LUCIACALOI
Dipartimento di Scienze della Terra, Università degli Studi "La Sapienza", Roma
THE TWO EQUIDS OF THE MIDDLE PLEISTOCENE OF THE SITE VENOSA-LORETO (SOUTHERN ITALY): FUNCTIONAL MORPHOLOGY OF THE CRANIAL REMAINS
We examine two partial jaws coming from the fossiliferous levels indicated as "reddish sands" = leve! A (Chiap- pella, 1964; Segre 1978). Most of the remains of the two equids, attributed to Equus altidens and Equus aff. E. silssen- bornensis by Alberdi et al. (1988), come from these levels. The two examined remains, consisting in two incisive regions, even if largely incomplete, are very important in order to reconstruct the functional adaptations. The different body sizes would suffice to suggest that the two species are ecologically distinct. The different shape of the incisive region and simphysis shows that each of the two species occupied a distinct and particular ecologica! niche and that they exploited different food resources. We put in evidence the importance of the appearance of species with short and broad muzzles among the Plio-Pleistocene equids, both in stenonoids and caballoids.
KEY WORDS: Equidae, Pleistocene, ltaly, dietary adaptations.
PAROLE CHIAVE: Equidae, Pleistocene, Italia, abitudini alimentari.
Introduction
The remains of the two equids found in the site Venosa-Loreto (Basilicata, Southem ltaly) have been the subject of an analytical morpho-taxonomical study (Alberdi et al., 1988). With this report w e intend to carry out a morphologica1 and functional analysis of the cranial and dental remains as well as of the post- crania1 skeleton to specify the dietary habits and 1ifestyle of the two ungulates in arder to better charac- terise their niche and their position within the func- tional structure of the herbivores of the time. In this paper we will examine only the few cranial and mandibular fragments.
The remains of the two equids come from the fos- siliferous levels known as "reddish sands"
=
level A (Chiappella, 1964; Segre, 1978). In a recent geo1ogic- palaeontological synthesis about the Venosa- Notarchirico basin (Cassali et al., 1999; Lefèbre &Raynal, 1999; Lefèbre et al., 1999; Pipe m o et al., 1999) the Loreto-A sedimentation is approximately dated to 600.000 years ago; the faunal association would thus be referred to the late Middle Galerian (sensu Gliozzi et al., 1997).
Systematics
The examined remains belong to two equid species different in size and are part of a 1ot of teeth and long bones referred by A1berdi et al. (1988) to Equus alti- dens von Reichenau and Equus aff. E. siissenbornensis Wiist. The systematics of the two species as well as of
stenonoid equids s .s. have been discussed by various authors and were object of recent revisions (e.g. Alber- di et al., 1998; Eisenmann, 1995; Forsten, 1998, 1999;
Koufos et al., 1997). Not intending to discuss about such interpretations, we will emp1oy the taxonomic cat- egories used in the previous works (Calai, 1995, 1997).
Description
Cranial remains are limited to a body of the inci- sive bone of the skull and two incisive regions of the jaw. These finds, which bave only been mentioned in Alberdi et al. (1988), are vastly incomplete but very important to provide inforrnation about the distribution of the niche between herbivores that exploit similar food resources (Damuth & MacFadden, 1990; Janis &
Ehrhardt, 1988; Owen Smith, 1985; Solounias &
Dawson-Saunders, 1988; Spencer, 1995; etc.).
Even recent studies on equids and hipparions pointed out the variety of adaptations that can be drawn from a large scale of muzzle morphologies and from the position and forrn of the incisors, in animals whose diet could be considered very monotonous in a first approximation (cf. e.g. Eisenmann, 1998, Fig. 5;
Shockey, 1997).
Morphology of the Venosa-Loreto specimens
Specimen 86 - Mandibular symphysis (Pl.1, fig. 1- 3), referable to the species smaller in size, from a male, as shown by the presence of massive canines immediately behind
P,
with prominent anterior and posterior crest. The centrai incisors are absent but,GEOLOGICA ROMANA, 36: 275-287, 5 fig, l tav, l tab, Roma (2000-2002)
276 L. CALO!
judging by tbe sockets, Jl and P are almost on tbe same line. Tbe simpbysis is sbort and tbe muzzle is enlarged in its front, immediately before an evident simpbysis constriction. In tbe lateral view tbe incisors are relatively straigbtened but would form witb tbe superior ones an ogival profile. Putting tbe inter-inci- sive region on a borizontal piane, tbe occlusal surface of tbe incisors results almost parallel.
In tbe upper view tbe rostrum is almost piane in tbe area between incisive arcade and canines; bebind, cor- responding witb tbe constriction, it forms a narrow and deep gorge, vertically ending in tbe simpbysis, in correspondence witb tbe sub-rounded mental forami- na. Tbe inter-alveolar margin is straigbt.
Tbe I2 are relatively small, a little larger tban I1, judging by tbe sockets; tbe P are large. Tbe F are tri- angular and quite close to levelling; tbe P are levelled and tbe infundibulum is open inside. In a domestic fiorse tfie wear of tbe incisors would indicate an age of about 15 years.
Specimen 85 - Mandibular sympbysis (Pl.l, fig 4- 6) of a female, referable to tbe larger size species; tbe Jl are absent. Witb tbe same sympbysis constriction of the specimen 86, tbe lengtb of tbe simpbysis is consid- erably greater and tbus, in proportion, tbe anterior widening is more graduai. Tbe incisors form a round- ed arcade. Tbeir axis is less inclined upwards tban in tbe specimen 86; tbeir dimensions are more bomoge- neous, above all P is in proportion sborter. Tbe F are levelled, wbile tbe P bave preserved a small centrai enamel ring and bave infundibula opened lingually, as otber isolated specimens of P (Alberdi et al., 1988). In a domestic borse tbe wear of tbe incisors would indi- cate an age of about 10-12 years.
In tbe dorsal view tbe incisive region is more con- cave tban in tbe specimen 86 and tben tbe surface becomes deeply grooved and transversally concave.
Tbe mental foramen is not preserved, but it sbould open bebind tbe simpbysis, tbus being more posterior tban in tbe specimen 86. In tbe lateral view tbe upper margin rapidly descends forward towards tbe incisors.
Tbe deptb of tbe mandibular corpus bebind tbe incisors is very scarce, in tbe absolute sense lower tban in tbe specimen 86.
Specimen 80 - Body of tbe incisive hone, witb oval incisive foramen, supporting F and P left, refer- able for dimensions and arrangement of tbe incisive arcade to tbe bigger sized species. Tbe incisors are levelled and would give an ogival profile witb tbe lower incisors. Apparently tbe specimen was about 10 years old.
Morphologies in the main species of Plio-Pleistocene l) Hipparions (Fig. 1). Even if they are not included in this report, we briefly mention tbem to stress tbe ali-
mentary flexibility sbown during tbeir long bistory:
according to the morpbology of the mandibular rostrum, greatly varying from one species to anotber, forms from browsers to specialised grazers, witb a wide scale of intermediate typologies are recognisable (cf. e.g. Eisen- mann, 1998; Hulbert, 1988; MacFadden, 1984)
2) Stenonoid equids s.s.: E. stenonis and E. stehli- ni (Fig. 2).
Tbe earliest forms of Equus stenonis from Western Europe are cbaracterised by long muzzles (lengtb P2-
P) and incisors arranged to an arcb, even if there are differences between tbe various deposits: in the skulls of La Puebla, for example, tbe disposition of incisors is straigbter than in tbe skulls of Saint Vallier, Senèze and Cbilbac (cf. Boeuf, 1986; Eisenmann, 1980; Prat, 1980; Viret, 1954).
Even tbe jaw of Equus stenonis of tbe Olivola deposit (Azzaroli, 1965; De Giuli, 1972) (Fig. 2d, e) bas a very long sympbysis but tbe incisive region is large and tbe arrangement of tbe incisors is only sligbtly rounded. Tbe diastema is very long. Tbe incisor's axis forms witb tbe occlusal surface of tbe jugals a wider angle tban in E. stehlini. In tbese cbar- acters tbe specimen 86 of Venosa-Loreto is more sim- ilar to E. stehlini, tbe specimen 85 to E. stenonis. P is not mucb bigger tban P and F, tbat are relatively tbick in tbe vestibular-lingual sense. Tbe canines of males are not particularly big, less in proportion tban E.
stehlini.
E. stehlini bas a sbort sympbysis and a forwardly enlarged rostrum (Fig. 2g). Cbaracteristic for tbe species is the position of tbe P almost forming a right angle witb tbe F, wbicb are al~ost aligned witb tbe 11, tbus determining tbe square form of tbe mandibular rostrum, similarly to tbe square form of tbe intermax- illary rostrum (cf. Azzaroli, 1965, Pl.3, fig. 2a). Tbe incisors are tbinner in tbe vestibulo-lingual sense tban in E. stenonis from Olivola, tbe canines of males are very big; tbey are situated immediately behind tbe incisors. Tbe diastema is sborter tban in E. stenonis from Olivola. Tbe upper incisors descend almost straigbtly as in caballoid borses. Form and dimensions of tbe incisive arcade are similar to tbose of E. steno- nis mygdoniensis (Koufos, 1992) (Fig. 2b), but tbe lengtb of metapodials is clearly smaller (cf. Privat Defaus, 1986).
Tbe incisive arcade of tbe specimens of E. stenon- is from Olivola is decidedly less curved tban in tbe specimen 80 of Venosa-Loreto. Furtbermore tbere is a clearer difference in dimensions between 12 and P and tbe two rigbt and left P are subparallel, wbile tbey are sligbtly diverging in tbe specimen 80.
3) Stenonoid equids s.I.: Equus altidens and Equus ex gr. E.bressanus-E. siissenbornensis (Fig. 3a-c)
Tbe possibility of a comparison witb specimens referred to tbe two examined species or to similar
THE TWO EQUIDS OF THE MIDDLE PLEISTOCENE OF THE S!TE VENOSA-LORETO (SOUTHERN ITALY) 277
Fig. l - Lower incisor arrangement in hipparions from the Old and New W or! d
a) Megahippus mattewi, browser, from Nebraska; b) Pseudhipparion skinneri, grazer, from Nebraska; c) Calippus regulus, specialised grazer, from Texas (from MacFadden, 1992, redrawn); d) and d') Nannippus peninsulatus, spe- cialised grazer, from Florida (from MacFadden, 1984, redrawn); e) Hippa- rion afarense, browser, from Hadar, Etiopia; f) Hipparion sp., grazer, from Melka Kunturé, Etiopia; g) Hipparion cf. cornelianum , specialised grazer, from Olduvai, Bed II, Tanzania (from Eisenmann, 1976, redrawn). 7110 natu- ra! size.
-Arcate incisive inferiori in ipparionini del Nuovo e del Vecchio Mondo.
a) Megahippus mattewi, brucatore, dal Nebraska; b) Pseudhipparion skinneri, pascolatore, dal Nebraska; c) Calippus regulus, pascolatore specializzato, dal Texas (da MacFadden, 1992, ridisegna- to); d) e d') Nannippus peninsulatus, pascolatore specializzato, dalla Florida (da MacFadden, 1984, ridisegnato); e) Hipparion afarense, brucatore, da Hadar, Etiopia; f) Hipparion sp., pasco- latore, da Melka Kunturé, Etiopia; g) Hipparion cf. cornelianum , pascolato- re specializzato, da Olduvai, Bed II, Tanzania (da Eisenmann, 1976, ridise- gnati). 7/10 della grandezza naturale.
forms is limited because of the scarce findings and/or adeguate illustrations.
The Equus altidens specimens from Venta Micena (Guerrero-Alba & Palmquist, 1997, Fig. 4) have a very short symphysis, a marked constriction, an incisive region rapidly enlarged towards the incisors. In lateral view the specimen VM-3665 (Fig. 4,3), has the profile of the inter-alveolar margin and of the lower symph- ysis' margin similar to the specimen 86 from Venosa- Loreto. In the specimen VM-3654 (Fig. 4,1) the I' and F are aligned, the P are larger than the other incisors and disposed obliquely backwards and extemally thus further widening the front of the rostrum (Fig. 3a).
c b
~
d'g
In the two almost complete jaws of Selvella (De Giuli, 1987) the simphysis and the inter-alveolar mar- gin seem to be longer than in the great part of speci- mens from Venta Micena, while the specimen VM- 3653 (Guerrero-Alba & Palmquist, 1997, Fig.3, 5) would seem the most similar in the proportions. The male specimen with less wom teeth, IGF 14312, from Selvella has P and F almost aligned and smaller than P, which are also slightly thick and disposed oblique- ly backwards and extemally. The canines are massive (Fig. 3b).
Arrangement and proportion of the upper incisors (De Giuli, 1987, P1.14, fig.7) are analogous to those of
278 L. CALO/
a
the lower ones. The straight arrangement of the upper incisors is different from the arched arrangement in the specimen 80 of Venosa-Loreto, thus making likely a reference to Equus ex gr. E.bressanus-E.siissenbor- nensis, by elimination.
The only jaw example known to the author refer- able to Equus ex gr. E. bressanus-E. siissenbornensis
Fig. 2 - Lower incisor arrangement in stenonoid equids.
a) Equus stenonis vireti, Saint Vallier, o id male; b) Equus stenonis senezensis, Senèze, female n°374; c) Equus steno- nis senezensis, Senèze, female Sel855 (from Prat, 1980, redrawn); d) Equus stenonis olivolanus, Olivola, male IGFI2733; e) E. stenonis olivolanus, Olivola, female IGFII024 (from De Giuli, 1972, redrawns); f) Equus steno- nis stenonis, Terranova, male IGF560;
g) Equus stehlini, Upper Valdarno, male IGFIII60 (from Azzaroli, 1965, redrawn); h) Equus stenonis mygdo- niensis, Gerakarou-1, male GER-32 (from Koufos, 1992, redrawn). 7110 natura! size.
-Arcate incisive inferiori in equidi ste- noniani.
a) Equus stenonis vireti, Saint Vallier, maschio senile; b) Equus stenonis sene- zensis, Senèze, femmina n°374; c) Equus stenonis senezensis, Senèze, femmina Se1855 (da Prat, 1980, ridise- gnati); d) Equus stenonis olivolanus, Olivola, maschio IGF12733; e) E.ste- nonis olivolanus, Olivola, femmina IGFI1024 (da De Giuli, 1972, ridise- gnati); f) Equus stenonis stenonis, din- torni di Terranova, maschio IGF560; g) Equus stehlini, Valdarno Superiore, maschio IGF11160 (da Azzaro1i, 1965, ridisegnati); h) Equus stenonis mygdo- niensis, Gerakarou-1, maschio GER-32 (da Koufos, 1992, ridisegnato ). 7 Il O della grandezza naturale.
(cf. Calai, 1995) consists in the rostrum part of Bor- gonuovo (Azzaroli, 1984, Pl. 30, fig. la-b) (Fig. 3c).
The difference in dimensions between P and F is greater than in the jaws of Venta Micena and Selvella.
The disposition of I' and F, less aligned than in these specimens, and of 13, less open, determine a more curved arrangement of the incisive arcade.
THE TWO EQUIDS OF THE MIDDLE PLE/STOCENE OF THE SITE VENOSA-LORETO (SOUTHERN ITALY) 279 4) Caballoids (Fig. 3d-g) Even in this group, which
appeared relatively recently, we can observe different specialisations. For example E. ferus mosbachensis (Fig. 3d) and similar Middle Pleistocene forms have a long simphysis and a relatively curved incisive arcade, while in E. ferus germanicus (Fig. 3e) and E.ferus gal- licus (Fig. 3f) and similar Upper Pleistocene forms the symphysis are decidedly shorter and the incisive arches larger because of the aligned disposition of P and F an d for the inclination backwards and externally of 13 (cf.
Reichenau, 1915; Mourer-Chauviré, 1980; Prat, 1980).
The horse of San Sidero 6 (specimen IGF 16328) (Puglia, Southern ltaly, cf. De Giuli, 1983; Eisenmann
Fig. 3 - Lower incisor arrangement in stenonoid equids s.I. and in caballoids.
a) Equus altidens, Venta Micena, fema- le VM-3575 (from Guerrero-Alba &
Palmqvist, 1998); b) Equus altidens, Selvella, male IGF14312 (from De Giuli, 1987, redrawn); c) Equus ex gr.
E. bressanus-E. siissenbornensis, Bor- gonuovo, male IGF1010 (from Azzaro- li, 1984, redrawn); d) Equus ferus mosbachensis, Mosbach, male; e) Equus ferus germanicus, Wildscheuer von Steeden, male (from Reichenau, 1915, redrawn); f) Equus ferus galli- cus, Solutré, female (from Prat, 1980, redrawn); g) Equus ferus ssp., S.Sidero, male IGF16328 (from Azzaroli, 1999, redrawn); h) Equus hydruntinus, Grotta Romanelli, male (from Stehlin & Gra- ziosi, 1935, redrawn); i) Equus zebra, from zoo; l) Equus burchelli, Katanga;
m) Equus grevyi, Somalia (from Eisen- mann, 1979, redrawn). 6/10 natura!
size.
- Arcate incisive inferiori in stenoniani s. l. e in caballini.
a) Equus altidens, Venta Micena, fem- mina VM-3575 (da Guerrero-Alba &
Palmqvist, 1998); b) Equus altidens, Selvella, maschio IGF14312 (da De Giuli, 1987, ridisegnato); c) Equus ex gr. E. bressanus-E. siissenbornensis, Borgonuovo, maschio IGF1010 (da Azzaroli, 1984, ridisegnato ); d) Equus ferus mosbachensis, Mosbach, maschio; e) Equus ferus germanicus, Wildscheuer von Steeden, maschio (da Reichenau, 1915, ridisegnati); f) Equus ferus gallicus, Solutré, femmina (da Prat, 1980, ridi segnato); g) Equus ferus ssp., S.Sidero, maschio IGF16328 (da Azzaroli, 1999, ridisegnato); h) Equus hydruntinus, grotta Romanelli, maschio (da Stehlin & Graziosi, 1935, ridise- gnato); i) Equus zebra, da zoo; l) Equus burchelli, Katanga; m) Equus grevyi, Somalia (da Eisenmann, 1979, ridise- gnati). 6/10 della grandezza naturale.
et al., 1985; Azzaroli, 1999) (Fig. 3g), probably of Upper Pleistocene age, has a large incisive region, short symphysis and diastema, aligned incisors. The whole of these characters would suggest an alimentary specialisation (grazer?).
5) Equus hydruntinus (Fig. 3h). The jaw (cf.
Stehlin & Graziosi, 1935, Pl.6, figs. 3-4) has a short simphysis, a relatively enlarged incisive region, incisors not very different in dimensions and disposed to form an arch. In the specimen 86 of Venosa-Loreto the wider arrangement of the incisors determines a greater widening of the front part of the muzzle.
280 L. CALO/
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60
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Fig. 4 - Width of constriction plotted against symphyseal lenght of the jaw, in some stenonoid equids. The upper regression line refers to grazer equids, the lower one to browser tapirs (from Eisenmann, 1998).
,~~~--~--~~--~--r---~--,-12~
Following symbols are used: l) Equus stenonis vireti; 2) E. stenonis guthi; 3) E. stenonis senezensis; 4) E. stenonis olivolanus; 5) Equus stehlini; 6) Equus altidens from Venosa-Loreto: specimen 86; 7) Equus altidens from Selvella; 8) Equus ex gr. E. bressanus-E. siissen- bornensis from Venosa-Loreto: speci- men 85; 9) Equus ex gr. E. bressanus- E. siissenbornensis from Borgonuovo;
IO) Equus hydruntinus from Grotta Romanelli; (from Prat, 1980; Boeuf, 1986; Eisenmann,l976; own data). For comparison: Il) Hipparion sp., from Melka Kunturé, Etiopia and 12) Hippa·
rion cf. cornelianum from Olduvai, Bed Il, Tanzania (from Eisenmann, 1976).
50 60 70 80 90 100 110
- Diagramma di dispersione della lar-
l
(mm) ghezza della costrizione sulla lunghez- za della sinfisi mandibolare, di alcuni equidi stenoniani s.s. e s. l. Le due rette di regressione si riferiscono, la superiore ad equidi pascolatori (cavalli ed emioni), l'inferiore a tapiri, come rap- presentanti di animali brucatori, e sono state riprese da Eisenmann (1998).Sono stati usati i seguenti simboli: l) Equus stenonis vireti; 2) E. stenonis guthi; 3) E. stenonis senezensis; 4) E. stenonis olivolanus; 5) Equus stehli- ni; 6) Equus altidens di Venosa-Loreto: es. 86; 7) Equus altidens di Selvella; 8) Equus ex gr. E. bressanus-E. siissenbornensis di Venosa-Loreto: es. 85;
9) Equus ex gr. E. bressanus-E. siissenbornensis di Borgonuovo; IO) Equus hydruntinus di Grotta Romanelli; (dati da Prat, 1980; Boeuf, 1986; Eisen- mann,l976; dati personali). Per comparazione sono stati aggiunti i valori di due ipparion: Il) Hipparion sp., da Melka Kunturé, Etiopia e 12) Hippa- rion cf. cornelianum da Olduvai, Bed II, Tanzania (da Eisenmann, 1976).
Discussi o n
The distribution of food resources in present ungu- lates occurs on different levels. At least three of these levels have been recognised: primary choice of food, preference for a certain habitat, preference for the height of the food (Spencer, 1985). The existence of different behaviours in the choice of food is also reflected in the morphological characters of skull and jaw. These correlations have been amply studied in bovids, where in generai it is possible to distinguish grazers (with a large muzzle) from browsers (with a narrow muzzle) from bovids with an intermediate di et (Janis, 1990; Marean, 1992; Schuette et al., 1998;
So1ounias & Moelleken, 1993; Spencer, 1995; etc.), according to the muzzle morphology. Similar studies have been carried out about other taxonomic cate- gories: for example camels (Dompierre & Churcher, 1996), cervids (Calai & Palombo, 1995), giraffes (Solounias et al., 1988) and notoungulates (Shockey, 1997). It has also been attempted to quantify differ- ences in habits toward the three distribution levels of the niche (Gwynne & Beli, 1968; Spencer, 1995;
Schuette et al., 1998).
The muzzle form has been studied also in equids (e.g. Owen-Smith, 1985; Janis & Ehrhardt, 1988;
MacFadden 1992; Forstén, 1999). Generally a U-
shaped incisor arrangement indicates a browsing atti- tude, a rounded shape a grazing attitude, a linear shape may be a sign of a specialised graze. Mixed feeders have muzzles morphologies intermediate in form between the grazing and browsing species (Fig. 1).
Even the relative dimensions of incisors can inform about the favourite kind of food: browsers have a larg- er centrai incisor, grazers tend to have equal or sube- qual sized incisors. Thin incisors with a reduced sec- tion in the vestibulo-lingual sense, with an increased cutting function, are generally present in grazers; a spathulate form, an inclination forward, a reduction in 13 c an indicate a specialised cropping mechanism (cf.
Nannippus peninsulatus, MacFadden, 1984; Hippari- on afarense, Eisenmann, 1976) (Fig. ld-e).
Recently Eisenmann (1998) tried to quantify the muzzle proportions in fossil equids and hipparions basing on the analysis of two variants (the length of the mandibular symphysis and its rninimal width) in present species as tapirs (that are considered browsers) and equids (as an example of typical graz- ers). According to this analysis zebras are placed between the line of browsers and the line of grazers (Eisenmann, 1998) (Fig. 5). However, judging by the disposition of the upper incisors, the Grévy's zebra, that has J1 and F a1most aligned and P forrning a right angle, would be a "specialised grazer", while the
THE TWO EQUIDS OF THE MIDDLE PLEISTOCENE OF THE SITE VENOSA-LORETO (SOUTHERN ITALY) 281
Burchell's zebra, or lowland zebra, with less thick incisors and aligned P and F, would represent a typi- cal grazing species (cf. Eisenmann, 1979, 1980, 1998;
Azzaroli & Stanyon, 1991). This zebra lives in grass- covered seasonally damp territories (Marean, 1992) an d is considered by Grunow in Eisenmann ( 1980) and Gwynne and Bell (1968) a typical grazer. In the damp season Burchell's zebras are 100% grazers, in the dry season they introduce O, l% of dicoty ledo n vegetables. The monocoty1edon grass parts intro- duced, mainly consist in the stem (that is the highest part of the plant) and the sheath and only by 0,2% in the leaf. Thus the diet is rich in fibre with high con- tents in cellulose (Bell, 1971; Gwynne & Bell, 1968).
On the opposite, the gnu (in the examined case the sub-species Connochetes taurinus albojubatus), a bovid grazer that lives together with the Burchell's zebra in the Serengeti ecosystem, lives mainly on the leaves to the same monocotyledon grasses (in the damp season) or on the sheath (in the dry season), thus introducing more proteins and carbohydrates and less cellulose than the Burchell's zebra (Gwynne &
Bell, 1968). The relationships between these two species are not competitive but facilitative and favour
60
50
-
EE 40
-
~30
50 60 70 80 90 L
(mm)100
a determined grazing sequence and a selection of the vegetation (first the zebra, them the gnu, finally the Thomson's gazelle, with a mixed diet: up to 40% of dicotyledon grasses).
In the specimen 86 of Venosa-Loreto the incisors, not so big with respect to molars and not particularly thick in the vestibulo-lingual sense, the aligned P and F and the P slightly shifted backwards with respect to the F indicate a marked grinding mechanism of oppos- ing incisors. The width of the incisive region and the enlarged and deep form of the rostrum allow to swal- low with every bite a good quantity of monocotyledon grasses, because their spreading is generally homoge- neous. As for the ratio between symphisial width and length (measures A and B in Eisenmann, 1998) the specimen 86 lies above the line of grazers (Fig. 4), left from Hipparion houfenense (cf. Eisenmann, 1998, Fig.
4, l), thus suggesting an attitude to a specialised graze.
On the other side, the rostral region is very short and this morphology would seem to contradict the attitude to graze, generally associated to a long muzzle. How- ever, such a conformation could suggest a specialised graze. In fact it reminds some species of the genus Calippus of Clarendonian and Lower Hemphillian
110
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11
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12
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156 16®
Fig. 5 - Width of constriction plotted against symphyseal lenght of the jaw, in fossi! and recent caballoid horses and zebras. The upper regression line refers to grazer equids, the lower one to browser tapirs (from Eisenmann, 1998). Following symbols are used: l) Equus ferus mosbachensis from Mos- bach; 2) E. ferus palustris from Lune!
Vie!; 3) Equus ferus germanicus from Wildscheuer von Steeden; 4) Equus ferus cf. germanicus from Combe Grenal and 5) from Les Rivaux; 6) Equus ferus gallicus from Solutré; 7) E.
ferus cf. gallicus from Jaurens and 8) from S. Germain-la-Rivière; 9) "Equus przewalskji"; 10) Grevy's zebra; 11) Hartmann's zebra; 12) Grant's zebra;
13) Chapmann's zebra; 14) Burchell's zebra (from Bonifay, 1980; Eisen- mann,1980; Gromova, 1949; Mourer- Chauviré, 1980; Prat, 1968, 1980;
Reichenau, 1915); 15) Equus altidens from Venosa-Loreto: specimen 86; 16) Equus ex gr. E. bressanus-E. siissenbor- nensis from Venosa-Loreto: specimen 85. Areas of present half-asses (=h-a), asses (=a) and zebras (=z) and of fossi!
horses from Mosbach, Achenheim, Pair-non-Pair and Jaurens (=h) drawn on data supplied by A. Forstén.
- Diagramma di dispersione della larghezza della costrizione sulla lunghezza della sinfisi mandibolare, di alcuni equidi caballini fossili, di caballini attuali e di zebre.Per le rette di regressione vedi fig.4. Sono stati usati i seguenti simboli: l) Equus ferus mosbachensis da Mosbach; 2) E.ferus palus- tris da Lune! Vie!; 3) Equus ferus germanicus da Wildscheuer von Steeden; 4) Equus ferus cf. germanicus da Combe Grenal e 5) da Les Rivaux; 6) Equus ferus gallicus da Solutré; 7) E. ferus cf. gallicus da Jaurens e da 8) S.Germain-la-Rivière; 9) "Equus przewalskji"; 10) zebra di Grevy; 11) zebra di Hartmann; 12) zebra di Grant; 13) zebra di Chapmann; 14) zebra di Burchell (dati da Bonifay, 1980; Eisenmann,1980; Gromova, 1949; Mourer- Chauviré, 1980; Prat, 1968, 1980; Reichenau, 1915); 15) Equus altidens di Venosa-Loreto: es. 86; 16) Equus ex gr. E. bressanus-E. siissenbornensis di Venosa-Loreto: es. 85. Aree di distriuzione di emioni (=h-a), asini (=a) e zebre (=z) attuali e di caballini fossili da Mosbach, Achenheim, Pair-non Pair, e Jaurens (=h) disegnate in base a dati fomiti da A. Forstén.
282 L. CALO!
Specimen 86 Specimen 85 Specimen 80
Symphysis
length 68.8 88.0 -
Width Iri3 62.0 70.0 -
Constriction
width 38.9 39.4 -
Lenght I2 11.2 9.6 -
Wiòth 12 11.9 11.2 -
Lenght I3 9.0 10.6 -
Width I3 12.9 15.5 -
Lenght F - - 10.5
Width I2 - - 17.5
Lenght P - - -
Width P - - 19.0
Table l - Measurements in mm of the Venosa-Loreto specimens: speci- men 86 = incisive regions of Equus altidens; specimen 85 = incisive regions of Equus ex gr. E. bressanus-E. siissenbornensis; specimen 80
= body of the incisive bone of Equus ex gr. E. bressanus-E. siissenbor- nensis (incisors' width: in mesio-distal sense; incisors' lenght: in vesti- bular-lingual sense).
Tabella l - Misure in mm degli esemplari di Venosa-Loreto: es. 86 regione incisiva di Equus altidens; es. 85 regione incisiva di Equus ex gr. E. bressanus-E. siissenbornensis; es. 80 corpo dell'osso incisivo di Equus ex gr. E. bressanus-E. siissenbornensis.
(about 12-6 m.a.) (Hulbert, 1988) of the Great Plains, Texas and Florida, in which characters as the "align- ment of the incisors" and "shortness and width of the rostrum" are even more stressed (Fig. le). In faunas nearer to ours the disposition of incisors and a short- ness of the simphysis analogously to the specimen 86 are present in the equids of Selvella and Venta Micena (Fig. 3a, b). Also considering the structural and physi- ological differences between bovids and equids, we must not forget that a large and flat premaxillary bone with a short diastema is characteristic for the gnu (Connochaetes taurinus), a very specialised grazer eating short and damp grasses and scarcely tolerating high and dry grasses (Marean, 1992). The particular conformation of the short and large rostrum of the specimen 86 could be explained with the presence of short and fresh grasses, at least for a part of the year, near the Venosa-Loreto deposi t. The hypsodonty of the molars (Alberdi et al., 1988) would sustain this
hypothesis because short grasses contain a higher quantity of silica compared to the high ones. The I3 would seem more wom than F and this could be a sign of specialisation for a lateral food grasping, at least in some periods of the year; at least i t would indicate that the whole incisive arcade was in contact with the veg- etables. However, dealing with a single specimen the caution in interpretation is required.
The great thickness of the mandibular body of the jaw ( even if i t cannot be measured canonically between M2 and M3 ; Spencer, 1999), more frequent in grazers, could be considered a further proof for a graz- ing trend of the smaller sized equid from Venosa-Lore- to. Strong mandibular body also characterises the Selvella equid.
The very strong canines indicate a marked sec- ondary sexual character and a probable differentiation in the composition of herds (young stallions on one side, mothers with offspring on the other).
The hypsodonty in molars suggests that this species lived in an open environment.
In the specimen 85 the big incisors disposed to form an arch with a wide ray would suggest an attitude to graze without a marked specialisation. The P are less wom than F. to indicate that in this species only the centrai incisors had the principal function of cut- ting. As for the ratio between symphisyal constriction and length, the specimen 85 lies under the line of graz- ers (Fig. 4).
The thickness of the mandibular body is smaller than in the specimen 86. The more complex enamel in molars favours a smaller wear of the tooth and would indicate an attitude to graze (Hulbert, 1988) and a diet based on coriaceous hard vegetables, as for example the stems of monocotyledon grasses. However, the opinions about the interpretation of this character are not in agreement at all, and in some cases opposing (cf. Gromova, 1949; Eisenmann, 1985; Forsten, 1981;
Fortelius, 1985).
The hypsodonty of jugals (Alberdi et al., 1988) would suggest a predominant living in an open envi- ronment.
Conclusions
The two equids of Venosa-Loreto clearly have dif- ferent sizes and a weight that can be calculated at about 300 kg for E. altidens and about 600 kg for Equus ex gr. E. bressanus-E. sussenbornensis (Damuth & MacFadden, 1990; Alberdi et al., 1995, 1998). The differences in size and weight by them- selves would suffice to consider the two species eco- logically distinct. The differences in the body struc- ture, particularly in the limbs (cf. Calai, 1995), strengthen this hypothesis. The analysis of the scarce cranial remains of the to equids of Venosa-Loreto pro- vided further paleo-ecological and alimentary indica-
THE TWO EQUIDS OF THE MIDDLE PLEISTOCENE OF THE SITE VENOSA-LORETO (SOUTHERN ITALY) 283 tions, particularly about the food the two ungulates
preferred. According to the slendemess of the metapo- dials and of the first phalanxes and the hypsodonty of the molars we can suppose that the smaller sized species, Equus aff. E. altidens, preferred an open envi- ronment; the short and large muzzle would suggest a specialised graze with short and fresh grasses, above all leaves and sprouts. Even the body structure of the species bigger in size, Equus ex gr. E. bressanus-E.
sussenbornensis, would suggest the preference for an open environment; the relatively wide but elongated muzzle suggests a graze preferring short monocotyle- don grasses, above all stems and seeds. In periods of diminished food availability (dry seasons?), the diet of the two species probably further diverged, both for the typology of the parts of grass introduced and because the bigger species included in its diet a certain amount of dicotyledon vegetables.
On the basis of the bivariate analysis of present half-asses, asses and zebras and of fossil horses from Mosbach, Achenheim, Pair-nan-Pair and Jaurens (data supplied by A. Forstén), the various groups of equids seem to have distinct distribution areas (fig. 5). It seems impossible do delimit clearly the different gen- era and/or species of zebras. The two specimes of Venosa-Loreto fall respectively in the area of half- asses (sp. 86) and of zebras (sp. 85), so confirming divergent adaptations.
The presence of a species with an expanded muz- zle and aligned incisors represents a novelty within the Upper Pliocene-Lower Pleistocene equids. The most ancient stenonoid forms in Western Europe (La Puebla, Saint Vallier, Chilhac, Senèze) have long and narrow rostra, nearer, except for a very old specimen of Saint Vallier, to the line of browsers (Fig. 4), even if it is not much likely that they were pure browsers.
In following phases, corresponding to the Faunistic Units of Olivola and Tasso, it appeared populations with a decidedly wider rostrum (E. stenonis olivolanus, Caloi, 1995) or with an aligned disposi- tion of the four centrai incisors (E. stenonis myg- doniensis, Koufos, 1997; E. stehlini, Azzaroli, 1965) (Fig. 2d-h). The next appearance in Western Europe of Equus altidens, with an expanded muzzle and almost aligned incisors, testifies the strengthening of the signals indicating an environmental change. This species was also present in the Galerian together with E. sussenbornensis.
The character "alignment of the incisors" is not very frequent in equids. Among the hipparions of North America it appears within the genus Calippus (Fig. le) with the ungulate-rich savannah-mosaic Clarendonian faunas (c. 11.5-9 m.a.) an d i t expanded particularly with Hemphillian faunas (c.9-7 m.a.;
A gusti et al., 1997), with the expansion of grass-cov- ered open spaces besides a considerable decrease of biodiversity (Hulbert, 1988). The genus Calippus dis- appeared, with many other taxa, about 6 m.a. ago, in a
period in which ecosystems dominated by vegetables fixing carbon through the Calvin cycle (so-called C3
plants) were replaced by ecosystems with vegetables using the C4 photosynthesis (so-called C4 plants). This transition was a global event (Northern America, Eura- sia and Africa) and seemed to be caused by a C02
deficit in the atmosphere (Barry, 1995; Bonnefille, 1995; Cerling, 1992; Cerling et al., 1993; de Menocal
& Bloemendal, 1995; Yang Wang et al., 1994; Vrba,
1995). The character "expanded muzzle" also appeared in hipparions in Europe and Africa, some- times associated with particular adaptations, as shown in some cases of reduction of the P (cf. Eisenmann, 1976) (Fig. lg). It is likely that during the Upper Vil- lafranchian in Western Europe, the climatic condi- tions, with a glacial-interglacial cyclicity of 41 ky and frequent dryness episodes leading to the expansion of open spaces (perhaps in concurrence with the expan- sion of C4 plants in Africa in the Upper Bed I deposits of the Olduvai Gorge, about 1.8 and 1.2 m.a. ago, Cer- ling, 1992) and the increased biodiversity in ungulates, favoured the development of short grasses and the reappearing of the character "expanded muzzle and alignment of the incisors". This ensemble of charac- ters reappeared, even more markedly, in Upper Pleis- tocene caballoids. The so-called caballoid 1ine seems to appear in Western Europe in specimens with a long and narrow muzzle, that prevailed for the whole Mid- dle Pleistocene. During the Upper Pleistocene, perhaps in concurrence with the development of vaste grass- lands more or less dry in the glacial phases, horses, particularly in Centrai-Western Europe, were present with specimens with expanded muzzles and almost aligned incisors (E. ferus germanicus and similar forms; Equus ex gr. E. ferus gallicus-E. ferus arce lini).
These features appeared also in the Mediterranean environment, as in the Puglie (Southern Italy) with the above mentioned horse of S. Sidero, while in the Iber- ian Peninsula E. ferus antunesi (Cardoso & Eisen- mann, 1989) had a curved upper incisive arcade and a relatively long diastema, thus probably testifying dif- ferent paleoenvironmental and climatic conditions.
The presence of musks and twigs in the stomach of deep-frozen horses (Ann Forstén, pers. comm.) is probably linked to the extreme climatic conditions characterising the northern territories in the last Glacial compared with southem territories, particular- ly the Mediterranean environment (Alberdi et al., 1998). Even in order to better evaluate these probable geographica1 differences in paleodiets, we would wish a compared analysis in detail of the functional mor- phology of more complete skulls and jaws, besides studies about microwear and chemical analysis of the tooth enamel.
Acknowledgments. We sincerely thank the referees Véra Eisenmann and Ann Forstén for the important ad vice and suggestions and Ann Forstén al so for the kind communication of some present equid's measures. M.
Salvati an d U. Nicosia are also aknowledged for their technical help.
284 L. CALO!
SOMMARIO
Vengono prese in esame due porzioni mandibolari provenienti dai livelli fossiliferi indicati come "sabbie rossastre" = livello A (Chiappel- la, 1964; Segre, 1978). Da questi livelli proviene la maggior parte dei resti di due equidi, riferiti da Alberdi et al. (1988) ad Equus altidens ed Equus aff. siissenbornensis. I due reperti in esame, costituiti da due regioni incisive, anche se ampiamente incompleti, sono significativi ai fini di una ricostruzione degli adattamenti funzionali. Le differenti dimensioni corporee sarebbero sufficienti di per sé a far considerare le
due specie ecologicamente distinte. La diversa conformazione della regione incisiva e della sinfisi rende ancora più evidente che le due spe- cie occupavano ciascuna una nicchia ecologica particolare e distinta e sfruttavano diverse risorse alimentari. Si mette in evidenza il significa- to della comparsa tra gli equidi del Plio-Pleistocene di forme con musi corti e larghi, sia nella "linea stenoniana" sia nella "linea caballina".
Accettato per la stampa il 30 marzo 2001
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Lucia Caloi, Dipartimento di Scienze della Terra, Università degli Studi "La Sapienza", P.le A. Moro, 5, 00185 Rome, Italy.
e-mail: lucia.caloi @uniromal.it
286 L. CALO/
PLATE l
1-3) - Lower jaw of Equus altidens (specimen 86) from Venosa-Loreto, l) dorsal view, 2) ventral view, 3) lateral view; about 112 nat. size.
4-6) -lower jaw of Equus ex gr. E.bressanus-E.siissenbornensis (specimen 85) from Venosa-Loreto, 4) dorsal view, 5) ventral view, 6) lateral view; about 112 nat. size.
TAVOLA l
1-3)- Mandibola di Equus altidens (es. 86) da Venosa-Loreto, nelle norme superiore (1), inferiore (2), laterale (3);
112 gr. nat.
4-6) mandibola di Equus ex gr. E.bressanus-E.siissenbornensis (es. 85). da Venosa-Loreto, nelle norme superiore (1), inferiore (2), laterale (3); circa 112 gr. nat.
THE TWO EQUIDS OF THE MIDDLE PLEISTOCENE OF THE SITE VENOSA-LORETO (SOUTHERN JTALY) 287
l 4
2 5
