# Revisiting the anatomy of the Florisbad hominin cranium: visualization of new internal features and observations on its supposed pathologies

Antoine Balzeau, Jiaming Hui, Victor Giolland, Sharon Holt, Frederick E Grine

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Antoine Balzeau, Jiaming Hui, Victor Giolland, Sharon Holt, Frederick E Grine. Revisiting the anatomy of the Florisbad hominin cranium: visualization of new internal features and observations on its supposed pathologies. Paleoanthropology, 2025. hal-05346946

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1 Revisiting the anatomy of the Florisbad hominin cranium:
2 visualization of new internal features and observations on its
3 supposed pathologies.

4 Running title: Inside the Florisbad calotte

5
6 Antoine Balzeau¹,², Jiaming Hui¹,³, Victor Giolland¹, Sharon Holt⁴,
7 Frederick E. Grine⁵,⁶

8 1. PaleoFED team, UMR 7194 Histoire Naturelle de l'Homme
9 Préhistorique, MNHN-CNRS-UPVD, Paris, France

10 2. Department of African Zoology, Royal Museum for Central Africa,
11 Tervuren, Belgium

12 3. Sorbonne Université, Paris, France

13 4. Florisbad Quaternary Research Station, National Museum,
14 Bloemfontein, 9301, South Africa.

15 5. Department of Anthropology, Stony Brook University, Stony Brook,
16 New York 11794 USA

17 6. Department of Anatomical Sciences, Renaissance School of Medicine,
18 Stony Brook University, Stony Brook, New York 11794 USA

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Corresponding author: Antoine Balzeau (antoine.balzeau@mnhn.fr)
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ABSTRACT

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Among the Middle Pleistocene African fossils that are central to discussions about the evolution of *Homo sapiens* is the partial cranium from Florisbad, South Africa. The fossil, dated to MIS 8 (300 – 243 ka BP), combines some primitive traits that are shared with *Homo erectus* or *H. rhodesiensis* relative to *H. neanderthalensis* and *H. sapiens*, together with derived features shared with *H. sapiens* relative to *H. erectus*. It has been proposed that the specimen suffered from pathological conditions that resulted in an asymmetric and exaggeratedly thick vault together with external and internal lesions. Such pathologies could complicate anatomical comparison and attribution of the specimen. The purpose of the present work is to re-examine the calotte and provide new information on several aspects of its anatomy. We review the purported pathological conditions of the specimen, particularly those related to calotte asymmetry and the structural composition and thickness of the vault bone, employing micro-CT scan data, which also enabled description of the frontal sinuses, details relating to the diploic vessels and cerebral imprints on the endocranial surface. We compare several cranial traits seen in Florisbad with those observed in different hominin specimens.

Detailed investigation of the supposed pathological traits of Florisbad reveals that they are all consistent with conditions observed for non-pathological living human and fossil hominin crania. The claim that pathology has altered the symmetry of the vault, as well as its thickness, distribution, and internal structure, is not supported.

We also describe previously unreported aspects of anatomical features in which Florisbad differs from those observed exclusively in *H. sapiens*, including aspects of bone thickness distribution, the extension of the diploic system and proportions of the
44 endocast. Our results illustrate that in terms of cranial bone distribution and endocranial
45 proportions, Florisbad most closely resembles the somewhat older Middle Pleistocene
46 cranium from Kabwe, but it does not share the exceptionally large frontal sinuses seen
47 in the Kabwe 1, Bodo and Petralona crania. In sum, the results of this study suggest that
48 the attribution of the Florisbad cranium to *Homo sapiens* may be unwarranted owing to
49 the number of features in which it lacks the apomorphic states exhibited by our species.

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51 Keywords: Florisbad calotte, frontal sinus, vault thickness, endocast, diploic vessels

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# INTRODUCTION

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The purpose of the present work is to examine the Florisbad cranium in order to provide information on aspects of its anatomy, including several previously undocumented features. We review the putative pathological conditions of the specimen, particularly those related to calotte asymmetry and the bone thickness and the structural composition of the vault. In addition, we compare several cranial traits seen in Florisbad with observations for different hominin species in order to contribute to the discussion on the affinities of this Middle Pleistocene fossil.

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Most genetic studies indicate that the earliest population divergence within *Homo sapiens* was between the ancestors of present-day Khoe-San and all other living populations (Veeramah and Hammer 2014) and this likely occurred sometime between ca. 200 - 100 ka (Gronau et al. 2011; Schlebusch et al. 2012; Veeramah et al. 2012; Schiffels and Durbin 2014; Chan et al. 2015; Mallick et al. 2016; Song et al. 2017; Henn et al. 2018; Ragsdale et al. 2023). However, these estimates are dependent on assumed parameters such as known germline mutation rates and generation time and, thus, even earlier divergence dates of 350 - 250 ka have been proposed (Scally and Durbin 2012; Schlebusch et al. 2017, 2020). A temporal range of ca. 350 to 100 ka BP would place the earliest population divergence within *H. sapiens* between the onset of Marine Isotope Stage (MIS) 10 at about 374 ka BP and the end of MIS 5d at about 100 ka BP (Imbrie et al. 1984; Bassinot et al. 1994; Lisiecki and Raymo 2005). Recent analyses have estimated the *H. sapiens* lineage to have split from the ancestor of the Denisovan - Neandertal lineage between about 765-550 ka BP (Prüfer et al. 2014, 2017; Mafessoni and Prüfer 2017; Petr et al. 2020). Some authors suggest that the
Sima de los Huesos hominin assemblage, possibly dated to around 430 ka (Pantoja-Pérez and Arsuaga 2024), should be subsumed within the Neandertal record, which means that the paleogenetic divergence estimate significantly predates the earliest fossils.

In addition to the genetic evidence, the hominin fossil record provides evidence supporting the evolution of *Homo sapiens* in Africa (e.g., Pearson 2013; Scerri et al. 2014, 2018; Stringer 2016; Hublin et al. 2017; Galway-Witham and Stringer 2018; Meneganzin et al. 2022). However, there are also discussions about specimens that do not display the entire suite of *H. sapiens* apomorphies and about biological and taxonomic diversity in the Middle Pleistocene. Recently, several new *Homo* species have been proposed based on new discoveries or built on interpretation of the existing fossil record (e.g., *H. floresiensis*, *H. luzonensis*, *H. naledi*, *H. longi*, and *H. juluensis* (Détroit et al., 2019; Hurst et al., 2024; Kaifu et al., 2024; Ni et al., 2021; Roksandic et al., 2022; Bae, Wu, 2024; Hautavoine et al., 2024). Some of those taxa appear to be employed to replace the designation “archaic” *Homo sapiens*, but ultimately do not help to resolve the question of the origin of our species. However, information obtained from the genetic diversity of current humanity concludes that our origin is indeed African, while the oldest fossil specimens indisputably attributed to our species, from the Omo and Herto Bouri sites, come from this continent.

Among the Middle Pleistocene<fnref n="1" /> African fossils have been proposed to have been involved in the evolutionary history of *H. sapiens* is the partial cranium from Florisbad,

<footnote n="1">¹ The base of the Middle Pleistocene is 774 ka BP and the base of the Late Pleistocene is 129 ka BP (Head et al. 2021).</footnote>
97 South Africa (Figure 1). It comprises a partial calotte (most of the frontal and portions of
98 both parietals), a partial facial skeleton (much of the **right zygomatic, some of the right**
99 **maxilla, together with the frontal process and the incisive alveolus of the left maxilla**) and
100 an isolated right maxillary third molar (RM³).

<figure><img src="image_2.png" /></figure>

102 **FIGURE 1 HERE**

103 **PRINT COLUMN WIDTH**

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105 The first artifacts and fossil bones at the site **of Florisbad (28.76° S, 26.07° E)**, some
106 45 km NW of the city of Bloemfontein, Free State, were discovered by Floris Venter, who
107 owned the warm springs there and converted them to a recreational spa (Florisbad is
108 Afrikaans for Floris' Bath). **They were** found in 1912 when Venter was digging to enlarge
109 one of the spring baths **and came** to the attention of Robert Broom, who named two
110 extinct species (*Cobus venteri* and *Connochaetes antiquus*) **on** them (Broom 1913).
111 These finds prompted Dreyer to initiate excavations at the site in 1917, which were
112 continued in 1926, 1928 and 1932. The **hominin fossil** was discovered in July, 1932 by
113 Thomas F. Dreyer and Willeboer Venter (Dreyer and Kappers 1935; Dreyer 1938, 1947;
114 Hoffman 1955; Meiring 1956).

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116 **Geochronological Age of the Florisbad Cranium**

117 The pieces that constitute the hominin fossil derive from a saline warm water spring
118 that vented through two stratigraphic horizons – the “Brown Sand” and “Peat I” layers -
119 from which optically stimulated luminescence (OSL) dates of 279 ± 47 ka and 281 ± 73
120 ka, respectively, have been obtained (Kuman and Clarke 1986; Kuman et al. 1999;
Kuman 2023; Toffolo 2024). Additionally, enamel from the hominin RM³ has been dated with electron spin resonance (ESR) to 259 ± 35 ka BP (Grün et al. 1996; Grün 2006; Grün and Stringer, 2023). As such, there is reasonable concordance among the age estimates for the Florisbad cranium, although all must be regarded with some reservation owing to uncertainties around the site's reconstructed radioactive environmental history. However, Pinder (2021) has demonstrated that single grain OSL readings from a separate excavation pit at Florisbad show good agreement for many of the MSA samples reported earlier, indicating that sedimentation at the site occurred from >254 ka BP into the Holocene, with a relatively recent hiatus that lasted approximately 100,000 years. Pinder (2021) noted that her data agreed with the previously reported ESR age for the hominin M³.

Berger and Hawks (2023) have recently suggested that the ESR age estimate from the molar may not pertain to the cranium itself. However, the only stratigraphic horizons from which the cranium and the tooth could have derived and the M³ itself have concordant dates. In addition, the degree of occlusal attrition on the molar crown detailed by Smith et al. (2015) is consistent with the full endocranial and partial ectocranial fusion of the coronal and sagittal sutures in indicating an advanced adult ontogenetic age for this individual. Moreover, both Berger and Hawks (2023) and Grün and Stringer (2023) are in error when they state that the maxillary fragment does not preserve the portion that could confirm or reject a physical conjoin with the tooth, and that the molar cannot be fitted to the cranium directly. As noted by Grine et al. (2019: 151), the alveolar margin of the right maxilla has suffered taphonomic loss from the canine to the M² (it is not resorbed, contrary to Curnoe and Brink [2010]; rather it has been chewed away, probably by the same carnivore that left its canine puncture marks
on the frontal [Tappen 1987]). However, the roof and part of the mesial wall of the RM³
socket are preserved, and the molar root fits comfortably in it (Grine et al., 2019: 151).
Therefore, as noted by Grün and Stringer (2023: 37) the molar is "most likely part of the
same individual, considering that all other human bone fragments seem to be," and that
"it is the only dental material that can unequivocally be associated with the human
bones." Thus, there is currently no reason to doubt that the Florisbad cranium likely
dates to MIS 8 (i.e., between 300 – 243 ka BP [Lisiecki and Raymo, 2005]).

152

153 Evolutionary Interpretations of the Florisbad Cranium

154 The Florisbad cranium was attributed by Dreyer (1935) to the species *Homo*
155 (*Africanthropus*) *helmei*, named after Captain R. Egerton Helme, who had provided
156 funding for Dreyer's excavations. It is consistently identified as a form that was a
157 potential source population for *H. sapiens* (e.g., Rightmire 1978, 1984; Clarke 1985;
158 Smith et al. 1989; McBrearty and Brooks 2000; Mounier and Lahr 2019; Bruner and
159 Lombard 2020), or as an 'archaic' member of *H. sapiens* (e.g., Bräuer and Rimbach
160 1990; Bräuer 2008; Stringer 2016; Hublin et al. 2017). Some workers recognize *H.
161 helmei* as a potentially distinct taxon but they note that "*H. helmei* is a somewhat
162 problematic taxon, as there is as yet no formal diagnosis for the species and its unique
163 autapomorphies are not defined... *H. helmei* may be expected to exhibit a mix of
164 primitive and derived features" (McBrearty and Brooks 2000, p. 480).

165 The cranium shows as a well-developed supraorbital torus, a broad face, a thick
166 cranial vault, and a pattern of restricted meningeal vascularization (Singer 1958; Tobias
167 1968; Rightmire 1978; Bruner and Lombard 2020) in which it resembles the crania from
168 Kabwe and Saldanha (Rightmire 1978; Clarke 1985; Bruner and Lombard 2020). Clarke
169 (1985: 302) also noted the presence of “an extensive frontal sinus measuring 31.5 mm 170 laterally and 21 mm posteriorly.” At the same time, however, the cranium exhibits a 171 number of derived traits that approximate the condition observed in *H. sapiens* such as 172 a rather vertically domed (bulging) frontal, a relatively high and rounded cranial vault, a 173 distinct maxillary canine fossa, and an incipiently divided supraorbital torus (Galloway 174 1937; Rightmire 1978; Stringer and Andrews, 1988; Bruner et al. 2013).

175 There has been some disagreement over details of Florisbad's facial morphology 176 owing to its fragmentary nature and to the various pieces having been reconstructed in 177 different configurations by Dreyer and Kappers (1935), Clarke (1985) and Schwartz and 178 Tattersall (2003). The problem, as noted by Clarke (1985), is that there are no positive 179 joins between the major facial elements. Measurements recorded from these different 180 reconstructions will undoubtedly affect the results of comparisons with other hominin 181 fossils and modern human samples.

182
183 **Taphonomic Damage to the Florisbad Cranium**

184 The specimen has suffered from postmortem or perimortem taphonomic damage. As 185 noted by Clarke (1985), there are several tooth puncture marks on the frontal, including 186 a large punctate depression from a carnivore tooth posterior to glabella and chewing 187 marks along the left side of the calotte. In addition, the left supraorbital margin has been 188 gnawed away, as has the lateral alveolar margin of the right maxilla.

189 Finally, a large (27 mm²) piece of the right parietal just posterior to the coronal suture
190 was removed by Protsch (1975: Table 1).

191
192
**Pathology of the Florisbad Cranium**
Pathological conditions have been convincingly demonstrated to have affected
several hominin crania from the Middle - Late Pleistocene of Africa, including those from
Singa, Sudan (Brothwell 1974; Stringer et al. 1985; Spoor et al. 1998), Salé, Morocco
(Hublin 1985, 2009) and Eliye Springs, Kenya (Bräuer et al. 2003). The identification of
paleopathology is of importance beyond a basic interest in the expression of disease in
hominin fossils, as an appreciation of its potential impact on cranial morphology is
crucial in assessing their morphological affinities (e.g., Spoor et al., 1998). This is,
indeed, relevant in the three cases noted above. Hublin (1985, 2009) has inferred that
the Salé individual suffered from congenital torticollis related to an abnormal (deformed
and asymmetrical) planum nuchae, and that the latter has impacted morphometric
assessments that include the occipital. Similarly, the Singa 1 specimen has been
suggested to display morphological resemblance to a recent African population, with its
accentuated parietal bossing interpreted by early workers as indicating Khoe-San
affinities (Woodward 1938; Wells 1951). However, this feature appears to be unduly
developed owing to the cranium's asymmetry and underlying pathology (Brothwell 1974;
Stringer et al. 1985; Spoor et al. 1998). The partial cranium from Eliye Springs (KNM-ES
11693) has a highly porotic ectocranial surface and greatly exaggerated vault thickness,
which likely affects its overall morphometric assessment (Bräuer et al. 2003).

Curnoe and Brink (2010) argued that the Florisbad cranium exhibits numerous
pathological conditions, including among others: 1) an asymmetrical vault; 2) thick
cranial vault bones with pathological expansion of the diploë; 3) internal neurocranial
lesions and irregular depressions; 4) external neurocranial lesions; 5) cribra orbitalia;
and 6) dentoalveolar lesions affecting the incisor and canine alveoli. Previously,
Schwartz and Tattersall (2003: 81) described its anterior palatal depth as probably
having been affected by "bony resorption due to abscessing" of the right maxilla in the
region of the canine. We agree that resorption has affected the anterior alveolar margin
in the region of the incisors and canines; however, its most dramatic manifestation is in
the form of an abscess cavity associated with the $LI^2$ alveolus.

The endocranial aspect of the calotte shows relief that corresponds to impressions
from the cerebrum and the blood circulation between the brain and skull. In addition,
Pacchionian depressions (the variably shallow pits in the inner table of the vault
produced by the arachnoid granulations which typically protrude into the superior sagittal
[dural] venous sinus and contribute to cerebrospinal fluid reabsorption) are visible, as is
the course of the sagittal sinus and imprints of the anterior and middle meningeal arterial
systems. Curnoe and Brink (2010) considered a number of these features to be related
to pathological lesions. An exhaustive review of the evidence proffered by them relating
to the multitude of pathological conditions that they envisioned affecting the Florisbad
fossil is beyond the scope of this study.

Some aspects, such as the suspected presence of cribra orbitalia, even if correctly
diagnosed, are of little importance in view of the fact that the porosity that defines cribra
orbitalia (*sensu stricto*) is a normal vascular / developmental phenomenon (Cole and
Waldron 2019; Rotschild et al. 2021; Zdilla et al. 2022). Indeed, cribra orbitalia is present
in over 12% of recent North American and nearly 17% of South African adults (and in
40% of North American and 25% of South African juveniles) (Steyn et al. 2016).

In this context, we aim to provide a more accurate appreciation of the anatomy and
morphology of this fossil by concentrating on the more salient features described by
Curnoe and Brink, namely (1) the asymmetry of the cranial vault, (2) the thickness of the
vault bones and the pathological expansion of the diploë, and (3) the presence of
241 internal neurocranial lesions and irregular depressions. Because these purported

242 pathologies could affect the general anatomy of the specimen, it is important to establish

243 their validity before investigating other anatomical details of the fossil. We also examine

244 in details the Florisbad cranium in order to provide information on several aspects of its

245 anatomy, including several previously undocumented features.
The Florisbad cranium was examined over a period of two weeks at the National Museum, Bloemfontein in February, 2011 by one of us (FEG) aided by a 10x Triplet geological hand lens and a Leica M Series Stereo Zoom microscope. The cranium and molar were micro-CT scanned by two of us (FEG and SH) at the Stellenbosch University CT Scanner Facility (du Plessis et al., 2016) in 2018. The facial and calotte portions of the cranium were scanned separately as was the third molar using the General Electric Phoenix VTOMEX L240 micro-computed tomography (µCT) system. We employed a current of 880 µA and an accelerating voltage of 170 kV. Voxels are isometric (same size in the three dimensions) and measure 0.0125 mm³ for the cranial bones and 0.0136 mm³ for the molar. X-ray projection images were acquired at between 2300 - 65000 steps during a full rotation of the sample. At each step position, the first image was disregarded, and the subsequent three images averaged to produce higher quality images than standard. A detector shift was activated to minimize ring artefacts. The resulting micro-CT scan data were visualized using Avizo 7 and Volume Graphics VGSTUDIO MAX 3.1.

Curnoe and Brink (2010) employed standard medical grade CT scans recorded at the Bloemfontein MediClinic in 2008. These scans had relatively low resolution (0.625 mm³ voxel size at 140 kV and 400 mA). As such, they are not optimized to illustrate bone structure at the level of details they describe (at the nearest 0.1 mm). In this context, our imaging dataset should aid in determining whether the traits previously described are pathological. We utilized micro-computed tomography (µCT) to overcome the modest
resolution of medical grade CT scans in order to provide a detailed assessment of the
anatomy of the vault of the Florisbad cranium. In particular, we 1) measured the
thickness and structure (i.e., respective thickness of the internal table, the diploic layer
and the external table) of the cranial vault, 2) visualized the diploic channels within the
vault bones, 3) examined the surface of the endocast, as reconstructed from the
endocranial surface of this specimen, and 4) visualized the compartments of the frontal
sinus.

276 **Cranial vault thickness and composition**

277 A reassessment of the position of the median sagittal plane enables an evaluation of
278 the supposed vault asymmetry observed by Curnoe and Brink (2010).

279 We measured the overall thickness and **composition** (i.e., respective thickness of the
280 internal table, the diploic layer and the external table) of the cranial vault at selected
281 points to evaluate **the claim by Curnoe and Brink (2010)** that vault thickness **was altered**
282 by its pathological condition. A crucial methodological point is that thickness can only be
283 quantified accurately on either 2D CT or micro-CT slices **but also in 3D** (e.g., Copes,
284 2016) when measurements are recorded perpendicular to the vault. **Curnoe and Brink**
285 (2010) used oblique slices and therefore their measurements cannot be repeated.
286 Therefore, we followed Balzeau (2007) in employing the median sagittal plane as the
287 reference by which repeated measurement of bone thickness could be **assessed** along
288 its length. This **protocol** permitted the measurement of cranial vault thickness (CVT) and
289 **vault composition** at bregma and the center of the frontal bone **in the median sagittal**
290 plane. Those two points were also employed by Curnoe **in his study**. We **also recorded**
291 **thickness measurements** at the center of the right parietal bone by reconstructing a slice
292 perpendicular to the midsagittal plane that passes through the selected location on the
parietal. This slice was selected to cross this point with an orientation perpendicular to bone thickness to enable accurate measurements. This modification of our protocol permits comparison of our measurements with those obtained at a supposedly similar point to that used by Curnoe and Brink (2010). Finally, we could not repeat the measurement at two of the other locations used by Curnoe and Brink. In the first instance, the actual location of the landmark they identified as "frontal squama" was not clearly defined, so we could not repeat it. Moreover, because several cracks run along the right side of the frontal squama, the different layers of bone cannot be reliably identified in this area. In the second instance, we did not measure thickness at the so-called 'mid-sagittal suture' as defined by Curnoe and Brink (2010) for three reasons. The first relates to the fact that they misidentified the median sagittal plane, and the second to the fact that the remnant suture is present endocranially, which precludes measurement of the internal layer of bone. The antero-posterior location of the point is not detailed by them, so we cannot identify the position of the measurement they recorded.

Bone thickness can also be quantified using a second approach that entails measurement over a larger anatomical area than at specific landmarks. Following Balzeau (2013), we delimited a parasagittal region that extended several centimeters on either side of the median sagittal plane with parallel borders running posteriorly from a postorbital line that delineated the section at which vault thickness was no longer influenced by the supraorbital structures (see Balzeau 2013: fig.1). Although the limits of the region of interest are not perfectly reproducible on all crania included in the comparative sample, cranial vault thickness distribution can be generated and represented by colormaps and directly compared to the description by Curnoe and
Brink. The colormaps were generated following published protocols (Balzeau 2013; Balzeau et al. 2017; Balzeau and Charlier 2016; Beaudet et al. 2022; Hui and Balzeau 2024). The 'SurfaceDistance' algorithm of Avizo v9.0 was used to automatically calculate the distance between the ecto- and endocranial surfaces for regions of interest. The range of the color scale was adjusted to highlight thicknesses ranging between 2 mm and 22 mm for comparison with previously published data (Balzeau, 2013; Balzeau et al. 2017). The colormaps were displayed on the ectocranial surface. The resulting data for Florisbad are compared to the results published by Balzeau (2013; Balzeau et al. 2017) to examine the distribution and asymmetry of CVT in a comparative framework. The comparative samples are the same as employed by Balzeau (2013) and are detailed in Table S1. They comprise fossils attributed to *H. erectus*, *H. neanderthalensis* and fossil *H. sapiens*. The recent *H. sapiens* sample comprises 20 male and 20 female crania from Europe.

The diploic channels within the cranial vault bones were described following Hui and Balzeau (2023), where the 2D tomographic images of the Florisbad cranium were inspected slice by slice in 3D Slicer (v4.13) and the 3D cranial model was rendered transparent to observe its embedded diploic structures. By visually inspecting the 2D images and the transparent 3D models, we located diploic cavities in the shape of vessels, which are regarded as the channels that housed the diploic venous network. The diploic channels were segmented manually using the 'Paint' function in 3D Slicer. The segmented diploic channel models were displayed inside the transparent cranial model to investigate their distribution and drainage routes. Comparative information was available for fossil *H. sapiens*, *H. neanderthalensis* as well as for several other
specimens attributed to *H. erectus* and *H. naledi* (Hui, 2024). The list of the specimens is provided in Table S1.

## Endocranial anatomy

With reference to the surface of the Florisbad endocast, we restrict our analysis to features that are clearly visible and that we could interpret with a high level of confidence based on our previous experience (e.g., Hurst et al., 2024; Labra et al., 2024; Hui et al., in revision). Because the endocranial surface of this specimen is incomplete, we have reconstructed the virtual model of the left lateral wall of the frontal lobe using the preserved area on the right to enable morphometric comparisons. The mirrored surface was aligned on the preserved anatomical area on that side. Doing so allowed us to estimate the position of the missing third frontal convolution on the left side. Figure 2 shows the actual preservation of the specimen and illustrates that only minor reconstruction was necessary to locate this landmark. The frontal lobes of the endocast were measured using the available landmarks of the frontal bec, the bilateral points on the Broca's cap, the points at the maximal width of the frontal lobe and the intersection of the central sulci. As such, the frontal cord that extends between the frontal bec and the junction of the central sulci (denoted FalCE), the width at the Broca's cap (denoted WBE), and the maximum width of the frontal lobes (denoted MFWE) can be measured (Figure 2). Morphometric data for Florisbad and the comparative samples of fossil hominins and recent humans were scaled using their respective endocranial volumes (EV) according to the formula ((xi/(3√EVi)*100)). The value for Florisbad is from the literature (Bruner and Lombard, 2020). Even if the specimen is not complete, the use of the cube-root of the volume limits the influence of the approximation in the estimation
of the complete volume. Principal component analyses (PCA) were calculated on the
variance-covariance matrix of respectively the three absolute dimensions (FalCE, WBE
and MFWE) and for those variables scaled using their respective endocranial volume.

Univariate analyses were carried out using the adjusted z-score (Azs) (Scolan et al., 2011), in which 95% of the variation of the reference population is included between -1 and +1. An Azs lower than -1 or higher than +1 is beyond 95% of the variation of the reference sample. The comparative samples used here are the same as in Hurst et al. (2024) and include specimens of australopiths, *H. sapiens*, *H. neanderthalensis* and *H. erectus*, as well as specimens for which specific attribution is debated (LH 18, Kabwe 1 and Djebel Irhoud 1). The details are given in Table S1. Early hominins (e.g., australopiths) are included because they inform on the size and shape of the endocranial cast in ancient fossils and help to distinguish later groups. Specimens with a debated taxonomic attribution are included as they can provide important comparative information about Florisbad.

FIGURE 2 HERE

Frontal pneumatization morphology and dimensions

Finally, we investigated the frontal sinus in order to describe its morphology, and to
compare its reconstructed volume with the sizes of those in other Middle and Late
Pleistocene African hominin crania. Because the left supraorbital region is almost
entirely missing, and the inferior walls (limits) of the air cells in the bregmatic region and
the adjacent right supraorbital torus are lacking (Figure 3), we measured the volumes of
these cavities as preserved and as reconstructed by us utilizing the contours of the
surrounding bone (Figure 2).

FIGURE 3 HERE

3D reconstruction of the sinuses and assessment of the volumes were performed
using the methods detailed by Balzeau et al. (2017, 2021) and Butaric et al. (2022).

Segmentation was done manually with Avizo 7.0. We recorded 8 linear measurements

on the 3D models of the sinuses (Table 1) as defined by Balzeau et al. (2022) in order to
perform a linear discriminant analysis (LDA) to facilitate comparison between Florisbad
and other specimens listed in Table S1. Comparative samples for this analysis contain

94 specimens from most hominin species and 105 recent *H. sapiens* (Balzeau et al., 2022). The groups were early hominins (N=12), *H. erectus* (N=14), *Homo neanderthalensis* (N=21), and *H. sapiens* (N=105). It should be noted that these linear measurements were not utilized in the reconstruction of the volume of the frontal sinus.

Moreover, the description of the preserved area of the sinuses is by itself informative of
the anatomy of this pneumatization. Because the inferior margins of the sinus on the
right side are incomplete, some of the dimensions required estimation. Our
measurements are taken in projection on the 3D models and correspond to the overall
extension of pneumatization in space. Thus, a small break, a missing area does not
necessarily affect the overall maximum extension in one direction. As a result, the
protocol we used permitted direct measurement of 5 of the 8 variables that are not
affected by incomplete preservation on Florisbad. Estimation of the other 3 was based
on the shape of the preserved area and on the configuration of the cell on the left
compared to that on the right side. Indeed, only minimal estimation of the missing area of the sinus (as visible on Figure 2) was necessary to estimate the linear dimensions in 411 412 413 3D as defined for our protocol. Measurements were repeated to ensure that no 414 important error was made. We chose to reconstruct the extension of the left sinus in the 415 area where it is incomplete to allow for comparison of this specimen with our database. 416 This reconstruction concerned only its maximal extension to ensure the feasibility of our 417 linear measurement. This approach was mandatory as the asymmetry in the extension 418 of the pneumatization in this specimen (Figure 2) made doubling the values observed on 419 the preserved side to estimate frontal sinus size and shape in Florisbad a poorer proxy 420 than our estimation that takes into account this parameter. 421

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TABLE 1 HERE

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The three estimated dimensions relate to the anterior and superior lengths of the left 424 sinus (variables All and SLI) as well as the total width of the frontal sinus (W) because 425 the lateral extent of the left sinus is not preserved. The height and antero-posterior 426 dimensions are not affected by the incomplete preservation of the left sinus. Indeed, the 427 preserved medial border of the left sinus shows that both its vertical and AP extensions 428 are more restricted than on the right **and therefore that those dimensions can be** 429 **measured directly on the preserved areas of pneumatization.** Indeed, the right side is** 430 **informative of the global extension of the whole pneumatization in those orientations.** To 431 estimate the lateral extension of the left **sinus we compared it to the right side, where the** 432 **sinus** extends to a point just medial to the most elevated point of the orbit. A similar 433 lateral position on the left side was used to estimate **the left anterior and superior length** 434

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(ALI and SLI, respectively) and the total width (W) of the sinuses. Based on the preserved shape of the sinuses and the general symmetry of the extension of the sinuses observed in our comparative samples, it is highly likely that the global extension of the sinuses was included within the extension that we have estimated. Although these variables are approximations, the globular shape of the sinus renders our estimation of its original size very likely. The dimensions are very unlikely to have been much larger than estimated here because the available areas in the frontal bone would not have permitted a much larger expansion of the pneumatization. Because all the linear measurements were used in the linear discriminant analyses and because of the limited impact of incomplete preservation in relation with our protocol, the estimates for the three variables likely had limited impact on the results and the interpretation of the position of Florisbad within the large comparative context.

Finally, the volume of the sinuses was simply calculated by measuring with the software the volume of the pneumatization that is it preserved on the specimen and estimating the volume of the missing part. We estimated that approximatively two-thirds of the total volume of the sinuses was preserved based on the relative sizes of the preserved parts of the left and right sinuses, their globular shapes and our experience with large numbers of fossil and recent human sinuses (Balzeau et al., 2022; Greening et al., 2023; Grine et al., 2024). So, our estimation of the volume corresponds to the preserved volume multiplied by 3/2. Although this is an estimation, this imprecision does not have a significant impact on our comparisons when we employ the cube-root of the estimated volume in this analysis.
# RESULTS

## DETAILLED ANATOMICAL DESCRIPTION OF THE FLORISBAD FOSSIL

The results of our analyses of the Florisbad cranium are presented in relation to (1) the proposed asymmetry of the cranial vault, (2) the thickness and composition of the vault bones, (3) the identification of diploic channels within the vault, (4) the endocranial anatomy, and (5) the shape and volume of the frontal sinus.

### Cranial Vault Asymmetry

Curnoe and Brink (2010: 505) state that “the Florisbad vault is both thick and asymmetrical in its thickness,” noting that “this is especially clear along the posterior course of the parietal bones where the calvaria have been broken postmortem” and directing the reader to contrast the left and right sides of the parietal vault illustrated in their Figure 2A, reproduced here as Figure 4A. According to its legend, the white arrow indicates the sagittal suture. However, it is clear the white arrow is placed some 17.3 mm to the left of the median sagittal plane. This plane, and hence the placement of the sagittal suture can be ascertained by inspection of the endocranial aspect of the specimen (Figures 3 and 4), where some 25 mm of the frontal crest is preserved. The frontal crest, which serves as the attachment of the midline dural reflection, the falx cerebri, corresponds to the median sagittal plane (Figure 4B, green dashed line). Successive coronal sections through the parietals just anterior to the fractured posterior margin (Fig. 4C) and just posterior to the coronal suture (Fig. 4D) reveal the symmetry of the two sides of the cranium and in the distribution of its thickness across the preserved
480 elements. In fact, Curnoe and Brink misidentified the midline as being coincident with a
481 postmortem crack.

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483 FIGURE 4 HERE

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487 Cranial Vault Thickness and Composition

488 A superior view of the calotte (Figure 5) reveals the presence of a median sagittal
489 depression (the “interparietal groove”) that was first observed by Galloway (1937).
490 Habgood (1989) also noted it, as did Bruner and Lombard (2020), who suggested that it
491 might be related to a reduction of the diploë in the midsagittal region. Habgood (1989:
492 18) regarded the presence of an interparietal groove as a “Khoisan feature,” presumably
493 because it had been identified on a number of Later Stone Age crania from the Cape
494 coastal belt of South Africa by earlier studies (e.g., Laing 1929; Galloway 1936; Cassel
495 et al. 1942; Kohler 1942; Grobbelaar and Goodwin 1952). However, this depression
496 occurs in relatively high frequency (ca. 36%) in other recent sub-Saharan African
497 populations (de Villiers 1968) and Shore (1938) has recorded its presence in 12% of
498 recent Egyptian crania. This feature has only limited (if any) impact on the cranial vault
499 thickness variation in this area, which does not show a decrease in total bone thickness
500 (Figure 6).

501

502 FIGURE 5 HERE

503 PRINT COLUMN WIDTH
Curnoe and Brink suggested that the distribution of the cranial vault bone thickness in the Florisbad cranium was asymmetrical. However, the heat map representing the distribution of bone thickness does not reveal any remarkable variation in CVT between the right and left parietal bones nor in the frontal bone (Figure 6). Accordingly, the general distribution of CVT is rather homogenously distributed between both sides over the preserved areas of calotte.

FIGURE 6 HERE

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Concerning the variation in different parts of the calotte, the pattern of distribution shows a thickening along the course of the internal frontal crest, around the bregmatic area and along the median sagittal plane at the junction of the parietal bones. Restricted thinning of the frontal bone corresponds to the locations of the middle and superior frontal gyri as observed on its endocranial surface. Regions of minimum CVT (displayed in white and light blue in Figure 6) are located in the medial parts of the ascending frontal gyri where arachnoid (Pacchonian) granulation pits are present.

The bone thickness values at key locations of the calotte -- bregma, midfrontal median sagittal plane and mid-parietal right side -- are presented in Table 2. Some of the absolute values differ from those reported by Curnoe and Brink, and this is most likely due to differing definitions of the points at which the measurements were recorded. For example, while we measured thickness at bregma, Curnoe and Brink (2010: 506) recorded it a point "near bregma, measured just posterior to bregma". Our measurement
of thickness at bregma is **11.6 mm** as compared to **8.5 mm** in Curnoe and Brink (2010: 506), and our mid-parietal point differs from their “parietal mid-external surface” (8.8 mm vs 10.8 mm). However, we obtain similar values for the mid-frontal point in the median sagittal plane (11.3 mm vs 11 mm), which further reflects the symmetry of the frontal as their point is some 17 mm from the actual median sagittal plane. Additionally, pixel size for the data collected by Curnoe and Brink (2010) is 0.625 mm, and this degree of resolution does not allow precision beyond the nearest 0.5 mm. Finally, our quantification at specific points is consistent with the values observed through the colormap of bone thickness distribution.

TABLE 2 HERE

An important consideration is that overall vault thickness may be related to its compositional structure involving the internal table, external table and diploic layer (Figure 7). At the three locations defined above (bregma, mid-frontal point and mid-parietal point), we find that the proportion of the diploë relative to the total thickness varies between 63% and 75% (Table 2). Although Curnoe and Brink (2010) reported values of between 67% and 86%, it should be noted that their measurement of thickness recorded to the nearest 0.1 mm, including, for example, a value of 0.1 mm for the external table at two locations. However, this is methodologically unattainable with a resolution of 0.625 mm³ because theoretically, measurement error cannot be less than half the size of the pixels. It is clear from their published figures that the image quality is clearly not sufficient to adequately and precisely delimitate the three components of the vault thickness.
FIGURE 7 HERE

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Moreover, Curnoe and Brink **assessed cranial thickness** on parasagittal sections **that** were not perpendicular to bone thickness (Figure 8), which results in an artificial increase of bone thickness values. **This explains the discrepancy between at least some** of the measurements recorded by them and by us. Our use of specific landmark and methodological protocols (i.e., using orthogonal images to quantify CVT and by mapping thickness variation) and the use of higher resolution images mean that our measurements more accurately reflect the characteristics of the vault of this specimen compared to the data published by Curnoe and Brink.

FIGURE 8 HERE

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Diploic Channels

Most of the diploë have been infiltrated by sediment, which renders most of the diploic channels (DC) unidentifiable. However, several DC and emissary channel branches can be observed in the frontal and parietal bones (Figure 9). Incomplete DC branches that are distributed along the frontal crest and the right superior temporal line can be identified. The DC branch near the frontal crest is connected to a large foramen on the endocranial surface, which very likely forms a connection between the DC network and
576 the superior sagittal sinus. The DCs near the superior temporal line are adjacent to the
577 meningeal vessels, possibly the orbital meningeal vessels (OMV) or middle meningeal
578 vessels (MMV), and there are evident connections between them.

579

580 **FIGURE 9 HERE**

581 **PRINT PAGE WIDTH**

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583 In the supraorbital torus, a DC branch courses mediolaterally over the orbit and
584 connects to the periorbital or superficial temporal vessels through a large foramen on
585 the external surface. Due to taphonomic damage, only a short channel is visible near the
586 sinus that connects the diploë (Figure 10). Additionally, many emissary channels can be
587 identified in the supraorbital torus, bridging the frontal sinus and the periorbital vessels
588 (Figure 10). The DC branches that are visible in the parietal bones are also incomplete.
589 These branches are adjacent to the imprints of the posterior branch of the middle
590 meningeal vasculature, but only a single foramen on the endocranial surface links a DC
591 branch. The drainage pathways of other parietal DC branches are unclear due to their
592 poor preservation.

593

594 **FIGURE 10 HERE**

595 **PRINT PAGE WIDTH**

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598 **Endocranial Morphology**
The physical endocast of the Florisbad vault preserves the **imprints** of portions of the frontal and parietal lobes of the brain (Figure 11). Although it is affected by several cracks, the endocast, especially as reconstructed from the detailed micro-CT scans (Figure 12), retains a good deal of anatomical information beyond that described from the physical cast used by Dreyer and Kappers (1935) and from the laser surface scan employed by Bruner and Lombard (2020).

FIGURE 11 HERE

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FIGURE 12 HERE

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The **imprints** of the anterior meningeal vessels comprise several branches that course medially and posteriorly **along the imprints of the** middle and superior frontal convolutions on the right side. An imprint that could correspond to the sphenoparietal sinus is visible on the left frontal lobe, and a branch of the middle meningeal system is visible anteriorly to this. Three other branches run medio-posteriorly on the left frontal and parietal lobes. The posterior extension of three meningeal vessels is visible on preserved part of the **right parietal lobe** although they do not reach the superior parietal lobule. The superior sagittal sinus is visible between the parietal lobes and several sizeable Pacchionian impressions are visible.
Concerning the imprints of the gyri and sulci, small parts of the inferior, medial and superior frontal sulci are visible in the anterior portions of the frontal lobes. Part of the central sulcus is observable in its uppermost extension on the left side.

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## Frontal Sinus Development

The right frontal sinus is nearly complete (Figure 13), although its inferomedial extent is missing. Only the superior and medial extensions of the left sinus are preserved as the roof of the left orbit is damaged. The right sinus is a large, globular cell that extends laterally to the level of the summit of the orbit and medially to the left of the median sagittal plane. Based on the preserved part of the left sinus, it is very likely that it was somewhat smaller than that on the right, with more restricted medial, posterior and supero-inferior extensions. Although its other width dimensions cannot be measured directly, its probable size can be estimated based on its shape and by comparison with the sinus on the right side.

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FIGURE 13 HERE

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On the basis of the preserved parts of the frontal pneumatization, we measured its dimensions in 3D using the variables defined by Balzeau et al. (2022) (see Table 1 for the definitions of the various measurements, and Table 3 for the results). The anterior length of the right sinus (ALr 31.4 mm), superior length (SLr 32.6 mm), as well as the height (H 22.8 mm) and the two dimensions that describe the antero-posterior extension of the sinuses, AP (21.4 mm) and AP2 (21.0 mm), could be measured without being

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compromised by the incomplete preservation of the left pneumatic space. Estimated dimensions are width (58.2 mm), the anterior length of the left sinus, All (21.0 mm) and the superior length of the left sinus, SLI (18.6 mm). These estimates were based on the preserved shape of the left sinus and the comparison with the shape and dimension of the right sinus, which is globally larger, providing an estimate of the maximum expansion of pneumatization.

The entire frontal sinus is estimated to have had a volume of approximately 9.7 cm³ (mL) as determined by segmentation of the right sinus and extrapolation to the left.

TABLE 3 HERE
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COMPARISONS WITH OTHER PLEISTOCENE FOSSILS

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The results of our analyses of cranial vault thickness, endocranial dimensions and frontal sinus size invite comparison with published data on other Middle and Late Pleistocene *Homo* fossils and with recent human samples.

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*Cranial Vault Thickness*

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In terms of average CVT as measured along the parasagittal section across the frontal and parietal, the Florisbad cranium has a thinner vault than the other two Middle Pleistocene crania included in our dataset, Kabwe and Petralona (Table 4). Topographic mapping (Figure 14) indicates that the thickest regions of the Florisbad calotte are located in the same areas as those in the Kabwe 1 cranium even if the former does not reach the same values of thickness. In Florisbad, the reddish hues that highlight the areas with thickness of over 17 mm appear only locally along the frontal torus, with thickening also around the anterior border of the bregmatic region. In Kabwe 1, while the vault immediately behind the supraorbital torus is very thick, the median sagittal band tends to be thinner than the frontal and parietal bosses, although there is a small region of thicker bone at bregma, whereas the midline and especially the bregmatic regions are thicker in Florisbad (Figure 14). The bregmatic region also shows thickening in Asian *H. erectus* crania (Balzeau 2013).

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FIGURE 14 HERE

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682 TABLE 4 HERE

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684 Thickness distribution across the vault in Florisbad does not follow the patterns for either *H. sapiens* or *H. neanderthalensis* (Balzeau 2013) (Figure 14). In particular, there is no clear thinning along the midline of the frontal and parietal as is frequently observed in fossil *H. sapiens*. Rather, there is a thickening anteriorly to the bregma and thinning in the anterior part of the parietal bones. The medial aspects of the Florisbad parietals are relatively thick.

690 The mean CVT value obtained for Florisbad (8.6 mm) is within the upper limits of the observed ranges for the *H. erectus* and fossil *H. sapiens* samples, and slightly exceeds the range observed for *H. neanderthalensis* and recent *H. sapiens* (Table 4).

693 Finally, the arachnoid villi (Pacchionian) depressions in Florisbad, which are associated to reduced internal bone thickness, are distributed over a similar extended area over the medial and anterior part of the parietal as in Cro-Magnon 1. The sizes of the depressions in Florisbad are similar to those reported for Kabwe 1 and Cro-Magnon 1 (Figure 14; see also Balzeau et al. 2013, 2017). The sizes of the arachnoid depressions fall comfortably within the range of variation of non-pathological samples of various hominin species (Holloway et al. 2003).

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701 Diploic Channels

702 The diploic channels (DCs) may provide a taxonomic signal at some level, as revealed by studies that have shown that the DC networks of non-human primates are much less developed than those of hominins (Hershkovitz et al., 1999; Hui, 2024). 703 Anastomoses between the DCs and parietal foramina are frequent in non-human 704
primates, most fossil hominins, and extant humans, while the absence of parietal
foramina and their connections with DCs is specific to *H. neanderthalensis* (Hui &
Balzeau, 2023). Another feature of *H. neanderthalensis* is the isolation between the
parietal DC and the transverse sinus, while these two vessels are usually anastomosed
in other *Hominidae* species (Hui, 2024). Moreover, anastomoses between DCs and the
frontal sinus is consistently present in non-human primates and most hominin species.
Still, this DC anastomosis with frontal sinuses is not regularly found in *H. sapiens* (Hui,
2024). However, in the Florisbad cranium, these areas and structures with taxonomic
significance were not well preserved. This hindered us from applying DCs in estimating
the affinities of Florisbad.

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717 Endocranial Dimensions

We were able to measure three linear distances on the Florisbad endocast.
Comparison of the absolute values of the three linear distances assessed in Florisbad
and in the comparative Pleistocene *Homo* fossils and recent humans (Table 5) confirms
the large size of the Florisbad endocast. A PCA was computed on these linear
dimensions. The three variables have positive loadings along PC1, which represents
nearly 90% of the total variance (Figure 15). PC1 is therefore highly related to variations
in global size of the analyzed specimens. The loadings of the 3 measurements are
respectively 0.66 for FalCE, 0.44 for WBE and 0.6 for MFWE along PC1. This
component discriminates specimens of *Australopithecus africanus* and *H. habilis*, in the
negative quadrant, from *H. erectus* in the middle and, in the positive quadrant, from
large-brained *H. sapiens*. Florisbad plots comfortably in the latter area. Florisbad is
729 significantly larger than early hominins and it is larger also than *H. erectus* for the
730 maximum width measured at the Broca's cap (Table 5), as revealed by the adjusted z-
731 scores. No discrimination between the different groups is apparent along PC2. The
732 loadings of the 3 measurements are respectively -0.75 for FalCE, 0.36 for WBE and
733 0.56 for MFWE along PC2.

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735 TABLE 5 HERE

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737 FIGURE 15 HERE

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740 With regard to the relative values of the endocast, those for Florisbad **differ** from
741 recent *H. sapiens*, and **approximate those of** Kabwe 1 (Figure 16). This is due to a
742 relatively restricted AP length of the frontal lobes compared to their width. In this PCA,
743 the discrimination between the different groups is not very clear due to the small number
744 of variables involved. PC1 represents 53.8% of the total variance; *Homo sapiens*
745 specimens mostly **occupy the negative area of the axis while the fossil groups tend to be**
746 in the positive area. The loadings of the 3 measurements are respectively -0.01 for
747 FalCE, 0.68 for WBE and 0.72 for MFWE along PC1 and 0.99 for FalCE, 0.06 for WBE
748 and -0.08 for MFWE along PC2.

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751 FIGURE 16 HERE

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The adjusted z-scores provide a direct comparison between Florisbad and the comparative samples (Table 5). With regard to the relative dimensions, the frontal cord in Florisbad has lower values in comparison to all other samples, and the width at Broca's cap is significantly larger than in recent *H. sapiens*.

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These analyses are, of course, limited by the restricted amount of information that we could quantify on the incomplete Florisbad endocast. Nevertheless, they are informative of the general shape of the preserved areas.

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## Frontal Sinus Size

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The absolute volume estimated for the frontal pneumatization of Florisbad, which includes both the left and right sinuses is compared to the values recorded for several Middle Pleistocene *Homo* fossils and the means for samples of *H. erectus*, *H. neanderthalensis* and recent sub-Saharan African populations in Table 6. At 9.70 ml, the Florisbad sinus is notably smaller than those of Kabwe 1 and especially Petralona and Bodo. It is somewhat larger than the mean value of the *H. erectus* sample and only slightly smaller than the *H. neanderthalensis* sample mean, but it falls very comfortably within the fiducial limits for both samples. Moreover, the Florisbad sinus volume exceeds the means of all five recent sub-Saharan African samples, although it is within 1 SD of the means of the South African sample reported by Greening et al. (2024) and the West African sample reported by Butaric et al. (2022). The Florisbad sinus volume is, however, significantly larger than the comparatively small mean volume reported for the South African Later Stone Age Khoe-San sample (Grine et al., 2024).

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777 TABLE 6 HERE

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779 The linear dimensions for the frontal sinuses of Florisbad were projected into a linear discriminant analysis computed from the data compiled by Balzeau et al. (2022: S3).

780 The groups in those analyses were early hominins, *H. erectus*, *Homo neanderthalensis*, and *H. sapiens*. Florisbad classifies as *H. erectus* with respect to the absolute dimensions and as *H. neanderthalensis* with respect to the relative dimensions for the frontal sinus. The percentages of correct classification are 79.6% for the absolute and 64.5% for the relative dimensions (and respectively 79 and 62.5% with cross-validation).

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786 Such levels of correct classification are quite high despite the considerable variation in the shape and size of the frontal sinuses, and are likely related to the fact that we have used large comparative samples. However, it shows that differences are indeed present between those groups. The calculated classifications for Florisbad, as *H. erectus* and *H. neanderthalensis*, are related to the globular sinuses that fill a large part of the medial part of the supraorbital torus. In those aspects, this specimen is different from the characteristics observed in *H. sapiens* (Balzeau et al., 2022).
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DISCUSSION AND CONCLUSIONS

795

Our results do not support the presence of cranial vault asymmetry in Florisbad as suggested by Curnoe and Brink (2010). Rather, data from micro-CT scans confirm that the internal composition and distribution of bone thickness in this calotte correspond to those observed in other Middle and Late Pleistocene hominin specimens with no pathological alteration.

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The vault in this specimen is not particularly thick when compared to other fossils from various hominin species (Balzeau 2013; Copes and Kimbel 2016; Balzeau et al. 2017), including *H. sapiens* (Marsh 2013) contrary to the suggestion of Curnoe and Brink (2010). The distribution of CVT is seen as normal when it is compared to other fossil hominins, and is not asymmetric. In addition, the internal composition of the vault bone is not affected by any pathology and falls within the variation observed in samples of *H. erectus* (Balzeau 2006) and recent *H. sapiens* (Copes 2016). The proportions measured here for Florisbad are well within the range of variation observed among our comparative samples, indicating the lack of a pathological condition. In fact, clinical indicators of pathology in the proportion of the diploë relative to the tabular tables in living humans (e.g., Stuart-Macadam 1987) appears not to be appropriate for interpretive inferences relating to fossil hominin crania whose CVT is larger than that of living people.

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Concerning the Pacchonian depressions that are visible on the endocranial surface of the calotte, they are not particularly large compared to those seen in many other fossil hominins, including Kabwe 1.

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Thus, the features listed by Curnoe and Brink (2010) to suggest a pathological condition for the Florisbad cranium are not confirmed by the present study. Part of the discrepancy is likely due to the fact that they employed imaging technology that was inadequate for the task. In addition, their use of unique parasagittal slices is methodologically problematic and results in erroneous observations. The same limitation has been reported in previous descriptions of possible pathological traits in *H. floresiensis* by Jacob et al. (2006) and Henneberg et al. (2014), which have been corrected by Balzeau and Charlier (2016) with more precise imaging datasets. While researchers have to employ all data available to them, they should carefully consider the methodological limitations of such information in order to avoid overinterpretation.

This study of the Florisbad cranium has served to expand our knowledge of the anatomy of the specimen, including previously undocumented features. In this context, we observe that several anatomical traits differ from the condition observed in recent *H. sapiens*. The vault is relatively thick, with no thinning in the medial extension of the frontal and parietal lobes. The pattern of distribution of CVT is similar to that of Kabwe 1 (Balzeau et al. 2017), and differs from that in both *H. neanderthalensis* and *H. sapiens* (Balzeau et al. 2013). On the endocast, the middle meningeal vascular system is not well-developed. Endocranial dimensions are large, and illustrate a lateral expansion of the frontal lobes relative to their lengths. Overall, the shape of the frontal lobes is more similar to that seen in Kabwe 1 and *H. neanderthalensis* than to what is characteristic of *H. sapiens* (Balzeau et al. 2013).

The diploic venous system is important to cranial blood circulation, as it facilitates the exchange between extra- and intra-cranial blood. The specific differences between hominins and non-human great apes (Hui and Balzeau, 2023, 2024) suggest that the
diploic venous system has potential application in taxonomic and phylogenetic discussions, especially in distinguishing between *H. neanderthalensis* and *H. sapiens*. The system of diploic channels, even if not fully preserved in Florisbad, appears to have been less expanded than in *H. sapiens* (Hui and Balzeau 2023).

Finally, the globular frontal sinus in Florisbad fills the medial region of the frontal torus. In this regard, the specimen more closely resembles the sinuses observed in *H. erectus* and *H. neanderthalensis*. The volume of the frontal sinus in Florisbad is within the fiducial limits for *H. erectus*, *H. neanderthalensis* and most recent sub-Saharan African population samples. It is notably larger than the average volume recorded for South African Later Stone Age (Holocene) Khoe-San.

In terms of its cranial bone distribution and endocranial proportions, Florisbad resembles the Middle Pleistocene cranium from Kabwe. Florisbad, however, does not share the exceptionally large frontal sinuses seen in this specimen, which are evident also in the Bodo and Petralona crania. Further comparison of the internal anatomical features described here may help in the future to clarify the polarity of these traits, and aid in the interpretation of various Pleistocene fossils.

## ACKNOWLEDGEMENTS

This study was funded by the French National Research Agency (ANR-20-CE27-0009) and the China Scholarship Council (JH), and by Stony Brook University (FEG). We are grateful to the National Museum, Bloemfontein, South Africa for having granted permission to FEG and SH to micro-CT scan the Florisbad cranium. We thank Ron Clarke for discussions relating to the preservation and morphology of the Florisbad
862 fossil. We thank the editor and the three anonymous reviewers who provided useful
863 comments that served to strengthen this paper.

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DATA AVAILABILITY STATEMENT

866 The Florisbad cranium is curated by the National Museum, Bloemfontein, South Africa.

867 The measurements for Florsibad have been provided in this article. The data for the
868 comparative samples are available in the various papers we have published on the
869 different anatomical areas studied here.

870
871 REFERENCES

872 Bae, C.J., Wu, X. 2024. Making sense of eastern Asian Late Quaternary hominin variability. Nat. Commun. 15, 9479.

874 Balzeau, A., 2006. Are thickened cranial bones and equal participation of the three structural bone layers autapomorphic traits of *Homo erectus*? Bull. Mém. Soc. Anthropol. Paris 18, 145-163.

877 Balzeau, A., 2007. Variation and characteristics of the cranial vault thickness in Krapina and Western European Neandertals. Period. Biol. 109, 369-377.

879 Balzeau, A., 2013. Thickened cranial vault and parasagittal keeling, correlated traits and autapomorphies of *Homo erectus*? J. Hum. Evol. 64, 631-644.

881 Balzeau, A., Charlier, P., 2016. What do cranial bones of LB1 tell us about *Homo floresiensis*? J. Hum. Evol. 93, 12-24.

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