Journalof Biogeography (1 980) 7, 11-22

Raftingmammals or driftingislands?: biogeographyof theGreater Antillean insectivores Nesophontesand Solenodon

BRUCE J.MAC FADDEN FloridaState Museum, University of Florida, Gainesville,Florida 32611, U.S.A.

ABSTRACT.During the late Mesozoicand earlyCenozoic, certain soricomorph insectivoreswere distributed throughout North America, Nuclear Central America, and the proto-Antilles.A regionaltectonic reorganization during this time resultedin the decouplingof Caribbeanlithosphere from surrounding plates and movementof the Greater(proto-) Antilles eastward relative to the Americas. This movementresulted in biogeographicsubdivision (vicariance sensu Rosen, 1975) of the ancestralsoricomorph distribution. As far as we know, the Americanpart of the distribution,represented by apternodontidsand possibly geolabidids,became extinct by thelate Oligocene.The GreaterAntillean part of the distribution,represented by Nesophontesand Solenodon,has persisted throughto the Recent.In short,these Caribbean insectivores are islandrelicts of a once morewidespread ancestral distribution of soricomorphinsectivores. Similardistributional evidence from numerous other elements of theCaribbean biota supportthe biogeographichypothesis proposed forNesophontes and Solenodon.

'I do not deny that there are many and grave the absence of 'top' carnivores.Phylogenetic- difficultiesin understandinghow several of ally primitiveforms, or 'relicts,' tend to be the inhabitants of the more remote islands, preserved in island biotas. In recent years whetherstill retainingthe same specific form much work has been done on quantitative or modified since their arrival, could have descriptionsof island biotas (e.g. MacArthur, reached theirpresent homes.' 1972; Simberloff, 1974). Hypotheses that Charles Darwin (1859, p. 396) explain the origin of these biotas from an external source have been assumed to be adequate when dealing with easily dispersed forms such as plants and mobile animals, but Introduction fall short when considering immobile and exclusivelyterrestrial animals. Biogeographers have long recognized the The Greater Antilles possess a peculiar peculiarities of island biotas. Darwin (1859) assemblage of relict insectivoresthat include discussed this problem as seen in the Gala- the genera Nesophontes and Solenodon. pagos. It is known that islandstend to exhibit Workers such as Matthew (1939), Simpson a high degree of endemism. Biotic diversity (1956) and Patterson (1962) have tradition- is lower on islands than on mainland regions ally explained the presence of these insecti- with comparable areas. Frequently islands vores in the Caribbean by sweepstakes, or show an apparent ecological imbalance of overwater dispersal from the Americas. trophic group structure,for example, with Recently, Rosen (1975) hypothesized that 0305-0270/80/0300-0011$02.00 ? 1980 BlackwellScientific Publications 11 12 Bruce J. MacFadden

virtuallythe entireCaribbean biota, including However, when dealing with groups with Nesophontes and Solenodon, was biogeo- relatively poor fossil records, one is never graphicallyseparated (by vicariance) froman sure if the oldest representativesare in fact ancestral American biota as a result of plate closest to the centre of origin. Centres of tectonics in that region. The purpose of this origin and subsequent dispersal events are paper is to extend Rosen's study and focus hypothesized with some confidence in geo- on the biogeographic origin of Nesophontes chronologically controlled sequences for and Solenodon throughexamination of rele- certain abundant groups, such as marine vant phylogeneticand geologicalinformation. planktonic microfossils and late Cenozoic mammals. The problem remains as to when a fossil group is well enough sampled and Models of vertebratebiogeography supported by enough temporal data so that discussions of biogeography are meaningful. Matthew (1939) and Simpson (1940, 1952, The solution to this dilemma is certainly and numerous other references)were instru- elusive. mental in the formulationof a widely used Croizat, Nelson & Rosen (1974) summa- biogeographicmodel for terrestrialmammals. rized the 'vicariance' model by which syste- Simpson's model includes the concept of matists can reconstruct the biogeographic sweepstakes, filter, and corridor dispersal history of monophyleticgroups by analysing routes. The 'traditional (Matthew-Simpson) cladistic interrelationshipsof constituenttaxa dispersal' model for mammals was founded (also see more recent discussion by Rosen, on the assumption that the relativepositions 1978, and Platnick& Nelson, 1978). Ancestral of continents have remained stable through- geographic distributions of taxa may be out geological time. Recent discussions of separated by the formation of barriers vertebratebiogeography that modifythe ideas (vicariance). The separation of ancestral of Matthew and Simpson in the light of distributions results in evolutionary diver- plate tectonics have been presented by gence (e.g. allopatric speciation) of the taxa workers such as McKenna (1972, 1973), involved. This process of biogeographicsub- Hallam (1974), Cracraft (1974) and Cox division could have occurred numeroustimes, (1974). Many of these studies incorporate resulting in repeated events of speciation. the recognitionof centresof originand subse- Withinthe groups being studied, more recent quent direction of dispersal for faunas or biogeographic subdivisions (and allopatric particularfaunal constituents. speciations) would result in more closely Centres of origin can be recognized for related species (or sister) groups. Evidence taxa that have undergone dispersal during from other groups of organismswith similar historical times, e.g. the introduction of phylogeneticand biogeographichistories could starlings (Sturnus vulgaris) into North be used to support an hypothesis of the America (Krebs, 1972), rabbits (Oryetolagus biogeographic subdivision events. Vicariance cuniculus), into Australia (Ricklefs, 1974), has been used to explain the biogeography and the northward spread of the nine- of spiders (Platnick, 1976), corals, seagrasses banded armadillo (Dasypus novemcinctus) and mangroves(McCoy & Heck, 1976), and into southern North America (Humphrey, parts of the Caribbean biota, particularly 1974). In prehistoricaltimes, recognitionof fishes(Rosen, 1975). centres of origin becomes somewhat more The vicariance model is not a panacea for complex. Some biogeographersworking with interpretingall biotic distributions; but it wholly extant taxa state that, withina mono- does provide an elegant explanation for phyletic group, the most primitivetaxon will organismswhose biogeographyhas been pro- be closest to the centreof origin.Others state foundly influenced by barriers,such as those that the most derivedtaxon will be closest to produced by plate tectonics.Despite claims to the centreof origin.Dispersal hypotheses used the contrary, vicariance is not generally by palaeontologists usually assume that the applicable to many relativelyrecent biogeo- older fossil record of a group in one area graphic subdivisions.A complex biota might indicates a closeness to the centre of origin. have been affected by several major biogeo- Antillean insectivorebiogeography 13

graphicevents which producedits present- The insectivoresinclude the generaNeso- day taxonomic composition.As McDowall phontes and Solenodon. Nesophontes consists (1978) has shown,the biogeographichistory of at least six species foundpredominantly of a complex biota could combine both in Quaternary cave deposits on Cuba, vicarianceand traditionaldispersal models. Hispaniola, Puerto Rico, and smallersur- roundingislands (Allen, 1918; Koopman & Ruibal, 1955; McDowell, 1958).Nesophontes Antilleaninsectivores has beenreported to be extantuntil as recently as the 1930s. A possibilityexists that this Knowledgeof the Antilleanbiota has greatly genusstill may be extant.During the begin- increasedsince the turnof the centuryas a ningof thiscentury, some naturalistsclaimed result of numerousnatural history expedi- that Solenodon had become extincton His- tions to this region.Classic papers dealing paniola. Verrill(1907, p. 55) stated that: withthe fossiland extantmammals collected 'For manyyears it has been commonlycon- duringthe early expeditionswere published sidered extinct, and when, in December, by G. M. Allen (e.g. 1911, 1918) and 1906, I undertooka collectingtrip to San Anthony(e.g. 1918). Particularlycentral to Domingo with the avowed intention of the presentdiscussion, Matthew (1939), in obtainingSolenodon, prominentzoologists his Climate and evolutdon,devoted an entire stated that the quest was hopeless,one of chapter to the biogeographyof Antillean themsaying that I wouldbe as likelyto secure mammals.In recentyears numerous Antillean specimensof ghosts as of Solenodon para- studies have been presentedon Quaternary doxus.' Solenodon is representedby at least cave faunas(e.g. Koopman& Ruibal, 1955; two extantand severalextinct species from Varona & Garrido,1970), generalsurvey of Cuba and Hispaniola (McDowell, 1958). mammals(Varona, 1974), bats (e.g. Silva- Patterson(1962) named a new solenodon, Taboada & Koopman, 1964), primates Antillogale,from Quaternarycave deposits (Williams& Koopman, 1952; Hershkovitz, in Hispaniola.Van Valen (1967) questioned 1970), rodents(e.g. Varona,1970), edentates the genericvalidity of Patterson'sAntillogale; (e.g. Matthew& de PaulaCouto, 1959) insecti- Solendon is used here in a broad sense to vores(e.g. McDowell,1958; Patterson,1962) includeit. and zoogeography (e.g. Simpson, 1956; Nesophontes and Solenodon are shrew-like Hershkovitz,1972). It was soon recognized in their morphology.This similarityis evi- that the Caribbean mammalsdemonstrate dencedin theirskulls, dentitions, postcranials, characteristicspeculiar to island faunas. and, for Nesophontes, size. Solenodon is Notably,mammalian ordinal diversity is low, certainlylarger than most shrewsand has representedby primates, bats, rodents, body lengthsof about 15-16 cm and weights edentatesand insectivores. of 40-46g (data for S. paradoxusborn in

FIG. 1. Adult female of Solenodon paradoxus Brandt1833 (taken fromAMen, 1910, plate 3). Approxi- matelya quarter naturalsize. Reproducedwith the permissionof the Museumof ComparativeZoology, HarvardUniversity. 14 BruceJ. MacFadden captivity;see PeniaFranjul, 1977). Solenodon methodology and classification (see e.g. is nocturnal and lives in caves, burrows and Hecht, 1976); however, many of the ideas rotted trees. Its elongate rostrum(Fig. 1) is incorporated in his work, whether new or often used for diggingto obtain food, which resurrected from previous studies, will un- consists of various small animals, fruitsand doubtedly stimulateideas concerninga group vegetables (Verrill,1907; PefiaFranjul, 1977). for which higher-leveltaxonomic innovation The morphologicalresemblance of the Antil- has been largelywanting. lean insectivoresto shrews,although of large There has been a long-standingrecognition size in the case of Solenodon, has been used of Haeckel's two major insectivore subdivi- in support of phylogeneticrelatedness (e.g. sions, the Menotyphla and the Lipotyphla. McDowell, 1958) or has been dismissed as The Menotyphla includes the extant macro- convergentevolution (Van Valen, 1967). scelidids and tupaiids and severalfossil groups (Simpson, 1945; Patterson, 1965; Van Valen, 1967; Butler, 1972). Essentially following Phylogeneticrelationships of soricomorph Butler (1972), McKenna (1975) chose to insectivores exclude menotyphlansfrom the Insectivora. In this scheme the Insectivora are equated The Insectivorarepresent one of the greatest with Haeckel's Lipotyphla, which can be problemsin systematics.Until recently,many treated as a natural, or monophyletic,group workershad used thisgroup as a polyphyletic, based on the shared-derivedcharacters pre- or horizontal, 'wastebasket' for primitive, sented in Table 1. These characterscorroborate archetypical,eutherians. In a novel and some- dichotomy 1 in Fig. 2. what controversialapproach, McKenna (1975) Saban (1954) proposed two major lipo- presenteda cladisticanalysis of the Mammalia, typhlansubdivisions, the Erinaceomorphaand and in the process reorganizedthe traditional Soricomorpha. These two are represented insectivoregroups (see discussion below). For as most closely related taxa (sister-groups) the systematicspresented in this discussion, by points 2 and 3 in Fig. 2. McKenna (1975), McKenna (1975) and numerous other works incorporating earlier interpretations (e.g. (cited therein) have been used. Objections Gregory, 1910), has changed the taxonomic have been raised concerning McKenna's content of Saban's insectivore subdivisions.

TABLE 1. Synopsisof shared-derivedcharacters used to corroboratebranching points in Fig. 2 *

Branching Taxon Shared-derivedcharacters References point

1 Insectivora= Loss of caecum of gut,jugal bone reduced, Butler(1972), McKenna Lipotyphia maxillarybone expanded in orbitalwall, (1975) and numerous medial branchof internalcarotid artery otherscited therein lost, and reduced pubic symphysis. 3 Soricomorpha Jugalbone lost, ectopterygoidlaminae reduced, McDowell (1958), entoglenoidprocess modified into a post- McKenna (1975) glenoidprocess. 5 'Solenodontoids' Narrowtubular snout, zygomaticarch lost, McDowell (1958), posteriorlyshifted optic foramen,large McKenna (1960), and anteriorlyshifted lacrimal foramen, Butler(1972), shortenedand anteriorlyshifted infra- McKenna & Lille- orbitalcanal. graven(1979), McKenna (1979), McKenna (pers. comm. 1977) 7 Unnamed Positionof originof levatorlabii superioris, McDowell (1958) funnel-likelacrimal foramen, buccal styles on molars.

* Points2, 4 and 6 in Fig. 2 are primitivearbitrary operational taxa (see discussionin text). Antilleaninsectivore biogeography 15

revisionof thisgroup is in progress(McKenna, 6 1979). Apternodus and other apternodontids are known from middle Eocene to middle Oligocene deposits of North America (McKenna, Robinson & Taylor, 1962; Emry, Bjork & Russell, 1979; McKenna, 1979). Apternodontids seem to have been biogeo- graphically widespread; they are known to 5 Solenodontolds have ranged as far north as Montana (Emry et al., 1979; McKenna, 1979) and as farsouth 3 Soricomorpha as Texas (Novacek, 1976a). The geolabidids are known from Eocene 1 Insectivoras Lipotyphia early to late Oligo- cene deposits of North America (McKenna FIG. 2. Hypothesis of phylogeneticrelationships & Lillegraven,1979). (cladogram) of insectivore taxa relevant to the Many workers have recognized a close present discussion. Points 2, 4 and 6 represent arbitraryoperational taxa. Shared-derivedcharacters relationship between apternodontids and used to corroboratedichotomies 1, 3, 5 and 7 are Solenodon. This relationship is most often listedin Table 1. supported by the shared presence of zalamb- dodont dentitions.On the other hand, Neso- He considered the Erinaceomorpha to be phontes has a dilambdodont dentition plesiomorphouslipotyphlan insectivores. It is (McDowell, 1958) and geolabidids have been not centralto the presentdiscussion to corro- characterized as having 'incipient zalamb- borate whether or not this subdivision is dodont' dentitions(McKenna, 1960). Despite natural; for our purposes we can treatit as an problems encountered when dealing solely arbitrary'operational taxon' that is the primi- with dentitions, there are several cranial tive (plesiomorphic) sister-group of the characterslisted in Table 1 that corroborate Soricomorpha. dichotomy 5 in Fig. 2 and thereforeunite The Soricomorpha are set apart from the apternodontids,geolabidids, Nesophontes and Erinaceomorpha as a natural taxon at dicho- Solenodon as a monophyletic group, the tomy 3 in Fig. 2 based on the shared-derived Solenodontoids. characters presented in Table 1. For the Point 6 in Fig. 2, which includes apterno- present analysis, the 'Other Soricomorpha', dontids and possibly geolabidids, represents representedby point 4, is also treated as an the primitivesister group of Nesophontes and arbitrary operational taxon whose detailed Solenodon. McDowell (1958) concluded that, interrelationshipsare not central to this based on cranial characters,apternodontids discussion. This taxon is merely used as a were not at all closely related to Solenodon primitive(and potentiallyunnatural, or poly- and Nesophnontes. Furthermore, apterno- phyletic) sister-groupof those taxa united at dontids were not even considered to be dichotomy 5. The Other Soricomorpha at soricomorphinsectivores. This view is a rather point 4 include several families listed in radical depa*ture from other studies that McKenna (1975; also see Saban, 1954; Van identifya close relationshipbetween, at least, Valen, 1967; Butler, 1972; Schmidt-Kittler, apternodontidsand Solenodon (e.g. Matthew, 1973). 1910; Van Valen, 1967; Butler, 1972; Dichotomy 5 in Fig. 2 representsa mono- McKenna, 1975). In all fairnessto McDowell's phyletictaxon thatis called,for this discussion, thoroughstudy, his interpretationswere based the 'Solenodontoids' (the informal suffix is on a smaller sample of relevantApternodus used here to avoid proposinga formaltaxon). than is presentlyavailable. Butler (1972) and As envisaged here, the Solenodontoids McKenna (1975, see especially p. 38; pers. include the Greater Antillean genera Soleno- comm., 1977; 1979) forcefullyargue for a don and Nesophontes, apternodontids, and close relationship between apternodontids, possibly geolabidids. The apternodontidshave geolabidids, Nesophontes and Solenodon. In been described by numerous workers (e.g. short, the geolabic1ids are here tentatively Matthew, 1910; McDowell, 1958), and a placed with the apternodontidsat point 6 in 16 Bruce J. MacFadden

Fig. 4 as an arbitrary operational taxon analysis presented here. The importantcon- pending any modification warranted by the clusion to be derived from this analysis is studies presentlyin progress(McKenna, 1979; that the apternodontids and possibly geo- McKenna & Lillegraven,1979). labidids, on the one hand, and Nesophontes Dichotomy 7 in Fig. 3 unitesNesophontes and Solenodon, on the other,are almostclosely and Solenodon as most closely related sister related sister-groupsforming the monophy- groups based on the characterslisted in Table letic taxon Solenodontoids withinthe shrew- 1. This hypothesis of close relationship like, or soricomorph,insectivores. between Nesophontes and Solenodon has been suggested by workers such as Allen (1918), McDowell (1958) and Weingart Caribbean plate tectonics (1974). McDowell (1958, p. 121) stated that: 'One author, G. M. Allen (1918), has ques- Based on a review of primarysources, Rosen tioned this prevailingview [based on dental (1 975) presentedan analysis of the geological morphology] and pointed out that in most events in the Caribbean regionrelevant to the features of osteology Solenodon and Neso- present biogeographic considerations. The phontes are very similar, and that dental hypothesis of Caribbean geological history differences are not irreconcilable .. . Solenodon presented here is similarto that discussed in is, indeed, very closely related to Neso- Rosen (1975), with the addition of some phontes. ..' more recent primary source references. It It is realized that readers familiarwith the should be emphasized that this is merelyone problems of insectivoresystematics may take hypothesis based on existingdata and alter- exception to certain aspects of the cladistic nativescould certainlybe proposed.

A B C

NORTH AMERICA

NUCLEAR CENTRAL AMERICA

GREATER ANTILLES

PROTO- LOWER ANTILLES CENTRAL AMERICA

SOUTH AMERICA

LATE MESOZOIC LATER MESOZOIC- LATER CENOZOIC EARLY CENOZOIC FIG. 3. Schematicrepresentation of Caribbeanplate tectonicsshowing events relevant to presentdiscus- sion. (A) During the late Mesozoic the proto-Antilleswere in between Nuclear Central Americaand South America. (B) During the later Mesozoic and early Cenozoic a major regionaltectonic reorgani- zation resultedin the relativeeastward movement of the GreaterAntilles (on the Caribbeanplate). This relative movementwas certainlyinitiated by Eocene time. (C) Duringthe later Cenozoic the Greater Antilles have continued relativemovement to their present-dayposition. Also see discussionin text (fi'gureadapted fromRosen, 1975). Antilleaninsectivore biogeography 17

During the late Mesozoic an island arc Greater Antilles,it is difficultto demonstrate system termed the 'proto-Antilles' (Fig. 3) that these islands were continuouslyabove sea lay to the south of North America and level prior to the Cenozoic. Since the early Nuclear Central America and to the north of Cenozoic the sedimentary record indicates South America (see Malfait & Dinkelman, shallowwater or terrestrialpalaeoenvironments 1972; Rosen, 1975). At this time the Carib- (Schuchert, 1935; Malfait & Dinkelman, bean lithospherewas part of the Pacific and 1972; Perfit & Heezen, 1978). Khudoley & American plates. During the later Mesozoic Meyerhoff(1971) presentedpalaeogeographic and early Cenozoic a major tectonicreorgani- maps forthe Cenozoic of the GreaterAntilles. zation resultedin the decouplingof Caribbean These maps clearly demonstratethat there is lithosphere from the surrounding plates. no time duringthe Cenozoic when all of these During the process of decoupling in late islands were entirely submerged. In fact, Cretaceous and early Cenozoic times the tec- relatively large land masses, with areas in tonic reorganization resulted in relative excess of thousands of square kilometres, eastward movement of the Caribbean plate are indicated thrcughout post-Eocene times with respect to the American plates (e.g. forat least Hispaniola and Puerto Rico. Ladd, 1976; Jordan, 1975; Bowin, 1976; In summary,it is possible to hypothesize Christofferson,1976). Perfit& Heezen (1978), that since at least the Eocene the Greater based on studies of sea-floorspreading in the Antilles (nee proto-Antilles,and excluding Cayman trench,state that the decouplingand most of Cuba) have moved a significantrelative relative eastward movementof the Caribbean distance eastward with respect to Nuclear plate was initiatedno later than Eocene time. Central America. Furthermore, it is also This relative plate movementwould result in plausible at least some relativelylarge areas the eastward migrationof the proto-and then of the Greater Antilles have been above sea Greater Antilles away from Nuclear Central level since the late Cretaceous or early Ceno- America to their present-dayposition. Based zoic when eastward relative movement on rates of sea-floorspreading in the Cayman initiated. trench,which have been stated to rangefrom 0.5 to 2 cm/yr(references in Perfit& Heezen, 1978), the absolute amount of eastward Biogeographyof GreaterAntillean insectivores relative movement since at least the Eocene of the proto-and GreaterAntilles with respect The presence of mammals on the Greater to Nuclear Central America has indeed been Antilles has generallybeen attributedto dis- significant,with possible estimates ranging persal from the Americas. Some workers froma minimumof severaltens of kilometres (e.g. Barbour, 1914) have suggesteddry land to a maximum of several hundreds of kilo- connections for this dispersal route, but the metres. majorityhave suggestedoverwater, or island- It is importantto note here that most of hopping, routes (e.g. Darlington, 1938; the island of Cuba has not been part of the Matthew, 1939; Simpson, 1956; Hershkovitz, Caribbean plate. Malfait & Dinkelman (1972) 1972; Patterson & Pascual, 1972). Many suggestedthat the northernboundary of the workers have stated that the mammalian Caribbean plate is below the southeastern fauna of the GreaterAntilles probably resulted portion of Cuba. There are major problems from several dispersal events during the yet to be resolved concerningthe position of Cenozoic. Principallybecause of theirphylo- the remainder of Cuba with respect to the genetic primitivenessit has been assumed NorthAmerican and Caribbean plates. For the that Nesophontes and Solenodon resulted purposes of this discussion,it will be assumed from one of the earlier dispersal events. that most of Cuba has not had the same geo- Patterson (1962, p. 10) stated that: 'The logical history as the 'passengers' on the possibility,I would go so far as to say proba- Caribbean plate. As used here, the term bility, exists that solenodontidswere derived 'Greater Antilles' excludes Cuba (see impli- from relativelyunspecialized apternodontids cations forinsectivore biogeography below). that inhabitedthe CentralAmerican peninsula With regardto the palaeogeographyof the duringthe earlier Tertiary.'These hypotheses 2 18 Bruce J. MacFadden have generally incorporated traditional 1960; 1979; McKenna et al., 1962; Novacek, dispersal models. The major point of this 1976a, b). Patterson (1962) and Novacek paper is that plate tectonic movementsin the (1976b) have suggested that soricomorphs Caribbean provide an active biogeographic also existed in Central America during this mechanismresulting in the origin of Greater time. As far as we know, this biogeographic Antillean insectivores. The following hypo- distribution did not extend into South thesisis proposed: America (see Patterson & Pascual, 1972), During the late Mesozoic and early Ceno- although it would not detract from this zoic the proto-Antilleswere south of, and hypothesis if soricomorphs were found in probably contiguous with, Nuclear Central South America during this time. Sometime America (Fig. 4). During at least part of this duringthe late Mesozoic and early Cenozoic time there was a biogeographic distribution a major tectonic reorganization resulted in of soricomorph insectivoresthroughout the the decoupling of Caribbean lithosphere proto-Antilles,Nuclear Central America and from surrounding plates, and the Antilles North America. This biogeographic distri- moved eastward relativeto the Americas.The bution included soricomorphssuch as apter- process of eastward relativemovement of the nodontids, and possibly geolabidids. As Antillesresulted in biogeographicsubdivision, mentioned above, these insectivores are i.e. the ancestralsoricomorph distribution was known to have been widely distributed separated into two parts; one that included throughout western North America during North America and Nuclear Central America Eocene and Oligocene times (e.g. McKenna, and the other that included the Antilles. As

...... NORTHK.- AMERICA ~ ~ ~ ~ ~ ~ ~ ~ .i::> * :::::.i::B:OT --:MRC : ';....-..;-2.-;-:-g::*-: - ~:: :: ...... :::v ...... >: -::->.>i-. 5 .i:.>:-:>::...... :.:.>:>::

NUCLEAR :CENTRAL | AMER IC

:.y ::.-.>>::->:...... :...... GREATER ANTILLES, PROTO- LOWER ANTILLES CEN~TRAL Liii LW ~~~AMERICA SOUTH AMERICA

LATE MESOZOIC LATER MESOZOIC - LATER CENOZOIC EARLY CENOZOIC FIG. 4. Biogeographicmodel of GreaterAntillean insectivores. Shaded regionsindicate past and present biogeographicdistributions of soricomorphinsectivores discussed in text,i.e. Nesophontes,Solenodon, apternodontidsand possiblygeolabidids. (A) Duringthe late Cretaceous throughearly Cenozoic there was an hypotheticalancestral distributionof soricomorphinsectivores throughout North America, Nuclear Central America, and the proto-Antilles.(B) Biogeographicsubdivision (vicariance) of this soricomorphdistribution occurred sometime during later Mesozoic throughearly Cenozoic. (C) During the later Cenozoic the American part of the ancestral distributionbecame extinct. On the Greater Antilles,inter-is!and dispersal occurred, resulting in, forexample, the presenceof Caribbeaninsectivores on Cuba. In short,Nesophontes and Solenodon are island relictsof a once morewidespread ancestral distributionof soricomorphinsectivores. A ntilleaninsectivore biogeography 19

far as we know, the American part of the buted the origin of Greater Antillean distribution, represented by apternodontids caddisflies (genus Polycentropus) to biogeo- and possibly geolabidids, became extinct by graphicsubdivision of the proto-Antillesfrom the late Oligocene. On the Greater Antilles the Americas as a result of plate tectonics. various biotic elements underwent allopatric Rosen (1975) stated that the presence of speciation, which resulted in forms such as freshwaterpoecillid fishesin both the Greater Nesophontes and Solenodon. Furthermore, Antilles and Central America support the there also was subsequent dispersal of hypothesis of biogeographic subdivision of Caribbean insectivoresto Cuba. In short,the the once-continuous ancestral distribution. Greater Antillean insectivores Nesophontes Support for this hypothesisis also suggested and Solenodon are island relicts of a former by distributionalevidence fromother groups biogeographic distribution of soricomorph discussed in detail elsewhere (Rosen, 1975), insectivoresthat was once found throughout such as crayfishes,amphibians and reptiles. North America, Nuclear Central America and In summary,the coincident phylogenetic the proto-Antilles during part of the lAte and distributionalevidence from numerous Mesozoic and early Cenozoic. elements of the Caribbean biota, including Nesophontes and Solenodon, would tend to support the hypothesis of an early Cenozoic Evidencefrom other taxa generalized (i.e. many taxa involved)ancestral distribution that was subsequently biogeo- There are numerous elements of the Carib- graphicallysubdivided. It is true that some of bean biota whose similardistributions can be these taxa can be 'more easily' explained used to support the biogeographichypothesis by the model presented here, whereas other proposed here for Nesophontes and Soleno- taxa of the Caribbean biota with different don. Olson (1 976) described a new genus of phylogenetic histories can be 'more easily' tody, Paleotodus emryi(Aves: Coraciiformes), explained by traditionalbiogeographic models frommiddle Oligocene sedimentsof Wyoming. that incorporate active dispersal mechanisms This representsthe only knownpre-Quaternary such as rafting(see below). record of todies. The Quaternary todies, representedby the genus Todus, are endemic Concludingcomments to the Greater Antilles. Taylor (in McKenna et al., 1962) described the gastropodPlanor- As Darwin (1859) noted, thereare difficulties bina pseudoammonius from Bridgerian in explaining the originof island faunas. For (approximately middle Eocene) sedimentsof example, with regardto Caribbean mammals, Wyoming.He stated that this gastropod may it is perplexing that certain groups are not be conspecific with the West Indian (and represented in the biota, e.g. medium- to South American)species, P. glabrata. large-sizedungulates. It is particularlycurious As we know, salt water is an effective that thereare no carnivorousmammals known biogeographic barrier for many groups of from the GreaterAntilles. Perhaps the preda- exclusivelyor predominantlyfreshwater orga- tory birds of the Caribbean, including owls, nisms. Richards (1937) was particularly eagles and vultures (Arredondo, 1976) have impressed with the similarities between filled this carnivorous adaptive zone on the freshwater and terrestrial molluscs of the Greater Antilles. These birds could have Yucatan and the Caribbean.He concluded that functioned as 'ecological carnivores'through- the best explanation for this strikingbiogeo- out much of the Cenozoic. Alternatively, graphic similaritywas the presenceof an early carnivorous mammals may have existed in Tertiary 'land bridge' connecting these two the pre-QuaternaryCaribbean biota, and they regions. In his discussion of the freshwater could have become extinct before the time triclad planarian Dugesia, Ball (1971) stated when mammals are represented by fossils. that the presenceof thisgenus in the Americas This hypothesisis not unreasonable as some and the Caribbean probably resulted from(p. sixty-fivemammals are known to have be- 21) '...fragmentation of a previouslywide- come extinct from the West Indies (Rosen, spread parent population.' Flint (1 976) attri- 1975). 20 Bruce J. MacFadden

Rosen (1975) should be applauded for his References monumental biogeographic synthesisof the Caribbean biota. However, one criticismof Allen, G.M. (1910) Solenodon paradoxus. Mem. Rosen's strictlyinterpreted vicariance model Mus. comp. Zool. 40, 1-55. is that the origin of virtually the entire Allen, G.M. (1911) Mammals of the West Indies. Bull. Mus. comp. Zool. 54, 175-263. Caribbean biota is explained by the early Allen, G.M. (1918) Fossil mammals from Cuba. Cenozoic biogeographicsubdivision event that Bull. Mus. comp. Zool. 62, 131-148. resulted fromthe eastwardrelative movement Anthony,H.E. (1918) The indigenousland mammals of the Greater Antilles.As McDowall (1 978) of Porto Rico, livingand extinct. Mem. Amer. has discussed, this wholesale use of the Mus. nat. Hist. new ser. 2, 331-435. Arredondo, 0. (1976). The great predatorybirds vicariancemodel is as inductiveas the whole- of the Pleistoceneof Cuba. In: Collected papers sale use of the traditionaldispersal model. It in avian paleontology honoringthe 90th birth- is clear that the Caribbean biota has had a day of Alexander Wetmore(Ed. by S. L. Olson), complex history that resulted from several pp. 169-187. SmithsonianContrib. Paleont. Ball, I.R. (1971) biogeographic events. These events could Systematic and biogeographical relationships of some Dugesia species (Trich- have included: (1) an early Cenozoic biogeo- ladida, Paludicola) from Central and South graphic subdivision of the ancestral biota America. Amer. Mus. nat. Hist. Novitates, no. resultingfrom plate tectonic mechanisms,i.e. 2472, 1-25. the eastern relativemovement of the Greater Barbour, T. (1914) A contributionto the zo6geo- graphyof the WestIndies, with especial reference Antilles; (2) a series of dispersal events to amphibians and reptiles. Mem. Mus. comp. (between the Americasand the Caribbean and Zool. 44, 209-359. withinthe Caribbean) in later Cenozoic times Bowin, C. (1976) Caribbean gravityfleld and plate resulting from mechanisms such as island- tectonics. Geol. Soc. Amer. Spec. Paper, 169, 1-79. hopping, i.e. rafting; and (3) modifications Butler, P.M. (1972) The problem of insectivore of thisisland biota by extinction. classification.In: Studies in vertebrateevolution (Ed. by K. A. Joysey& T. R. Kemp), pp. 253- 265. Oliver& Boyd, Ediburgh. Christofferson,E. (1976) Colombian basin magne- tism and plate tectonics.Bull. Geol. Soc. Amer. 87, 1255-1258. Acknowledgments Cox, C.B. (1974) Vertebrate palaeodistributional patterns and continental drift.J. Biogeogr. 1, The motivationfor the presentdiscussion was 75-94. Cracraft,J. (1974) Continentaldrift and vertebrate in a large part due to, and an extension of, evolution.Ann. Rev. Ecol. Syst. 5, 215-261. ideas contained in Rosen's (1 975) study. This Croizat, L., Nelson, G. & Rosen, D.E. (1974) Centers manuscript has been substantiallyimproved of origin and related concepts. Syst. Zool. 23, through discussions with the following col- 265-287. Darlington,P.J. leagues: Jon Baskin, Robert J. Emry, George (1938) The origin of the fauna of the GreaterAntilles, with discussionof dispersal F. Engelmann,John J. Flynn, Richard Franz, of animals over waterand throughthe air. Quart. John A. W. Kirsch, Malcolm C. McKenna, Rev. Biol. 13, 274-300. LarryG. Marshall,Michael J. Novacek, Michael Darwin, C. (1859) On the originof species. In: A R. Perfitand S. David Webb. I would particu- facsimile of the first edition (Ed. by E. Mayr, 1966). HarvardUniversity Press, larly like to thank McKenna for Cambridge. access to Emry, R.J., Bjork, P.R. & Russell, L.S. (1979) The presently unpublished manuscripts on geo- Chadronian, Orellan, and Whitneyan North labidids and apternodontids. Jon Baskin, American Land Mammal Ages. In: Vertebrate Malcolm C. McKenna, Michael J. Novacek paleontology as a discipline in geochronology and S. David Webb criticallyreviewed various (Ed. by M. 0. Woodburne). Uziv. California Publ. Geol. Sci. (in press). versions of the manuscript. The synthesis Flint, O.S. (1976) The GreaterAntillean species of presented here is not necessarilyendorsed by Polycentropus(Trichoptera, Polycentropodidae). all of the personsacknowledged. Proc. Biol. Soc. Wash.89, 233-246. Nancy Halliday and Eugene Hanflingpre- Gregory,W.K. (1910) The ordersof mammals.Bull. Amer.Mus. nat. Hist. 27,1-524. pared Fig. 4. I thank Silvie M. Sidaway, Hallam, A. (1974) Changingpatterns of provinciality Rhoda J. Rybak and PriscillaA. Williamsfor and diversityof fossilanimals in relationto plate theireditorial and typingskills. tectonics.J. Biogeogr. 1, 213-225. Antilleaninsectivore biogeography 21

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