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of the
FLORIDA STATE MUSEUM

Biological Sciences

Volume 25 1980 Number 1

NANNIPPUS PHLEGON (MAMMALIA, EQUIDAE )
FROM THE PLIOCENE (BLANCAN) OF FLORIDA

BRUCE J. MACFADDEN
AND

JOHN S. WALDROP

.lur . ms . 8**&
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UNIVERSITY OF FLORIDA GAINESVILLE



Numbers of the BULLETIN OF THE FLORIDA STATE MUSEUM, BIOLOGICAL
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NANNIPPUS PHLEGON (MAMMALIA, EQUIDAE )
FROM THE PLIOCENE (BLANCAN) OF FLORIDA

BRUCE J. MACFADDEN AND JOHN S. WALI)ROpt

SYNOPSIS: Dental and postcranial remains of the three-toed horse, Nannippus phlegon,
are described from four localities in Florida: Santa Fe River, Haile XVA, Sarasota, and
Port Charlotte. As is the case elsewhere in North America, the presence of N. phlegon
at these Florida localities appears to indicate a Blancan age, which spans a time inter-
val from about 4.5 to 2 million years ago. Specimens of N. phtegon from Florida are
similar to those found elsewhere in North America, e.g. the typotypic material from Mt.
Blanco in the Texas Panhandle. Diagnostic characters of N. p/degon include: small and
gracile stature, no preorbital facial fossa, elongate rostrum and symphysis, very hypso-
dont teeth, cement relatively thick above oval border, oval protocones, moderately
complex enamel plications, deep ectoflexids, ectoparastylid absent, metapodials tridac-
tyl and elongate, and trapezium absent. Postcranial remains demonstrate that N.
phlegon was a functionally advanced and highly cursorial "antelope-like" hipparion.
Several derived characters are presented here to support the hypothesis that a mor-
phocline, which also is interpreted to represent an ancestral-decendent sequence, pro-
ceeds from N. minor (particularly from the Bone Valley district) to N. beckensis (from
the early Blancan of Texas) to N phlegon

TABLE OF CONTENTS

INTRODUCTION. 2

ACKNOWLEDGMENTS . .. 3

ABBREVIATIONS 3
LOCALITIES .. . 4

SYSTEMATIC PALEONTOLOGY 4
HOLOTYPE 4
TYPE LOCALITY 4
DISTRIBUTION . 4

DIAGNOSIS. 4

REFERRED SPECIMENS 6
DESCRiPTION 7

DENTITION 7

POSTCRANIALSKELETON. 16
DISCUSSION 27

Nannippus phlegon FROM FLORIDA . 27
ORIGIN OFNannipusphtegon. 29

LITERATURE CITED 35

Bruce J. MacFadden is Assistant Curator in Vertebrate Paleontology, Department of Natural Sciences, Florida
State Museum. and Joint Assistant Professor, Departments of Zoology and Geology, University of Florida,
Gainesville 32611.
John S. Waldrop received his M.S. degree in geology at the University 6f Florida and is presently Director of the
Timberlane Research Organization, Rt. 2, Box 5853, Lake Wales, FL 33853. University of Florida Contribution to
Vertebrate Paleontology No. 169.

MACFADDEN, BRUCE J., and JOHN S. WALDROP. 1980. Nannippus phtegon
(Mammalia, Equidae) from the Pliocene (Blancan) of Florida. Bull. Florida State Mus.,
Biol. Sci. 25(11:1-37.



2 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

INTRODUCTION

Nannippus phlegon is one of the most poorly known species of late
Cenozoic horses. It is traditionally recognized as a hipparion, which is
a horizontal or polyphyletic group of late Cenozoic (Neogene) horse
genera with isolated protocones in their upper cheek teeth and tridac-
tyl limbs. At present the phylogenetic interrelationships of N. phlegon
to other hipparions remain obscure. Matthew and Stirton (1930) ex-
anded the concept of the genus Nannippus to include the earlier
species "N. " lenticularis and suggested a close interrelationship with
N. phlegon, but this hypothesis has not been adequately justified.

N. phiegon is somewhat of an evolutionary curiosity as it was ap-
parently adapted to a highly cursorial mode of life, even more so than
most of the presumably more advanced one-toed horses. Its relatively
small skelton is graceful and antelope-like. The limbs are long and
slender, and the lateral digits are extremely reduced in function. The
cheek teeth are the most hypsodont (index of crown area to height) of
the Equidae. In short, Nannippus phlegon was an extremely pro-
gressive grazer and open-country runner.

It is extraordinary to find N. phlegon in the Blancan of Florida. The
richest accumulations of this open-country antelope-like little horse
are found at the Santa Fe River sites in some 10 m of water bordered
by lush hydric hammock vegetation. The following evidence shows N.
phlegon flourished in Florida only a few million years ago. Clearly, as
indicated by studies of paleoclimate, there were significant fluctua-
tions in Florida habitat types during the latest Cenozoic.

Cope (1893) originally described this hipparion as Equus minutus
based on a fragmentary lower molar from Mt. Blanco in the Texas
Panhandle. Hay (1899) provided the replacement name Equus phlegon
because the name minutus had previously been used for a Eurasian
species of Equus. Although referring phlegon to Protohippus, Gidley
(1907) suggested that if upper cheek teeth had been available to him,
he might have placed this species in either Neohipparion or Hipparion.
Matthew (1926) proposed Nannipus as a subgenus of Hipparion for
very hypsodont, small, and extremely graceful hipparions with three
toes but without remains of the fifth digit or trapezium. His concept of
this subgenus was based on the M phlegon material collected from
Crawfish Draw during the American Museum of Natural History ex-
pedition to Mt. Blanco in 1924 (for an anecdote about collecting at this
locality, see Simpson 1951:93-95). This important 1924 collection has
never been adequately described in the literature. Subsequently, Nan-
nippus was elevated to generic rank (e.g. Stirton 1940), and numerous
species of small North American hipparions have been included in it



1980 MACFADDEN & WALDROP: FLORIDANANNIPPUS PHLEGON 3

without careful consideration of phylogenetic interrelationships. Mor-
ris F. Skinner (in Skinner and Hibbard 1972:117), one of the foremost
students of the Equidae, stated that: "The practice of assigning all
small forms of Hipparion-like equids to Nannippus without careful
consideration of other characters clouds the relationship of many of
the dwarf forms and prevents the recognition of true Nannippus."
Also, this practice lessens the temporal value of Nannippus and the
other relatively unrelated small Hipparion-like forms.

Besides Mt. Blanco and other localities in Texas (see also Strain
1966, Akersten 1972, Dalquest and Donovan 1973, Dalquest 1975,
Schultz 1977), N. phlegon has been reported from Arizona (Gazin 1942,
Johnson, Opdyke, and Lindsay 1975), Kansas (e.g. Hibbard 1941,
1956, 1970), Nebraska (Skinner and Hibbard 1972), and two localities
in Florida (Webb 1974, Robertson 1976). This horse apparently is
restricted to sediments of Blaiican (Pliocene) age, which spans a time
interval from about 4.5 to 2 million years ago.

This report describes Nannippus phlegon from four localities in
Florida and discusses its biostratigraphic significance and
phylogenetic origin.

ACKNOWLEDGMENTS

We thank Beryl Taylor and Richard H. Tedford of the American Museum of Natural
History, Clayton E. Ray of the National Museum of Natural History, and Ernest L.
Lundelius of the Univerity of Texas at Austin for lending us specimens from their in-
stitutions. Roy H. Burgess of Venice, Florida, let us study an important specimen in
his private collection. Walter W. Dalquest of Midwestern State University also helped
us with our study of Nannippus beckensis. S. David Webb and Jon A. Baskin critically
reviewed the manuscript. Waldrop would like to acknowledge assistance in the field
from John Beaudua, C. David Frailey, and Henry Galiano. Work at the Santa Fe River
sites was supported by National Geographic Society and National Science Foundation
grants to Webb. The figures were prepared by Nancy Halliday; Rhoda J. Rybak typed
and copystyled the manuscript.

ABBREVIATIONS

The following institutions are referred to in the text: AMNH; Department of
Vertebrate Paleontology, The American Museum of Natural History, New York; BEG,
Bureau of Economic Geology, now part of Texas Memorial Museum (TMM) collection,
University of Texas, Austin; F:AM, Frick:American Mammals, Department of
Vertebrate Paleontology, The American Museum of Natural History, New York; FGS,
Florida Geological Survey (formerly at Tallahassee), now part of the Vertebrate Paleon-
tology Collection, Florida State Museum, University of Florida, Gainesville; MU,
Midwestern State University, Wichita Falls, Texas; RHB, Private Collection, Roy H.
Burgess, Venice, Florida; TRO, Timberlane Research Organization, Lake Wales,
Florida; UF, Vertebrate Paleontology Collection, Florida State Museum, University of
Florida, Gainesville; USNM, National Museum of Natural History, Smithsonian In-
stitution, Washington, D.C.



4 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

The dental nomenclature used in this paper and illustrated in Figure 1 follows Stir-
ton (1941) and Skinner and Taylor (1967). The postcranial terminology follows Camp
and Smith (1942), Sisson and Grossman (1953), Barone (1966), Sondaar (1968), and Hus-
sain (1975).

LOCALITIES

Nannippus phtegon is now known from four localities in Florida (Fig. 2). Except for
Haile XVA, which was collected in an isolated fissure, these localities represent at least
several local sites in an area. This horse had previously been reported from only the
first two localities listed below.

Santa Fe River I, IA, IB, and 4A: About 10 m underwater and consisting of collec-
tions found in deeper holes along the river bottom or in situ in the bank (IB), Columbia
County, localities collected by B. Waller, R. R. Allen, C. E. Ray, J. H. Hutchinson, S. D.
Webb, K. M. Ainslie, J. S. Robertson, and J. S. Waldrop (see Brodkorb 1963, Hibbard et
at. 1965, Webb 1974).

Haile XVA: On land formerly owned by Parker Brothers Limestone Products, Inc.,
near Haile, Alachua County, locality collected by P. Kinsey, J. S. Robertson, S. D.
Webb, and R. R. Allen (see Webb 1974, Robertson 1976).

Sarasota: A series of at least three'localities in non-marine sediments that overlie the
Pinecrest Formation west of Sarasota city, Sarasota County, locality collected by J. S.
Waldrop, 1976-1977.

Port Charlotte: Canal spoil dumps on north edge of Port Charlotte, Charlotte Coun-
ty, localities collected by D. Wilson and field crews from the USNM during numerous
field seasons, M. C. Thomas, and J. S. Waldrop in 1967; also a locality of Roy H.
Burgess "collected from a canal bank (in situ) near Port Charlotte, Florida" (Skinner
1972:117).

For the Sarasota and Port Charlotte localities, detailed geographic and geologic
data are available in Waldrop's field notes.

SYSTEMATIC PALEONTOLOGY

CLASS MAMMALIA LINNAEUS 1758

ORDER PERISSODACTYLA OWEN 1848
FAMILY EQUIDAID GRAY 1821

Genus Nannippus MATTHEW 1926
Nannippus phlegon (HAY) 1899

FIGURES 1-14, TABLES 1-10

HOLOTYPE.-BEG 18586, fragmentary lower molar.
TYPE LOCALITY.-Crawfish Draw, Mt. Blanco, Crosby County,

Texas Panhandle (see discussion of type locality in Skinner and Hib-
bard 1972). The local fauna from Mt. Blanco typifies the Blancan
North American Land Mammal Age (e.g. Schultz 1977).

DISTRIBUTION.-Blancan (Pliocene, sensu Berggren and Van
Couvering 1974, Lindsay, Opdyke, and Johnson 1975) of Florida,
Texas, Kansas, Nebraska, and Arizona (see references in
Introduction).

DIAGNOSIS.-Small and gracile hipparion. No preorbital facial
fossa. Elongate rostrum and symphysis. Teeth very hypsodont, even



1980 MACFADDEN & WALDROP: FLORIDA NANNIPPUS PHLEGON 5

A mesostyle
parastyle metastyle

prefossette < postfossette

protoloph » hypoconal
groove

plicaballin hypocone

protocone metaloph

B isthmus
metaconid metastylid

paralophid entoconid

protoconid  hypoconulid

ectoflexid hypoconid

0 1 2 3 4 5cm

FIGURE 1.-Left upper (A) and lower (B) cheek teeth of Nannippus phlegon with dental
nomenclature used in this study. Anterior is to the left.



6 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

more so than N. minor, and moderately curved in the anteroposterior
plane; thick covering of cement above alveolar border; upper cheek
teeth with oval protocones and moderately complex plications; lower
cheek teeth with moderately deep ectoflexids and widely separated
metaconids and metastylids; ectoparastylid absent in lower cheek
teeth. Limbs functionally one-toed and metapodials relatively long and
gracile. Facet for trapezium on the medial (III) metacarpal absent.

REFERRED SPECIMENS.-Santa Fe River I and IA: UF 7258, partial
right ramus with P4-Mt; UF 7259, partial left ramus with Pa-M:; UF
10696, articular condyle of left ramus; UF 22621, right dPs or dP'; UF .
22629, left dr; UF 22607, UF 22625, left dr or dP'; UF 11887, right
~ps or P4; TRO 544, right Ps or Pt TRO 543, right M'; UF 1143, left Ps
or P'; UF 10694, left Mt or M'; UF 22627, left upper cheek tooth; UF

12

1. Santa Fe River

2. Haile XV A
3

3. Sarasota 4
4. Port Charlotte

0

6.

FIGURE 2.-Nannippus phtegon localities in Florida.



1980 MACFADDEN & WALDROP: FLORIDA NANNIPPUS PHLEGON 7

10593, UF 22626, upper cheek teeth fragments; UF 22624, left ?It; UF
22623, right dP:; UF 22606, left PS or P,; UF 22628, right Mt or M,; UF
7261, left M, or M:; UF 7262, UF 7380, left lower cheek teeth
fragments; UF 22622, ?left lower cheek tooth fragment; UF 7260, UF
7263, left radii with medial and distal portions of fused ulnae; UF
21325, right ?magnum; UF 7264, UF 22619, left metacarpal III; UF
7431, proximal right femur fragment; UF 7436, distal right femur
fragment; UF 7256, left femur; UF 7432, left medial and distal femur
fragment; UF 7435, left distal femur fragment; UF 21323, left
astragalus fragment; UF 10697, right navicular; UF 21324, left
navicular; UF 22630, right metatarsal III; UF 22620, left metatarsal
III; UF 21326, proximal lateral metapodial (II or IV) fragment; UF
7388, medial metapodial (III); UF 7257, UF 7426, medial and distal
medial metapodial (III) fragment; UF 7427, UF 22632, first medial
phalanx (III); UF 10695, second medial phalanx (III).

SANTA FE RIVER IB: UF 118888, left P' or Pt UF 11888b, right Ma;
UF 12226, left incisor; UF 11889, right ?P2; UF 22644, ?left magnum;
UF 21322, right navicular; UF 11890, UF 21321, distal lateral
metapodial (II or IV) fragments.

SANTA FE RIVER 4A: UF 21319, partial right ramus with dpz-dPS;
UF 21320, partial left ramus with dP:-dPS; UF 22609, left dPZ; UF
22617, right P2; UF 22614, right P' or PA; UF 22610, Pi UF 22616, left
Ps or PI; UF 22611, TRO 546, right M' or M2; TRO 545, left Mi or M'
UF 21327, UF 22615, UF 22613, UF 22634, UF 22633, left upper
cheek teeth; UF 22618, upper cheek tooth fragment; UF 22612, right
Ma; UF 22608, left M3; TRO 548, right lower cheek tooth; TRO 547,
left lower cheek tooth; UF 22645, right humerus fragment.

HAILE XVA: UF 17484, left ?dp' or dP*; UF 17485, upper cheek
tooth fragment.

SARASOTA: TRO 553, right dp' or dP'; TRO 554, upper cheek tooth
fragment; TRO 552, right P,-Mt; TRO 555, right Ma; TRO 556, left Ma
fragment.

PORT CHARLOTTE: UF 22631 (=RHB 1964 and =F:AM 104712),
right ramus with symphysis, left C, left I3-Il, right Il-I3, right C, P2,
Mt-Ma; USNM 214432, right P„ Pa, Ml-Ma; USNM 214820, left Mt or
Mz; TRO 550, left dP' or dp4; UF 22646, upper cheek tooth fragment;
TRO 549, left M3; TRO 551, right lower cheek tooth; UF 17285a, UF
17285b, UF 22647, UF 22649, UF 22650-UF 22652, lower cheek teeth
fragments.

DESCRIPTION

DENTITION.-Considering the small size of Florida Nannippus
phlegon, the teeth are very hypsodont relative to other hipparions.



8 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

The Florida N. phlegon dentitions have a thinner covering of cement
than do the AMNH specimens from Crawfish Draw, Mt. Blanco,
although this difference may be related to diagenetic phenomena.
Nevertheless, both these samples of N. phlegon have a relatively thick
covering of cement above the alveolar border in contrast to those of
many other late Cenozoic horses.

No complete upper dentition is known from the Florida sample, and
the following description is based on isolated teeth. The upper molars
are moderately curved in the anteroposterior plane and slightly curved
in the transverse plane. In cross-section, P' is triangular and Ps-Ma are
rectangular, with the anteroposterior length being greater than the
transverse width (Fig. 3, Table 1). P: has a moderately developed

- pseudoparastyle posterior to the true parastyle on the ectoloph. The
protoloph connects directly to the true parastyle on P: The anterior
part of Pi including the parastyle, is often expanded in many Cenozoic

A M3 M~ or M2 p2 ps®udopormlyle

~ eo#A Poros,Yle

B
S

nm// 111 1i - \\\„ma- 1 )1Tll u,*41 -f ..f \ Ir / gl - 11 N·1 1 1 , \ 1
\1

0 1 2 3 4 5cm

FIGURE 3.-Isolated upper cheek teeth of Nannippus phlegon from Florida. (A) occlusal
view, M; UF 11888b, Santa Fe River 18, Mt or M; UF 22611, Santa Fe River 4A, P''
UF 22617, Santa Fe River 4A; (B)'medial (internall view, UF 11888b, UF 22611, UF
22617.



1980 MACFADDEN &WALDROP: FLORIDA NANNIPPUSPHLEGON 9

horses resulting in a triangular outline for this tooth. However this
area is not well developed in N. phlegon. In P2-Ms the parastyle and

TABLE 1.-MEASUREMENTS OF ISOLATED UPPER CHEEK TEETH OF Nannippus phlegon

FROM FLORIDA.

AP* T HT
Specimen Tooth length Width t

UF 22617 R pz 19.5 15.0 >40.6
UF 22621 Rdp' or dpi 26.6 11.3 -
TRO 553 RdP' or dP' 21.4 12.6 -
UF 22614 R Pa or P, 18.0 16.4 51.0
TRO 554 R ps or P4 17.2 17.3 35.9
UF 22611 R M, or M: 16.3 14.9 59.1
UF 11888b M' 15.6 12.2 55.4
TRO 546 R Ml or M2 16.1 15.3 55.7
TRO 543 Ma 16.7 13.4 28.3
UF 11887 R upper 15.4 15.6 -
UF 22629 Ldp, 24.9 12.6 -
UF 22609 Ldp: 24.4 13.3
UF 22607 LdP' or dP' 20.5 11.1 -
UF 22634 ?LdP' or dP' 14.4 15.9 24.4
UF 22613 ?LdP' or dP, 12.8 14.7 21.4
UF 22610 Lp, or P3 19.7 14.7 42.1
UF 11888a Lps or PI 17.6 17.2 42.6
UF 1143 Lpa Or P. 20.0 17.5 > 46.3
UF 22616 LP; or P' 18.5 15.5 55.0
UF 10810 LM' or M, 17.1 16.4 55.8
UF 22615 LMl or M2 17.9 14.1 62.8
TRO 545 LM' or M, 17.0 13.7 66.0
USNM 214820 LM' or M: 16.2 15.6 48.5
UF 7380 L upper 19.5 - 58.3*
UF 21327 L upper 19.1 12.9 > 54.9
UF 22627 L upper 17.0 14.3 22.2
UF 17484 L upper 17.3 19.9 24.9
*Anteroposterior length and transverse width measurements include cement.
tGreatest crown height measured from mesostyle to base of longest root. Maximum measurements indicate speci-
mens in very early wear stages.

*Measurement approximate.

TABLE 2.-MEASUREMENTS OF UPPER DECIDUOUS DENT[TlONS OF Nannippus phlegon

FROM MT  BLANCO, TEXAS.

dp: dp, dp• Mi M~ M3

AP T AP T AP T AP T AP TAPT
AMNH 104708

Right 23.8 15.3 20.1 16.0 21.3 16.4 20.1 16.5 - - - -
Left 24.2 15.3 20.5 15.9 19.8 16.3 19.8 15.0* - - - -

AMNH 104709
Right 24.2 15.2 21.8 15.2 22.5 14.4 - - - - -
Left 23.8 15.2 20.6 15.3 22.3 14.4 - - - - - -

*Measurement approximate.



10 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

mesotyle are well developed; the metastyle is not so well developed.
The anterior and posterior borders of the pre- and post-fossettes are
moderately plicated, whereas the external and internal borders are
relatively simple. The plicaballin is usually represented by a single
loop, but in a few specimans this structure is absent. The protocone is
oval or bean-shaped and does not exhibit the angular character seen in
"Nannippus" lenticularis. The protocone is united with the protoloph
in late wear stages. The hypoconal groove varies progressively from
moderately developed during early and middle wear stages to absent
during late wear stages.

The mandible has an elongate symphysis (Fig. 4.) in contrast to
other small "Hipparion "-like horses such as Calippus and Pseudhip-
parion. The lower incisors have cement-filled infundibula not recessed
below the occlusal surface. The incisor series is curved and relatively
procumbent (or spatulate). The precanine diastema is very short in
relation to the postcanine diastema. The mental foramen is approx-
imately midway between C and P2. Pi is absent.

The lower molars are moderately curved in the anteroposterior
plane and slightly curved in the transverse plane. The lower deciduous
premolars, e. g. UF 21319 and UF 21320 (almost certainly from the
same individual), are more elongate anteroposteriorly and narrower
transversely than are the permanent premolars and molars (Fig. 5,
Tables 3,4). The protoconids and hypoconids have flattened external
borders and are narrow transversely. The ectoflexid is relatively
shallow. The metaconids and metastylids are anteroposteriorly
elongated (transversely compressed) and are widely separated. The en-
toconid is much larger than the hypoconulid. These two parts are
distinct and widely separated. The enamel foldings are simple except
for some plications on the anterointernal border of the hypoconid. In
summary, the individual teeth, as well as the constituent parts, such
as conids, lophids, and stylids, are anteroposteriorly more elongate in
the deciduous dentition than in the permanent dentition. The elongate
character of the deciduous dental row (both lower and upper), which is
characteristic of horses in general, is related to a maximum occlusal
surface needed during early growth stages after weaning. The lower
deciduous dentition from Florida is similar to that of Nannippus
phlegon from Mt. Blanco (e.g. AMNH 104710), although the former
has a thinner investment of cement.

In cross-section the lower permanent premolars and molars are
longer than wide (Figs. 4,6,7). The paralophid is slightly expanded
anteriorly in P2, but much less so than in most hipparions. The exter-
nal borders of the protoconids and hypoconids are rounded. The ec-
toflexid varies (either within an individual tooth row or with pro-



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0 1 2 3 4 5 cm
liallilillia

FIGURE 4.-Right mandibular ramus of Mannippus phtegon, UF 22631 (=RHB 1964 F:AM 104712) from Port Charlotte,
Florida. (A) right lateral view with symphysial dentition, P:, MfM,; (B) occlusal view.



12 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

A
L'"'ll-'11'"""Ill'./1

B

91'

C

r

iX

D
4 + I.

1!1

0 1 2 3 4 5cm

FIGURE 5.-Immature Nannippus phlegon from Santa Fe River 4A. Florida. (A) UF
21319, lateral view of right mandibular ramus with dP: - dPs; (B) UF 21319, occlusal
view; (C) UF 21320, lateral view of left mandibular ramus with dPs - dP., (D) UF 21320,
occlusal view. Because of the same provenance and stage of wear, these two specimens
are almost certainly from the same individual.



1980 MACFADDEN & WALDROP: FLORIDA NANNIPPUSPHLEGON 13

gressive wear) from shallow to moderately developed, in which case it
can partially divide the isthmus (into the anteroisthmus, metaisthmus,

TABLE 3.-MEASUREMENTS OF LOWER DENTITION5 OF Nannippusphlegon FROM FLORIDA
AND SELECTED SPECIMENS FROM MT. BLANCO, TEXAS.

P, P, P, Mi MY M,
AP T AP T AP T AP T AP T AP T

UF 7259 - - 14.3 10.6 14.8 11.2 12.9 9.9 15.0 9.4 - -
Left

TRO 552 - - - - 15.5 11.2 15.5 9.9 - - - -
Right

AMNH 104710* 23.0 11.0 21.7 16.8 26.7 10.3 - - - - - -
(Mt. Blanco)

Left
AMNH 104711 17.2 11.4 18.0 13.2 17.3 12.9 16.5 11.7 16.7 11.5 - -

(Mt. Blanco)
Right

UF 22631 14.4 9.6 - - - - 15.3 10.5 15.7 10.4 18.0 7.9
(sharp cast
of RHB 1964)

Right
UF 21319* 21.0 8.6 20.7 8.7 - - - - - - - -

Right
UF 21320* - - 21.1 8.5 24.2 8.1 - - - - - -

Left
UF 7258 - - 14.2 10.9 14.7 11.1 12.9 9.4 - - - -

Right
USNM 214432 16.2 11.2 16.8 11.Ot - - 17.4 10.5 15.3 9.6 16.6 9.4

Right
*Includes deciduous premolars.
tcould also be P,.

TABLE 4.-MEASUREMENTS OF LOWER ISOLATED CHECK TEETH OF Nannippus phlegon
FROM FLORIDA.

AP T
Specimen Tooth length width Ht*

UF 22623 RdP, 22.7 7.0 -
UF 11889 Rp: 19.4 8.3 -
UF 22633 RdP: or dP, 20.4 6.5 -
UF 22628 R M, or M, 19.0 9.7 63.0
UF 22612 R M3 20.7 8.0 60.2
UF 22625 L dP, or dP, 21.4 9.4 -
UF 22606 L Pi or P, 15.3 12.1 -
UF 22608 L M3 18.5 9.0 -
UF 7262 L lower 17.8t 9.3t -
UF 7261 L lower 17.Ot 10.5t >56.2
*Greatest crown height (see Table 1).
tMeasurement approximate.



14 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

and postisthmus). There is generally a progressive deepening of the ec-
toflexid posteriorly in the tooth row. The plicaballinid is rudimentary
or absent. The metaconids and metastylids are rounded, widely
separated, and approximately equal in size. The entoconids and
hypoconulids have rounded marginsand are not widely separated. The
enamel is very simple with few plications. The lower permanent denti-
tions described here are similar to those of N. phlegon from Mt. Blanco
(e.g. AMNH 104711).

Although no comprehensive list of dental measurements has been
published for N. phlegon from Mt. Blanco, the specimens from this

A

B
0 

1
I e

.

N.1

0 1 2 3 45cm

FIGURE 6.-Nannippus phlegon, UF 7259, from Santa Fe River 1, Florida. (A) lateral
view of left mandibular ramus with P. - M,; (B) occlusal view.



1980 MACFADDEN & WALDROP: FLORIDA NANNIPPUS PHLEGON 15

A M3 Mi or M2

B

/1

il

0 1 2 3 4 5cm

FIGURE 7.-Isolated lower molars of Nannippus phlegon from Florida.CA) occlusal
view, M3; UF 22612, Santa Fe River #A, Mt or M:, UF 22628, Santa Fe River 1; (B)
medial (internal) view, UF 22612, UF 22628.



16 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

type locality and from Florida are of generally similar size (compare
Tables 1-4).

POSTCRANIAL SKELETON.-The following postcranial elements are

represented in the Florida specimens of Nannippus phlegon (for in-
dividual numbers see Referred Material above): right humerus, left
radius, left ulna, right magnum, ?left magnum, left medial (III)
metacarpal, left lateral (II) metacarpal, right and left lateral' CIV)
metacarpals, femur, astragalus, navicular, right medial (III) metatar-
sal, left medial (III) metatarsal, medial (III) metapodials, lateral (II or
IV) metapodials, first medial (III) phalanx, and second medial (III)
phalanx. These postcranial elements are assigned to N. phlegon with
some certainty because: (1) they are very much smaller than those
associated with Equus (Dolichohippus = Plesippus).1 in the same
deposits; and (2) of their similarity to articulated N. phlegon material
(in the AMNH) from Crawfish Draw, Mt. Blanco.

UF 22645 is a distal fragment of a right humerus. On the dorsal
side the olecranon fossa is preserved. On the volar side the coronoid
fossa is preserved. The medial epicondyle is smaller than the lateral
epicondyle. On the distal trochlea the medial condyle is smaller than
the lateral condyle, and these are separated by a well-developed
parasagittal ridge.

The left radius and ulna are represented by two specimens, UF
7260 and UF 7263 (Fig. 8, Table 5). The proximal articular surface of
the radius is divided into two facets for articulation with the medial
and lateral condyles of the humerus. Approximately midway down the
shaft the cross-section of the radius is roughly oval, although the volar
surface is slightly concave. The distal articular surface of the radius
consists of facets for the proximal row of carpal bones, i.e. scaphoid
(this term is preferred to navicular, which is restricted here to the bone
in the tarsus) and lunatum. The proximal shaft of the ulna is broken so
that the olecranon process is not preserved. The proximal portion of
the shaft that is preserved is separated (unfused) from the radius by
the interosseous space. The remainder of the ulna, i.e. medially and
distally, is fused to the radius. The distal articular surface of the ulna
has facets for the triquetrum and pisiform.

The right and possibly left magna are represented by UF 21325 and
UF 22644. Both specimens are somewhat waterworn, but several im-
portant features are preserved. The magnum of N. phlegon is relative-
ly wider than in some more primitive horses. The medial facet for the
scaphoid is concave and somewhat larger than the lateral facet for the
lunatum. The posterior keel is not preserved in these specimens. The

'Following the synomy of Skinner and Hibbard (1972), the subgenus Equus fDolichohippus) is used here in place of E
(pksippus).



1980 MACFADDEN & WALDROP: FLORIDA NANNIPPUS PHLEGON 17

A
'1 /fm\,

--
I \

r
a ib

/

I \'
/

\.\/

1 /8 -1% ' . r *1 D '\3*r /
1IV·-r: ** 
/

'-f
g

P ,
4/1 h1 111,

11 2

<111'11 f 411 1 ,

/44

cde
C ~ *5~.1 -h

0]23; Scm

FIGURE 8.-Left radius and ulna, UF 7260. (A) proximal view; (B) dorsal view; (C) distal
view; (D) lateral view; a, facet for medial condyle of humerus; b, facet for lateral condyle
of humerus; c, ligament attachment; d, scaphoid facet; e, lunatum facet; f, ulna; g,
interosseus space; h, pisiform facet on ulna; i, triquetrium facet on ulna.



18 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

TABI,£ 5.-MEASUREMENTS OF RADII FOR Nannippus phlegon FROM FLORIDA.

Trans. Trans.
AP diam. width AP diam. width
prox. art. prox. art. dist. art. dist. art.

Specimen Length surface surface surface surface*

UF 7260 224.6 22.8 41.3 23.6 38.3
UF 7263 197.7 19.5 34.8 20.7 32.4
* Includes tuberosity for medial liga.ment and distal articular surface of ulna.

distal articular surface is only slightly concave, which is the condition
in advanced horses (Sondaar 1968).

The left medial metacarpal, represented by UF 7264 and UF 22619,
is elongate with a relatively narrow shaft (Fig. 9, Table 6). On the prox-
imal articular surface the transverse width is greater than the
anteroposterior diameter, which is the condition in advanced horses
(Sondaar 1968). This proximal surface consists of a large and roughly
triangular facet for the magnum. Lateral to this facet is another facet
for the hamatum. Sondaar (1968) noted that the angle between the
facets for the magnum and hamatum is 3=100° in Mesohippus, *120°
in Parahippus, and * 160° in Equus. This angle in the two Florida N.
phlegon specimens is approximately 139° and 148° (Table 6). On either
side of the volar part of the shaft, distal to the proximal articular sur-
face, are concavities with small facets for the lateral metacarpals II
and IV. The medial metapodial shaft is approximately oval in cross-
section, although the volar surface is somewhat concave. About
halfway down the volar side of the shaft is a nutrient foramen. On
either side of the volar surface roughened elongate areas serve as at-
tachments for the interosseous lateral metacarpal ligaments. These
surfaces become poorly defined distally; they appear to extend at least

TABLE 6.-MEASUREMENTS OF MEI)IAL (III) METACARPALS FOR Nannippus phlegon

FROM FLORIDA.

UF 7264 UF 22619
Left Right

Length* 200.6 208.8
AP length prox. surf. 20.1 23.8
Trans. width prox. surf. 27.1 28.8
Angle on prox. surf. schaphoid/hamatumt 139° 148°
Width distal prominences 23.1 23.1
Width distal art. surf. 22.5 24.4

Ratio width dist. prom./width dist. art. surf. 1.02 .95
Angle inscribed dist. art. sag. ridget 240° 265°

*Scaphoid facet on proximal articular surface to sagittal crest on distal articular surface.
tProbably accurate to approximately *15°.



1980 MACFADDEN & WALDROP: FLORIDA NANNIPPUS PHLEGON 19

D
A nko

U!1/
.

j
a b

B /C E F
d i irt

1111lip 1 1

lili R j I pal !,11 " 913111~ 1 «1 11 1 ~111 1 1 1-1 9- ill, 9
1 1

r 

111111

1 
1 

4
)

 /
 

IIi 11 j',,11 ~

hn:*4 1 .. n i -g s-c<-4-,-6211-sLIKJ NI1 4

0;~?1 5111

FIGURE 9.-Left medial (III) metacarpal, UF 22619, of Florida Nannippus phtegon from
Santa Fe River lA; (A) proximal view; (B) dorsal view; (C) volar view; a, facet for
magnum; b, facet for hamatum; c, articular area for lateral metacarpal (II); d, articular
area for lateral metacarpal (IV); e, nutrient foramen; f, roughened areas for attachment
of interosseus lateral metacarpal ligaments; g, distal prominences for attachment of
superficial collateral ligaments; h, depression that accommodates first medial (III)
phalanx; i, sagittal ridge on distal trochlea.

Left medial (III) metatarsal, UF 22620, of Florida Nannippus phlegon from Santa
Fe River lA; (D) proximal articular surface; (E) dorsal view; (F) plantar view; j, dorsal
ectocuneiform facet; k, plantar ectocuneiform facet; 1, mesentocuneiform facet; m,
cuboid facet; n, depression for articulation of lateral (II) metatarsal; 0, depression for
articulation of lateral (IV) metatarsal; p, nutrient foramen; q, roughened areas for at-
tachment of interosseus lateral metatarsal ligaments; r, distal trochlea; s, medial prom-
inence for superficial collateral ligaments; t, lateral prominence for superficial collateral
ligaments; u, depression that accommodates the first medial (III) phalanx; v, sagittal
ridge on distal trochlea.



20 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

two-thirds to three-quarters of the way down the volar:side of the
metacarpal.

On the shaft, just proximal to the distal trochlea, are prominences
(medially and laterally) for the attachment of the superficial collateral
ligaments. Sondaar (1968) noted that these prominences are more dor-
sal in Hipparion than in, for example, Anchitherium or Ptiohippus,
where they are more centrally located on the medial and lateral sur-
faces of the metacarpal. In relatively primitive horses such as Parahip-
pus, a depression just proximal to the dorsal surface of the distal
trochlea accommodates the first medial (III) phalanx. Sondaar
(1968:30-31) stated that this depression: "gives the proximal [first
mediall phalanx more freedom when the fetlock joint is flexed." This
depression is reduced or absent in advanced horses such as Equus. In
Florida N. phlegon this depression is very poorly developed relative to,
for example, Parahippus. The distal trochlea is bilaterally symmetrical
with a strong sagittal ridge. This distal ridge is very well developed in
Florida N. phlegon, as in other more advanced horses. Also, the distal
ridge increases in circumference in more advanced horses; it extends
about 180° in Parahippus whereas it spans about 220° in Equus (Son-
daar 1968). In the two UF specimens this distal ridge extends from
roughly 240° to 265° around the trochlea (Table 6). Apparently this
distal ridge was most progressively developed in N. phlegon, but this
should be confirmed by more than the two specimens available in the
present study.

Sondaar (1968) noted that the ratio of width of the deep collateral
ligament prominences to the width of the distal trochlea is greater
than 1 in relatively primitive horses and less than 1 in relatively ad-
vanced horses. This ratio is close to 1 (.95 and 1.02) for the two UF
specimens of Florida N. phlegon.

The right and left lateral (IV) metacarpals are represented by UF
22637 and UF 22636 (Fig. 10). Proximally there is an articular facet for
the unciform and two articular facets for the medial (III) metacarpal.
It is difficult to determine from these specimens whether or not
metacarpal V was present. The shaft is three-sided, relatively slender,
and tapered. On its medial surface are rugose areas for attachment
with the interosseus metacarpal ligaments. The distal trochlea for ar-
ticulation with the lateral phalanges is not preserved (see discussion of
distal lateral metapodials below).

The left lateral (II) metacarpals are represented by UF 22635 and
UF 21326 (Fig. 10). Proximally there is a triangular-shaped facet for
articulation with the trapezoideum. Proximodorsally are two small
facets for articulation with the medial (III) metacarpal and the
magnum. The proximovolar area, which is well preserved, has no ar-



1980 MACFADDEN&WALDROP: FLORIDA NANNIPPUSPHLEGON 21

A D

~ a 
e ~

B C E F

r-2 b « b fe 4 f

,

f*/1

I 'll 1
c g

\
// 1

////
Nl

0 1 2 3 4 5cm

FIGURE 10.-Left lateral (IV) metacarpal, UF 22636, from Santa Fe River lA. (A) prox-
imal view, (B) external view, (C) internal view; a, facet for articulation with unciform; b,
facets for articulation with medial (III) metacarpal; c, rugose area for attachment of col-
lateral ligaments.

Left lateral (II) metacarpal, UF 22635, from Santa Fe River lA. (D) proximal view,
(E) external view, (F) internal view; d, facet for articulation with trapezoideum; e, facet
for articulation with magnum; f, facets for articulation with medial (III) metacarpal; g,
rugose area for attachment of interosseous lateral metacarpal ligaments.



22 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

ticular facet for the trapezium. Evidently the trapezium was absent.
Primitive horses normally have a trapezium (Sondaar 1968), and
Chubb (1912) found this bone in 57% of the Equus specimens that he
examined. Matthew (1926) stated that the absence of the trapezium is
one of the characters of Nannippus, which the M phlegon specimens
from Florida support. The shaft of metacarpal II is three-sided,
relatively slender, and tapers below the proximal articular region.
Again, the distal articular areas are not preserved in these specimens
(see discussion of metapodials below).

UF 7256 is a virtually complete left femur (Fig. 11, Table 7).
Fragmentary femora are represented by UF 7436 (right), UF 7432
(left), and UF 7435 (left). Proximally the head does not have a complete
and distinct rim, in contrast to the condition seen in Equus (Hussain
1975 for example). The fovea capitus, which serves for attachment of
ligaments, is triangular in outline. As in all horses, the greater, lesser,
and third trochanters are well developed. The nutrient foramen is ap-
proximately halfway down the shaft, which is oval in cross-section.
The medial epicondyle is well developed. The distal trochlea is
assymetrical and relatively deep. The medial condyle is larger than the
lateral condyle. UF 7256 shows an additional thickening of spongy
bone on the medial condyle (this is also developed in some UF
specimens of Equus), whereas the three other specimens, UF 7432,
7436, and 7435 have no bony thickening.

The astragalus (UF 21323) is too water-worn to be described here.
The navicular (Fig. 12, Table 8) is represented by UF 21324 (right),

UF 10697 (left), and UF 21322 (left). Hussain (1975) noted a trend in
the evolution of the equid navicular for the transverse width to become
greater than the anteroposterior length. This feature is clearly related
to its increased importance in transmitting weight to the medial (III)
metatarsal. Hussain's "navicular diameter/width index" (ratio X 10)

TABLE 7.-MEASUREMENTS OF FE:MORA FOR Nannippus phlegon FROM FLORIDA.

AP length' Transverse' Transverses
proximal width prox. AP length' width
articular articular distal distal

Specimen Lengthl surface surface trochlea trochlea

UF 7436, Right - - 59.0 46.6
UF 7256, Left 272.5 53.2 79.4 73.3 64.1
UF 7432, Left - - 66.9 56.2*
UF 7435, Left - - 68.1 -
'Proximal tip of greater trochanter to distal-most part of medial ridge.
:Distance between dorsal-most and plantar-most points of greater trochanter.
'Medial-most point on head and lateral-most point of greater trochanter.
*Dorsal-most and plantar-most points on medial condyle.
5Medial-most point on niedial epicondyle to lateral·most point on lateral epicondyle.
*Measurement approximate.



1980 MACFADDEN & WALDROP: FLORIDA NANNIPPUS PHLEGON 23

A B

-

e-\cpi 1, d
d Y &1 C

411111'C
i

11\1111 fi
-

X
g- ·r<.221~~ ' f h

il li 1 1 liwk

01234 5cm

FIGURE 11.-Left femur, UF 7256, of Florida Nannippus phiegon from Santa Fe River
1. (A) dorsal view; (B) plantar view; a, head; b, fovea capitus; c, greater trochanter; d,
lesser trochanter; e, third trochanter; f, nutrient foramen; g, medial epicondyle; h,
lateral epicondyle; i, medial condyle of distal trochlea; j, lateral condyle of distal
trochlea; k, intercondyloid fossa.



24 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

ranges from 10.0-11.3 for Mesohippus to 7.2-8.9 for Equus. This same
index for Florida N. phlegon ranges between 9.3-10.2, which is greater
than Hussain's study predicted for advanced three-toed horses. The
proximal surface, which articulates with the navicular, is concave and
has a well-developed medial non-articular groove, which is poorly
developed or absent in such primitive horses as Mesohippus or
Parahippus. The distal articular surface has two (dorsal and lateral)
confluent ectocuneiform facets, one cuboid facet, a non-articular area,
and one mesentocuneiform facet. In the Florida N. phlegon specimens
the mesentocuneiform facet and lateral-most portion of the ec-
tocuneiform facet are confluent, as in Hipparion illustrated by Hus-
sain (1975:199, Fig. 7C).

The right and left medial (III) metatarsals are represented by UF
22630 and UF 22620, respectively (see Fig. 9, Table 9). The proximal
articular surface is transversely wider than it is anteroposteriorly long
and bears two large ectocuneiform facets (dorsal and plantar), one

TABLE 8.-MEASUREMENTS OF NAVICULARS OF Nannippus phlegon FROM FLORIDA.

Specimen AP length Width Index*

UF 21324, Right 26.0 28.1 9.3
UF 10697, Left 28.2 29.2 9.7
UF 21322, Left 27.6 27.2 10.2
*Ratio length/width x 10 (Hussain 1975).

A B
-i .

e
f , '11' ,b w,w1-/ d m

01234 5cm

FIGURE 12.-Right navicular, UF 21324, of Florida Nannippus phlegon from Santa Fe
River lA. (A) proximal articular surface (dorsal view); a, astragalar facet; b, non-
articular area; (B) distal articular surface (plantar view); c, cuboid facet; d, ec-
tocuneiform facets; e, mesentocuneiform facet; f, non-articular area.



1980 MACFADDEN & WALDROP: FLORIDA NANNIPPUSPHLEGON 25

mesentocuneiform facet (medial), and one cuboid facet (lateral). These
mesentocuneiform and cuboid facets, which are as well developed as in
other advanced horses, indicate a functional de-emphasis of the lateral
(II and IV) metatarsals (Hussain 1975). Just below the proximal ar-
ticular surface, on the plantar portion of the shaft, are medial and
lateral depressions with facets for the lateral (II and IV) metartarsals.
The nutrient foramen is approximately one-quarter of the distance
down the plantar side of the shaft, which is oval in cross-seetion. It has
roughened areas that extend about two-thirds to three-quarters of the
distance down theplantar surface for attachments of the interosseous
lateral metatarsal ligaments. The distal portion of the medial (III)
metatarsal is very similar to the medial (III) metacarpal of M phlegon
described above. Proximal to the distal trochlea are medial and lateral
prominences for the superficial collateral ligaments. In between these
prominences on the dorsal side is a shallow depression for the first
medial (III) phalanx. A well-developed sagittal ridge on the distal
trochlea extends approximately 260° around the trochlea (see Table 9).
Hussain (1975) noted that the distal tuberosities (superficial collateral
ligament prominences) are wider than the distal trochlea in three-toed
horses, except in Nannippus, where he noticed the reverse. This condi-
tion in Nannippus is similar to that of one-toed horses. The
measurements for the two Florida N. phlegon specimens (.98 and 1.00,
Table 9) appear to be intermediate, i.e. the widths of both the distal
prominences and distal trochlea are approximately the same.

Several incomplete specimens represent metapodials whose exact
position in the manus or pes cannot be determined. UF 7257, UF 7426,
and UF 7388 are fragmentary or water-worn medial (III) metapodials.
UF 22639 and UF 22640 are fragments of the medial region of the
lateral (II or IV) metapodials. Three specimens, UF 11890, 21321, and
22638 show the distal articular surface of lateral (II or IV)

TABLE 9.-MEASUREMENTS OF MEI)IAL (III) METATARSALS FOR Nannippus phlegon

FROM FLORIDA.

UF 22630 UF 22620
Right Left

Length* 227.2 210.7
AP length prox. surf. 24.8t 26.5
Trans. width prox. surf. 27.7 28.2
Width distal prominences 21.5 23.1
Width distal art. surf. 22.0 23.0
Ratio width dist. prom./width dist. art. surf. .98 1.00
Angle inscribed dist. art. sag. ridget 260° 260°
*Cuboid facet on proximal articular surface to distal sagittal ridge.
tMeasurement approximate.
1:Probably accurate to approximately * 15'.



26 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

metapodials. As in more advanced horses, these specimens of N.
phlegon do not have sagittal ridges on the distal articular surfaces.
(Stirton [1940] noted that faint sagittal ridges are developed on
primitive species of "Nannippus. ")

The great similarity in the distal trochlea of the medial (III)
metacarpal and metatarsal makes it difficult or nearly impossible to
distinguish between the first medial phalanx of the manus and pes.
The classic work on equid digital ligaments by Camp and Smith (1942)
and later studies (Sondaar 1968; Hussain 1975) showed these
phalanges have many characters of functional significance. UF 2427
and UF 22632 are first phalanges of the medial (III) metapodial (an ad-
ditional specimen, UF 17548, is discussed in Robertson 1976). These
phalanges are relatively long and slender (Fig. 13, Table 10). Sondaar
(1968) noted that in the manus the length of the first phalanx increases
from about 1/6 that of the medial (III) metacarpal in Mesohippus to
about 1/3 that of the medial (III) metacarpal in Equus. In the two UF
specimens of N. phlegon the length of the first phalanx is about 1/4 the
length of the medial (III) metapodials.

The proximal articular surface is concave with a deep groove to ac-
commodate the well-developed sagittal ridge on the distal trochlea of
the medial (III) metacarpal. This deep groove and well-defined ridge
system is characteristic of advanced horses and is related to restric-
tion of lateral movement in the fetlock. In. more primitive horses
lateral movement was somewhat restricted by the presence of more
elongate lateral metapodials (Sondaar 1968). In this regard N. phlegon
is more like one-toed horses, for example Equus, than it is to other
three-toed horses, such as Hipparion.

8 - r'/~
\, , imra 5 6.,7

1 4,41 D ~-~

504~111' *\\\Imr.:gy BH

0 1 2 3 45cm

FIGURE 13.-Medial (III) phalanges of Florida Nannippus phtegon from Santa Fe lA.
First phalanx, (A) dorsal view; (B) volar or plantar view; a, V-scar; b, oval perforatus
scars. Second phalanx, (C) dorsal view; (D) volar view.



1980 MACFADDEN & WALDROP: FLORIDA NANNIPPUS PHLEGON 21

TABLE 10.-MEASUREMENTS OF PHALANGES OF MEDIAL (III) METAPODIALS FOR

Nannippus phlegon FROM FLORIDA.

Width Width Length Length
prox. art. dist. art. V-cscar V-scar/length

Specimen Length surface surface first phalanx first phalanx

UF 7427
First phalanx 52.5 25.6 20.5 41.7 .79

UF 22632
First phalanx 54.2 27.0 21.4 42.7 .79

UF 10695
Second phalanx 29.7 23.7 22.1 -

The volar, or plantar, surface of the first phalanx bears a complex
of scars that serve as attachments for the digital ligaments. During
the course of equid evolution the length of the V-scar (Fig. 13) increas-
ed greatly relative to the length of the phalanx. Sondaar (1968) stated
that in advanced horses this scar extends about 1/2 the length of the
phalanx in M phlegon and "primitive" Equus (Dolichohippus) and
about 2/3 the length of the phalanx in "advanced" Equus. (Figures of
Equus in Camp and Smith [1942:100] and Sondaar [1968:36] suggest
that the V-scar extends far more than 2/3 the length of the phalanx,
but as Camp and Smith noted, it is indeed difficult to delimit the distal
extent of this scar.) Based on the two UF specimens of Florida N.
phlegon (Table 10), the V-scar extends for more than 3/4 the length
(.79) of the phalanx. Lateral to the distal apex of the V-scar are two
well-developed oval perforatus scars (Fig 13B, b).

The second medial phalanx is represented by one specimen, UF
10695. As in other three-toed horses, the length of this phalanx ex-
ceeds the width, whereas the reverse is true in one-toed horses (Table
10, Hussain 1975).

DISCUSSION

Nannippus phlegon FROM FLORIDA.-In size, degree of hypsodonty,
and dental pattern the Florida N. phlegon specimens resemble the
topotypic material from Mt. Blanco. The Florida sample is also com-
parable to published descriptions of this species from other localities
(Hibbard 1941, 1956, Gazin 1942, Dalquest 1975). Prior to this study
M phlegon was reported from only two localities in Florida, Haile
XVA (Robertson 1976) and Santa Fe River (Webb 1974). Two addi-
tional localities are now known, Sarasota and Port Charlotte.

Evidently this horse was not rare in Florida, and its apparent scar-
city reflected the meager sample of appropriate age. With its northern-
most occurrence in Nebraska (Skinner and Hibbard 1972), N. phlegon



28 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

was apparently Neotropical in distribution (although Blancan faunas
are not known in Central America). In the well-sampled more northern
Hagerman L. F. and Grand View L. F. of equivalent age in Idaho, N.
phlegon is not represented (Gazin 1936, Shotwell 1970). Its presencein
Florida seems to be another example of the Neotropical influence of
late Cenozoic faunas of the Gulf Coastal region.

Fossil horses, because of their rapid evolution and wide distribu-
tion both geologically and geographically, are among the best in-
dicators of time in terrestrial Cenozoic sequences. The occurrence of
Nannippus phlegon is also consistent with this generally held view. In
organizing the biochronology of the North American continental Ter-
tiary, the Wood Committee (1941) presented a synthesis of the stages
of mammalian evolution. The Blancan North American Land Mammal
Age was proposed in that report. This time term is a faunal
characterization that includes a combination of first appearances, last
appearances, index fossils, and characteristic fossils. As a result of the
recent advent of precise geochronological tools such as radiometric
and paleomagnetic dating, it is now known that the Blancan spans a
period of time from about 4.5 to 2 million years ago (although not in
total agreement, see Berggren and Van Couvering 1974, Johnson, Op-
dyke, and Lindsay 1975, Lindsay, Opdyke, and Johnson 1975, Tedford
et aL, in press).

With regard to horses, "primitive" Equus (Dolichohippus) is con-
sidered an index fossil of Blancan time. Nannippus is stated to last ap-
pear during this time (Wood et aL 1941). Besides the last occurrence of
this genus, the species N. phlegon is taken as an index of Blancan time,
with its presence in characteristic faunal assemblages (based on other
constituent taxa) such as the type Blancan of the Texas Panhandle,
Arizona, Kansas, and Nebraska. Similarly, Webb (1974) stated that
the presence of Nannippus phlegon in Florida, again based on
associated characteristic faunal elements, is consistent with an inter-
pretation of Blancan time for the Santa Fe River and Haile localities.

The two additional localities reported here also appear to be of
Blancan age. Besides Nannippus phlegon, the Sarasota TRO localities
include the following taxa collected in situ: Equus (Dolichohippus) cf
simplicidens, Kraglievichia cf floridanus, Megalonyx, leptostomus,
Hemiauchenia macrocephalg Tapirus cf ueroensis, Cuuieronius sp.,
primitive capybara, and Chrysemys platymarginata. This assemblage
is taxonomically similar to the Santa Fe River and Haile Blancan
localities (Webb 1974, Robertson 1976). The field associations and
small faunal assemblages of the Port Charlotte localities are of doubt-
ful significance; besides Nannippus phlegon, only primitive Equus and
Chrysemys platymarginata have been collected from spoil piles.



1980 MACFADDEN & WALDROP: FLORIDANANNIPPUS PHLEGON 29

However, the concurrent range zone of N. phlegon and Equus is an in-
dicator of Blancan time at all other published localities of this time in-
terval. Also, the turtle Chrysemys platymarginata appears to be
restricted to the Blancan (Webb 1974). More work is needed to increase
the faunas from southwestern Florida. The complex interfingering of
marine and non-marine facies in that region (see e.g. DuBar 1958)
would provide an excellent opportunity to analyze late Cenozoic faunal
correlation and geological history of the Gulf Coast.

ORIGIN oF Nannippus phlegon.-Dental characters have tradi-
tionally been used to distinguish fossil horse taxa. In many cases the
phylogenetic significance of minor dental variations so used is poorly
understood. This practice has been especially true for hipparions,
which consist of an unnatural or horizontal group of several genera of
predominantly Mio-Pliocene horses with isolated protocones in the up-
per molars and tridactyl feet. Attempts have been made to resolve this
undesirable taxonomic assemblage by recognizing discrete groups of
hipparions based on other characters, as well as those of the dentition.
The configuration of facial fossae has recently been shown to be of
great significance in determining phylogenetic interrelationships of
fossil horses (MacFadden and Skinner 1977, Skinner and MacFadden
1977, MacFadden 1980).

As stated above, Nannippus phlegon is one of the rarest and least-
studied members of the late Cenozoic Equidae. It is instructive to ex-
amine the cranial morphology of this horse in order to discuss its
phylogenetic affinities later in this section. Until now, skulls of this
horse have not been described in the literature. Unfortunately no
skulls of this horse are known from Florida. There is one skull in the
AMNH collected during the 1924 expedition to Crawfish Draw, Mt.
Blanco, Texasi.

AMNH 104708 is a fairly well-preserved skull of a subadult N.
phlegon (Fig. 14). The cheek teeth include right and left dPLMI.
Despite some crushing, the preorbital region of this specimen
preserves some important characters. The nasal notch is not retracted
and it lies above the buccinator fossa anterodorsal to dP'. The premax-
illary bone extends posteriorly to a position that lies over dP: There is
a moderately inflated malar crest. The lacrimal bone extends anterior-
ly to a position that lies over M: The preorbital region is smooth with
no trace of a facial fossa. The infraorbital foramen lies over dp3-dp'.

Numerous workers have speculated on the origin of N. phlegon.
Matthew and Stirton (1930), Webb (1969), and Dalquest and Donovan
(1973) stated that "Nann*pus " lenticularis appears to be closely

'Two other partial skulls of Nannippus Dhlegon, JWT (Johnston - West Texas) 771 and JWT 1028, from Cita Can-
yon, Texas, are housed in the Panhandfe Plains Museum, Canyon. Texas.



30 
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IN

 F
LO

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ID

A
 S

TATE
 M

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S

E
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Vol. 25, N
o. 1

--

\ I. .-I .i..' - 1 --, -* i-E~ < | 1 Zi "'1\\
\

1 /

1 / --I

I \I --\ \ tx '

012345cm

B AM %,RAF9/3-

01234 5 cm

FIGURE 14.-Nannippus phlegon, AMNH 104708, collected by the AMNH expedition of 1924 from Crawfish Draw, Mt. Blanco,

Crosby Co., Texas Panhandle (Blancan Land Mammal Age). (A) right lateral view of skull (reconstructed areas indicated by

dashed lines, matrix stippled), (B) occlusal view of right upper cheek teeth.



1980 MACFADDEN & WALDROP: FLORIDA NANNIPPUS PHLEGON 31

related, or ancestral, to N. phlegon. Cope (1893) originally described
the species Protohippus lenticularis based on two upper molars of late
Hemphillian age from Mulberry Canyon, near Goodnight, in the Texas
Panhandle. Gidley (1907) described more complete material (par-
ticulary a well-preserved skull, AMNH 10584) of what he called
Neohipparion lenticularis from older deposits of Clarendonian age in
Donley County of the Texas Panhandle. In Osborn's (1918) monograph
on the fossil Equidae, he listed AMNH 10584 as the neotype of Hip-
parion lenticulare [sic], but as Cope's original type specimens were
never lost, designation of a neotype was not necessary. Matthew and
Stirton (1930) refer hipparion material from the late Hemphillian Cof-
fee Ranch locality in the Texas Panhandle to Hipparion lenticularis.

The recognition of the species "Hipparion" or "Nannippus" len-
ticularis is difficult because of the lack of well-preserved specimens
from the type locality. As envisioned by some workers, the broad
definition of this species that includes Clarendonian through latest
Hemphillian material is certainly open to question. Thus it is difficult
to defend an ancestral-descendent relationship for "N" lenticularis
and N. phlegon until the former species becomes better defined.

It should also be noted that in Sondaar's (1968) discussion of the
equid manus, he stated that (p. 69): "There are smaller Hipparion-like
animals that do not belong to the genus Nannippus, for example the
species lenticulare [sic], which do not have the generic characters."
This statement suggests that the species "N. " lenticularis and N.
phlegon, the latter of which is the genotypic species of Nannippus, are
not very closely related based on an analysis of postcranial remains.

We suggest the hypothesis that Nann*pus minor, M beckensis,
and N. phlegon are relatively closely related. N. minor is best known
from Mio-Pliocene deposits of central and northern Florida (Sellards
1916, Simpson 1930), and it has also been described from Georgia
(Voorhies 1974)~, Texas (Akersten 1972), and Chihuahua, Mexico
(Lance 1950, Mooser 19689. It should be noted that the holotype of N.
minor, FGS 5867, from the Bone Valley district, has been lost since
about the 1920's (see original description in Sellards 1916). We
designate here the neotype of N. minor, UF 17570, consisting of left
P).M' and right MZ-Ma from Palmetto Mine in the Bone Valley district,
Polk County, Florida (Fig. 15, Table 11).

Dalquest and Donovan (1973, also see Dalquest 1978) described a
new species, Nannippus beckensis, from the early Blancan Beck Ranch

'Ikidy (1860) described a small and poorly known N. minor-like horse, "Hipparion  uenustum, from the Ashley River
of South Carolina.

'Nannippus aztecus, described by Mooser ( 1968) from the Ocote L. F. of Mexico, is probably a junior synonym of N
mi-nor (Waldrop 1971).



32 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

L.F. of Scurry County, Texas. They stated that (1973:34): "The new
form is intermediate in most respects between the middle Pliocene
(Hemphillian) Nannippus lenticularis and N. phlegon of the latest
Pliocene and earliest Pleistocene, with some distinctive characters of
its own." Despite the conclusion that "Nannippus" lenticularis is
closely related to both N. phlegon and N. beckensis, Dalquest and
Donovan presented important informati6n with regard to the present
study that supports a close relationship among N. minor, M beckensis,
and N. phlegon.

In most hipparions the anterior regions of both P: and P: are ex.
panded. In the P2 this expansion includes the presence of a
pseudoparastyle and true parastyle (Fig. 3). In the P2 the paralophid
usually exhibits a triangular anterior projection. In N. minor, N.
beckensis, and N. phlegon the anterior regions of both P2 and P2 are
unexpanded relative to other hipparions (compare Fig. 17 with Fig. 4,
also see Dalquest and Donovan 1973:38, text-fig. 4B).

TABLE 11.-MEASUREMENTS OF Nannippus minor, NEOTYPE, UF 17570, FROM PAL-
METTO MINE IN THE BONE VALLEY DISTRICT, POLK COUNTY, FLORIDA.

AP T
Tooth Length Width Ht*

LP' 16.1 15.3 28.9
LP, 15.6 15.0 32.8
LM, 14.0 13.7 27.8
LM' 14.3 13.7 31.7
LM3 12.8 9.7 31.5
RM2 14.7 13.5 32.3
RM' 13.0 9.3 31.9
Length LP'-LM':72.1
*Greatest crown height (see Table 1).

0 
iL Y-

0 1 2 3 4 5cm

FIGURE 15.-Left upper cheek tooth row, P'-M'' of Nannippus minor, UF 17570.
neotype, from Palmetto Mine, Bone Valley district, Polk County, Florida. (Remainder
of neotype, M'-M', not illustrated here.)



1980 MACFADDEN & WALDROP: FLORIDA NANNIPPUS PHLEGON 33

Many hipparions have an ectoparastylid (projection or isolation of
paralophid, also called parastylid by some workers) developed on the
anteroexternal region of P2-M3• Primitive N. minor shows a reduction
in the presence of the ectoparastylid, which is further reduced in both
advanced N. minor and N. beckensis. In N. phlegon the ectoparastylid
is normally absent (see Waldrop 1971 and Dalquest and Donovan 1973
for quantitative data). In other words, a character morphocline pro-
ceeds from primitive hipparions (ectoparastylid present) to primitive
N. minor (reduction in frequency of ectoparastylid) to advanced N.
minor-N. beckensis (further reduction in frequency of ectoparastylid)
to N. phlegon (ectoparastylid normally absent).

N. minor, N. beckensis, and N. phlegon have numerous other dental
characters that support a hypothesis of close relationship, for exam-
ple, complexity of enamel plications and shape of dental parts. Both N.
minor and N. beckensis are smaller in maximum crown height (in both
the uppers and lowers) than N. phlegon. The maximum crown height of
M minor is normally less than 50 mm (Waldrop 1971) whereas the
maximum crown height of N. phlegon is somewhat greater than 50 mm
(see Tables 1,4). For N. beckensis Dalquest and Donovan (1973) noted
crown heights of 56.2 mm to 60.0 mm (lowers) and 51.2 mm to 55.7 mm

TABLE 12.-MEASUREMENTS OF LEFT LOWER CHEEK TEETH OF Nannippus minor, TRO

567, FROM PALMETTO MINE, BONE VALLEY DISTRICT, POLK COUNTY,

FLORIDA.

AP T
Tooth length width HT*

P2 13.3 7.5 25.2
K 13.6 7.9 -
P, 14.0 7.6 33.5
M1 13.0 6.4 35.0
M: 13.4 6.6 -
M, 16.6 5.3 39.3
*Crown height at mesostyle.

0 1 2 3 4 5cm
1, ''1

FIGURE 16.-Left lower cheek teeth, P,-M„ of Nannippus minor, TRO 567, from Palmet-
to Mine, Bone Valley district, Polk County, Florida.



34 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 1

(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 M 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, M 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



1980 MACFADDEN & WALDROP: FLORIDA NANNIPPUS PHLEGON 35

have been a similar ecological exclusion among equids and other large
herbivores in the Gulf Coastal region during Hemphillian and Blancan
times.

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(Washington, D.C., Amen Inst. Biol. Sci.).

MSS must be submitted in duplicate (please no onionskin) and satisfy the following
minimal requirements : They should be typewritten , double-spaced lespecially tables ,
figure captions, and "Literature Cited"), on one side of numbered sheets of standard
(8-1/2 x 11 in.) bond paper, with at least one-inch margins all around. Figure legends and
tables should be typed on separate sheets. All illustrations are referred to as figures.
They must comply with the following standards: Photographs should be sharp, with
good contrast, and printed on glossy paper. Drawings should be made with dense black
waterproof ink on quality paper or illustration board. All illustrations should have a
cover sheet. All lettering will be medium weight, sans-serif type Ce.g. Futura Medium,
News Gothic) in cutout, dry transfer, or lettering guide letters. Make allowance so that
after reduction no lower case letter will be less than 1 mm high (2 mm is preferred) nor
any capital letter greater than 5 mm high. The maximum size for illustrations is 8-5/8 x
14 in (twice typepage size); illustrations should not be less than typepage width (4-5/16
in.). Designate the top of each illustration and identify on the back with soft pencil by
author's name, MS title, and figure number.

All manuscripts not submitted in BULLETIN format will be returned to the author for
retyping.

Manuscripts and all editorial matters should be addressed to:

Managing Editor of the BULLETIN
Florida State Museum
Museum Road
University of Florida
Gainesville, FL 32611