Radiocarbon dating of charcoal from sediment removed from within the endocranial cavity of LL 1 provided an age of 11,510±255 cal. yr BP (OZM369) (Table 1; see also, Table S1). Three U-Th age determinations were attempted on ~25 mg sub-samples of the flowstone attached to the LL 1 vault (Table 2). Two of these were too contaminated with detrital Th from cave sediments to allow calculation of useable age estimates, but were able to be used to derive a robust estimate of initial 230Th/232Th activity in this contaminating phase (0.82±0.20). The remaining less-contaminated age determination has been corrected using this figure to provide an absolute age of 7.8±0.5 ka (UMB03650) for the flowstone (Table 2). The flowstone must have formed after the skeleton was deposited, but its dating confirms the Pleistocene-Holocene transition age based on radiocarbon dating of charcoal.
Table 1. Radiocarbon age calculations (arranged by depth: see also, Table S1).†doi:10.1371/journal.pone.0031918.t001
Table 2. Uranium series results and age calculations.¶doi:10.1371/journal.pone.0031918.t002
During the original excavation at Maludong three stratigraphic layers were identified . However, in our recent research on the remaining ~3.7 m section at the site we identified 11 distinct stratigraphic aggregates (Figure 2). AMS radiocarbon ages from 14 charcoal samples were used to determine an age versus depth profile (Table 1, Figure 2; see also, Table S1), providing unambiguous absolute ages for the stratigraphic units recognised at Maludong. Radiocarbon dating of bone was unsuccessful due to a lack of preserved collagen. A magnetic susceptibility record corroborates the stratigraphically coherent and internally consistent radiocarbon-based chronology for the site, indicating that the dated charcoal was deposited at the same time as its enveloping sediments (Figure 2; see also, Text S1).
Figure 2. Maludong site.
(A) stratigraphic sequence; (B) GIS plotted stratigraphy based on total station data and indicating excavation units and plotted finds; (C) stratigraphic aggregates; (D) Upper and Lower age limit of calibrated radiocarbon ages; and (E) magnetic susceptibility record (×10−6 m3 kg−1).
Calibrated radiocarbon ages show that the entire sequence spans the interval 17,830±240 cal. yr BP (OZM152) to 13,290±125 cal. yr BP (OZM870) (Table 1). All of the human remains were recovered from within a series of deposits dating from 14,310±340 cal. yr BP (OZM149; 292 cm depth) to 13,590±160 cal. yr BP (OZM145; 166 cm depth), a period of about 720 years. Moreover, the high fine-grained ferrimagnetic content of the deposits (Text S1), with their high magnetic susceptibility, suggests these were formed under warm, wet conditions, consistent with the Bølling-Allerød interstadial (~14.7-12.6 ka ). Human remains recovered in situ during the 2008 excavation and a reasonably complete calotte (specimen MLDG 1704) derived from a subsection of these deposits dated between 13,990±165 cal. yr BP (OZM148; 235 cm) and 13,890±140 cal. yr BP (OZM146; 200 cm) (Figure 2).
Morphological description and comparison
A full list of human remains recovered from Longlin and Maludong is provided in Table 3. Here we describe and compare the cranial, mandibular and dental remains, as they are the most informative with respect to evolution and systematics. Details of comparative samples are provided in Table 4 (see also data sources, Text S2). The grade term ‘modern’ is used interchangeably with H. sapiens sensu stricto (i.e. beginning with Omo-Kibish 1, Herto and other so-called anatomically modern humans to recent humans), while ‘archaic’ grade refers to all other hominin specimens/taxa.
Table 3. Human remains recovered from Longlin and Maludong.doi:10.1371/journal.pone.0031918.t003
Table 4. Cranial series employed in comparisons (where data were compiled by the present authors: see Text S2 for a list of data sources for metrical and morphological data and dating estimates).doi:10.1371/journal.pone.0031918.t004
The LL 1 partial skull (Figure 3) preserves a mostly complete frontal squama with left supraorbital margin, but lacks the right lateral supraorbital part and zygomatic process. The superior section of the nasal bones and superomedial orbital walls are present, as are the left and right frontal processes of the maxillae. Most of the left facial skeleton is present and comprises a nearly complete zygomatic process, alveolar process from mid-line to M1, and a largely intact left zygomatic. The right maxilla is incomplete save much of the lateral margin of the piriform aperture and alveolar process. What remains has been rotated ~45° from the median sagittal plane owing to post-burial compression. The left side (MSP to lateral) is largely free of distortion, with the landmarks prosthion and nasospinale readily identifiable. The tip of the anterior nasal spine is broken away, but its base is easily discerned. The bony palate lacks most of the left and right palatine processes. The morphology of the preserved left maxillary tuberosity is consistent with M3 agenesis. Parts of the sphenoids, anterior occipital, including anterior margin of the foramen magnum, partial left occipital condyle and basioccipital clivus remain. The temporal fragment (Figure 4) preserves a section of the squama, the base of the mastoid process (tip broken away), tympanic part with a damaged external acoustic meatus, mostly complete and pathologically unmodified mandibular fossa, base of the styloid process, vaginal process and stylomastoid foramen, large carotid canal, preserved foramen lacerum, foramen ovale and foramen spinosum, and a largely intact petrous part.
Figure 3. Longlin 1 partial skull (each bar = 1 cm).doi:10.1371/journal.pone.0031918.g003
Figure 4. Longlin 1 temporal fragment (each bar = 1 cm).doi:10.1371/journal.pone.0031918.g004
The MLDG 1704 calotte (Figure 5) comprises mostly complete frontal and paired parietal bones, but lacks its occipital, temporals and most of the sphenoids, as well as the entire viscerocranium. Evidently the specimen lost its base and facial skeleton owing to anthropogenic alteration, with cut-marks seen along the walls of the vault and on the zygomatic process. Its preserved morphology is unaffected by this alteration. The specimen is free from post-deposition distortion as indicated by visual inspection and scrutiny of CT-scans.
Figure 5. Maludong 1704 calotte (each bar = 1 cm).doi:10.1371/journal.pone.0031918.g005
The LL 1 mandible (Figure 6) and two partial mandibles recovered from Maludong (MLDG 1679 and MLDG 1706: Figure 7) are also compared. Specimen LL 1 comprises a largely complete body, but is missing its left ramus save the root and coronoid process, and lacks the entire right ramus. The position of the take-off of the left ramus relative to M3 makes clear that a retromolar space would have been present (M3 being uncovered ). The external surface of the symphysis has been displaced superiorly such that the bone is out of alignment with the alveolar process. This makes accurate assessment of chin development problematic. The left alveolar part retains the roots and crowns of I1, canine, P3, partial P4, M2 and partial M3. The first molar is missing and the alveolar bone shows signs of ante-mortem tooth loss with resorption and new bone growth/remodelling. Much of the right body is preserved and retains the mental foramen, I1-P4 and M2 roots and crowns. The right M1 seems again to have been lost ante-mortem, with signs of remodelling of the alveolar bone. The transverse tori are somewhat thickened such that the internal surface of the symphysis is not vertical, a small internal plane being present.
Figure 6. Longlin 1 mandible (scale bar = 1 cm).doi:10.1371/journal.pone.0031918.g006
Figure 7. Maludong mandibles MLDG 1679 (left) and MLDG 1706 (right) (scale bar = 1 cm).
NB: MLDG 1706 is broken through its symphysis just lateral to the MSP.
Specimen MLDG 1679 (Figure 7) comprises a right mandibular body fragment preserved from just anterior to M2, with intact M2-M3 crowns and roots, and including a complete ramus in two pieces. The internal morphology of the body and ramus is well preserved including the mandibular foramen, pterygoid surface, and coronoid and condylar parts (the former having been modified somewhat by osteoarthritis).
Specimen MLDG 1706 (Figure 7) is a right hemi-mandible, broken just lateral to the symphysis (left side), through to a mostly complete ramus. The body is damaged (abraded) along its inferior border, while scoring marks the external surface of the symphysis. No dental crowns were recovered with the specimen, but all of the alveoli are open and lack signs of bony remodelling, indicating a full (adult) set of dentition would probably have been present about the time of death. Externally, the mental foramen is present and well preserved. Internally, the morphology of the surface of the body and ramus is clear: the symphysis expresses enlarged tori, the mandibular foramen is clear, and the pterygoid surface and coronoid and condylar parts are well preserved (the former being modified slightly by osteoarthritis).
The supraorbital part of LL 1 is conspicuous, with a well-developed glabella. It lacks the obvious signs of division typically seen among modern humans (i.e. lacks a dividing sulcus between medial and lateral parts), but it does thin in the vertical dimension mediolaterally. The supraorbital torus of MLDG 1704 is marked by a strongly developed glabella and superciliary ridges, but also thins laterally. Its supraorbital part is, however, divided into medial and lateral components by a distinct sulcus, being bipartite in form. The presence of a supraorbital torus is a condition rarely seen in recent humans , but is more frequent among Pleistocene H. sapiens . A bipartite supraorbital like that seen in MLDG 1704 is characteristic of H. sapiens and distinguishes it from archaic taxa .
Table 5 compares supraorbital projection and vertical thickness dimensions. Supraorbital projection at the medial location  is moderate in LL 1 (11 mm), but high in MLDG 1704 (17 mm, measured in MLDG 1704 on CT-scans). Longlin resembles European early H. sapiens (or EUEHS) in this regard (13±3 mm; z-score adjusted for the size of the comparison sample  −0.63), while MLDG 1704 is identical to West Asian early H. sapiens (or WAEHS) crania (i.e. Skhul and Qafzeh: mean 17 mm). Values for both specimens are below the H. neanderthalensis (or NEAND) mean (20±2 mm), the difference from LL 1 being significant (z-score −4.27, p0.001; MLDG 1704 z-1.42). At mid-orbit , supraorbital projection is comparatively weak in LL 1 (11 mm; EUEHS z-1.58), but moderate in MLDG 1704 (16 mm), and identical to the EUEHS mean (Table 5). In contrast, mid-orbit projection  is strong in WAEHS (20 mm) and NEAND (22±2 mm; MLDG 1704 z-2.97, p0.002; LL 1 z-5.44, p<0.0001). At the lateral position , projection in LL 1 is similar to EUEHS (20±3 mm; z-0.32), while in MLDG 1704 it is strong (~23 mm; EUEHS z0.95), the specimen closely resembling WAEHS (24 mm, n4) and NEAND (24±2 mm; z-0.49; LL 1 z-2.47, p0.009).
Table 5. Bone thickness measurements compared (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t005
Vertically thickness of the supraorbital at the medial location  is similar in LL 1 (15 mm) and MLDG 1704 (L 16.5/R 17 mm) to EUEHS (17±3 mm; LL 1 z0.64; MLDG 1704 z-0.08) and NEAND (17±3 mm; LL 1 z-0.63; MLDG 1704 z-0.08). Their values are, however, slightly reduced compared to WAEHS (18±3 mm; z-0.94, z-0.39). Mid-orbit thickness  is moderate in LL 1 (7 mm) and similar to WAEHS (8±3 mm; z-0.31), but well below the NEAND mean (10±2 mm; z-1.48). In MLDG 1704, thickness at this location is marked (10/13 mm), and while exceeding mean values for all comparative samples, it is most similar to NEAND (z0.74; contrasting with EUEHS z3.11, p0.005; and WAEHS z1.09). Finally, vertical thickness at the lateral location  is comparatively thin in LL 1 (7 mm) and MLDG 1704 (7/6.5 mm). They both closely resemble the laterally thin supraorbitals of EUEHS (8±1 mm; LL 1 z-0.96; MLDG 1704 z-1.20) and WAEHS (10±3; LL 1 z-0.94; MLDG 1704 z-1.01). In contrast, NEAND tori are laterally thick (12±2 mm; LL 1 z-2.47, p0.008; MLDG 1704 z-2.59, p0.006).
Vault thickness measurements are presented for LL 1 and MLDG 1704 and compared in Table 5. At bregma, LL 1 has a thick vault (10 mm), being most similar to the H. erectus (ERECT) mean (9±2 mm; z0.49). While its value is within one standard deviation unit of the EUEHS sample mean (7±3 mm; z0.94), it is significantly different to the NEAND mean (7±1 mm; z2.89, p0.006). Thickness at bregma in MLDG 1704 (7 mm) is identical to mean values for EUEHS, WAEHS and NEAND (Table 5). At the parietal eminence, thickness in MLDG 1704 (7.6/6.4 mm) is within one standard deviation unit of means for EUEHS (6±1 mm, z0.97) and WAEHS (both 8±2 mm, z-0.47), but distinct from the means of East Asian Middle Pleistocene (archaic) hominins (or EAMPH) and ERECT (both 10±2 mm; z-1.37 and z-1.47).
Tables 6–7 compare a range of vault measurements for LL 1 and MLDG 1704 with various Pleistocene modern (Table 6) and archaic hominin (Table 7) samples. A comparison of African early H. sapiens (or AFEHS) and NEAND helps to sort the polarities of features found in Eurasian samples. The Herto (BOU-VP-16/1) cranium possesses a large endocranial volume (ECV) (1450 cm3). It is, however, only slightly enlarged compared with NEAND (1407±172 cm3). In contrast, the greatly enlarged ECV of WAEHS (Skhul-Qafzeh: 1556±25 cm3) is significantly larger than Herto (z-3.87, p0.008) and NEAND (t-5.44, p0.002), indicating that ECV enlargement is a derived characteristic of Pleistocene Eurasian H. sapiens. Reconstructed ECV for MLDG 1704 (~1327 cm3: Figures S1, S2, S3, S4) is small in comparison with all H. sapiens sample means: its value sits outside of (below) the ranges of WAEHS (z-8.36, p0.0005) and EUEHS (z-1.71, p0.05). ECV for East Asian early H. sapiens (or EAEHS) (1407±146 cm3; MLDG z-0.51) is identical to the NEAND mean (Table 7). Among all samples, MLDG 1704 is closest to these latter sample means. Thus, MLDG 1704 shares with EAEHS and NEAND a reduced ECV. This reduction contrasts late Pleistocene humans in East Asia with earlier Eurasian and African modern humans with their large ECVs.
Table 6. Vault measurements (cm3, mm) and indices (%) compared to Pleistocene modern humans (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t006
Table 7. Vault measurements (cm3, mm) and indices (%) compared to archaic hominins (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t007
The frontal bone of the earliest modern humans is long (AFEHS frontal chord 124-131 mm, arc 153 mm) and contrasts with the short frontals of NEAND (chord 112±6 mm, arc 123±9 mm). The frontal bones of LL 1 (chord 112 mm, arc 134 mm) and MLDG 1704 (chord 116 mm, arc 133 mm) are moderate in length, being similar to EUEHS and ERECT, but distinguishable from the very long frontals of AFEHS. Minimum frontal breadth is wide in AFEHS (i.e. Herto 112 mm), contrasting with the narrower post-orbitals of NEAND (103±5 mm). This region is even narrower in LL 1 (94 mm) and MLDG 1704 (95 mm), contrasting with the moderately broad anterior frontals of EAEHS (99±5 mm), EUEHS (101±5 mm; z-1.36, z-1.17), and WAEHS and NEAND (both 103±5 mm; WAEHS z-1.67, z-1.48; NEAND z-1.76, p0.04, z-1.56, p0.06). The LL 1 and MLDG 1704 values are most similar to the mean for ERECT (93±10 mm; z0.10, z0.20). Maximum frontal breadth, measured at the coronal suture, is moderate in AFEHS and EAEHS (120 mm), and WAEHS (119±4 mm) and NEAND (122±6 mm). MLDG 1704 possesses a broad maximum frontal width (125 mm), in common with EUEHS (124±7 mm, z0.14).
The parietal bones of AFEHS are long (chord 125 mm, arc 135 mm) and contrast strongly with the short parietals of NEAND (chord 108±4 mm, arc 115±5 mm). The parietals of MLDG 1704 are short (chord 107 mm, arc 123 mm) by Pleistocene H. sapiens standards (Table 6). Its parietal chord is significantly shorter than the EAEHS (117±4 mm; z-2.34, p0.02) and EUEHS (120±7 mm; z-1.81, p0.04), and most closely resembles NEAND (z-0.24). Its arc dimension is, however, closer to H. sapiens (means 132–135 mm; MLDG 1704 z-0.94 to z-1.19) than to archaic species (means 106–117.5 mm; MLDG 1704 z1.17 to z3.33; with p0.001 for ERECT). Broad parietals are characteristic of NEAND (148±7 mm), distinguishing them from H. sapiens (means 138–145 mm) and ERECT (142±6 mm). The absolutely narrow bi-parietal breadth of MLDG 1704 (141 mm) is most similar to the mean of EUEHS (143±7 mm, z-0.28).
The ratio of parietal/frontal chord and parietal/frontal arc distinguishes samples of Eurasian H. sapiens (means: chord 104–107%, arc 99–107%) from NEAND (chord 98±8%, arc 96±10%). The shortened parietals of AFEHS (chord 98%, arc 85%) are, in contrast, a putative ancestral trait shared with NEAND. Thus, parietal sagittal expansion is characteristic of Pleistocene Eurasian H. sapiens. For these indices, MLDG 1704 (both 92%) is highly distinct from H. sapiens (EAEHS z2.24, p0.03; EUHS z1.67, p0.05), and most closely resembles archaic hominins such as East Asian Middle Pleistocene hominins (or EAMPH: chord index 92%), ERECT (chord: 87±7%, z0.41) and NEAND (arc: 96±10%, z-0.38).
A commonly deployed index of postorbital width is the frontal constriction index, or ratio of minimum/maximum frontal breadth. Its value for MLDG 1704 (76%) is unusually low, and while it sits (just) within the lower part of the range of EAEHS (76–89%), it is most similar to the mean for ERECT (82±5%, MLDG z-1.17). In contrast, MLDG 1704 is distinct from mean values for EUEHS (82±2%; z-2.91, p0.005), WAEHS (83±3%; z-3.04, p0.01) and NEAND (86±5%; z1.93, p0.03).
Measurements of the left mandibular fossa of LL 1 (Figure 4) are compared in Table 8. Its mandibular fossa is moderate in length (A-P 17 mm), being similar to the WAEHS (Skhul-Qafzeh: 19 mm), ERECT (20±2 mm; z-1.04) and EUEHS (21 mm) means. It is, however, significantly different to the means of recent Africans (11±1 mm; z5.97, p<0.00001), a sample of Pleistocene early H. sapiens (comprising Ngaloba, Jebel Irhoud 1 and 2, Singa 1, Omo-Kibish 2, Skhul 4 and 5 ) (11±2 mm; z2.81, p0.01) and NEAND (11±1 mm; z5.74, p<0.00001). The mandibular fossa of LL 1 is very broad (M-L c31 mm) and lies outside of the range of all comparative samples, being closest to EAMPH (30 mm). Its breadth is significantly different to the means of recent Africans (20±2 mm; z5.47, p<0.00001), Pleistocene early H. sapiens (composition, see above: 23±2 mm; z3.74, p0.004) and NEAND (21±3 mm; z3.19, p0.004). Its mandibular fossa is comparatively deep (S-I 13 mm) like ERECT (12±4 mm; z0.23), but shallower than EAMPH (17 mm). In contrast, samples of H. sapiens exhibit smaller mean values or much shallower fossae (5–6 mm; z6.55–7.96; p0.0003-<0.00001). Shallow fossae are also characteristic of NEAND (6±2 mm; z3.35, p0.003).
Table 8. Mandibular fossa dimensions (mm) of Longlin 1 compared (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t008
The facial skeleton of LL 1 is unusual compared with early H. sapiens in exhibiting strong alveolar prognathism. The mid-face is flat, both at the nasal root and piriform aperture, and zygomatic process of the maxilla. The specimen lacks a canine fossa, but possesses a deep sulcus maxillaris. The left zygomatic arch is laterally flared. The zygomatic bone is strongly angled such that its inferior margin sits well lateral to the superior part. The zygomatic tubercle is small and sits lateral to a vertical line projected from the orbital pillar. The anterior section of the masseter attachment is marked by a broad and deep sulcus, but the zygomatic tubercle is small. The anterior wall of the zygomaticoalveolar root is in an anterior position (above P4/M1). The lateral orbital margin (pillar) exhibits strong transverse incurvation when viewed in lateral aspect. In most of these features, LL 1 displays the putative plesiomorphic condition for later hominins, being highly distinguishable from the modal condition of H. sapiens.
Tables 9–10 compare standard measurements and indices of the facial skeleton for LL 1 and a single measurement for MLDG 1704 with Pleistocene modern human (Table 9) and archaic (Table 10) samples. Data for superior facial breadth are unavailable for AFEHS. However, the narrower upper face of NEAND (118±4 mm) distinguishes them from the very broad upper facial skeletons of WAEHS (Qafzeh-Skhul: 123±7 mm). This later morphology is shared by WAEHS with ERECT (123 mm). Contrasting with both of these conditions are later Eurasian samples of H. sapiens with their markedly narrow superior facial skeletons (EAEHS and EUEHS: mean 112 mm). A narrow superior facial breadth is a shared condition of LL 1 (c110 mm) and MLDG 1704 (109 mm), both with each other and with later Pleistocene Eurasians. Their values are, however, highly distinct from WAEHS (LL 1 z-1.72, p0.07; MLDG 1704 z-1.85, p0.06) and NEAND (LL 1 z-1.96, p0.03; MLDG 1704 z-2.21, p0.01).
Table 9. Facial skeleton measurements (mm) and indices (%) compared to Pleistocene modern humans (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t009
Table 10. Facial skeleton measurements (mm) and indices (%) compared to archaic hominins (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t010
The facial skeleton of LL 1 is broad. Bizygomatic breadth is estimated to be wide (c144 mm), strongly distinguishing it from EAEHS, the value for LL 1 being outside of (slightly above) its range. Its bizygomatic most closely resembles NEAND (145±8 mm; z-0.12), and is similar also to AFEHS (142 mm). A second index of postorbital constriction is the ratio minimum frontal breadth/bizygomatic breadth, providing a more direct measure of the relative size of the temporal fossa. The value for LL 1 is large (66%) by later hominin standards. While it is equal to the minimum value for EUEHS and WAEHS, its value is distant from their means (EUEHS (73±4%; z-1.67, p0.06; WAEHS 70%). It also contrasts strongly with EAEHS (73±3%; z-2.16, p0.04) and NEAND (74±2%; z-3.70, p0.006). In contrast, bimaxillary breadth in LL 1 (108 mm) is most similar to EAEHS (105±6 mm; z0.47). While the index of upper/mid-facial (bimaxillary) breadth is high for LL 1 (98%), it is similar to EAESH (93±5%; z0.65) and NEAND (95±5%; z0.57).
Superior facial height is greatly reduced in LL 1 (64 mm), a condition distinguishing Eurasian early H. sapiens from AFEHS (79 mm) and archaic hominins (means: 80.5–87 mm). The superior facial height of LL 1 is in fact significantly shorter than the mean for WAEHS (73±3 mm; z-3.35, p0.01). Facial shortening is also seen in archaic EAMPH (74 mm), but not to the great extent characterising late Pleistocene H. sapiens (but more so than the AFEHS specimen from Herto). The facial index (superior height/bizygomatic breadth) for LL 1 (44%) shows its bony face to be very short relative to breadth. The value in the specimen is not especially close to any sample mean and is significantly different to EAEHS (50±2%; z2.81, p0.01) and NEAND (59±2%; z-6.94, p0.0004).
While the left orbit of LL 1 is broad (45 mm), being identical to the WAEHS mean, this measurement has little discriminating power, as LL 1's value lies within one standard deviation unit of EAEHS (44±2 mm), EUEHS (43±4 mm) and NEAND (44±3 mm). In contrast, orbit height is moderate in LL 1 (34 mm), distinguishing the specimen from the short orbits of EAEHS (31±1 mm; z2.81, p0.01) and EUEHS (30±3 mm; z1.29), and tall orbits of NEAND (38±1 mm; z-3.88, p0.0007). The value for LL 1 is identical to AFEHS and similar to WAEHS (33±3 mm). This combination of a broad and moderately tall orbit results in a moderate orbital index value (76%), being most similar to WAEMH (74±7%; z0.26), but distant from NEAND (87±6; z-1.76).
The piriform aperture is broad in LL 1 (maximum nasal width 32 mm), being identical to the NEAND mean (Table 10). It is substantially broader than the means for all H. sapiens samples: EAEHS 28±2 mm (z1.89), EUEHS 26±2 mm (z2.89, p0.006) and WAEHS 30±1 mm (z1.83). Nasal height is short (45 mm), its value being distant from the means of early H. sapiens (means 42–51 mm; z1.37–1.44). It is, however, significantly different to the NEAND mean (61±3 mm; z-4.94, p0.002). The nasal index for LL 1 (71%) is large by later Pleistocene hominin standards, its value being significantly different to all comparative sample means (EAEHS z3.54, p0.004; EUEHS z3.35, p0.003; WAEHS z4.56, p0.005; NEAND z4.94, p0.002).
Multivariate cranial comparisons.
Table 11 summarises the results of principal components analysis of size-adjusted  variables for three sets of analyses comparing LL 1 or MLDG 1704 to fossil specimens. The first analysis included LL 1 (Figure 8) and 22 other crania, employed 9 variables (Table 11), and generated three principal components. For principal component (PC) 1, the highest loading variables were frontal chord and frontal arc, and these were contrasted mostly with measures of facial height (orbit height and upper facial height) and breadth (chiefly nasal breadth) (Table 11). For PC 2, facial breadth (orbit breadth and bimaxillary breadth) accounted for most of the variance (Table 11), while PC 3 contrasted maximum frontal breadth with bizygomatic breadth (Table 11). A bivariate plot of object scores for PC 1 and PC 2 (Figure 8A) shows that PC 1 distinguishes crania belonging to H. sapiens from those of NEAND, H. heidelbergensis sensu stricto, H. rhodesiensis and ERECT. Specimen LL 1 lies within the range of H. sapiens, clustering with Skhul 5, Mai Da Nuoc and Combe Capelle. A plot of PC 2 versus PC 3 (Figure 8B) shows the third principal component to distinguish ERECT from all other taxa. In this plot, LL 1 sits in a unique position, well away from all crania owing to a combination of a high positive score for PC 2 and moderate score for PC 3. Z-tests of object scores indicate that the difference between LL 1 and the H. sapiens mean is not significant for all PCs (PC 1 z-0.89; PC 2 z0.95; approaching significance for PC 3 z1.70, p0.05).
Figure 8. Object plots from principal components analysis including LL 1 and 23 later Pleistocene fossil crania.
(A) PC 1 versus 2, and (B) PC 2 versus PC 3 (NB: Gray star = LL 1; AFEHS = African early H. sapiens; Amd = Amud; BG = Barma Grande; CC = Combe Capelle; CM = Cro Magnon; Kei = Keilor; Hof = Hofmeyr; Kab = Kabwe; LaC = La Chapelle; LaF = La Ferrassie; Liu = Liujiang; MDN = Mai Da Nuoc; Mld = Mladec; Oas = Oase; Pred = Predmost; S = Sangiran; SCr = Sima de Los Huesos cranium; Skh = Skhul; Tab = Tabun; UC = Upper Cave-Zhoukoudian; and Zkd = Zhoukoudian ERECT).
Table 11. Results of principal components analysis (two highest loading variables for each component in bold).doi:10.1371/journal.pone.0031918.t011
The second analysis included MLDG 1704 and 23 other crania, employed eight variables (Table 11), and generated three principal components. For PC 1, the highest loading variables were parietal chord and parietal arc, and these were contrasted mostly with measures of vault width (biparietal breadth and superior facial breadth) (Table 11). For PC 2, frontal chord and frontal arc accounted for most of the variance (Table 11), while PC 3 was mostly explained by maximum frontal breadth (Table 11). A bivariate plot of object scores for PC 1 and PC 2 (Figure 9A) shows PC 1 to separate crania belonging to H. sapiens from those of NEAND, H. heidelbergensis sensu stricto and ERECT. Specimen MLDG 1704 sits just outside of the convex hull for H. sapiens, but clusters close to Cro Magnon 1 and 3 (Figure 9A). A plot of PC 2 versus PC 3 (Figure 9B) shows that these principal components do not discriminate well among taxa. Principal component 3 does, however, distinguish MLDG 1704 from all other crania, with its high positive score. For PC 3, its score is outside of the range of all crania, exceeding the next highest score by 0.29 eigenfactor units (almost double the difference between the H. sapiens and NEAND means). Z-tests of object scores indicate that the difference between LL 1 and the H. sapiens mean is not significant for all PCs [PC 1 z0.75; PC 2 z1.51; approaching significance for PC 3 (z1.62, p0.06)]. In contrast, the mean difference for NEAND is significant for PC 1 (z-6.89, p0.001), but not for PC 2 (z1.70) or PC 3 (z1.22).
Figure 9. Object plots from principal components analysis including MLDG 1704 and 23 later Pleistocene fossil crania.
(A) PC 1 versus 2, and (B) PC 2 versus PC 3 (NB: Gray star = MLDG 1704; BG = Barma Grande; CM = Cro Magnon; GdE = Grotte de Enfants; LaC = La Chapelle; LaF = La Ferrassie; Liu = Liujiang; LQ = La Quina 5; MC = Monte Circeo; MDN = Mai Da Nuoc; Nea = Neandertal; Pet = Petralona; Pred = Predmost; S = Sangiran; Skh = Skhul; UC = Upper Cave-Zhoukoudian; and Zkd = Zhoukoudian ERECT).
The final analysis included MLDG 1704 and 43 other crania, employed 6 variables (Table 11), and generated two principal components. For PC 1, parietal chord and parietal arc explained most of the variance (Table 11). For PC 2, frontal arc was contrasted with maximum frontal breadth (Table 11). A bivariate plot of object scores for PC 1 and PC 2 (Figure 10) shows good separation between H. sapiens on the one hand, and NEAND and ERECT on the other. Specimen MLDG 1704 sits just within the H. sapiens convex hull, but near the edge of the ERECT range. It also sits close to the Nazlet Khater 2 cranium from Egypt, a late Pleistocene specimen also possessing a mix of modern and archaic characters . The object score of MLDG 1704 for PC 1 is closest to the archaic Petralona (0.08 eigenfactor units difference) and NEAND Amud 1 (0.13) crania. Moreover, z-tests indicate that for PC 1, the difference is significant between MLDG 1704 and the H. sapiens mean (excluding Nazlet Khater 2) (z2.00, p0.03), but not for NEAND (z-0.01) or ERECT (z-1.04). For PC 2, the difference is significant between MLDG 1704 and NEAND (z2.19, p0.03), but not for H. sapiens (excluding Nazlet Khater 2: z0.42) or ERECT (z-0.03).
Figure 10. Object plot from principal components analysis including MLDG 1704 and 43 later Pleistocene fossil crania.
NB: Gray star = MLDG 1704; AFEHS = African early H. sapiens; Amd = Amud; BG = Barma Grande; Buk = Buku; CC = Combe Capelle; CM = Cro Magnon; Kei = Keilor; Hof = Hofmeyr; GdE = Grotte de Enfants; Kab = Kabwe; LaC = La Chapelle; LaF = La Ferrassie; Liu = Liujiang; LQ = La Quina 5; MC = Monte Circeo; MDN = Mai Da Nuoc; Mld = Mladec; Nea = Neandertal; Ng = Ngandong; NK = Nazlet Khater 2; Oas = Oase; Pet = Petralona; Pred = Predmost; S = Sangiran; SCr = Sima de Los Huesos cranium; Skh = Skhul; Sp = Spy; Tab = Tabun; UC = Upper Cave-Zhoukoudian; and Zkd = Zhoukoudian ERECT.
Comparison of crania to recent humans.
In Tables 12–14 we compare cranial measurements of LL 1 and MLDG 1704 with mixed sex recent humans: East Asian and Eskimo (Table 12), European and African (Table 13) and Australian (Table 14). These samples are compiled from Howells'  worldwide dataset (see also, Table 4). Overall, measures of facial width strongly distinguish LL 1 from recent humans, with its very broad face. Bizygomatic breadth (c144 mm) contrasts strongly with recent human means (125–135 mm; z1.49–3.16, p0.06-0.0008). Bijugal breadth (c134 mm) is similarly enlarged (recent human means 113–117 mm; z2.57–4.19, p0.005-0.00001). Its bimaxillary breadth (c108 mm) contrasts strongly with recent sample means (92–97 mm; z1.83–3.19, p0.03-0.0007). Bifrontal breadth (c106 mm) is greatly enlarged (96–100 mm; z2.00-1.50, p0.06-0.02). Biorbital chord (c114 mm) also contrasts strongly with recent humans (97–99 mm; z3.40–5.66, p0.001-<0.00001), its value being outside of the range of all samples. Finally, interorbital breadth in LL 1 (25 mm) is also broad compared with recent populations (means 18–23 mm; z1.00–3.48, p0.15-0.0003).
Table 12. Comparison of LL 1 and MLDG 1704 with Howells  recent East Asian and Eskimo samples (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t012
Table 13. Comparison of LL 1 and MLDG 1704 with Howells  recent European and African samples (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t013
Table 14. Comparison of LL 1 and MLDG 1704 with Howells  recent Australian samples (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t014
Frontal chord length for LL 1 (112 mm) is long, but lies within one standard deviation unit of all samples (means 108–111 mm; z0.20–0.80). The value for frontal subtense is, however, high (30 mm), and when this measurement is combined with frontal chord to calculate the frontal curvature index (subtense/chord), it is clear that LL 1 exhibits an exaggerated degree of frontal curvature (27%). This index distinguishes the Chinese fossil from recent humans (means 23–25%; z1.00–2.00, p0.15–0.02). Glabella projection (4 mm) is well within the range of recent humans except for Africans (non-African: means 3–5 mm, z1.00 to -1.00; African: 2±1 mm, z2.0, p0.02). Supraorbital projection (6 mm) is indistinguishable from recent humans (means 5–7 mm; z0.00–1.00/−1.00). Posterior breadth of the frontal bone (STB) is narrow (103 mm) and closely resembles Australian (102±7 mm; z0.14) and Eskimo (101±7 mm; z0.28) means.
Facial height, or nasion-prosthion height in LL 1 (64 mm), is short, but well within the range of recent humans (means 62–67 mm; z0.40 to -0.50). In contrast, its face is short relative to its breadth (facial index = height/bizygomatic breadth) (c44%), distinguishing the specimen from most recent human samples (means 47–51%; z-1.00 to -2.33, p0.16-0.01). Nasal height (47 mm) is identical to the mean for Africans (47±4 mm) and similar to Australians (48±3 mm), but distinct from all other samples (means 50–51 mm; z1.00 to -1.66). The nasal breadth of LL 1 (c32 mm) is broad and significantly different to all recent human sample means (means 24–28 mm; z2.00–3.98, p0.02-0.00006). The nasal index (breadth/height) (c71%) indicates the nasal skeleton of LL 1 to be unusually broad and highly distinct from recent humans (means 45–59%; z2.40–6.47, p0.008-<0.00001). The value for orbit height (34 mm) sits well within the range of recent humans (32–36 mm; z0.00 to -1.00), while orbit breadth (44 mm) contrasts strongly with them (means 39–41 mm; z1.49–2.50, p0.06-0.006). Orbit index (height/breadth) reinforces the relatively short (for its breadth) left orbit of LL 1 (76%), its value being significantly different to the sample means for East Asian (87±5%; z-2.20, p0.01) and Eskimo (87±5; z-2.19, p0.01). The simotic chord is small in LL 1 (4 mm), emphasising the narrowness of its nasal bones superiorly. Its value strongly distinguishing the specimen from East Asian (8±2 mm; z-2.00, p0.02), Australian (9±2 mm; z-2.50, p0.006), European (9±2 mm; z-2.50, p0.006) and African (9±3 mm; z-1.66, p0.04) samples.
The inferior length of the zygomatic bone of LL 1 (26 mm) is short and distinguishes the fossil from East Asian (35±4 mm; z1.67, p0.04), Eskimo (40±4 mm, z-3.48, p0.0003) and European (35±3 mm; z1.66, p0.04) means. Malar subtense, providing a measure of projection of the malar at its angle, is low in LL 1 (8 mm), in keeping with its broad and laterally flared zygomatics. Its value is significantly different to means for the East Asian (12±2 mm; z-2.00, p0.02) and Eskimo (12±2 mm; z-1.99, p0.02) samples.
Specimen MLDG 1704 can be compared with mean values for five measurements (Tables 12–14). Bistephanic breadth (114 mm) lies within the range of recent humans (means 101–116 mm), but its value is significantly different to the Eskimo (101±7 mm; z1.85, p0.03) and Australian (102±7 mm; z1.71, p0.04) means. Maximum frontal breadth (125 mm) is also wide in MLDG 1704 and distinguished from the means of recent humans (means 109–115 mm; z1.00–3.73, p0.15-0.0008). Bifrontal breadth (107 mm) is characterised by statistically significant values when compared with all recent human samples (means 96–100 mm; z2.20 to -3.50, p0.01-0.0003). The frontal chord of MLDG 1704 is comparatively long (116 mm), but sits within the range of recent humans (means 108–110 mm; z1.00–1.60). The parietal chord is short (107 mm), but sits comfortably within the recent human range (110–114 mm; z-0.43 to -1.00). Finally, the ratio parietal/frontal chord in LL 1 is low (92%). Its value is distant from the means of most recent humans samples (non-Australian means 98–102 mm; z-1.00 to -1.66, p0.15-0.05), being significantly different to the Australian mean (105±6 mm; z-2.16, p0.01).
A 3D virtual endocast was rendered from CT-scans of MLDG 1704 (Figure 11A–D; Figures S1, S2, S3, S4). Measurements of the frontal and parietal lobes were made and are compared in Table 15. They reinforce the visual impression of modern frontal lobes, which are long (86 mm), broad (121 mm) and tall (92 mm), being most like EUEHS (breadth: 120±8 mm, z0.11; height: 100±6 mm, z-0.15; chord length: 90±7 mm, z-0.52). Compared to recent East Asians, its frontal lobe is very long. The Maludong endocast is broader and taller than the Chinese Pleistocene H. sapiens cranium from Liujiang (breadth 115 mm, height 95 mm), and much broader than the endocast of the late Upper Pleistocene Japanese Minatogawa I cranium (112 mm). Its frontal lobe is, however, very distinct from the endocast of the H. rhodesiensis Kabwe cranium (breadth 108 mm, height 88 mm, chord 78 mm), broader and longer than NEAND endocasts (breadth 107 mm, chord 82 mm) and broader, longer and taller than ERECT (breadth: 99±8 mm; z2.64, p0.01; height: 74±11 mm; 2.18, p0.02; chord: 76±6 mm; z1.60).
Figure 11. Virtual endocast of MLDG 1704.
Left panel: (A) left lateral aspect, (B) superior aspect, (C) anterior aspect, and (D) posterior aspect. Right panel: (E) plot of frontal breadth versus frontal height, and (F) plot of frontal chord versus parietal chord (Gray star = MLDG 1704; ellipses are ranges for samples; Chinese = recent Chinese; Japanese = recent Japanese; Kab = Kabwe; Liu = Liujiang; Min 1 = Minatogawa 1; Nea = Neandertal Pred = Predmost; Zkd = Zhoukoudian).
Table 15. Endocast chord measurements (mm) compared (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t015
In contrast, the parietal lobes of MLDG 1704 are very short (99 mm), contrasting with the long parietal lobes of EUEHS (122±7 mm; z-3.00, p0.01), recent Chinese (106±4 mm; z-1.72, p0.04) and recent Japanese (107±7 mm; z-1.13). The parietal chord length for NEAND is also moderate (106 mm), like Liujiang (107 mm) and Minatogawa 1 (103 mm). While the parietal lobes of MLDG 1704 are short, much shorter even than Kabwe (104 mm), they are longer than ERECT (87±7 mm, z1.64).
Figure 11E is a bivariate plot of the breadth of the frontal lobes versus frontal height. It confirms the modern size and shape of the frontal of MLDG 1704, its value sitting well within the range of EUEHS (i.e. Predmost crania) and recent Japanese. Figure 11F compares frontal chord and parietal chord dimensions of the endocast and shows MLDG 1704 to be just within the range of recent Chinese, outside of the range of fossil H. sapiens, and very close to the ERECT specimen Zhoukoudian 10.
Table 16 compares a range of commonly employed mandibular characters and Table 17 body metrics for distinguishing among later Pleistocene hominins. While the symphyseal region of LL 1 has been damaged, in our judgement, it would probably have possessed a chin of Rank 3 . The chin of MLDG 1706 is Rank 3 , and while relatively common among Eurasian early H. sapiens (29.2–49.5%), the Chinese Tianyaun 1 and Zhirendong 3 mandibles possess Rank 4 chins. Specimens LL 1 and MLDG 1706 lack a vertical keel and lateral tubercles, features which form the major components of the modern human ‘inverted-T’ form chin . In inferior view, the anterior border of the body (beneath the symphysis) is rounded in both LL 1 and MLDG 1706, more like the condition seen in archaic hominins . The mental foramen is located below P4/M1 in LL 1 and MLDG 1706. Location of this foramen mesial to M1 is characteristic of early H. sapiens (88–100% presence versus 12.2% NEAND). Mandibular foramen bridging is absent in MLDG 1679, but present in MLDG 1706 (cannot be scored on LL 1). Absence of bridging is common in NEAND (57.1% presence), but rare in Eurasian early H. sapiens (0–7% presence).
Table 16. Mandibular body traits compared.¶doi:10.1371/journal.pone.0031918.t016
Table 17. Mandibular body measurements compared (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t017
Both Maludong mandibles show asymmetry of the mandibular notch. However, the coronoid process of MLDG 1679 is disproportionately large, a feature common among NEAND, while in MLDG 1706 it is greatly reduced, the H. sapiens condition. In LL 1, the coronoid process is large, but its proportions cannot be assessed owing to an absence of the notch and condylar process. Specimens LL 1 and MLDG 1679 possess a retromolar space (M3 is uncovered ), a common characteristic of NEAND (presence: 75%, versus 32.9–40% in early H. sapiens). In MLDG 1706, the M3 is partially covered; scored here as absence of a retromolar space. While the medial pterygoid attachment area is strongly scarred in both Maludong mandibles, they lack a prominent superior pterygoid tubercle (present: NEAND 81.2%, Eurasian early H. sapiens 10–76.7%). Finally, the crest of the mandibular notch meets the condyle laterally in MLDG 1679, but it is more medially located in MLDG 1706. Medial placement of the crest is found frequently in NEAND (63% presence, versus 100% absence in Western and European H. sapiens) and characterises the Dar-es-Soltane 5 mandible with its apparent archaic affinities , .
Internally, the alveolar plane of LL 1 and MLDG 1706 is posteriorly inclined and the transverse tori are thickened. This is a common feature among archaic later Pleistocene hominins such as Témara 1 (North Africa), but is largely absent from early H. sapiens . Externally, the symphysis is somewhat undercut in lateral aspect, and its anterior symphyseal angle is low (77°), a value closest to NEAND (80.8±7.3°; z-0.51) and the Témara 1 mandible (80°). In contrast, Pleistocene H. sapiens angles are more acute (means 86.6–96.5°; z-1.34 to -3.02), as seen also in the East Asian mandibles Tianyuan 1 (~96°) and Zhirendong 3 (91°). Body height (26.9 mm) and thickness (13.3 mm) at the level of the mental foramen in MLDG 1706 are comparatively low, showing the specimen to be similar to modern humans in its size. Its body height sits just outside of the range of Pleistocene East Asian H. sapiens mandibles (range 27.4–33.7 mm), but body thickness is comfortably within their range (11.3–14.4 mm). Body height (28 mm) and thickness (14 mm) measured slightly posterior to the mental foramen in LL 1 is similar to the Maludong specimen (Table 16).
The mostly well preserved, but worn, dental crowns of LL 1 and MLDG 1706 (Figure 6–7), and an isolated maxillary third molar (MLDG 1747: Figure 12), also reveal important information about their morphology and affinities. Buccolingual (BL) crown diameters and descriptive statistics for comparative samples are provided in Table 18 (mandibular dentition) and Table 19 (maxillary dentition).
Figure 12. Isolated M3 – specimen MLDG 1747 (scale bar = 1 cm) exhibiting marked taurodontism.doi:10.1371/journal.pone.0031918.g012
Table 18. Comparison of mandibular dental crown buccolingual diameters (mm) (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t018
Table 19. Comparison of maxillary dental crown buccolingual diameters (mm) (significant z-scores in bold).¶doi:10.1371/journal.pone.0031918.t019
The LL 1 I2 crown (6.7 mm) is narrow, its value sitting well within the range of comparative samples except NEAND with their broad incisors (H. sapiens means 6.9–7.2 mm; z-0.20 to -0.95; NEAND 7.7±0.5; z-1.97, p0.02; ERECT 7.1±0.5 mm; z-0.77). The mandibular canine crowns of LL 1 are also small (8.4/7.6 mm), and while not significantly different to any comparative sample mean, its BL diameter is closest to EAEHS (8.3±0.5 mm; z-0.56) and a Middle Palaeolithic H. sapiens sample (8.3±0.8 mm; z-0.36). In contrast, its P3 BL diameters (9.3/9.4 mm) are large like NEAND (9.0±0.7; z0.56) and ERECT (10.0±0.6 mm; z-0.97). Its P3 crown width is significantly different to mean values for EAEHS (8.4±0.1 mm; z-9.13, p0.0003) and a Western Middle Upper Palaeolithic Human sample (8.5±0.5; z-1.75, p0.04). The M2 crown of MLDG 1679 is broad (11.9 mm), but its value is not significantly different to comparative sample means (11.0–12.8 mm; although it is approaching significance for EAEHS z1.87, p0.05). Mandibular M3 crown BL diameters for LL 1 (10.7/10.3 mm) and MLDG 1679 (11.6 mm) are moderate to large. The crown of the former specimen is not significantly larger than comparative means (10.4–11.5 mm; z-0.23 to -0.88), while the latter is distinct from EAEHS (10.4±0.4 mm; z2.81, p0.01).
The measurable maxillary crowns of LL 1 are comparatively broad. Its P4 BL (11.0 mm) is most like ERECT (11.5±1.0 mm; z-0.49, p0.31) and is distinct from H. sapiens (Qafzeh-Skhul 10.2±0.8 mm; z0.95; Upper Palaeolithic H. sapiens 9.9±0.6 mm; z1.80, p0.04) and NEAND (10.0±0.7 mm; z1.40). In contrast, its M1 crown is narrow (11.7 mm), and while its value is well within the range of all comparative samples, it is closest to the NEAND mean (12.0±0.8; z-037). The BL diameter of an isolated M3 MLDG 1747 (12.5 mm) is comparatively large, but sits within the range of all samples listed in Table 19, being equally close to the Qafzeh-Skhul (11.7±0.6; z0.42) and NEAND (11.9±1.4; z0.42) means.
Measurements made on CT-scans of the in situ M3 of MLDG 1679 (not given) indicate that this tooth is taurodont (Taurodontism index  26.1%, or hypotaurodont). Additionally, MLDG 1747 is also taurodont (Figure 12), its three roots being fused for most of their course. Taurodontism is rare among recent and EUEHS humans –, but is commonly considered a distinguishing feature of NEAND –.