally larger than those found in M2s, and is tribes Potamochoerini, Hippohyini, and Suini of Thenius more posteriorly extended than those in M2s. Thus, it may (1970),basedonp4charactersofKorynochoerus, represent a small- to medium-sized suid and bears an inflated Microstonyx, and Dicoryphochoerus. Pickford (1993) later main cusp and a very weak talon. The three incisors (ZT- erected Propotamochoerini for Propotamochoerus, 2007-02-024, I1, DMD > 10, DLL = 6.4; ZT-2015-2418, Hippopotamodon,andMicrostonyx, which is a synonym of DI1, DMD = 7, DLL = 5.1; ZT-2015-1820, I3, DMD = 8.2, Dicorypochoerini. DLL = 5.6) have mesio-distal lengths within the range of Recently, abundant large-sized Suinae specimens were Pr. wui (I1, DMD = 10.2–12.8, DLL = 5.5–6.3; DI1, discovered from Shuitangba, a terminal Miocene site (6.5– DMD = 6.5, DLL = 3.6; I3, DMD = 12.2, DLL = 4.2), but 6.0 Ma) located in northeastern Yunnan Province (Ji et al. are less labio-lingually compressed, and the I1 crown is low- 2013; Jablonski et al. 2014;Fig.1). Most of these new er than those of Pr. wui. As these specimens are only isolated Suinae remains show great similarity to many of the teeth and appear to be different from the other specimens Chinese late Miocene large-sized Suinae and provide an recovered from Shuitangba, they are referred to Suinae opportunity to better understand the classification and indet. and are not considered further in this paper.

Fig. 1 Site location map J Mammal Evol (2019) 26:557–571 559

Materials and Methods Tooth measurements follow van der Made (1996); tooth width was measured at the base of the crown at its widest part. The Pr. hyotherioides specimens described in this paper were recovered from Shuitangba between 2007 and 2015 (Figs. 2, 3, 4, 5, 6, 7, 8,and9,Tables1, 2,and3), including six Data Availability Statement maxillary fragments, three mandiblular fragments, and several isolated teeth, which are all housed in the Zhaoyang Museum All data generated or analyzed during this study are included in Zhaotong city, Yunnan Province. in this published article. The Shuitangba Pr. hyotherioides specimens were compared with those of medium-large sized fossil Suinae from both northern and southern China and with those of Systematic Paleontology Hippopotamodon cf. H. hyotheroides from Thailand (Pickford et al. 2004b) to better understand the relation- Order Artiodactyla Owen, 1848 ships among these medium- to large sized suids bearing a Superfamily Suoidea Cope, 1887 Dicoryphochoerus-type p4 morphology. Family Suidae Gray, 1821 Tooth orientation and dental nomenclature of common fea- Subfamily Suinae Gray, 1821 tures on all tooth crowns (main cusps and accessory cusps) Genus Propotamochoerus Pilgrim, 1926 mostly follow Pickford (1986, 1988). The work of Boisserie et al. (2010) was also used for crest nomenclature on premolars. Propotamochoerus hyotherioides (Schlosser, 1903)

Fig. 2 Incisors of Propotamochoerus hyotherioides (a-c, g) and Suinae indet. (d-f) from Shuitangba. a Left i1 (ZT- 2015-0240), (1) labial, (2) lingual, (3) mesial, (4) distal, (5) occlusal; b Right i1 (ZT-2007-01-149), (1) labial, (2) lingual, (3) mesial, (4) distal, (5) occlusal; c Left i1 (ZT- 2015-0366), (1) labial, (2) lingual, (3) mesial, (4) distal, (5) occlusal; d Left I1 (ZT-2007-02-024), (1) labial, (2) lingual, (3) mesial; e Left DI1 (ZT-2015-2418), (1) labial, (2) lingual, (3) mesial; f Right I3 (ZT-2015-1820), (1) labial, (2) lingual, (3) occlusal; g Right I2 (ZT-2015-1166), (1) labial, (2) lingual. Scale bar equals 5 cm 560 J Mammal Evol (2019) 26:557–571

Fig. 3 Upper cheek teeth of Propotamochoerus hyotherioides from Shuitangba (ZT-2015- 1062). a Left DP3-M2*, (1) occlusal, (2) lingual, (3) buccal; b Right DP3, (1) occlusal, (2) buccal, (3) lingual; c Right DP4, (1) occlusal, (2) buccal, (3) lingual; d Right P1, (1) occlusal, (2) buccal, (3) lingual; e Right P3, (1) occlusal, (2) buccal, (3) lingual; f Right P4, (1) occlusal, (2) buccal, (3) lingual; g Right M1, (1) occlusal, (2) buccal, (3) lingual; h Right M2, (1) occlusal, (2) buccal, (3) lingual. Scale bar equals 5 cm. * Note that in 3a, the DP3 is improperly positioned against the broken surface of the DP4. There should be a gap between the distal margin of the DP3 and the broken surface of the DP4 that would have accommodated the missing anterior half of the broken DP4

Description root is compressed mesio-distally and slightly curved. There is a shallow median groove on both the mesial and the distal Permanent Incisors sides of the root.

Only one isolated upper second incisor (Fig. 2g, Table 1)is Permanent Premolars and Molars preserved. It is compressed labio-lingually and elongated mesio-distally. There may be a tiny facet on top of the mesial There is one isolated upper first premolar (Fig. 3d, Table 2), side of the crown, but it is not clearly visible. The incisal edge which is small and narrow. The paracone is conical. The pre- is divided into several distinct and unequally sized lobes, and postparacristae are similar in length and form a straight which are delimited lingually by shallow grooves. A small line. There are two similar accessory cusps on the cusplet is present at the mesio-lingual corner of the crown. postparacrista, which are visible in occlusal view on the wear The cingulum is absent. facet. The talon is small and low, but forms a separated The lower central incisor (Fig. 2a-c, Table 1)hasahigh cusplet, so the posterior part of the P1 is wider than the ante- crown, with a strong median ridge on the lingual side that rior part. The anterior cingulum is developed and extends to extends nearly to the incisal edge. The slightly worn i1 (Fig. the anterolingual corner of the paracone. The tooth is two- 2b) shows that the incisal edge is divided into two lobes by a rooted, with the posterior root being wider than the anterior shallow groove on the lingual side. There is no cingulum. The and appearing to consist of two fully fused roots. J Mammal Evol (2019) 26:557–571 561

the postparacrista. The preparacrista connects with the anterior cingulum. There are usually one or two small accessory cusplets on the postparacrista, and the postparacrista is connected with the posterior cingulum. The anterior cingulum is strong and usually bears a separate cusplet in the middle. The posterior cingulum is weakly developed or absent. The talon is very small and low, but usually bears a distinct cusplet at the posterolingual corner of the tooth. A lingual cingulum is present in specimen ZT-2015-1728 (Fig. 4a) and ZT-2007-01-265 (Fig. 5h). Specimen ZT-2015-1062 preserves an unerupted P3 (Fig. 3e). The paracone is less inflated and weakly separated from the metacone at the tip; the pre- and the postmetacristae are weakly serrated; the anterior, lingual, and posterior cingula are strong and continuous; the main cusplet of the talon occupies the posterolingual quadrant of the crown and is relatively large but thin. The upper fourth premolar (Figs. 3f, 4a-b, 5b, 6, Table 2)is wider than the P3 but shorter. It is nearly rectangular in occlusal view, with the width slightly greater than the length. The paracone and metacone are well separated and similar in size. The protocone is similar in size to the paracone and metacone, or slightly larger. It is situated at the antero-posterior midline or slightly anteriorly. The three cusps are all notably inflated, with thick furrows on their internal surfaces. Both the anterior and the posterior cingula are prominent, continuous, and serrated. Most P4s bear anterior and posterior accessory cusps within the occlusal basin, with the exception of ZT-2009-03- 547 (Fig. 6). Fig. 4 Upper cheek teeth of Propotamochoerus hyotherioides from Shuitangba. a Left P3-M2 (ZT-2015-1728), (1) occlusal, (2) lingual, (3) The upper first molar (Figs. 3a, g, 4a-b, 5a-b, d, 6, Table 2) buccal; b Right P2-M1 (ZT-2015-2017), (1) buccal, (2) occlusal, (3) is longer than it is wide. The protocone and hypocone are lingual. Scale bar equals 5 cm similar in size and slightly larger than the paracone, while the metacone is the smallest. The intercuspal fissures are strongly developed, with the presence of furrows or crenula- The upper second premolar (Figs. 4b, 5g, Table 2)isa tions on cusp surfaces that increase the complexity of the relatively small tooth compared with the P3. The paracone is occlusal surface. The anterior cingulum is prominent and ser- not as inflated as in the P3, but neither is it sharp. The rated. A small anterior accessory cusp is sometimes present paracone is located somewhat anterior to the middle of the and contacts both the paracone and the protocone at the base. crown, so the preparacrista is shorter than the postparacrista. The median accessory cusp is larger than the anterior acces- There are two small accessory cusplets on the postparacrista, sory cusp, contacting both the metacone and hypocone. The which are similar in size. The preparacrista connects with the posterior cingulum is more restricted than the anterior cingu- anterior cingulum at the base. The anterior cingulum is prom- lum. The lingual and labial cingula are usually absent or only inent and on ZT-2015-2017 (Fig. 4b)formsadistinctcusplet slightly developed at the lingual and labial notches. that is separated from the preparacrista by a deep groove. The The upper second molar (Figs. 3a, h, 4a, 5a-b, 6, Table 2s)i talon is small and low and occupies the posterolingual quad- similar morphologically to the M1, but much larger in size. rant of the crown. The P2 is two-rooted. Specimen ZT-2015- And the M2s have relatively larger hypocones than the M1s. 2017 (Fig. 4b) preserves the alveolus of the P1, revealing the The upper third molar is preserved in a maxillary specimen absence of a P1-P2 diastema. (ZT-2009-03-547, Fig. 6, Table 2) and as an isolated tooth The upper third premolar (Figs. 3e, 4a-b, 5b, h, Table 2)isa (ZT-2014-0009, Fig. 5c, Table 2). The paracone and metacone large tooth, notably wider and longer than P2. Outlines of the are high and sharp, while the protocone is rounded due to P3 are variously quadrilateral to trapezoidal to ellipsoidal in wear. The hypocone is similar to the metacone in height, but occlusal view. The paracone is strongly inflated, with steep more rounded due to wear. Deep furrows are present on all the pre- and postparacristae of similar length, or with the main cusps. The anterior cingulum is strong and serrated, with preparacrista slightly shorter and more steeply angled than a small anterior accessory cusp developed in the midline and 562 J Mammal Evol (2019) 26:557–571

Fig. 5 Upper cheek teeth of Propotamochoerus hyotherioides (a-h) and Suinae indet. (i) from Shuitangba. a Right M1-M2 (ZT- 2015-0758), (1) occlusal, (2) buccal, (3) lingual; b Left P3-M2 (ZT-2015-2226), (1) occlusal, (2) lingual, (3) buccal; c Left M3 (ZT- 2014-0009), (1) occlusal, (2) lingual, (3) buccal; d Right M1 (ZT-2015-1503), (1) occlusal, (2) buccal, (3) lingual; e Right DP3 (ZT-2015-0538), (1) occlusal, (2) buccal, (3) lingual; f Left DP3 (ZT-2015-1022), (1) occlusal, (2) buccal, (3) lingual; g Right P2 (ZT-2015-1070), (1) occlusal, (2) buccal, (3) lingual; h Left P3 (ZT- 2007-01-265), (1) occlusal, (2) buccal, (3) lingual; i Left M3 (ZT- 2009-03-511), (1) occlusal, (2) buccal, (3) lingual. Scale bar equals 5 cm

separated from both the protocone and the paracone. The me- The lower fourth premolar (Figs. 8, 9, Table 3) is larger dian accessory cusp is a distinct cusplet situated in the middle than the p3. The protoconid and metaconid are well separated. of the main cusps. The talon of the M3 is well developed and The metaconid is similar to the protoconid in size and is situ- bears numerous accessory cusplets of varying size, the largest ated posterolingual to the protoconid. The cusplet of the being positioned just posterior to the hypocone. Remnants of talonid is well developed but lower than the metaconid, and lingual and labial cingula are only developed at the bases of fused with the posterior cingulid at its base. The anterior and the labial and lingual notches as small cusplets. the posterior cingulids are well developed. The two-rooted lower second premolar (Fig. 7d, Table 3)is The m1 and m2 (Figs. 7a-b, 8, 9, Table 3) are rectangular, small and labio-lingually compressed. The enamel of the with the m2 being larger than the m1. The metaconid is the crown is very thin. The main cusp is clefted at the summit. largest cusp while the protoconid, hypoconid, and entoconid The posterior width of the tooth is almost the same as the are similar in size. The furrows of the cusps are well devel- width at the main cusp. There is no cingulid. oped. The anterior cingulid is moderately developed but the The lower third premolar (Figs. 7c, 8, Table 3)istwo-root- anterior accessory cusp is either weakly expressed or absent. ed. A metaconid is only weakly separated from the protoconid The median accessory cusp is well developed and rounded, at the tip. The protoconid is slightly larger than the metaconid. and contacts the hypoconid at its base. In some specimens The preprotocristid is connected with a prominent anterior there is a secondary, more mesially positioned, median acces- cingulid, while the postmetacristid is variably serrated and sory cusp that is separated from the first by the central lingual- connects with the posterior cingulid. labial fissure and contacts the metaconid. The posterior J Mammal Evol (2019) 26:557–571 563

developed furrows. The anterior cingulum is strong. The posterior cingulum is weak. The lingual and the labial cingula are only weakly seen at the lingual and labial notches. The median accessory cusp is weak. The posterior accessory cusp is very weak to absent. There is a very faint cusplet at the posterior cingulum. The dp4 (Figs. 7a, e-h, Table 3) is three-lobed. The anterior lobe is the narrowest and the third lobe is the widest. The anterior two cusps are small and similar in size; the lingual cusp is relatively labio-lingually compressed and slightly anteriorly located. The main cusps of the second lobe are also similar in size. The labial cusp of the third lobe is slightly anteriorly located and connected to an accessory cusp. All of the main cusps have well-developed furrows. The cingulid is only weakly developed posteriorly.

Comparative Discussion

Dicoryphochoerini is a tribe consisting of medium- to large- sized Suinae that bear p4s in which the metaconid falls posterolingual to the protoconid and the talonid is lower than the main central cusps (=Dicoryphochoerus-type p4). With its Fig. 6 Upper cheek teeth of Propotamochoerus hyotherioides from p4 morphology, the Shuitangba suine assemblage undoubted- Shuitangba (ZT-2009-03-547), Left P4-M3. a occlusal; b lingual; c buccal. Scale bar equals 5 cm ly belongs to Dicoryphochoerini. Dicoryphochoerini fossils are abundant in China. Currently, reported cingulid is well developed. The hypoconulid is well devel- Dicoryphochoerini from China include Propotamochoerus oped, but low, and not separated from the posterior cingulid. (includes Hippopotamodon hyotherioides)fromsouthern The labial cingulid is confined to the base of the buccal notch. and northern China (Schlosser 1903; Pearson 1928; Dong There is no lingual cingulid. 1987; van der Made and Han 1994;PickfordandLiu2001; The positioning and relative sizes of the cusps of the m3 Liu and Ji 2004; Pan et al. 2006), Microstonyx from northern (Figs. 8, 9,Table3) are similar to those of the m2. The median China (Pearson 1928; Zhang et al. 2002; Liu et al. 2004), accessory cusp is relatively larger than that in the m2, as is the Potamochoerus from northern China (Li 1963; Chang secondary median cusp. The hypoconulid is large and sepa- 1974), Dicoryphochoerus from northern China (Liu et al. rated from the distal cusps. The talonid is a well-developed, 1978;Tangetal.1985;Dong1987), Miochoerus from north- distally projecting heel and consists of several cusplets of ern China (Chen 1997), Molarochoerus from southern China varying size in addition to the large distal accessory cusp. (Liu and Pan 2003), and Hippopotamodon ultimus from The anterior and posterior cingulids are prominent. As in the southern China (Han 1987; Dong and Zhang 2014). A com- m1 and m2, the labial cingulid is expressed only at the base of parison of dental size among these taxa (Tables 4, 5)shows the labial notch, while the lingual cingulid is absent. that the Shuitangba materials are comparable to many of the other large forms, only larger than Pr. wui from Lufeng and Molarochoerus from Yuanmou, and most similar to Pr. Deciduous Dentition hyotherioides from Lufeng (van der Made and Han 1994) and northern China (Pearson 1928). The dental characters of The DP3 (Figs. 3a-b, 5e-f, Table 2) is triangular in occlusal the Shuitangba specimens also most resemble Pr. view. It has three cusps - one anterior and two posterior. The hyotherioides, for instance, p4s have a separated metaconid, anterior cusp and the posterolingual cusp are similar in size, which is situated posterolingual to the protoconid; M3s and the posterolabial cusp is relatively small. The enamel is have a simple and lingually located hypoconule; and I2 thin and the furrows are notably developed. The anterior and crowns are mesio-distally elongated and labio-lingually posterior cingula are well developed, and the lingual cingulum compressed. Therefore, they were attributed to the species is partly developed or absent. Pr. hyotherioides. The DP4 (Figs. 3a, c,Table2) has four main cusps. It is The dental morphology of Pr. hyotherioides shows broad notably smaller than the M1. The labial main cusps are smaller similarity to the large-sized Dicoryphochoerus and than the lingual main cusps. The enamel is thin, with well- Microstonyx found from the late Miocene of China, as well 564 J Mammal Evol (2019) 26:557–571

Fig. 7 Lower cheek teeth of Propotamochoerus hyotherioides from Shuitangba. a Left dp4-m1 (ZT-2015-1591), (1) occlusal, (2) buccal, (3) lingual; b Left m2 (ZT- 2007-01-246), (1) occlusal, (2) buccal, (3) lingual; c Right p3 (ZT-2007-01-170), (1) occlusal, (2) buccal, (3) lingual; d Left p2 (ZT-2015-2130), (1) occlusal, (2) lingual, (3) buccal; e Right dp4 (ZT-2009-03-071), (1) occlusal, (2) buccal, (3) lingual; f Right dp4 (ZT-2009-03-057), (1) occlusal, (2) buccal, (3) lingual; g Right dp4 (ZT-2015-0989), (1) occlusal, (2) buccal, (3) lingual; h Right dp4 (ZT-2009-03-109), (1) occlusal, (2) buccal, (3) lingual. Scale bar equals 5 cm

as H. ultimus from the early Pleistocene of southern China Potamochoerus. Pickford (1988) reviewed Pilgrim’s four (Han 1987; Dong and Zhang 2014) and specimens of these species of Propotamochoerus, and validated Pr. hysudricus genera were often confused with one another. Pickford (1993) as the only species within the genus, while specimens of Pr. has argued that evolution in the skull and dentition in suids is salinus, Pr. uliginosus,andPr. ingens were reassigned to often dissociated, making taxonomic identification of isolated Conohyus or Hyotherium. Pickford (1988) also questioned suid teeth difficult. As a consequence, the classification of the validity of Dicoryphochoerus, and reassigned most of fossil suids has long been mired in controversy, particularly Pilgrim’sninespeciesofDicoryphochoerus into Conohyus or when complete skulls were not available. For example, Propotamochoerus, while specimens of the giant Lydekker (1877)establishedHippopotamodon sivalense for Dicoryphochoerus robustus and Dicoryphochoerus titanoides a large Siwalik suid, but later, moved the fossils to a newly were moved to Hippopotamodon.Finally,H. sivalense established species, Sus titan (Lydekker 1884). The specimens erected by Ledykker (Lydekker 1877), was regarded as the were again transferred to a new genus, Dicoryphochoerus by only species of this genus. Pickford’s classification has been Pilgrim (1926), who also erected another eight species for followed by some authors (Liu 2003; Liu and Pan 2003;Pan this genus. The original name, H. sivalense, was ignored. et al. 2006; Dong and Zhang 2014). However, van der Made The genus Propotamochoerus was also differentiated from and Hussain (1989) reassigned the smaller H. titanoides ma- Potamochoerus by Pilgrim (1926), who thought the former terial to Microstonyx based on its similar size to Microstonyx had a relatively primitive skull and a verrucose or sub- major, which was accepted by Fortelius et al. (1996). Though verrucose lower canine. As many of Pilgrim’s taxa were Pickford and Liu (2001) later rejected the presence of established based on only a few, subtle characters, Microstonyx in India and China, the skulls of Mic. major from Pilgrim’s classification was contested and modified by Linxia Basin (Liu et al. 2004) demonstrated the presence of many later authors. Matthew (1929), Colbert (1935), Viret Microstonyx in China, but specimens of H. titanoides were (1961), and Li (1963) argued that there were not enough retained in Hippopotamodon due to their extremely stout differences to separate Propotamochoerus from premolars. J Mammal Evol (2019) 26:557–571 565

Fig. 8 Lower cheek teeth of Propotamochoerus hyotherioides from Shuitangba (ZT-2015-2649), Left p3-m3, a occlusal; b buccal; c lingual. Scale bar equals 5 cm

Propotamochoerus hyotherioides was first described by Fig. 9 Lower cheek teeth of Propotamochoerus hyotherioides from Schlosser (1903) under the name Sus hyotherioides; the genus Shuitangba (ZT-2015-0798), Right p4-m3, a occlusal, b lingual, c Propotamochoerus was later established by Pilgrim (1926) buccal. Scale bar equals 5 cm based on fossil suids from the Siwaliks of Pakistan. Pilgrim (1926) named four species of Propotamochoerus,but protoconid and metaconid, with the metaconid situated Pickford (1988) recognized only the type species, Pr. posterolingual to the protoconid; the M3s have a simple hysudricus. He reassigned specimens of Pr. salinus, Pr. hypoconule, which is smooth and lingually located; the I2 uliginosus,andPr. ingens to Conohyus or Hyotherium. crown is mesio-distally elongated and labio-lingually com- Propotamochoerus hysudricus, a medium-sized species, was pressed. There are also differences: the Shuitangba P3 has widely accepted by later authors (van der Made and Han weakly separated paracone and metacone, some of its P4s 1994; Liu and Pan 2003; Pan et al. 2006; Dong and Zhang have an incipient hypocone, and there are more and larger- 2014). The large-sized Pr. hyotherioides material from China, sized pillars around the main cusp of its M3 hypoconule than however, has rarely been compared with the type species and observed in the specimens from Lufeng and Yuanmou. These their classification is, as a consequence, controversial characters suggest that the Shuitangba specimens may be (Schlosser 1903; Pearson 1928;Li1963; Dong 1987; van der Made and Han 1994; Pickford and Liu 2001; Zhang Table 1 Measurements of the suid incisors from Shuitangba (in mm) et al. 2002; Liu and Pan 2003; Liu et al. 2004; Pan et al. 2006;DongandZhang2014). DMD DLL H Propotamochoerus hyotherioides has been found in both ZT-2015-2418 LDI1 7.0 5.1 16.0 northern and southern China. Propotamochoerus ZT-2007-02-024 LI1 >10 6.4 12.4 hyotherioides from southern China include Pr. hyotherioides ZT-2015-1166 RI2 16.6 11.5 from Lufeng (van der Made and Han 1994)and ZT-2015-1820 RI3 8.2 5.6 5.9 Hippopotamodon hyotherioides (Pan et al. 2006) from ZT-2015-0240 li1 7.0 12.5 28.5 Yuanmou. Both assemblages share similar tooth dimensions ZT-2015-0366 li1 8.0 12.5 37.2 to the Shuitangba material and are also morphologically similar. The Shuitangba specimens resemble those of Lufeng and ZT-2007-01-149 ri1 8.3 12.6 >31 Yuanmou in the following aspects: the p4s have separated DLL, labio-lingual diameter; DMD, mesio-distal diameter; H,height 566 J Mammal Evol (2019) 26:557–571

Table 2 Measurements of the upper cheek teeth of the fossil suids from Table 3 Measurements of the lower cheek teeth of Propotamochoerus Shuitangba (in mm) hyotherioides from Shuitangba (in mm)

DAP DTa DTp DTpp H DAP DTa DTp DTpp H

ZT-2015-1062 LDP3 15.5 ZT-2015-2649 lp3 17.7 8.1 9.2 15.1 ZT-2015-1062 LDP4 13.9 ZT-2015-2649 lp4 19.3 11.2 12.1 17.4 ZT-2015-1062 LM1 21.4 16.9 17.5 10.0 ZT-2015-2649 lm1 21.6 13.3 13.0 13.8 ZT-2015-1062 LM2 25.5 21.9 23.0 13.7 ZT-2015-2649 lm2 26.7 17.2 16.6 17.1 ZT-2015-1062 RP1 12.3 6.9 7.3 ZT-2015-2649 lm3 >36.5 ZT-2015-1062 RDP3 15.0 8 11.3 7.1 ZT-2015-0798 rp4 17.0 9.1 11.4 13.0 ZT-2015-1062 RDP4 13.8 ZT-2015-0798 rm1 20.5 13 13.3 9.3 ZT-2015-1062 RP3 16.8 14.8 15.0 ZT-2015-0798 rm2 25.7 15.8 16.8 11.1 ZT-2015-1062 RP4 15.4 18.8 13.7 ZT-2015-0798 rm3 ca. 39 19.4 17.5 15.0 14.8 ZT-2015-1062 RM1 20.3 16.3 17.1 10.1 ZT-2015-1591 ldp4 25.5 8.9 10.2 11.4 5.0 ZT-2015-1062 RM2 26.3 22.0 23.0 14.2 ZT-2015-1591 lm1 14.5 10.3 ZT-2015-2017 RP2 17.0 8.7 10.2 11.8 ZT-2009-03-071 rdp4 7.0 8.1 ZT-2015-2017 RP3 18.1 13.0 14.9 14.9 ZT-2015-0989 rdp4 22.0 8.0 10 10.9 7.6 ZT-2015-2017 RP4 14.5 17.9 19.2 11.0 ZT-2009-03-057 rdp4 23.0 8.3 10.8 12.0 4.2 ZT-2015-2017 RM1 18.9 17.7 18.8 9.0 ZT-2015-2130 lp2 10.7 4.4 8.6 ZT-2015-2226 LP3 ca. 20 15.7 8.52 ZT-2007-01-170 rp3 16.3 8.0 8.0 14.4 ZT-2015-2226 LP4 15.0 18.0 8.53 ZT-2009-03-109 rm1 ca. 18 9.9 10.6 9.1 ZT-2015-2226 LM1 18.0 9.5 ZT-2007-01-246 lm2 21.8 12.4 18.7 10.7 ZT-2015-2226 LM2 ca. 24 ca. 23 22.0 11.39 ZT-2015-2544 lm2 19.0 15.0 12.2 9.3 ZT-2015-1728 LP3 18.8 10.2 13.1 13.1 DAP, length of premolar and molar; DTa, width of the first lobe of a ZT-2015-1728 LP4 15.2 17.0 18.4 18.5 cheek tooth; DTp, width of the second lobe of a cheek tooth; DTpp, ZT-2015-1728 LM1 21.1 18.5 18.1 18.1 width of the third lobe of the third molar and the deciduous fourth lower ZT-2015-1728 LM2 25.6 23.0 22.8 22.8 premolar; H height ZT-2015-0758 RM1 17.6 15.9 17.1 17.1 ZT-2015-0758 RM2 22.2 19.5 19.9 19.9 ZT-2009-03-547 LP4 13.2 17.4 17.3 12.8 have continuous labial cingulid; and the hypoconulid of the ZT-2009-03-547 LM1 20.0 17.6 18.5 10.0 m3 is more labially located than in Pr. hyotherioides from ZT-2009-03-547 LM2 23.0 14.0 southern China. All these characters differentiate Pr. ZT-2009-03-547 LM3 36.0 24.3 >22 17.0 17.5 hyotherioides in northern China from Pr. hyotherioides in ZT-2015-1022 LDP3 15.7 7.9 12.0 6.6 southern China. The P3 of northern Chinese Pr. hyotherioides also has a weak metacone, which resembles the Shuitangba ZT-2015-0538 RDP3 18.3 8.5 13.0 P3s, suggesting a relatively derived status for Shuitangba and ZT-2015-1070 RP2 16.4 >8.2 11.5 northern Chinese Pr. hyotherioides compared to Pr. ZT-2007-01-265 LP3 18.6 13.6 13.4 13.0 hyotherioides from Lufeng and Yuanmou. ZT-2015-1503 RM1 20.5 17.0 16.9 11.3 Hippopotamodon cf. H. hyotheroides from Chiang Muan ZT-2014-0009 LM3 38.3 24.6 21.1 14.0 16.2 hominoid site, northern Thailand, is represented by a mandib- ZT-2009-03-511 LM3 22.3 16.8 16.8 ular fragment with left p3-m3. Pickford et al. (2004b) did not DAP, length of premolar and molar; DTa, width of the first lobe of a provide a detailed description nor measurements for this spec- cheek tooth; DTp, width of the second lobe of a cheek tooth; DTpp, imen. From the figures provided by Pickford et al. (Pickford width of the third lobe of the third molar and the deciduous fourth lower et al. 2004b:fig.5a, b), the Chiang Muan Hippopotamodon cf. premolar; H, height H. hyotheroides has a large p1 that is positioned close to the p2, suggesting there might not have been a p1-p2 diastema. more derived than those from Lufeng and Yuanmou. The p3 has a labio-lingually compressed protoconid that is tall Propotamochoerus hyotherioides from northern China and sharp; there is no metaconid and its talonid is very small (Pearson 1928) has a P1 lacking the posterolingual basin, such and low. The metaconid is separated from the protoconid in that its paracone is located in the middle of the crown; the M1 the p4 and is posterolingually located, and the talonid has a and M2 have relatively narrow transverse valleys; the p4 has a height of about half of the main cusps. The main cusps of the smaller metaconid and more posteriorly located protoconid; lower molars are simple with relatively smooth enamel. The the anterior accessory cusp is absent in the p4; the m1 and m2 third lobe of m3 consists of a small hypoconulid and a single J Mammal Evol (2019) 26:557–571 567

Table 4 Comparison of the premolars of Propotamochoerus hyotherioides from Shuitangba with related suids (in mm)

P1 P2 P3 P4

DAP DT DAP DT DAP DT DAP DT

Pr. hyotherioides* 12.3 6.9 16.4~17 10.2 16.8~20 13.1~15.7 13.2~15.4 17.3~19.2 Pr. hyotherioides1, 2 15.4~16.7 8.7~9.5 17.5 11.1~11.2 14.8~15.7 16.4~17.2 Pr. hyotherioides 3 13.9~17 15.4~19.5 Pr. wui1 9.5~11.2 4.6 11.2~12.3 7.0~9.0 10.3~12.2 9.7~10.4 9.3~10.9 11.0~12.9 Pr. hysudricus4 12.3 5.3 13.0~14.0 8.7 13.0~14.7 11.0~13.0 12.5~14.6 15.0~17.0 M. major5 9.4~9.6 4~4.3 13.6~14 7.9~8.9 14.5~15.5 12~14.5 13.9~15.5 16.4~17 D. medius6 13.9 9.8 15.9 15.2 D. binxianensis7 15.0 9.0 15.0~15.1 13.5~14.0 14.0~15.0 16.0~17.0 Mo. yuanmouensis8 10.1~11.0 5.6~6.0 12.8~15.0 9.1~10.5 14.1~18.0 14.2~16.4 14.1~18.0 15.0~17.9 H. sivalense4 13.0~15.6 6.0~7.6 15.6~22.1 11.4~13.6 19.0~21.0 17.5~22.0 19.4~21.8 22.7~26.6 H. ultimus9 13.6~13.8 6,5~6.6 18.3~16.8 9.2~9.3 18.0~18.3 15.1~15.2 16.3~17.0 19.3~21.2 p1 p2 p3 p4 DAP DT DAP DT DAP DT DAP DT Pr. hyotherioides* 10.7 4.4 16.3~17.7 8~9.2 17~19.3 11.4~12.1 Pr. hyotherioides 1, 2 16.7~17.4 8.3~8.5 16.2~17.6 10.7~13.2 Pr. hyotherioides3 15.6 10.9 Pr. wui1 8.5~10.3 3.3~4.0 12.3~12.4 5.4~5.6 11.3~14.0 5.9~7.4 11.7~13.6 7.9~9.6 Pr. hysudricus4 14.7 6.4 14.7~16.7 7.6~10.0 13.6~18.0 9.2~12.5 M. major5 13~13.5 6.1~6.2 16.4~16.6 8.7~12.3 18.5~18.8 12.3~12.4 D. medius6 15.8 9.1 18.0 12.9 D. binxianensis7 12.5~14.0 6.0~6.6 16.0~16.5 8.3~8.5 17.0~18.0 11.2~12.5 Mo. yuanmouensis8 14.9~16.3 9.8~10.4 16.4~18.6 12.0~13.5 H. sivalense4 10.9~12.0 6.5~8.0 18.2~25.3 8.8~13.2 22.4~24.3 13.2~15.6 23.0~26.4 18.6~21.3 Mi. youngi10 8.5~9.2 4.3~4.4 10.4 5.1 11.4~12.6 6.1 12.5~12.6 7.8~8.0

*Pr. hyotherioides from Shuitangba; 1 van der Made and Han 1994; 2 Pan et al. 2006; 3 Pearson 1928;4Pickford1988;5Liuetal.2004;6Liuetal. 1978; 7 Tang et al. 1985; 8 Liu and Pan 2003; 9 Dong and Zhang 2014;10Chen1997 DAP, length of premolar and molar; DT, maximum width of a cheek tooth cusp on the posterior cingulid. The lower molars are similar in Zhang et al. 2002; Liu and Pan 2003;Liuetal.2004;Pan size to those of Pr. hyotherioides from Lufeng and Yuanmou et al. 2006; Dong and Zhang 2014), Pr. wui specimens have (but slightly longer in length) and are slightly smaller than been placed within the genus Propotamochoerus with little those of the Shuitangba specimens. The lower premolars are controversy (van der Made and Han 1994; Liu and Pan relatively longer than those of Pr. hyotherioides from Lufeng 2003; Pan et al. 2006; Dong and Zhang 2014), although and Yuanmou and similar to those of Pr. hyotherioides from Pickford and Liu (2001) did suggest synonymy of Pr. wui Shuitangba. The relatively small and low talonids of the p3 with Pr. parvulus from Xiaolongtan, Yunnan. Liu and Pan and p4, simple molars, and the simple talonid of the m3, suggest (2003) and Sein et al. (2009), however, re-advocated the that the Chiang Muan specimen may represent a relatively validity of Pr. wui. primitive form of Pr. hyotherioides. Propotamochoerus wui differs from Pr. hyotherioides in Propotamochoerus wui (van der Made and Han 1994)is having smaller body size, a non-reduced P1, a more inflated asmallPropotamochoerus alsofoundinChina;itiseasily P3 main cusp, a relatively larger posterolingual basin and distinguished from the large Pr. hyotherioides by size. This cusplet on the P3 talon, absence of the lingual cingulum on species has a typical Dicoryphochoerus-type p4, mesio- the P4, M1/M2 with large posterior accessory cusps but no distally enlarged I2, and the talon of the third molar is sim- transverse valley pillar, and relatively small and simple m3 ple. Although the status and identification of the Chinese talonid. On the other hand, Pr. wui resembles Pr. Pr. hyotherioides material has been in general disarray for a hyotherioides by the relatively large posterolingual basin with long time (Schlosser 1903;Pearson1928;Li1963;Dong cusplet in P2 and the relatively high crown height of the lower 1987; van der Made and Han 1994;PickfordandLiu2001; premolars. The larger body size, reduced P1, and large labial 568 J Mammal Evol (2019) 26:557–571

Table 5 Comparison of the molars of Propotamochoerus M1 M2 M3 hyotherioides from Shuitangba DAP DT DAP DT DAP DT with related suids (in mm) Pr. hyotherioides * 17.6~21.4 17.1~18.8 22.2~26.3 19.9~23 36~38.3 24.3~24.6 Pr. hyotherioides 1, 2 22.2~24.0 19.8~23.1 31.3~36.3 20.3~26.9 Pr. hyotherioides 3 22.5~28.3 21.3~23.5 31.4~42 21.8~26.5 Pr. wui1 13.0~14.9 11.6~13.0 16.5~19.1 14.1~17.7 20.8~25.9 15.0~18.5 Pr. hysudricus4 16.0~17.5 15.1~17.0 20.8~25.0 18.3~22.0 26.5~31.4 17.8~22.6 M. major5 15.9~21.3 17.9~19.7 23.2~27.3 22.1~23.7 34.5~40.1 23.5~25.8 D. medius6 19.5 17.3 24.9 22.1 D. binxianensis7 16.1~19.2 17.0~18.0 25.0~26.0 21.2~23.5 36.2~28.3 24.0~25.7 Mo. yuanmouensis8 17.1~19.6 15.5~18.9 20.4~23.4 17.0~20.1 22.5~28.6 16.0~19.5 H. sivalense4 18.0~27.7 20.4~28.0 29.0~39.7 25.5~36.0 46.5~65.0 31.0~41.5 H. ultimus9 22.3~23.2 20.9~23.7 26.2~27.8 20.3~27.0 38.2~41.6 24.0~27.7 P. chinhsienensis11 16.0 16.2 27.5 21.5 40.0 27.3 m1 m2 m3 DAP DT DAP DT DAP DT Pr. hyotherioides* 20.5~21.6 13.3 25.7~26.7 16.8~17.2 39.0 19.4 Pr. hyotherioides 1, 2 19.3 14.2 21.8~23.8 14.9~17.9 34.5~35.2 19.0~21.1 Pr. hyotherioides 3 18.5 12.0 21.9~24.4 15.6~16.5 35.1 17.6~18.6 Pr. wui1 11.7~14.5 8.5~11.4 15.9~18.9 12.4~14.3 23.1~29.0 12.5~16.0 Pr. hysudricus4 14.5~18.8 10.8~13.0 19.0~24.0 14.3~18.0 28.5~36.0 15.0~19.5 M. major5 21.1~21.4 14.0~14.3 26.2~26.8 18.3~18.9 D. medius6 18.5 13.8 25.2 18.4 37.1 19.6 D. binxianensis7 18.3~19.0 13.0~13.8 25.0~25.5 17.6~18.3 41.0 20.2 Mo. yuanmouensis8 17.5~20.4 12.3~13.1 19.2~22.8 13.1~16.2 28.5~32.8 15.2~17.0 H. sivalense4 24.0~29.6 16.8~20.5 303~39.0 21.8~26.3 51.5~66.0 26.6~35.0 H. ultimus9 22.4~24.5 16.2~18.4 24.4~25.9 17.1~18.8 39~39.5 19.1~20.4 Mi. youngi10 12.5~12.8 9.0~9.1 15.0 10.9 22.7~22.9 10.4~11.1

*Pr. hyotherioides from Shuitangba; 1 van der Made and Han 1994;2Panetal.2006;3Pearson1928;4Pickford 1988;5Liuetal.2004; 6. Liu et al. 1978; 7 Tang et al. 1985; 8 Liu and Pan 2003; 9. Dong and Zhang 2014;10 Chen 1997;11Li1963 DAP length of molar; DT maximum width of molar pillars on the M3 of Pr. hyotherioides may suggest that it is Siwaliks Propotamochoerus,andPr. hyotherioides, which ex- more derived than Pr. wui; however, the relatively smaller hibited an increase in body size and was more widely distrib- posterolingual basin and smaller cusplet on the P3 uted in both northern and southern China. It is likely that some posterolingual basin in Pr. hyotherioides appear to be more of their shared morphologies, e.g., the relatively large primitive than in Pr. wui. Therefore, these two Chinese posterolingual basin with cusplet in P2 of both Pr. wui species may represent different branches of the Chinese and Pr. hyotherioides and the presence of a weak metacone Propotamochoerus. in P3 of both the northern Chinese and Shuitangba Pr. The Shuitangba locality is dated as terminal Miocene (6.5– hyotherioides, were the result of parallel evolution. 6.0 Ma), contemporary with the hominoid site in the Lufeng Microstonyx major from the late Miocene of the Linxia Basin, which is dated to 6.9–6.2 Ma (Yue and Zhang 2006). Basin, Gansu Province, China (Liu et al. 2004)hasasmall The hominoid sites that bear Propotamochoerus in the I3-C and i3-c diastema but a large P1-P2 diastema, an I1 with Yuanmou Basin are dated to ca. 8.2–7.1 Ma (Yue and Zhang a buccal cingulum, an upper canine curved in an inferior- 2006); the main Propotamochoerus locality in northern China anterior direction, a P1 that lacks a paracristid cusplet, a P2 (loc. 49) is considered to be ca. 7 Ma (Kaakinen et al. 2013); that has a labio-lingually compressed main cusp, a P3 with a the Chiang Muan locality is correlated to ca. 12.4–12.2 Ma small posterolingual basin and a small cusplet in the talon, a (Coster et al. 2010). It appears that after leaving the Siwaliks, P4 that has a posteriorly located protocone, an absent p1, a p3 Propotamochoerus was separated into two branches in China with multiple cusplets on the postcristid, and a p4 with a small – Pr. wui, which was endemic to the Yunnan Province of metaconid. Propotamochoerus hyotherioides resembles Mic. southern China and retained the relatively small size of the major in tooth dimensions, but morphologically they are quite J Mammal Evol (2019) 26:557–571 569 different. The P3 of Mic. major is broader and has a more placed in Hippopotamodon), including separated metaconid prominent talon, its P4 is relatively shorter, and its M3 talon and protoconid of the p4, a rectangular P4 with anterior and is more developed. The metaconid of its p4 is located more posterior cingula and a large lingual cusp, relatively simple transversely to the protoconid, which differs from the more molars with developed anterior cingula and furrows, and the posterolingually located metaconid on the Shuitangba p4s, presence of small median accessory cusps on the molars. and it has a long P1-P2 diastema, which is absent from the However, as BH.^ hyotherioides is now placed in Shuitangba specimens. Propotamochoerus in this paper, it is necessary to rethink Dicoryphochoerus was erected by Pilgrim (1926) for ma- the classification of H. ultimus. Hippopotamodon ultimus dif- terial from the Siwaliks. Its p4 has separated metaconid and fers from the type species, H. sivalense, in its relatively small protoconid, the metaconid is positioned posterolingual to size, absence of accessory cusplet on the premolar cristae, the protoconid, and the talonid is lower than the main cusp. weakly separated metacone and paracone in the P4, more Pickford (1988) questioned the validity of Dicoryphochoerus anteriorly located paracone in the P4, absence of cusplet in and reassigned most of Pilgrim’sninespeciesasConohyus or the sagittal valley of the P4, absence of lingual and labial Propotamochoerus, while the giant D. robustus and cingula in the P4, more complicated furrows on the molars, D. titanoides were moved to Hippopotamodon. But the relatively median position of the M3 talon (lingual in Chinese Dicoryphochoerus was not included in this analysis H. sivalense), absence of lingual and labial pillars of the M3, (Pickford 1988). There are two Dicoryphochoerus species re- absence of a 2/3 cusplet in the p3 and p4, absence of ported from China: D. medius from Lantian (Liu et al. 1978) metaconid in the p3, high metaconid of the p4, and the pres- and D. binxianensis from Binxian (Tang et al. 1985), Shaanxi ence of a third pair of cusps in the m3. Given these salient Province. Both species are represented by fragmentary tooth differences, we would consider removing H. ultimus from the rows and isolated teeth. Due to the paucity of the material, it genus Hippopotamodon. Hippopotamodon ultimus appears to has been difficult to reach a consensus for their taxonomy and be more derived than Pr. hyotherioides by its larger size, the classification. They were previously synonymized with presence of a P1-P2 diastema, and the presence of a third pair H. hyotherioides (Pickford and Liu 2001), then moved into of cusps in its m3 (Dong and Zhang 2014), characters which Mic. major by Zhang et al. (2002) and Liu et al. (2004)based are also found in Potamochoerus chinhsienense (Li 1963). on tooth dimensions. Both D. medius and D. binxianensis Hippopotamodon ultimus also resemble Po. chinhsienense have been suggested to represent a transition between in the absence of P4 pre- and postprotocristae and the centrally Dicoryphochoerus and Sus. They have p4s with separated located M3 hypoconule, which are common characters of the metaconid and protoconid, with the metaconid extant S. scrofa and Po. porcus,whileinPr. hyotherioides,the posterolingually located, and talonid with similar height to hypoconule of M3 is more lingually located. Furthermore, the main cusp or only slightly lower. The position of the H. ultimus shares significant characters with Mic. major,i.e., metaconid of the p4 resembles that of Propotamochoerus, large body size, long snout, and presence of P1-P2 diastema, but differs from the more transversely arranged protoconid but differs from the latter in having relatively short C-P1 and and metaconid in Microstonyx, while the similar height of P1-P2 diastemas and better separated P4 metacone and the talonid and the main cusp resemble Sus. The talon of the protocone. Hippopotamodon ultimus resembles third molar is more reduced than in Mic. major but broader D. binxianensis in the elongated snout. The p4s of than in Propotamochoerus. There is a notable p1-p2 diastema H. ultimus, however, have weakly separated and transversely in the mandible of D. binxianensis, which could suggest an arranged protoconid and metaconid, which are similar to Sus elongated snout. Microstonyx major also has a long diastema, and Microstonyx and different from Propotamochoerus, but the material from Hezheng lacks the p1. In Sus, the p1-p2 D. binxianensis, and D. medius. The relatively low talonid diastema is also notable. The small lower canine of D. of p4s in H. ultimus resembles Propotamochoerus and differs binxianensis resembles Mic. major and Sus.Incombination, from Sus, Microstonyx,andDicoryphochoerus. To sum up, D. medius and D. binxianensis exhibit complex morphologies H. ultimus and Po. chinhsienense share complex characters that variously resemble Propotamochoerus, Microstonyx,and with Propotamochoerus, Microstonyx, and Sus, as well as Sus, which might indicate that they are transitional forms be- D. binxianensis and D. medius, which may suggest a transi- tween Propotamochoerus, Microstonyx,andSus. Therefore, tional status for these species. Further taxonomic and system- the validity of the Chinese Dicoryphochoerus as a genus will atic analyses of H. ultimus, Po. chinhsienense,andthe need further analysis when more material is recovered. Chinese Dicoryphochoerus when more material is recovered Propotamochoerus hyotherioides had been placed in will clarify their taxonomic status. Hippopotamodon based on its large size (Pickford and Liu The genus Molarochoerus established by Liu and Pan 2001). The Pleistocene H. ultimus (Han 1987; Dong and (2003) and later discussed by Pickford et al. (2004a), for the Zhang 2014) was attributed to Hippopotamodon due to its medium-sized suid discovered from Yuanmou, a late Miocene similarity to Pr. hyotherioides (when this species was still hominoid locality in Yuannan Province, China, is only slightly 570 J Mammal Evol (2019) 26:557–571 larger than Pr. wui from Lufeng and is notably smaller than Pr. need further analysis when more material is recovered. The hyotherioides. Its premolars are not as reduced as in Pr. genus Molarochoerus, due to the uniquely molarized fourth hyotherioides, and the uniquely molarized P4s distinguish this premolars, may represent the most derived taxon of the genus from Propotamochoerus except for the Shuitangba ma- medium-sized Dicoryphochoerini. Miochoerus youngi was terial, which shows a small hypocone in some of the P4s. suggested to be grouped with Sus and Microstonyx, which Molarochoerus also resembles Shuitangba specimens in hav- may represent a primitive form of this group. ing a more inflated main cusp of the premolars, and a weakly cleft main cusp of P3, which may suggest a more derived Acknowledgements We thank all of those who participated in the field- status. On the other hand, Molarochoerus has an elevated p4 work that resulted in the retrieval of these specimens. We would like to particularly acknowledge the assistance of the following individuals and talonid, lacks a posterior cingulid on the p4, and lacks pillars institutions in providing field logistical support: Guodong Mao, Yuxi in the m3 transverse valley, features which differ from the Museum, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Propotamochoerus. The height of the p4 talonid of Chinese Academy of Sciences, Yunnan Institute of Cultural Relics and Molarochoerus is similar to the height of the main cusp, as in Archaeology, Qujing Institute of Cultural Relics, Chuxiong Prefectural Museum, Zhaotong Government. Financial support is gratefully ac- Sus, H. sivalense,andMic. major but differing from knowledged from the National Science Foundation of the United States Propotamochoerus. It may represent the most derived taxa of America (BCS-1035897, BCS-1227964, BCS-1227927, BCS- of the medium-sized Dicoryphochoerini. 1227838), the National Natural Science Foundation of China Miochoerus youngi was placed in BPropotamochoerinai^ (41202002, 41430102), Yunnan Natural Science Foundation (Grant 2010CC010), Zhaotong Government, and Institute of Vertebrate when the genus was established (Chen 1997), but van der Made Paleontology and Paleoanthropology, Chinese Academy of Sciences. S. (2010) considered it as a junior synonym of Hyotherium.The Hou was funded by National Science Foundation of the United States of most recent cladistic analysis suggested that Mio. youngi is America BCS-1227964 (to D.F. Su) while undertaking this study. We are most closely related to Sus and Microstonyx (Hou and Deng grateful to two anonymous reviewers and J.R. Wible for their insightful comments, which improved the quality and clarity of the manuscript. 2014). 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