BULLETIN FLORIDA STATE MUSEUM


(uppers), and, for the topotypic material of N. phlegon from Crawfish
Draw, Mt. Blanco, 60.0 mm to 63.4 mm (lowers) and 66.7 mm to 72.7
mm (uppers). It should be noted that only the maximum crown height
is significant; broken or well-worn teeth should not be considered.
 Other characters besides dental similarities support a close rela-
tionship between N. beckensis and N. phlegon (unfortunately relevant
material is not available for N. minor). Both N. beckensis and N.
phlegon have an elongate rostrum and correspondingly elongate sym-
physis. Also the lower incisors are relatively procumbent and
spatulate (Dalquest and Donovan 1973, this report). As discussed
above, the one skull of N. phlegon examined during this study, AMNH
104708, has no facial fossa (Fig. 14). The only skull of N. beckensis,
MU 8362 (now TMM 41542), is crushed but it also appears not to have
either a malar fossa or dorsal (also called lacrimal or nasomaxillary)
fossa.
 Based on the dental similarities discussed here, we conclude that N.
minor, N. beckensis, and N. phlegon share derived characters that im-
ply a close relationship among these species. Within this species group
is a morphocline, chronocline, and ancestral-descendent sequence from
N. minor to N. beckensis to N. phlegon. Even though N. beckensis ap-
pears intermediate based on reduction in the presence of the ec-
toparastylid and crown height, it is clearly unique in one very distinc-
tive character complex: the occlusal surface area of the cheek teeth is
larger than either N. minor or N. phlegon. This hypothesis of close rela-
tionship is also consistent with the paleobiogeography of these
species; it appears that N. minor, N. beckensis, and N. phlegon were
essentially Neotropical in their distributions.
 Dalquest and Donovan (1973) noted what they interpreted to be an
ecological exclusion between species of Nannippus and other contem-
poraneous horses. For example, at Beck Ranch, N. beckensis is
relatively abundant, whereas Equus (Dolichohippus) of simplicidens is
relatively rare. At Mt. Blanco N. phlegon is relatively rare in contrast
to abundant Equus, except at one site associated with a diatomite.
Dalquest and Donovan conclude that N. beckensis and N. phlegon
were probably adapted to pond-margin or swamp habitats. At the
Florida Bone Valley sites N. minor occurs in association with several
taxa of horses and other open-country forms like antilocaprids and
deer (Webb and Tessman 1968). Similarly Florida N. phlegon is found
at four sites in association with Equus (Dolichohippus) cf simplicidens,
and, notably, with abundant Capromeryx arizonensis in the Santa Fe
River Sites (Webb 1974, this report). In short, if Dalquest and
Donovan's observations about High Plains Nannippus and Equus are
a true reflection of ecological preferences, then there does not appear to


Vol. 25, No. 1