Breaking the constraint on the number of cervical vertebrae in mammals: on homeotic transformations in lorises and pottos

Data-collection

Specimens. We analysed 1090 skeletons of wild-born primates belonging to 60 species of ten families (Table 1). These skeletons are held in collections of ten European and American natural history museums (Naturalis Biodiversity Center, Leiden (Naturalis); The Natural History Museum, London (NHMUK); the Royal Museum for Central Africa, Tervuren (RMCA); the Royal Belgian Institute of Natural Sciences, Brussels (RBINS); the Natural History Museum of Denmark, Copenhagen (ZMUC); Naturhistorisches Museum Wien, Vienna (NHMW); the Swedish Museum of Natural History, Stockholm (NRM); Museum fur Naturkunde, Berlin (MfN); and the National Museum for Natural History, Paris (MNHN), Natural History Museum Oslo, American Museum of Natural History, New York, Field Museum of Natural History, Chicago (FMNH). Five families belonged to the Strepsirrhini (Lorisidae, Galagidae, Daubentoniidae, Lemuridae, Indriidae) and five to the Haplorrhini, of which two Platyrrhini (Cebidae, Atelidae) and three Catarrhini (Cercopithecidae, Hylobatidae, Hominidae).

Cervical vertebrae and transitional cervicothoracic vertebrae. We determined the number of cervical vertebrae and transitional cervicothoracic vertebrae (vertebrae with both cervical and thoracic characteristics, i.e. a seventh vertebrae with a rudimentary rib or one full rib instead of two, or an eighth vertebrae with rudimentary ribs or without ribs on one side). The identification of transitional cervicothoracic vertebrae was based on the presence of cervical or rudimentary first ribs. In the case of a fusion of rudimentary cervical ribs with the transverse process (apophysomegaly), the vertebra was counted as a transitional cervicothoracic vertebra when the transverse process was at least 15% longer than that of the first thoracic vertebra, or when traces of the articulation were still visible.

Explanatory variables. Per specimen where we determined the vertebral pattern, we recorded the species, life style ("fast" vs. "slow"), individual age class and sex and whether the animal was kept in a zoo later in life or not. This last indicator variable can accommodate effects of relaxed selection in captive environments on the probability of finding an abnormal pattern.

Phylogeny. We used the consensus phylogeny of primates provided by the 10k Trees Project (Arnold & Nunn, 2010) to represent our data per species graphically and to calculate correlations between species effects

Statistical analysis. The R script with our analysis is added.