Erinaceus europaeus, Linnaeus, 1758

ASHER, ROBERT J., 2001, Cranial Anatomy in Tenrecid Insectivorans: Character Evolution Across Competing Phylogenies, American Museum Novitates 3352, pp. 1-55 : 39-42

Erinaceus europaeus (ZIUT, SVL 37 mm)

Posteriorly, the vomeronasal organ begins at a point slightly posterior to the anterior tip of the first ethmoturbinal (e.g., slice 21.3.2) and ends 1.6 mm anteriorly, over the incisive foramina. The vomeronasal organ comprises about 22% of nasal capsule length (7.3 mm) and 8% of head length (19 mm). No major blood vessels accompany the vomeronasal organ along its length.

The paraseptal cartilages are J­shaped (e.g., slice 17.2.3). Anteriorly, the vomeronasal duct is completely enclosed by the out­ er bar (slice 15.1.4), which begins posteriorly from the inferior arm of the paraseptal cartilage, runs dorsally over the vomeronasal duct, and joins the medial arm of the paraseptal cartilage as the duct empties into the nasopalatine canal. Erinaceus displays a paired vomeronasal duct, leaving the vomeronasal organ anteriorly and connecting directly into the nasopalatine duct (slice 14.5.1). The paired nasopalatine duct empties into the mouth on either side of a well­defined palatine papilla (e.g., slice 14.3.3; fig. 26). A small nasopalatine duct cartilage, continuous with the inferior portion of the paraseptal cartilage, is evident medially and anterolaterally to the nasopalatine canal (slice 14.2.4; fig. 26).

Anterior to the nasopalatine ducts, both inferior and superior septal ridges are apparent, without cartilaginous support (slice 12.5.2). As in Potamogale , the medial processes of the paraseptal cartilages are continuous anteriorly with the anterior transverse lamina. This lamina is continuous with the nasal sidewall, roof, and septum throughout a large portion of the external nose anterior to the premaxilla (e.g., slice 9.2.3).

The superior alar processes show most continuity with the anterior floor of the nasal capsule (slice 9.1.4); anteriorly, they bifurcate around the external nares.

LIST OF NASAL CHARACTERS

Several morphological differences are evident in specimens of different age. For example, like other cranial sense organs (e.g., eyes), the vomeronasal organ grows with negative allometry relative to body mass and is proportionately larger in younger specimens. Thus, a fetal Micropotamogale specimen (AIG 22733–3) with a head length of about 9 mm shows a posterior margin of the vomeronasal organ overlapping the anterior extent of the first ethmoturbinial. The vomeronasal organ in an adult Micropotamogale (IZEA 939) with a head length of about 50 mm, on the other hand, ends posteriorly near the upper canines, as described above. Even so, the vomeronasal organ in an embryo of Potamogale is considerably longer than that of similarly aged Micropotamogale , Echinops , Tenrec , and Microgale individuals examined in this study.

Adult specimens (e.g., ZIUT Sorex, AIG 1227 and IZEA 939 Micropotamogale ) show resorption of certain regions of nasal cartilage not evident in fetal representatives of these taxa. This includes the medial wing of the paraseptal cartilage, the connection between the nasal septum and roof, and the connection between the paraseptal cartilage and anterior transverse lamina. The connection between the paraseptal and nasopalatine duct cartilages appears less ontogenetically variable, as both structures persist intact postnatally, and two relatively older specimens ( Setifer and Solenodon ) with erupted deciduous teeth show a connection between the two. Finally, as described above, tubercle­like ‘‘spurs’’ on the dorsum of the nasal cupulae are evident in the fetal Potamogale (fig. 23A) and two fetal Micropotamogale specimens. However, these are absent in the two available adult Micropotamogale specimens, and must therefore be presumed to disappear during the course of ontogeny.

There is of course nothing wrong with attempting to extract phylogenetic information from characters that are expressed only during a certain point in ontogeny. The problem arises when a given sample contains taxa representing different ontogenetic stages. Such is presently the case; therefore, I attempt to use characters that are consistently expressed in individuals of various ages. The remaining morphological differences described above are constant in those taxa represented in this study by adult and fetal specimens (table 2). This enables comparisons between taxa represented by only postnatal ( Geogale ) or fetal ( Potamogale ) specimens.

Some of the morphological variation described above (i.e., relations and cartilaginous support for the inferior septal ridge and connections of the superior alar cartilage and nasal cupulae) may provide valuable character information for phylogenetic purposes. However, based on the present sample, it is difficult to unambiguously refine the observed morphology into discrete character states. Hence, these characters are for present purposes not considered in the following pages.

Table 4 includes character data for several taxa that are not described above. This information is based on observations of specimens listed in table 2, as well as the work of authors cited below. Specifically, data on nasal structure in Bradypus is taken from Schneider (1955); in Dasypus from Broom (1897) and Reinbach (1952a, 1952b); in Echinosorex from Broom (1915a) and Wöhrmann­Repenning (1984); in Orycteropus from Broom (1909) and W. Maier (personal commun.); in Procavia from Broom (1898), Lindahl (1948), and Weisser (1992); in Talpa from Fischer (1901) and Broom (1915b); and in Tupaia from Broom (1915a), Maier (1980), and Wöhrmann­Repenning (1984). Not all characters relevant to this study are described by these authors; hence, where information on a given character is lacking, I code it as ‘‘missing’’.

The following characters are numbered after the nine arterial characters described above, so as to correspond with the matrix

TABLE 4

Soft­Tissue Character Matrix (Characters correspond in number to those listed in the text and in table 3. Taxa representing endemic African orders are in bold; insectivorans are marked with an asterisk. See text for sources of character information for taxa not represented by histological sections listed in table 2. A indicates a polymorphism between states 0 and 1, B between states 0 and 2, and C between states 0 and 3. 9 indicates an inapplicable character, which is treated by parsimony algorithms as missing data.)

presented in table 4 (see also table 3). As detailed previously, a ‘‘0’’ character state assignment does not necessarily imply primitiveness.

10. Anterior relation of vomeronasal duct: Solenodon and Dasypus differ from other animals examined here in possessing a vomeronasal duct that empties directly into the nasal fossa (state 1) rather than into the nasopalatine duct (e.g., Tenrec , state 0).

11. Paraseptal cartilage and anterior vomeronasal organ (‘‘outer bar’’): Among marsupials, a strut of paraseptal cartilage consistently encloses the vomeronasal organ anterolaterally (e.g., Didelphis , state 0; Sán­ chez­Villagra, 2001). This is variably present among placental mammals; in many taxa the paraseptal cartilage is laterally open along its anterior half (e.g., Micropotamogale , state 1).

12. Oral opening of nasopalatine duct: The nasopalatine duct opens into the oral region via a single, unpaired channel in Echinops and Setifer (state 1; Hofer, 1982a). In other taxa, the nasopalatine duct is paired and opens into the mouth on either side of the palatine papilla (e.g., Tenrec , state 0).

13. Presence of nasopalatine duct cartilage: Broom (e.g., 1898) noted that marsupials consistently lack cartilaginous support for the nasopalatine duct as it passes ventrally from the nasal fossa into the oral cavity (e.g., Didelphis , state 0). Some placentals, on the other hand, often show a cartilage medial and/or lateral to the nasopalatine duct (e.g., Tenrec , state 1). Many authors assign the medial (nasopalatine) and lateral (palatine) components different names (e.g., Maier, 1980); however, as mentioned above, Kuhn (1971) noted that these cartilages may be continuous and difficult to distinguish from one another. Due to this ambiguity, all cartilaginous support for the nasopalatine duct is here labeled ‘‘nasopalatine duct cartilage’’.

14. Connection of nasopalatine duct and paraseptal cartilages: When present, the nasopalatine duct cartilage may show a connection to the paraseptal cartilage posterior to the nasopalatine duct (e.g., Tenrec , state 1). Alternatively, it may appear adjacent to the duct with no connection to the paraseptal cartilage (e.g., Microgale , state 0).

15. Presence of nasolacrimal duct: Most taxa show a glandular duct running from the anteromedial margin of the eye, along the sidewall of the cartilaginous nose ventral to the maxilloturbinal, and opening anteriorly within the nasal cupula adjacent to the external nares (e.g., Tenrec , state 0). Potamogalines, on the other hand, show no trace of any such duct (state 1).

16. Lateral cover of nasolacrimal duct: The extent to which the nasolacrimal duct is shielded laterally by cartilage varies (W. Maier, personal commun.). In Echinops , there is no cartilaginous barrier lateral to the duct at any point except for its anterior extreme, when it opens into the nasal cupula (state 0). Erinaceus , on the other hand, shows a lateral extension of the anterior transverse lamina dorsal to the anterior margin of the premaxilla that shields the nasolacrimal duct laterally, well before it empties anteriorly into the nasal cupula (state 1).

17. Papillary cartilage: Some taxa exhibit a cartilaginous structure within the palatine papilla (e.g., Geogale , state 0). Broom (1896) and Sánchez­Villagra (2001) noted the presence of a papillary cartilage in most marsupials; however, such a structure is lacking in a Didelphis individual examined in this study (table 2) and in those examined by Wöhrmann­Repenning (1984), although it is present in others (Sánchez­Villagra, personal commun.). Most placentals lack a papillary cartilage (e.g., Tenrec , state 1).

18. Vomeronasal organ blood vessels: In several taxa, a prominent blood vessel travels anteroposteriorly along with the vomeronasal organ tucked into its lateral side, giving the vomeronasal organ a kidney­shaped appearance when viewed coronally (e.g., Didelphis , state 0). Other animals show blood vessels scattered throughout the vomeronasal epithelium that do not travel in any single, welldefined fossa in the vomeronasal organ (e.g., Potamogale , state 1).

19. Shape of nasal septum: Sánchez­Villagra (2001) noted that a parallel­sided nasal septum (when viewed coronally) is ubiquitous among marsupials (e.g., Didelphis , state 0), and contrasts with the ventrally ovoid septum present in many placental mammals (e.g., Echinops , state 1).

20. Zona annularis: Anterior to the premaxilla, the nasal cartilages may form a complete, uninterrupted ring of cartilage around the nasal fossa, joining the anterior transverse lamina with the nasal sidewall and roof (e.g., Echinops , state 0). Alternatively, these structures may not be fully continuous at any point anterior to the premaxilla (e.g., Solenodon , state 1).