Overriding vertebral spinous processes in the extinct horse, Equus occidentalis.

This study examined the vertebrae of the extinct horse species, Equus occidentalis, and found that human-induced stresses may not have caused certain spinal abnormalities commonly seen in modern horses.

Objective of the Study

• The objective of this study was to inspect lumbar and thoracic vertebrae of the extinct horse species, Equus occidentalis, for evidence of overriding spinous processes. This is a condition where vertebrae overlap each other and it’s common in the domestic horse, E caballus caballus.

Methodology

• A sample of 2,661 vertebrae was investigated of which 580 had intact spinous processes.
• Out of these, 36 intact spinous processes, which bore resemblance at a gross level to the overriding spinous processes found in modern horses, were subjected to radiographic examination.

Findings

• Only 2 out of the 36 vertebrae radiographed showed signs consistent with a diagnosis of overriding spinous processes. These signs were radiographically observed lysis (bone breakdown) and/or sclerosis (hardening of tissue).

Conclusion

• The research suggests that the stresses imposed by human interaction, such as weight bearing, may not have been the cause of the signs of overriding spinous processes.
• Thus, this condition may be naturally occurring in the horse species rather than induced by human activities.