the contraction mechanism may be arigid attachment of the globular headof the myosin molecule to the actinfilament and an active change in theangle of attachment associated with thesplitting of adenosine triphosphate. Theavailability of purified preparations of"head" subunits now opens up the prob-lem to detailed attack.

References and Notes

1. J. Hanson and H. E. Huxley, Nature 172,530 (1953).

2. H. E. Huxley and J. Hanson, ibid. 173, 973(1954); A. F. Huxley and R. Niedergerke,ibid., p. 971.

3. J. Hanson and H. E. Huxley, Symp. Soc.Exp. Biol. 9, 228 (1955); A. F. Huxley,Progr. Bfophys. Biophys. Chem. 7(1956),255 (1957); H. E. Huxley, in ProceedingsAlberta Muscle Symposium (Pergamon, Ox-ford, 1965), p. 3; , Harvey LecturesSer. 60(1964-65), 85 (1966).

4. H. E. Huxley, J. Biophys. Biochem. Cytol. 3,631 (1957).

5. , in The Cell, J. Brachet and A. E.Mirsky, Eds. (Academic Press, New York,1960), vol. 4, p. 365.

6. , Biochim. Biophys. Acta 12, 387(1953).

7. A. G. Szent-Gyorgyi, Arch. Biochem. Bio-phys. 42, 305 (1953).

8. D. F. Cain, A. A. Infante, R. E. Davies,Nature 196, 214 (1962).

9. W. 0. Fenn, J. Physiol. London 58, 175(1923); ibid., p. 373.

10. H. E. Huxley, unpublished manuscript.11. , J. Mol. Biol. 7, 281 (1963).12. R. V. Rice, Biochim. Biophys. Acta 52, 602

(1961).

13. W. F. H. M. Mommaerts and I. Green, J.Bfol. Chem. 208, 833 (1954).

14. W. Hasselbach, Z. Naturforsch. 7b, 163(1952).

15. S. V. Perry, Physlol. Rev. 36, 1 (1956).16. S. Ebashi, Nature 200, 1010 (1963); -

and F. Ebashi, J. Bfochem. Tokyo 53, 604(1964).

17. S. V. Perry and T. C. Grey, Biochem. J. 64,SP (1956).

18. N. Azuma and S. Watanabe, J. Biol. Chem.240, 3847 (1965); , ibid., p. 3852; H.Mueller, Biochem. Z. 345, 300 (1966).

19. A. Weber, J. Biol. Chem. 234, 2764 (1959);and S. Winicur, ibid. 236, 3198 (1961);

A. Weber, R. Herz, I. Reiss, J. Gen. Physiol.46, 676 (1963); , Federation Proc. 23,896 (1964); , Proc. Roy. Soc. LondonSer. B 160, 489 (1964); T. Nagai, M. Maki-nose, W. Hasselbach, Biochim. Biophys. Acta43, 223 (1960); W. Hasselbach and M. Maki-nose, Biochem. Z. 333, 518 (1961); -Ibid. 339, 94 (1963); W. Hasselbach, Proc.Roy. Soc. London Ser. B 160, 501 (1964);S. Ebashi, J. Biochem. Tokyo 48, 150(1960); , ibid. 50, 236 (1961);and F. Ebashi, Nature 194, 378 (1962).

20. A. Weber and R. Herz, J. Biol. Chem. 238,599 (1963).

21. R. Niedergerke, J. Physlol. London 128, 12P(1955); K. R. Porter and G. E. Palade,J. Blophys. Biochem. Cytol. 3, 269 (1957);A. F. Huxley and R. E. Taylor, J. Physiol.London 144, 426 (1958); P. C. Caldwell andG. Walster, ibid. 169, 353 (1963); H. E.Huxley, Nature 202, 1067 (1964); R. J. Podol-sky and L. L. Constantin, Federation Proc.23, 933 (1964); S. Winegrad, J. Gen. Physiol.48, 997 (1965).

22. K. Bailey, Blochem. J. 43, 271 (1948).23. S. Ebashi and A. Kodama, J. Biochem.

Tokyo 58, 107 (1965); ibid. 59, 425 (1966).24. S. Ebashi, F. Ebashi, A. Kodama, ibid. 62,

137 (1967).25. H. E. Huxley and J. Hanson, Biochim. Bio-

phys. Acta 23, 229 (1957); S. V. Perry and

A. Corsi, Blochem. 1. 68, 5 (1958); 3. Han-son and J. Lowy, 3. Mol. Blol. 6, 46 (1963).

26. F. A. Pepe, J. CeU RIol. 28, 505 (1966).27. M. Endo, Y. Nonomura, T. Masakd, I.

Ohtsuki, S. Ebashi, J. Blochem. Tokyo 60,605 (1966).

28. S. Ebashl, In Proc. Intern. Congr. Physlol.23rd, Tokyo (965), p. 405; D. R. Kominzand K. Maruyama, 3. Bfochem. Tokyo 61,269 (1967).

29. A. M. Gordon, A. F. Huxley, P. 3. Julian,J. Physiol. London 184, 170 (1966).

30. S. Page and H. E. Huxley, 3. CeU Biol. 19,369 (1963).

31. H. E. Huxley, thesis, University of Cam-bridge (1952).

32. G. F. Elliott, J. Lowy, C. R. Worthington,J. Mol. Blol. 6, 295 (1963).

33. G. F. Elliott, J. Lowy, B. M. Millman, Ibid.25, 31 (1967).

34. E. Rome, ibid. 27, 591 (1967); ibid. 37, 331(1968).

35. G. F. Elliott, J. Theoret. Blol. 21, 71 (1968).36. - , Proc. Roy. Soc. London Ser. B 160,

467 (1964).37. H. E. Huxley and W. Brown, 3. Mol. Biol.

30, 383 (1967).38. S. Lowey, L. Goldstein, S. Luck, Biochem.

Z. 345, 248 (1966); S. Lowey, L. Goldstein,C. Cohen, S. Luck, J. Mol. Biol. 23, 287(1967).

39. S. Lowey, in Symposium on Fibrous Proteins,Australia, 1967 (Butterworths, London, 1968),p. 124.

40. F. A. Pepe, J. Mol. Biol. 27, 203 (1967).41. J. Hanson, Quart. Rev. Blophys. 1, 53 (1968)42. H. E. Huxley, J. Mol. Biol. 37, 507 (1968).43. E. Eisenberg, C. R. Zobel, C. Moos ko-

chemistry 7, 3186 (1968).44. M. K. Reedy, K. C. Holmes, R. T. Tregear,

Nature 207, 1276 (1965).45. J. W. S. Pringle, Progr. Biophys. 17,1 (1967).46. D. R. Kominz, E. R. Mitchell, T. Nihei, C.

M. Kay, Biochemistry 4, 2373 (1965); S.Lowey, H. S. Slayter, A. Weeds, H. Baker,J. Mol. Biol., in press.

-Elephants, which are among themost popular and decorative of ani-mals, stand as a witness of prehistory,having been a part of the environmentof our ancestors. The dinosaur was notcontemporary with early man, as manyfilms and stories insist, but the mam-moth was. Although prehistoric or ex-

The author is professor in the Departmentof Paleontology of the Universidad de Madrid,Spain, and dean of the Colegio Mayor NuestraSefiora de Africa, Madrid, Spain.

1366

tinct elephants are frequently referredto as mammoths, such a designationis not always correct. The true mam-moth is but one of many species ofextinct elephants; furthermore, it be-longs to one of a few genera, whichinclude four or five species that haveaffinities with the woolly elephant.These different genera and species aregrouped by zoologists into a family,Elephantidae. Because this family orig-inated by the beginning of the Pleisto-

cene period, elephants can be consid-ered contemporary with man.

Anthropologists and prehistorianshave often attempted to establish achronology of sites of fossil manthrough correlations based upon thespecies of elephant associated withthem (1), but the systematics of theElephantidae is quite confused. Thedocumented monograph of Osborn (2)established 10 genera and some 59species of elephants; to these Garutt(3) added two more genera. However,many taxonomists have recognizedonly one genus and no more than fiveor six valid species. In the museumcollections from most major sites thereare many samples with dubious iden-tifications and many intermediateforms labeled either with two namesor with a composite or new name. Ithas been assumed that many differentspecies have lived contemporaneouslyin a single area, as was the case forthe sample excavated in the railwaytrench of San Paolo, Italy, in the firstyears of this century. Explanations ofthe phylogeny of elephants have hadone feature in common: the patternsfor the phyletic trees have agreed withthe fashionable evolutionary theories

SCIENCE, VOL. 164

Evolutionary History of theElephant

A tentative phylogeny of Elephantidae based on

morphological and quantitative analysis is given.

Emiliano Aguirre

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of the particular period. Thus all thetrees are dichotomic and linear from1881 to 1888 (4), fairly dichotomicfrom 1888 to 1912 (5), and polyphy-letic until 1923 (6). After 1940 dicho-tomic (7) patterns are again found.A review of the evolutionary history

of the Proboscidea before the appear-ance of the elephants may help us tounderstand the significance of theevolving character in the latter. ForProboscidea since the Old Tertiaryperiod, two major characteristics havebeen defined: the anterior teeth aremissing except for one or two pairs oftusks; and there is an increasing num-ber of rows of cusps, with every newtransversal row appearing behind theother and elongating the molar teeth.

Trends in Late Tertiary and

Pleistocene Proboscideans

During the Middle Tertiary periodthe most important branch of Pro-boscidea, the Mastodontoidea, evolvedinto some differentiated groups or fam-ilies (8, 9). It is difficult to identifyfossil mastodonts by skeletal remains;on the other hand, fossil molars are

very plentiful, and these exhibit definitesequences of variations in the morpho-logical features of the molar crownwhich are important in the origin andevolution of elephants.

In a major division, the familyGomphotheriidae Cabrera, the maincusps are only slightly subdivided ornot subdivided and are round andbreastlike in shape; well-differentiatedcentral conules are detached from thewall of the rows of cusps and invadethe transversal valleys between them. Alongitudinal or median sulcus thatseparates the lingual cusps or cones ineach row or ridge from the labial onesis always conspicuous. TrilophodonFalconer, Tetralophodon Falconer, andthe American Cuvieronius Osborn arerepresentative genera of this family.A second group, the family Masto-

dontidae Girard, is characterized bymolar teeth with cusps (cones) sub-divided into conelets which are fusedtransversally into acute ridges; theseare thereby transformed into linearcrests, and the valleys between themare V-shaped and open. Only the prim-itive forms have regressive centralconules, which are missing in most ofthis family as is the median sulcus.

Some of the representatives of thisfamily are Mastodon Cuvier andTuricius Osborn.

In addition to morphological char-acteristics, we must also consider sev-eral measurable traits, which vary inthe mastodonts, as well as in the Pleis-tocene proboscideans, stegodonts, andelephants, in more or less the sameway, but with different "tempo"; thatis, there are some common biometricaltrends in the different evolutionarybranches of these animals. These traitsinclude the following characteristics.

1) Multiplication of the transversalridges of cusps, which is exceptionalamong other mammals and very pecu-liar to most proboscideans.

2) Increasing height of the ridges(hypsodonty), an allometric character-istic present in many other orders ofmammals, Which is expressed as aratio, relating the height to the lengthor width of the crown. The best for-mula for elephants seems to be

K = H/Awhere K is the index of hypsodonty,H is the height of a complete ridge,and A is the maximum width of themolar tooth.

-LStogodon CUf/;iNIS. iftSigWS

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1.4 1.8 2.2 2.6 3.0 3.4 3.8 4.2 4.6Thickness of enamel (mm)

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Fig. 1. Trend of diminishing thickness of enamel (in millimeters) in different species of elephants arranged in hypothetical phyleticgroups. Size of the sample is shown by a circle superimposed on the mean value; double lines indicate range of variation; singlelines show doubtful samples; solid circles represent single individuals or two of the same value. Wavy lines separate geologicalperiods. Different tempos in evaluation appear through stratigraphical divisions. The inset illustrates the basis of the method;e, enamel; c, cement; d, dentine.20 JUNE 1969 1367

Recent and £4,Pleistocene

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Fig. 2. Variation of the erupting angle A. The large degree of overlap of Elephastrogontherii with E, primigenius is the result of difficulties associated with the identifi-cation of the advanced forms of the former species, which may be considered as transi-tional forms or a pool of mutant populations. Sample size is indicated by the numberin parantheses.

3) Diminishing thickness of theenamel, which is very conspicuous andconstant. Almost every book and mu-seum exhibition is illustrated with aseries of outlines in which the thick-ness of the enamel in a mastodont, astegodont, a primitive elephant, and amammoth is represented with an ever-thinner black line. Nevertheless, thismeasurement is very seldom used inelephants because the variability of theenamel cover in the molars of pro-boscideans is great; the thickness variesnoticeably not only among teeth of in-dividuals in one species, but alsoamong the ridges of one molar andalong the section of a single ridge.Since statistics are the only valid rep-resentative figures for any magnitudein biological species, a mean of a ran-dom series of measurements in a molarwould give a valid representative fig-ure for the thickness of its enamel.This method (10) seems to be useful inpermitting one to differentiate betweenspecies within an evolutionary branchand to make comparisons among dif-ferent genera (Fig. 1).

4) Reduction of the total length ofthe grinding surface (the brevirostrinetrend), which occurs in many masto-donts, and, most remarkably, in mam-moths and their relatives. It is in har-mony with the multiplication of ridgesby their mesiodistal shortening. Thusthe ridges become plate and are namedridge-plates in elephants. In classifyingelephants the usual practice has beento use the number of plates or thelength of the molar. The ratio of the

1368

number of plates to the length of themolar is a better means of identifyingthe genera and species of elephantsthan either of these characteristics sep-arately. Many formulas have been pro-posed for- this particular ratio, and itwould be safer not to introduce a newformula. However, since evolutionarytrends follow measurable variations infunction, it is more effective to takeinto account the length of the grindingsurface (LF) at the time of the ani-mal's death and the number of platesactually working at that time (U). Inthis way data for two different speciesplotted in a scatter diagram show lessdispersion and slightly less overlapthan data plotted for the conventionaltotal length and total number of plates(which is almost always approximate).The ratio of the functional density ofthe plates (Q) is given by

Q = 100U/LF5) The brevirostrine trend and a

trend to longevity which are relatedto a general quality of mammal denti-tion exaggerated in Proboscidea:namely, a delay in tooth eruption atdefinite intervals, which permits recog-nition of an individual's age. In mam-mals generally, the whole potentialchewing surface works completely atan adult age, all teeth being presentbut in slightly different degrees ofwear. However, in Proboscidea theanterior teeth are completely worn be-fore eruption of. the posterior ones.Thus in mastodonts and stegodonts, butparticularly in elephants, every tooth

is worn out and its roots are ejectedbefore the one just posterior to it iseven half-worn and long before themore posterior tooth has erupted. Thuselephants have only one grinding toothin each half series at a given time (orhave the rear of one and the front ofthe next, which is equivalent). Such adelay in tooth eruption in mastodontsand elephants is favored by the inclina-tion of the erupting tooth relative tothe occlusal surface; this inclinationcan be measured as an angle betweenthe occluding surface and the base ofthe molar crown; it is progressive inevery species of both mastodonts andelephants (Fig. 2). With the increaseof this angle, a smaller length of thegrinding surface is exposed to wear; asthe functional length is reduced, thelife of each tooth is increased and,consequently, the longevity of the ani-mal is favored.

6) The width of the molars whichevolves differently in elephants; thistrait is for the most part constant inthe different species related to mam-moth (Mammuthus) whereas the mo-lars tend to be narrow in the lessbrevirostrine living elephants and inthe extinct Elephas antiquus Falconer(Fig. 3). The pattern of variation ofwidth in the different plates of a singleelephant molar is also peculiar for eachphyletic group.

Each group reflects different evolu-tionary trends. Since some trends areexpressed by a single measurement andsome by a ratio (simple and con-structed variable, respectively), we canseparate not only species but also evo-lutionary branches in scatter diagramsaccording to a pair of those ratios or

measurements more easily than we can

by simple measurements alone (Figs. 4and 5) (11).

Other trends in the evolution oftusks, skull, and the postcranial skele-ton are known in elephants as well as instegodonts and in Tertiary mastodonts.Most mastodonts have two pairs ofhighly specialized incisors, upper andlower. The upper incisors are developedas tusks, which vary in section, curva-

ture, and divergence in their basal por-tion (the portion included in premaxil-lar bones) and may or may not have a

longitudinal band of enamel. Thelower incisors in mastodonts have verypeculiar and different adaptations;these disappear in some advancedspecies such as Anancinae Hay. In allknown stegodonts and elephants thereare no lower tusks.

The skull of proboscideans variesSCIENCE, VOL. 164

widely anmong individuals of each spe-cies and in different species and genera;similar trends in evolution and differ-entiation occur in separate familiessuch as Elephantidae and Stego-iontidae. Such trends aid in the char-acterization of species and genera, ifthese are carefully established, becausethe sexuLal dimorphism and the onto-genetic and phenogenetic variations are'.cry wide. Long, low skulls are inter-preted as primitive. Shortening of thecranial base and the palatal bones: de-pressing, elevating, or expanding thefrontoparietal region; pneumatization;and development of the torus aretrends exhibited by stegodonts andelephants as specializations. Some ofthese cranial formations are apparentlycorrelated with the specializing curva-ture, size, and direction of the eruptingtusks. If this hypothesis is sound. someof the most striking features of ele-phant skulls could have a biomechanicalinterpretation and could be subject to alarge ontogenetic variation (Fig. 6).The skeleton of the proboscideans isnot as well known and cannot con-tribute to phylogenetic studies, becausethe specialized features are less remark-able and the fossil record is largelyinsufficient to permit estimation of therange of individual variation.

Origin of Elephants and

the Plio-Pleistocenc Boundary

During the Pliocene (the latter por-tion of the Tertiary period), severallines of mastodonts evolved in Africa,Asia, and Europe, among which werethe ancestors of elephants. AnancinaeHay, with the genera Anancits Ay-nmard, Penttalopliodon Falconer, andSycIonolophus Osborn (in addition tothe American representatives) are ad-vanced in the loss of lower tusks,somewhat advanced in hypsodonty, di-xersified in the multiplication of ridgesand the folding of the enamel in molarteeth, and advanced in the breviro-strine trend that delays the substitutionof molars. Species of these genera arecontemiiporaneous with most of theHippoarion faunas from Spain (Alfa-car, Teruel), the Danube Valley, andIndia., and they may have evolved laterin Africa. The anancoid molars havca particularly oblique disposition, halfot the cusps of each ridge overlappingthe other half; this pattern cannot de-velop into the morphology of elephantmolars.

Stegodon Falconer and Cautley is

20 JUNE 1969

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an Asiatic genus that appears in theEarly Pliocene. Its members are char-acterized by a short skull and shortmaxillar bones. The molars havecrowns with a high number of ridges;these are roof-shaped and consist oflittle conules that are regularly multi-plied; these ridges are separated bylarge V-shaped valleys. No longitudinalvalley is marked; no central conulesare visible. Elephant molars cannotderive from such teeth; thus the stego-donts are classified as a separate fam-ily, Stegodontidae Young and Hop-wood (not a superfamily). Their an-cestors reside in the Mastodontidae,where this peculiar morphology appearsin an advanced form.

Since the Early Pleistocene, ele-phants have possessed parallel andrapidly multiplying plates in their molarteeth and very hypsodont crowns; how-ever, over a long period, many havepreserved in their former ridge-platesthe longitudinal medial valley and akind of residual central conule, whichare typical features of the Gompho-theriidae Cabrera of the Miocene peri-od. These features are still present tosome extent in elephants and in severalforms referred to as Stegolophodon.

The elephant could have originatedwithin or derived from this group.

Stegolophodon Schlessinger is a ge-nus that appears in the Late MiddleMiocene in Spain (12) and in the Si-walik Hills of India. It cannot be thetransitional form between Mastodon-tidae in the narrow sense and Stegodon(2, 9), because Stegolophodon is lessadvanced in mastodontine trends. Ithas round or bunodontlike cusps andthe mark of a longitudinal valley andcentral conules at least in the anteriorridges. Rather it could represent abranch of Gomphotheriidae, havingcharacteristics convergent or isomor-phic with those of the Mastodontidae-Stegodontidae; on the other hand, sev-eral African forms of Stegolophodonapparently display true elephantinecharacteristics such as higher hypso-donty, thinner enamel, a rapidly in-creasing number of plates' and irregu-lar multiplication of median coneletson the transversal ridge-plates.

Stegolophodon sahabianus Petrocchihas central conules in the two anteriorvalleys, a remarkable hypsodonty (K =0.62), very thin enamel, and a densesubdivision of median conelets that re-sembles enamel folding. As with the

elephants, the anterior portion of /themolar teeth in this species, includinga few plates, is gomphotheriumlike inmorphology, whereas the rest is morecharacteristically elephantlike; the for-mer trait is inherited or conservative,and the latter is new and progressive.This Libyan species has lateral conulesthat are half-developed and that oc-clude the transversal valleys, a featurewhich appears later with character-istic frequency in Elephas atlanticusand E. mnaidriensis, and less frequent-ly in other species (13).

Stegotetrabelodon Petrocchi is an im-portant genus of Sahabi, also of thePliocene age, and is represented by twospecies (14). Although it is not worthyof designation as a new family, it mayrepresent a subfamily, Stegotetrabel-odontinae, because of its particularposition with reference to some evolu-tionary characteristics. This species hasfour tusks, the lower ones being regres-sive; the ridges of its molar teeth aregomphotheriumlike, with central con-ules in almost every transversal valleyand with a longitudinal sulcus; thereare eight ridges, which are hypsodont,with the conelets fusing near the top sothat in half-worn ridges the enamel

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Fig. 5. (Top) Dispersion of grinding teeth of elephant according to absolute wxidth (A) and mean thickness of the enamel (c)cover of plates. (Bottom) Dispersion of grinding teeth according to hypsodonty (K) and thickness of enamel. Symbols are thoseused in Fig. 4; a and b, two distinct forms of the Lan-ebaanri-e- site known only by little fragments.

20 JUNE 1969

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cover resembles the plates of primitiveelephants. The section of its lowertusks is elliptic. In Granada I recov-ered the skull -of a female Elephasmeridionalis with elliptic section inboth the proximal and distal portion ofits upper tusks (15). Arambourg re-ports finding an elliptic-sectioned, tuskamong a population of E. africanavusin North Africa (16).

In Langebaanweg, South Africa, twoforms have been collected, representedby very fragmentary remains. One formhas been designated Stegolophodon sp.(17). I shall refer to it as form a andto the other as h. Three fragments ofform a have ratios that fall within thedispersional area of Elephas subplani-frons and synonyms (18). These ratiosmight be slightly biased because theyrepresent estimates on a fragment; nosignificant error is made in comparinga fragment of what is probably a sec-ond adult molar with a third molar,for such characteristics as mean thick-

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ness of enamel and hypsodonty; how-ever, the functional densities of theplates (Q) in molar 2 (M2) and molar3 (M3) are somewhat different (10)(Figs. 1, 4, and 5). The second form,b, is represented by three minor frag-ments that appear to be relatively hyp-sodont, having a thin cover of enamelapparently similar to that of elephan-tine plates.

In South Asia there are several formsof Stegolophodon which are imperfect-ly known. As judged from the mor-phology of molar teeth, it is morereasonable to attribute the ancestry ofAsiatic elephants to these than to anyother proboscidean; however, there isno close evidence for such a descent.A preserved skull of a juvenile Stego-lophodon cautleyi Lydekker very muchresembles that of a juvenile Elephashysudricus in almost every detail; how-ever, the parietal bones are greatlyexpanded and elevated in the latter(19). Only minor changes are required

4

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Fig. 6. Front view of the skull of various elephants (not to scale). (A) 1, Elephasplanifrons; 2, E. meridionalis; 3, E. primigenius; 4, E. antiquus "germanicus"; 5, E. afri-canus; 6, E. platycephalus; 7, E. mnaidriensis; 8, E. hysudricus; 9, E. indicus "daun-tela"; 10, E. recki (26). Lateral view of elephant skulls showing individual and sexvariation within a phylum. (B) Elephas primigenius (1, male, 2, female); 3, E. jefler-soni; 4, E. "primigenius hungaricus"; 5, E. "primigenius-trogontherii"; 6, E.. primigenius"fraasi"; 7, E. jefJersoni (27); 8, E. primigenius (27); 9, E. primigenius "compressus."

1372

to permit derivation of the skull ofeither Elephas planifrons or E. hy-sudricus Falconer and Cautley fromthis kind of skull with its narrowpremaxillae and convergent alveoli, or-bital rings in advanced position, highlateral parietal bones with a medialV-shaped valley, and a frontal bonethat is laterally narrowed and dorsallyflat.

The question of the presence of trueelephants in the Pliocene period ofEurope is -associated with that of thePlio-Pleistocene boundary. If thisboundary is defined as the time of thefirst appearance of the faunal associa-tion of Elephas, Leptobos, and Equus,the entry of Equus is the closest identi-fication of this boundary since Equuswas the last to arrive in the Old World.Great complexity characterizes the Vil-lafranchian fauna; but the name Villa-franchian had been used formerly asthe latest division of the Pliocene, andsince 1948 it has been used synony-mously with the Lower Pleistocene.Now its older beds, including the strat-otype and the type locality for Elephasmeridionalis Nesti, is recognized asLate Pliocene. Some remains from LaMalouteyre and Rezols, France, andfrom Grosni, U.S.S.R., as well as E.meridionalis gromovi Garutt and Alex-eieva from Rostov, U.S.S.R., also derivefrom the Late Pliocene (20). Elephantsconsequently originated some 4 millionyears ago, as judged by present stan-dards, and are polyphyletic, havingoriginated from separate lines of Stego-lophodontinae, at least one Indian andanother African.

Differentiation of Elephants

A few long-living species of ele-phants are known to have existed inthe Early Pleistocene, and in the fau-nal revolution of the Early MiddlePleistocene these evolved into newspecies. These species extended fromtransitional forms to highly specializedforms which have become extinct. Thetwo living forms are conservative andpolymorphic representatives of a bigfamily with many extinct branches orspecies.

Elephas meridionalis Nesti appears inEurope as a primitive species in the LatePliocene. A sampling of 72 well-pre-served, half-worn molars from Italy,Spain, England, Austria, France, and theU.S.S.R. exhibits a normal distributionand dispersion in diagrams, thus tes-tifying to the unity of the species. The

SCIENCE, VOL. 164

reported variations of the skull do notexceed the limits of the probable varia-bility of a common specific pattern. Thetusks of this species are known for theirincurvature in two different planes, therebeing sexual dimorphism of this trait(15). The molars of E. meridionalis areheavy with thick cement and thickenamel, which is irregularly and ran-domly folded; the digitations of enamel(conelets) are deeply divided, a centralsection being more deeply separated; inocclusal figures of abrasion, a noticeablebend of enamel in an almost centralposition (a vestige of gomphotheriinecentral conules) is inconstant and ir-regular. The origin of this species isunknown. Elephas planifrons Falconerand Cautley has been assumed as itsancestor; however, E. meridionalis withits high, rounded skull could not havea contemporary ancestor such as theIndian elephant with its flattened front-al and parietal bones which tend to

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expand upward and sideward. Elephasplanifrons has, on the average, highervalues for the angle of eruption, whichis an advanced characteristic. Thesetwo primitive forms originated inde-pendently. Notwithstanding the similar-ities in morphology of molar teeth anda wide overlapping in scatter diagramsfor these two species, all remainsattributed to E. planifrons in Europehave been shown to be those of E.meridionalis (10).By the Early Middle Pleistocene,

a new form appeared close to the geo-graphical dominion of E. meridionaliswhich was better adapted to graze inthe gramineous steppe. A higher num-ber of plates, increased hypsodonty,thinner and narrowly folded enamel,reduced functional length, and widerangle of molar eruption are character-istic of Elephas armeniacus Falconer.That this form is identical with E.trogontherii Pohlig of the Danube Riv-

2 M3E.ifidicuS

er and Western Europe and with E.wusti of the U.S.S.R. is confirmed bythe fact that in Capellini's Collection(Museum of Geology, Bologna, Italy)there are some specimens formerlyidentified by Falconer as E. armenia-cus, whose cards have been correctedby Pohlig himself to E. trogontherii.The former name has priority, but thesecond has wider use. The speciesranges from Seville, Spain, and south-ern England to Japan, and from cen-tral U.S.S.R. to Israel. The descent ofE. trogontherii from E. meridionalisis suggested by their morphological andbiometrical affinities and by their geo-graphical distribution and chronology.It is difficult to distinguish some evolvedforms of this species from the formersteppe elephant in Hungary, northernItaly, and Voigstedt, East Germany.The transition from one species to theother could probably occur by way ofisomorphic evolutionary trends through

-EcoIumbi0- ,. typeCO - toneotype of Ei.mpero/or"OSBORN03 - sneotype of E.columbim OSBORNCD - 42IffersoniM-"impero'or columbi',' Seward Co.Na.

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Q I 100 J;L/LFFig. 7. Plotting of 43 specimens of the last (some penultimate) molars of American elephants (Elephas primigenius excluded),relative to hypsodonty (K) and functional plate-density (Q), compared to dispersional areas of the main species of the Old world(Fig. 4). American elephants are midway in the scale of those with high dispersion. Two species can be separated with transi-tional forms between them; there is also a late branching of E. columbi, with the characteristics of E. jeffersoni not consistentlyunderstood. The inset shows the histogram for the width of 86 adult molars of American elephants classified at present undertwo generic and ten specific names. The figures preceding the specific names indicate the size of the sample; for instance, 46M3 E. antiquus represents the dispersional area of 46 specimens of t he last adult molar of E. antiquus. [Elephas trogontherii includesMammuthus armeniacus and relatives, that is, the "progressive forms," as discussed in the text.] Simple dots: E. imperator.20 JUNE 1969 1373

natural selection in several contempo-rary populations.

In the Middle Pleistocene, this spe-cies rapidly progressed in the numberof plates, hypsodonty, erupting angle,shortness of occlusal surface, and thin-ness of enamel. It split into variousforms, maintaining a position midwaybetween E. armeniacus and E. primi-genius Blumenbach, which differed inthe frequency of plates and hypsodonty,among others. All these represent a poolof forms from which E. primigeniusoriginated by selection; thus it couldbe considered as a transient and poly-morphic species. If so, the prior validname for this group is E. intermediusJourdan (names such as E. trogentherii-primigenius or primigenius-trogontheriiare confusing). Its range is the same asthat for the preceding species; this isalso the original area for E. primi-genius, which has an exceedingly highnumber of plates and a minimum thick-ness of enamel, but is not substantiallyadvanced in hypsodonty. The result isan adaptation to the soft vegetation of

the taiga and of the ephemeral warmseason during the last glacial age; thenew species extended to North Ameri-ca and was actively hunted by man onboth continents. Evidence is lackingto support the existence of any validsubspecies of E. primigenius, which iseverywhere a widely variable species(Figs. 4 and 5).

Immigration of elephants to NorthAmerica did not occur frequently. Themost primitive form was found in Pe-cos, New Mexico. The Irvington fauna,Gilliland formation, Seymour, Texas,contains a form of elephant which isadvanced in several significant charac-teristics such as hypsodonty; a K/Aage of 1.36 million years (21) conse-quently poses some questions. The skulland tooth morphology of all Americanelephants is decidedly similar to thatof the whole phyletic group E. meri-dionalis to E. primigenius, the differ-ences being irrelevant for a genus. Themost primitive forms surpass E. ar-meniacus in significant trends as hyp-sodonty and could be the offspring of

rapidly evolving immigrants derivedfrom a population of E. meridionalis.If we recall the high individual varia-bility of elephants and take intoaccount the dispersion in scatter dia-grams based on evolutionary trends,we can distinguish only two validspecies of American elephants (Figs. 4and 7)-E. imperator Leidy and E. co-lumbi Falconer (22), both more or lesspolymorphic. Elephas columbi jeffer-soni, since it has the highest numberand frequency of plates, can be retainedas a subspecies of the latter. The largeCentral Plains of North America seemmore favorable to the preservation ofspecies, through migration southwardand northward following the advance-ment and retreat of ice, than do Europeand Asia, where the latitudinal disposi-tion of geographical barriers favoredinstead evolution through selection. Allforms mentioned above, from E. meri-dionalis through E. primigenius andE. columbi jejffersoni, thus belong to aphylogenetically well-defined genus,Mammuthus Bumett 1830.

Fig. 8. Proposed phylogeny of Elephantidae.SCIENCE, VOL. 1641374

Elephas antiquus Falconer, a Euro-pean elephant certainly not known eastof the Volga River, has affinities withthe Asiatic E. namadicus Falconer,which has a similar original pattern ofdistribution and folding of enamel, gen-eral morphology of molar teeth andtheir plates, parietal expansion andfrontal torus, and wide premaxillaewith divergent tusks. Both are attrib-uted to a different genus PalaeoloxodonMatsumoto. The oldest forms are diffi-cult to distinguish as species. LaterP. antiquus developed high, long, nar-row molars with rather thick plates, aconstant median fold of enamel (differ-ent from the typical loxodont sinus ofthe African elephant), and separatelateral rings of enamel at a stage ofmedium wear in the abrasional surface.Its ancient representatives with largemolars and a primitive morphologyseem to suggest a descent from Elephasnmeridionalis, but both the morphologyand the ontogenic and sexual variationsof the skull as well as the tusks andthe evolutionary trends in some signifi-cant ratios fail to support the idea of aclose common ancestor (Figs. 4 and5). The same criteria seem to conflictwith the idea that a close relation ex-ists between Elephas recki of EastAfrica and E. hysudricus, as a resultof a spectacular convergence of highlateral expansions of the skull; rather,the large forehead of E. recki and itsrather flat parieial expansions andfrontal torus, as well as its dentalratios and morphology, seem to relateit to Palaeoloxodon (Fig. 6). There is alist of specific names given to differentspecimens of an evolved form ofPalaeoloxodon in South Africa: ac-cording to Cooke (23), these must bereferred to P. transvaalensis Osborn.The Upper Pleistocene dwarf elephantsfrom Sicily and other islands of theMediterranean (E. melitensis, E. fal-coneri) derive from peninsular Italianpopulations of P. antiquus and conse-quently belong to the same genus.An interesting African fossil elephant

is E. atlanticus Pomel, which lived inthe Early and Middle Pleistocene; itappears to be the unchallenged ances-tor of the recent African elephantLoxodonta africana. The pattern ofenamel distribution in the latter isoversimplified, and the enamel remainsrather thick; forms transitional to ithave been preserved from the EarlyMiddle Pleistocene from L. atlantica(Pomel). This species is also charac-terized by a high frequency of indi-viduals with lateral conelets detached20 JUNE 1969

from the ridge-plates that most fre-quently alternate with them and oblit-erate the transversal valleys; fre-quently deep angular folds of ratherthick enamel concentrate in the medianpart of the plate, sometimes in a radi-ating pattern. Such features also occurin the half-size elephant of Sicily,E. mnaidriensis Adams, whose generalmorphology of grinding plates andthick enamel cover could never haveoriginated from either Palaeoloxodonantiquus or P. namadicus. In some in-dividuals the characteristics resemblethose of the living elephant. ThereforeI suggest that E. mnaidriensis Adamsbe included in the genus LoxodontaCuvier. Its record in Sicily starts in theSicilian stage (24) (the African conti-nent and the central islands of the Medi-terranean were probably linked in theLate Lower Pleistocene, that is, beforethe late main tectonic activity in theMediterranean and East Africa). Ele-phas mnaidriensis is contemporaneouswith P. antiquus, if not older, and itsspecialized skull morphology is striking-ly similar to that of P. antiquus and itsAsian relative. Still its affinity withLoxodonta africana cannot be denied.A close common heritage is very prob-able. On the other hand, it is very ques-tionable whether and to what extentthese species could hibridize.

Until new data (25) is published, wecan tell very little about E. africanavusArambourg, a primitive species ofelephant in North Africa. The ratiosfor the few samples known to me fallin the range characteristic of Mammu-thus meridionalis. Laminar density inthe grinding surface is minimum; hyp-sodonty, being higher in numbers, rep-resents a primitive stage as the largersection of the crown is in its basal part,with a conspicuous cingulum; the widthis rather small; digitations of enamelare deeply separated; central conules areconstant. All this closely resembles thegomphotheriine morphology of theNorth African Stegolophodontinae. Thisform can be related to the origin ofLoxodonta or Palaeoloxodon morethan to Mammuthus, and it overlaps intime with P. recki. It cannot be as-signed to a genus at present. Let uscall it "Elephas" in a wider sense. Thesame is true for "Elephas" subplani-frons Osborn (including E. proplani-frons, E. andrewsi) from South Africa,of an uncertain age, for which thereare but a few specimens. These seemto represent the most primitive ele-phants both in morphology and inmeasurable trends (Figs. 1, 4, and 5)

and could be related to a Stegolopho-don in South Africa, such as one ofthose found at Langebaanweg.

In India and southeast Asia, E.hysudricus is probably a side-branch ofa unique evolutionary line which cor-responds to the phyletic group ElephasLinnaeus in the strict sense; its highlyspecialized skull with lofty parietal ex-pansions and narrow frontal bone withlateral constrictions cannot mask acomplex series of affinities with theliving forms of E. indicus and also withthe Lower Pleistocene E. planifrons(Fig. 6). Elephas platycephalus Osbornis a variation of this polymorphicphyletic group.

Summary

Polymorphism within each evolvingbranch, a wide range of variation, con-vergent adaptiveness, common heredity,large size, and overlapping of measure-ments make difficult the systematics ofelephants. Only the identification ofevolutionary trends may enable us toidentify genera and species with suffi-cient reliability for regular samples.

It is uncertain to what extent manyof the quantitative differences can beexplained as simple variations result-ing from local conditions of climateand food supply. Morphological varia-tions are large; thus the affinities andtrends in form have to be establishedcarefully. It is probable that the diver-sification of elephants summarized inFig. 8 relies on a genetic basis, and itis very difficult to decide at whatmoment the interbreeding of differentforms has terminated.

References and Notes

1. K. P. Oakley, Frameworks for Dating FossilMan (Weidenfeld and Nicolson, London,1964), p. 35.

2. H. F. Osborn, Proboscidea (American Mu-seum, New York, 1942), vol. 2, p. 1602.

3. V. I. Garutt, Dokl. Akad. Nauk SSSR 114(1), 189 (1957); Zool. J. 37 (10), 1541 (1958).

4. A. L. Adams, British Fossil Elephants(Palaeontographical Society, London, 1877-1881); A. Gaudry, Les ancatres de nosanimaux dans ks temps g&ologiques [as quotedby Ch. Deperet and L. Mayet, in Ann. Univ.Lyon (New Ser.) 43, 197 (1923)].

5. K. A. Weithofer, Morphol. Jahrb. 14, 507(1888); W. Soergel, Paleontographica 60, 1(1912); G. Schlesinger, Jahrb. Geol. Reich-sanstalt 62 (1), 87 (1912).

6. C. Airaghi, Mem. Soc. Ital. Sci. Nat. 8 (3),193 (1917); H. F. Osborn, Amer. Mus.Novitates 1, 1 (1921); Ch. Dep6ret and L.Mayet, Ann. Univ. Lyon (New Ser.) 43, 197(1923).

7. L. Trevisan, Palaeontogr. Ital. 44, 1 (1964);K. D. Adam, Stuittgarter Beitr. Natturk. 78,4 (1961).

8. A. Cabrera, Rev. Mus. La Plata 32, 61(1929).

9. H. F. Osborn, Proboscidea (American Mu-seum, New York, 1936), vol. 1, p. 735.

10. E. Aguirre, Revisidn sistemdtica de Elephanti-dae por sit otorfologia y morfometria den-

1375

taria (Estudios Geol6gicos, Madrid, 1968).The measurements of the enamel thicknessare taken either at a regular distance frombase to top in a vertically cut ridge-plate,or on each figure of abrasion in the grindingsurface, since here each plate appears wornout at a different height; the value of themean for each species is a constant independ-ent of the collection, preservation technique,measuring instrument, and the differentsingle values obtained with either method orin either molar of the same individual.

11. The need to isolate evolutionary trends inthe study of elephants was emphasized byJ. B. S. Haldane, in L. Trevisan, Ric. Sci.19, 10 (1949).

12. F. M. Bergounioux and F. Crouzel, Estud.Geol. 14, 260 (1958).

13. C. Petrocchi, Rend. Accad. Naz. IX 76-77, 1(1953-1954).

14. It is primitive, since the presence of lowertusks is a regressive tendency; the elephantlikemorphology of its molar ridges is advanced[C. Petrocchi, in (13), Figs. 3, 4, and 5].

15. C. Fuentes, Bol. Roy. Soc. Espaii. Hist. Nat.Biol. 64, 277 (1966).

16. C. Arambourg, perfonal communication.17. R. Singer and D. A. Hooijer, Nature 182,

101 (1958).18. "Elephas proplanifrons," "E. andrewsi."19. H. F. Osborn, in (2), p. 1354, Figs. 1211,

1212, and 1213.

20. L. Ginsburg, personal communication; V.I. Garutt, Tr. Comm. Izuch. ChetverttchnogoPe ioda 10 (2), 8 (1954).

21. J. F. Evernden and G. H. Curtis, Curr.Anthropol. 6, 343 (1965).

22. The former types must be retained; neitherthe neotype of Elephas imperator [H. F.Osborn, in (2), p. 1000], which is E. columbifrom Guadalajara, Mexico, nor the neotypeof E. columbi [H. F. Osborn, in (2), p. 1075],which seems to be a transient form withmost primitive traits except hypsodonty, mustbe admitted. F. C. Whitmore, Jr., has sup-plied me with one specimen of elephanttooth from the Atlantic continental shelf[F. C. Whitmore, Jr., K. 0. Emery, H. B.S. Cooke, D. J. P. Swift, Science 156,1477 (1967)]. I do not consider it a newspecies, since, in different scatter diagramsfor diverse ratios, when the size of thesample is sufficient, this species lies withinthe range of variability of E. columbi andE. columbi jeffersoni Osborn; in the thick-ness of the enamel and some other traits,these forms overlap with E. primigenius; themorphology of the specimen known to meis that of E. coluinbi and E. columbi lefier-soni; a mixed assemblage in the continentalshelf is possible.

23. "Elephas sheppardi" Dart, "E. hanekomi"Dart, "E. wilimani" Dart [see H. B. S. Cooke,in African Ecology and Human Evoluttion,

F. C. Howell and F. Bourliare, Eds.(Methuen, London, and Wenner-Gren Foun-dation for Anthropological Research, Ltd.,New York, 1963), p. 105].

24. B. Accordi, B. Campisi, R. Colacicchl, AttiAccad. Gioenia Sci. Nat. Catania 12, 168(1959).

25. C. Arambourg, in preparation.26. , Mission Scientifique de L'Omo (Edi-

tions du Museum, Paris, 1949), vol. 3, p.254 (Fig. 7), p. 267 (Fig. 13), plate II(Fig. 2).

27. Mammuthus hungaricus from M. Kretzoi,Foldt. Kozl. 71, 7-12 (1941); the rest fromH. F. Osbom (2).

28. I thank A. C. Blanc and M. Crustafont forthe initial ideas for this study and the di-rectors and paleomammalogists of museumsin London, Vienna, Basil, Darmstadt, Mainz,Heidelberg, Stuttgart, Ferrara, Padua, Bolog-na, Florence, Pisa, Rome, Naples, Leningrad,Budapest, Rabat, Paris, Washington, NewYork, Yale University, Harvard University,University of Michigan, University of Nebras-ka, University of Chicago, University of Colo-rado, Idaho State University, University ofCalifornia, Oviedo, Barcelona, La Corufia,Santander, Seville, Toledo, Soria, Madrid,Capetown, and Nairobi. Supported by theSpanish Council of Research, the NSF, theWenner-Gren Foundation, and the StateMuseum, University of Nebraska, Lincoln.

NEWS AND COMMENT

CBW: Pressures for Control Buildin Congress, International Groups

The highly classified issue of chemi-cal and biological warfare (CBW) isunder intense public scrutiny this yearas pressures build up to bring germ andgas weapons under stricter control.Several Congressional subcommitteeshave recently held hearings on aspectsof the U.S. Army's CBW program andhave subjected the Army's gas warfareexperts to the most hostile questioningfrom Capitol Hill in a decade or more.A spate of books, television shows,and "educational" meetings held byscientific groups have tried to enlightenthe public on the dangers of CBW.And at least three major internationalorganizations, including the UnitedNations, are preparing detailed reportson the nature and effects of germ andgas weapons. These reports are ex-pected to be the most comprehensiveand authoritative analyses of CBWever made public.

The net result of all this activity isthat the public and its political leaderswill be better informed about thissecrecy-ridden subject than ever be-fore, and the groundwork will havebeen laid for a serious drive to bring

1376

CBW under a strict arms-controlagreement.The recent inquiries on Capitol Hill

are notable for their reflection ofdeep-seated hostility and skepticismamong congressmen toward the mili-tary CBW program. The hearings havenot yet produced a full-scale review ofthe entire CBW program. Indeed, theyseem to have been launched almostby accident and have focused on con-venient targets of opportunity, such asthe safety of outdoor CBW testing andof dumping surplus gas weapons intothe ocean. Nevertheless, persistent prod-ding by hostile congressmen has forcedthe Army to release new informationabout the American CBW effort.

Congressional concern this year haslargely been sparked by Representa-tive Richard D. McCarthy, a Democratfrom Buffalo, N.Y., who happened tobe sitting at home watching televisionwith his wife in early February whenhe saw an NBC-TV documentary onCBW. McCarthy found the program"rather gripping and shocking" and,at the urging of his wife, set out toinform himself about the weapons. He

first arranged a Pentagon briefing for19 congressmen and senators. Then,finding that unsatisfactory, he fired offletters asking further questions of theDefense Department and other agen-cies.

In response to McCarthy's queries,the Pentagon, for the first time in sev-eral years, publicly revealed the dollarmagnitude of the American CBW pro-gram. Expenditures for fiscal year1969, according to John S. Foster, Jr.,director of defense research and engi-neering, will total $350 million. Thebulk of this-$240 million-is for pro-curement of smoke, flame, and in-cendiary weapons; tear gas; herbicides;and defensive equipment-all usedprimarily in the Vietnam War. Some$20 million has been spent for opera-tion and maintenance of CBW facili-ties, and about $90 million has financedresearch, development, and testing ac-

tivities, including work on the lethalagents that arouse the most fear andcontroversy. Foster stated categoricallythat the Pentagon is no longer procuringlethal chemical or biological agentsfor the weapons stockpile.The Pentagon's figures have been

disputed by some CBW critics. Con-gressman McCarthy finds it "difficultto accept" the $350 million estimate.And journalist Seymour M. Hersh,author of a book on CBW, has assertedthat "CBW spending exceeds $650million a year."McCarthy has raised a number of

broad policy issues during his crusade.He has questioned the tight secrecy

SCIENCE, VOL. 164