At present, there are three jackal species in Africa: the arid-adapted golden jackal (Canis aureus) that occurs in northern and eastern Africa, the black-backed or silver-backed jackal (Canis mesomelas) that is found in eastern and southern Africa and the side-striped jackal (Canis adustus) that is found in sub-Saharan Africa up to the borders of the equatorial forest.³ DNA studies examining the phylogenetic relationships of 23 extant Canidae species suggest that Canis mesomelas and Canis adustus cluster close together, within a larger group of ‘wolf-like canids’, whilst the raccoon dog clusters with the African bat-eared fox (Otocyon megalotis) in a ‘basal canid’ position.⁴

Fossil canids, such as C. mesomelas and C. adustus and smaller foxes, such as the Cape fox (Vulpes chama), are common in the deposits from the Pliocene and well into the late Pleistocene and early Holocene in southern Africa.⁵ Elsewhere on the continent, Nyctereutes appears in the deposits of north-western Africa. The presence of a small canid with clearly defined mandibular traits indicative of Nyctereutes has been reported from the Moroccan site of Ahl al Oughlam. ⁶ Recently, a new species of fossil raccoon dog has been announced from the Lower Awash site of Dikika, Ethiopia. This species, Nyctereutes lockwoodi, comes from deposits dated to approximately 3.20 Ma.⁷ A possible primitive Nyctereutes has also recently been reported from Laetoli.⁸ Elsewhere, several fossil raccoon dog species are known from Pliocene deposits of Western Europe and China and these specimens are larger than modern day raccoon dogs, suggesting a size decrease in the lineage ofNyctereutes from the Pliocene to the present.⁹

Morphologically, the genus Nyctereutes closely resembles the African jackals and foxes (genera Canis and Vulpes, respectively). In general, the raccoon dog can be distinguished by its smaller body size, shorter tooth row, reduced carnassial blade and relatively larger molars, suggestive of a greater degree of crushing ability, than can be observed in either Canis or Vulpes.^10,11 The presence of a marked subangular lobe on the mandible is observed in modern raccoon dogs, as well as in the samples of later, more derived fossils of this genus. However, primitive fossil samples attributed to the raccoon dog genus do not appear to have this trait.⁸

The South African fossil raccoon dog species, Nyctereutes terblanchei, was first identified as Thos terblanchei from collections by Robert Broom. The skull and mandibular specimen from Kromdraai A (KA 1290), in the Sterkfontein Valley (now part of the Cradle of Humankind World Heritage Site), is the type specimen for this species.¹² A second area from where these fossils were collected, was a locality known only as ‘KA 2’ which was labelled as Kromdraai–Coopers (two sites lying very close to Sterkfontein). Subsequently, the exact location of this site has been lost, and the isolated Nyctereutes material (n = 8 fossils) is now housed in the Palaeontology Department of the Ditsong Natural History Museum in Pretoria, South Africa (at that time called the Transvaal Museum). The seven specimens from the KA 2 site comprise five partial mandibles (KA. 2 3 YY; K2.82; K2.81; KA.72; KA2. 82) and two maxillary specimens (KA. 2 83 and KA. 2 3). Other specimens assigned to this species include a left maxilla from Sterkfontein Member 5 (SE 125) and one additional specimen (Specimen SAM 15605) from the Middle Pleistocenesite of Elandsfontein (lying approximately 100 km from Cape Town).¹¹ The specimens from Sterkfontein and Elandsfontein were not considered as part of this study.

In the original description of the material, Ficcarelli and colleagues¹¹ noted that N. terblanchei showed a marked subangular lobe on the mandible and an ascendingramus with a more anterior orientation. When viewed as a whole, the ascending ramus and the horizontal corpus of the mandible appear to intersect at right angles.¹¹ The basal portion of the ascending ramus is massive, but the horizontal portion shows a distinct taper towards the mandibular symphysis, whilst retaining a straight inferior border. However, the authors concluded that, of the small sample of southern African fossils, only KA 1290 and K2.82 could confidently be assigned to N. terblanchei.¹¹

Despite the many new discoveries in the Cradle of Humankind and various studies which have reviewed and synthesised the fossil carnivores of this importanthominin region,^{5,13,14,15,16,17} no further fossil raccoon dog material has come to light since the study by Ficcarelli and colleagues¹¹. This absence suggests either: (1) that the raccoon dog is underdiagnosed in the South African fossil sites, as was previously suggested,¹¹ or (2) that the sample assigned to N. terblanchei may represent another canid species. Certainly, there are carnivore species that are only rarely recovered in the Cradle of Humankind sites, such as the cheetah (Acinonyx jubatus)and certain sabre-toothed cat species (Homotherium latidens).⁵ This study compared extant and fossil jackals, as well as extant and fossil raccoon dog data, to the fossil sample from the Sterkfontein Valley to assess the likelihood of N. terblanchei being a rare, but valid, species identification or, alternatively, that the fossils represent a different canid species. The question is of importance to the reconstruction of fossil faunal communities and the understanding of the causes of Pleistocene extinctions.

FIGURE 1: Raccoon dogs are an indigenous canid species found in eastern Asian countries and parts of Europe.

FIGURE 2: Canis sp. mandible illustrating the measurements used in this study.

The second important characteristic is the orientation of the ascending ramus, which is almost 90 degrees in the fossil Nyctereutes¹¹ (Figure 3). However, this angle is variable, both in the modern samples (Figures 4 and 5), as well as the fossils, with specimens such as KA.82 showing a relatively acute angle that is not so clearly marked in the other specimens (KA.72 and K2.81). The type specimen also shows an acute angle.¹¹ In contrast, the angle observed in the published image of N. lockwoodi from Ethiopia is quite obtuse.⁷ Both the occurrence of the subangular lobe and the angle of the coronoid process are variable, thereby diminishing the overall usefulness of these traits as indicators of Nyctereutes. However, the development of the increasingly marked subangular lobe through time may be a fruitful avenue for future research on the fossil raccoon dogs.

FIGURE 3: Buccal views of the mandibles of three of the most complete fossil specimens assigned to Nyctereutes terblanchei.

FIGURE 4: Mandibular shape variation between modern side-striped jackals, Canis adustus (left) and the Asian raccoon dog, Nyctereutes procyonoides (right). Arrows indicate the position of the subangular lobe and the angle of ascending rami relative to the tooth rows.

FIGURE 5: Within-species variation of mandibles of the side-striped jackal (Canis adustus). Arrows indicate the position of the subangular lobe and the angle of the ascending rami relative to the tooth rows.

For the log 10 lengths of the lower premolar and molar rows, there is a clear separation between the cluster of modern raccoon dogs and the modern and fossil jackalsand fossil N. terblanchei (Figure 7). One fossil specimen (KA. 72) falls within the latter group, whilst the type specimen, KA 1290, is larger than that of the modern black-backed jackals and side-striped jackals. The majority of the fossil Canis specimens fall well within the size range of modern jackals, with the exception of the STS 137 jackal from Sterkfontein Member 4 that is markedly smaller (Figure 7), and the STS 136 specimen which is markedly larger. The STS 137 specimens were originally published as a new species, Canis brevirostris, and the STS 136 specimen as part of the type specimen of Canis antiquus.^24,25 Whilst the taxonomic attributions of these two species are not well understood, this lack of understanding does not affect the position of the N. terblanchei specimens relative to C. mesomelas, C. adustus and the other fossil canids.

The dimensions of the log 10 lengths and breadths of the lower first molars show that three N. terblanchei specimens (K2.81; KA2. 81 and K2. 3 YY) fall within the range of variation of modern African side-striped and black-backed jackals (Figure 8). Two Nyctereutes specimens, namely K2.82 and the type specimen KA 1290, have slightly greater breadths relative to the remaining fossil Nyctereutes and Canis sp. sample. In contrast, the Nyctereutes specimen with the very narrow breadth (KA.72) is from an old individual with advanced wear on the dentition, which may have contributed to the narrowness of this specimen.

The log transformed dimensions of the upper fourth premolar show very similar patterns to those of the lower first molars (Figure 9). Modern raccoon dogs have significantly smaller upper fourth premolars (in both length and breadth) than the fossil Nyctereutes sample from South Africa. There is a certain degree of overlap in the breadths between the modern Nyctereutes specimens and those of the published specimens of N. lockwoodi from Ethiopia (Figure 9). There is also a similarity between the fossil Nyctereutes specimens from Ethiopia and the published means reported for the European fossil Nyctereutes (N. m. megastoides and N. donnezani). In contrast, the three fossil raccoon dog specimens from South Africa (KA. 2 3; KA. 2 83 and KA 1290) show overlap with the modern jackals. The largest upper fourth premolar dimensions are those of Sterkfontein Member 4 assigned to C. antiquus (STS 141) and the Swartkrans Canis sp. specimen (SKX 1136a). These specimens fall well outside the range of variation for the modern samples of black-backed and side-striped jackals (Figure 9).

When combinations of dental metrics are considered, a similar pattern becomes evident. The log transformed length of the upper fourth premolar against the lengthof the upper first molar (Figure 10) shows that modern Nyctereutes are once again the smallest of all the species considered here, with the published N. lockwoodi fossils from Ethiopia having an intermediate position between the modern raccoon dogs and the modern jackals (C. mesomelas and C. adustus). The three specimens of N. terblanchei (KA 1290, KA. 2 3 and KA. 2 83) fall close to the published means of the European raccoon dog species, but also well within the range of the C. adustus and C. mesomelas specimens. The specimens with the largest metrics examined here are those derived from Sterkfontein Member 4, which were previously assigned to C. antiquus, and the unpublished Canis sp. specimens from Sterkfontein Dump 7 (BP/3/18785 and BP/3/18767).

A comparison of the log transformed lower first and second molar lengths shows a clear separation between C. adustus and C. mesomelas, with the former possessing larger lower second molar lengths (Figure 11). The five N. terblanchei specimens overlap largely with the C. adustus specimens, with K2.81 and KA2. 81 being slightly larger than the extant jackals. The largest metrics were those of the type specimens of C. antiquus (STS 136) and C. brevirostris (STS 137). The remaining fossil Canis spp. overlap with the extant C. mesomelas (Figure 11).

FIGURE 6: A comparison of the anterior (HMAND-ant) and posterior (HMANDpost) height of the mandibles of modern and fossil canids.

FIGURE 7: A comparison of the length of the mandibular premolar row versus that of the molar row of modern and fossil canids.

FIGURE 8: Lengths and breadths of the lower first molar of modern and fossil canids.

FIGURE 9: Lengths and breadths of the upper fourth premolar of modern and fossil canids, including published means for European and Chinese samples of fossil raccoon dog species.

FIGURE 10: Lengths of the lower first and second molars of modern and fossil canids. Nyctereutes terblanchei shows some overlap with Canis adustus, whilst the largest fossil specimen (STS 136) is from Sterkfontein Member 4, and has been previously assigned to an extinct short-faced jackal species, Canis brevirostris.24,25

FIGURE 11: Lengths of the upper fourth premolar and upper first molar of modern and fossil canids. Nyctereutes terblanchei shows overlap with Canis adustus, as well as with the published means of the Ethiopian fossil raccoon dog, N. lockwoodi,7 and the European and Chinese fossil raccoon dog species (N. tingi, N. vulpinus and N. donnezani).9

The diagnosis of the genus Nyctereutes rests largely on the presence of three primary features: (1) the subangular lobe on the mandible, (2) the forward rotation of the ascending rami and (3) the progressive distomedial taper of the mandibular ramus.¹¹ However, not all of these traits need necessarily be present: for instance, certain north-west African specimens assigned to Nyctereutes lack the subangular lobe.⁶ The enlarged subangular lobe provides a larger insertion point for the digastric muscle in fossil and modern canids,⁷ suggesting that this feature is related primarily to dietary behaviour, and is perhaps less useful for distinguishing between species that behave similarly. In modern raccoon dogs and jackals, these traits are present in the majority of specimens, but the degree to which they are pronounced is variable, thus suggesting that they are of limited usefulness for distinguishing between species. The results indicate that, in terms of size and shape even for combinations of dental metrics, N. terblanchei falls well within the range of variation of the African jackals, in particular the side-striped jackal (Canis adustus). Whilst it is possible that N. terblanchei can only be definitively diagnosed using non-metric traits, such as the morphology of the entoconid and hypoconid on the talonid of the lower first molar, or subtle variations in the cranial morphology, this present study, using only metric traits, could find no metric or combinations of metrics that could be used to distinguish successfully between the fossil raccoon dog and C. mesomelas and C. adustus.

The second point for discussion is that fossil jackals examined in this study were larger in the past relative to modern Canis conspecifics. Larger Plio-Pleistocene jackals may mean that: (1) environments in which they were living were more seasonal or arid, thus promoting selection for larger body sizes as has been documented in other African faunas of this time period²⁶ or (2) selective forces led to a different pattern of community-wide character displacement in the Pleistocene than today. Jackal species in eastern Africa demonstrate morphological variation in areas where their distributions overlap, presumably to reduce competitionbetween sympatric species.²⁷ Given the presence of such size variability, it is highly possible that the sample of Nyctereutes represents the lower end of the fossil variation in jackals, instead of a completely different species.

Although the southern African ‘raccoon dog’ dentition appears very similar to other raccoon dog tooth metrics published from Pliocene deposits in France and China (Figures 7 and 8), this similarity may simply reflect that these canids were living in comparable environments, and not necessarily that they are taxonomically related to each other. The probability of raccoon dogs dispersing into sub-Saharan Africa from Europe and China, whilst slight, cannot be discounted. However, even larger carnivores, such as the African wild dog (Lycaon pictus), with a larger body size and a greater degree of mobility, show that the gene flow has been affected by barriers, such as the African Rift, that have contributed to the genetic divergence observed in the wild dogs of eastern and southern Africa.²⁸ It is therefore improbable that this small sample of raccoon dogs represents a valid species, but rather that these samples represent a morphological variant of a more common canid species. This conclusion may also be true of the two other fossil canid species: C. brevirostris and C. antiquus.

C. adustus). For all metrics considered in this study, the fossil sample of the raccoon dog fell well within the range of variation for the African jackals. Future work will need to focus on the generic traits which separate the Canis lineage from the Nyctereutes lineage, such as the transverse crest linking the entoconid and hypoconidon the lower first molar talonid, to determine if N. terblanchei most resembles racoon dogs or members of the Canis lineage. However, the dearth of additional fossil specimens since the species was named suggests that the sample assigned to the raccoon dog most likely represents a variant Plio-Pleistocene population of Canis, a genus that is well represented in the Cradle of Humankind sites.