Figure 1. NHMUK PV R2095, the holotype and only known vertebra of the rebbachisaurid sauropod Xenoposeidon proneneukos. A: left lateral view. B: right lateral view. Pneumatic fossa and “M”-shaped complex of laminae highlighted in pale red; pneumatic foramina within fossae highlighted in deep red. Note that, while the general outline of the pneumatic features is the same on both sides, there are numerous differences in detail: the fossae and their contained foramina are different shapes, the fossa on the right contains an accessory lamina, the “M” is better defined on the left, etc. Scale bar = 20 cm. After Taylor (2018:figure 1).

Figure 2. Proximal tail skeleton (first 13 caudal vertebrate) of LACM Herpetology 166483, a juvenile specimen of the false gharial Tomistoma schlegelii. A: close-up of caudal vertebrae 4–6 in right lateral view, red circles highlighting vascular foramina: none in Ca4, two in Ca5 and one in Ca6. B: right lateral view. C: left lateral view. In right lateral view, vascular foramina are apparent in the centra of caudal vertebrae 5–7 and 9–11; they are absent or too small to make out in vertebrae 1–4, 8 and 12–13. In left lateral view, vascular foramina are apparent in the centra of caudal vertebrae 4–7 and 9; they are absent or too small to make out in vertebrae 1–3, 8, and 10–13. Caudal centra 5–7 and 9 are therefore vascularised from both sides; 4 and 10–11 from one side only; and 1–3, 8 and 12–13 not at all.

Figure 3. Brontosaurus excelsus holotype YPM 1980, caudal vertebrae 7 and 8 in right lateral view. Caudal 7, like most of the sequence, has a single vascular foramen on the right side of its centrum, but caudal 8 has two; others, including caudal 1, have none.

Figure 4. Fossae and foramina adjacent to the neural canal in ornithodiran archosaurs. Fossae are shown in dark grey, foramina in black. Neural canals are labelled “nc”. A: Pterosauria, represented by cervical vertebra 9 of Pteranodon sp. YPM 2767 in anterior view (traced from Bennett 2001: figure 42). B: Theropoda, represented by dorsal vertebra 14 of Allosaurus fragilis UUVP 6000 in anterior view (traced from Madsen 1976: plate 23). C: Basal Sauropodomorpha, represented by a posterior dorsal vertebrae of Aardonyx celestae BP/1/6566 in posterior view (traced from Yates et al. 2012: figure 7). D: Neosauropoda, represented by cervical vertebra 5 of Diplodocus carnegii CM 84 in posterior view (traced from Hatcher 1901: plate 6).

Figure 5. Giraffatitan brancai tail MB.R.5000, part of the mounted skeleton at the Museum für Naturkunde Berlin. Caudal vertebrae 24–26. in left lateral view While caudal 26 has no pneumatic features, caudal 25 has two distinct pneumatic fossae, likely excavated around two distinct vascular foramina carrying an artery and a vein. Caudal 24 is more shallowly excavated than 26, but may also exhibit two separate fossae.

Figure 6. Domestic duck Anas platyrhynchos, dorsal vertebrae 2–7 in left lateral view. Note that the two anteriormost vertebrae (D2 and D3) each have a shallow pneumatic fossa penetrated by numerous small foramina.