The ethmoidal region of the skull of <i>Ptilocercus lowii</i> (Ptilocercidae, Scandentia, Mammalia) – a contribution to the reconstruction of the cranial morphotype of primates

Abstract

The ethmoidal region of the skull houses one of the most important sense organs of mammals, the sense of smell. Investigation of the ontogeny and comparative anatomy of internal nasal structures of the macrosmatic order Scandentia is a significant contribution to the understanding of the morphotype of Scandentia with potential implications for our understanding of the primate nasal morphological pattern. For the first time perinatal and adult stages of Ptilocercus lowii and selected Tupaia species were investigated by serial histological sections and high-resolution computed tomography (µCT), respectively. Scandentia show a very common olfactory turbinal pattern of small mammals in having two frontoturbinals, three ethmoturbinals, and one interturbinal between the first and second ethmoturbinal. This indicates a moderately developed sense of smell (moderately macrosmatic). The observed septoturbinal is probably an apomorphic character of Scandentia. A general growth in length occurs during postnatal ontogeny; thus the adult ethmoidal region is proportionally longer compared to the rest of the skull. Throughout ontogeny Ptilocercus has a proportionally longer nasal cavity than Tupaia. Major differences exist between Ptilocercus and Tupaia in regard to the proportions of the nasal cavity which correlate with the position of the orbits. Compared to Tupaia, Ptilocercus shows more anteriorly oriented orbits and has a proportionally longer nasal capsule than Tupaia and based on anatomy probably a higher level of olfactory discrimination. Furthermore, Ptilocercus has a platybasic skull base that resembles a derived feature of Ptilocercidae. In contrast, Tupaia has a distinct septum interorbitale leading to a tropibasic skull, a pattern that is a plesiomorphic character of Tupaiidae and Scandentia in general. This finding helps us to understand the septum interorbitale pattern in Primates. Our results indicate that differences among the investigated Scandentia species are correlated with adaptations to foraging and behavioural biology.

Ontogeny and phylogeny of the mammalian chondrocranium: the cupula nasi anterior and associated structures of the anterior head region

“…6 . a Ptilocercus lowii , CRL 45 mm [ 89 ], b Erinaceus europaeus , CRL 19 mm [ 6 ], c Cryptoprocta ferox, CRL 54 mm [ 15 ]. Drawings by Timea Bodogán, modified from cited sources.…”

“…Potamogale velox [ 39 ] 1_1_?_1_?_•_?_?_?_?_?_•_1_?_1_1_?_•_1_?_?_?_?_•_?_?_?_?_?_•_?_1?_?_?_?_•_?_0_?_?_0_•_1_1_1_?_?_•_?_?_? Procavia capensis [ 25 ] 1_?_?_1_1_•_?_?_?_?_?_•_?_?_?_?_?_•_1_?_?_1_?_•_?_?_?_?_?_•_?_?_?_?_?_•_?_?_?_?_0_•_?_?_?_?_1_•_1_?_1 Ptilocercus lowii [ 89 ] 1_?_?_?_?_•_?_?_?_?_?_•_?_?_1_?_?_•_?_?_?_1_?_•_?_?_?_?_?_•_?_1_?_?_?_•_?_?_1_?_?_•_1_1_?_1_1_•_1_?_? Sciurus vulgaris [ 38 ] 1_1_?_?_1_1_•_?_?_1_?_1_•_?_?_1_1_?_•_1_?_?_1_?_•_?_?_?_?_?_•_?_?_?_1_?_•_?_?_1_1_?_•_?_?_?_?_?_•_?_?_?…”

The ethmoid and presphenoid of cetaceans

“…Also, some confusion arises over the term spina mesethmoidalis. Its use is limited to embryology or chondrocranium (Zeller, 1987;Silva Neto, 2000;Jastrow and Oelschl€ ager, 2006;Schunke and Zeller, 2010;St€ oßel et al, 2010;Ruf et al, 2015), but Domning (1978) and Gingerich (1994) referred to the spina mesethmoidalis in adult fossil sirenians, and Arnold and Heinsohn (1996) used the term for a grown individual of the Irrawaddy dolphin Orcaella brevirostris.…”

“Forever young”—Postnatal growth inhibition of the turbinal skeleton in brachycephalic dog breeds (Canis lupus familiaris)

“…Generally, in mammals, the maxilloturbinal and the rostral part of the nasoturbinal are covered by respiratory epithelium for warming, filtering, and moistening the inhaled air. The caudal part of the nasoturbinal, the fronto‐, ethmo‐, and interturbinals are covered by olfactory epithelium (Allison & Turner Warwick, 1949; Hillenius , 1994; Le Gros Clark, 1951; Rowe, Eiting, Macrini, & Ketcham, 2005; Ruf, Janßen, & Zeller, 2015; Seydel, 1891). However, the position of the turbinal skeleton within the nasal airflow correlates with the species‐specific distribution of the different epithelia (e.g., Smith, Bhatnagar, Tuladhar, & Burrows, 2004; Smith, Eiting, & Bhatnagar, 2012; Smith, Eiting, & Rossie, 2011).…”

“…Based on μCT sagittal sections and airflow experiments, the ethmoturbinals are spatially separated from the respiratory region, so the former are suggested to be covered only by olfactory epithelium (Craven et al, 2007; Craven, Paterson, & Settles, 2010; Dawes, 1952; Van Valkenburgh et al, 2014). Although covered by olfactory epithelium as well, the lamina semicircularis is not a turbinal, but an internal outgrowth of the cartilaginous nasal side wall (Ruf et al, 2015; Smith & Rossie, 2008). Beside the prominent interturbinals, smaller additional interturbinals are observed whose presence and morphology are less uniform among the specimens (Paulli, 1900a, 1900b, 1900c; Ruf , 2014; Wagner & Ruf, 2019).…”