Phylogenetic systematics of the North American fossil Caninae (Carnivora, Canidae). (Bulletin of the American Museum of Natural History, no. 325)
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Date
2009
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[New York] : American Museum of Natural History.
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Abstract
The canid subfamily Caninae includes all the living canids and their most recent fossil relatives. Their sister taxon is the Borophaginae with which they share an important modification of the lower carnassial, namely the presence of a bicuspid talonid, which gives this tooth an additional function in mastication. Contributing to this function is the enlargement of the posterolingual cingulum of M1 and development of a hypocone. The Caninae diverged from the Borophaginae in the narrowing and elongation of the premolars separated by diastemata and placed in a shallow ramus and narrow muzzle. These latter features allow the Caninae to be recognized in the fossil record as early as the beginning of the Oligocene (34 Ma) and constitute evidence that they represent a monophyletic group. In striking contrast to the history of the Borophaginae, the Caninae remain confined to a closely similar group of fox-sized species (Leptocyon spp.) throughout the Oligocene and showing very limited cladogenesis into the end of the medial Miocene (12 Ma), a span that saw marked adaptive divergence in the Borophaginae and the origin of all its major clades. By 12 Ma (beginning of the Clarendonian Land Mammal age) few fox-sized borophagines remained and most of those held hypocarnivorus adaptations. At that point the Vulpini appear both as mesocarnivores (Vulpes spp.) and hypocarnivores (Metalopex spp.) reproducing, on a much smaller scale, the range of adaptations shown in the initial radiation of the Borophaginae. By the end of the Clarendonian (9 Ma) the first members of the tribe Canini appear. Initially this group was represented by the genus Eucyon, largely by a single widespread North American species E. davisi. Our cladistic analysis predicts that the roots of the South American clade subtribe Cerdocyonina, sister taxon to E. davisi and Canis species (together, subtribe Canina), must also have been present, but taxa representing this group do not appear in the North America record until the earliest Pliocene (latest Hemphillian, 5 Ma). Species of three genera (Cerdocyon, Chrysocyon, and possibly Theriodictis), now confined to South America, appear in the fossil record of the southern United States and northern Mexico prior to and just after the opening of the Panamanian Isthmus (ca. 3 Ma), indicating that important cladogenesis within the South American clade took place in North America. Species of Eucyon make their appearance in the Old World in the late Miocene, and E. davisi has a Pliocene record in Asia. Species of this genus undergo a modest adaptive radiation in Eurasia during the Pliocene. In the late Miocene and early Pliocene two species of Canis appear in North America (C. ferox and C. lepophagus), representing the initial cladogenesis within the genus. These animals are all coyote-sized and represent a broadening of body size range within a mesocarnivorous dental adaptation. Toward the end of the Pliocene and into the Pleistocene in North America a curious and rare group of jackal-like species (C. tho¨oides, C. feneus, and C. cedazoensis) seem to form an endemic clade arising near C. lepophagus. These taxa are dentally similar to jackals, especially C. aureus, but share no synapomorphies with them. The early cladogenesis of Canis in the Pliocene of North America produced a somewhat larger form, C. edwardii, that appears in the late Blancan at ca. 3 Ma. It also seems to have a sister relationship with C. lepophagus and with the coyote C. latrans, which appears much later in the record (late Irvingtonian) and quickly becomes distributed across the United States. The golden jackal (C. aureus) shares synapomorphies with the coyote and C. edwardii but does not appear in the fossil record until the early Pleistocene of North Africa. Canis edwardii is extinct by the end of the Irvingtonian. Large wolflike species of Canis seem to be the products of evolution in Eurasia. They appear early in the North American record as immigrants of the crown group of Canis that augment the essentially stem group native species of the New World. The first of these is Canis armbrusteri, which appears early in the Irvingtonian, initially in the Southwest but later in the eastern United States where it survived into the early Rancholabrean of Florida. This is a large wolf, a sister taxon of C. lupus, whose appearance early in the Pleistocene predates the earliest midcontinent occurrence of C. lupus by nearly 1 m.y. In the New World C. armbrusteri gave rise to the native dire-wolf (C. dirus), as evidenced by intergrading morphologies of late Irvingtonian examples that show the transformation to the more hypercarnivorous giant form. The earliest evidence of C. dirus is in the midcontinent and it appears to have displaced C. armbrusteri into the eastern part of the continent while it expanded westward and particularly southward into South America during the late Pleistocene. Canis lupus itself does not appear in midlatitude North America until the late Rancholabrean (0.1 Ma, last glacial cycle), although it was a resident of Arctic North America since the mid-Pleistocene (ca. 0.8 Ma). North America has a limited record of canine diversity during the Pleistocene. Most clades of vulpines and canines that reached the Old World during that span underwent significant cladogenesis so that the canid fauna of Eurasia was always more diverse than that of the New World. From time to time waifs from the Old World centers of origin wandered south into midcontinent North America to briefly enrich the fossil record: Xenocyon spp. in the late Irvingtonian; Cuon alpinus and Canis lupus in the late Rancholabrean, along with the living fox species Vulpes vulpes (late Rancholabrean) and perhaps the swift-fox earlier in the Pleistocene. The center of evolution of the Caninae thus shifted to Eurasia and to South America when avenues of dispersal to those continents were available at the end of the Cenozoic. Because of the diversity of Old World forms that became resident in North America, our analysis of the New World fauna has been expanded to include relevant Old World taxa and to present a broader phylogenetic reconstruction than could be offered only on the basis of strictly New World evidence. This expanded view brings in a greater diversity of morphology, which allows us to better separate homoplasy from true homology. We have considered only Old World taxa that are represented by the most complete material so that missing data are kept to a minimum in our analysis. This still affords sufficient taxa so that the major structure of the phylogeny of Canis can be discerned. Our cladistic analysis found two robustly recognized crown clades within Canis: the mesocarnivorous lupus clade, and the hypercarnivorous Xenocyon clade. The first contains the wolf, C. lupus, and its sister taxon C. armbrusteri + C. dirus, with the latter showing some dental features related to hypercarnivory as an autapomorphy. The Chinese late Pliocene wolf C. chihliensis appears to be a stem group in the Lupus clade and may be closely allied to C. armbrusteri. The Xenocyon clade is also Eurasian in origin and is marked by character reversals to states primitive within Canis. Its earliest record is in the medial Pliocene of eastern Asia (Xenocyon dubius), after which it dispersed to western Eurasia in the early Pleistocene (X. lycaonoides). In the Pleistocene Xenocyon achieved a Holarctic distribution including midlatitide North America (X. texanus and X. lycaonoides). During this episode of expansion the sister taxa Cuon and Lycaon arose in Eurasia and Africa, respectively, most likely from isolated Xenocyon populations. In the latest Pleistocene Cuon alpinus expanded its range into the middle latitudes of the New World. A number of Pliocene and Pleistocene wolf and coyote-sized Eurasian Canis species (C. arnensis, C. etruscus, C. palmidens, C. mosbachensis, and C. variabilis) were included in our cladistic analysis, but the relationships of those forms were difficult to resolve beyond their paraphyletic relationship to the crown clade.
Description
218 p. : ill. ; 26 cm.
"Issued September 3, 2009."
Includes bibliographical references (p. 184-193).
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Book
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Keywords
Caninae., North America., Canidae, Fossil.