Eucyon davisi ( Merriam, 1911 )

Rook, Lorenzo, 2009, The wide ranging genus Eucyon Tedford & Qiu, 1996 (Mammalia, Carnivora, Canidae, Canini) in the Mio-Pliocene of the Old World, Geodiversitas 31 (4), pp. 723-741 : 727-728

Eucyon davisi ( Merriam, 1911)

TYPE LOCALITY. — Rattlesnake Creek, early Hemphillian, Oregon.

AGE. — Hemphillian (late Miocene to earliest Pliocene).

GEOGRAPHIC RANGE. — United States; Eastern and Central Asia (see below).

This is a widely distributed species, first appearing in the Early Hemphillian (middle late Miocene) of western United States (Oregon, Nevada) and widely distributed in the late Hemphillian (latest Miocene to earliest Pliocene) through most of United States (Oregon, Nevada, Arizona, New Mexico, Kansas, Oklahoma, Texas) ( Harrison 1983; Rook 1993; Tedford et al. 2009) ( Fig. 1 ). The intraspecific variability of this taxon, which has a very large temporal range, is considerable (cf. Rook 1993). Eucyon did not survive the late Hemphillian in North America ( Wang & Tedford 2007, 2008).

A typical Canini trait that first occurs within North American species is the enlargement of the frontal sinuses that expand backwards with the tendency to extend at the level of the post-orbital constriction ( Tedford et al. 1995; Wang & Tedford 2008). This is coupled with a more derived morphology (in respect to basal Caninae Leptocyon Matthew, 1918 ), in the external brain anatomy characterised by longer cruciate sulci, more expanded sigmoid gyri (although still relatively small) and by the presence of postcruciate and ansate sulci ( Lyras & van der Geer 2003).

In living Canini , the expansion of frontal sinuses is linked to the increase of nasals cavity and the noticeable development of turbinate processes and thus to the olfactory system ( Tedford et al. 1995). The complex maxilloturbinates, with their increase action of breath and moisture exchange, has been a key for canid success in both cold and arid environmental conditions ( Wang & Tedford 2008). Such anatomical trait could be also used as an indirect, speculative, inference social behavioural of the genus. Social behaviour is usually not preserved in the fossil record and the typical canid pack hunting social behaviour can only be approached in an indirect way (Andersson 1991; Van Valkenburg & Koepli 1993; Van Valkenburg et al. 2003). Nowadays, social hunting in the Caninae is mostly confined to the Canis clade ( Canis and Lycaon Brookes, 1827 ; Macdonald et al. 2004) and probably began to develop within this early member of the tribe Canini . The genus Eucyon , with its developing expanded turbinates/frontal sinuses, was probably one of the first members of the tribe to possibly use the developed olfactory system as a capability for developing social behaviour (pack hunting). The dramatic change in environmental scenario by the late Miocene was responsible of the replacement of forests and woodlands of the North American mid-continent by extensive grasslands ( Cerling et al. 1997; Janis et al. 2002). This environmental shift coincided with the Hemphillian faunal turnover, which severely affected the diversity of mammals both in the ungulate and carnivore faunas ( Van Valkenburg 1988; Webb & Opdyke 1995; Janis et al. 2002; Hunt 2004). A scene in which “the canine’s ultimate triumph in the world” ( Wang & Tedford 2008: 131) is recorded, and in which the evolution of a behaviour common in living Canini , but very difficult to be detected in the fossil record, more probably emerged as well.

ASIA

Figures

FIG. 1. — The latest Miocene Eucyon Tedford & Qiu, 1996 dispersal: A, oldest record of E. davisi (Merriam, 1911) is from Early Hemphillian localities in the western North America (●). The genus quickly expands its record to east in the central and south eastern North America, where it is a common element in late Hemphillian local faunas (□). The late Miocene (MN 12-13 in the European mammal biochronology; ○ locations correspond to time of transcontinental dispersal of the genus, across the Beringia, towards Asia, Europe, and Africa; B, type specimen of E. davisi, right M1-2 in occlusal view (M1 length measures about 10 mm) from Rattlesnake creek, early Hemphillian, Oregon (UCMP545; Earth Sciences Dept., University of Florence); C, D, E. monticinensis (Rook, 1992) left M1 in lingual (C) and occlusal (D) views (M1 length about 17 mm) from Monticino Quarry near Brisighella (BRS27/6; Earth Sciences Dept., University of Florence); E, the figure is completed by a reconstructed scene of a group of adult Eucyon moving eastward in a late Miocene Central Asia grassland scenario. The artistic scene aims to ideally represent the dispersal of the genus Eucyon from North America to the Old World during the latest Miocene.