Nyctereutes, Temminck, 1838

Lyras, George A. & Van Der Geer, Alexandra A. E., 2003, External brain anatomy in relation to the phylogeny of Caninae (Carnivora: Canidae), Zoological Journal of the Linnean Society 138 (4), pp. 505-522 : 517

NYCTEREUTES

The phylogenetic position of the Nyctereutes is not clear. Huxley (1880), using cranial and dental characters, considered it ‘essentially a low Thooid of the South-American type’, although it is an Old World canid. A century later, in their phenetic study, Clutton- Brock et al. (1976) placed Nyctereutes either together with Pseudalopex sechurae and P. vetulus (using teeth and cranial characters only) or alternatively in a clade on its own, not related to any other canid (using all the characters of their analysis). Later, again based on osteological and dental morphology, it was placed as a sister taxon of Cerdocyon thous ( Berta, 1988; Tedford et al., 1995). On the other hand it was also placed as a sister taxon to Vulpes ( Wayne et al., 1987a; Wayne et al., 1987b), based on karyology using G-banded chromosomes. A biochemical analysis of allozymes yielded nothing more than a position somewhere at the stem of the Caninae multichotomy ( Wayne & O’Brien, 1987). Finally, in Wayne et al.’s (1997) combined analysis of mitochondrial DNA and morphological data, the raccoon dog is not closely related to any other living species. Thus, Nyctereutes may be close to Pseudalopex , to Vulpes , to Cerdocyon or to none of the living canids.

The fossil Asian Nyctereutes , represented by the primitive † N. tingi and the derived † N. sinensis , are considered sister taxa, and appear suddenly somewhere in the Early Pliocene ( Tedford & Qiu, 1991). † N. tingi became extinct in the Late Pliocene; † N. sinensis disappeared in the Middle Pleistocene, either through extinction, or through evolution into Nyctereutes sp. ( Tedford & Qiu, 1991). This latter species was described by Pei (1934), but is also considered synonymous with N. procyonoides ( Soria & Aguirre, 1976) . The European forms, represented by the primitive † N. donnezani and the derived † N. megamastoides , became extinct before the beginning of the Pleistocene, without known descendants ( Martin, 1971).

The brains of the fossil Asian Nyctereutes († N. tingi , † N. sinensis ) appear to be more advanced than that of the living species ( N. procyonoides , Fig. 10 ), as the fossil species have cerebral gyri that are more wavy, and a more distinct ansate sulcus ( Radinsky, 1973a). In addition, the proreal gyrus is long and narrow and the orbital gyrus wide in the fossils, compared to the living species ( Figs 4 , 10 ). A simple explanation might be that the brains of the fossil species were larger than the living raccoon dog: in our endocasts by about 25%. The degree of the complexity of the gyri is a common difference between brains of different size. Moreover, the absence of the ansate sulcus in the living raccoon dog could be due to their smaller brain. However, the differences in the proreal gyrus are significant, and it is easy to distinguish Nyctereutes procyonoides ( Fig. 10 ) from N. sinensis ( Fig. 8 ).

The fossil Nyctereutes is, in external brain morphology, not close to the living species. It appears to be similar only to Cerdocyon thous . They not only have the same heart-shaped sulcal pattern, but they also have an ansate sulcus. A more important similarity is found in the proreal gyrus, which has the same development and shape in † N. tingi and † N. sinensis as in Cerdocyon thous . If, however, we take the living raccoon dog into account, it appears that although the sulcal pattern is also heart-shaped, the postcruciate region in N. procyonoides is more elongated, and it misses the ansate sulcus. The most striking difference is found in the degree of development of the proreal gyrus, which is long and bilaterally constricted in Cerdocyon , but not so in N. procyonoides . In fact, the endocasts of the fossil Nyctereutes have more similarities with Cerdocyon than with the living Nyctereutes . This implies that Berta’s (1988) and Tedford et al.’s (1995) hypotheses might be confirmed as far as the fossil species are concerned ( Fig. 12 ).

Figures

Figure 4. Endocasts from Pliocene Nyctereutes and Pleistocene †Canis (Xenocyon) lycaonoides, lateral and dorsal views. Lateral views of †N. tingi F:AM 96757, †N. sinensis F:AM 22336 and †N. sinensis F:AM 96750 reversed from the left side.

Figure 8. Endocasts from Pseudalopex spp. and Cerdocyon thous, dorsal and lateral views.

Figure 10. Endocast from Nyctereutes procyonoides, dorsal and lateral view.

Figure 12. The living raccoon dog (Nyctereutes procyonoides) is considerably smaller than the fossil †Nyctereutes sinensis, which is considered its ancestor (see discussion in the text). As presented in this study, the fossil Nyctereutes species have a larger proreal gyrus than the living species. A similar development is seen in the frontal sinus, which is also larger in the fossil species than in the living form (Tedford et al., 1995). These two points are the subject of the cartoon: in China 3 million years ago, a Vulpes (which lacks a frontal sinus and has a proreal gyrus very small) is very enthusiastic with the new ideas of a Canis (in which both features are very well developed), however, the Nyctereutes does not seem to be interested at all.