Vertebral pattern variation in the North Sea harbor porpoise ( Phocoena phocoena ) by computed tomography.

Vertebral series in the harbor porpoise (Phocoena phocoena) include cervical,
thoracic, lumbar, and caudal. In contrast to studying skeletons from museums,
in which small bones can be missed, evaluation of full body computed tomography (CT) scans provides an overview of the vertebral column, while
maintaining interrelationship of all structures. The aim of this study was to
document variations in vertebral patterning of the harbor porpoise via evaluation of CT images of intact stranded harbor porpoises. The harbor porpoises
were divided into age classes, based on developmental stage of reproductive
organs on postmortem examination and closure of proximal humeral physis
on CT. Numbers of vertebrae per series, fusion state of the syncervical, type of
first hemal arch, number of double articulating ribs, and floating ribs were
recorded based on CT images. Included in the study were 48 harbor porpoises
(27 males and 21 females), which were divided in two age classes (27 immatures and 21 adults). Total vertebral count varied from 63 to 68 with vertebral
formula range C7T12-14L12-16Cd29-33. Twenty-five different vertebral formulas were found, of which C7T13L14Ca30 was the most common (n = 8, 17%).
Thoracic vertebrae with six, seven, or eight double articulating ribs and zero,
one, or two vertebrae with floating ribs were seen. Four different fusion states
of the syncervical and four types of hemal arches were recognized. This study
showed a great variation in vertebral patterning in the harbor porpoise, with
homeotic and meristic variation in the thoracic, lumbar, and caudal vertebral
series.