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ISSN 0067-928
.!lll #;s*l'di$'rysN DIE NASI.NALE MUSEUM
NATURAL SCIENCES
DECEMBER 2006
FLORISIAN MAMMAL FOSSILS FROM EROSIONAL GULLIES ALONG THE
MODDER RIVER AT MITASRUST FARM, CENTRAL FREE STATE,
SOUTH AFRICA
by
r,r-oyo nossouw t''
I Florisbad Quatemary Research, National Musetn, Bloemfontein. South AJrica.
2 Dept. oJ Plant Sciences, university of the Free State, South A.ftica.
E-nail : I I ovd(dus nus co. za
ABSTRACT
Lloyd Rossou*. 2006, Flo sian mrmmal fossils from €rosionel gullies rlong the Modd€r River at Mitrsrust
farrn, centrrl Free State, South Africx. Nrvors. nas. Mus., Bloemlontein 22(6): 145-162, This pap€r d€scribes
a fossil bone assemblage eroding out of the overb6nk sediments ofthe Modder River. Direct dating ofthe fossils
proved difficult but the sedimentary context and faunal profile suggest a late Quatemary age for the assemblage.
Located in th€ Grassland Biom€, th€ assemblage is represented by a variety of extinct as w€ll as living grazing
ungufates, namely Equus bnchellii, E. capehsis, Phacochoerus aethiopicus, Connochaetes gnou, Damaliscus
pygargus, Megalouagus prisclts sftd Homoioceras anli4r.ir.lJ. The species composition conforms to the Florisian
Land Mammal Age and supports the model of a dynamic grassland ecosystem during lh€ late Quatemary on the
high central plateau ofsouth Africa.
(Florisien mammal fossils, Late Pleistocene, Modder Rivcr, Fre€ Stete Province)
OPSOMMING
Floriiens€ soogdi€r-fossiele in eroderingslote (dongas) langs die Modderrivier op die pleas Mitasrust,
sentrale vrystaat, Suid-Afrik!. Grootsoogdier-fossiele wat erodeer uit die fluviale sedimente aan die oewers van
die Modderrivier word beskryf. Die sedimencre konteks en spesie-profiel van die versameling dui op 'n laat
Kwarcmete ouderdom vir die soogdiere. Die versameling bestaan uit a v€rskeidenheid van uitgestorwe sow€l as
modeme grasvreters, naamlik die reuse Langhoringbuffel. Homoioceras antiquus,'n groot hartebees,
Megalotragus priscus, en di. Kaapse zebn, Equ s caperrB. Ook ingesluit is Burchell se Zebra, tquus burchelli,
die onlangs uitgestorwe Ka pseylakyatk, Phacochoerus aethiopicus, die swartwildebees, Connochaetes gnou, en
die bl€sboh Darnoliscus dorcas. Hie:die fossiele ondersteun die model van 'n ryk en dinamiese grasland-
ekosisteem gedurende die laat KwanCr in die sentrale binneland van Suid-Afiika.
(Floriaanse soogdier-fossiele, Lsat-Pleistoseen, Modd€rrivier, Provinsie Vrystrst)
ISBN t 86847 103 9
VOLUME 22, PART 6
DISCUSSION ......
INTRODUCTION
Fossil remains of large mammal fauna were discovered on the farm Mitasrust during a
survey oferosional gullies (dongas) along the Modder River drainage. The Modder River is
a southem tributary ofthe Vaal River and its alluvial deposits are associated with abundant
Quaternary mammalian fossils (Churchill et al. 2O00).Its fossil-bearing potential has been
known for almost 150 years, with a frontlet and hom cores of Homoioceras qntiquus
recovered as far back as 1839 (Cooke 1955) and the remains of Megalotragus priscus
discovered around the turn of the previous century (Broom 1909a). More recent fieldwork
has led to the discovery of a number of fossil localities along denudations on the banks of
the Modder River (Churchill et al.200O; Rossouw 1999,2000), including Mitasrust, the
locality discussed in this paper.
FIELDWORK
The fossils were recotded in eroded, r€ddish_coloured overbank silts and sandy clays along the Modder
Rivet drainage, about l6 kilometers north€ast ofBloemfontein, on the farm Mitasrust (Figure l)
The site is situated about eighty metrcs south ofthe activ€ river channel and approximately s€ven
metres above the riverbed. The fossiliferous sediments consist of an eroded alluvial fill, covered
by a veneer of carbonate concretions Fragmented fossil bone material was evenly distributed
over an eroded area that may Possibly represent an old land surface (Figure 2)
Florisian mammal fossils - Lloyd Rossouw
. Florileb3d
lJd' n,, '''.a Mrtasftr$l
\
sloqnFo TE|N
Figure 1: Map of the Mitasrust locality, showing its position in relation lo other fossil
localities in the area
r48 Navors. nas. Mus., Bloeufontein Volume 22, Part 6
(a) .f. +
North I
ll
;r f .,r,
r .f 'Ift.
I
il0m
0m 35m 70m
(b) South
Towards Modder River r{qder$ !a$d' 5yfa99
- " ..'o '-; '^'.--
o t S;t-i
rl 0vl
tiY w i
0-5m o
!g
q
o
t
o
!J
c
3
3.0m
Figure 2: Scatt€rplots of horizontal (a) and vertical distribution (b) of vertebrate
fossil specimens from Mitasrust.
Some specimens were collected from the surface, but the majority ofthe fossil material was
still in situ, being covered by the overbank sediments. After a temporary datum point was
set up, all visible and eroded fossils were plotted in, removed and studied at the Florisbad
Quatimary Research Station. Regular monitoring of the site subsequent to the discovery of
the fossils has yielded no freshly eroded or exposed material to date.
Fossil samples sent away for radiocarbon dating were processed, but did not yield a date
due to i deficiency in preserved organic material (S. Woodbourne, personal
communication). However, the fossils at Mitasrust are eroding out of calcretized overbank
sediments typical of the numerous fluvial sites that are exposed by erosion along the
2006 Florisian mammal fossils - Lloyd Rossouw
Modder River drainage. The fluvial history ofthe Modder River is more firmly established
at some of these localities. The upper calcr€tized layers of the Florisian fossil locality at
Erfkroon, which is located 70 kilometers west and downsteam from Mitasrust, on the
northern bank ofthe Modder River (Churchill el a/. 2000), presumably represent palaeosols
formed under semi-arid to arid conditions (Hancox et ol. 2002). Two optically-stimulated
Iuminescence dates derived from the upper calcretized layers and the topmost reaches of an
upward-fining gravel unit lower down in the sequence, provided a range of between 25 000
and ll3 000 years Before Present for the younger phase of site formation at Erfkroon
(Churchill et ql.2000). The association between the age ofthe younger overbank sediments
at Erfkroon (Churchill et aI.2000), and fossiliferous overbank sediments at Mitasrust, as
well as the Iikelihood of more arid environmental conditions indicated by these sediments,
suggest a Last Glacial sensu /alo age (possibly between Isotope Stage 4 and Isotope Stag€
2) for the Mitasrust fossils.
MATERIALS AND METHODS
The fossil material from Mitasrust was compared to fossil material from the Florisbad
Quaternary Mammal Collection and modem skeletal material from the Florisbad Modem
Mammal Collection (Tables I - 4). Measurements were taken with a slide caliper to the
nearest 0.1 mm. Nomenclature used for osteometrical descriptions and abbreviations is
consistent with the system given by Von den Driesch (1976) and Eisenmann et al. (1988).
The fossils were sorted taxonomically according to minimum numbers of individuals
(MNI) and numbers of identified specimens (NISP) (Table l).
Table l: Mitasrustr A taxonomic summary according to minimum numbers of individuals (MNI) and
numbers of identified specimens (NISP).
t49
MAMMALIA
PERISSODACTYLA
Equidae
Equus burchellii (Burchell's zebra)
Equus sp. cf. E. capensis (Extitl'ct Cape znbra)
Equidae indet.
ARTIODACTYLA
Suidae
Phacochoerus aethiopicus (Extinct Cape warthog)
Bovidae
Connochaetes gnou cf antiquus (Black wildebeest)
D am al is cus pygar gus (ttlesbok)
Megalotragus pris clJ (Extinct hartebeest)
antiquus (Extinct giant buffalo)
Bovidae indet-
MNI NISP
2
I
3
8
3
3
3
4
8
6
6
I
I
I
I
I
l
150 Nqvors. nqs Mus., Bloemfontein, Volume 22, Part 6
RESULTS
Taphonomy and Site Formation
Biological as well as non-biological taphonomic agents contributed to post-mortem
modification of the fossil material. The characteristically even scrape marks made by
porcupine gnawing are visible on a few specimens. The majority of bone surfaces are
characterized by expanded longitudinal cracks and patches of roughly textured compact
bone, indicating extensive surface weathering, which implies that the bones were exposed
sub-aerially for a relatively long period before final burial (Behrensmeyer 1978; Maguire et
al 1980). The available calcium carbonate in the soil provided a suitable chemical
environment for preservation of the fossils, but this also contributed to bone damage as a
result of carbonate formation on the bone surfaces. Virtually all the specimens were heavily
calcretized and had to be prepared with air drills in the lab. Root etching is visible on some
bone surfaces.
Evidence to support a single agent of accumulation is not conclusive. Absence of rolling
damage to the fossils, their somewhat clustered distribution and the fact that the
depositional orientation of the bones appeared to be random, makes deposition by fluvial
action unlikely. There are no preserved coprolites or camivore damage, which are usually
good indicators of hyaena burrows. Obvious signs of porcupine gnawing on several of the
bones suggest the likelihood of a bunow or burrow system. However, up to 9004 of bones
found in porcupine lairs show porcupine gnaw-marks (Maguire er a/. 1980), while in the
Mitasrust assemblage less than one (0.88%) of the total number of bones show signs of
porcupine gnaw marks.
Stone tools were scattered across erosional gullies on the site and the effects of gradual
downward erosion have removed numerous Later Stone Age and a few Middle Stone Age
artefacts from their original contexts. It is noted, however, that two MSA triangular flakes
were recorded from the calcrete layer and are in pdstine condition, with one bearing clear
signs of calcium carbonate concretions on its dorsal as well as ventral surfaces. This may
suggest a temporal association between the MSA artefacts and the fossils.
Fossil Mat€rial
Equidae
Equus burchelli (G ray 1824)
Material: R. maxilla with M1-3,P2-4 early wear (MRT 28ll); L. maxilla with Ml-3, P2-4
early wear (MRT 2812); anterior part oflowerjaw (MRT 20); L. Iowerjaw Ml,P2-4 eatly
wear (MRT 5); R. lower jaw Ml, P3-4 early wear (MRT l3); L. acetabulum (MRT 43); R
lateral halfofproximal radius (MRT l2).
Criteria to separate equids through dental features (Eisenmann el a/. 1988) were used and
the Mitasrust equid teeth are tentatively assigned to Equus burchellii (Table 2). The
t-
l5l2006 Florisian mammal fossils - Lloyd Rossouw
morphology of the lingual fold in the lower molars is 'V'-shaped and the buccal fold
completely penetrates beyond the metaflexid and entoflexid in the lower Ml (MRT 5; MRT
l3). The M3 and P4 ofboth the right and left maxillae are newly erupted with the P4 still
unwom (MRT 28/l; MRT 28D). The ectolophs in the upper molars are rounded and
convex. The protocones are elongated and slightly bilobate. There are no signs of the pli-
caballine between the protocone and the h)?ocone ofthe upper molars.
In the acetabulum (MRT 43) the acetabular cavity is relatively shallow with undefined
margins and a crescentic articular facies.
Burchell's zebra fossil material has been previously recorded at Florisbad (Churcher and
Richardson 1978; Brink 1987).
Equus capensis (Broom 1909)
Material: L upper P4 (MRT 14); L. proximal metatarsal (MRT l5ll); anterior proximal
phalanx (MRT 6).
The left upper fourth premolar is large, but unwom and therefore cannot give reliable
occlusal observations or measurements. The metatarsal (MRT l5/2) is covered by calcium
carbonate concretions and the distal extremity is broken off. The palrnar surface is severely
pitted by post-depositional weathering while the dorsal surface has multiple longitudinal
cracks. The shaft is cylindrical but widens medio-laterally and flattens anterior-posteriorly
towards the distal end. The proximal articular surface is well preserved with the facets for
the second, third and fourth tarsals all distinctly visible. The anterior proximal phalanx
(MRT 6) is completely preserved and is noticeably larger than the anterior proximal
phalanges in any ofthe living South African equids (Table 2).
All large later Pleistocene zebras frorn southern African sites are generally assigned to the
species Eqzzs capensis (Chvrcher and Richardson 1978). The original description by
Robert Broom is based on lower teeth, characterizing the animal as an extinct species with
a larger skull than, and the lower molars similar to, that ofthe living zebra (Broom 1909b).
The species is recorded at Florisbad (Brink 1987) and is known to have been present in all
the ecozones of southern Africa until the end of the Pleistocene (Churcher and Richardson
1978). The disappearance of Equus capensis from the soutlern Cape Province also
coincided with the disappearance of several bovids such as Homoioceras antiquus,
Megqlotragus ptiscus and Antidorcas azstralrs from the Cape coast (Klein 1974).
I
t52 Nqvors. nqs. Mul, Bloemfontein, Volume 22, Part 6
Table 2: Equidae: m€asurements of ,q/r.r , urchellii and Equus cap.nsis.
E. burchellii
E. capensis
MRT-28/l
RMI
MRT-28/l
RM2
MRT-28/2
LMI
l3.l
Length of
Protocon€
t2.0
I t.0
I 1.5
t1.2
Bd
Early
Early
Occlusal
Length
23.s
Occlusal
Breadth
Length of
Double
Knot
(metaconid
&
metastylid)
t2.4I t.3
l t.728.2
Early
Early
Early
Early
22.5
24.2
23.9
24.4
CL
2t.2
2l.4
Bp Dp
MRT-6 Ant. Prox.
phalanx
153
2006 Florisian mammal fossils - Lloyd Rossouw
Suidae
Phacochoetus aelhiopicus (Pallzs, 17 61)
Material: Upper M3 (MRT 1&2); lower M3 (MRT 4l )
The extinct Cape warthog was identified fiom dental material (Table 3). In this species,
root formation of both the upper and lower third molar is delayed until well after the last
columns come into wear (van Hoepen and van Hoepen 1932; Cooke and Wilkinson 1978).
In contrast, root formation in the extant Phacochoerus africanus, occurs at about the same
time that the last column of the third molar starts to wear (van Hoepen and van Hoepen
1932). Third molars of both the P. africanus and P. aethiopicus types are found at the
Florisbad Spring Assemblage (Brink 1987).
Table 3: Suidae: meas|lrcm.nts of Phacochoetus aelhiopicus.
Bovidae
Homoioceras anliqras (Duvornoy, 1851)
Material: L lower jaw with molar flagment (MRT 44); R. talus (MRT 36) damaged by
porcupine gnawing; L. scapula (MRT 7); distal metacarpal fiagment (MRT 40); R.
metacarpal (MRT 8); lateral halfof L. metatarsal (MRT 9).
The left lower jaw shows evidence of post-depositional weathering. The dental roots as
well as a badly damaged molar are visible in a fragment ofthe horizontal ramus (MRT 44).
Bovine traits are indicated by the complicated central cavities, rugose enamel and thick
cementum in the molar fragment.
The scdpula is larger than that ofthe modern buffalo Syncerus caffer (Table 4). The glenoid
cavity is circular with no notches and an even margin (MRT 7). The acromion is broken off
but the spine appears fairly straight so that it remains within the line of the cranial margin
of the scapula when viewed dorsally. The neck is wide and its posterior border is straight.
The metatarsal bone (MRT 9) is relatively slender compared to that ofs. caffer (Table 4).
The nutrient foramina on tlle metacarpal (MRT 8) could not be detected, because of a thin
veneer of calcium carbonate covering tle bone. In addition, the shaft shows signs of
porcupine gnawing and weathering. It is wide and flat and the lateral condyle is broken off.
The specimen is longer than in S. cafer. The greatest length of the metacarpal was
measured llom the anterior edge ofthe articular facets for the fused second, third and fourth
carpal bones, to the articular surface of the most projecting part of the medial condyle
(Table 4). The condyle of the distal metacarpal bone fiagment (MRT 40) displays a well-
defin€d sagittal ridge that extends dorsally to almost beyond the palmar fossula.
t54 Navors. nas. Mus., Bloemfontein, Volume 22, Part 6
The metatarsal (MRT 9) is approximately 20 percent longer than the corresponding
metacarpal bone (MRT 8) in the assemblage. The diaphysis widens abruptly at the junction
with the distal epiphysis. The medial condyle is broken off, but the lateral condyle is
prominent and exhibits a well-defined sagittal ridge. Greatest length of the metatarsal was
measured from the highest point on the proximal articular surface to the articular surface of
the most projecting part ofthe lateral condyle (Table 4).
Differences of opininion regarding its phylogenetic relationship with the East African
species Pelorovis oldowoyensis Reck, have stimulated ongoing debate on the suitability of
the generic name for the long-homed btffalo, Pelorovis qntiquus (Gentry 1967; Gentry
1978; Gautier and Muzzolini l99l; Klein 1994; Peters et ql. 1994:, ceraads 1995). Lately,
Pelorovis oldowtryensis has been regarded as more closely related to the genus Bos, which
means that the long-horned buffalo should be removed from Pelorovis and included in the
extinct buffalo gents, Homoioceras (Geraads 1995). Bovine fossil material assigned to the
long-homed buffalo is listed in the Florisbad Spring Assemblage and also found at Erfkoon
(Brink 1987; Churchiu e/ 41 2000).
There is no evidence to show that the long-homed buffalo existed in South or East Afiica
after the beginning of the Holocene epoch ten thousand years ago. Homoiocerqs qntiquus
had longer metapodials and shorter upper limb bones than S cafer (Gentry 1967; Peters et
al. 1994), suggesting that the long-homed buffalo was probably more cursorial than the
living buffalo, whereas the animal's exceptionally long homs probably excluded it from
generally wooded environments (Klein 1994).
Megalotragus ptisczs (Broom 1909)
Material: R. lower M3 (MRT l8); R. upper M3 (MRT 25); R. scapula (MRT 33ll); L.
distal humerus (MRT 23); proximal femur (MRT 30); R. lateral portion of distal tibia
(MRT 32); R. proximal metatarsal (MRT 3/l); Metatarsal diaphysis (MRT 26).
The teeth are larger than in the modem black wildebeest and hartebeest (Connochaetes
gnou and Alcelaphus buselaphus) and exhibit rypical alcelaphine attributes in being
hypsodont with no basal pillars (Table 4). The posterior lobe is damaged in the lower M3
(MRT l8). It has rounded buccal lobes that are moderately rugose. No goat folds are
present. The posterior lobe is broken off in the upper M3 (MRT 25). The tooth has
outbowed ribs and round€d, rugose lobes (on the lingual side).
The rim ofthe glenoid cavity ofthe scapula is well rounded on the caudal side but follows a
straight line cranially (MRT 33ll). There is a gentle notch on the cranial side of the rim.
The supragleniod tuberculum is prominent and extends cranially. The breadth of the
glenoid cavity, the greatest length of the glenoid process and the length of the glenoid
cavity is shown in Table 4.
The distal humerus is extremely weat}ered with porcupine gnawing marks and cracks
covering the specimen (MRT 23). The lateral and medial epicondyles are damaged. The
radial fossa is moderately incised but this appearance is most likely as a result of the post-
depositional wear on the condylar surfaces. The coronoid fossa is well defined and there is
a minor indentation at the top ofthe medial condyle.
t
I
a
I
I
1552006 Florisian mammal fossils - Lloyd Rossouw
The femur consists ofthe articular head and a portion ofthe neck ofthe proximal exfemity
(MRT 30). In the metatarsal shaft (MRT 3/l), the proximal extremity projects far plantaro-
medially and has a large, elongated synovial fossa in the centre ofthe articular surface. The
proximal breadth and the depth ofthe metatarsal are given in Table 4.
M. priscus is regarded as a terminal species of an exlinct lineage ald an endemic to
southern Africa (Gentry 1978). It is represented in the fossil record ofthe central interior,
the Cape Ecozone as well as the central Karoo (Klein 1980, 1984; Brink 1987; Brink et ql.
1995; Churchill 2000). The last recorded occurence of M. priscus is around 7500 years
B.P. at Wonderwerk Cave in the Northern Cape Province (Thackeray 1984a, 1984b).
Its original description ofM prisczs was based on "the postorbital portion ofthe skull with
the proximal part ofthe hom core", discovered on the banks ofthe Modder River between
Bloemfontein and Kimberley (Broom 1909a). Dentition from the Florisbad Spring
Assemblage indicates that the Florisian form was a specialized grazer, while the
morphology of the homcores from Florisbad, Erfkroon and Mahemspan represents a later
stage ofthe genus's development in southem Africa (Brink 1987; Churchill er a/. 2000).
Megqlotqgus eucornutua van Hoepen, an earlier form that lacks the fused pedicles at the
base of the horncore, is known from the late Early Pleistocene faunal type-site at Comelia
in the north-eastem Free State (Cooke 1974; Bender and Brink 1992; Brink and Rossouw
2000).
Connochaeles gnoz (Zimmerman, 1780)
Material: R. upper jaw, Ml-3 (MRT I l/l); L. proximal tibia (MRT 34ll); L. distal
metatarsal (MRT 4).
The teeth are badly preserved, but their size and other diagnostic features make them
comparable to that of Connochaetes (MRT ll/l). The upper molars are hypsodont, not
rugose and the lobes are evenly rounded in occlusal view. The central cavities are crescent-
shaped and not complicated. The styles are defined and prominent.
The medial and lateral condyles of the proximal tibia are preserved (MRT 34ll), but the
margini of the articular surfaces are damaged. The intercondylar eminence is pronounced
and its proximal projection is noticeable.
u
The distal metatarsal is comparatively robust (MRT 4). Its distal proportions fall within the
metrical range ofC gnou antiquus from Florisbad (Figure 3 & 4).
r56 Navors. nas. Mus., Bloemfontein, Volume 22, Part 6
xx&
XX
b<
.s28
o.
o
!
i
.9
az6
A
Aa
X
A4 .MTR 4
X FLO
A Mod€.n C. gnou
A
24 12 43
Distal Breadih
Figure 3: Measurement of distal metatarsal size in C. gnou lfollowing Brink
(1993)1.
The black wildebeest is a southem Aflican endemic species and has a southern Allican
origin (Brink 1993). Fossil homcores from the spring deposits at Florisbad were originally
described as Connochaetes antiquus (Btoom l9l3) but Gentry (1978) later refered to an
extinct subspecies, C. gnou antiquus. This form is regarded as the evolutionary link
between the modern black wildebeest and C. gnou laticornutus, which is an earlier stage
ffom Cornelia and Elandsfontein (Brink 1993).
Dsmaliscus pygaryur (Pallas, 1766)
Material: L. lower M3 (MRT33); L. lower M3 (MRT 37); L. lower M2 (MRT 3l); L, distal
femur (MRT 4212).
Size and morphology indicate that the teeth belong to D. pygargus. The molars are
hypsodont, rugose and the lobes are pinched. The central cavities are crescent-shaped and
not complicated while goat folds or basal pillars are absent.
tn the distal femur the medial and lateral condyles as well as the fochlea are preserved
(MRT 42/2). The intercondylar fossa is deep and the medial epicondyle is prominent. The
proximal portion of the lateral condyle has a defined margin that projects proximo-
medially.
Damaliscus pygqrgus contains two extant subspecific forms, namely the blesbok
Damaliscus pygargus phillipsi formerly distributed over the central interior of South
Allica, and the bontebok Dqmqliscus pygargus Wgargus, with a restricted range in the
south€m Cape. The Free State Province is generally regarded as the type locality of the
blesbok (Grubb 1999). The bontebok is currently preserved in the Bontebok National Park
near Swellendam in the Western Cape Province. Its type locality has been selected as the
tt-
2006 Florisian mammal fossils - Lloyd Rossouw l5'l
Riversdale district in the southern Cape (Grubb 1999). D. pygargus fossils have been
recorded fiom Florisian sites in the central interior, with Gladysvale the oldest dated site
(Brink 1987; Grtn et al. 1996; Brink et al. 1999:' Laquz et q|.2002), but it has also been
found at Swartkrans Member 2 and Haasgat Cave, both estimated to be greater than one
rrillion years old (Vrba 1976; Plug and Keyser 1994). Fossil remains of D. pygqrgus ln the
Cape have been recorded fiom Pleistocene localities such as Boomplaas (Klein 1978), the
Sea Harvest site at Saldanha Bay (Grine and Klein 1993) and Duinefontein (Klein et al.
l9e9).
Table4: Eovidae: measurements of Homoiocerus antiquus. Megalolrcgus ptisc s, Connochaeles Snou
and Damaliscus pygargus.
tr
pleareus
MRT-7 L. scapula
MRT-8 R.metacarpal
MRT-9 I- metatarsal
233.0
289.0
occlusal
Breadth
MRT.I8 R.
M3
MRT-33/r
R. scapula
MRT-3/I R
metatarsal
MRT.3I L.
M2
MRT.33 L.
M3
MRT-37 L.
M.l
14.3
55.2 s09
s91494
Occlusal
Breadth
92
158 Navors. nas. Mus., Bloemfontein, Volume 22, Part 6
DISCUSSION
The Florisian Land Mammal Age (LMA) is one of several biochronological stages of
chronologically arranged, late Tertiary and Quaternary mammalian faunal assemblages
from southem Africa (Hendey 1974). It spans the latter part of the Pleistocene and is
primarily composed of modem species, more or less characterized by individuals that are
larger in size than their modem counterparts, as well as six extinct ungulate grazers
(Hendey 1974; Klein 1980; Brink 1987). The older age limit of the Florisian LMA has
recently been dated to around 400 000 years ago (Grun et a/.1996) but is now considered to
approach 700 000 years Before Present (Lacntz et al.2002).
The extinct fauna identified at Mitasrust is typical of the Florisian LMA. There is no
evidence ofE capensis, or H. antiquus in lhe palaeontological record after the beginning of
the Holocene in South Africa (Hendey 1974; Klein 1980) and M. priscus became extinct
during the early Holocene (Thackeray 1984a, 1984b). Their disappearance coincides with
an extinction event at the end of the Pleistocene when six ungulates became extinct in
southern Africa (Hendey 1974; Klein 1980; Brink 1994). M. priscus is usually well
represented at Florisian fossil localities (Klein 1980; Brink 1987; Mckee 1995; Brrnk et al.
1999; Churchill et al. 2000) and therefore a helpful marker for this period. The presence of
D. pygargus is also significant. Although the animai is recorded at early Pleistocene sites in
the Witwatersrand area (Vrba 1976; Plug & Keyser 19941Lacruz et al. 2002), the oldest
dated site of D. pygargus south of the Vaal River is at Florisbad (Brink 1987; Grun et
all996 Brrry'{- et al 1999). Body-size changes over time in C. gnou, provide added clues to
the age ofthe site. Brink (1993) has demonstrated that the body size ofthe black wildebeest
has generally reduced since the Last Interglacial period. The distal proportions of a
metatarsal of C. gnou from the Mitasrust assemblage (MRT 4) lies closer to metrical range
of C. gnou antiquus from Florisbad than to that of the modern black wildebeest (Figure 3),
suggesting a pre-Holocene age for the specimen (Brink 1993).
CONCLUSION
A conservative but cautious age estimation places the Mitasrust assemblage firmly in the
Florisian LMA. The similarities in the depositional context between Mitasrusrust and
Erfkroon (Churchill et al. 2000) may be taken to point to a late Pleistocene age for the
fossils. Since the older age limit ofthe Florisian LMA is presently considered to be around
700 000 years Before Present (Lacruz et a|.2002), and the oldest dated site of D. pygargus
south of the Vaal River is Florisbad (Brink 1987), the Mitasrust faunal profile serves as a
record for a period spanning roughly the lasl quarter of the Pleistocene on the southern
highveld.
The Mitasrust assemblage contains several extinct ungulates, the long-horned buffalo
Homoiocerqs antiquus, a large alcelaphine Megqlotragus priscus, and the Cape zebra
Equus capensis. Also included are the plains-zebra Eqwts burchellii, the recently extinct
wtthog Phacochoerus qethiopicus, the wildebeest Connochqetes gnou, and the blesbok,
Damaliscus pygargus. The variety of different-sized herbivore species at Mitasrust supports
the model that a productive and sustainable grassland ecosystem prevailed during the mid-
late Pleistocene in the central interior of South Africa (Brink and Lee Thorp 1992).
I
I
2006 Florisian mammal fossils - Lloyd Rossouw
Although the Mitasrust fossil assemblage is not extensiYe or unique, it is a useful record in
the ongoing exploration of interior river drainages as sources ofQuatemary fossil deposits'
ACKNOWLEDGEMENTS
Mr. Andre Wiese (farm owner) is thanked for his kind permission to work at Mitasrust'
Estie Esterhuizen prepared the figures. I thank James Brink and Zo€ Henderson for their
critical remarks with regard to the manusffipt. Reviewers Dr J.F Thackeray (Transvaal
Museum, Pretoria) and Dr S. Reynolds (School of Anatomical Sciences, University of the
Witwatersrand) provided comments and suggestions that greatly improved the Paper.
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