The effect of ontogeny on estimates of KNM-WT 15000's adult body size

Quantifying the relationship between bone and soft tissue measures within the rhesus macaques of Cayo Santiago

OBJECTIVES

Interpretations of the primate and human fossil record often rely on the estimation of somatic dimensions from bony measures. Both somatic and skeletal variation have been used to assess how primates respond to environmental change. However, it is unclear how well skeletal variation matches and predicts soft tissue. Here, we empirically test the relationship between tissues by comparing somatic and skeletal measures using paired measures of pre- and post-mortem rhesus macaques from Cayo Santiago, Puerto Rico.

MATERIALS AND METHODS

Somatic measurements were matched with skeletal dimensions from 105 rhesus macaque individuals to investigate paired signals of variation (i.e., coefficients of variation, sexual dimorphism) and bivariate codependence (reduced major axis regression) in measures of: (1) limb length; (2) joint breadth; and (3) limb circumference. Predictive models for the estimation of soft tissue dimensions from skeletons were built from Ordinary Least Squares regressions.

RESULTS

Somatic and skeletal measurements showed statistically equivalent coefficients of variation and sexual dimorphism as well as high epiphyses-present ordinary least square (OLS) correlations in limb lengths (R2 >0.78, 0.82), joint breadths (R2 >0.74, 0.83) and, to a lesser extent, limb circumference (R2 >0.53, 0.68).

CONCLUSION

Skeletal measurements are good substitutions for somatic values based on population signals of variation. OLS regressions indicate that skeletal correlates are highly predictive of somatic dimensions. The protocols and regression equations established here provide a basis for reliable reconstruction of somatic dimension from catarrhine fossils and validate our ability to compare or combine results of studies based on population data of either hard or soft tissue proxies.

The earliest Pleistocene record of a large-bodied hominin from the Levant supports two out-of-Africa dispersal events

The paucity of early Pleistocene hominin fossils in Eurasia hinders an in-depth discussion on their paleobiology and paleoecology. Here we report on the earliest large-bodied hominin remains from the Levantine corridor: a juvenile vertebra (UB 10749) from the early Pleistocene site of 'Ubeidiya, Israel, discovered during a reanalysis of the faunal remains. UB 10749 is a complete lower lumbar vertebral body, with morphological characteristics consistent with Homo sp. Our analysis indicates that UB-10749 was a 6- to 12-year-old child at death, displaying delayed ossification pattern compared with modern humans. Its predicted adult size is comparable to other early Pleistocene large-bodied hominins from Africa. Paleobiological differences between UB 10749 and other early Eurasian hominins supports at least two distinct out-of-Africa dispersal events. This observation corresponds with variants of lithic traditions (Oldowan; Acheulian) as well as various ecological niches across early Pleistocene sites in Eurasia.

Late subadult ontogeny and adult aging of the human thorax reveals divergent growth trajectories between sexes

Sexual dimorphism is an important feature of adult thorax morphology, but when and how sex-related differences in the ribcage arise during ontogeny is poorly known. Previous research proposed that sex-related size differences in the nasal region arise during puberty. Therefore, we explore whether ribcage sexual dimorphism also arises at that time and whether this sexual dimorphism is maintained until old age. We measured 526 (semi)landmarks on 80 CT-based human ribcage reconstructions, on individuals ranging from 7 to 65 year-old. The 3D coordinates were submitted to the Procrustes superimposition and analyzed. Our results show that the trajectories of thorax size and shape between sexes diverge at around 12 years of age, and continue slightly diverging until old age. The differential ontogenetic trends cause adult male ribcages to become deeper, shorter, and wider than female. Our results are consistent with the evidence from the cranial respiratory system, with the development of sexual dimorphism probably related to changes in body composition during puberty combined with changes in the reproductive system.

Reevaluation of the body mass estimate for the KNM-ER 5428 Homo erectus talus

OBJECTIVES

In this study, we reexamined the body mass estimate for the Homo erectus specimen KNM-ER 5428 based on talus dimensions. Previous estimates of >90 kg for this fossil are large in comparison to body mass estimates for other H. erectus specimens.

MATERIALS AND METHODS

The study sample consisted of tali and femora of 132 modern cadaver males from a documented body mass skeletal collection. We recorded the talus trochlear mediolateral (TTML) breadth and femoral head diameter (FHD) for each modern human specimen, and obtained KNM-ER 5428's TTML values from the literature. We developed regression formulae based on TTML using the body mass estimated from FHD for the entire human sample and for known body masses from a normal-BMI subsample, and then used these formulae to calculate body mass for KNM-ER 5428. In addition, we examined the range of body masses for individuals with TTML measurements comparable to KNM-ER 5428.

RESULTS

The body masses of normal-BMI individuals with a TTML ≥32.3 mm (the smaller of the two fossil measurements from the literature) ranged between 60.3 and 86.2 kg and averaged 72.3 kg. The body masses of normal-BMI individuals with a TTML ≥33.7 mm (the larger measurement) ranged between 63.5 and 86.2 kg with a mean of 73.6 kg. The correlations between TTML and body mass are moderate. Revised body mass point estimates for KNM-ER 5428 ranged between 69.2 and 81.6 kg based on TTML, and average 70.5 and 76.0 kg.

DISCUSSION

Results suggest previously published body mass estimates of KNM-ER 5428's are too large. Its body mass was likely between 70 and 76 kg rather than >90 kg.