Overall, both the geometric morphometric analysis and the scoring of morphological features included in our phenetic study support the uniqueness of H. heidelbergensis as a species that was distributed on a wide geographical horizon, including Eurasia and Africa; at the same time, it was a rather polymorphic taxon and was probably ancestral to the origin of both the Neandertals and our own species, H. sapiens.
The DFA based on geometric morphometrics and Procrustes analysis () distinguishes between the three pre-defined groups: Early Pleistocene humans (H. habilis, D2280 and D2700 from Dmanisi, H. ergaster, H. erectus), Neandertals (H. neanderthalensis), and modern humans (H. sapiens). Along the first axis (80.9% of variance), we observe an overall consistency with their respective chronologies and phylogenetic positions. The empty chronological space between the Early Pleistocene archaic sample and the more recent as well as derived groups (Neandertals and modern humans) is filled by Mid-Pleistocene specimens, including Ceprano.
However, the morphological space identified by the cranial shape of Ceprano does not show clear affinities with other Mid-Pleistocene fossils. Along the first discriminant function it appears close to the Early Pleistocene sample attributed to H. erectus
and, particularly, to Asian fossils such as Sangiran 17 (near Ceprano along the second discriminant function as well). The other Asian specimens (Mid-Pleistocene fossils from Zhoukoudian, China, and Late Pleistocene specimens from Ngandong, Java) also exhibit affinities with fossils dated to the Early Pleistocene. Despite the observed differences in shape between the Asian sample and the African fossils attributed to H. ergaster
(e.g. widening of the braincase at the stephanion
level), it is difficult to conclude whether these differences are able to distinguish Asian and African specimens as separate taxa with the widespread and highly variable taxon referred to as H. erectus
. Nevertheless, the main result from this geometric morphometrics analysis supports previous claims that Ceprano definitively displays an “erectus
-like” morphological architecture 
By contrast, other Mid-Pleistocene specimens show different morphological trends. particularly – disregarding the position of Steinheim and Jinniu Shan, which seems to reflect the important deformations affecting both these specimens 
– fossils like SH5, Petralona, Dali, and Kabwe share a similar position in the shape space, somewhat midway between H. erectus
and H. neanderthalensis
We should conclude that Ceprano is characterized by an archaic shape. At the same time, however, it shows a peculiar combination of discrete features 
, as the second part of our protocol demonstrates ().
Similarly to the previous analysis, the discrete features succeeded in identifying different taxonomic entities (). Asian and African specimens of the Early Pleistocene show regional differences, supporting the existence of two distinct taxa or, at least, two diverging evolutionary lineages: H. erectus
sensu stricto in Asia and H. ergaster
in Africa 
. The H. sapiens
group includes the Qafzeh/Skhūl sample and “pre-modern” late Mid-Pleistocene specimens from Africa (Omo II, LH18, Singa, and Jebel Irhoud 1). Although this study does not focus on Early Pleistocene Homo
or on the origin of modern humans, we note that these results support the validity of our phenetic approach.
From this analysis it is clear that Ceprano displays a unique combination of morphological features (). It shows traits that are found among Mid-Pleistocene specimens (e.g. frontal tuber weakly developed and medially positioned, supraorbital region medially concave, incomplete sulcus supraorbitalis, intermediate position of the external auditory meatus in regard to the processus zygomaticus temporalis, see, ), but also traits that are considered as derived (straight torus occipitalis transversus, medio-lateral concavity of the articular tubercle) 
. However, none of these are really Neandertal autapomorphic features, since they are widespread in Eurasia during the Middle Pleistocene. Actually, most of the Neandertal morphological features occur in the upper face of the European Mid-Pleistocene humans 
, but in Ceprano only the suborbital region can be examined and it does not show any Neandertal resemblance. Conversely, Ceprano exhibits features that are common among H. erectus
and/or H. ergaster
(e.g. torus angularis parietalis, petro-tympanic crest orientated downward, processus retromastoideus and opisthocranion coincident with inion) 
. The result of this peculiar morphology is that Ceprano clusters in our analysis with other European, African and Asian Mid-Pleistocene specimens – such as Petralona, Dali, Kabwe, Jinniu Shan, Steinheim, and SH5 – furnishing a rather plesiomorphic phenetic link among them.
Statistically significant traits that describe the Mid-Pleistocene cluster including Ceprano.
On the basis of this morphological affinity, it seems appropriate to group Ceprano with these fossils, and consider them as a single taxon. The available nomen for this putative species is H. heidelbergensis 
, whose distinctiveness stands on the retention of a number of archaic traits combined with features that are more derived and independent from any Neandertal ancestry. Especially, the morphology of the frontal bone seems to bear most of these traits (shape of supraorbital torus and occurrence of frontal tuber, in particular) 
. This conclusion is further supported by the position of the Ethiopian calvarium known as Daka in the analysis, where it emerges as part of the H. ergaster
cluster along with OH9 and other African specimens (). This result would suggest that H. ergaster
survived as a distinct species until 1 Ma, and would discard the validity of the species H. cepranensis 
, which was based on the claimed affinities between Daka and Ceprano that we did not observe. At the same time, it should be noted that the mandible AT-888 associated with the SH5 cranium from Atapuerca has been shown to share affinities with the holotype of H. heidelbergensis
: the Mauer mandible 
. Thus we can include the so-called “Ante-Neandertals” from Europe in the same taxonomical unit with other Mid-Pleistocene samples from Africa and continental Asia.
Combining the results of the two approaches of our phenetic analysis, Ceprano should be reasonably accommodated as part of a Mid-Pleistocene human taxon H. heidelbergensis, which would include European, African, and Asian specimens. Moreover, the combination of archaic and derived features exhibited by the Italian specimen represents a “node” connecting the different poles of such a polymorphic humanity. In this respect, it appears of particular interest that:
1) Ceprano shows strong morphological affinities with extra-European Mid-Pleistocene specimens, even more than with many of its European counterparts, supporting the above-mentioned conclusion of a widespread single species;
2) This morphological proximity suggests a dispersal that occurred approximately around the Early/Middle Pleistocene boundary (0.780 Ma), in Africa and Eurasia, and that is referable to a single species of derived (i.e. encephalized) humans;
3) Ceprano combines a rather primitive architecture of the braincase with derived features, thus possibly representing the ancestral (i.e. the most archaic-looking) morphotype of this taxon distributed both in Africa and Eurasia;
4) From this perspective, the morphology of Ceprano constitutes a phylogenetic “bridge” between Early Pleistocene Homo representatives and related forms (H. erectus sensu lato), and more recent and derived populations included in the species H. heidelbergensis;
5) These conclusions are also coherent with the new chronology proposed for Ceprano (ranging between 430 and 385 ka, 
), when assuming a great variability in the Middle Pleistocene of Europe, with the occurrence of, some populations or single individuals that exhibit retention of a more archaic shape while others appear more derived 
In sum, our analysis demonstrates that Ceprano, as a calvarium, could represent an appropriate “counterpart” of, the holotype of Homo heidelbergensis
(the mandible from Mauer 
), bringing together both features observed on the human samples of the Middle Pleistocene referred to this widespread species and plesiomorphic traits shared with earlier or more archaic humans.