CHAPTER 18 •

The fflO&/ SfriJcing!eature a/pas! and pres!!nl di$lriOOfiOllS [of &[ is Ihe fUndamental ;md consislenr associaliOl1 of disrriburiOll$ of each group with eilher Laura.sia or Gondwanaland,. and Ihose • fragments thaI by cominental drift have wme /0 form /oday's major land areas.

Jay M. SllVaSe (1 973)

•."

oR • E scientific discoveries have influenced historical bution because of its unique evolutionary history and biogeography so significantly as the accumulating data particular ecological requirements, it is possible to deter­ on plate tectonics beginning in the early 1960s. Most mine patterns (generalized tracks) of coinddent distri­ syntheses of historica1 biogeography before the late 1960s butions of many monophyletic groups. This is the first were influenced by the arguments of Matthew (1915) step in biogeographic analysis. Second, it is necessary to that the evolution and distribution of mammals could be determine disjunct clusters of distributions within the overaU explained adequately by continental isostasy. Among distribution of an inclusive taxonomic unit. These clusters Matthew's many influential disciples was Noble, who, in commonly define the geographic limits of major modem a series of papers culminating in his synthesis of amphib­ biOtas, have a high degree 01 endemism, and constitute ian biology (l931b), attempted 10 explain the distribution centers of adaptive radiation. Third, it is desirable to iden­ of families of by dispersal between static con­ tify the historical source units that contributed to the tinents. With the advent of extensive geophysical evi­ modem bialaS, lor the biota in any given may dence in support of continental drift, biogeographers be­ have been derived from several historical source units at gan to reexamine earlier biogeographic arrangements. different times. The results have been striking changes in biogeographic A myears with the formulation of vi ­ In order to address the biogeographic problems, one cariance biogeography (see G. Nelson and Platnick, 1981. must formulate working principles and review the geo­ and G. Nelson and D. Rosen, 1981, for reviews). Con­ logic and climatic changes that have taken place since siderable controversy exists between adherents of the the time of the origin of amphibians. This chapter dis­ dispersal theory and the proponents of the vicariance cusses these subjects and then analyzes the historical and theory, who argue that the vicariance approach provides modem distributions of the three living orders of am­ testable hypotheses, whereas the dispersalist approach is phibians. untestable. J. Savage (1982) took a balanced view and outlineclthe conceptual framework of each approach, as given below. BIOGEOGRAPHIC PRINCIPLES The documentation of the distribution 01 organisms in Dispersal Theory space and time is the raw material for biogeographic 1. A monophyletic group arises at a center of or­ analysis. Although each taxon has its individual distri- igin. 477 EVOLUTION

478 2. Each group disperses from this center. mented and the geographically associated taxa in each 3. A generalized track corresponds to a dispersal fragment evolved together. route. The major patterns of amphibian distribution at the 4. Each modem biota represents an assemblage familial and subfamilial levels can be explained best by derived from one to several historical source vicariance biogeography. Some facets of peripheral dis­ units. tributions definitely are the result of dispersal, but these 5. Diredion of dispersal may be deduced from are relatively minor in comparison with the overall dis­ tracks, evolutionary relationships, and past tribution patterns, except for some widespread genera, geologic and climatic history. such as Bulo, Hyla, and Rana, in which both phenomena 6. Climatic and/or physiographic change provides seem to have been important. Any biogeographic sce­ the major impetus andlor opportunity for dis­ nario is only as good as the understanding of the phy­ persal. logenetic relationships of the organisms involved. Unre­ 7. Biotas are constituted by dispersal across bar­ solved phylogenetic relationships of many amphibian riers and subsequent evolution in isolation. groups, especially some anurans, make some aspects of 8. Dispersal is the key to explain modern pat­ the biogeographic analysiS tenuous at best. terns; related groups separated by barriers have Ideally, all biogeographic syntheses should be based dispersed across them when the barriers were on phylogenetic analyses of component taxa. This has absent or relatively ineffective, or less com­ not been the case, nor is it likely that this ever will be a monly by passing over or through existing reality. Instead, the methodology suggested by J. Savage barriers. (1982) has been used to a great extent, especially with 9. Dispersal is of primary significance in under­ the anurans. This method uses events in the history of standing current patterns; dispersal preceded the to predict general patterns of phylogenetic re­ barrier formation and vicariance, and occurs lationship. This approach implies a redprocal relationship again when barriers subsequently are re­ between the history of the earth and the history of the moved or become ineffective. biota. However, even this approach presents some problems, Vicariance Theory especially in the anurans, a group in which familial as­ 1. Vicariants (a1lopatrtc taxa) arise after barriers signments of many taxa are open to question (see Chap­ separate parts of a formerly continuous pop­ ter 17). Many assumptions are made in the following ulation. discussion, and in some cases alternatives are offered. 2. Substantial numbers of monophyletic groups Moreover, if the scenarios depicted are correct, many are affected simultaneously by the same vi­ groups as now recognized are para·phyletic. These in­ cariating events (geographiC barrier forma ­ clude the families , Myobatrachidae, Lepto­ tion). dactyliciae, Bufonidae, HyUdae, and Ranidae, the subfamUy 3. A generalized track estimates the biotic com­ Microhylinae, and the genera Eleutherodactylus, Bulo, position and geographic distrtbution of an an­ Hyla, and Rano. cestral biota before it subdivided (vicariated) The application of times of divergences of lineages de­ into descendant biotas. rived from biochemical studies provides a data set inde­ 4. Vicariance after geographic subdivision pro­ pendent of the phylogenies based on morphology and duced modem biotas. biogeography based solely on earth history. Although the 5. Each generalized track represents a historic evolutionary clock hypothesis of albumen changes has source unit. been criticized by some workers (see Chapter 16), the 6. Sympalry of generalized tracks reflects geo­ results are encouraging. In most cases in which phylo­ graphic overlap of different biotas owing to genetic analyses and earth history agree, there also is dispersal. congruence of the molecular data. 7. The primary vicariating events are change in The fossil record and the biochemical information em­ geography that subdivided ancestral phasize the antiquity of many lineages of lissamphibians. biotas. As gaps are filled in the fossil record, more molecular 8. Biotas evolve in isolation after barriers arise. data accumulated, and more cladistic studies completed, 9. Vicariance is of primary importance in under­ the biogeographic picture of amphibians should improve. standing modem patterns; related groups separated by barriers were fragmented by the appearances of barriers. HISTORICAL SETTING The fossil record of modem groups of amphibians ex­ These two approaches differ mainly in their emphases. tends back to the early (Table IS"I). Therefore, In the dispersal model, geographically associated taxa in order to interpret the distributional histories of the liv­ dispersed together so as to form a common pattern. In ing groups, it is necessary to project the hypothesized the vicariance model, Original distrtbutions are frag- phylogenetic relationships of each of the orders (see Biogeography _'k__ '_'_'_' _' _"'c'",-c"""'"cc~' c'codcca~'moccoc~Ecwc'c'cAclc'''=='cgc~ · cDOC· C"C· ,,==oo.CC.:cACm:phc:'''=· =':' ______:: 479 • Earliest ..... 0 •• ...... oappeara.uo o' r epoc:•• - ....plolb'-'> fa.Ui~

At Permo-Triassic boundary, east consisted of High-ka titude humid belts Protobatrachidbe ""'.~Om . \I . sever~1I separate blocks south and east of major separated from tropical humid \, Asian Otherwise, most if not all belt by midlatitude llrid .wnes: united in single land maSS-Plmgllea. eKpllnsion of northern in . East Asian blocks unite with . Breakup of Contraction of arid zones and Karauridae (U) '"""190 my. Pangaea initiated about ISO m.y. when North expansion of high latitude and Prosirenidae (M) Amerial and began to separate. By 160 especially tropiQlI humid belts. Leiopelmatidae (L) m.y., Tethys Sea separnted east from OiscoglOSSidae (Ul east Gondwanaland: epeiric seas probably Palaeobatrachidae (Ul conn«ted Tethys Sea with North Atlanti(: lind possibly with East Pacific via Caribbean Basin. At about 140 m.y. , Gondwa~nd £r."gmented into three major bIocks---Africa. -, - . etaceous. Turgai Sea separated east lind west . Temperate humid zones Sireniclae (UI 135 m.y. Midcontinental Sea separated east and west North discontinuous In high latitudes. Amphiumidae (Ul America 100 10 7S m.y. Kolyma Block united with Tropical and subtropical $capherpetontidlle (U) Asi11120 m.y. Sooth Atlanoc Ocean separated c1iTnaltes dominating most Land Batrachosau~e (Ul Sooth America lind Africa (.:!: 100 m.y.l. masses; and zones smaU and (Ll Madagascar separated from Indian-SeycheUe3n discontinuous. Pelobatidae {Ll PLate. New Zealand separ3ted from AUSlJ3lia. POSSible conn«tion between Central and South AmeriCil in Late Creta<:eous. ,!eocene, Turgai Sea separated east and west Eurasia. Equable tropical and subtropical. Cryptobranchidae 65m.y. separnted from Indian Plate. Australia Proteidae se!)3raled from Antarctica. Formation of Greater Oic3mptodontidae Antilles. DeGeer passage between and Caedliidae R . intermittent. Brief con­ Rhinophrynidae nection of South America with Central Ameril;a. Bufonidae Hylidae xene, Turglli Sea separnted east and west Eurasil!. Thule EqU3ble tropical aond subtropical. ~mandridlle 54 m.y. tonnection of Europe lind North AmeriCil. Pelodytidae Beringia intermittent. Myobatrachidae ligocene. T urgal Sea subsided. Indian Plate colUded with Asia. Polar cooling and latitudifl31 Ambystomlltidae 36m.y. Ja!)3nese Archipelago 5epllrated fTom Asia. zonlltion of climates. Leptodactylidae Southern edge of Orienl3l Plate formed proto-Ellst Ranidae Indies. Beringia. intermittent 6ocene, Australian Plate co!Iided with Oriental Plate. Lesser Continued cooling: eliminlltion of 23 m.y. Antilles began to form. AfriC3 briefly connected ttopics in North America and Mic::rohylidae with Eurasia. Beringia in termittent Uplih of And€!; Eurasia. Expansion of arid and Sierra Nevada ranges. climates. Uocene, South America tonnected with . Continued poLar cooling, 10 m.y. Beringia submerged. Latitudinaol zonation, and aridity.

llme since beginning; m.y ... million $. "L. .. lower. M .. middle, U _ upper.

:hapter I7} on the pa.ttems of changing continental con­ Geologic Events. At the Pe1T11o-Triassic boundary, gurations and dimates during the past 200 million years. eastern Asia consisted of several separate blocks south he continental configurations used here in reconstruct- and east of the major Asian land mass. Otherwise, most, 19 the biogeography of amphibians were taken from the if not aU, continental masses were united into a single aleogeographic maps prepared by Banon et aI. (1981). land mass-Pangaea. "he d istribution of paleoclimates was synthesized from arious sources, principally Axelrod (l960) and P. Rob­ Ison (1973). All dates are given in millions of years be­ Climatic Events. Latitudinal zonation of climates ex­ )re the present (my). isted. A tropical (equatorial) humid zone was bordered by midlatitude arid belts. Humid temperate conditions "riassic existed at high latitudes. Toward the end of the Triassic, "he earliest period of the extended from about the northern humid zone expanded westward across cen­ ~20 to 190 my. tral and western Laurasia. EVOLUTION 480

Rs-e 18-1. Paleogeog:raphic rNlps depk:ling continental move ...... n($. A.. Middle JurassM; (160 m.1/.). B. Middle Cma«0U5 (100 Ul.y.). Edges of wntint:ntal crusts art ouUined. Srn.ded areas art ~rg

Jurassic south. Epeiric seas probably connected the Tethys Sea The initial breakup of Pangaea was in this period, 190 with the North Atlantic Ocean and possibly, by way of to 135 my (Rg. IS-lAl. the Caribbean Basin, with the eastern Pacific Ocean. Ex­ tensive epeiric seas inundated North America and Eurasia Geologie Events. At the beginning of the the from the Arctic Ocean and Am from the Tethys Sea. By east Asian blocks united with Pangaea, the breakup of 140 my, that epeiric sea (now called the Turgai Sea) which was initialed at about 180 my by the opening of fragmented southern Europe and southwestern Asia into the North Atlantic Ocean and separation of North Amer­ many large islands, and separated Europe from Asia, At ica from Africa. One plate (the Kolyma Block) rifted from about 140 my, the breakup of Gondwanaland also was northwestern North America about ISO my and drifted initiated by fragmentation into three major land masses­ westward. By 160 my, the Tethys Sea separated eastern South America-Africa, Antarctica-Australia, and Mada­ Laurasia to the north from eastern Gondwanaland to the gascar-Seychelles-India, Biogeography :Umatlc Events. Climatic zonation became less dis­ Climatic Events. The climates throughout mosl of the 481 ,1ctive with an expansion of the humid zones, especially Cretaceous were equable and tropical or subtropicaL Ie tropics, with resulting contraction of mid-latitude arid Temperate humid zones were discontinuous in the far )nes. north; arid zones were small and discontinuous. • ~retaceous "his is the longest period in the Mesozoic, 135 to 65 my. During the last 65 my the continents moved to their present positions and modem climatic patterns became estab­ ieologic Events. Epeiric seas fragmented many con· lished. nents. Although pans of southern Europe and south­ !eStern Asia were united temporarily with the rest of Geologic Events. The Turgai Sea persisted intermit­ :urope about 120 my, and northern Europe with north· tently throughout the first half of the Cenozoic; contin­ Jeslern Asia about 100 my, the Turgai Sea persisted uous land connection between Europe and Asia has per­ hroughout the Cretaceous (Rg. IS-1Bl. The Midconti­ sisted since the end of the Eocene, about 35 my (Fig. lental Sea separated eastern and western North America 1S-2). The Seychelles broke off from the Indian continent n the mid- to late Cretaceous (100 to 75 myl, a time about 64 my, and India continued its northeastward arc vhen epeiric seas fragmented northwestern Africa into at to collide \!lith Asia in the Oligocene (about 35 my). The east two large islands and separated the western part of collision resulted in the orogenic uplift of the Himalayas, \ustralia from the Antarctic-Australian continent The which in time effectively separated the Indian subconti­

FIlii" 18-2. PaIeogeographk map depicting the alTangement of the continents in the late Eocene (40 11\.\1.). Edges of continental a\ISIS ill( outlined. Shaded il:r'U$ .ore emergent land. Adapted from Mercalor protections of BarTon a aI. (1981). EVOLUTION

482 lished contact with the Central American appendage of western edges 01 the continents; the Andes and Siem!l North America in the Pliocene (3--6 my). Nudear Central Nevada chains uplifted at various times during the Cen­ America was variously connected and separated from ozoic, and by the time of the major uplifts in the Miocene North Amelica throughout most of the Cenozoic. The and Pliocene they interrupted moisture-laden onshore opposing movements of the Caribbean Plate (eastward) winds and created rain shadows to the east. During the YJith respect to North America and South America (west­ last 2 my, Pleistocene climatic fluctuations resulted in four ward) resulted in the formation of the Greater Antilles, or more major advances of polar and montane glaciers perhaps as early as the Cretaceous but certainly by the with concomitant latitudinal and altitudinal shifts in tem­ Paleocene (54-65 my), possibly with a continuous land perature belts and the restriction of humid tropical con­ connection with Central America. Beginning in the Mio­ ditions during glacial phases and restrictions of the arid cene, the Lesser Antilles began to arise as oceanic islands tropics during interglacials. along the arc of the Caribbean Plate to form the chain of islands between South America and the Greater An­ tilles. Africa had a restricted connection with Eurasia via Arabia from the late Miocene (aboul 8-10 my); with the rifting of the Red Sea this is now restricted to the Sinai The fossil record of early lissamphibians is 100 poor to region. Also in the late Miocene andlor early Pliocene provide any meaningful information on the early distri­ bution of the group. J . Savage (1973) emphasized that there was a connection between Africa and the Iberian the early history of was associated with Peninsula. In the Northern Hemisphere there were tv.ro intermittent connections between Eurasia and North laurasia, whereas and most anurans were re­ America. The Beringia land connection between North stricted to Gondwanaland. If P. Robinson's (1973) inter· America and Asia was intermittent throughout most of pretation of Permo-Triassic climatic zonation is correct, the distribution of lissamphibians at that time may have the Cenozoic and finally submerged in the Pliocene (3-5 been divided by the midlatitude arid belt that isolated my). In the Paleocene-Eocene (50-60 my), two inter­ prosalamanders in the high-latitude humid zone and pro­ mittent connections have been postulated to have existed between northern Europe and North America (McKenna, caecilians and proanurans in the equatorial humid zone. 1975)-(1) the DeGeer passage via Spitzbergen, north­ ern Greenland, and Ellesmere Island, and (2) the Thule route via southern Greenland and Ellesmere Island. The fOssil history of the salamanders extends back to the Climatic Events. At the beginning of the Cenozoic Middle Jurassic, so the evolutionary geography of these most of the land masses of the world were under equable amphibians is closely correlated with the breakup of Pan· or subtropical climates; temperate climates existed only gaea, especially Laurasia (essentially all fossil and living at high latitudes. Beginning in the Oligocene, polar cool­ salamanders are associated with Laurasian land masses). ing brought about a more distinctive latitudinal zonation Milner (1983) provided a geologically well-documented 01 climates with a gradual elimination of tropical condi­ model for the biogeography of salamanders, but her phy­ tions and vegetation in North America and Eurasia, and logenetic arrangement is notably different from that pro­ with the restriction of tropical groups to the southern pa­ posed here (Chapter 17). Although Milner's emphasis on leopeninsulas (Malay-Indonesian region 01 southeastern Laurasian cosmopolitanIsm of salamanders by the Middle Asia and Central America) by the Miocene. Concomitant Jurassic is correct, some of the details of the model do with the restriction of the tropics, there was an expansion not fit the phylogenetic history. of temperate climates into the lower latitudes 01 North The earliest known fossil is the prosirenid America and Eurasia. During the northeastward drift of Albane1pdon from the Middle Jurassic of Europe. If the Australia in the Cenozoic, the continent changed latitu­ hypothesized phylogeny of salamanders is correct, the dinal positions with the consequence that the climate lour suborders were extant by the Middle Jurassic. How­ changed from moist temperate to arid and semiarid over ever, the fossil record of early salamanders provides only much of the continent in the latter part 01 the Cenozoic. limited suppor1 for this idea. The Karauroidea is known Also at this time, most terrestriallile was eliminated from only from the Upper Jurassic of Asia, and the Sirenoidea Antarctica. From the Miocene onward, there was an ex­ and Salamandroidea (other than prosirenids) are un­ pansion of the arid and semiarid climates and vegetation known before the Late Cretaceous. Furthermore, the over southwestern North America, southwestern Asia, Cryptobranchoidea is unknown belore the Paleocene. western South America, and northern Africa. The de­ Nevertheless, the changing continental configurations and velopment of arid conditions on western sides of conti­ climates in the Mesozoic provide a basis for a biogeo­ nents was caused by cooling of high-latitude oceans and graphie interpretation of the phylogenetic model. the patterns of cold currents from high to low latitudes If protosalamanders were distributed throughout the along the west sides of continents. Also tectonic processes northern humid zone at the beginning of the J urassic, the of the continental crusts of North and South America earliest fragmentation of Laurasia would have played an resulted in orogenies producing high mountains along the important role in their early evolution. Moreover, only Biogeography 483 OTHERS KAR U> ~ 60 · 1 w~ L ~ I ., >- I I~ 'k ~ 0 I{; .. ~ V ~O' - K8 ICR I.. - I- L- ~

the northern fragmentation would have affected sala­ 3. Fragmentation of Euramerica (150 my) result­ manders, because they were excluded from the middle Ing In the Sirenoidea surviving only in eastern and lower latitudes by the arid midlalitude climates. The North America and the Salamandroido!a sur­ combination of continental fragmentation (drift and epeiric viving only in Europe (then completely sep­ seas) and expanding humid climates resulted in a series arated from Asia by the Turgai Sea). of vicariance events thai could have given rise to the four suborders of salamanders by the Middle J urassic. These Thus, by the Middle Jurassic, four stocks of salaman­ ge:ological and vicariance events are (Fig. 18-3): ders were present on at least five land masses. From this point in time, the biogeography of each of the suborders 1. Opening of the North Atlantic Ocean in the can be treated separately. Early JurassH:: (180 my) resulting In the sepa­ The Karauroidea may have existed in parts of Asia east ration of ancestrlllJ salamanders into two stocks of the Turgai Sea until sometime in the CenozoiC, but along the northern margins of Asia and Eu­ the absence of fossils (other than the type) of this extinct ramerica. The stock in Asia gave rise to the suborder precludes any definitive biogeographic state­ Karauroiclea and the one in Euramerica was ments. the stock for all other salamanders. According to the vicariance events that isolated the 2. Separation of the northern part of Euramerica suborders on separate continental blocks, the Sirenoidea by the Midconlinental Sea (160 my) resulting was widespread east of the Midcontinental Sea in North in the separation of si renoids in aquatic hab­ America in the Upper Cretllceous and early Cenozoic. itats in eastern North America and crypto­ Presumably, Iimb!essness and aquatic habits evolved early brnnchoids and saJamandroids in terrestrial in the history of the suborder. Concomitant VJith the zo­ habitats in western and eastern Euramerica, nation of climates beginning in the Oligocene, the distri­ respectively. Cryptobrcmchoids also were bution of sirenids became restricted to southeastern North present on the Kolyma Block, which subse­ America. quently rifted from western North America. Early in its history, the Cryptobranchoidea was re- EVOLUTION

I 484 stricted to North America. In the Early Jurassic, crypto­ are three groups 01 salamandlids. Pleurodeles in Euro hranchoids probably resembled hynobiids; such a stock and T ylototriton and Echinotriton in eastern Asia shi remained relatively unchanged on the Kolyma Block as ptimitive characters and may represent relicts of a f· it drifted westward from North America and collided with merly widely distributed group of primitive salamandri· eastern Asia in the Early Cretaceous (120 my), thereby Salamandra and its relatives are restricted to western ! introducing cryptobranchoids into Asia, This was the an­ rasia and presumably never existed east of the T ur cestral stock of the hynobiids. These salamanders prob­ Sea; Salamandra is known in the fossil record of Eure ably did not reach their eastemmost distribution until the since the late Eocene. The so-called T riturus groUJ: Himalayan Orogeny and the disappearance of the Turgai holarctic in distribution. ThiS group undelW€nt its e~ Sea in the Oligocene. However, they probably were on differentiation in western Eurasia in the Cenozoic (fo the land mass that became the Japanese Archipelago Triturus known as early as the Eocene in Europe) z before that block separated from Asia in the late Oligo­ apparently did not disperse into eastern Eurasia until cene or early Miocene. The patterns of distribution of the subsidence of the T urgal Sea at the beginning of living hynohiids suggest that lineages were isolated in the Oligocene. This timing is in accordance with thiS gre mesic montane areas by continental desiccation in the reaching eastern Asia prior to the separation of the Ie: middle and late Cenozoic. The cryptobranchoid stock mass that was destined to be the Japanese Archipelc that remained in North America evolved through arrested and also for the dispersal of salamandrids into Nc development to become obligate neotenes, the crypto­ America via Beringia (the first salamandrid fossils in Nc branchids. Presumably, these aquatic salamanders were America are from the late Oligocene). widespread throughout North America and Eurasia (via If the cladistic arrangement of the ambystomatids c the DeGeer Passage) in the early Cenozoic. Latitudinal plethodontids is correct, there is no major geologic ev climatic zonation and continental desiccation in the Cen­ that could have separated these groups in North Amel ozoic resulted in the distributional relicts of Cryptobrrm­ after the Cretaceous, at which time the anceslrcll st. chus in southeastern North America and Andrias in might have been split by the Midcontinental Sea. P southeastern China and Japan. bystomatids do not appear in the fossil record until The fragmentation of what now is Europe and south­ Oligocene, and plethodontids are unknown as fossils p western Asia by the Tethys Sea probably resulted in sal­ to the Miocene. However, ages of separation of gen amandroids on several small land masses. Contraction of of plethodontids suggested by immunological distan midlatitude arid zones in the and Early Cre­ are much older; some are placed in the Paleocene (M taceous would have allowed the expansion of the range son et a!., 1979). These data suggest that the separat 01 salamandroids into North America before the complete of ambystomatids and plethodontids in the Cretace< separation of Europe and North America in the early is reasonable. Ambystomatids seem to have adapte( Cenozoic. The stocks of salamandroids that gave rise to subhumid climates better than any other North Ameli. the prosirenid-batrachosauroidid-proteid lineage, to the salamanders. Their major centers of differentiation ar. dicamptodontid-scapherpetontid lineage, and possibly to southeastern North America and along the southern e' the amphiumids must have differentiated prior to the Late of the Mexican Plateau. Cretaceous. All of these families are known from late The evolution of the plethodontids seems to have b Mesozoic or early Cenozoic deposits in both Europe and associated with the Appalachian uplands of eastern N< North America, except amphiumids and scapherpeton­ America. peneric differentiation between Plethodon ; tids, which are known only from North America. There­ Ensatina took place in the Paleocene, and differentia' fore, the differentiation of these lineages of salaman­ between the eastern and western groups of Pletho< droids seems to be associated with the complex occurred in the Eocene (dating based on immunolQ!; fragmentation of Euramerica in the Middle JuraSSiC. distances given by Maxson et a!., 1979). Presume The prosirenids, balrclchosauroidids, and scapherpe­ Plethodon became separated into eastern and wes; tontids are extinct. Proteids survive as the subterranean groups as the result of climatic desiccation in midce Proteus in southern Europe and as five species of Nec­ nental North America beginning in the Oligocene .. turus in eastern North America. The only living dicamp­ dispersal of the plethodontid genus Hydromantes fl todontids are Dicamptodon and Rhyacotriton living in North America to Eurasia presumably took place via I cold streams in northwestern North America. The only ingia in the Oligocene; dating is based on immunolQ!; surviving amphiumid is Amphiuma in southeastern North data (D. Wake et al., 1979). On the basis of that da! America. All of these living salamanders are relicts of it can be assumed that plethodontines of the tribe E formerly more diverse and widespread groups of sala­ toglossini evolved prior to the Oligocene. manders. The vicariance of the salarnandrid and the am­ The supergenus Bo/itoglossa contains 11 genera ; bystornatid-plethodontid lineage also may have occurred 140 species in the tropical lowlands and the mount toward the end of the Mesozoic, when the last major land of and Central America; two genera (Bolitog/( connections between Europe and North Amelica were and ) have representatives in South Arne broken. According to Ozetiand D. Wake (1969), there (see section: Inter-American Interchange under Anu Biogeography According to dates suggested by genic differentiation, India and on the Seychelles. But why are there no cae- 485 Bo/itoglossa entered South America in the late Miocene, cilians on Madagascar? prior to the establishment of the present continuous land The spread of ichthyophiids into southeastern Asia and connection in the Pliocene (Hanken and D. Wake, 1982). adjacent islands must have occurred after the collision of The greatest differentiation of genera of bolitoglossines is the Indian Plate with Asia in Oligocene. Some caeciliids in the mountains of southern Mexico, and the greatest (Derrnophls and Gymnopls) dispersed from South Amer­ differentiation of species is in the highlands of south­ ica into Central America during a brief connection in the eastern Mexico (Oaxaca and Veracruz) and nuclear Cen­ Paleocene . Others {e.g., Caedlia and Oscoecilia) dis· tral America (Guatemala and Chiapas, Mexico) and the persed northward only after the closure of the Panama· highlands of Costa Rica and adjacent Panama (D. Wake nian Portal in the Pliocene. andJ. F. Lynch, 1976; D. Wake and P. Elias, 1983). This hypothesized history of caecilians is supported (in It might be expected that the differentiation of bolito-­ part) by immunological data (Case and M. Wake. 1977). glossines in Mexico and Central America occurred in as­ An estimated divergence time of Dennophis from Cae­ sociation with the orogenic events that took place prin­ cilia of 57 my coincides with the Paleocene separation of dpaUy in the Miocene and Pliocene. Immunological South and Central America. Estimated times of diver­ distances provide possible dates for differentiation of spe­ gence of African {Bou/engell.l/a and ) and des of Pseudoeurycea from the Eocene to the Pliocene neotropica1 (Dennophis) caeciliids of 99 and 120 my are (8-50 my); differentiation of the genera Chiropterotnton. consistent with the separation of Africa and South Amer­ Dendrotriton, and Pseudoeurycea occurred in the Paleo­ ica. An immunological distance of 210 units between cene and Eocene according to immunological data (Max­ IchthVOphis and Dennophis suggests an andent separa­ son and D. Wake, 198 1). tion of these taxa. but the limits of accurate measurement of immunological distance is at about 200 units. Thus it is possible to suggest only that divergence occured more GYIIINOPHIONA than 120 my. With the exception of a few caedliids in Central America and Mexico and a few ichthyophiids in southeastern Asia, all living caectlians occur on Gondwanan land masses. ANURA Moreover. the single fossil n is from the Paleocene J . Savage (1973) provided a lengthy discussion of the of . Therefore, the evolutionary history of caedIians distribution of anurans, in which he showed. that the his­ must be associated with the history of the southern con­ tories 01 the family groups were intimately associated with tinents. the histories of the land mZosses that they occupied in the If the phylogeny proposed here (Fig. 17-2) is correct, Mesozoic and Cenozoic. In some cases, Savage took un­ the major vicariance events of the families of caecilians warranted liberties with the classification 01 anurans. For must have occurred prior to the breakup of ­ example, he eliminated the disbibutional enigma of a land. The most primitive caecilians, the rhinatrematids, dyscophine microhylid in the Oriental Region by assign­ presently are restricted to the northern Andes and Guiana ing the genus Calluela to the Asterophryinae; otherwise, Shield in South America. Presumably rhinatrematids are the Dyscophinae is restricted to Madagascar. Also, he relicts of a group that was \l.li.despread in Gondwanaland split the melanobatrachine microhylids and placed Mel­ prior to the breakup of the continents in the Late Jurassic. anobatrochus in the Microhylinae a nd recognized the Af­ Also, the ichthyophiids that survived on the Indian Plate rican genera in the Hoplophryninae. Moreover, he con­ as it drifted from Africa to Asia are relicts of a fonnerly sidered the AustraJo...Papuan hylids 10 be Zo separate 1amiIy, more widely distributed group. Possibly the uraeotyphlids the Pelodryadidae, having a history independent from and scolecomorphids evolved in situ in peninsular India the neotropical Hylidae. Savage's rearrangements make and tropical Africa. respectively. The caeciliids have a perfectly good sense biogeographically, and he may be classic Gondwanan pattem-South America, Africa, and correct evolUtionarily; existing phylogenetic evidence nei­ India, including the Seychelles Islands. The aquatic !y. ther supports nor refutes his changes. Savage's phylo­ phlonectids presumably evolved in situ in South America geny of the suborders of anurans was based on P. Star­ from a caecillid-Iike ancestor. rett's (1973) suggestion that the pipoid and microhyloid The distributional data. in combination with the phy­ were p rimitive sister groups. This idea was based logenetic arrangement of caecilians, dictate an earty di· on her interpretation of the evolution of larval characters. vergence of most of the families--prior to the Late Ju­ Starrett's phylogeny has been disputed by evidence from rassic, except for typhlonectids. The drift of the Indian larvae provided by Sokol (1975) and Wassersug (1984). Plate must have carried ichthyophiids, uraeotyphlids, and As emphasized by J . Savage (1973), the historical bio­ caeciliids to Asia; of these, only the ichthyophiids have geography o f anurans is associated mainly with Gond­ extended beyond the The presence wanaland., However, limited fossil evidence and presenl of caeciliids on the India·Madagascar-Seyc.helles Plate is distributions 01 some families of anurans indicate that obvious because of their presence today in peninsular differentiation of some anuran stocks was associated with-- EVOLUTION 486 the initial breakup of Pangaea in the Early Jurassic of South America, and various Cenozoic ages in Africa • (160--180 my). The Triassic Triadobatrachus- from Mad­ and South America; living pipids occur in tropical South agascar generally is considered 10 be an early . The America and sub-Saharan A£tica. earliest known fossil that unquestionably is a frog is Vi- Protopipoids apparently were widely distributed in the ~ - J;mella from the Lower Jurassic of . By the Late humid tropical zone in Pangaea. The vicariance of mi­ Jurassic there are diverse anuran fossils from Europe. n_ophrynids from other pipoids may have resulted from North America., and South America, so it may be as­ their isolation in North America after the initial opening sumed that frogs became widespread In the world during of the North Atlantic Ocean in the early Jurassic (180 the Jurassic. my). Subsequently, the vicariance of palaeobatrac:hids Leiopelmatids generally are considered to be the most and pipids could have been associated with the separa­ primitive living anurans: The Jurassic Vieraella Imd No­ tion of western Laurasia from western Gondwanaland by tobatrochus tn Argentina and the living Ascaphus in North the Tethys Sea in the mid-Jurassic (160 my) . Palaeo­ America and in New Zealand provide evi­ batrachids still had access to North America until the dence that the primitive frogs grouped in the Leiopel­ Eocene. In Europe at least, this family seems to have matidae were widely distributed prior to the breakup of been the Laurasian counterpart to the Gondwanan pip­ Pangaea and that the living genera are relicts of this an­ ids. The palaeobatrachids were widespread and diverse cient group of anurans. The histories of the other families in Europe; their disappearance at the end of the Pliocene of anurans (with the possible exception of the pipids) are possibly was caused by the cold climates and glaciation associated with either Laurasia or Gondwanaland in the Pleistocene. The history of the Pipidae is associated with the separation of Ahica and South America and is Laurasia. laurasian groups include the DiScoglossi­ discussed in the following section on Gondwanaland. dae, Palaeobatrachidae, Rhinophrynidae, Pelobatidae, The pelobatoids include the pelobatids (Eopeloba­ and Pelodvtidae. tinae, Pelobatinae. and Megophryinae) and the pelody­ Discoglossids presumably were associated with the hu­ tids in Laurasia. Estes (1970) considered the eopeloba­ mid temperate climates of Laurasia; the earliest fossils 01 tines, which are known from the Late Cretaceous of North the family are from the Late Jurassic of Europe and the America and Asia, to be the most primitive group. Pe­ Late Cretaceous of North America. Therefore. it seems lobatines are well represented in the fossil record begin­ likely that discOgiossids evolved prior to the breakup of ning in the Eocene of Europe and in the Oligocene of Laurasia in the Jurassic. DiscogJossids seem to have di­ North America; however, immunological dating of the versified In Eurasia west of the T urgai sea, where four living European Pe/obates and North American $caphio­ genera survive. Subsequent to the subsidence of the Tur­ pus indicates divergence in the Cretaceous (Sage et aI .. gai Sea in the Oligocene, the European Bombina dis­ 1982). Pelodytids first appear in the mid-Eocene of Eu­ persed eastward. Ages of differentiation 01 species of rope, where the living Pe/odytes survives; they also are Bombino determined from immunological distances by known from the Miocene of North America, where the Maxson and Szymura (1979) show that the eastern Asian family is extinct. living and fossil pelobatines have greatly species B. orienta/is differentiated in the Miocene, whereas enlarged metatarsal tubercles, and living species are 10s­ B. bombino and B. ooriegata are late Pliocene or Pleis­ soria\. Eopelobotes has only slightly enlarged metatarsal tocene vicariants. Climatic deterioration in midcontinen­ tubercles and may be a grade in the evolution of the tal Eurasia in the late Cenozoic andlor Pleistocene cli­ fossorial pelobatines. POSSibly these anurans evolved in matic fluctuations resulted in great discontinuities in the the Laurasian arid zone and dispersed throughout xeric distribution o f Bombino. However, Borbouru/a presum­ habitats in Laurasia prior to the separation of North ably was in Asia, where it became adapted to tropical America and Eurasia. in the Early Jurassic and prior to conditions. As climatic cooling restricted tropical organ­ the contraction of the arid zones in the Mid- and Late isms to the Indo-Malay region, Borbourulo survived in Cretaceous. The megophryines inhabit humid tropical and and dispersed to the . subtropical regions in southeastern Asia and adjacent ar­ Assuming that their unique lalVae evolved only once, chipelagos, and some taxa in the Himalayas: there are the pipoids (Rhinophrynidae, Palaeobatrachidae, and no fossils. Presumably they evolved from an eopeloba­ Pipidae) can be considered a natural group. Early fossil tine-li ke ancestor (Estes. 1970). If pelodytids are a his­ remains exist from Laurasia and Gondwanaland, ana -pl ~ torical reality, they must have diverged from propelo­ poids now occur in tropical North America, South Amer­ batids prior to the mid-Jurassic; however, there is no . lea, and Africa. The palaeobatrachids are known from fossil evidence for such an early vicariance . the uppermost Jurassic through the Pliocene of Europe, and from the late Cretaceous of No rth America. Rhino­ Gondwanaland_ The vicariance of the other family phrynids are known from the late Paleocene through the groups of anurans is associated primarily ....,;th the breakup Oligocene of North America; the single living species is of Gondwanaland. It is safe to assume thai an ancestral restricted to Mexico and Centra! America. P\pids are known stock of arciferal anurans was in Gondwanaland prior to from the Lower Cretaceous of Israel, Upper Cretaceous the separation of that southern land mass from Laurasia Biogeography t.ble 1... 2. FMIifies of Anur.m$ ~nd Their Association ....,th myobatrachine genera occurred in the mid-Cretaceous 487 hy Gondwanan Continents In the Late Ju~$k (Assa) or Late Cretaceous (Arenophryne, Geocrinia, Myobatrochus, Paracrinia, Rheobatrachus, and Taudac- 11 tylus from erioia); Uperoleia presumably diverged from LeiopeJmalidae Myobatrochidae? leiopelmatidae ennia in the late Eocene. On the other hand, hylid dif- Pipidlle Bufonidae? Myobatrachidae ferentiation is a CenOZOic phenomenon (Maxson el aI., leptod~ctylidae MicrohyJidae Hylidae 1982). [n this view divergence of the Cydorana-Litoria Hylidae aurea lineage from other Litoria occurred in the late Bufonidae "''''''''HyperoUidae Microhylidae Rhacophoridae Eocene, and Cye/orana and the Litona aurea group vi - Ranidae canated in the late Oligocene. Therefore, it Is possible Hyperoliidae that most, If not aI! , of the autochthonous genera of Aus- tralian frogs, as well as some species groups, were in existence before Australia made contact with the Oriental -- Region. in the mid.Jurassic. At that time, this group of anurans The Australian Plale contacted the Oriental Plate in the shared Gondwanaland with leiopelmatids and pipids. Prior Miocene and caused the complex uplift of New Guinea. to the initial breakup of Gondwanaland in the late Ju­ This contact provided the first opportunity for inter­ rassic (140 my), this ancestral stock differentiated into change of biotas that had been separated for 120 million three major groups that can be referred to as the bufon­ years since the initial fragmentation of Gondwanaland. aids, ranoids, and microhyloids. The association of dif­ At this time, hylids and myobatrachids from Australia be­ ferent lineages of these three major groups with different came associated with Oriental microhylids in New Guinea, Gondwanan continents necessitates further differentia­ and one stock of Papuan hyJids evolved into Nyctimystes. tion within each group prior to the fragmentation of the Although there have been bnef periods of continuous continents (Table 18-2). The initial breakup of Gond­ land connection between New Guinea and Australia via wanaland resulted in three continental masses; the his­ the Torres Strait as recently as the Pleistocene, few Pap­ tories of the anuran faunas associated with each are dis­ uan taxa have dispersed southward into Australia These cussed separately. include a few species of Nyctimystes, several species of Antarctica-Austrolia.-The anuran fauna of the Ant­ two genera of microhylids (Cophixalus and Spheno­ -Australian continent definitely was composed of phryne), and one species of Rona. leiopelmatids and myobatrachids, and probably hylids. Madagoscar-Seychelles-Austrolia.- The anuran fau ­ J. Savage (1973) suggested that m!crohylids reached the na of the Madagascar-Seychelles-Indian continent that Oriental Region by being on Antaroca-AustraJia. As em­ nfted from the rest of Gondwanaland about 140 mil!ion phasized by Tyler (1979), there is no evidence for the years ago contained only tropical groups. Present on this presence of m!crohylids in Australia until the late Ceno­ conlinent were ranids. hyperoliids, macophonds, and mi­ zoic. when a few species reached northern AustraUa from crohylids. M~trachids also are presumed to have been New Guinea. If the Australa-Papuan hylids represent a present, and probably bufonids were present The ranids lineage independent from the neotropical hylids, the Hy­ consiSted of ranines and the stock that gave rise to the lldae (sensu stricto) was not present on Antarctica·Aus­ mantellines. The rnkrohylids minimally consisted of mel­ tralia. anobatrachines, microhylines, and a stock, perhaps much This continent had temperate and tropkal climates; like living scaphiophrynines, that was to give rise to five leiopelmatids apparently became restricted to the former subfamilies. If the Eocene /ndobatrachus is indeed a and myobatrachids to the latter. In the Late Cretaceous, myobatrachid, that family must have been represented the land mass destined to b2COme New Zealand frag­ on the continenl Also, the presence of myobatrachids is mented from the temperate part of the continent. leia­ supponed by evidence that myobatrn.chids and soogIos­ pelmatid frogs survived as the only anurans on New Zea­ sids are related. J. Savage (1973) suggested that the ra­ land and became extinct on Antarctica·Austraiia. diation of bufonids in southeastem Asia was a late Cen­ Biochemical evidence suggests that the three species of ozoic event fo!lOVJing the dispersal of Bu/o into that region Leiopelmo diverged in the Miocene and Pliocene from North America via Beringia. The diversity of bufonid (Daugherty et Zit, 1981). Antarctica and AustrnliZi split genera (e.g. , Ansonia and Pedostibes) in southeastem apart in the Paleocene (55 my). Antarctica remained in Asia and adjacent islands strongly suggests an earlier ar­ its polar position and beginning in the Oligocene was rival of a bufonid stock. This arrival could have been via subjected to extreme cold; the extensive polar icecap now the drifting continenl Unfortunately, there is no fossil conceals the fossils of the former biota. Australia drifted evidence whatsoever. Savage also suggested that ma­ northeastward and late in the Cenozoic became increas­ coporids dispersed from Africa to Madagascar by waifing inglyarid. and to southeastern Asia by terrestrial dispersal via south­ According to dates derived from immunological data weste rn Asia, and that hypero!iids dispersed from Africa (Daugherty and Maxson, 1982), the differentiation of many to Madagascar and the Seychet!es. If these groups o f EVOLUTION 488 Eocene l' V O-Soogiossids •_t1' Hyperoliids 0·'-- Scaphiophrynine. Dyscophine. & Cophyhne Microhylids Ahacophorids. Hypero riids. Ranine & ManteHine Ram

V Oligocene Rana Bufon ids I Ranines ns-- ..... Sequentialle(tonic ~ allndia and aQOdatcd Rhacophorids \.and masses during the Ml'1y ami MicrohyHds middle Cenozoic.. showing (tOp) the CGnHqUenI isolation of anuran taxa on Madagascar and thoe Seychelles Is!.nds and (bottom) tM di$petSal of taxa from India to Asia.

anurans were present on the drifting continent, these The SeycheUes Islands have a small but significant independent long·distance dispersals are not necessary. anuran fauna.. Except for Ptychadena mascoriens:is, a wail Duling its drift from western Gondwanaland. the Mad­ from Africa via Madagascar, the anuran fauna consists of agascar-Seychelles-Indian continent fragmented. Mada­ three species of the endemic family SoogIossidae and the gascar split away from the rest of the continent in the monotypic hyperoliid genus Tachycnemis. If soogIossids mid·Cretaceous (100 my) and moved northward to its indeed are related to myobatrachids, as suggested by J. present position off the coast of Africa. As the Indian D. Lynch (1973) and Nussbaum (1979b), sooglossicls continent continued in its arc toward Asia, the small land can be viewed as isolated relicts, perhaps derivatives of mass that later became known as the Seychelles Islands an ancient lineage that is represented only by fndobatro­ broke off in the early Paleocene (64 my), India finally chus from the Eocene of India. Most likely the anuran collided with AsIa in the Oligocene (35 my). This drifting fauna of the Seychelles was much more diverse in the land mass provided transportation for several groups of early Cenozoic than it is now. There is no reason to Gondwanan anurans to the Oriental Region and resulted assume that microhylines, ranines, and rhacophorids did in the isolation of various groups of anurans on fragments not exist there; those groups presumably met the fate of left along its path. many island popuJations--. The major part of the anuran fauna of Madagascar When India collided with Asia in the Oligocene, the consists of scaphiophrynine, ciyscophyne, and cophyline subcon'inent contained Tomoptemo (also present today microhylids, mantelline ranids, rhacophorids, and hyper­ in Madagascar and Africa), Melanobatrochus (other mel­ oliids. Ranines are represented by one species of To­ anobatrachine microhylids in Africa), ranines, rhaco­ mopterna, a genus that also has species in Africa and phorids, bufonids, microhylines, and an ancestor to the India. With the exception of Tomoptema and the dys­ dyscophine Calluela. Once the land connection was ef­ cophine genus CaJluela, which occurs in southeastern fected, these groups (with the exception of Tomoptema Asia and adjacent islands, all of the subfamilies of ranids and Melanobatrochus) dispersed eastward and thence and microhylids on Madagascar are endemiC, as are the southward into the area that fragmented in the late Oli­ macophoricl genera Ag/yptodactylus and Boophis, and gocene and Mlocene into the Greater Sunda Islands (Fig. the hyperoHid genus Hetenxalus. The subfamilies en­ 18-4). Most of this dispersal occurred prior to the marine demic to Madagascar presumably evolved in situ after transgression into the Assam-Burma region in the late the separation of the island from the rest of the drifting Cenozoic. Bufonids, rhacophorids, and microhylids ap­ continent, which carried with !t Tomoptema and an parently waifed 10 the Philippines, which arose in the ancestor to CaJluela (Hg. 18-4). Oligocene. Biogeography The ancestral Calluela (Microhy6dae) dispersed through were there) became extinct, and the leptodactylid slock 489 hy this now insular region and differentiated into a stock that suIVived only as Heleophryne in cool streams in South gave rise to the Genyophryninae, represented today by Africa, PrIor to the separation of the Madagascar-Sey­ '1 the widespread lowland genera CophbooJus, Oreophtyne, cheUes-lodian continent, microhylids in Africa already had and Sphenophtyne. With the uplift of New Guinea re­ differentiated into melanobatrachines and microhylines. sulting from the collision of the Aust:ralian Plate with the The former now is restricted to a few taxa in the moun- southern edge of the Ortental Plate in the Miocene. this tains of East Africa. The latter differentiated into two lin­ microhylid stock differentiated into the diversity of gen­ eages-phrynomerines and brevicipitines, both of which yophrynine and asterophryine microhylids known there presently are widely distributed in sub-Saharan Amca. today. In Africa, the pipids differentiated into numerous spe­ The early ranines in the Oriental Region proabably cies; today, H ymenochirus and Pseudhymenochirus are were the stocks thaI gave rise to two groups of ranids. restricted to tropical West Amca. whereas the more spe­ One of these differentiated inlo several Oriental genera. ciose genus Xenopus is widespread in sub-Saharan Af­ (e.g., Am%ps and Occidozyga) thaI are distributed on rica. Among the tree frogs, the hyperoliids have differ­ the mainland (some in peninsular India) and in some entiated into an array of 12 genera. and nearly 200 species cases also in the Greater Sunda Islands and the Philip­ throughout sub-Saharan Africa. whereas the rhacophor­ pines. The other group is the so-called platymantine ran­ ids suIVive only as Chiromantis with three species in trop­ ids (Batrnch ylodes, Ceratobatrochus. Discode/es. Pal­ ical Africa. Bufonids have diversified into a number of matoroppia. and Platymantis). This group is widely genera, and the genus Bu/o is represented by many spe­ distributed from the Philippines to Aji but does not occur cies. The presence of Bu/o in the Paleocene of Brazil on the mainland; the greatest diversity is in the Solomon indicates thaI the genus was in existence before the sepa­ Islands. The genus Rona seems to have anived in the ration of Africa and South America. TImes of divergences Indo-Malayan region more recently. based o n immunological data corroborate the Creta­ A/rico-South Americo.- The separation of South ceous occurrence of Bulo (Maxson, 1981a); furthermore, America from Africa was initiated in the mid-Cretaceous her data. indicated that Schismadermo differentiated in (100 my), bul land connections between the continents the Eocene and at least some species of African Bulo are may have persisted until 90 million years ago. Prior 10 Miocene in origin. the separation of the continents. the anuran fauna con­ Africa is the site of the major radiation of ranids. A sisted of pipids, bufonids, leptodactylids, and microhylids ranid stock represented by the Astylosteminae is re­ (Ag. 18-5). Additionally, but apparently restricted 10 the stricted to humid habitats in tropical , and the African part of the continent, there were ranlds. hyper­ Petropedetinae is widespread in sub-Saharan Africa.. T er­ oliids, and rhacophorids. Assuming that the dendrobatids restrial-breeding arthroleptines and fossorial hemisines and petropedetine ranids are sister groups, the immecilale represent two adaptive types in sub-Saharan Africa. The ancestor of these groups must have been present before African ranines are highly diversified in nine genera, of the separation of the continents. Also, if the Australo­ which only Rona, Ptychadena, and Tomoptemo occur Papuan hylids are confamilial with the neotropical hyIids, outside of Africa. the Hylidae would have had to be present at least in the Climatic deterioration in the latter part of the Cenozoic South American part of the continenl made much of Africa uninhabitable for many kinds of Once South America and Africa were separated, the anurans. Humid forest refugia persisted in some lowland anuran faunas diversified independently on the two con­ areas in West Africa and on ancient mountain masses; tinents. In Africa, the lelopelmatids (and hylids, if they many a nurans suIVived the vicissitudes of the Pleistocene

Ear ly Late

Pipids Leptodactylids Bufonids Microhylids fIs-re 18-5_ Separation of South America and Africa in the cmao;eous. Taxa of anuraM listed are lhose prUUmed 10 have i n hah i ~ d th ~ major part of each contiMnl E' EVOLUTION

4 490 in such refugia. These include bufonids such as Nedo­ During the Cenowic, the humid temperate regions and phrynoides, hyperoliids such as ChrysoOOtrochus, and humid tropical regions contracted be<:ause of climatic microhylids such as Hop/ophryne. w nation. The elevation of the Andes interrupted wind In South America, the leiopelmatids became extinct. currents and modified patterns of rainfall. The ancient Severa! genera of pipicls were extant in South America highland areas-the Brazilian and Guianan shields­ in the Cretaceous and Paleocene, including Xenopus harbor presumed relicts of primitive groups (e.g., Bra­ (Estes, 1975). Xenopus sUrvives only in Africa, zmd the chycephalus and elosiines in Brazil, and Oreophrynel/a only living pipids in South America CITe members of the and Otophryne in the Guianas). Late Tertiary and Qua­ genus Pipa. The major radiations among South American ternary climatic changes are thought to have resulted in anurans took place in the !eptodactylids lind hylids. the contraction of lOONland rainforests during arid phases Ptimitive leptodactylids, the telmatoblines, diversified correlated wlth glacial stages in the Pleistocene and con­ in the southern, humid temperate region, where many traction 01 non-forest habitats during humid phases cor­ primitive telmatobiine genera (e.g., Caudiuerbem and related INith intergladal stages. These changing condi­ Eupsophus) survive, as does an apparent early deriva­ lions, logether wlth correlated altitudinal fluctuations in tive, the Rhinodermatidae. Other lineages of !eplodac­ climate, are responsible for many of the distributional tylids differentiated and disper.;ed throughout South patterns existing in South America. Also, patterns of spe_ America. These are recognized now as ceratophryines ciation in some groups of anurans can be associated with and leptodactylines: the latter are especially diverse in Pleistocene relugia (Duellman, 1982a, 1982b), but the the tropical lowlands east of the Andes. The hylodines spedation of other groups is much older (Heyer and are associated with the Brazilian Shield. The largest group Maxson, 1982). of leptodactylids is the Telmatobiinae, which occurs Detennination of the time of differentiation by immu­ throughout the tropical and subtropical parts of the con­ nological distances suggests that many leptoclactylid gen­ tinent, as ~ll as in the humid temperate region. This era (e.g., Caudiverbera, Ceratophrys, Cyc/oramphus, subfamily contains diverse genera. such as the stream­ Leptodactylus, Odontophrynus, Proceratophrys, T e/ma­ d~l1ing Telmawbius in the Andes and the extremely robius, and Thoropo) date back at least to the Eocene spedose genus Eleutherodactylus that occurs throughout (Maxson and Heyer, 1982). Furthennore, speciation in the humid tropical part of the continent. many leptodactylids, especially those associated wlth the The Hylidae is of unknown origin. Whether the Aus­ Brazilian Shield, took place in the Paleocene to Miocene tralo-Papuan hylids are closely related or the neotropical (Heyer and Maxson, 1982); also, many of the species in hylids evolved independently from a leptodactylid-like the wldespread lowland genus Leptodactylus date from ancestor in South America, the family underwent a tre­ the Eocene. The differentiation among some genera of mendous radiation in South America. Fossil hylids are hylids seems to have occurred as long ago as the Late known from the Paleocene of Brazil, but probably before Cr.etaceous or early CenOZOic. For example, Cryptoba­ the Late Cretaceous three lineages had differentiated­ trachus in the northern Andes and Stejania in the Guiana the arboreal forest-dwelling phyllomedusines, the egg­ Shield were estimated to have diverged in the Late Cre­ brooding hemiphractlnes, and the more generalized hy­ taceous (Duellman and Hoogmoed, 1984), and some Hnes. Presumably even earlier, two other groups wlth lowland species of Gastrotheca differentiated in the Pa­ intercalary elements evolved from a prohylid ancestor; of leocene or Eocene (Scanlan et aI. , 1980), as did some these, the pseudids evolved into a specialized lowland groups of Bujo (Maxson, 1984). On the other hand, spe­ aquatic group, and the centrolenids inlo a principally dation in some old genera is relatively recent. For ex­ montane, arboreal group. Maxson's (1976) historical in­ ample, Andean spedes of Telmatobius differentiated in terpretation of immunological data supports an Early the Miocene to the Pleistocene (Maxson and Heyer, 1982). Cretaceous divergence of the neotropical subfamilies of Similar recent dates of speciation were determined for hyHds: her limited data also indicated smaller immuno­ Andean species of Gastrotheca (Scanlan et aI. , 1980). logical distances between neotropical hylines and Aus­ Although representing relatively few taxa, the immuno­ tralo-Papuan hylids than between neotropical phyUo­ logical data strongly suggest that many of the genera and medusines and hemiphractines. some of the spedes of South American anurans evolved Within South America, the Bufonidae evolved into early in the Cenozoic. various lineages of Bujo and some specialized, prindpally Inter-American Interchange_-The complex history montane groups, recognized as separate genera (e.g., of the Central American isthmus and the West Indies has Ate/opus and Oreophrynella ). One presumed derivative received considerable attention from biogeographers. J. of a bufonic! stock, the Brachycephalidae, survives as two Savage (1982) provided a detailed analysis of the Central monotypic genera in the forests of eastem Brazil. Micro­ American herpetofauna. He proposed that a brief Late hylines diversified into numerous genera and species; they Cretaceous and/or early Paleocene connection between are distributed throughout tropical South America. the Central American appendage of North America and The dendrobatids are wldespread in South America South America allowed for the dispersal of taxa from one but are especially speciose in the northwestern part of continent to another. There is no evidence for any North the continent, where aU four genera occur. American amphibians having dispersed to Soulh America Biogeography in the Paleocene, but several groups dispersed northward ~,--.------,------, ~91 (Rg. 18-6), These include caecilians, phyUomedusine hy­ Late Cretaceous­ lids (ancestral stock of Agalychnis and Pachymedusa), Early Paleocene microhylines (ancestral stock of Gastrophryne and Hy­ popachus), two slocks of Bu/o, alleast one stock of hylids ~dO O,," ' (including Hyla ), and at least one slock of leptodactylids (including E/eutherodactylus). These Paleocene entrants inlo Central America were the stocks thai evolved into several Mesoamerican groups ~s, of Hyla, Bu/o, and Eleutherodactylus, plus many en­ LeptodactylidS" demic genera (e.g., Crepidophryne, Plectrohyla, Tri­ Bufonids , prion, and the eleulherodactyline derivatives--Hylacto­ Hyllds & Mlcrohyllds phryne, Syrrhophus, and Tomodactylus). Moreover, some of these stocks presumably were associated with the for­ Eocene - Miocene mation of the Greater Antilles, where hylids are respre­ sented by three lineages of Hyla, plus Osteopilus and CalYPtahyla. Some West Indian Eleutherodactylus (including the Cuban Sminthillus) seem 10 have been derived from Central American groups, whereas olhers apparently represent the evolutionary results of the dispersal of Eleutherodacty/us from South America via the Lesser Antilles 10 the Greater Antilles. The Bufonidae is repre­ sented in the Greater Antilles by the endemic Pelto­ phryne (8 species), which may have been derived from a Central American bufonid stock. Late Pl iocene The Paleocene separation of North American and South American stocks of some hylids is supported by immu­ nological data, which used as an evolutionary clock, in­ 7~ dicate times of divergence of Agalychnis from PhyJ/o­ Plethodontids c::. medusa to have been no later than the Late Cretaceous 'Ranids ., (Maxson, 1976) and groups of North and South Amer­ ~~ac t YIUS'; ican Hyla 10 have been in the Paleocene (Maxson and A. Wilson, 1975). Moreover, distances between the West Centroleni ds Indian hylid Osteopilus septentriona/is and various North Dendrobat ids & Pipids American hylids indicate a divergence in the Paleocene (Maxson and A Wilson, 1975). Aa_ 18-6. Obipersal of families of amphibians between Nonh With the closure of the Panamanian Portal in the Pli­ Americ;a. Central America, South America, and the West Indies ocene, a great interchange of South American and Cen­ from the Late CrdaceOlls through the PlioceM. tral American taxa took place. Principal groups of anu­ rans that dispersed northward include some Eleuthero­ traJ Amelica, southern MexiCO, and the West Indies, and dactylus, Leptodacty/us, Physalaemus, Ate/opus, some the Gondwanan groups that occur in the Oriental tropics. Bu/o, dendrobatids, centrolenids, some Hyla, Phryno­ there are only three genera of anurans thai are Gond­ hyas, and Phy/Jomedusa. Some Soulh Amelican taxa wanan in oligin and widely distributed in the northern have dispersed no farther than Panama; this may be the continents. Three other genera of hylids are endemic to result of either temporal or ecological limitations. in­ North Amelica. cluded in this group are Pipa, Pleurodema, Rhampho­ Bufo presumably was extant before South America phryne, Gastrotheca, Hemiphractus, Chiasmocleis, and separated from Africa, and there is evidence that there Relictiuomer. At the same time, some Central American was dispersal of South Amelican Bu/o back to Africa groups dispersed inlo South America. Some genera (e.g., toward the end of the connection (Maxson, 1984). Sub­ the hylids Aga/ychnis and SmiliscaJ dispersed only into sequently, at least two stocks of Bu/o entered North the northwestern part of the continent. Rana seems to Amelica from South America in the Paleocene. These be a recent invader from North America; it is represented dispersed into Eurasia via Beringia. The first of these was in South America by a species that also occurs in Central a tropical group that probably entered Eurasia in the America. Eocene and had a secondary radiation in southern Asia. The second was a temperate-adapted group that crossed Laurasian Dispersal of Gondwanan Groups. With Belingia in the Oligocene and became holarctic in distri­ the exception of South American taxa that occur in Cen- bution. EVOLUTION

492 Tree frogs of the genus Hyla also dispersed from South ingia. At least one invasion occurred prior to the late America to North America in the Paleocene; they appear Miocene, when Rena first appears in the fossiL record of in the North American fossil record in the Oligocene. In North America. Southward dispersal of Rona is limited. North America. the hylk:l stock differentiated into a num­ Only one species reaches South America, and only one ber of species, some of which are recognized as different reaches Austrelia. During the late Miocene and early Pli­ genera----Aclis. Umnaoedus. and Pseudacris. A temper­ ocene when a land connection existed between north­ ate-adapted H yla crossed Beringia probably in the Oli­ western Africa and the Iberian Peninsula of Europe, Rena gocene; the earliest Eurasian fossil Hyla are from the was able to disperse southward into mesic habitats in Miocene of Europe. From this spedes, the Hyla arborea North Africa. group of species evolved in temperate habitats in Asia TmUng of divergence of some lineages of hoIardic Rona and Europe. Dating of times of divergence from immu­ has been determined from immunological data. Uzzell nological data shows the differentiation of hylids in North (1982) noted that several European species of Rona dif· America to be a Cenozoic phenomenon and the diver­ ferentiated. in the Oligocene and Miocene (15-35 my). gence of the Eurasian Hy/a arborea from North American Divergence of the North American R. catesbeiana group hylids to be no less than 28 my tn the Oligocene (Maxson from the Eurasian R. temporaria complex was In the Oli­ and A Wilson, 1975), gocene, and times of separation of the western North J. Savage (1973) suggested that Rana invaded Europe American R. boy/ii complex from the Eurasian R. tem­ from Africa in the early Tertiary. However, after the for­ porana compLex vary from 33 to 17 million years (Oli­ maticn of the Tethys Sea in the Jurassic, Africa was oot gocene and Miocene) (Post and Uzzell, 1981). Immu­ connected with Eurasia until the end of the Miocene. nological distances between the European R. pere:zi and Rena is known in the fossil record from the OLigocene the North African R. sahanca indicate a divergence time through the Pleistocene of Europe. Therefore, it seems of about 7 million years, which is in accord with the time more likely that the ranine stock that reached Asia via of the land connection between those continents (Uzzell, drifting India was the source for the non-African members 1982). These data are not owrly informative, but they of the genus Rene. Beginning in the Oligocene, Rene do not refute the hypothesis of an Asian origin of hoJarctic dispersed and differentiated Probably at least two stocks Rona. of Rene dispersed from Asia to North America via Ber-