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. 2010 Jan 22;277(1679):229-36.
doi: 10.1098/rspb.2009.0203. Epub 2009 May 6.

New basal eutherian mammal from the Early Cretaceous Jehol biota, Liaoning, China

Yaoming Hu  1 , Jin Meng, Chuankui Li, Yuanqing Wang
Affiliations

New basal eutherian mammal from the Early Cretaceous Jehol biota, Liaoning, China

Yaoming Hu et al. Proc Biol Sci. .

Abstract

A new genus and species of eutherian mammal, Acristatherium yanensis gen. et sp. nov., is described from the Early Cretaceous Jehol biota, China. The new taxon is based on a partial skull that is preserved in three dimensions from the Lujiatun bed of the Yixian Formation and dated 123.2+/-1.0 Ma. Its right upper and lower dentitions are nearly complete and it has a dental formula 4.1.5.3/3.1.5.3. The new mammal reveals several craniodental characteristics of Early Cretaceous eutherians previously unknown in fossil records of therians, such as a possible vestige of the septomaxilla. The craniodental features of the new taxon are compared with those of relevant Early Cretaceous eutherians and therians. Phylogenetic analyses based on a data matrix containing 70 taxa and 408 characters place A. yanensis as the most basal eutherian in the selected group. The morphological differences between Acristatherium and Eomaia indicate that eutherians already had a significant degree of generic diversification ca 125 Ma.

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Figures

Figure 1
Figure 1
Stereo photographs of the partial skull of A. yanensis (holotype, IVPP V15004). de, dentary; fr, frontal; nfs, nasofrontal suture; fps, frontoparietal suture; ju, jugal; la, lacrimal; mx, maxilla; iof, infraorbital foramen; na, nasal; pa, parietal; pm, premaxilla; sm, septomaxilla; sq, squamosal. Scale bar, 5 mm.
Figure 2
Figure 2
Snout of A. yanensis (holotype, IVPP V15004) with the septomaxilla marked with an arrow. mps, maxillopremaxillar suture; mx, maxilla; na, nasal; pm, premaxilla; sm, septomaxilla.
Figure 3
Figure 3
Dentitions of A. yanensis (holotype, IVPP V15004). (a,c) Stereo photographs of lingual views of mainly lower molars; (b,d) Stereo photographs of labial views of mainly upper molars. (e) Lateral view of upper and lower dentitions. al, alveolus for posterolabial root of M3; e, cusp e of m1; me2, metacone of M2; pr1, protocone of M1; pr2, protocone of M2. Measurements in mm: upper tooth length: I1, 0.25; I2, 0.4*; I3, 0.4; I4, 0.4; C, 1.0; P1, 0.7; P2, 0.6; P3, 0.5; P4, 1.0; P5, 1.3; M1, 1.3; M2, 1.4 (width, 1.5; M3, 0.7; lower tooth length, i1, 0.4; i2, 0.5; i3, 0.4; c, 0.8*; p1, 0.8; p2, ?; p3, 0.9; p4, 0.9; p5, 1.0; m1, 1.3; m2, 1.3*; m3, 1.4 (asterisks indicate estimated measurements). Scale bar, 1 mm.
Figure 4
Figure 4
Phylogenetic position of A. yanensis. See text for discussion of the tree. All characters and states are adopted from Wible et al. (2007). Only those applicable to Acristatherium, based on the sole specimen of A. yanensis (IVPP V15004), are listed below. The numbers correspond to those of characters in the list of Wible et al. (2007) and the state scored for each character is in parentheses. Character scoring for Acristatherium: 1(0); 2(0); 3(0); 4(0/1); 5(0); 6(0); 7(1); 8(1); 9(0); 10(0); 11(0); 12(0); 13(0); 14(2); 15(0); 16(4); 17(1); 18(0); 19(0); 20(0); 21(1); 22(0); 23(0); 24(1); 25(0); 26(1); 27(0); 29(0); 31(1); 32(0); 33(0); 34(1); 35(0); 36(0); 37(0); 38(0); 39(0); 40(0); 41(0); 42(0); 43(0); 44(0); 45(0); 46(0); 47(0); 48(0); 49(1); 50(0); 51(0); 52(0); 53(0); 54(0); 55(0); 56(0); 57(0); 58(0); 59(0); 60(0); 61(1); 62(1); 63(1); 64(1); 65(1); 66(1); 67(0); 68(1); 69(1); 70(0); 71(0); 72(0); 73(0); 74(0); 75(0); 76(0); 77(1); 78(1); 79(0); 80(0); 81(0); 82(0); 83(0); 84(0); 85(0); 86(0); 87(1); 88(0); 89(0); 91(1); 92(2); 93(0); 94(0); 95(0); 96(0); 97(0); 98(0); 101(0); 103(1); 106(0); 107(0); 108(0); 109(0); 110(0); 111(1); 112(0); 113(0); 115(1); 117(0); 118(1); 119(1); 120(1); 122(1); 123(0); 124(0); 125(0); 126(0); 127(0); 131(0); 132(1); 133(0); 134(0); 135(0); 136(1); 138(0); 139(1); 148(0); 149(0); 150(1); 153(0); 159(0); 160(0); 161(0); 162(0); 163(0); 164(1); 165(1); 166(0); 167(1); 168(0); 170(0); 171(0); 172(1); 173(0); 174(0); 175(1); 176(0); 177(0); 178(1); 179(1); 180(0); 181(0); 196(0); 197(1); 198(0); 199(0); 200(0); 201(0); 202(1); 203(0); 205(0); 213(1); 215(0); 216(2); 218(0); 219(0); 226(0); 227(1); 228(1); 229(0); 230(0); 232(1); 233(0/1); 251(0); 252(0); 253(0); 254(1); 256(1); 337(0); 338(1). Diagnoses for the node of Eutheria (only characters scored for Acristatherium): diastema posterior to first upper premolar present; three molars; preorbital length relative to postorbital more than one-third; zygomatic process of maxilla vestigial; zygomatic arch delicate; postorbital process absent; frontoparietal suture with anterior process of parietal off the midline; glenoid process of jugal present without facet.
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