COLYMBOSAURINAE Benson and Bowdler, 2014

Sassoon, Judyth, 2019, Congenital and late onset vertebral fusions in long necked plesiosaurs: The first report of spondylosis deformans in Sauropterygians, Palaeontologia Electronica (1 A) 22 (1), pp. 1-15 : 4

Subfamily COLYMBOSAURINAE Benson and Bowdler, 2014

Type Genus Colymbosaurus Seeley, 1874

Description

Specimen CAMSM J63919. Colymbosaurus megadeirus (Benson and Bowdler, 2014) is an incomplete vertebral series consisting of 36 cervical (excluding atlas-axis complex), four pectoral, 17 dorsal, three sacral and 28 caudal vertebrae. An atlas-axis complex for this specimen was reported by Barrett (1858) but is now missing. There are also broken fragments of dorsal ribs, at least five with healed fractures.

Rounded, anteroventrally projecting, spur-like expansions are present on the ventral surfaces of four cervical vertebrae previously identified as belonging in positions 26-28 and 31 on the basis of museum notes (Benson and Bowdler, 2014). The expanded spurs project from the anterior surface of the vertebra to touch and cover the posterior surface of the preceding vertebra. However, detailed observations of the pathological vertebrae suggest they are a series with no gaps (museum numbers J63919 v, w, x, aa; estimated positions 26 to 29) ( Figure 2.1-3 ). Benson and Bowdler (2014) also observed that the expansions contacted rugosities on the preceding vertebra, considered to be traumatic exostoses due to the irritation. However, closer observations discovered rugosities on almost every cervical vertebra not only those adjacent to the pathological expansions, so the rugosity seems to be a normal feature in this specimen. Other pathologies found on CAMSM J63919 were rib fractures, which may not be associated with the vertebral pathology.

Figures

FIGURE 2. Pathological cervical vertebra from Colymbosaurus megadeirus (CAMSM J63919) in 1. anterior view 2. right lateral view 3. ventral view. 4. Left lateral view of pathological vertebrae in series, museum numbers CAMSM J63919 v, w, x, aa; estimated positions in cervical series 26 to 29. 5. Plesiosauroid (indet) (GPIT.RE.03173) terminal cervical and first pectoral in left lateral view and 6. right lateral view. Abbreviations: cv, cervical vertebra; pv, first pectoral vertebra; ve, pathological ventral expansions. Scale bar equals 3 cm.

FIGURE 3. Cervical vertebral series from Callawayasaurus columbensis UCMP 38349 in ventral aspect. 1. Vertebrae 23,24,25, anterior end, to right. Scale bar, 5 cm. 2. Enlargement of osteophytic bridging between vertebrae 23-24, 24- 25. Abbreviations: ns, neural spine; cr, cervical rib. Scale bar equals 5 cm.