Cervical ribs in human early life: morphological variability and first identification as a morbidity criterion in a past population

Abstract

Despite the medical literature on supernumerary cervical ribs in extant adult samples, little is known about their development and occurrence in early infancy. The documentation of cervical ribs in modern samples of fetuses and neonates is indeed affected by ethical as well as technical limitations. The aim of the present study was to investigate their frequencies and morphological variability in the first known archaeological collection of very young children with this anatomical variant. The study sample comes from the 8B-51 necropolis on the Saï island (Sudan) and dates to the Classic Kerma Period (XVIIIe-XVIe centuries BC). It consists of 64 individuals deceased between 24 weeks of amenorrhoea and 2 years of age. Bilateral or unilateral cervical ribs were found in 27 individuals. A total of 43 cervical ribs were identified, 38 of which are fully preserved. According to these observations, at least 42% of the individuals have unilateral or bilateral cervical ribs, with an average maximum length of < 1 cm. This frequency is very high compared to those observed in contemporary adult samples (up to 3%). First, the comparison of our results with biological and genetic research demonstrating the link between the occurrence of cervical ribs and a reduced chance of survival during infancy allows the first identification of this trait as an indicator of morbidity in an archaeological collection, a morbidity to which a genetic homogeneity or even endogamy could contribute. Second, the number of ribs studied makes it possible to propose a morphological classification based on the general shape and the shape of the articular facets, classification that can be used tos refine the analyses of the trait in future samples.

Keywords: Kerma; Sudan; developmental anomalies; discrete traits; neonatal death; risk marker; supernumerary rib.

Figure 1

Morphological types of adult cervical ribs usually distinguished based on clinical studies. (A) 'rudimentary' or 'atrophied' type, (B) 'phalanx‐like' type, (C) 'rib‐shaped' type, modified after Patterson (1940, pp. 534–535, figures 4, 6 and 21)

Figure 2

Location of the necropolis on the (A) Sudan scale and (B) Saï Island scale, and (C) map of the location of burials according to the age at death of the individuals, modified after Murail et al. (2004, pp. 268–269, Figures 1 and 2)

Figure 3

In situ identification of the cervical ribs, examples. (A) Right cervical rib of the individual S56, (B) bilateral cervical ribs of the individual S11, (C) right cervical rib of the individual S58, and (D) left cervical rib of the individual S71

Figure 4

Illustration of the measurements acquired during the biological study on the right cervical rib of the individual S60. L, maximum length; Min W, minimum width; Max W, maximum width

Figure 5

Repositioning with orientation of the cervical rib in relation to the vertebral hemi‐arches and the vertebral centrum, example of the individual S11. Arrows, articular surfaces; A, anterior; L, lateral; P, posterior

Figure 6

Morphological variability of cervical ribs in early life: classification proposition. Superior view. L, lateral articular surface; M, medial articular surface. A‐type: right cervical rib of the individual S11 and cervical rib of the individual S9. B‐type: cervical ribs of the individual S70 and the individual S39. C‐type: left cervical rib of the individual S11