Comparative topographic analyses on the foramen magnums of two hystricomorphs: the crested porcupine (Hystrix cristata) and greater cane rat (Thryonomys swinderianus). Implications for typology, phylogeny and evolution in rodents.

BACKGROUND: This investigation aims to assess species comparison of foramen magnums in two hystricomorphs and endeavours an inter-species categorisation of individual shape outline. MATERIALS AND METHODS: This study utilised 35 skull samples of different ages from the crested porcupine (H. cristata) (17) and the greater cane rat (T. swinderianus) (18) through. Elliptical Fourier Analysis, and the two-block Partial Least Squares analysis. Elliptical Fourier descriptor analyses presented marked amplitude related attenuations according to harmonics factor (1/10 to 2,980) in T. swinderianus though angular orientations in the major axis were not profoundly affected by size-normalisation in this species but up-regulated in H. cristata; (1/10 to1/95). RESULTS: Within and between groups analyses revealed PC1&2 contributed 98.94% and 1.06% but 100% PC1 between groups. The 1st to 4th harmonics gave full topographic description of the foramen magnums in both, 1st-3rd harmonics details compared differently revealing shape variance concentrated in posterolateral and posterior regions of the foramen magnum in the porcupine but antero-lateral and dorsal in cane rats, components of morphological asymmetry were demonstrated from 6th to 12th harmonics. Stepwise discriminant analysis of harmonic increments and Mahalanobis distance exposed increasing disparities between both up to the 5 th harmonic (Bonferroni-corrected p-values [277.2, p < 0.002] group centroids) and a slightly lower value in variance for cane rats 0.421 and 0.378 for porcupines. A (58.3% and 33.3%); (94.1% and 11.1%) proportion before and after size-normalised evaluations of porcupines and cane rats size factor removal yielded 35.8% increase in accuracy among crested porcupines but 22.2% decline in cane rats. Dimorphic variations were less frequently expressed in cane rats corresponding to 33.3% and 44.2%. Size normalisation effect brought a reverse situation with an increased difference (11.1% in T. swinderianus; 5.9% in H. cristata). Individual specimen distribution along discriminant axis pooled by discriminant scores depicted less morphologic variability with greater overlaps. CONCLUSIONS: We observe that complexities in foramen magnum architecture between these indicates parcellation of shape and size variance and contributes as evidence for structural evolution, systematics, fundamental similarities and differences offers an explanation that both are related through evolutionary proces of descent as baseline data and further support the suggestion; hystricidae in phylogenetic tree are better evolved and separate from thryonomidae.

Rostro-dorsal and rostro-lateral skull morphologic variability in three age-groups of the Egyptian mongoose (Herpestes ichneumon) (Linnaeus, 1758): implications of certain orbital parameters - angular geometric approach.

This study evaluated 30 skulls of the grey mongoose divided into three age-groups (6 pups, 10 juveniles and 14 adults) for skull shape variability determination. Specific geometric shapes were drawn from defined points. Angular geometric measurements of shapes derived from rostro-dorsal and rostro-lateral parts of the skull included; orbital angles (with and without the mandible), comprising of viscero-cranium, skull and orbital index that was calculated to evaluate the correlations, if any, with angles measured. It was observed that orbital height and width became higher with age; there was stronger correlation in this regard between pups and juveniles compared with juveniles and adults. There is a reduction (narrowing) in BrEcEc, BrEcN, EcPEc, EcEnN and NwNNw angles with concomitant enlargement of BrEcP, BrEcN, EcNEc, EnNEn, EcNNw and EnNP with age. The decline in the skull index shows a decrease in rate of skull width growth relative to rostro-facial length and demonstrates non-proportionality to zygoma bowing. Significantly varied orbital parameters include the inter-canthii distance and implications of certain significant variables observed in some geometric orbital measurements of the tropical mongoose (Herpestes ichneumon). The survey hypothesizes the observations follow typical carnivoran phylogenic affinity, differentiates this species from similar herpestid versions and is an estimation of functional morphology with respect to bite size. It is further suggested to contribute to visual acuity in timing of bite delivery as well an adaptation in prey summarisation. This study will serve as baseline information in herpestid cranial investigations. Such facial features are useful in population studies, species identification, eco-migrant species surveillance and species ontogenic evolution.