The study of the lower limb entheses in the Neanderthal sample from El Sidrón (Asturias, Spain): How much musculoskeletal variability did Neanderthals accumulate?

https://doi.org/10.1016/j.jhevol.2020.102746Get rights and content

Abstract

Entheses have rarely been systematically studied in the field of human evolution. However, the investigation of their morphological variability (e.g., robusticity) could provide new insight into their evolutionary significance in the European Neanderthal populations. The aim of this work is to study the entheses and joint features of the lower limbs of El Sidrón Neanderthals (Spain; 49 ka), using standardized scoring methods developed on modern samples. Paleobiology, growth, and development of both juveniles and adults from El Sidrón are studied and compared with those of Krapina Neanderthals (Croatia, 130 ka) and extant humans. The morphological patterns of the gluteus maximus and vastus intermedius entheses in El Sidrón, Krapina, and modern humans differ from one another. Both Neanderthal groups show a definite enthesis design for the gluteus maximus, with little intrapopulation variability with respect to modern humans, who are characterized by a wider range of morphological variability. The gluteus maximus enthesis in the El Sidrón sample shows the osseous features of fibrous entheses, as in modern humans, whereas the Krapina sample shows the aspects of fibrocartilaginous ones. The morphology and anatomical pattern of this enthesis has already been established during growth in all three human groups. One of two and three of five adult femurs from El Sidrón and from Krapina, respectively, show the imprint of the vastus intermedius, which is absent among juveniles from those Neanderthal samples and in modern samples. The scant intrapopulation and the high interpopulation variability in the two Neanderthal samples is likely due to a long-term history of small, isolated populations with high levels of inbreeding, who also lived in different ecological conditions. The comparison of different anatomical entheseal patterns (fibrous vs. fibrocartilaginous) in the Neanderthals and modern humans provides additional elements in the discussion of their functional and genetic origin.

Introduction

In the past decades, skeletal attachments for muscles, tendons, ligaments, and joint capsules (entheses) have received much attention because, being subject to mechanical stress, it was deemed that their study could be useful for the detection of past customary physical activities. In paleoanthropology, knowledge of usual behavior and physical activity levels of past hominins is a major objective in understanding the biological and cultural aspects that have driven human evolution. However, without a definition of the range of variability in the robusticity of these features in past hominins in comparison with that of modern humans, any interpretation of these aspects remains speculative. It is worth pointing out the term robusticity refers to the modifications of the entheseal surface (roughness, crests, bone formation, and so on), as defined by Hawkey and Merbs (1995) and Mariotti et al., 2004a, Mariotti et al., 2004b, Mariotti et al., 2007. The same term is also used with other meanings in the field of biomechanics (Ruff et al., 1993).

The lack of standards of reference for observing and recording the entheses, characterized by a multifactorial etiology, and for a knowledge of their wide-ranging variability in current human populations has long typified the studies in this field, in many cases arriving at interpretive deviations (Dutour, 1986, Hawkey and Merbs, 1995, Peterson and Hawkey, 1998, Foster et al., 2014 and references therein). In an attempt to record these skeletal features with a more systematic approach, qualitative and quantitative standardized methods have been used for fibrous and fibrocartilaginous entheses (Hawkey and Merbs, 1995, Robb, 1998, Wilczak, 1998, Mariotti et al., 2004b, Mariotti et al., 2007, Mariotti et al., 2009, Villotte, 2006, Villotte et al., 2010, Henderson et al., 2013, Henderson et al., 2016). The two types of entheses differ depending on bone attachment location (diaphysis vs. epiphyses and apophyses, respectively), histology (fibrous entheses, in which the tendons attach to bone directly in bony fibrous entheses, or via the periosteum in periosteal fibrous entheses; and fibrocartilaginous entheses, in which four histological zones are recognizable, namely, tendon, uncalcified fibrocartilage, calcified fibrocartilage, and bone), and biomechanics. Fibrous entheses are characterized by a distribution of the mechanical stress over a larger insertion area, thus decreasing the magnitude of the force at the site, whereas fibrocartilaginous entheses involve a relatively smaller area, resulting in a high concentration of stress (Benjamin et al., 1986, Benjamin et al., 2002). On dry bones, bony fibrous entheses are recognizable as raised ridges or definite roughening (e.g., humeral deltoid enthesis, femoral gluteal enthesis), whereas the periosteal ones leave smooth surface on extensive areas (the fleshy origin of the infraspinatus on the scapula). In both cases, the boundaries of the attachment site are not well defined. Fibrocartilaginous entheses are typically found at epiphyses (the muscles of the rotator cuff, the common flexor and extensor origins) or apophyses (e.g., iliopsoas). In fibrocartilaginous enthesis “The surface of the bone is smooth although not necessarily flat, it is free of vascular foramina and the color and texture are more likely those of an articular surface than the areas of bone covered by periosteum” (Benjamin et al., 1986: 96; see also Benjamin et al., 2002). These sites of attachment are well circumscribed (Fig. 1).

In this context, to investigate the variability of the entheses, different kinds of features have been defined: robusticity, referring to the degree of entheseal development (Mariotti et al., 2007), enthesophytes (possible presence of exostosis of various shapes and dimensions), and ‘osteolytic’ formations (possible presence of porosity or erosions; Mariotti et al., 2004a, Mariotti et al., 2004b). Other authors later suggested referring to these features as entheseal changes (Jurmain and Villotte, 2010, Villotte et al., 2016).

Taking into account the multietiological factors (e.g., age, sex, genetic background, activity) of the entheseal expressions, to define the range of variability of the development of the entheses, modern (19th to 20th century) European-identified (by sex, age, activity, and cause of death) human skeletal collections have been used (Mariotti et al., 2004a, Mariotti et al., 2004b, Mariotti et al., 2007, Villotte et al., 2010, Milella et al., 2012, Milella et al., 2015, Belcastro et al., 2017). Significant variations in robusticity were observed with age (Weiss, 2004, Mariotti et al., 2007, Villotte, 2009, Cardoso and Henderson, 2010; Milella et al., 2012). Milella et al. (2012) identified a sort of threshold of around 50 years, which may mark the biological limit to age-related robusticity development. Sex-related variations were also observed (Milella et al., 2012, Wallace et al., 2017, Wilczak et al., 2017). Age seems to be the most evident factor affecting robusticity, although some patterns (scant or strong development of only specific entheses compared with that of others) may stem from microtraumatic events (overuse in specific, repeated movements), as well as from peculiar postural characteristics (Belcastro and Mariotti, 2000, Mariotti, 2001).

The relationship between the type and amount of physical activity and enthesis development is still a subject of discussion and falls within the broader sphere of ‘bone functional adaptation’ and the information that may be provided by adult bone morphology with regard to adult mechanical loading (Ruff, 1994, Ruff et al., 2006, Foster et al., 2014). A relationship between entheseal features and biomechanical stress has been suggested by some authors considering entheseal morphology. Particularly, Weiss (2003) has reported a statistically significant correlation of enthesis morphology with bone robusticity, among other factors (i.e., age and body size). A multivariate analysis of robusticity scores also identified broad clusters on the basis of the amount of mechanical loading demanded by the occupations of individuals (Milella et al., 2015). Maki and Trinkaus (2011) adopted an original approach with direct biomechanical implications, considering hand entheses as good proxies for the muscle's moment arm and efficiency in muscle force production. Moreover, a recent experimental study confirmed the relationship between changes in entheseal morphology and biomechanical stress in mice, by documenting structural changes in entheses at hierarchical scales relative to variation in mechanical loading (i.e., surgical muscle unloading; Deymier et al., 2019).

Karakostis et al. (2017) examined a raw 3D area of some hand entheses, reporting a consistent correlation between entheseal patterns and long-term physical activity using a documented modern human sample. This correlation was only observable when comparing multivariate analysis of 3D area measurements from different entheses, not when comparing single entheseal areas across individuals. This multivariate approach was recently applied to Neanderthal entheses, highlighting an association between entheseal pattern and habitual grasping behavior (Karakostis et al., 2018). In fact, the use of entheses to reconstruct muscle use and physical activity patterns was validated by two recent experimental studies on mice, relying on 3D multivariate analysis and ‘blind’ analytical protocols, suggesting the presence of an association between entheses and muscle function (Karakostis et al., 2019a, Karakostis et al., 2019b). On the other hand, other animal experimental studies highlighted criticalities in using entheseal morphology as a tool for inferring functional aspects, finding no association between entheses and muscle architecture or physical activity (Zumwalt, 2006, Rabey et al., 2015, Williams-Hatala et al., 2016, Wallace et al., 2017).

Other studies based on 3D area quantification found a relationship with body size, as expected (Zumwalt et al., 2000, Zumwalt, 2005, Zumwalt, 2006, Nolte and Wilczak, 2013), while activity alters only the limb bone structure (Wallace et al., 2017). A recent study conducted on corpses criticized the use of the morphology of the entheses to infer soft-tissue anatomy, and then muscular development, to reconstruct patterns of past behavior, while underscoring the complex architecture of the bone-tendon interface in fibrous and fibrocartilaginous entheses (Williams-Hatala et al., 2016). Conversely, the development and morphogenesis of the tendon-to-bone insertion have been demonstrated to be affected by mechanical factors (muscle loading), which play an important role in the formation of a functional tendon-bone attachment unit (Thomopoulos et al., 2010, Thomopoulos et al., 2015). Bones, tendons, muscle, and joints are patterned in utero, their maturation continues through the early postnatal period, and muscle contractions in utero have been demonstrated to be crucial to the development of sesamoid bones, knee meniscus, and proper bone and joint formation, as well as for the formation of the tendon-bone attachment tissue (Zelzer et al., 2014). The effect of the mechanical load on bone eminence extends beyond embryonic development, as observed in an enlarged deltoid tuberosity in human patients with muscle contracture (Zelzer et al., 2014). However, although there are age-specific differences, the sensitivity to mechanical loading does not end with growth; bone maintenance in adults depends on a continuation of the ‘normal’ mechanical loadings established earlier in development, thus supporting the suggestion that adult bone morphology may reflect differences in adult behavior (Ruff et al., 2006). Finally, the complexity of the bone and tendon-muscle system, the still unclear nature of enthesis robusticity as an adaptation to mechanical loads, and the not well-defined and largely used notion of robusticity in skeletal remains require caution in the use of these traits to reconstruct activity patterns during life (Foster et al., 2014).

In a paleoanthropological context, the various Neanderthal fossils offer the possibility to investigate the entheseal morphology and robusticity. Although the literature on the morphological and biomechanical traits of Neanderthals, mainly in relation to postural aspects and manual skills, is abundant (Trinkaus, 1976a, Trinkaus, 1976b, Trinkaus, 1977, Trinkaus, 1978, Trinkaus, 1983, Trinkaus, 1986, Trinkaus, 1997, Trinkaus, 2006, 2007; Trinkaus and Ruff, 1989; Ruff, 1994; Trinkaus et al., 1998), little attention has been paid to their lower limb entheseal morphology (Trinkaus, 1976a, Belcastro et al., 2006, Pearson and CorderoBusby, 2006, Niewoehner, 2008, Maki and Trinkaus, 2011, Mariotti and Belcastro, 2011, Belcastro and Mariotti, 2017, Karakostis et al., 2018, Karakostis et al., 2019a, Karakostis et al., 2019b). Recent studies on Neanderthal entheses highlighted a correlation of humeral torsional strength and breadth of pectoralis major insertion (Pearson and CorderoBusby, 2006); Niewoehner (2008) partly used entheseal robusticity through geometric morphometric analysis in assessing Neanderthal manual capabilities; Maki and Trinkaus (2011) adopted an original approach to associate Neanderthal entheseal projection with muscle force in relation to tool use; and Karakostis et al. (2018) recently reported the first association of Neanderthal hand entheses with habitual grasping behavior and Mousterian tool use.

To study the enthesis variability in Neanderthals, some specific survey methods designed and tested on Homo sapiens by some authors of the present study have been used (Belcastro and Mariotti, 2000, Belcastro et al., 2001, Mariotti, 2001, Mariotti, 2001, Mariotti et al., 2004a, Mariotti et al., 2004b, Mariotti et al., 2007, Mariotti et al., 2009; Milella et al., 2009, Milella et al., 2012, 2015). The study of lower limb entheses of adult and subadult Krapina Neanderthals (Croatia, 130 ka), conducted using the aforementioned methods, made it possible to uncover some interesting differences in the entheses between Neanderthals and modern humans. In particular, a specific morphology of the entheses of the gluteus maximus and vastus intermedius, with a variability beyond the range of variation in modern humans, has been observed. In particular, the features of the gluteus maximus entheses, which seem to be of a fibrocartilaginous type according to the description of the corresponding features on dry bone given by Benjamin et al. (1986), are the same in adult and subadult individuals, whereas the peculiar imprint of the vastus intermedius is present only in the adult sample (Belcastro et al., 2006, Mariotti and Belcastro, 2011, Belcastro and Mariotti, 2017).

Within the framework of these investigations, we enlarged the Neanderthal sample, analyzing the previously unpublished lower limbs from El Sidrón (Asturias, Spain; ca. 49 ka). The collection has been extensively studied (Bastir et al., 2015, Bastir et al., 2017, Lalueza-Fox et al., 2012, Rosas et al., 2006, Rosas et al., 2008, Rosas et al., 2012, Rosas et al., 2013, Rosas et al., 2015, Rosas et al., 2017a, Rosas et al., 2017b, Rosas et al., 2018, Estalrrich and Rosas, 2013, Estalrrich et al., 2017, Pérez-Criado and Rosas, 2017, Kivell et al., 2018, Ríos et al., 2019). The features of the fossil deposit and the taphonomic conditions suggested that the assemblage was the result of a single event involving simultaneously the human remains and the archeological material (lithic tools; Rosas et al., 2006). They belonged to a small Neanderthal group with close kinship relationships (inbreeding), as molecular evidence, low genetic variability, and skeletal congenital anomalies have shown (Lalueza-Fox et al., 2011; Ríos et al., 2019). The sample consists of more than 2500 human remains, and the postcranial skeletal elements studied in detail up to now are the upper limb, ribs, clavicles (Rosas et al., 2015, Bastir et al., 2015, Bastir et al., 2017, Pérez-Criado and Rosas, 2017, Kivell et al., 2018), and tali (Rosas et al., 2017a). The phylogenetic origin of some upper limb features shows that they have evolved in a mosaic fashion and were inherited from Early Pleistocene populations, while other characters emerged in the specific H. sapiens and Homo neanderthalensis lineages, sometimes appearing as primitive (Rosas et al., 2015, Pérez-Criado and Rosas, 2017). The lower limb elements from El Sidrón, compared with other postcranial bones (mainly consisting of hand and foot metapodials and phalanges), are poorly represented (Rosas et al., 2006, Rosas et al., 2013, Rosas et al., 2016, Rosas et al., 2017a). We investigated for the first time the variability of the lower limb entheses in the Neanderthal sample from El Sidrón to test the following hypotheses: (1) similar to Krapina Neanderthals, the morphology of gluteus maximus and vastus intermedius entheses of El Sidrón falls outside the range of morphological variability of modern humans, whereas the other lower limb entheses are similar in the three groups of hominins considered, and (2) the two Neanderthal groups are more similar to each other than to modern humans.

Section snippets

Materials and methods

In the sample from El Sidrón, which is housed at the Department of Paleobiology at the National Museum of Natural History (MNCN-CSIC) in Madrid, Spain, all the skeletal parts are represented, and at least 13 individuals—seven adults (at least three females and three males) and six immature individuals (one infant, two juveniles, and three adolescents)—have been identified by morphological and paleogenetic analyses (Rosas et al., 2006, Rosas et al., 2012, Rosas et al., 2013, Rosas et al., 2017a,

Results

The imprints of the gluteus maximus, iliopsoas, vastus medialis, and vastus intermedius have been observed in 7 adult femurs (Table 1). A general low robusticity of the femoral entheses was observed in the lowest grade range. The adult enthesis of the gluteus maximus is a wide, raised, and relatively rough imprint in the proximal part, extending distally into a crest, showing features in the range of fibrous enthesis morphology (Figure 2, Figure 3). The morphology of the two juvenile femurs of

Discussion

Despite the fragmentary status of the lower limb elements from El Sidrón, it was possible to make some observations on the enthesis development. In general, the adult sample shows a low degree of robusticity.

The shape of the gluteus maximum imprint of the El Sidrón sample exceeds the range of modern human variability, although its morphology suggests a bony fibrous enthesis, as in modern humans. In 1 of 2 (SD-105) adult specimens, the aspect of the anterolateral surface corresponding to the

Conclusions

The lower limb enthesis variability and additional elements for the reconstruction of the biological profile of some El Sidrón specimens is described for the first time and allows us to make the following considerations:

  • 1.

    Some Neanderthal entheses (gluteus and vastus intermedius imprints) exceed the range of modern human variability. Thus, the available methods to study entheseal morphology are not always suitable to record the Neanderthal entheses.

  • 2.

    The entheses of the gluteus and vastus

Acknowledgments

This work is funded by the Spanish Ministry of Economy and Competitiveness: CGL2016-75109-P. We would like to thank Jakov Radovčić, former curator of the Krapina collection in the Croatian Natural History Museum in Zagreb, for allowing us access to the original Krapina specimens. We also thank Simona Bonara for the photographs of the subadults of the Certosa Collection.

References (139)

  • J.-J. Hublin et al.

    Ebb and flow or regional extinctions? On the character of Neandertal occupation of northern environments

    C. R. Palevol

    (2009)
  • T.L. Kivell et al.

    New Neandertal wrist bones from El Sidrón, Spain (1994–2009)

    J. Hum. Evol.

    (2018)
  • C. Lalueza-Fox et al.

    Palaeogenetic research at the El Sidrón Neanderthal site

    Ann. Anat.

    (2012)
  • J.L. Locht et al.

    Timescales, space and culture during the Middle Palaeolithic in northwestern France

    Quat. Int.

    (2016)
  • V. Mariotti et al.

    Lower limb entheseal morphology in the Neandertal Krapina population (Croatia, 130 000 BP)

    J. Hum. Evol.

    (2011)
  • L. Pérez-Criado et al.

    Evolutionary anatomy of the Neandertal ulna and radius in the light of the new El Sidrón sample

    J. Hum. Evol.

    (2017)
  • K.N. Rabey et al.

    Locomotor activity influences muscle architecture and bone growth but not muscle attachment site morphology

    J. Hum. Evol.

    (2015)
  • T.C. Rae et al.

    The Neanderthal face is not cold adapted

    J. Hum. Evol.

    (2011)
  • A. Rosas et al.

    The Neandertals from El Sidrón (Asturias, Spain). Updating of a new sample

    Anthropologie

    (2012)
  • A. Rosas et al.

    Identification of Neandertal individuals in fragmentary fossil assemblages by means of tooth associations: the case of El Sidrón (Asturias, Spain)

    C. R. Palevol

    (2013)
  • A. Rosas et al.

    A geometric morphometrics comparative analysis of Neandertal humeri (epiphyses-fused) from the El Sidrón cave site (Asturias, Spain)

    J. Hum. Evol.

    (2015)
  • A. Rosas et al.

    Adult Neandertal clavicles from the El Sidrón site (Asturias, Spain) in the context of Homo pectoral girdle evolution

    J. Hum. Evol.

    (2016)
  • J.L. Arsuaga et al.

    Postcranial morphology of the middle Pleistocene humans from Sima de los Huesos, Spain

    Proc. Natl. Acad. Sci. USA

    (2015)
  • D.M. Badoux

    Probabilité d’une différenciation due au climat chez les Neandertaliens d'Europe

    L'Anthropologie

    (1965)
  • M.G. Belcastro et al.

    Morphological and biomechanical analysis of a skeleton from Roman Imperial necropolis of Casalecchio di Reno (Bologna, Italy, II-III c. A.D.). A possible case of crutch use

    Coll. Antropol.

    (2000)
  • M.G. Belcastro et al.

    A muscular imprint on the anterolateral surface of the proximal femurs of the Krapina Neandertal collection

    Am. J. Phys. Anthropol.

    (2017)
  • M.G. Belcastro et al.

    Skeletal markers of actvity in the Early Middle Ages necropolis of Vicenne-Campochiaro (Molise, Italy)

    J. Paleopathol.

    (2001)
  • M.G. Belcastro et al.

    Musculoskeletal stress and adult age markers in the Krapina Hominid collection: the study of femora 213 Fe.1 and 214 Fe.2

    Period. Biol.

    (2006)
  • M.G. Belcastro et al.

    The history and composition of the identified human skeletal collection of the Certosa cemetery (Bologna, Italy, 19th–20th century)

    Int. J. Osteoarchaeol.

    (2017)
  • M.G. Belcastro et al.

    Variations in epiphyseal fusion and persistence of the epiphyseal line in the appendicular skeleton of two identified modern (19th–20th c.) adult Portuguese and Italian samples

    Am. J. Phys. Anthropol.

    (2019)
  • M. Benjamin et al.

    Fibrocartilage in tendons and ligaments. An adaptation to compressive load

    J. Anat.

    (1998)
  • M. Benjamin et al.

    The histology of tendon attachments to bone in man

    J. Anat.

    (1986)
  • J.M. Bermúdez de Castro et al.

    Early Pleistocene human humeri from the Gran Dolina-TD6 site (Sierra de Atapuerca, Spain)

    Am. J. Phys. Anthropol.

    (2012)
  • J. Bermúdez de Castro et al.

    The medial pterygoid tubercle in the Atapuerca Early and Middle Pleistocene mandibles: Evolutionary implications

    Am. J. Phys. Anthropol.

    (2015)
  • F.A. Cardoso et al.

    Enthesopathy formation in the humerus: Data from known age-at-death and known occupation skeletal collections

    Am. J. Phys. Anthropol.

    (2010)
  • J.M. Carretero et al.

    Los humanos de la Sima de los Huesos (Sierra de Atapuerca) y la evolucion del cuerpo en el género Homo

  • S.E. Churchill

    Bioenergetic perspectives on Neanderthal thermoregulatory and activity budgets

  • S. Condemi

    I Neandertaliani dal 1856 ai giorni nostri

  • C.S. Coon

    The Origin of Races

    (1962)
  • C.B. Davis et al.

    Patterns of interobserver error in the scoring of entheseal changes

    Int. J. Osteoarchaeol.

    (2013)
  • J. Dorfl

    Migration of tendinous insertions. I. Cause and mechanism

    J. Anat.

    (1980)
  • J. Dorfl

    Migration of tendinous insertions. II. Experimental modifications

    J. Anat.

    (1980)
  • O. Dutour

    Enthesopathies (lesions of muscular insertions) as indicators of the activities of Neolithic Saharan population

    Am. J. Phys. Anthropol.

    (1986)
  • A. Estalrrich et al.

    Handedness in Neandertals from the El Sidrón (Asturias, Spain): Evidence from instrumental striations with ontogenetic inferences

    PLoS One

    (2013)
  • A. Estalrrich et al.

    Evidence of toothpick groove formation in Neandertal anterior and posterior teeth

    Am. J. Phys. Anthropol.

    (2017)
  • V. Fabre et al.

    Genetic evidence of geographical groups among Neanderthals

    PLoS One

    (2009)
  • A. Foster et al.

    Using enthesis robusticity to infer activity in the past: a review

    J. Archaeol. Method Theory

    (2014)
  • R.G. Franciscus

    Comparing internal nasal fossa dimensions and classical measures of the external nasal skeleton in recent humans: inferences for respiratory airflow dynamics and climatic adaptation

    Am. J. Phys. Anthropol.

    (2003)
  • A. Gómez-Robles

    Dental evolutionary rates and its implications for the Neanderthal–modern human divergence

    Sci. Adv.

    (2019)
  • D. Guatelli-Steinberg et al.

    Anterior tooth growth periods in Neandertals were comparable to those of modern humans

    Proc. Natl. Acad. Sci. USA

    (2005)
  • Cited by (0)

    View full text