Revista de la Asociación Geológica Argentina 64 (1): 147 - 159 (2009) 147

INTRODUCTION

Charles Darwin collected fossil mammalsfrom various South American localitiesduring his voyage aboard HMS Beagle.He recovered his first fossil at Punta Alta(Buenos Aires Province, Argentina) onSeptember 23, 1832, and continued co-llecting intermittently at this locality untilOctober 16. Three days later he collectedseveral specimens from Monte Hermoso

(Buenos Aires Province, Argentina). Dar-win returned to Punta Alta betweenAugust 29 - 31, 1833. Several weeks la-ter, around September 19, he collectedin Guardia del Monte (Buenos Aires Pro-vince); the Rio Carcarañá or Tercero(Santa Fe Province, Argentina) on Octo-ber 1; and the Bajada Santa Fe (Paraná,Entre Ríos Province, Argentina) on Oc-tober 10. Moving to Uruguay, he collec-ted fossils during November 25 - 26

from the Arroyo Sarandí near the city ofMercedes (Soriano Department). He re-turned to Argentina and collected his lastspecimens at Puerto San Julián (SantaCruz Province) during the first severalmonths of 1834 (see Fig. 1). All the spe-cimens, sent to his mentor John StevensHenslow and later deposited in the RoyalCollege of Surgeons (London, England),were studied by Richard Owen beginningin 1836.

THE FOSSIL MAMMALS COLLECTED BY CHARLESDARWIN IN SOUTH AMERICA DURING HIS TRAVELS ON BOARD THE HMS BEAGLE

Juan Carlos FERNICOLA1, Sergio F. VIZCAÍNO2 and Gerardo DE IULIIS3

1 Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales "Bernardino Rivadavia". Buenos Aires, Argentina.Email: jctano@macn.gov.ar2 División Paleontología Vertebrados, Museo de La Plata, La Plata, Argentina. CONICET. Email: vizcaino@fcnym.unlp.edu.ar3 School of Nursing, George Brown College of Applied Arts and Technology, Toronto; and Department of Ecology and EvolutionaryBiology, University of Toronto, Toronto, Canada. Email: gerry.deiuliis@utoronto.ca

ABSTRACTDuring the first two years of his voyage aboard HMS Beagle, Charles Darwin collected a considerable number of fossil mam-mals from various localities in Argentina and Uruguay. Among these remains are those of large mammals that Darwin infor-mally assigned to Megatherium and Mastodon, the only large taxa then known for South America, and of small and medium-sized mammals that Darwin recognized as representing at least two rodents and a horse. The study of Darwin's collection wasentrusted to Richard Owen, who described eleven taxa between 1837 and 1845, including the six following ones: Toxodon pla-tensis, Macrauchenia patachonica, Equus curvidens, Scelidotherium leptocephalum, Mylodon darwini and Glossotherium sp. This contributionprovides a synthesis of Darwin's preliminary assignments and evaluates the reasons that led him to recognize only megathe-res and mastodonts for the large fossil remains. Also, it discusses the current taxonomic status of the taxa described or erec-ted by Owen between 1837 and 1845 and the influence that Owen's taxonomic and phylogenetic conclusions had on the deve-lopment of Darwin's ideas on evolution.

Keywords: Darwin, Taxonomy, South America, Fossil mammals.

RESUMEN: Los mamíferos fósiles colectados por Charles Darwin en América del Sur durante su viaje a bordo del HMS Beagle. Durante los dosprimeros años de su viaje a bordo del HMS Beagle, Charles Darwin colectó en distintas localidades de Argentina y Uruguayun considerable número de mamíferos fósiles. Entre estos se cuentan los grandes mamíferos que informalmente Darwin asig-nó a Megatherium y Mastodon, únicos grandes taxones conocidos hasta ese momento para América del sur y entre los pequeñosy medianos mamíferos reconoció la presencia de al menos dos tipos de roedores y un caballo. El estudio posterior de todoslos ejemplares colectados por Darwin fue llevado a cabo Richard Owen, quien entre 1837 y 1845 describió once taxones, entrelos cuales, seis eran nuevos taxones: Toxodon platensis, Macrauchenia patachonica, Equus curvidens, Scelidotherium leptocephalum, Mylodondarwini y Glossotherium sp. En esta contribución se brinda una síntesis de las asignaciones preliminares efectuadas por CharlesDarwin y se evalúan los motivos que lo habrían llevado a reconocer sólo megaterios y mastodontes entre los grandes mamí-feros fósiles por él colectados. También tiempo, se discute el estatus taxonómico de los taxones descritos o fundados porRichard Owen entre 1837 y 1845 y la influencia que habrían tenido las conclusiones taxonómicas y filogenéticas de Owen enel desarrollo de las ideas evolutivas de Darwin.

Palabras clave: Darwin, taxonomía, América del Sur, mamíferos fósiles.

Regrettably, the intense bombardmentsuffered by this institution during April10 and 11, 1941, destroyed a large part ofits paleontological treasures. Cave's (1942)catalogue of the surviving specimensrevealed that some 95% of the collectionhad been lost - of 5,000 specimens, only175 remained. Among these, fortunately,are various of the specimens collected byCharles Darwin and described by Ri-chard Owen (1837-1845) as new taxa, in-cluding Equus curvidens, Glossotherium sp;Macrauchenia patachonica, Mylodon darwini,Scelidotherium leptocephalum and Toxodonplatensis (Cave 1942). Beginning in 1946,nearly all of Darwin's collection wastransferred to the Natural History Mu-seum (London), where it is still housed(see appendix 1). The Royal College of

Surgeons retained only a single specimen,the remains of the Megatherium america-num specimen that apparently allowedOwen (1840) to recognize the presenceof a fifth upper molariform in this taxon(see appendix 1).The aim of this contribution is to provi-de an update on the taxonomic status ofthe various taxa recognized or establis-hed by Owen (1837-45), and to considerthe influence the specimens and theirassignment had on the development ofDarwin's ideas.

HISTORICAL BACKGROUND

The first notices of South American"fossils" appear in the reports of earlySpanish explorers to South America and

in the earliest histories of America (e.g.Cieza de León 1553, Falkner 1774). The-se objects were interpreted as the re-mains of an ancient race of giant hu-mans that inhabited this part of theworld before being smitten by divineforce. Cieza de León (1553, p. 183) pro-vided the following vivid tale about hugebones found in Santa Elena, Ecuador: "Yasí, dicen que, estando todos juntos envueltos ensu maldita sodomía, vino fuego del cielo temero-so y muy espantable, haciendo gran ruido, delmedio del cual salió un ángel resplandeciente, conuna espada tajante y muy refulgente, con la cualde un solo golpe los mató a todos y el fuego losconsumió, que no quedó sino algunos huesos ycalaveras, que para memoria del castigo quisoDios que quedasen sin ser consumidas por elfuego. Esto dicen de los gigantes; lo cual creemosque pasó, porque en esta parte que dicen se hanhallado y se hallan huesos grandísimos. Y yo heoído a españoles que han visto pedazo de muelaque juzgaban que a estar entera pesara más demedia libra carnicera, y también que habíanvisto otro pedazo del hueso de una canilla, que escosa admirable contar cuán grande era, lo cualhace testigo haber pasado…".This sort of general belief persisted, inSouth America at least, until the end ofthe 18th century, even though some ofthe remains were recognized as nonhu-man, as indicated in the following passa-ges by the English Jesuit Thomas Falkner(1774, p. 54-55) "On the banks of the RiverCarcarania, or Tercero, about three or four lea-gues before it enters into the Parana, are foundgreat numbers of bones, of an extraordinarybigness, which seem human. There are some gre-ater and some less, as if they were of persons ofdifferent ages. I have seen thigh-bones, ribs, bre-ast-bones, and pieces of skulls. I have also seenteeth, and particularly some grinders which werethree inches in diameter at the base. These bones(as I have been informed) are likewise found onthe banks of the Rivers Parana and Paraguay,as likewise in Peru. The Indian Historian,Garcilasso de la Vega Inga, makes mention ofthese bones in Peru, and tells us that the Indianshave a tradition, that giants formerly inhabitedthose countries, and were destroyed by God forthe crime of sodomy.I myself found the shell of an animal, composed

148 J. C. FERNICOLA, S. F. VIZCAÍNO AND G. DE IULIIS

Figure 1: Map of the localitieswhere Charles Darwin collec-ted fossil mammals.

The fossil mammals collected by Charles Darwin in South America ... 149

of little hexagonal bones, each bone an inch indiameter at least; and the shell was near threeyards over. It seemed in all respects, except it's[sic] size, to be the upper part of the shell of thearmadillo; which, in these times, is not above aspan in breadth."It was during this period that the illus-trious French naturalist George Cuvier(1796) published the first scientific workon a South American fossil, which hedescribed and named Megatherium america-num based on the specimen recovered byFray Manuel Torres in 1787 from Lujánin Buenos Aires Province, Argentina andsent the following year by the Marquis ofLoreto, Viceroy of Río de la Plata, to theReal Gabinete de Historia Natural in Ma-drid, Spain. Mones (1986) considered theerection of this species as the first Lin-nean nomenclatorial act for a SouthAmerican fossil species. This specimenhad, however, previously been describedand figured by Juan Bautista Bru de Ra-món, an artist and first taxidermist of theReal Gabinete de Historia Natural. In thisregard, Garriga (1796, as quoted in Ló-pez Piñeiro and Glick 1993, p. 126) notedthat "… restaba superar la dificultad de quepermitiese Bru que se diese a luz una obra queél había tenido en otro tiempo intento de publi-car, y por varias circunstancias imprevistassepultó en el olvido." López Piñeiro andGlick (1993, p. 66) maintained that thepreparation of the monograph "… no fueentonces editada, pero su preparación debía estartan adelantada que un tal Roume, representan-te del gobierno de francés en Santo Domingo,consiguió un juego de pruebas de las planchas asu paso por Madrid en 1793.Roume envió las pruebas de las planchas alInstitut de France, del que era miembro corres-pondiente, acompañadas de una "corta descrip-ción" del esqueleto. La sección de ciencias del Ins-titut encargó a George Cuvier un informe sobreel tema, que apareció publicado en 1796…"Cuvier (1806) also studied fossil probos-cidean remains found by Dombey in Pe-ru and by Humboldt in various localitiesin Bolivia, Chile, Colombia, and Ecua-dor, among which he recognized threemorphotypes, designated informally as"mastodonte a dents étroites", "mastodonte Cor-

dillierès" and "mastodonte humboldien". Cu-vier (1823) later formally named themMastodon angustidens, Mastodon andium andMastodon humboldti, respectively (see Ca-brera 1929). In this paper, Cuvier (1823,p. 179) included a handwritten communi-cation by "don Dámaso Antonio Larrañaga,a priest of Montevideo, to Mr. Augusto deSaint-Hilaire" that briefly described agroup of fossil specimens, including apartial exoskeleton (or carapace), underthe name "Dasypus (Megatherium Cuv)."Cuvier (1823) thus acknowledged thatthis carapace probably belonged to Mega-therium. Whatever the reasons that prom-pted Larrañaga's subgeneric assignment(that is, in recognizing the existence ofarmored megatheres), the fact that hisopinion appeared in a work by Cuvier en-sured its credibility, so that several in-complete remains later sent to Europewere similarly recognized (e.g., as byWeiss 1830, Clift 1835). It was not untillater that Owen (1839a) demonstratedthat megatheres were not armored andthat the remains belonged instead to thegroup of mammals he termed glypto-donts, a group closely related to armadi-llos.Knowledge of South American fossilmammals remained at this elementary le-vel for much of the early part of the 19thcentury, as is made clear from Owen's(1838, p. 13) opening paragraph on hiswork on the fossil mammals in Darwin'sThe Zoology of the Voyage of H.M.S. Beagle:"It may be expected that the description of theosseous remains of extinct Mammalia, whichrank amongst the most interesting results ofMr. Darwin's researches in South America,should be preceded by some account of the fossilmammiferous animals which have been pre-viously discovered in that Continent. The resultsof such a retrospect are, however, necessarilycomprised in a very brief statement; for theSouth American relics of extinct Mammalia,hitherto described, are limited, so far as I know,to three species of Mastodon, and the giganticMegatherium." It was against this systematic frameworkthat Darwin began his efforts in collec-tion and preliminary taxonomic assign-

ments that Owen (1837-1845) later mo-dified. Several of his assignments wereconsidered taxonomic errors or misinter-pretations (e.g., Sulloway 1982, Keynes2001), even though his inferences were inaccordance with what was then known.

DARWIN'S FOSSIL MAMMALS

The following presents a synthesis ofOwen's initial taxonomic assignments(1837-45) of the remains collected byDarwin in South America, including thepreliminary assignments made by Dar-win. The latter's assignments were glea-ned from field notes (Darwin 2002-2008), personal correspondence (Darwin1985) and Charles Darwin's Beagle Diary(in Keynes 2001), all material written byDarwin before 1836, the year of hisreturn to England. The supragenericclassification used here follows McKen-na and Bell (1997).

SYSTEMATICPALEONTOLOGY

Grandorder Ungulata Linnaeus, 1776Mirorder Meridiungulata McKenna, 1975Order Notoungulata Roth, 1903Suborder Toxodontia Owen, 1853Family Toxodontidae Owen, 1845Subfamily Toxodontinae Owen, 1845Genus TTooxxooddoonn Owen, 1837

TTooxxooddoonn ppllaatteennssiiss Owen, 1837Fig. 2

The specimens assigned to this taxon byOwen (1837, 1838) were recovered byDarwin from various South Americanlocalities. On October 1 and 10, 1833, hecollected at Río Carcaraña o Tercero(Santa Fe Province) and at Bajada SantaFe (Paraná, Entre Ríos Province). Hisfield notes (Darwin 2002-2008) describea fossil specimen as "…a large rotten tooth& in the layer large cutting tooth", a descrip-tion that agrees with those included inhis Beagle Diary ("… a curious & large cut-ting tooth"; in Keynes 2001, p. 193) andwritten to John Stevens Henslow ("In ye

R. Carcarana I got a tooth, which puzzles evenmy conjectures, it looks like an enormous gna-wing one"; Letter 229 in Darwin 1985).Darwin's (2002-2008) field notes for No-vember 26, 1833, state: "Started went roundby a house to see large head & bones, washedout of Barranca & found after a flood. - pieceshere also of Casca - Barranca" while his Bea-gle Diary (in Keynes 2001) records: "Be-gan my return in a direct line to M. Video; wentby an Estancia where there was a part, very per-fect, of the head of a Megatherium. I purcha-sed it for a few shillings". An alveolus of thisspecimen, recovered from Arroyo Saran-dí, Departament of Soriano, Uruguay,easily accommodated a molariform toothfound by Darwin in Carcaraña (Owen1838).

TTooxxooddoonn sp.

The mandible and isolated molariformsassigned by Owen (1837, 1838) to thisgenus were collected between September23 - October 16, 1832, at Punta Alta(Buenos Aires Province, Argentina). Onthe molariforms, Darwin (1985, Letter192) noted that "some large molar teeth,which in some respects would seem to belong toan enormous Rodentia". Burmeister (1866)based the species Toxodon darwini on themandible described by Owen (1838)Bond (1999) acknowledged the possiblesynonymy of Toxodon darwini with Toxo-don platensis, although he recognized thata revision of the genus was required.Owen (1837, 1838, p. 16) recognized To-xodon as "A gigantic extinct mammiferous ani-mal, referrible to the Order Pachydermata, butwith affinities to the Rodentia, Edentata, andHerbivorous Cetacea". Darwin (1839, p.180) summarized the morphological ba-sis leading to this idea of multiple affini-ties: "Mr. Owen says, judging from the portionof the skeleton preserved, the Toxodon, as faras dental characters have weight, must be refe-rred to the rodent order. But from that order itdeviates in the relative position of its supernu-merary incisors, in the number and direction ofthe curvature of its molars, and in some otherrespects. It again deviates, in several parts of itsstructure which Mr. Owen enumerated, both

from the Rodentia, and the existing Pachyder-mata, and it manifests an affinity to the Dino-therium and the Cetaceous order. Mr. Owen,however, observed, that the development of thenasal cavity and the presence of frontal sinuses,renders it extremely improbable that the habitsof he Toxodon were so exclusively aquatic aswould result from the total absence of hinderextremities; and concludes, therefore, that it wasa quadruped, and not a Cetacean; and that itmanifested an additional step in the gradation ofmammiferous forms leading from the Rodentia,through the Pachydermata to the Cetacea; a gra-dation of which the water-hog of South Ame-rica (Hydrochærus capybara) already indi-cates the commencement amongst existing Ro-dentia, of which order it is interesting to observethis species is the largest, while at the same timeit is peculiar to the continent in which the re-mains of the gigantic Toxodon were discovered".The genus Toxodon is now consideredamong the more derived native notoun-

gulates of South America. The Notoun-gulata, a clade of the Mirorder Meridiun-gulata, shares an ancestry with NorthAmerican condylarths (Cifelli 1993) Inother words, Toxodon has no close phylo-genetic relationships with the groupsmentioned by Owen (1838).

Grandorder Ungulata Linnaeus, 1776Mirorder Meridiungulata McKenna, 1975Order Liptopterna Ameghino, 1889Superfamily Macrauchenioidea Gervais,1855Family Macraucheniidae Gervais, 1855Subfamily Macraucheniinae Gervais, 1855Genus MMaaccrraauucchheenniiaa Owen, 1838

MMaaccrraauucchheenniiaa ppaattaacchhoonniiccaa Owen, 1838Fig. 3a

In a letter from March, 1834, to JohnStevens Henslow, Darwin (1985, Letter

J. C. FERNICOLA, S. F. VIZCAÍNO AND G. DE IULIIS150

Figure 2: Skull of Toxodonplatensis in ventral view (fromOwen 1838). Scale bar = 10cm.

The fossil mammals collected by Charles Darwin in South America ... 151

238) recounted that "At Port St Julian Ifound some very perfect bones of some large ani-mal, I fancy a Mastodon". On this speci-men, the only one found by Darwin inPuerto San Julián, Owen (1838, p. 35)erected Macrauchenia patachonica, which heconsidered "A large extinct MammiferousAnimal, referrible to the Order Pachydermata;but with affinities to the Ruminantia, and espe-cially to the Camelidae". The evolutionarysignificance of this purported kinshipimpressed Darwin (1839, p. 210): "Themost important result of this discovery, is theconfirmation of the law that existing animalshave a close relation in form with extinct species.As the guanaco [Camelidae] is the characteris-tic quadruped of Patagonia, and the vicuna ofthe snow-clad summits of the Cordillera, so inbygone days, this gigantic species [Macrauche-nia patachonica] of the same family musthave been conspicuous on the southern plains".The genus Macrauchenia is now conside-red as among the more derived nativeSouth American litopterns. As with theNotoungulata, the Litopterna comprisesa clade of the Mirorder Meridiungulataand is closely related to North Americancondylarthrans, rather than camelids, aserroneously proposed by Owen (1838).

Grandorder Ungulata Linnaeus, 1776Mirorder Altungulata Protero and Schoch,1989Order Perissodactyla Owen, 1848Suborder Hippomorpha Word, 1937Family Equidae Gray, 1821Genus EEqquuuuss Linnaeus, 1758

EEqquuuuss ssp.Fig. 3b

The remains assigned to this genus re-present the first fossil horses found inSouth America. The two molars fromArgentina were recovered from PuntaAlta (Buenos Aires Province) and BajadaSanta Fe (Entre Rios Province). The spe-cimen from Bajada Santa Fe was referredto by Darwin as a horse (in Keynes2001). We have not been able to find anymention of the other specimen in hisfield notes (Darwin 2002-2008), Beagle

Diary (in Keynes 2001), or personal co-rrespondence (Darwin 1985). AlthoughOwen (1840) did not attempt specific as-signation of these molars, he did notethat the only difference between themand those of Equus caballus was the sma-ller size of the former. Owen (1845)erected Equus curvidens based on Darwin'sspecimens, a species which is consideredsynonymous with Equus (Amerhippus) neo-geus Lund by Prado and Alberdi (1994).

Grandorder Ungulata Linnaeus, 1776Order Uranotheria McKenna and Bell,1987Suborder Tethytheria McKenna, 1975Infraorder Behemota McKenna and Bell,1987Parvorder Proboscidea Illiger, 1811Superfamily Elaphantoidea Gray, 1821Family Gomphotheriidae Hay, 1922Subfamily Rhynchoteriinae Hay, 1922Tribe Cuvieroniini Cabrera, 1929Genus MMaassttooddoonn Rafinesque, 1814

MMaassttooddoonn sp.

The specimens assigned to this taxon,collected by Darwin at Bajada Santa Fe(Entre Ríos Province) and Río Carcarañáor Tercero (Santa Fe Province), werenoted by Owen (1840, p. 180) as "…thefragments of the teeth and portions of the skele-ton which reached England, are not sufficient tolead to a determination of the species; but suffi-ciently prove it to have been nearly allied, if notidentical, with the Mastodon angustidens ofCuvier, and unquestionably distinct from theMastodon giganteum of the United States".

Currently Stegomastodon platensis is the onlyproboscidean species recognized fromthe areas yielding Darwin's specimens(Alberdi and Prado 1995).

Magnorder Xenarthra Cope, 1889Order Pilosa Flower, 1883Suborder Phyllophaga Owen, 1842Infraorder Mylodonta McKenna andBell, 1987Superfamily Mylodontoidea Gill, 1872Family Scelidotheriidae Ameghino, 1889Subfamily Scelidotheriinae Ameghino,1889Genus SScceelliiddootthheerriiuumm Owen, 1839b

SScceelliiddootthheerriiuumm lleeppttoocceepphhaalluumm Owen, 1839bFig. 4

This taxon was based by Owen (1839b)on the only nearly complete skeletonfound by Darwin at Punta Alta (BuenosAires Province). We are unable to findany preliminary assignment of this speci-men by Darwin, although Sulloway(1982, p. 353) noted that Darwin consi-dered the specimen as "allied to the Rhi-noceros". Darwin made this conjecture onSeptember 23, 1832 (in Keynes 2001) inthe following Beagle Diary entry: "… Iwalked on to Punta Alta to look after fossils; &to my great joy I found the head of some largeanimal, imbedded in a soft rock. … It took menearly 3 hours to get it out: As far as I am ableto judge, it is allied to the Rhinoceros. … Idid not get it on board till some hours after it wasdark". However, the specimen assignedby Owen (1839b) to Scelidotherium was co-llected by Darwin in Punta Alta in Au-

Figure 3: a) Cervical vertebraof Macrauchenia patachonica inlateral and ventral views (fromOwen 1838). Scale bar = 5 cm;b) Tooth of Equus sp. inocclusal and lateral views(from Owen 1840). Scale bar= 1 cm.

J. C. FERNICOLA, S. F. VIZCAÍNO AND G. DE IULIIS152

gust, 1833, the time during which Darwinhad returned to this locality (Keynes2001, p. 178). Further confirmation ofthis date appears in a letter from Darwin(1985, Letter 188), dated September 20,1833, to Caroline S. Darwin, in which herecounts that "I likewise at Bahia Blancafound some more bones more perfect than those Iformerly found, indeed one is nearly an entireskeleton". As indicated below, Darwin's"allied to the Rhinoceros" comment maymore likely have been a reference to oneof the cranial remains that Owen (1840)later assigned to the genus Megatherium,particularly as Owen's generic assigna-tions of the sloths are for the most partstill considered correct.

Magnorder Xenarthra Cope, 1889Order Pilosa Flower, 1883

Suborder Phyllophaga Owen, 1842Infraorder Mylodonta McKenna andBell, 1987Superfamily Mylodontoidea Gill, 1872Family Mylodontidae Gill, 1872Subfamily Mylodontinae Gill, 1872Genus MMyyllooddoonn Owen, 1839b

MMyyllooddoonn ddaarrwwiinnii Owen, 1839bFig. 5a

The specimen assigned to this genus byOwen (1839b, p. 69) consists of "…thelower jaw with the series of teeth entire on bothsides: but the extremity of the symphysis, thecoronoid and condyloid processes, and the angu-lar process of the left ramus, are wanting".This specimen was recovered by Darwinat Punta Alta (Buenos Aires Province),but we were unable to determine whe-

ther it was collected during his first orsecond sojourn to this area. In a lettersent to John Stevens Henslow in No-vember, 1832, Darwin (1985, Letter 192)noted a completed list of fossils collectedin Bahia Blanca, among which he empha-sized "… the upper jaw & head of some verylarge animal, with 4 square hollow mo-lars….& the head greatly produced in front….I at first thought it belonged either to the Me-galonyx or Megatherium…. In confirma-tion, of this, in the same formation I found alarge surface of the osseous polygonal plates,which ``late observations'' (what are they?) showbelong to the Megatherium". A footnote onthis page, presumably inserted by the edi-tors, indicates that this specimen was"Described in Fossil Mammalia, p. 63-73, byRichard Owen, who identified it as belonging toa distinct subgenus of Megatheroid Edentata, towhich he gave the name Mylodon darwinii".However, we believe this to be incorrect- the specimen is not the one that Owen(1839b) later assigned to Mylodon darwini,as Dar-win indicated that the specimenwas an upper jaw and skull, rather thanthe mandible on which Mylodon darwini isbased. Darwin's indication of the presen-ce of four molariforms possibly led tothe assumption (i.e., in the footnote) thatthe specimen belonged to Mylodon darwi-ni, given that five upper molariforms arepresent in Megatherium. However, theearliest descriptions of Megatherium indi-cate four upper molariforms. As notedabove, it was Owen (1840, p. 102) whorecognized the presence of a fifth uppermolariform: "Upon clearing away the matrixfrom the palatal and alveolar surface of one ofthe cranial fragments of the Megatherium inMr. Darwin's collection, I was gratified by thedetection of the crown of a fifth molar".The taxonomic history of Mylodon isamong the more complex for the taxaerected by Owen (1838-1840), due main-ly to the ambiguity in the type species.Owen (1839b) erected Mylodon for twospecies, Mylodon darwini and Mylodon harla-ni. The former species was based on aleft dentary from Punta Alta (Buenos Ai-res Province), whereas the second wasbased on a cast of a mandible from

Figure 4: Partial skeleton ofScelidotherium leptocephalum inventral view (from Owen,1838b). Scale bar = 10 cm.

The fossil mammals collected by Charles Darwin in South America ... 153

North America that Harlan (1835) hadassigned to Megalonyx laqueatus. Owen(1839b) was unclear about his choice oftype species, given that in the title of hisdescription of his new genus he referredto the fossil collected by Darwin, but inthe text Owen noted that Mylodon darwiniwas the second species of the genus.This ambiguity would be trivial if the twospecies were congeneric, but they havebeen subsequently considered as belon-ging to different genera. Consequently,some later researchers, such as Reinhardt(1879), Lydekker (1887) and Brown(1903), considered Mylodon harlani as thetype of the genus, whereas other, such asLeidy (1855), bestowed this status onMylodon darwini. The issue was resolvedby Kraglievich (1928) in favor of Mylodondarwini based on the following reasons:

1) the title of the generic description re-fers to the mandible collected by Dar-win;2) the original material available to Owenwas the dentary from Punta Alta;3) Owen (1842) recognized Mylodon harla-ni as the second species of the genus;4) in his "Conspectus familiarum, generum etspecierum", Owen (1842, p. 169) listed My-lodon darwini as the first species of thegenus.Kraglievich's (1928) logic has been ac-cepted by the scientific community, sothat Mylodon darwini is currently conside-red the type species of Mylodon, whereasMylodon harlani is placed in the genusParamylodon. The taxonomic solution pro-vided by Kraglievich (1928) not only re-solved the taxonomic problem with My-lodon, but also helped clarify the proble-matic nomenclature of the genus Glosso-therium (see below).

Magnorder Xenarthra Cope, 1889Order Pilosa Flower, 1883Suborder Phyllophaga Owen, 1842Infraorder Mylodonta McKenna andBell, 1987Superfamily Mylodontoidea Gill, 1872Family Mylodontidae Gill, 1872Subfamily Lestodontinae Ameghino, 1889

Tribe Glossotheriini McKenna, 1987Genus GGlloossssootthheerriiuumm Owen, 1839b

GGlloossssootthheerriiuumm sp.Fig. 5b

This genus was erected by Owen (1839b)based on the posterior half of a skullrecovered from Arroyo Sarandí (SorianoDepartament, Uruguay). In his BeagleDiary, Darwin (in Keynes 2001) notedthat "We heard of some giants bones, which asusual turned out to be those of the Megatherium- With much trouble extracted a few brokenfragments". As with Mylodon darwini, thetaxonomic history of Glossot-herium iscomplex. Owen (1842) erected the newspecies Mylodon robustus on remainsincluiding a nearly complete skull; andassigned to Mylodon darwini (based on adentary) the cranial fragment previouslydescribed by Owen (1839b) as Glossothe-rium. Reinhardt's (1879) detailed descrip-tion of a fossil sloth skull and mandiblefrom Pergamino (Buenos Aires Pro-vince) recognized, 1) that the mandiblewas very similar to that described asMylodon darwini by Owen (1839b), 2) thatits skull features were sufficiently distinctas to suggest generic separation from

Mylodon robustus, and 3) that the cranialfragment originally assigned by Owen(1839b) to Glossotherium was closely alliedgenerically to Mylodon robustus. Not recog-nizing Mylodon darwini as type of thegenus, Reinhardt (1879) proposed thenew genus Grypotherium, in which he pla-ced the dentary assigned by Owen(1839b) to Mylodon darwini and the speci-men from Pergamino as the speciesGrypotherium darwini; and recognized My-lodon robustus as the type species of My-lodon. Ameghino (1889) accepted the ge-neric differences noted by Reinhardt(1879), but considered, as Owen (1842)had before, that the cranial fragment ofGlossotherium and the dentary of Mylodondarwini belonged to the same species, andso included these specimens - as well asthe skull and mandible from Pergamino -in Glossotherium darwini, given that in thisscenario Glossotherium has priority overGrypotherium. Smith-Woodward's (1900)revision of Darwin's South Americanfossil sloth collection concluded that thecranial fragment originally assigned toGlossotherium was congeneric with thespecimen assigned to Mylodon robustus byOwen (1842) and that the dentary ofMylodon darwini and the specimen from

Figure 5: a) Mandible ofMylodon darwini in occlusalview (from Owen, 1839b).Scale bar = 10 cm; b)Cranial fragment of the skullof Glossotherium in lateralview (from Owen 1839b)Scale bar = 10 cm.

Pergamino, described by Reinhardt(1879), were conspecific. However, asSmith-Woodward did not recognizeMylodon darwini as type species of Mylo-don, he resurrected Reinhardt's (1879)Grypotherium. Kraglievich (1928) modified the taxo-nomy of these taxa based on a detailedrevision of the group. This author heldthat the root of the problem was therejection of Mylodon darwini as type spe-cies of Mylodon and the lack of agree-ment on the assignment of the cranialfragment assigned to Glossotherium byOwen (1839b). Once Kraglievich (1928)had established Mylodon darwini as typespecies of Mylodon, Grypotherium fell as asynonym of Mylodon. Kraglievich (1928)agreed with Reinhardt (1879) and Smith-Woodward (1900) that the cranial frag-ment of Glossotherium was congenericwith Mylodon robustus but not conspecificwith it. Consequently, and with the gene-ral understanding that Mylodon robustuswas generically distinct form Mylodon dar-wini, Kraglievich (1928) revalidated Glos-sotherium, but with two species, i.e., Glos-sotherium robustus and Glossotherium urugua-yense, the latter including Owen's (1839b)cranial fragment. These nomenclaturalconclusions were accepted by Cabrera(1936), although in this author's revisionof the species of Glossotherium, he recog-nized its two valid species as Glossotheriumrobustum and Glossotherium lettsomi (Owen),with Glossotherium uruguayense a synonymof the latter (Glossotherium lettsomi was ori-ginally assigned to Pleurolestodon lettsomi byGervais and Ameghino (1880), based onobservation of a skull exhibited in theNatural History Museum, London, thathad been labeled by Owen as Mylodon lett-somi (see Ameghino 1889).Esteban's (1996) review of Mylodonti-nae considered Glossotherium lettsomi (sen-su Cabrera 1936) a synonym of Glossothe-rium robustum, so that the cranial fragmentcollected by Darwin in Uruguay iscurrently assigned to the latter species.

Magnorder Xenarthra Cope, 1889Order Pilosa Flower, 1883

Suborder Phyllophaga Owen, 1842Infraorder Megatheria McKenna andBell, 1987Superfamily Megatheroidea Gray, 1821Family Megatheriidae Gray, 1821Subfamily Megatheriinae Gray, 1821Genus MMeeggaatthheerriiuumm Cuvier, 1796

MMeeggaatthheerriiuumm ccuuvviieerrii Desmarest, 1822Fig. 6a

Owen (1840) assigned to this species va-rious cranial fragments collected by Dar-win in Punta Alta (Buenos Aires Pro-vince). Although Darwin referred mostof the large remains he recovered toMegatherium, as shown by his field notes,Beagle Diary, and personal correspon-dence, Owen (1840) did likewise only forthe specimens collected from Punta Alta.In discussing Darwin's (in Keynes 2001,p. 107) "allied to the Rhinoceros" com-ment, we noted that it did not pertain tothe Scelidotherium skeleton but to variousskulls assigned by Owen (1840) to Mega-therium. Indeed, Darwin's comment, da-ted September 23, 1832, could only referto those skulls collected up to this time,effectively excluding Scelidotherium (see

above) from consideration, and leavingMegatherium as the only taxon to which heassigned skull material from Punta Alta.Owen's (1840) assignment to the speciesMegatherium cuvieri was based on acceptan-ce of the specific name change proposedby Desmarest (1822) for Megatherium ame-ricanum. However, this proposed nomen-clatural alteration is unsupported and thename was considered a nomen illegiti-mum by Mones (1986). In this context,the specimens assigned to Megatherium cu-vieri by Owen (1840) correspond to Mega-therium americanum.

Magnorder Xenarthra Cope, 1889Order Pilosa Flower, 1883Suborder Phyllophaga Owen, 1842Infraorder Megatheria McKenna andBell, 1987Superfamily Megatheroidea Gray, 1821Family Megalonychidae Gervais, 1855Subfamily Megalonychinae Gervais, 1855Tribe Megalonychini Gervais, 1855Subtribe Megalonychina Gervais, 1855Infratribe Megalonychi Gervais, 1855Genus MMeeggaalloonnyyxx Harlan, 1825

MMeeggaalloonnyyxx jjeeffffeerrssoonniiii (Desmarest, 1822)

J. C. FERNICOLA, S. F. VIZCAÍNO AND G. DE IULIIS154

Figure 6: a) Parasagittal sec-tion through the maxilla ofMegatherium cuvieri (=Megatherium americanum, seetext) showing the five mola-riforms (from Owen 1840).Scale bar = 10 cm; b)Mandible of Megalonyx jeffer-soni (= Mylodon darwini, seetext) in occlusal view (fromOwen 1840). Scale bar = 10cm.

The fossil mammals collected by Charles Darwin in South America ... 155

Fig. 6b

Owen (1840) assigned a mandible collec-ted by Darwin at Punta Alta (BuenosAires Province) to this species. A particu-lar feature of this specimen, figured byOwen (1840, pl. 29), is that it preservesonly one of the molariforms of the rightdentary. This agrees with the descriptiongiven by Darwin (in Keynes 2001, p. 109)for a mandible collected October 8,1832: "After breakfast I walked to PuntaAlta, the same place where I have before foundfossils… I obtained a jaw bone which containeda tooth: by this I found out that it belongs to thegreat ante-diluvial animal the Megatherium".Leidy (1852) erected a new taxon, Gna-thopsis oweni on this specimen, which Kra-glievich (1928) assigned to Mylodon darwini.

Magnorder Xenarthra Cope, 1889Order Cingulata Illiger, 1811Superfamily Glyptodontoidea Gray, 1869Family Glyptodontidae Gray, 1869Subfamily Hoplophorinae Huxley, 1864Tribe Hoplophorini Huxley, 1864Genus HHoopplloopphhoorruuss Lund, 1938

HHoopplloopphhoorruuss eeuupphhrraaccttuuss Lund, 1938Fig. 7a

In general, the carapace fragments andosteoderms collected by Darwin in SouthAmerica were assigned preliminarily toMegatherium. Certainly such assignmentswere due to Cuvier's (1823) tacit approvalof Larrañaga's (in Cuvier 1823) sugges-tion that megatheres were armored.Owen (1840, p. 107) recognized the closerelationship, still considered correct, bet-ween glyptodonts and living armadillosand remarked the following aboutHoplophorus euphractus: "The portions of thetesselated bony dermal covering of a Dasypodoidquadruped, figured in Pl. XXXII. figs. 5 and4, of the natural size, were discovered foldedround the middle and ungueal phalanges, figs. 2and 3, at Punta Alta, in Bahia Blanca, in anearthy bed interstratified with the conglomeratecontaining the remains of the fossil Edentals. In one of these fragments, measuring six incheslong by five broad, the tesserae are arranged in

rosettes, and so closely correspond in size andpattern with the bony armour described by M.Lund [1839], as characterizing his species,Hoplophorus euphractus, that I feel nohesitation in referring them to that animal".Burmeister (1870-1874) assigned the os-teoderms figured by Owen (1840, pl. 32,figs 4 and 5) to Hoplophorus ornatus (=Neosclerocalyptus ornatus) and Hoplophorus ele-gans, respectively. Ameghino (1889) syno-nymized the latter with Lomaphorus elegans.

Magnorder Xenarthra Cope, 1889Order Cingulata Illiger, 1811Superfamily Glyptodontoidea Gray, 1869Family Glyptodontidae Gray, 1869Subfamily Glyptodontinae Gray, 1869Tribe Glyptodontini Gray, 1869Genus GGllyyppttooddoonn Owen, 1839c

GGllyyppttooddoonn ccllaavviippeess Owen, 1839c

Owen (1840) tentatively assigned to thisspecies distinct osteoderms collected byDarwin from the Uruguayan locality ofArroyo Sarandí (Mercedes, of SorianoDepartament, Uruguay); and the Argen-tinean localities of Bajada Santa Fe (Pa-raná, Entre Ríos Province) and Guardiadel Monte (Buenos Aires Province).

Magnorder Epitheria McKenna, 1975Superorder Preptotheria McKenna, 1975Grandorder Anagalida Slazay and McKenna, 1971Mirorder Simplicidentata Weber, 1904Order Rodentia Bowdish, 1821Suborder Hystricognatha Woods, 1976 Infraorder Hystricognathi Tullberg, 1899 Parvorder Caviida Bryant and McKenna,1995Superfamily Cavioidea Fisher de Wald-heim, 1817Family Hydrochoeridae Gray, 1825Subfamily Hydrochoerinae Gray, 1825Genus HHyyddrroocchhooeerruuss Brisson, 1762

HHyyddrroocchhooeerruuss sp.

The fossils that Owen (1940) assigned tothis genus were collected by Darwin (inKeynes 2001) in Monte Hermoso on Oc-

tober 19, 1832. Owen (1840, p. 10) com-mented that "Mr. Darwin discovered thedecomposed molar of a Rodent, equalling insize, and closely resembling in the disposition ofits oblique component laminae, the hinder molarof the Capybara (Hydrochoerus.) The fossildiffers, however, in the greater relative breadth ofthe component laminae. I have, lastly, to notice the head of a femur, andsome fragments of pelvic bones from the sameformation which bear the same proportion to thetooth above alluded to, as subsists between theteeth and bones of the Capybara, and which aresufficient to prove that there once has existed inSouth America a species of the family Caviidæ,as large as the present Capybara, but now appa-rently extinct".These elements were among those thatDarwin (in Keynes 2001, p. 110-111) en-countered as follows: "The Captain landedfor half an hour at Monte Hermoso, (or Star-vation point as we call it) to take observations. -I went with him & had the good luck to obtainsome well preserved fossil bones of two or threesorts of Gnawing animals. - One of them musthave much resembled the Agouti but it is sma-ller". Even so, it is not possible to deter-mine which of the remains Darwinthought similar to an agouti, though it isworth noting that what Darwin conside-red an agouti was a Patagonian hare(Darwin, in Keynes 2001, p. 103).The following Hydrochoeridae are cu-rrently recognized from the fossiliferoushorizons of Monte Hermoso: Phugathe-rium cataclisticum, Anchimysops villalobosiand Chapalmatherium perturbidum. Vucetichet al. (2005) considered the type speci-mens of the first two species to representjuvenile individuals and that they mightbe conspecific with Chapalmatherium per-turbidum. If this is correct, then the validname, as determined by Vucetich et al.(2005), for the species would be Phu-gatherium cataclisticum. In this respect, thespecimen collected by Darwin mightrepresent this latter species.

Magnorder Epitheria McKenna, 1975Superorder Preptotheria McKenna, 1975Grandorder Anagalida Slazay and McKenna, 1971

Mirorder Simplicidentata Weber, 1904Order Rodentia Bowdish, 1821Suborder Hystricognatha Woods, 1976 Infraorder Hystricognathi Tullberg, 1899 Parvorder Caviida Bryant and McKenna,1995Superfamily Octodontoidea Waterhouse,1839 Family Octodontidae Waterhouse, 1839Subfamily Octodontinae Waterhouse,1839 Genus CCtteennoommyyss Blainville, 1826

CCtteennoommyyss pprriissccuuss Owen, 1840Fig. 7b

This species was erected by Owen (1840)based on remains collected by Darwin (inKeynes 2001) on October 11, 1832.Owen (1840, p. 109) allocated to this spe-cies a "…fragment of the upper jaw, figured inPl. XXXII. fig. 6" and a "...fragment of thelower jaw of the same fossil Rodent . figured atfig. 10 and 11". It should be noted thatOwen's (1840) figure 6 possibly does notrepresent an upper jaw, but a posteriorfragment of a mandible that may corres-pond to the posterior part of the mandi-ble figured by Owen (1840, figs. 10, 11)(D. Verzi, pers. comm.).Mones (1994) provided a detailed discus-sion of the taxonomy of Ctenomys priscus,concluding that it might belong to thegenus Dicoelophorus, erected by Ameghino(1888). However, the generic namecurrently in use for this species is Ac-tenomys, erected by Burmeister (1888).The reasons for maintaining Actenomyswere clearly set forth by Verzi (1994, p.183), as follows "Dicoelophorus Ame-ghino, 1888 es, por prioridad, un sinónimo "se-nior" de Actenomys Burmeister… . Sin em-bargo, luego de que Reig (1958) adoptara elnombre genérico Actenomys para todos losmateriales referibles a las formaciones MonteHermoso y Chapadmalal, este nombre ha sidoampliamente usado hasta el presente por lo cualnosotros nos inclinamos a mantenerlo".

Rodentia

A third rodent was briefly described by

Owen (1840) but not assigned to a genus.Owen (1840, p. 110) described "The por-tion of the right hind-foot of the Rodent figuredat fig. 12, includes the calcaneum, astragalus,cuboides, external and middle cuneiform bones,and the metatarsals and proximal phalanges ofthe toes corresponding with the three middle toesof five-toed quadrupeds. The metatarsals arechiefly remarkable for the well-developed double-trochlear articular surface, and intermediate rid-ge. These remains, as well as the jaws and teethof the Ctenomys, were discovered at MonteHermoso in Bahia Blanca". These pedal re-mains are possibly those that Darwin(1985, Letter 192) described in a letter,dated November 12, 1832, to John Ste-vens Henslow as "the Tarsi & Metatarsivery perfect of a Cavia" although it is notpossible to determine this with certainty.

Mastodonts and armored megatheres

As noted in the preceding historical sum-maries, the large South American fossilmammals recognized by Cuvier (1823)amounted to an armored megathere andthree mastodonts. A detailed considera-tion of Darwin's preliminary assign-ments demonstrates that he was stronglyinfluenced by Cuvier's taxonomic sche-me. In essence, the fossil specimens re-cognized by Darwin may be grouped aslarge vs. medium and small mammals.Among the latter is the first fossil of aSouth American horse, obviously identi-fied as such by Darwin, and three ro-dents, two of which were assigned byDarwin to Cavia and the Patagonian hare(Dolichotis patachonica), whereas the thirdwas later considered by Owen (1840) as

representing the genus Hydrochoerus.Among the large mammals, Darwin re-cognized an enormous rodent and fourgenera: Rhinoceros, Megalonyx, Megatheriumand Mastodon. The first two listed do notappear in Cuvier's (1823) taxonomic listof fossil South American mammals. Theassignment to Rhinoceros was the firstsuch attempt by Darwin (in Keynes 2001,p. 107) for a South American fossil skull,collected during his first visit to PuntaAlta (September, 1832). However, thisassignment does not appear in the taxo-nomic list of specimens collected fromPunta Alta and Monte Hermoso sent toJohn Stevens Henslow (Darwin 1985,Letter 192). Darwin may possibly havechanged his first impression, but it is noteasily ascertainable with the availableevidence.The only mention of Megalonyx appearsin the previously noted list as "2nd the upperjaw & head of some very large animal, with 4square hollow molars.-& the head greatly pro-duced in front.- I at first thought it belongedeither to the Megalonyx or Megatherium.- Inconfirmation, of this, in the same formation Ifound a large surface of the osseous polygonalplates, which “ate observations” (what are they?)show belong to the Megatherium.- Immediately Isaw them I thought they must belong to an enor-mous Armadillo, living species of which genusare so abundant here…". In this as in manyother cases (see below) Darwin decidedin favor of Megatherium based on the pre-sence of osteoderms collected in thesame formation.Owen (1838-1840) recognized the speci-mens assigned by Darwin to Megatheriumas glyptodonts, toxodonts, and large

J.C. FERNICOLA, S.F. VIZCAÍNO AND G. DE IULIIS156

Figure 7: a) Osteodermsassigned by Owen (1840) toHoplophorus euphractus (=Neosclerocalyptus ornatus, seetext) in dorsal and lateralviews (from Owen 1840).Scale bar = 1 cm; b) Maxillaand mandible assigned byOwen (1840) to Ctenomyspriscus (= Actenomys priscus,see text) (from Owen 1840).Scale bar = 5 mm.

The fossil mammals collected by Charles Darwin in South America ... 157

ground sloths. In our estimation, the on-ly factor that led Darwin to assign re-mains of such a heterogeneous group offorms to Megatherium was the presence ofosteoderms or carapace fragments in thesame horizon. In effect, all the specimensthat Darwin assigned to Megatherium wererecovered from the Arroyo Sarandí (Uru-guay) and Punta Alta (Argentina), andDarwin also reported carapace elements.Further evidence supporting our conten-tion appears in Darwin's (1985, Letter215) letter of September 20, 1833 sent toCaroline S. Darwin, in which he wrote"At the Guardia del Monte, I found some moreof the armour of the giant Megatherium,which was to me very interesting, as connectingthe Geology of the different parts of the Pam-pas". Indeed, Darwin used the presenceof osteoderms as a diagnostic feature ofMegatherium.In this context, one might hypothesizethat it was the absence of osteoderms inthe layers yielding the only Santa Cruzspecimen, which led Darwin to regardthis specimen as follows: "At Port St Ju-lian I found some very perfect bones of somelarge animal, I fancy a Mastodon" (Darwin1985, Letter 238) and Darwin (1839) lateradmitted that "I had no idea at the time, towhat kind of animal these remains belonged".Certainly, this is the only mention ofMastodon that was not later corroboratedby Owen (1838-1840).Lastly, Toxodon was the only species theremains of which Darwin (1985, Letter192, 2002-2008) assigned to differentspecies. Darwin assigned a molar collec-ted in Punta Alta to an enormous rodentand a skull from Arroyo Sarandí to Megat-herium. The latter assignment makessense in that the horizon yielding theskull also preserved osteoderms, whereasDarwin's inference on the molar isunderstandable given that the teeth ofToxodon, as noted by Owen (1838), bear acertain resemblance to those of rodents.

Implications of the "erroneous" as-signments of the youthful Darwin

Twenty years before the publication of

the Origin of Species and only two years af-ter he had begun recording his thoughtson transmutation, Darwin (1839, p. 209-210) had this to say about the SouthAmerican paleofauna: "The most importantresult of this discovery, is the confirmation ofthe law that existing animals have a close rela-tion in form with extinct species. As the guana-co is the characteristic quadruped of Patagonia,and the vicuna of the snow-clad summits of theCordillera, so in bygone days, this gigantic speciesof the same family must have been conspicuouson the southern plains. We see this same relationof type between the existing and fossil Cte-nomys, between the Capybara (but less plain-ly, as shown by Mr. Owen) and the giganticToxodon; and lastly, between the living andextinct Edentata. At the present day, in SouthAmerica, there exist probably nineteen species ofthis order, distributed into several genera; whilethroughout the rest of the world there are butfive. If, then, there is a relation between the livingand the dead, we should expect that theEdentata would be numerous in the fossil state.I need only reply by enumerating the Megathe-rium, and the three or four other great species,discovered at Bahia Blanca; the remains of someof which are also abundant over the whole im-mense territory of La Plata. I have alreadypointed out the singular relation between thearmadilloes and their great prototypes, even in apoint apparently of so little importance as theirexternal covering". Similarly, Darwin (1845,1859, p. 339) noted that "In South Ame-rica, a similar relationship is manifest, even toan uneducated eye, in the gigantic pieces of ar-mour like those of the armadillo, found in seve-ral parts of La Plata; and Professor Owen hasshown in the most striking manner that most ofthe fossil mammals, buried there in such num-bers, are related to South American types… …I was so much impressed with these facts that Istrongly insisted, in 1839 and 1845, on this'law of the succession of types,'-on 'this wonder-ful relationship in the same continent between thedead and the living".As noted by Sulloway (1982), the role ofthe naturalists who studied the SouthAmerican fauna was critical to the deve-lopment of Darwin's transformationistideas in that they provided a systematicframework. In reference to Darwin's

erroneous taxonomic assignments, Sullo-way (1982, p. 353) recognized that "Thegeneral effect of these confusions during the Bea-gle voyage was to minimize the evolutionaryimplications of the diverse fossil forms".Paradoxically, many of Owen's (1838-1840) proposed relationships that soinfluenced Darwin (1839, 1845, 1859) inthe development of his transformatio-nist theory were later rejected. Indeed,toxodonts and macrauchenids are highlyderived native South American ungulatesdistantly related phylogenetically torodents and guanacos, whereas the largeglyptodonts are not the ancestors ofarmadillos, but to the contrary, the latterare antecedent to the former. In this res-pect, we may suppose that the affinitiesproposed by Owen (1838-1840) maximi-zed the evolutionary implications of theSouth American paleofauna.

ACKNOWLEDGMENTS

We are grateful to the editors for the invi-tation to participate in this special issueof Revista de la Asociación Geológica Argen-tina, and to Greg McDonald and MarianoBond for their thoughtful comments andsuggestions that improved the manus-cript. Andrew Currant, Curator of FossilMammals Palaeontology, Natural Histo-ry Museum London, Simon Chaplin, Di-rector of Museums and Special Collec-tions and Sarah Pearson, Assistant Cu-rator, The Royal College of Surgeons ofEngland, for information on Darwin'sfossil mammal collections, and LouiseKing, Assistant Archivist of The RoyalCollege of Surgeons of England, forinvaluable help on the bibliography.

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APPENDIX 1

List of fossil mammal specimens collec-ted by Charles Darwin and housed in theNatural History Museum, London,England (provided by Andrew Currant,Curator of Fossil Mammals), and in theRoyal College of Surgeons of England(provided by Simon Chaplin, Director ofMuseums and Special Collections). Ab-beviations. RCSHM/CO: Royal Collegeof Surgeons of England Hunterian /College Museum. RCS: Royal College ofSurgeons of London. NHM: NaturalHistory Museum, London.

EEqquuuuss sp. NMH M16557: left uppermolar (ex RCS2012). NMH M16558:left upper molar (ex RCS2013).GGlloossssootthheerriiuumm sp. NMH M16586 part ofcranium (ex RCS3491).MMaacchhrraauucchheenniiaa ppaattaacchhoonniiccaa.. Holotype NMHM43402: vertebral fragments (ex NMHM16556 and ex RCS2209); detached pro-ximal and distal ends of right tibia andfibula (ex NMH M16559 and ex RCS2215); right femur (ex NMH M16561

and ex RCS2214); right astragalus (exM16569 and ex RCS2216); middle cervi-cal vertebrae (ex NMH M16570 and exRCS2208); fragments of pelvis (ex NMHM16571 and ex RCS2210); proximal endof fused radius and ulna (ex NMHM16572 and ex RCS2212); metacarpalsand phalanges of the right manus (exNMH M16573 and ex RCS2213); incom-plete left scapula (ex NMH M16574 andex RCS2211); metatarsal (ex M16575 andex RCS2216).MMeeggaatthheerriiuumm aammeerriiccaannuumm.. NMH M16585,posterior part of cranium (ex RCS3445);NMH M16588, fragment of left maxillawith M2 and M3 in horizontal section (exRCS3446); NMH M16589, part of lefttemporal (ex RCS3457). RCSHM/CO3443 fragment of cranium with teeth.MMyyllooddoonn ddaarrwwiinnii.. Holotype NMHM16563: mandible (ex RCS3490).MMyyllooddoonn ddaarrwwiinnii.. NMH M16587: frag-ment of left dentary with transverse sec-tion of teeth (ex RCS3491).SScceelliiddootthheerriiuumm lleeppttoocceepphhaalluumm.. Holotype:NMH M16579, deformed skull withhorizontal section taken from right den-tary (ex RCS3506); Holotype: NMHM16580, upper molariform (ex RCS3507); Holotype: NMH M16581, cervi-cal vertebrae (ex RCS3510); Holotype:NMH M16582, parts of ribs (ex RCS3511); Holotype: NMH M16583, leftastragalus (ex RCS3520); Holotype:M16584, right astragalus with distal endof right tibia (ex RCS3519).TTooxxooddoonn ppllaatteennssiiss.. Holotype NMHM16560: incomplete cranium lackingteeth (ex RCS2223).TTooxxooddoonn ppllaatteennssiiss.. NMH M16562 rightM2 (ex RCS2224); NMH M16564 partof left dentary with fragments of fourmolars (ex RCS2226); NMH M16565right lower molar (ex RCS2227); NMHM16566 fragment of right dentary withincisor roots and most of the molars (exRCS2225); NMH M16567 left lowerincisor (ex RCS2228); M16568 fragmen-tary teeth (ex RCS 2229).

Recibido: 25 de agosto de 2008 Aceptado: 7 de noviembre de 2008