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Apidima Cave Fossils – Earliest Evidence of Homo Sapiens in Eurasia

In the late 1970s 2 fossilised human crania were found (Apidima 1 and Apidima 2) in Apidima Cave, southern Greece, though as a result of heir incomplete nature, taphonomic distortion, and lack of archaeological and chronology they have remained enigmatic. In this study Harvati et al. virtually reconstruct both crania, provide detailed comparative descriptions and analyses and use U-series radiometric methods to date them. Apidima has been dated to more than 170 ka and has a morphological pattern that is like Neanderthals. Apidima 1, in contrast, dates to more than 210 ka and presents a mixture of modern human and primitive features. It is suggested by these 2 human groups from the late Middle Pleistocene were present at this site – an early Homo sapiens population, followed by a Neanderthal population. The findings of this study support multiple dispersals of early modern humans out of Africa, and highlight the complex demographic processes that were a characteristic of human evolution in the Pleistocene and a modern human presence in southeast Europe.

It is considered that southeast Europe was a major corridor for dispersal, as well as on of the principal glacial refugia in the European Mediterranean region (Dennell et al., 2011; Tourloukis & Harvati, 2018; Roksandic et al., 2018). The human fossil record in this region, as such, has been proposed to be more diverse than areas of Europe that are more isolated and less hospitable, which reflects the complexities of repeated dispersals, late survivals and admixture of human groups (Dennell et al., 2011; Tourloukis & Harvati, 2018; Roksandic et al., 2018). The result of palaeoanthropological finds from the Balkans being relatively scarce, this hypothesis has been difficult to test. The 2 fossil human crania recovered from Apidima Mani, (southern Greece) (Pitsois, 1999), are among the most important finds from the region, but have remained little known. In this study the U-series dating method was used in order to elucidate their chronology and history of dispersion. Both specimens were virtually reconstructed, and corrected for taphonomic damage, and detailed comparative description and geometric morphometric analyses were conducted.

Chronology

According to Harvati et al. the Apidima specimens were discovered in a block of breccia that was wedged high between the walls of the Apidima cave A (Tourloukis & Harvati, 2018; Pitsios, 1999; Bartsiokas et al., 2017; Harvati, Stringer & Karkanas, 2011), during research by the Museum of Anthropology, School of Medicine, National Kapodistrian University of Athens, which began in 1978. Their geological age has been difficult to assess due to the lack of associated context. The estimate of geological age proved to be inconclusive due to being difficult to assess, as a result of the lack of associated context (Liritzis & Maniatis, 1989). A Middle-Late Pleistocene is, however, indicated, and a bracket between 190 and 100 Ka (thousand years ago) has been proposed as the mist likely period for deposition of the “skull breccia” (Havarti, Stringer & Karkanas, 2011; Rondoyanni, Mettos & Georgiou, 1995). A minimum age of about 160 Ka by U-series dating of the Apidima 2 bone fragment, was calculated by previous work which suggests the time of deposition was probably about 190 ka (transition between marine isotope stage  (MIS) 7 and MIS 6) (Bartsiokas et al., 2017). 3 samples from the ’skull breccia’ which had been selected from fragments, that had been produced when cleaning the matrix, were analysed by Harvati et al. Included among these were fragments of human bones that (subsamples 3720A and B of Apidima 2; and subsamples 3754 and 3755 of Apidima 1), as well as 4 unidentified bone subsamples (3757 A-C and 3758). It was shown by their analysis that both crania are older than the solidification of the matrix, which occurred about 150 ka. Apidima 1 acquired its uranium from an environment that was considerably different from that of Apidima 2, in spite of their depositional proximity, in an accumulation event in MIS 7 (about 210 ka), whereas for Apidima 2 the uranium-uptake process took place in MIS 6 (about 170 ka). Therefore, the crania and associated bones was probably trapped on a surface of talus cone, Apidima 1 about 210 ka and Apidima 2 about 170 ka, and were transported to their final resting position prior to the cementation and solidification of the sedimentary matrix about 140 ka.

Description and comparative analyses

The more complete and better known of the crania is Apidima 2, and it a previously been considered to be an early Neanderthal or Homo heidelbergensis (Pitsois, 1999; Bartsiokas et al., 2017; Harvati, Stringer & Karkanas, 2011; Coutselin, Dritsas & Pitsios, 1991). This skull has an almost complete face and most of the vault, though it is distorted taphonomically. 4 virtual manual reconstructions were produced by 2 observers, which followed 2 different criteria from a CT scan of the original specimen.

The posterior cranium is preserved in Apidima 1. There is no distortion; therefore its virtual reconstruction consisted of mirror-imaging the side that is preserved better. It has been assumed to share the same taxonomic attribution as Apidima 2 (e.g., see a previously published study on the chronology of Apidima 2 (Bartsiokas et al., 2017), as to date there has not been a detailed study of Apidima 1.

Neanderthal-like features are shown by Apidima 2:

·       A continuous thick, rounded supraorbital torus that has no break between the glabellar, orbital and lateral regions;

·       Lack of a break in plane between the glabellar and lateral regions in superior view;

·       An anterior position of the nasal root;

·       Inflated infraorbital region; bi-level morphology of the inferior nasal margin; and

·       Rounded en bombe cranial profile in posterior view.

It is aligned with Neanderthals by most standard measurements. Comparative geometric morphometric analyses of the face and neurocranium (analyses 1 and 2) were conducted by Harvati et al., treating the Apidima 2 reconstructions and their mean configuration as separate individuals, projected into the principal component analysis (PCA). The reconstructions plotted closest to Neanderthals or between Neanderthals and Eurasians from the Middle Pleistocene (MPEs). They were classified by linear discriminant analysis as Neanderthal (with the exception of reconstruction 2, which was classified as MPE only is analysis 1). In Apidima 2 the overall shape of the reconstruction mean was closer to Gibraltar in Procrustes distance in the face and the face and to Spy 1 in the neurocranium, both of which are Neanderthals.

Apidima, in contrast, does not have features of Neanderthals; it’s linear measurements falling mainly in the region of overlap between taxa. It lacks the rounded en bombe in posterior view of a Neanderthal. The widest part of the Apidima 1 cranium is relatively low on the parietal walls are nearly parallel and converge only slightly upwards, a pleisomorphic morphology that is common in Homo from the Middle Pleistocene (Arsuaga et al., 2014; Stringer, 2016). It does not show the convexity of the occipital plane and lambdoid flattening associated with Neanderthal occipital ‘chignons’. Its midsagittal outline is, instead, rounded in lateral view, a feature that is considered to be derived for modern humans (Galway-Witham & Stringer, 2018). The superior nuchal lines are weak, and hove no external occipital protuberance. The occipital bone of not angled steeply and lacks a thick occipital torus, which contrasts with some specimens from the Middle Pleistocene. There is a small, very faint depression above the inion (length approximately 12 mm; height, approximately 4.55 mm). For Neanderthals, the suprainiac fossae are considered to be derived, and similar depressions are present among modern humans and in some early H. sapiens from Africa (Balzeau & Rougier, 2010). The typical combination of features in Neanderthals is not present in the Apidima 1 depression. It is much smaller (Verna et al., 2010) and less marked even than the ‘incipient’ suprainiac fossae of MPE specimens from Swanscombe and Sima del los Huesos, and in size it is closest to the small supranuchal depression of the Eliye Springs cranium, a Middle Pleistocene African (MPA) (Brӓuer, 1986). Therefore, Apidima 1 lacks the derived Neanderthal morphology, showing instead a combination of ancestral and derived modern human features.

A geometric morphometric analysis was conducted by Harvati et al. of the Apidima neurocranium and its midsaggital profile (analysis 3 and 4). In the PCAs Apidima clearly clustered with H. sapiens in both analyses and linear discriminant analyses (posterior probability 100% and 93.4% in analyses 3 and 4, respectively) classified it as H. sapiens. It was closest to Nazlet Khater 2 in its overall shape (analysis 3) and Doliní Vĕstonice 3 (analysis 4); both of which are modern humans. A neurocranial shape index was calculated by Harvati et al. that was based on the dataset from analysis 3 following a previous study (Gunz et al., 2019), using Neanderthal and a modern African sample (n = 15; Methods) and projecting Apidima 1 and all other specimens onto this axis. In this index fossil and recent H. sapiens are clearly separated from all archaic samples. Apidima fell within the range of fossil H. sapiens and just outside that of modern Africans, away from Neanderthals and samples from the Middle Pleistocene.

It is notable that the MPA crania from Jebel Irhoud, Morocco – which are considered to be early representatives of the H. sapiens lineage (Hublin et al., 2017) plotted with Neanderthals. A similar result was obtained by the same analysis for the midsagittal profile dataset. The Apidima specimens were compared by Harvati et al. for their common anatomy that was preserved. The cranial breadth of Apidima 2 is larger in its maximum cranial breadth, which reflects its le bombe outline in posterior view, though it is broadly similar in its bi-auricular breadth. Apidima 1 is shorter antero-posteriorly. The analysis of a restricted dataset of shared neurocranial landmarks and semilandmarks shows results that are similar to analysis 1-4. The Apidima 2 reconstructions fell with or close to Neanderthals along principal components 1 and 2 (PC1 and PC2) and were classified as Neanderthals. In overall shape their mean was closest to Saccopastore 1, which is an early Neanderthal. Apidima 1 plotted closest to the H. sapiens convex hull, was classified as H. sapiens (posterior probability 92%, and was closest to Nazlet Khater 2, which is a modern human, in Procrustes distance.

Implications for human evolution

 According to Harvati et al. a Neanderthal or early Neanderthal attribution is supported by their  assessment of overall features, linear measurements and shape analyses of the face and neurocranium of Apidima 2, and this is consistent with it chronological age of about 170 ka under the ‘accretion hypothesis’ (Hublin, 2009). Apidima 1, in contrast, lacks derived Neanderthal features, in spite of postdating the establishment distinct Neanderthal morphology (Hublin, 2009). It exhibits, instead, a rounded posterior cranium, which is considered to be derived for modern humans (Galway-Witham & Springer, 2018). Ontogenetic age, sexual dimorphism, cannot explain this morphology, or interindividual variability cannot explain this morphology. These factors should not result in the complete lack of occipital features (Caspari, 2006; Arsuaga et al., 1997), nor in the presence of derived human traits, though they might produce attenuated Neanderthal characteristics. Apidima 1 might be hypothesised to represent an early stage of Neanderthal lineage, when facial morphology was established, though derived features of the posterior cranium were not (Bartsiokas et al., 2017; Arsuaga et al., 2014). Apidima 1 differs, however, not only from Neanderthals that were similarly dated (e.g., Saccopastore and Biache-St-Vaast, but also from earlier specimens from Sima de los Huesos, Swanscombe and Reilingen, which exhibit occipital features that are Neanderthal-like (Hublin, 2009). It also differs from MPE specimens such as Petralona (Northern Greece) or Ceprano, which have angulated occipitals and thickened tori; features that are not present in Apidima 1. The Steinheim MPE specimen is heavily damaged (having undergone multidirectional distortions and erosion) appears relatively rounded in lateral view which makes its morphology and taxonomic attribution uncertain (Balzeau & Rougier, 2010).

Therefore, Apidima 1 does not fit in the ‘accretional’ scheme of Neanderthal evolution (Hublin, 2009), which has been proposed as the main explanatory model of human evolution in Europe. Rather, the combination of ancestral and derived human features and overall shape are consistent with a taxonomic attribution to early modern humans. It documents the earliest known presence of H. sapiens in Eurasia, to the knowledge of Harvati et al., if this interpretation is correct, which indicates that early modern humans first dispersed out of Africa much earlier, and reached much further, than has previously been thought. Contact with the Neanderthal lineage may also be suggested to have occurred during the Middle Pleistocene, as has been postulated from evidence of ancient DNA (Posth et al., 2017). Together, it is suggested by the Apidima cranium that there was a complex pattern of population dispersal and possible replacement for southern Greece that is not dissimilar to that which has been proposed for the Levant (Mercer et al., 1993; Hershkovitz et al., 2018; Stringer & Galway, 2018), which is a potential source area for the population that is represented by Apidima 1. In such a scenario, Neanderthals replaced early modern humans who were present in the region in the late Middle Pleistocene, and the subsequent presence of Neanderthals in southern Greece is well documented (Harvati, Panagopoulou & Karkanas, 2003; Harvati et al., 2013; Tourloukis et al., 2016). In the Upper Palaeolithic the Neanderthals were replaced by modern humans whose earliest appearance in the region is documented by Upper Palaeolithic lithic industries (Elefanti, Panogopoulou & Karkanas, 2008; Douka et al., 2011; Lowe et al., 2012) dates to about 40 ka. The scarcity of knowledge of the fossil record of humans in southern Europe and the importance of this region in understanding human evolution of humans and the dispersals of modern humans is highlighted by the results of Harvati et al.

According to Harvati et al., the noted the publication of a new study (De Lumley, 2019) as they completed this paper on the partial crania of Apidima 1 and Apidima 2. The authors of that study conclude that the 2 crania represent a transitional population between European Homo erectus and Neanderthals, a conclusion that according to Harvati et al. is not supported by their own study that they say is a more comprehensive analysis than the new study (De Lumley, 2019).

Harvati, K., et al. (2019). "Apidima Cave fossils provide earliest evidence of Homo sapiens in Eurasia." Nature, Volume 571(7766): 500-504.