Chrysocyon Smith, 1839

TEDFORD R. H., WANG X. & TAYLOR B. E., 2009, Phylogenetic Systematics Of The North American Fossil Caninae (Carnivora: Canidae), Bulletin of the American Museum of Natural History 2009 (325), pp. 1-218 : 83-84

Chrysocyon Smith, 1839

Type Species: Canis brachyurus Illiger, 1815 .

Included Species: Chrysocyon brachyurus and C. nearcticus , new species.

Distribution: For C. brachyurus, Ensenadan (medial Pleistocene) to Recent, South America ( Berta, 1987, 1987). For C. nearcticus , n. sp. early or medial Blancan (early Pliocene) of southern California, Arizona, and Chihuahua.

Revised Diagnosis: Chrysocyon shares a number of synapomorphies ( Tedford et al., 1995) with all other Cerdocyonina , including zygomatic arch with wide masseter muscle scar and corresponding enlarged insertion for medial masseter ventral to masseteric fossa of ascending ramus, and coronoid process with long base relative to height. It shares with more derived members of South American clade blunt angular process, fossa for inferior ramus of median pterygoid expanded, and M1–M2 more quadrate in occlusal outline so they appear transversely narrow for their length. A number of autapomorphies distinguish Chrysocyon from other South American canines: it primitively retains palate shorter than toothrow; like Canis , its forelimb is long relative to hindlimb (the radius/ tibia ratio is greater than 90%), although it shows great limb elongation (humerus + radius more than 50% of head-body length).

Discussion: Berta (1981, and more explicitly in 1988) proposed that Chrysocyon was a member of the clade containing Canis , a sister group to the other South American canines, mainly on the basis of its elongate forelegs, which have Canis -like proportions, and on the interpretation of the size of the frontal sinus and muscle scars on the angular process of the mandible. We have reevaluated these characters based on collections in the Department of Mammalogy of the American Museum of Natural History and find that the latter two features have the characters found in the South American clade ( Tedford et al., 1995). There is a frontal sinus, but it does not extend beyond the postorbital constriction nor does it markedly inflate the postorbital processes or penetrate the tips of those processes. The angular process is deep and short and shows a large area for insertion of the inferior ramus of the median pterygoid muscle as is typical of most Cerdocyonina . For these reasons we ( Tedford et al., 1995) have returned the maned wolf to relationship with the South American taxa as Langguth (1969) and Clutton-Brock et al. (1976) had previously concluded.

A recent study of the mitochondrial DNA ( Wayne et al., 1997) of a fairly comprehensive suite of living canids has explicitly linked the maned wolf and the South American bush dog ( Speothos ) as a sister taxon of either the Canina or the Canina plus the Cerdocyonina . A combined analysis of our morphological data ( Tedford et al., 1995) and the 2001 base pairs of the canid mtDNA ( Wayne et al., 1997: fig. 7) placed the maned wolf and bush dog as sister taxa, but relegated them to a position basal to the Cerdocyonina , the whole of which is a sister taxon of the Canina .

More recently Bininda-Emonds et al. (1999) presented a ‘‘supertree’’ comparing biomolecular and morphologic data by parsimony analysis to produce a composite tree of all living canid species. The resulting tree (their fig. 9) shows Chrysocyon , Atelocynus , Speothos , and Cerdocyon in a multichotomy with the dhole and hunting dog plus Canis species and the remaining South American taxa ( Dusicyon and Pseudalopex ). This result is not substantially different from that of Wayne et al. (1997), but it reduces the resolution of relationships of nearly half the total South American taxa to uncertainty at the tribal level.

In 2004 Zrzavý and Řiĉánková considered morphologic and molecular datasets to assess their relative reliability and utility in phylogenetic interpretations of living canids. They utilized 65% of the osteological characters used by Tedford et al. (1995), combining them with some features discovered by Clutton-Brock et al. (1976) and Berta (1987). Additionally, they combined the former with developmental, behavioral, and cytogenetic characters, all 188 of which were labeled ‘‘morphological characters.’’ The molecular data were based on three mitochondrial genes: cytochrome b and cytochrome c oxidase subunits I and II.

In their analysis of this dataset, the crown clade was labeled ‘‘DC’’ (dog clade) and included species of Canis and the ‘‘South American DC’’, but with the sister taxa Chrysocyon and Speothos as an outgroup to these. The Vulpes clade is also paraphyletic. Fennicus and Allopex are monophyletic and immersed within the Vulpes species clade. Otocyon and Nyctereutes are outgroups to all of the above, and the Urocyon species constitute a stem group of the living Canidae .

The fossil record, as interpreted here, shows that the problematic foxes at the base of the cladogram in combined analyses are all of early appearance, mostly late Miocene or early Pliocene. Their relationship to living Canina is distant in space (North America, Eurasia, Africa) as well. Their behavior in phyletic analysis may be the result of this history in contrast to the crown group whose history begins in the late Pliocene at the earliest and on continents already under the influence of Quaternary climates.