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Table 1 Overview of previous literature on skull and/or tooth morphology and morphometrics in extant equids

From: Shape variation and modularity of skull and teeth in domesticated horses and wild equids

Author

Species and/or breeds

Body part

Method

Summary

Bennett (1980) [38]

Equus andium, E. asinus, E. burchelli, E. caballus (including E. caballus alaskae, originally named E. niobrarensis alaskae by Hay, 1915), E. calobatus, E. conversidens, E. francisi, E. grevyi, E. hatcheri, E. hemionus, E. kiang, E. onager, E. occidentalis, E. quagga, E. scotti, E. zebra, and Dinohippus

Skull & teeth

Descriptive morphology

Living species of Equus can be differentiated by a number of morphological characters

Seetah et al. (2016) [14]

Icelandic, Thoroughbred, Przewalski’s horses, and potentially E. ferus

Teeth

2D geometric morphometrics

Tooth shape of horses largely resembles those of Pleistocene and recent wild horses until the onset of modern breeds

Seetah et al. (2014) [48]

Icelandic and Thoroughbred horses

Teeth

2D geometric morphometrics

Significant differences between the two horse breeds in tooth shape

Evans & McGreevy (2006) [63]

Thoroughbreds, Standardbreds, Ponies, Arabs, Anglo-Arabs, Quarter horse, Warmblood, and Appaloosa

Skull

Classic morphometrics

No overall shape differences exist but modular differences (nasal vs. cranial)

Zhu et al. (2014) [64]

E. asinus compared to ponies from Jie (1995) and Evans & McGreevy (2006)

Skull

Classic morphometrics

Supports the two modules from Evans & McGreevy (2006) and shows that donkeys have a longer nasal part

Hanot et al. (2017) [39]

Domestic horses (E. caballus) of various breeds (i.e. racehorses, draft horses, Shetland ponies, Icelandic ponies, Camargue horse, Pottok, Konik), Przewalski’s horses (E. przewalskii), domestic donkeys (E. asinus asinus) and wild asses (E. a. africanus), mules (E.asinus x E. caballus) and hinnies (E. caballus x E. asinus)

Skull & skeleton

3D geometric morphometrics

Occipital part of the skull is especially discriminant among species and it is possible to identify domesticated equids from archaeological sites

Cucchi et al. (2017) [16]

E. ferus caballus, E. f. przewalskii, E. africanus somaliensis, E. a. asinus, E. kiang, E. hemionus hemionus, E. h. khur, E. h. kulan, E. grevyi, E. zebra hartmannae, E. quagga quagga, E. q. burchelli, and hybrids (donkey*horse)

Teeth

2D geometric morphometrics

Enamel folding is a good phylogenetic marker; strong taxonomic pattern is visible in enamel folding

Eisenmann & Baylac (2000) [65]

E. grevyi, E. burchelli boehmi, E. zebra zebra, E. asinus, E. h. kulan, E. przewalskii, and E. caballus

Skull

Classic morphometrics

Domestic horses and Przewalski’s horses can be differentiated