Reinterpretation of tuberculate cervical vertebrae of Eocene birds (1 Viewer)

[Fred Ruhe]

Gerald Mayr, Ursula Göhlich, Zbynec Roček, Alfred Lemierre, Viola Winkles & Georgios L. Georgalis, 2023

Reinterpretation of tuberculate cervical vertebrae of Eocene birds as an exceptional anti-predator adaptation against the mammalian craniocervical killing bite

Journal of Anatomy.
doi:10.1111/joa.13980. PMID 37990985

Abstract: Reinterpretation of tuberculate cervical vertebrae of Eocene birds as an exceptional anti-predator adaptation against the mammalian craniocervical killing bite - PubMed

We report avian cervical vertebrae from the Quercy fissure fillings in France, which are densely covered with villi-like tubercles. Two of these vertebrae stem from a late Eocene site, another lacks exact stratigraphic data. Similar cervical vertebrae occur in avian species from Eocene fossils sites in Germany and the United Kingdom, but the new fossils are the only three-dimensionally preserved vertebrae with pronounced surface sculpturing. So far, the evolutionary significance of this highly bizarre morphology, which is unknown from extant birds, remained elusive, and even a pathological origin was considered. We note the occurrence of similar structures on the skull of the extant African rodent Lophiomys and detail that the tubercles represent true osteological features and characterize a distinctive clade of Eocene birds (Perplexicervicidae). Micro-computed tomography (μCT) shows the tubercles to be associated with osteosclerosis of the cervical vertebrae, which have a very thick cortex and much fewer trabecles and pneumatic spaces than the cervicals of most extant birds aside from some specialized divers. This unusual morphology is likely to have served for strengthening the vertebral spine in the neck region, and we hypothesize that it represents an anti-predator adaptation against the craniocervical killing bite ("neck bite") that evolved in some groups of mammalian predators. Tuberculate vertebrae are only known from the Eocene of Central Europe, which featured a low predation pressure on birds during that geological epoch, as is evidenced by high numbers of flightless avian species. Strengthening of the cranialmost neck vertebrae would have mitigated attacks by smaller predators with weak bite forces, and we interpret these vertebral specializations as the first evidence of "internal bony armor" in birds.

Enjot,

Fred

 

[Fred Ruhe]

FIGURE 1 (a) skull and (b) cranialmost cervical vertebrae (detail of the framed area in (a)) of Perplexicervix microcephalon from Messel (SMF-ME 11211a); coated with ammonium chloride, the vertebrae are numbered. (c–f) μCT-based surface reconstructions of the newly identified avian axis MHNT.PAL.2020.0.36.13 from the site La Bouffie of the Quercy fissure fillings in (c) dorsal, (d) craniolateral, (e) lateral,
and (f) caudal view. dns, dens; ftv, foramen transversarium; fve, foramen vertebrale; ntc, notch; psp, processus spinosus; pac, processus articularis caudalis. The scale bars equal 5 mm. [Colour online].


FIGURE 2 (a–p), (v), the new cervical vertebrae with tuberculate surfaces from the Quercy fissure fillings in comparison to (s), (x) vertebrae of Perplexicervix microcephalon from Messel and (r), (u), (w), (z) P. paucituberculata from the London Clay. (a–e) MHNT. PAL.2020.0.36.13, axis in (a) dorsal, (b) ventral, (c) left lateral, (d) caudal, and (e) cranial view. (f–j) UM BFI 3101, third cervical vertebra in (f) dorsal, (g) right lateral, (h) cranial, (i) ventral, and (j) caudal view. (k–p) NHMW 2019/0059/0013, fifth or sixth cervical vertebra in (k) dorsal, (l) ventral, (m) left and right lateral, (o) cranial, and (p) caudal view. (q), (t) MHNT.PAL.2020.0.36.13, axis in (q) dorsal and (t) ventral view. (r), (u) axis of P. paucituberculata (NMS.Z.2021.40.7) in (r) dorsal and (u) ventral view. (s) axis of P. microcephalon (SMF-ME 3548) in ventral view; coated with ammonium chloride. (v), NHMW 2019/0059/0013, fifth or sixth cervical vertebra in (v) dorsal and ventral view. (w), (z) fifth or sixth cervical vertebra of P. paucituberculata (NMS.Z.2021.40.7) in (w) dorsal and (z) ventral view. (x) fifth cervical vertebra of P. microcephalon (SMF-ME 11211a) in dorsal view; coated with ammonium chloride. The arrows indicate enlarged details of the tuberculate surfaces. cdl, caudal articulation facet; cra, cranial articulation facet; dns, dens; prj, cranially directed projection of processus articularis caudalis; sht, sheet-like expansion of lateral portion of vertebral body; sms, smooth vertebral surface that guided vessels and nerves that
passed through the foramen transversarium. The scale bars equal 5 mm. [Colour online].



FIGURE 3 μCT scans of transverse sections of (a), (b) the fossil vertebrae from the Quercy fissure fillings (a: the fifth or sixth cervical vertebra NHMW 2019/0059/0013; b: the axis MHNT.PAL.2020.0.36.13) and (c) the axis of the extant Mute Swan, Cygnus olor (NHMW 4.896). ftv, foramen transversarium; fve, foramen vertebrale; trb, trabecle. The scale bars equal 5 mm. [Colour online].


FIGURE 4 (a, b) μCT-based surface reconstructions of the skull of the extant rodent Lophiomys imhausi (SMF 34609) in (a) lateral and (b) dorsal view, with an enlarged detailed of the sculptured surface. (c) cross section through the skull in the area shown in the framed inset, with an enlarged detail of the tuberculate surface. (d, e) partial axis of an undetermined mammal from La Bouffie (UM BFI 3102) in (d) dorsal and (e) lateral view; the arrow denotes a detail of the trabecles. The scale bars equal 5 mm. [Colour online].


Fred