Description and univariate comparison

MLDG 1678 consists of a 175 mm long proximal segment of an adult right femur broken slightly inferior to the MS region (Fig 1). It preserves the greater trochanter and a mostly complete neck. An isolated partial femoral head was also recovered from Maludong (MLDG 1717), but it is unclear whether is belongs to MLDG 1678. The biomechanical neck length is long, and we estimate that it must originally have measured ~70 mm; assuming MLDG 1717 provides a reasonable indication of the size of the head of MLDG 1678. Thus, it would have resembled LPHO, MPHO and NEAN, with their long biomechanical necks, rather than AMH (MPMH and EULU), with their short ones [37,38]. The horizontal AP diameter is ~27 mm, a value that would sit comfortably within the range of both archaic hominins and AMH [39].

Anteriorly, although the intertrochanteric line is somewhat obscured by plaster, owing to breakage in this region, it must have been faint. Buttressing of the proximal medial diaphysis can be seen in anterior, posterior and medial views, and is pronounced (Fig 1). The greater trochanter is a large [ML broad and superoinferiorly (SI) tall] structure that bulges beyond the lateral wall of the diaphysis. The superior surface of the neck is partly missing along its medial course, and what remains of it has been partially obscured by plaster during restoration of the specimen (Fig 1). Posteriorly, the proximal diaphysis is dominated by a massive lesser trochanter, situated on the approximate mid-plane of the shaft, and projecting slightly medially (Fig 1). CT-scan slices also show the massive size of this feature, which is composed almost entirely of cancellous bone (Fig 1). In AMH, the lesser trochanter most frequently faces strongly medially. While anteversion of the femur resulting in a more posteriorly located lesser trochanter is seen in recent humans [40], the combination of its posterior orientation and massive size in MLDG 1678 would be rare (if present at all) in AMH.

The pectineal line is a crest-like buttress running SI along the median plane of the posterior diaphysis from the base of the lesser trochanter inferiorly (Fig 1). The hypotrochanteric fossa is extensive SI and ML, merging across a wide area with the gluteal crest (S1 Fig), rather than being a distinct and narrow fossa that distinguishes the lateral wall of the femur from the weakly developed proximo-lateral buttress, as is typically seen when this feature is developed in AMH femora. It closely resembles the condition seen in NEAN in its morphology, which is probably autapomorphic for this group [41]. The intertrochanteric crest is mostly missing (not preserved), and is moderately developed inferiorly. The quadrate tubercle is not preserved.

In Table 1 we present metric data for MLDG 1678. Values for the Maludong femur are compared with summary statistics for comparative samples in Figs 2 and 3. At the ST level, the AP diameter failed to show significant median differences among groups (Fig 2A). The value for MLDG 1678 is small (22.2 mm), being closest to the LPHO median, but sits within 1.5IQR of all samples except MPMH (Fig 2A). The ML diameter was also characterised by an absence of significant median differences (Fig 2B). MLDG 1678 possesses a small ML diameter (28.3 mm), again most similar to the LPHO median, but outside of the small 1.5IQR of this sample, and within 1.5IQR of all others (Fig 2B). TA at the ST level lacked significance when a Kruskal-Wallis test was performed, but post hoc Mann-Whitney tests revealed a significant difference between NEAN and EULU medians (p0.038). TA for MLDG 1678 (493.4 mm2) is unsurprisingly small, and once again is most similar to the LPHO median. However, its value sits with 1.5IQR of all samples except NEAN (Fig 2C). Median differences for CA also lacked significance with a Kruskal-Wallis test, but post hoc Mann-Whitney tests revealed a significant difference between LPHO and NEAN (p0.019), and NEAN and EULU (p0.032). CA for the Maludong femur (322.6 mm2) is also very small, again being most similar to the LPHO median, and with 1.5IQR only of LPHO and EULU (Fig 2D).

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larger image TIFF original image Download: Fig 2. Scatterplots comparing sample medians for subtrochanteric (ST) variables, neck-shaft angle and reconstructed body mass: (A) Anteroposterior (AP) diameter (mm). (B) Mediolateral (ML) diameter (mm). (C) Total area (TA: mm2). (D) Cortical area (CA: mm2). (E) %-Cortical area (%-CA). (F) Platymeric index (%). (G) Neck-shaft angle (°). (H) Reconstructed body mass (kg). (Error bars = 95% confidence interval of median [dark] and 1.5 x interquartile range [light]; Abbreviations: LPHO = Lower Pleistocene Homo; MPHO = Middle Pleistocene Homo; NEAN = Neanderthals; MPMH = Middle Pleistocene Modern Humans; EULU = Early Upper-Late Upper Palaeolithic humans [see S1 Table]). https://doi.org/10.1371/journal.pone.0143332.g002

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larger image TIFF original image Download: Fig 3. Scatterplots comparing sample medians for mid-shaft (MS) variables, size-adjusted variables and mid-shaft/subtrochanteric area index: (A) Anteroposterior (AP) diameter (mm). (B) Mediolateral (ML) diameter (mm). (C) Total area (TA: mm2). (D) Cortical area (CA: mm2). (E) %-Cortical area (%-CA). (F) Size-adjusted total area. (G) Size-adjusted cortical area. (H) Pilastric index (%). (I) Mid-shaft/subtrochanteric (MS/ST) area index (%). (Error bars = 95% confidence interval of median [dark] and 1.5 x interquartile range [light]; Abbreviations: LPHO = Lower Pleistocene Homo; MPHO = Middle Pleistocene Homo; NEAN = Neanderthals; MPMH = Middle Pleistocene Modern Humans; EULU = Early Upper-Late Upper Palaeolithic humans [see S1 Table]). https://doi.org/10.1371/journal.pone.0143332.g003

For the index %-CA (CA/TA x 100), median differences were found to be non-significant. Moreover, the %-CA for MLDG 1678 (65.4%) was most similar to the LPHO and EULU medians, but sat within 1.5IQR of all samples (Fig 2E). In terms of the platymeric index, a Kruskal-Wallis test revealed significant differences among sample medians (p0.040): post hoc comparisons revealed significant differences between MPHO and NEAN (p0.016), and NEAN and EULU (p0.014) (Fig 2F). With a high platymeric index (78.4%), the shaft of the Maludong femur is reasonably circular at the ST level, being most similar to the median for NEAN (Fig 2F). While the neck-shaft angle also lacked significance with a Kruskal-Wallis test, post hoc Mann-Whitney tests revealed significant median differences between MPHO and MPMH (p0.035), NEAN and MPMH (p0.008), and NEAN and EULU (p0.035) (Fig 2G). The neck-shaft angle of MLDG 1678 is estimated to lie within the narrow range of 116–120°, and taking the median of this (c118°), it was found to be within 1.5IQR of MPHO and EULU, and equal to the negative 1.5IQR value for NEAN (Fig 2G).

We reconstructed body mass for MLDG 1678 to be low (50 kg), a value very similar to the LPHO and MPHO medians, but within 1.5IQR of all samples; although, it is clearly small by Pleistocene AMH standards (Fig 2H). Kruskal-Wallis and post hoc Mann-Whitney tests failed to reveal any significant differences among sample medians.

The MS AP diameter was characterised by significant median differences (Kruskal Wallis: p0.002). Specifically, post hoc tests revealed important differences between all archaic samples and MPMH (Mann Whitney: p0.022–0.0067), between LPHO and MPHO (p0.012), and LPHO and EULU (p0.011) (Fig 3A). Thus, this variable serves to distinguish archaic femora from Pleistocene AMH ones. The MLDG 1678 value is small (24.7 mm) and found to be most similar to the medians of LPHO and MPHO (Fig 3A). It did, however, sit within 1.5IQR of all samples except MPMH (Fig 3A). The ML diameter was also found to show significant differences among sample medians (p0.018), only this time EULU was distinguishable from MPHO and NEAN (p0.024 & p0.002) (Fig 3B). The Maludong ML diameter (22.9 mm) is very small and was not especially similar to any sample median, but did lie within 1.5IQR of LPHO and EULU (Fig 3B). As at the MS region, TA lacked significance in a Kruskal-Wallis test. The small area for MLDG 1678 (444.2 mm2) was most similar to the LPHO median, but did sit within 1.5IQR of all samples (Fig 3C). While MS CA also lacked overall significance, post hoc Mann-Whitney tests revealed a significant difference between NEAN and EULU medians (p0.039) (Fig 3D). The Maludong femur CA is very small (337.0 mm2), but sat within 1.5IQR of all samples except MPMH (Fig 3D). %-CA was found to exhibit significant median differences among samples (p0.005), with post hoc tests showing this to be the case between LPHO and MPHO (p0.025), MPHO and NEAN (p0.049), MPHO and MPMH (p0.009), and MPHO and EULU (p0.001) (Fig 3E). %-CA in MLDG 1678 (75.9%) was virtually identical to the LPHO median, but it did sit within 1.5IQR of all samples (Fig 3E).

We also calculated size-adjusted TA and CA using reconstructed body mass. Size-adjusted TA lacked overall significance, but post hoc Mann-Whitney tests revealed a significant difference between MPMH and EULU (p0.016) (Fig 3F). The very small value for MLDG 1678 (8.8) was most similar to the LPHO median, although, not especially close to it. Its value did, however, sit within 1.5IQR of all samples except NEAN (Fig 3F). Significant median differences were found for size-adjusted CA (p0.044), with post hoc tests showing important differences between MPHO and EULU (p0.029), and MPMH and EULU (p0.037) (Fig 3G). The small value for the Maludong femur (6.7) was most similar to the EULU median, but it did lie within 1.5IQR of all samples except MPMH (Fig 3G).

The pilastric index was found to strongly distinguish archaic hominin from AMH femora (Kruskal Wallis: p7.4E-07) (Fig 3H). Mann Whitney tests showed that median differences were significant between all archaic and AMH medians: archaic versus MPMH (p0.001–0.0003) and archaic versus EULU (p0.001–2.07E-05). The Maludong femur (107.8%) was found to be intermediate between archaic and AMH medians, but within 1.5IQR of all samples (Fig 3H). Finally, we also calculated an index comparing the MS TA and ST TA (MS TA/ST TA x 100) and found median differences to be significant (Kruskal-Wallis: p0.043) (Fig 3I). Mann-Whitney tests revealed that MPMH typically possess significantly thicker shafts at the ST level compared with archaic femora (p0.033–0.023), but not EULU (Fig 3I). The MS/ST area index for MLDG 1678 (90%) was most similar to the median for EULU, but again sat within 1.5IQR of all samples (Fig 3I).