INTRODUCTION

The Family Canidae (Mammalia, Carnivora) share with the other families of the Order Carnivora the transformation of the 4th upper premolar and the 1st lower molar in the carnassial pairs or carnivorous molar tooth with cutting functions(1). The family members are characterized by the basicranium structure, in particular for an otic region with a unique auditory bulla that presents a partial anteromedial septum formed entirely by the inflected dorsal edge of the caudal entotympanic bone(2).

The family that includes coyotes, wolves, foxes, jackals and dogs, is formed by 16 genera and 36 species and it is cosmopolitan, being naturally present in most of the emerged lands, except of some islands from Eurasia and Australia, as well as the oceanic islands; however, it has been introduced in several of them by man(3). It is found from the hot desserts to the frozen fields of the Arctic, using holes, caves or empty trees as dens. It has a medium size, with a length of 0.3 to 2.0 m and weight between 1 and 80 kg; the tail is long, from 11 to 55 cm, very hairy and, generally, with smelly glands in the dorsum of it. The color is uniform and goes from white (Alopex) to grey, brown or spotted (Lycaon) or listed (Canis adustus)(1,3).

The canids are well adapted carnivores, which are shown by the morphology: the skull is large and has a big nasal chamber with a turbinal bone, associated with a very sensible sense of smell. Most canids have the teeth formula of the eutherian mammals (3/3, 1/1, 4/4, 2/3 = 42). The canines are large and strong, and the carnassial pair retain the cutting surface. The postcarnassial teeth have grinding surfaces, showing a more flexible diet than the Family Felidae that is strictly carnivorous; that explains that many canids can be considered omnivorous. The legs are large and digitigrades and the claws are well developed and are not retractile; it has five fingers in the front legs and four in the back legs(4). It does not have a clavicle and the humerus does not show an entepicondilar foramen; the buccula is well developed and shows a sulcus in the surface(1).

The genus Canis is currently constituted by eight species, four of them from Africa, two from America, one more with Holarctic distribution, and one domestic. It is characterized by a tall body, tall legs and hairy tail. The skull has a relatively big frontal sinuses, and the temporal crests, that are close, usually join to create the sagittal crest(3).

Most of the Canidae species are monoestric with a long pseudopregnancy for a pregnancy absence. The pregnancy period is from 51 to 80 days, with an average of 63. They are sexually mature within a year, although the North American wild canids take between two and three years; they have only one annual litter that can have 2 to 13 puppies. The life potential is at least 10 years(1, 3) and the males generally get older than females.

NORTH AMERICAN TERTIARY CANIDS

The Family Canidae has a large evolutive history in North America. It is in this continent that the first canids appeared and developed during the medium late Eocene (more than 37 million years [MY] ago), the best known genus was Hesperocyon from the early Oligocene. This primitive canid group formed the Subfamily Hesperocyoninae. This subfamily is offspring from the miacids (Family Miacidae,) and survived in the continent until the early Miocene (17 MY). Some of this family members already had characteristics that later were further evolved in the canids, such as the leg enlargement, a more specialized use of the carnassials, and the brain expansion(5,6). However, other characteristics, as the number of teeth or their function, has been maintained since it's origins.

At the end of middle Oligocene (30 MY), a second canid radiation took place, represented by genera like Archaeocyon and Cynartoides. These genera possessed short face and strong mandible, showing the beginning of the paraestilar enlargement of the superior carnassial. In the late Hemifordian (17 MY), during the Miocene, this radiation took place through the Tomarctus with the appearance of Cynarctos, Aelurodon and Boropaghus, all of those genera representing another Canidae subfamily, Borophaginae, the hyaenous canids or bone breakers. This group was formed by canids with a huge trophic spectrum, not just as hyenas as originally was defined but other procyonids look-likes (Family Procyonidae) or canids (Subfamily Caninae), showing that its habits were more diverse, and extending its existence during the medium and late North American Tertiary, being the most common predator in the Tertiary deposits(2,7); the genus Borophagus was still present in the early Pleistocene(8).

The third greatest canid radiation that originated the modern animals, began in the Early Miocene (24 MY) with the appearance of the genus Leptocyon (Subfamily Caninae). Some characteristics that distinguish this subfamily include the small but well spaced premolar and metatarsus I that is reduced to a proximal rudiment; therefore, with characters of the 2nd inferior premolar exclusive of the subfamily such as the large anterolabial cingulum, the presence of a posterior cingulum and the metaconid taller than the protoconid(2).

One of the earlier forms of the Caninae, Eocyon davisi, with a small-coyote size, crossed the Bering Strait and got inside Eurasia, probably at the end of the Miocene (8 MY). This immigrant gave origin to the bigger radiation in Asia that resulted in the modern canids appearance, such as wolves (Canis lupus), jackals and hunting dogs (Cuon), red foxes (Vulpes), and possibly the dog (Canis familiaris)(6). It is interesting to notice that the region where canids originally evolved, North America, had a minor role in the last greatest radiation of the family because the radiation center was supposed to be in Asia after the first canids got there during the Blancan (4.5-1.8 MY); in the contemporary deposits in North America, the only recorded species was the possible ancestor of the coyote, Canis lepophagus, and of the grey fox Urocyon. The wolf, the hunting dog, and the red fox possibly migrated from Asia to North America in the early Pleistocene (Irvingtonian, 1.8 MY); this age was at the same moment of the canids arrival to South America, including the genera Cerdocyon and Chrysocyon.

By the Pleistocene in North America three different types of wolves lived: the wolf Canis lupus, the red wolf C. rufus and the Pleistocene wolf C. dirus. This last is the canine version of the bone breaker canids (borophagines), the genus Aleurodon, the late Miocene. Therefore, the coyote C. Latrans, the hunting dog Cuon texanus, the red foxes Vulpes sp. and gray foxes Urocyon sp. were also present(6).

CANIDS FOSSILS TO MEXICO

In Mexico a borophaginid genus is known from the middle Miocene up to the late Pleistocene, Borophagus(7, 9, 10). For the Hemphillian, B. secundus (previously known as Osteoborus cyonoides) is found from the states of Aguascalientes, Guanajuato, Jalisco, Michoacán and San Luis Potosi. Another species of the subfamily is B. diversidens, known from the Blancan of the State of Mexico, Guanajuato, and Hidalgo(10).

At the same time that in the north of the continent, Eocyon davisi appeared and migrated to Asia, in Mexico there was a species recently founded and described as Canis ferox, which is only known in the late Hemphillian deposits (latest Miocene) of the State of Guanajuato. This finding turn to be of great importance because it represents the most ancient fossil assigned to the genus Canis in the American Continent(9). The quoted authors show that probably this species is the ancestor of C. lepophagus, species that lived from the end of the Miocene (7 MY) to middle Pliocene (4 MY), and also is considered as the direct ancestor of either the coyote C. latrans(11) or the red wolf C. rufus.

Few fossil findings of Canis are known from the rich pliocenic sites (5-2 MY) in the central part of the country(10). However it is noteworthy the record of Cerdocyon avius from the Blancan deposits of Baja California Sur, because it represents a taxon that eventually went to South America(10,12).

In the Pleistocene deposits (2-0.015 MY), where it was found the largest canid diversity of the history in the Mexican territory, we had 10 species pertaining to four genera(13). The red fox Vulpes sp. is only found in Cuatro Cienagas, Coahuila(14). The grey fox Urocyon cinereoargenteus has records from some localities of several states that cover most part of the country, from Sonora^a to Yucatán (Loltun Cave[15]). The hunting dog Cuon alpinus has its more austral record from the Cave of San Josecito, Nuevo Leon(8).

The genus Canis gender had a great diversity for the Pleistocene with seven species (Figure 5), although not all of them are contemporary ones. Canis cedazoensis, C. edwardii and C. rufus are only known from the early Pleistocene; the first one is from the Irvingtonian deposits from Arroyo Cedazo, Aguascalientes(16), while the second was recorded from Mina Erupcion, Chihuahua and has been proposed as the ancestor of the coyote(11). The red wolf C. rufus is only known from the El Golfo, Sonora(17) fauna and has not been found again in Mexican territory, although populations of this animal lived in historical times in Texas, USA, but in the XX century they were extirpated from the state(18).

The other four canids are considered Rancholabrean, including the wolf Canis lupus and the dog C. familiaris that are Asian immigrants; the other two evolved in the Americas Continent: the pleistocenic wolf C. dirus and the coyote C. latrans. The Pleistocene wolf was abundant in the late Pleistocene, dating its extinction at the end of that epoch: meanwhile the other three species still live in North America, although the wolf is considered as an extirpated species from Mexico(19). The dog might have arrived to the continent accompanied by the first human populations because its origin is in Asia; as part of the existing controversy about the peopling of the continent, there are not concrete evidence about the moment of arrival of this domestic animal, with some isolated facts about the presence of the dog at the late Pleistocene and early Holocene (20,000-8,000 years before present)(20,21).

The best known species was the pleistocenic wolf that distributed from southern Alberta (Canada) to Peru. Probably derived from C. armbrusteri(11) from South America, this wolf was bigger and stronger that the present grey wolf, with more powerful teeth, being hunter and scavenger(20). There has been no direct association with man in any place, although this could exist in the archaeological site of El Cedral, San Luis Potosi, Mexico(22). Its extinction could have been due of the competition with the grey wolf, and has been dated around 9,500 years before present(20).

Table 1. Species of the genus Canis that are known from the fossil deposits in Mexico.

The arrangement is cronological. The abbreviators of the states are: AGS--Aguascalientes, BCS--Baja California Sur; COAH--Coahuila; CHIH--Chihuahua; EDOMEX--State of México; GTO--Guanajuato; HGO--Hidalgo; JAL--Jalisco; NL--Nuevo León; PUE--Puebla; SLP--San Luis Potosí; SON--Sonora; YUC--Yucatán.

* follows Alroy, J. 2002. North American fossil mammal systematics database. http://www.nceas.ucsb.edu/~alroy/nafmsd.html - December 10th, 2004.

ACKNOWLEDGMENTS

I thank Dr. Raul Valadez, co-organizer of the symposium, who had the kindness to invite the author to participate in it. Oscar J. Polaco reviewed the text, which let me considerably improve it; Felisa Aguilar kindly prepared the maps; to my two colleagues and friends I thank their deference.

Endnotes

a. Cucurpe, A. Ocaña M. and T. Alvarez, unpublished study, 1982

References

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