Sauropod Vertebra Picture of the Week

Figure 1. Diagrams of the avian respiratory system. Drawings show the respiratory system in a pigeon, in lateral (A) and dorsal (B) views; pink = trachea and lungs, green = air sacs and diverticula. Redrawn from Müller (1907).

Figure 2. Phylogenetic tree showing clade-level sampling of this study (topology based on Prum et al., 2015). Diagram indicates the presence (green) or absence (lines) of paramedullary diverticula across vertebral regions. Cv = cervical, D = dorsal, S = sacral, Cd = caudal. Notably, for each clade for which more than one genus was sampled, all genera had identical patterns of presence/absence across vertebral regions.

Figure 3. Paramedullary diverticula as seen a dissection and a CT scan. A, fresh dissection of an ostrich neck. B, CT scan of an ostrich neck. In both visualizations, paramedullary diverticula are clearly visible as dark air spaces adjacent to the soft tissue of the spinal cord, contained within the hard bony tissue of the vertebral canal.

Figure 4. Reproductions of figures from select historical publications showing evidence of paramedullary diverticula; yellow = spinal cord; green = diverticula. Transverse sections through the neck of a domestic chicken modified from Campana (1875) at an intervertebral joint showing the connection between intertransverse diverticula and paramedullary diverticula near an intervertebral joint (A&B). C, Midsagittal section through the neck of a domestic chicken showing a series of paramedullary diverticula through this vertebral region, also modified from Campana (1875). D, Transverse section through the base of the neck of a duck showing associated air sacs and diverticula, modified from Sappey (1847); note that the bird is depicted lying supine, with the keel of the stenum pointed upward. E, Midsagittal section through the cranial and cervical skeleton of a duck, showing pneumatic foramina inside of vertebral canals (lines) where paramedullary airways entered the bone, modified from Sappey (1874). Abbreviations: PMD, paramedullary diverticulum; IMD, intermuscular diverticulum; ITD, intertransverse diverticulum; VM, ventral midline.

Figure 5. Morphological variation in paramedullary airways; yellow = spinal cord, green = diverticula. The spectrum of variation is discretized into four groups: i, branches of intertransverse diverticula contact spinal cord at intervertebral joints; ii, branches of intertransverse diverticula extend partially into the vertebral canal, but remain discontinuous; iii, paramedullary diverticula form sets of tubes that are continuous through vertebral canals of at least two consecutive vertebrae; iv, continuous paramedullary diverticula anastomose with supravertebral diverticula. Each variant is depicted diagrammatically (A, dorsal view; B, E, H, & K, transverse view) and shown in two CT scans; images in each column correspond to the same morphology. Morphology i: C, cormorant; D, scrub jay. Morphology ii: F, bushtit; G, common murre. Morphology iii: I, red-tailed hawk; J, black-crowned night heron. Morphology iv: L, M, pelican.

Figure 6. Observed variation in the shape, arrangement, and orientation of paramedullary diverticula relative to the spinal cord; yellow = spinal cord, green = diverticula. A, paired diverticula dorsal to spinal cord in an ostrich. B, paired diverticula lateral to spinal cord in a bushtit. C, paired diverticula ventral to spinal cord in a violet turaco. D, three diverticula dorsal to spinal cord in an ostrich. E, four diverticula dorsal to spinal cord in an eclectus parrot. F, single, c-shaped diverticulum dorsal to spinal cord in an ostrich. G, diverticula completely surrounding spinal cord and pneumatizing vertebra in a violet turaco. H, no paramedullary diverticula present in a Pacific loon. I, diverticula completely surrounding spinal cord in a pelican.

Figure 7. Osteological evidence of paramedullary diverticula. A, pocked texturing inside the vertebral canal of a pelican (LACM 86262). B, pneumatic foramen on the roof of the vertebral canal of an albatross (Phoebastria nigripes, LACM 115139). C, pneumatic foramina in the floor of the vertebral canal of an ostrich (Struthio camelus, LACM 116205). D, deep pneumatic fossae in the roof of the vertebral canal of an Eastern moa (Emeus sp., LACM unnumbered).