A comparative morphological study of the sixth and seventh spinous processes of the cervical vertebrae in extinct and extant species of Equus.
DOI:
https://doi.org/10.18435/vamp29373Abstract
The lateral profile of the 6th and 7th cervical spinous processes (CSPs) were examined in four extant
species of Equus (n=33); E. caballus (n=26), E. przewalskii (n=3), E. quagga boehmi (n=1), E. asinus (n=3)
and compared to pre-domesticated Equus specimens (n=66) representing three known species: E. occidentalis
(n=56), E. mosbachensis (n=2), E. curvedins/insulatis (n=1) and unknown Equus species (n=7) from five museums.
Six common morphological profiles were revealed: cuneate, curvate, falcate, rudimentary, scalenate,
and truncate. For the 6th CSP, the distribution of these morphologies amongst extant Equus is: cuneate, only
E. asinus; curvate, E. caballus and E. przewalskii always in combination with ligamentum lamina nuchae (lig.
lamina nuchae) attachments from the 2nd through to 7th CSP inclusive; falcate, E. caballus and E. przewalskii
always in combination with lig. lamina nuchae attachments from the 2nd through to 7th CSP inclusive;
rudimentary, E. caballus always associated with lig. lamina nuchae attachments from the 2nd through to 5th
CSP inclusive; scalenate, E. caballus in association with lig. lamina nuchae attachments from the 2nd through
to 5th (n=11) or 7th (n=4) CSP inclusive; truncate, not present. The 6th CSP in museum specimens of Equus
exhibits one of four profiles: cuneate (n=10), curvate (n=14), scalenate (n=11) and truncate (n=4). For the 7th
CSP, the distribution of these morphologies amongst extant Equus is: curvate, E. caballus mostly associated
with lig. lamina nuchae attachments from the 2nd through to 5th CSP inclusive, falcate, E. caballus mostly associated
with lig. lamina nuchae attachments from the 2nd through to 7th CSP inclusive, scalenate, E. caballus
associated with lig. lamina nuchae attachments from the 2nd through to 5th CSP inclusive. Only Rancho La
Brea and Tar Pits Museum provided samples suitable for examination of the 7th CSP. These exhibited four
profiles: curvate (n=7), falcate (n=11), scalenate (n=2), and truncate (n=7). These findings suggest that the
lateral profile of the 6th CSP is of potential use in identification of species; attachments of the lig. lamina nuchae
alter the morphology of the 6th and 7th CSP; and that attachments of the lig. lamina nuchae on the 2nd
to 7th CSP were likely present in species of Equus prior to domestication.
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