Journal of Archaeological Science 94 (2018) 12–20
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New osteological criteria for the identification of domestic horses, donkeys and their hybrids in archaeological contexts
T
Pauline Hanota,∗, Corentin Bochatonb Laboratoire "Archéozoologie et Archéobotanique: Sociétés, Pratiques et Environnements" UMR 7209 – CNRS, MNHN - Muséum National d’Histoire Naturelle - Sorbonne Universités, 55 rue Buffon, CP 56, 75005 Paris, France b Max Planck Institute for the Science of Human History, Department of Archaeology, Kahlaische Straße 10, D-07745, Jena, Germany a
A R T I C LE I N FO
A B S T R A C T
Keywords: Morphological variability Equus Osteology Taxonomic identification Zooarchaeology
The identification of domestic equid remains is a recurrent issue and an intense subject of discussion in zooarchaeological studies. Indeed, despite historical sources describing the key role of equids in numerous past societies, their accurate identification on archaeological sites is still problematic, and only few methods have been developed in order to distinguish the bones of horses, donkeys and their hybrids. Moreover, some of the extant published visual macroscopic criteria are considered as possibly unreliable, partly because of the absence of preliminary test on a large sample of modern specimens. In this work, we try to solve these issues by testing a set of macroscopic visual criteria, collected in the literature or newly described, on a comparative sample of 107 modern skeletons of domestic equids. We quantified the reliability of these criteria and found evidence of 26 osteological characters allowing for the identification of between 90% and 100% of the horses and donkeys of our comparative sample. A method to identify the complete or sub-complete skeletons of hybrids is also proposed using combinations of characters observed on several bones. Finally, the defined osteological criteria are observed on a set of archaeological skeletons, coming from antique to modern sites, in order to demonstrate the applicability of our approach to archaeological remains. The use of our methodology on zooarchaeological samples could allow for a better assessment of the presence of donkeys and hybrids in archaeological sites, and thus, could help improve the knowledge of their respective importance and use by human past societies.
1. Introduction The reliable identification of closely related taxa is a recurrent issue in zooarchaeology and this question is critical for taxa of specific socioeconomical interest, such as equids (Clutton-Brock, 1992). The latter are represented by two domestic species which may have been simultaneously present in European archaeological sites since the Iron Age (Bökönyi, 1991): the horse (Equus caballus Linnaeus, 1758), and the donkey (Equus asinus Linnaeus, 1758). The identification of these taxa is made even more complex by the fact that they can crossbreed, which implies the potential occurrence of their hybrids in archaeological deposits: mules (Equus asinus x Equus caballus), and hinnies (Equus caballus x Equus asinus). An accurate and systematic identification of archaeological equid remains is however mandatory for a good understanding of archaeological deposits, and for a correct description of animal exploitation strategies in past human societies. Indeed, domestic equids are known to have played a key role in the economy of many past civilizations worldwide, and many historical sources extensively describe their ∗
respective uses by humans (Clutton-Brock, 1992). For instance in the Roman empire, horses were largely used for riding, hunting and racing (White, 1970) because of their running ability, whereas donkeys were acknowledged for their endurance making them particularly suitable for traction, and as pack animal in farming activities (Hyland, 1990; Peters, 1998; Toynbee, 1973). Concerning mules, they were renowned for their vigor and were mostly employed for long distance transport of persons or goods (Armitage and Chapman, 1979). At the opposite, hinnies were rarely used, and are described as being of low working interest (Clutton-Brock, 1992; Loudon, 1825). This broad diversity of uses demonstrates that an accurate and reliable identification of equid archaeological remains is of high interest for a better understanding of socio-economic systems in past societies. Several methodologies have been developed in order to distinguish equid species from bone morphology. Approaches based on the observation of visual macroscopic criteria were first proposed (Arloing, 1882; Rosselli Vilá, 1921) and, more recently, methods using geometric morphometrics (GMM) have been applied to this question in order to provide more reliable identifications (Cucchi et al., 2017; Hanot et al.,
Corresponding author. E-mail addresses:
[email protected] (P. Hanot),
[email protected] (C. Bochaton).
https://doi.org/10.1016/j.jas.2018.03.012 Received 1 November 2017; Received in revised form 30 March 2018; Accepted 31 March 2018 0305-4403/ © 2018 Elsevier Ltd. All rights reserved.
Journal of Archaeological Science 94 (2018) 12–20
P. Hanot, C. Bochaton
two extant caballine species (both belonging to the subgenus Equus; Groves and Grubb, 2011): 23 domestic horses (Equus caballus Linnaeus, 1758) of various breeds, and 15 Przewalski's horses (Equus przewalskii Poliakov, 1881). Both males and females are included, in relatively equal proportions (see online Supplementary material S1). All specimens are adult with fully fused long bones epiphyses in order to discard the impact of growth on bone morphology. Our study focused on nine bone elements from cranial (skull and mandible) and postcranial (scapula, humerus, radius/ulna, third metacarpal bone, femur, tibia, and proximal phalanx) skeleton. Between one and five criteria were found as reliable on each bone, 15 of these criteria were newly described by the authors and 11 originated from the literature. These criteria are described in our study following the anatomical nomenclature of Barone (1976). For each criterion, two character states were defined corresponding to horse (“A”) and donkey (“B”). When the character state was not clearly recordable on comparative specimens, it was registered as such (“A/B”). A criterion which was impossible to observe (e.g. broken bone, bones kept in anatomical connection, etc.) was registered as unobservable (“-”). All the observations were carried out by a single observer (PH). To synthesize the observations, several quantification tools were defined. The Number of Observations (NObs) refers to the total number of times a criterion was observed should it be a clear character state (“A”, “B”) or not (“A/B”). The Number of Attributions (NA) corresponds to the number of times a criterion was unambiguously attributed to a character state (“A” or “B”). The Number of Correct attributions (NC) corresponds to the number of correctly-classified specimens for each criterion (sum of the number of horses correctly identified by the “A” state and of the number of donkeys correctly identified by the “B” state). This allows us to compute the Percentage of Assessment (PA=NA/NObs*100) and a Correct Identification Rate (CIR=NC/ NA*100). The PA is supposed to reflect the variability of the criterion and the difficulty to clearly define the character state. As for the CIR, it is also supposed to reflect the reliability of the criterion. Only the criteria with CIR above or equal to 90% and PA above or equal to 80% were retained and are described in this study.
2017). Nevertheless, GMM approaches remain challenging to implement, and they currently suffer from a low practicability in routine zooarchaeological studies due to the relatively long sequence of analytical protocols they require. On the other hand, the reliability of the methods based on macroscopic criteria is often called into question partly because of the surprisingly small amount of remains attributed to donkeys and hybrids in archaeological sites which contrasts with their seeming economic importance documented by historical sources (Albarella et al., 1993; Bökönyi, 1974; Johnstone, 2006; Manconi, 1995; Peters, 1998). Most of the currently used identification criteria are based on the morphology of teeth enamel (Armitage and Chapman, 1979; Davis, 1980; Eisenmann, 1986; Payne, 1991; Uerpmann, 2002), and of the skull (Albizuri and Nadal, 1991; Azzaroli, 1978; Eisenmann, 1986, 1980; Groves and Mazák, 1967; Kunst, 2000) but only few criteria are available for postcranial elements (Arloing, 1882; Barone, 1986; Eisenmann and Beckouche, 1986; Peters, 1998; Rosselli Vilá, 1921). Unfortunately, most of these characters are considered as unreliable or difficult to observe (Albarella et al., 1993; Baxter, 1998; Johnstone, 2004; Zeder, 1986). The main issue of these works is often related to the number of specimens included in the comparative sample used to describe the criteria. Indeed, the used sample size is often small and unfitted to a correct consideration of the intraspecific variability within each taxon. Moreover, these works generally lack preliminary tests performed on a reference sample in contrary to what has been done on other taxa (Bochaton et al., 2016; Zeder and Lapham, 2010; Zeder and Pilaar, 2010); this prevents to quantify the reliability of the defined identification criteria. These difficulties frequently result in identifications of archaeological equid remains mainly based on the largely criticized criterion of simple bone size (Forest, 2008), considering that horses and mules are larger than donkeys. However, this size criterion was recently demonstrated as irrelevant by a study of bone shape data which allowed for the identification of small size horse bones in archaeological contexts (Hanot et al., 2017). The same study also revealed that bone size is not appropriate for the distinction of modern horses, donkeys and hybrids. Another major limitation is the near-absence of criteria allowing for the identification of hybrids. This is mainly explained by the fact that they probably concomitantly display morphological characteristics of both their parents (Forest, 1997). In addition, the small number of hybrid skeletons available in osteological collections has likely contributed to restrain the development of identification methodologies (Johnstone, 2006). The aim of this study is to try to solve these different issues concerning the identification of archaeological equid remains by proposing an easily applicable identification method for isolated bones of horses and donkeys using reliable macroscopic osteological criteria. We also investigate the morphology of hybrids in order to evaluate their morphological variability and to propose an identification method. To do so we use a large comparative sample of 107 modern skeletons of horses, donkeys, and hybrids in order to assess the reliability of a set of morphological criteria defined on nine different bones. Eleven of these characters have been collected in the literature (Barone, 1986; Eisenmann, 1986; Kunst, 2000; Peters, 1998), but we also describe a set of 15 new criteria. Finally, in order to demonstrate the relevance of our approach, we performed an application of our identification methodology on a sample of five equid skeletons discovered on French archaeological sites.
2.2. Research of osteological criteria for the identification of hybrids Our modern comparative sample includes 25 skeletons of hybrids between horse and donkey: 8 hinnies (Equus caballus x Equus asinus) and 17 mules (Equus asinus x Equus caballus). The characters found as reliable for the identification of horses and donkeys were tested on hybrid specimens; among them four have been previously described by Peters (1998) as allowing to identify mules. 2.3. Archaeological application The applicability of the defined identification criteria to archaeological material was assessed using 5 archaeological equid skeletons (Table 1). All of these specimens are complete, or almost complete, and come from French sites dating from the 3rd to the 19th century. They were all recorded as articulated skeletons in the field and were considered as corresponding to single individuals. The only exception is the set of bones from Elbeuf - “Rue Guynemer” whose attribution to a single specimen is mainly related to the fact that they were discovered in the same archaeological feature (Barme and Clavel, 2015). All the skeletons have previously been identified (Table 1) on the basis of both visual macroscopic (Barme and Clavel, 2015; Derbois, 2006; Lepetz, 1996; Yvinec, 1998), and GMM criteria (Hanot et al., 2017). However, it should be mentioned that the identification of the specimen from Elbeuf has proven to be problematic. Indeed, it was primarily supposed to be a donkey on the basis of visual criteria observed on teeth coupled with the small size of its bones (Barme and Clavel, 2015); but a subsequent study using GMM data has suggested it was a mix between horse and donkey bones (Hanot et al., 2017).
2. Material and method 2.1. Research of osteological criteria for the distinction between horses and donkeys Our modern comparative sample includes 82 complete or subcomplete skeletons of horses (39 specimens) and donkeys (43 specimens) from several European museum institutions (see online Supplementary material S1). Horses specimens are represented by the 13
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Table 1 List of the archaeological specimens. Archaeological site "Fresnes-lès-Montauban"
Locality
Datation rd
c.
Anatomical connections
Previous identification
Preserved
Horse (Hanot et al., 2017; Lepetz, 1996) Horse (Hanot et al., 2017) Donkey (Hanot et al., 2017; Yvinec, 1998) Donkey/Horse (Barme and Clavel, 2015; Hanot et al., 2017) Donkey (Derbois, 2006)
3
"Le Village" "La Vieille Église" "Rue Guynemer"
Fresnes-lès-Montauban (Pas-de-Calais/ France) Longueil-Annel (Oise/France) Baillet-en-France (Val-d’Oise/France) Elbeuf (Seine-Maritime/France)
18 c. 10–11th c. 16th c.
Preserved Preserved Not preserved
"155 rue Anatole-France - Les Serres"
Méru (Oise/France)
18–19th c.
Preserved
th
Fig. 1. Distinctive characters of skull and mandible. A: Skull of donkey (MNHN-ZAAC, 1982.128) and horse (MNHNUMR7209-E1) in dorsal view; B: Posterior part of the skull of donkey (MNHN-ZA-AC, 1982.128) and horse (MNHN-UMR7209-E1) in lateral view; C: Premaxillary part of the skull of donkey (MNHN-ZA-AC, 1982.128) and horse (MNHN-ZA-AC, 1980.29) in ventral view; D: Postero-dorsal part of the mandible of donkey (MNHN-ZA-AC, 1982.128) and horse (MNHN-UMR7209ind.) in lateral view; E: Anterior part of the mandible of donkey (MNHN-ZA-AC, 1982.128) and horse (MNHN-ZA-AC, 1929.35) in lateral view. Abbreviations: c. p.: coronoid process; e. o. p.: external occipital process; f.: frontal; i. b.: inter-alveolar border; m. f.: mental foramen; n. p.: nuchal plane; o.: orbit; o. c.: occipital condyle; t. i.: third incisor.
3. Results
(2004). SK2 (N Obs = 65, PA = 85%, CIR = 100%): Posterior extension of the external occipital process (Fig. 1-B) – visible in lateral view. In horses, the external occipital process is weakly posteriorly extended above the nuchal plane (SK2A) whereas, in donkeys, this process presents a strong posterior projection that overcomes the posterior margin of the occipital condyle (SK2B). This last character state was mentioned by Barone (1976) as characteristic of donkeys, and by Arloing (1882) as observable on hybrids too. Moreover, the recent GMM study of Hanot et al. (2017) also signaled it. SK3 (N Obs = 65, PA = 88%, CIR = 96%): Morphology of the anterior part of the incisive bone (Fig. 1-C) – visible in ventral view. In horses, the inter-alveolar borders of the incisive bone are arched (SK3A) whereas they are more parallel and straight in donkeys (SK3B). This criterion was previously signaled by Johnstone (2004).
The full set of observations performed on each specimen of the modern sample is included as online Supplementary material S2. 3.1. Reliable criteria for the distinction between horses and donkeys 3.1.1. Skull SK1 (N Obs = 64, PA = 86%, CIR = 100%): Shape of the zygomatic process of the frontal bone (Fig. 1-A) – visible in anterior and dorsal views. In donkeys, the zygomatic process of the frontal bone is more laterally extended (SK1B) than in horses (SK1A). This difference concerning the morphology of the supra-orbital border of the frontal was first signaled by Barone (1976) and is also mentioned by Johnstone 14
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SK4 (N Obs = 65, PA = 92%, CIR = 93%): Morphology of the anterior margin of the temporal fossa (not figured) – visible in dorsal view. In horses, the anterior margin of the temporal fossa is bordered by a sharp crest prolonging the temporal line (SK4A). In donkeys, the anterior margin of the temporal fossa is thicker and blunted (SK4B).
characteristic of donkeys, and by Peters as also occurring on mules (1998). R2 (N Obs = 74, PA = 81%, CIR = 98%): Shape of the lateral tuberosity of the olecranon (Fig. 3-B) – visible in lateral view. In horses, the lateral tuberosity of the olecranon for the insertion of the lateral head of the triceps brachii is of rounded shape (R2A). In donkeys, this tuberosity is more expended and elongated in ventral direction (R2B). R3 (N Obs = 74, PA = 95%, CIR = 91%): Ossification of the interosseous proximal ligament (Fig. 3-B) – visible in lateral view. In horses, the interosseous proximal ligament is not ossified resulting in a gap between radius and ulna bones above the interosseous space (R3A). In donkeys, the interosseous proximal ligament tends to be ossified making the ulna completely fused to the radius above the interosseous space (R3B). This character was first signaled by Barone (1976).
3.1.2. Mandible MD1 (N Obs = 56, PA = 88%, CIR = 96%): Morphology of the coronoid process (Fig. 1-D) – visible in lateral view. In horses, the dorsal extremity of the coronoid process of the mandible is rounded or truncated in lateral view (MD1A). In donkeys, it is more triangular (MD1B). The shape of the coronoid process was also considered as discriminating by Barone (1976) who described it as incurved in posterior direction in donkeys. MD2 (N Obs = 65, PA = 91%, CIR = 90%): Orientation of the mental foramen (Fig. 1-E) – visible in lateral view. In horses, the mental foramen (“foramen mentonnier” sensu Barone, 1976) is oriented in posterior direction resulting in a medial border of the foramen visible in lateral view (MD2A). In donkeys, the mental foramen is more oriented in medial direction and so laterally deeper. As a consequence the medial delimitation of the foramen of donkeys is not visible in lateral view (MD2B).
3.1.6. Third metacarpal MC1 (N Obs = 69, PA = 91%, CIR = 97%): Shape of the distal extremity (Fig. 3-C) – visible in posterior view. In horses, the posterior intermediate projection of the distal condyle is well extended in dorsal direction making curvilinear the posterodorsal border of the distal epiphysis of the bone (MC1A). In donkeys, the posterior intermediate projection of the distal condyle is weakly extended in dorsal direction making straighter the postero-dorsal border of the distal epiphysis of the bone (MC1B). MC2 (N Obs = 72, PA = 86%, CIR = 94%): Depression on the distal posterior area (Fig. 3-C) - visible in posterior view. In horses, the distal posterior area of the third metacarpal is flat (A). In donkeys, this area is depressed (MC2B). This last character state was previously signaled by Arloing (1882) as characteristic of donkeys and mules, and by Peters (1998) as occurring on mules.
3.1.3. Scapula SC1 (N Obs = 69, PA = 84%, CIR = 97%): Shape of the tuberosity of the scapular spine (Fig. 2-A) – visible in lateral view. In horses, the tuberosity of the scapular spine is elongated (SC1A) whereas it is ovoid in donkeys (SC1B). 3.1.4. Humerus H1 (N Obs = 74, PA = 85%, CIR = 98%): Shape of the minor tubercle (Fig. 2-B) – visible in medial view. In horses, the anterior part of the minor tubercle is rounded and weakly extended in anterior direction (H1A). In donkeys, the minor tubercle presents a rectangular shape and is well-extended in anterior direction (H1B). H2 (N Obs = 74, PA = 91%, CIR = 97%): Morphology of the intermediate tubercle (Fig. 2-B) – visible in medial view. In horses, the intermediate tubercle is well-extended in anterior direction (H2A). In donkeys, the intermediate tubercle is weakly anteriorly extended (H2B). The prominence of the intermediate tubercle was also signaled by Barone (1976) as a distinctive character between horses and donkeys. H3 (N Obs = 75, PA = 96%, CIR = 92%): Shape of articular head (Fig. 2-C) - visible in dorsal view. In horses, the most anterior point of the articular head of the humerus is located at the level of the intertubercular groove, between the lateral and intermediate tubercles (H3A). In donkeys, this point is located at the level of the intermediate tubercle (H3B). H4 (N Obs = 75, PA = 97%, CIR = 90%): Lateral epicondylar crest (Fig. 2-D) – visible in ventral view. In horses, the posterior crest of the lateral epicondyle is blunted, giving to the posterior extremity a rounded shape in ventral view (H4A). In donkeys, the crest of the lateral epicondyle is sharper, giving to the posterior extremity a pointed shape in ventral view (H4B).
3.1.7. Proximal phalanx P1 (N Obs = 71, PA = 80%, CIR = 96%): Imprint of the distal middle sesamoidean ligament (Fig. 3-D) – visible in palmar and lateral views. In horses, the imprint of the distal middle sesamoidean ligament (“ligamentous insertions” sensu Barone, 1976) is weakly developed with a blunt margin (P1A). In donkeys, this imprint is strongly marked with a sharp margin (P1B). This last character state was signaled as occurring on mules by Peters (1998). 3.1.8. Femur F1 (N Obs = 74, PA = 97%, CIR = 100%): Occurrence of a crest linking the third to the greater trochanter (Fig. 4-A) – visible in lateral view. In horses, the femur bears a well-marked sharp crest linking the third trochanter to the greater trochanter (F1A). In donkeys, this crest is absent and this area is smooth (F1B). F2 (N Obs = 74, PA = 91%, CIR = 99%): Medial margin of the intertrochanteric crest (Fig. 4-B) – visible in medial view. In horses, the medial margin of the intertrochanteric crest delimiting the posterior limit of the trochanteric fossa is thick and blunted (F2A). In donkeys, the medial margin of the intertrochanteric crest is thin and sharp (F2B). F3 (N Obs = 74, PA = 96%, CIR = 97%): Morphology of the greater trochanter (Fig. 4-A) – visible in lateral view. In horses, the dorsal margin of the greater trochanter is of triangular shape (F3A). In donkeys, this structure is rounded and shorter (F3B). F4 (N Obs = 74, PA = 95%, CIR = 97%): Morphology of the convexity of the greater trochanter (Fig. 4-C) – visible in dorsal view. In horses, the convexity of the greater trochanter presents a welldelimited dorsal tuberosity that extends along an antero-posterior axis (F4A). In donkeys, this tuberosity presents a medial extension on the anterior margin of the epiphysis (F4B).
3.1.5. Radius/ulna R1 (N Obs = 74, PA = 95%, CIR = 100%): Morphology of the transversal crest of the radius (Fig. 3-A) – visible in posterior and ventral view. In horses, the radius presents a continuous and straight distal transversal crest (R1A). In donkeys, this transversal crest is dug by a wide furrow passing through the epiphyseal junction. In ventral view, this furrow gives a curved shape to the transversal crest (R1B). This last character state was previously mentioned by Barone (1976) as 15
Journal of Archaeological Science 94 (2018) 12–20
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Fig. 2. Distinctive characters of scapula and humerus. A: Scapula of donkey (MNHN-ZAAC, 1982.128) and horse (MNHN-ZA-AC, 1929.35) in lateral view; B: Dorsal part of the humerus of donkey (MNHN-ZA-AC, 1982.128) and horse (MNHN-ZA-AC, 1962.228) in lateral view; C: Humerus of donkey (MNHN-ZA-AC, 1982.128) and horse (MNHN-ZA-AC, 1929.35) in dorsal view; D: Humerus of donkey (MNHN-ZA-AC, 1982.128) and horse (MNHN-ZA-AC, 1929.35) in ventral view. Abbreviations: a. h.: articular head; i. t.: intermediate tubercle; l. e.: lateral epicondyle; l. t.: lateral tubercle; m. t.: minor tubercle; s. s.: scapular spine; t. s. s.: tuberosity of the scapular spine.
F5 (N Obs = 74, PA = 82%, CIR = 95%): Dorsal extension of the lesser trochanter (Fig. 4-B) – visible in medial view. In horses, the lesser trochanter extends dorsally toward the head of the femur in the form of a well-marked crest whose dorsal limit nearly reaches the head of the femur (F5A). In donkeys, the dorsal extension of the lesser trochanter is either absent or marked by a weakly defined crest whose dorsal limit reaches a maximum of two-third of the distance between the tuberosity and the head of the femur (F5B).
surface of the tibia does not extend to the medial and posterior margins of the bone, and its posteromedial margin forms an angle (T2B). T3 (N Obs = 75, PA = 92%, CIR = 94%): Shape of the lateral condyle of the proximal articular surface (Fig. 5-B) – visible in dorsal view. In horses, the posterior extremity of the lateral condyle of the tibia is enlarged (T3A). In donkeys, this extremity presents a more constricted and pointed shape (T3B). T4 (N Obs = 75, PA = 87%, CIR = 92%): Morphology of the tuberosity of the tibial crest (Fig. 5-C) – visible in anterior view. In horses, the tuberosity for attachment of the semitendinosus muscle located on the tibial crest is relatively weakly developed (T4A). In donkeys, the tuberosity is more developed (T4B). This last character state was previously highlighted by Barone (1976) and Arloing (1882) as a characteristic of donkeys.
3.1.9. Tibia T1 (N Obs = 74, PA = 91%, CIR = 99%): Shape of the distal articular surface (Fig. 5-A) – visible in ventral view. In horses, the posterior margin of the distal extremity of the tibia is quite straight providing a nearly rectangular shape to the articular surface (T1A). In donkeys, the articular surface is extended in posterolateral direction and presents a more trapezoidal shape (T1B). This last character state was previously signaled by Peters (1998) as occurring on mules. T2 (N Obs = 75, PA = 91%, CIR = 96%): Shape of the medial condyle of the proximal articular surface (Fig. 5-B) – visible in dorsal view. In horses, the medial articular surface of the tibia presents a rounded posteromedial margin (T2A). In donkeys, the medial articular
3.2. Characterization of hybrids specimens We found no reliable visual qualitative character for the identification of hybrids on the basis of osteology. According to our results, hybrids have proved to be strongly morphologically variable in regard of their character states with specimens displaying from 100% of donkey criteria to 95% of horse criteria (see online Supplementary 16
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Fig. 3. Distinctive characters of radius/ulna, third metacarpal and proximal phalanx. A: Radius/ulna of donkey (MNHN-ZA-AC, 1982.128) and horse (MNHN-ZA-AC, 1929.35) in ventral view; B: Proximal part of the radius/ulna of donkey (MNHN-ZAAC, 1982.128) and horse (MNHN-ZA-AC, 1929.35) in lateral view; C: Distal part of the third metacarpal of donkey (MNHN-ZA-AC, 1982.128) and horse (MNHN-ZA-AC, 1929.35) in posterior view; D: Proximal phalanx of donkey (MNHN-ZA-AC, 1893.634) and horse (MNHN-ZA-AC, 1975.124) in lateral and ventral views. Abbreviations: a. f. h.: articular facet with the humerus; d. p. a.: depression of the distal posterior area; d. t.: dorsal tuberosity of the olecranon; i. s. l.: imprint of the sesamoidean ligament; i. p.: intermediate projection; i. s.: interosseous space; l. t.: lateral tuberosity of the olecranon; o.: olecranon; t. c.: transversal crest.
donkey on the basis of its predominant attribution in the case it exceeds 85% of the recorded criteria (among at least 13 criteria recorded as “A” or “B” states); 2) a specimen presenting less than 85% of the criteria corresponding to one of the parent species cannot be undoubtedly identified as a horse or donkey and is possibly a hybrid. In our comparative sample, only hybrid specimens present less than 80% of the criteria of their predominant attribution.
material S3). However, it should be mentioned that the hybrid bones globally display more identification criteria recorded as “B” state (corresponding to a donkey character - 47%) than to “A” (horse - 33%) or “AB” (undefined - 20%) states. This means that donkey character states are more frequently recorded than horses ones on hybrid specimens. This remark is valid for the criteria from the literature (R1, MC2, T1, P1) signaled as occurring on hybrid specimens (see online Supplementary material S4) and that we observed in donkeys. However, our overall results show that hybrid skeletons present, for most of them, a patchwork of criteria we found as characteristic of horses and donkeys. This can appear as potentially useful for the identification of mostly complete skeletons of hybrids using the identification criteria of their parent species. In order to take advantage of this specificity, we considered the most complete skeletons of our sample (i. e. specimens on which more than half of the 26 retained criteria have been recorded as “A” or “B” states). Among the 63 most complete of our horse and donkey skeletons, 62 present more than 85% of character states corresponding to their species (see online Supplementary material S3). At the opposite, among the 21 most complete hybrid skeletons, only 3 present more than 85% of character states corresponding to one of their parents (see online Supplementary material S3). These data show that the combination of character states is useful to identify the hybrids of our sample considering that: 1) a specimen could be identified as a horse or a
3.3. Archaeological application Between 15 and 24 identification criteria have been observed (with clear “A” or “B” character state) on each archaeological skeleton (Table 1). The detail of the criteria observed on each specimen is provided in online supplementary material (see online Supplementary material S5). Most (more than 88%) of the criteria recorded on the bones from Fresnes-lès-Montauban and Longueil-Annel correspond to the “A” state. These two specimens can thus be identified as horses on the basis of our criteria. Conversely, the skeletons from Baillet-en-France and Meru predominantly display the morphological features corresponding to the “B” state (respectively recorded in 87% and 92% of the cases) and can be considered as donkey skeletons. For these specimens, although the identification would also have been possible on isolated bones, only the study of their complete skeleton allows us to discard the possibility that 17
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Fig. 4. Distinctive characters of femur. A: Proximal part of the femur of donkey (MNHN-ZA-AC, 1982.128) and horse (MNHN-ZA-AC, 1929.37) in lateral view; B: Proximal part of femur of donkey (MNHNZA-AC, 1893.634) and horse (MNHN-ZAAC, 1929.37) in medial view; C: Proximal part of the femur of donkey (MNHN-ZA-AC, 1893.634) and horse (MNHN-ZA-AC, 1980.29) in antero-dorsal view. Abbreviations: d. e. l. t.: dorsal extension of the lesser trochanter; g. t.: greater trochanter; h. f.: head of the femur; i. c.: intertrochanteric crest; l. t.: lesser trochanter; t. t.: third trochanter; t. g. t.: tuberosity of the greater trochanter; t. f.: trochanteric fossa.
identify on the basis of osteological criteria observed on isolated bones. In spite of this limitation, we found that hybrids are, for most of them, a patchwork of the criteria of both parent species. This strong osteological variability was also mentioned about hybrids from other species: indeed, hybrids are described as more often displaying morphological closeness with their parents rather than specific hybrid traits (Bochaton et al., 2016; Evin et al., 2015; Forest, 1997; McDade, 1990; Rieseberg et al., 1993). We nevertheless found that the identification of hybrids can be attempted using complete or mostly complete skeletons on which more than half of our criteria can be unambiguously recorded. Indeed, almost all of the hybrid skeletons of our sample present less than 85% of the criteria of one of their parent species, whereas nearly all modern horse and donkey skeletons present more than 85% of the character states of their respective species. Our results also show that most of the criteria precisely recorded (“A” or “B” states) on hybrid bones are associated to “B” states (corresponding to donkey; 56%) rather than to “A” states (corresponding to horse; 44%). This remark is valid for the four criteria defined by Peters (1998) as characterizing mules (R1, MC2, T1, P1) which, in spite of being retained in our study as donkey characters, were also recorded in most of our hybrid specimens (see online Supplementary material S4). These results obtained on the archaeological sample allow for the unambiguous identification of four of the five archaeological equid skeletons included in this study as horses (two specimens) or donkeys (two specimens). The only exception concerns the specimen from the site of Elbeuf - “Rue Guynemer” which presents criteria of both horse (ten criteria) and donkey (five criteria). This result could suggest that it
they could be hybrid specimens. The results obtained on the specimen from Elbeuf are more ambiguous. Indeed, the “A” state is predominant but was recorded in only 67% of the cases. This result would indicate that this specimen would be a hybrid specimen but only at the condition that the skeleton corresponds to a single individual. 4. Discussion We found evidence of 26 osteological criteria allowing for a reliable discrimination of horse and donkey bones. Among these criteria, four were reliable in 100% of the cases: the shape of the zygomatic process of the frontal bone, the morphology of the posterior extension of the external occipital process, the morphology of the transversal crest of the radius, and the occurrence of a crest linking the third to the greater trochanter of the femur. The other criteria were, for 14 of them, reliable on 95–99% of the horse and donkey skeletons, and the height last criteria provided correct identification on 90–95% of the cases. Several of these criteria were already signaled in the literature but were never tested on a large sample of specimens making their reliability difficult to assess. Thus, our results show that a robust identification of domestic equids is possible using isolated bones on the basis of macroscopic criteria. However, the identification of hybrid specimens has proved to be far more difficult considering we have been unable to find any typical osteological character allowing for their identification on isolated bones. This means that, following our results, hybrids are impossible to 18
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Fig. 5. Distinctive characters of tibia. A: Distal part of the tibia of donkey (MNHNZA-AC, 1982.128) and horse (MNHN-ZAAC, 1929.35) in ventral view; B: Proximal part of the tibia of donkey (MNHN-ZA-AC, 1982.128) and horse (MNHN-ZA-AC, 1929.35) in dorsal view; C: Proximal half of the tibia of donkey (MNHN-ZA-AC, 1982.128) and horse (MNHN-ZA-AC, 1929.35) in lateral view. Abbreviations: l. c.: lateral condyle of the tibia; m. c.: medial condyle of the tibia; t. c.: tibial crest; t. t. c.: tuberosity of the tibial crest.
5. Conclusion
could be a hybrid specimen displaying a mix of characteristics from both parents. However, the fact that this specimen was signaled as not discovered in anatomical connection does not allow us to confirm it. In addition, a previous study using GMM (Hanot et al., 2017) suggested this specimen would be likely a composite assemblage of bones from horses and, to a lesser extent, donkeys. This assumption mainly resulted from the absence of bones providing reliable attribution to hybrids following the GMM specific classification. In the later study, the authors suggested that cranial remains could belong to a donkey and most of the postcranial ones could be horse bones. This hypothesis appears as quite concomitant with our results and with dental and field data (Barme and Clavel, 2015). This example highlights the crucial importance of a good knowledge of the archaeological context and of collecting reliable field observations in order to allow for a proper study of archaeological skeletons. The case of this specimen also demonstrates the interest to use several methodological approaches jointly in order to obtain reliable identifications. However, in spite of being globally less powerful than GMM approaches (particularly on isolated bones), the identification method we propose presents the advantage of being simpler to use routinely by zooarchaeologists. Moreover, the fact that our identification criteria have been tested on a large sample of comparative specimens enabled us to quantify their reliability and to increase the robustness of the approach. Our results allow us to raise a final concern about the comparative samples used in identification methodologies, especially concerning hybrids which seem to present an important morphological variability. Indeed, using a small number of comparative specimens can lead to misleading identifications, no matter the method used, because it does not allow taking into account the full morphological diversity of the species. In summary, we demonstrated that visual criteria can be considered as a reliable tool for a first study of equid remains although they may be afterward completed by other methodological approaches (e. g. GMM, Zonkey or ancient DNA when preserved; Cucchi et al., 2017; Hanot et al., 2017; Orlando et al., 2015; Schubert et al., 2017) allowing to secure the identifications and obtain additional information about the bone remains.
In this study, we demonstrated that domestic horses, donkeys and, to a certain extent, hybrids can be identified on the basis of visual criteria using their bone remains. The provided method could allow for a better assessment of the respective presence of the horses, donkeys and their hybrids in archaeological sites. It could thus contribute to improve our knowledge about their place in human past societies. Further studies allowing for identification of the extinct Equus hydruntinus (Regalia, 1907) should also be carried out. Indeed, the chronology of extinction of the European wild ass is poorly understood and their remains could have possibly persisted in archaeological records until historical periods (Jourdan, 1976; Marquet and Poulain, 1985; Willms, 1989). Our identification tool can be used routinely and could initiate the development of more argumentative identification procedures. Indeed, we proposed a reproducible and refutable identification method based on criteria that have been tested on a large sample of modern skeletons. This kind of approach is mandatory in order to provide reliable identifications of archaeological remains that are potentially questionable and challengeable. Identification methods are a major issue of many zooarchaeological studies across the world, especially in places where important taxonomic diversity occurs in the archaeological deposits. Therefore, many works concerning the skeletal anatomy of vertebrate taxa have still to be conducted in order to perform more reliable and challengeable taxonomic identifications of the bone remains.
Funding This work was supported by the “ATM blanche”/MNHN.
Conflicts of interest The authors declare that they have no conflict of interest.
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Acknowledgments
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We are grateful to an anonymous reviewer who helps us to improve the quality of this work. We also would like to thank the researchers, curators and collection technicians who allowed us to access to the reference specimens: Luc Vives, Joséphine Lesur, Christine Lefèvre, Aurélie Verguin, Céline Bens and Karyne Debue (MNHN-Paris); Benoît Clavel and Sébastien Lepetz (CNRS/MNHN-Paris); Jean-Hervé Yvinec (INRAP/CRAVO-Compiègne); Gaëtan Jouanin and Maude Barme (CRAVO-Compiègne); Benoît Mellier (MSN-Angers); Wim Van Neer, Georges Lenglet, Sébastien Bruaux and Terry Walschaerts (IRSNBBruxelles); Michael Hiermaier (ZSM-Munich); Henriette Obermaier (SAPM-Munich); Renate Schafberg (MLU/ZNS/H-Halle/Saale); Erich Pucher (NHM-Wien). We also want to thank the excavation directors who recovered the archaeological specimens used in this study: Yves Desfossés (DRAC Champagne-Ardenne), Stéphane Gaudefroy (INRAP), François Gentili (INRAP), Bénédicte Guillot (INRAP) and Martine Derbois (INRAP). Appendix A. Supplementary data Supplementary data related to this article can be found at http://dx. doi.org/10.1016/j.jas.2018.03.012. References Albarella, U., Ceglia, V., Roberts, P., 1993. S. Giacomo degli schiavoni (molise): an early fifth century ad deposit of pottery and animal bones from central adriatic Italy. Pap. Br. Sch. Rome 61, 157–230. Albizuri, S., Nadal, J., 1991. Estudi de l’èquid aparegut en relació amb l’estructura E10 de l'Hort d’en Grimau. Olerdulae 3, 112–117. Arloing, S., 1882. Caractères ostéologiques différentiels de l’âne, du cheval et de leurs hybrides. Bull. Société Anthropol. Lyon 236–284. Armitage, P.L., Chapman, H., 1979. Roman mules. Lond. Archaeol. 3, 339–346. Azzaroli, A., 1978. On a late pleistocene ass from tuscany, with notes on the history of asses. Palaeontogr. Ital. Pisa 71, 27–47. Barme, M., Clavel, B., 2015. La pratique urbaine de l’équarrissage à la charnière du Moyen-Âge et de l’époque moderne : l’exemple d'Elbeuf (Seine-Maritime). Archéopages 41, 30–39. Barone, R., 1986. Anatomie comparée des mammifères domestiques: Ostéologie. Vigot, Paris, France. Barone, R., 1976. Anatomie comparée des animaux domestiques: Ostéologie. Vigot, Paris, France. Baxter, I.L., 1998. Species identification of equids from Western European archaeological deposits: methodologies, techniques and problems. In: Anderson, S., Boyle, K. (Eds.), Current and Recent Research in Osteoarchaeology. Oxbow, Oxford, pp. 3–17. Bochaton, C., Grouard, S., Breuil, M., Ineich, I., Tresset, A., Bailon, S., 2016. Osteological differentiation of the Iguana laurenti, 1768 (squamata: iguanidae) species: Iguana iguana (Linnaeus, 1758) and Iguana delicatissima laurenti, 1768, with some comments on their hybrids. J. Herpetol. 50, 295–305. https://doi.org/10.1670/14-170. Bökönyi, S., 1991. The earliest occurrence of domestic asses in Italy. In: Equids in the Ancient World, pp. 178–216. Bökönyi, S., 1974. History of Domestic Mammals in Central and Eastern Europe. Akadémiai Kiadó, Budapest. Clutton-Brock, J., 1992. Horse Power: a History of the Horse and the Donkey in Human Societies. Harvard University Press, Cambridge. Cucchi, T., Mohaseb, A., Peigné, S., Debue, K., Orlando, L., Mashkour, M., 2017. Detecting taxonomic and phylogenetic signals in equid cheek teeth: towards new palaeontological and archaeological proxies. Open Sci. 4 (160997). https://doi.org/10.1098/ rsos.160997. Davis, S.J., 1980. Late pleistocene and holocene equid remains from Israel. Zool. J. Linn. Soc. 70, 289–312. https://doi.org/10.1111/j.1096-3642.1980.tb00854.x. Derbois, M., 2006. Méru. ADLFI Archéologie Fr. - Inf. Picardie. https://doi.org/10.4000/ adlfi.4196. Eisenmann, V., 1986. Comparative osteology of modern and fossil horses, halfasses and asses. In: Meadow, R.H., Uerpmann, H.-P. (Eds.), Equids in the Ancient World. Ludwig Reichert Verlag, Wiesbaden, pp. 67–116. Eisenmann, V., 1980. Les Chevaux (Equus sensu lato) fossiles et actuels ;: crânes et dents jugales supérieures, CNRS. In: Cahiers de Paléontologie. Paris, France. Eisenmann, V., Beckouche, S., 1986. Identification and discrimination of metapodials from Pleistocene and modern Equus, wild and domestic. In: Meadow, R.H., Uerpmann, H.-P. (Eds.), Equids in the Ancient World. Ludwig Reichert Verlag, Wiesbaden, pp. 117–163.
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