DISTRIBUTION OF THE FISHES 37 (b) Vuleanism Along the borders of the western Andes are large areas in which the details of the upthrust formations are blotted out by lava beds and voleanic peaks. In Ecuador (outside our area) this also holds good for the Eastern Cordillera, along the Atlantic scarp. Central and Northern Peru have few volcanic areas, Southern Peru and Northern Chile many. They are largely responsible for the surface configurations where they occur.
(ce)Diastrophism The latest phases of the upthrust from the paleozoic sea may be seen in the Eastern Cordillera of Bolivia, which stands in magnificent relief (22000 feet) above Lake Titicaca (12500 feet) with the most youthful contours, and with a snowcapped granitic core. Thus the cordilleras are variously crowned with volcanic peaks, with sedimentary formations often on edge, or with granitic formations. Upon these the winds, frost, rainfall, ete. work their varied effects. (d) Aggradation On the western slopes we find many minute areas in which water has been the principal constructive agent, but few large areas, and no extremely large ones. Due to the deep sea close inshore and the small volume of the rivers, delta formations are very small. Inland the rivers are of youthful to extremely youthful form, with room only for very small playas at infrequent intervals. Such a cove in the hollow of the hills may be remote, yet if suited to crops is sure to be oecupied, even though of few acres, or even of fractional acreage. The mouths of rivers are the largest—the Rimac, the Santa, the Tambo, or the Camani. (See Johnson’s aerial photographs. ) The eastern slope on the contrary is aggraded terrain, or alluvial land, from the Andes to the mouths of the rivers. With a maximum precipitation, and having from 2600 to 8000 miles in which to make its final thousand feet of descent, it does so with an extremely slight gradient, and the well-known inundation. The valley land of the Amazon is the repayment on the old palaeozoic account which the Andes are making to Brazil for the materials borrowed from its eastern ranges. (Johnson, pages 144-150.)
The result of the interplay of these varied forces upon the varied substratum described above is a profound variation in the geographic and ecological regions and subregions. Add to these factors those of climate, elevation, latitude; clothe the land with the most diversified vegetation, and we have the background of a most heterogeneous fauna, aquatic as well as terrestrial.
(3) Masor TopoGrapHic FEATURES The Andes arise from the depths of the Antarctic, an island at a time, until the mainland is reached at the Straits of Magellan.
38 FISHES OF WESTERN SOUTH AMERICA Coming northward through Chile we encounter a single range of mountains most of the way, and elevations increasing from 3000 feet in the South to passes of 17000-18000 feet in middle Chile, and Aconcagua at 23000 feet. In the latitude of northern Chile and southern Bolivia a new range begins to rise out of the Argentine plain and run in a parallel line. The Chilean range becomes the Western Cordillera, and the new one the Eastern. In southern Bolivia, the valley between these cordilleras is raised to more than 12000 feet by an immense volcanic area which blocks the exit, and holds back the waters of the Titicaca-Poop6é basin from creating an exit southward. The western range on the Bolivian-Chilean border is largely obliterated by volcanic formations, while the eastern rises higher and higher to a crest of 22000 feet north of La Paz, and the great Sierra Nevada overlooking Lake Titicaca. North of that lake the two cordilleras draw nearer together until the Nudo de Vilcanota is reached, tying them together by transverse ridges running East and West, elevation above 14000 feet.
Departing northward from this high intercordilleran bridge, the ranges swing more northwestward, continuing at great elevations, and separated by great gorges. From here we may recognize three ranges. The westernmost, the Occidental, is separated from the Central by the Rio Apurimac, and the Eastern from the Central Cordilleras by the Vileanota and the Urubamba rivers. Unlike the southern intercordilleran basin, these of the middle section of Peru have made or retained their water-gaps to the outside, draining to the Amazon. The three cordilleras approach one another again and form a third transverse bridge, the Nudo de Pasco, draining north and south. Northward of Cerro de Pasco the three ranges are separated as before, by the rivers Maranon and Huallaga, not to reunite within our territory, but to be bridged across further northward, at the Nudo de Ampato of Ecuador. At about the eastern extremity of the Nudo de Pasco a chain of mountains strikes eastward toward the Amazon valley, contrary to the usual trend of the ranges elsewhere. This is the Cadena de los Cerros de la Sal. (4) GroGRAPHIC REGIONS OF WeEsT-CENTRAL SOUTH AMERICA With the physical background described above, the terrain is seen to be of a maximum relief, with its axis transverse to the course of prevailing winds, and, although wholly within the Torrid Zone, should have given rise to distinct biogeographical provinces. The accompanying diagram (Table I) is an attempt to analyze the geological, or rather, physiographical basis for such provinces. — First of all we must recognize the north-south lines of demarcation mentioned in all the books, the Western Cordillera and the Oriental, and the three resulting general regions, the Coast, the Sierra, and the Montana trending northwest-southeastward. In the fifteen hundred miles here considered, extending nearly from the Equator to the Tropic of Capricorn, latitude becomes a factor, and at the same time two great physical barriers are set up in an east-west direction, the Nudo de Pasco and the Nudo de Vilcanota mentioned above, the former above 14000 feet, the latter nearly as much.
The coastal provinces are not sharply divided, yet are sufficiently unlike that
DISTRIBUTION OF THE FISHES 39 you can very well identify in many a photograph the region from which it has come. Region A, the Northwest, is noteworthy for its recently elevated terraces, outwash plains, or tablazos, and dunes. The Western (B) presents a land of immense dry canyons of the Rimac and Santa, with somewhat extensive deltas. The Southwest (C) presents upland dunes and lava fields, with volcanic cones, and approaching topographic maturity as against the youthful west-central section. Part I of this work has dealt with the Coast; we are here dealing with portions of the remaining six.
Throughout most of the north-central region (D) the heights of the cordilleras are moderate. The western range forms the continental divide, drops from a height near Cerro de Pasco of nearly 20000 feet to the northern passes of SOOO feet, soaring again toward the voleanic heights of Ecuador. At the southwestward extremity of this region the Maranon has its source in Lake Lauricocha and other nearby lakes, at 17000 feet, rapidly traversing its gorge north-northwestward to emerge through its water-gap, the Pongo de Manseriche, upon the Amazonian plain. The Maranon eastwardly skirts the Central Cordillera, which also trends north-northwest from the Cerro de Pasco, reaching elevations of only 15000-16000 feet, but falling away to 2000 feet to allow the emergence of the river. Next eastward is the Rio Huallaga, which also has its birth on the northern slopes of Cerro de Pasco at 14000 feet altitude, traveling northward between the Central and Eastern Cordilleras, passing around the end of the latter, as it fades out into the plain, to become a tributary of the Maranon in northern Peru. The Eastern Cordillera falls away rapidly to the north from its 15000-16000 feet at Cerro de Pasco to mountains of 8OQ00—LOOOO feet about Hudnuco, then lower to the hills about the Pampa de Sacramento. This northern province is mostly one of immense gorges with abrupt lofty mountains. As rapidly as the ranges were elevated, the intercordilleran rivers kept pace with their erosive work, from Cretaceous time to the present.
A similar region is that designated as E, the Central. It also is bounded by the Eastern and Western Cordilleras, the latter still the continental divide, at the northern extremity bounded by the Nudo de Pasco, at the southern by the Nudo de Vileanota. The Western Cordillera remains consistently at elevations 16000 to 18000 feet or above; the Eastern has here overtaken the Western, often surpassing it in elevation, interposing a barrier of extreme magnitude to the moistureladen winds and to plant and animal distribution. Bowman graphically describes the assortment of climates from tropical lowlands to permanent ice-fields (1916). At the north of this region the Rio Mantaro, arising on the southern flank of the Nudo de Pasco, within the pampa de Junin, flows southeastward to join the Apurimac, where with united forces they break through the Central Cordillera. The Apurimac, having arisen in Laguna Villafrio, southern Peru, near Cailloma, courses northwestward between the Western and Central Cordilleras to the junction with the Mantaro. Then known as the Ene, and having penetrated the Central Cordillera, it travels between the latter and the Eastern Cordillera in search of a weak point in the last barrier toward the Atlantic. Here it is joined by the Urubamba which drains all of the southeast section. The high mountains
ivia ul lowlands of Bol 1a Trop Tropical lowland flood plains and elevated grasslands 1, lowland flood plains ropical Tr vuljuosty jo sudued puw oovyy uBty Jo sured poopy Jop.og ouljuod.ty JO UIRA19} OTUROTOA AoLLEG WoTNOY OUBI-IBSNS “RIOD “BUIZBAG “GULCTPY, BQUIRGBYYO,) ‘Zed BVT se OT[BA opi pue sured pooy YIM SUIBOTYS: pideyy “O70 “RALOpRyY ‘OABWODI ‘Mog, JO SloyBMpPvoP{ oul 00Z SB Yontu su ‘ATISSOOXO [[BJ -urey = *se5105 doop pue sureo.4s Surpusty-plwaysbo JO UOtsol VW peossip APPBIAS “QOOSL ©} 0OG APsout “JooJ OOO OF OOS OOUTAOT WL9SBOYINOG “TE Iastern Cordillera ue 5 Aopeeg ‘oyejod ‘suru ‘dooys ‘wordpy SunvUWOp UOHRJos0A oUIdye YM ‘spurR[sseas }OSop-leS = YPRJUTRA — oyRAOpOT\, BAI[[IPLO [BUA Jo syvod poSiouqns ‘yynos ye UOT) -RPBL9se YONUL SjopyNoO OU S| PBsULBA ayeiopout fuiseq odoog-Bowoty, opts UWloysBo SUOTE poss. “puso YyyNOsS PUB spIs JSoOM UO OIUBITOA + YINOS 4B sured qyes fyytou ye Surypor ‘omyeypy srdued purydn ‘Oooh 04 ONOSL ABSUL “4a2F YOOSZ OF OOOZI DUTTA [B-QU,) Tynog enan? pur BILIPBI SORT JO S1oPBM PBT, woaMyoq a[quydeodedut sioLtieg, Suizeas ‘ppos ‘ourumb ‘raqqna “Rood Sroquuny ‘10940,) PURISSBAT JO SVOIR poZIs-poos SSUIBJUNOUL JO JOO] OF JIUUMUUNS UWLO.LT juRpuNqe aft] [RuTUR pur quel prqiny ‘os.rey NOLOWUNU SUUBOAYS “YB, [Pe PULE YT Bening: ‘SOIc] ap olpeyy ‘kequeuy ‘yeas Sopuy jo sodoys Uld SB possnt YIM spuBpMo, ATSoTY (0001 qnoqe APsourt) ye} YNO0S OF OOOL DUTAOLY Woyseop [RAWAL “FT [8S Bl 9p BUopR,) astern Cordillera Kz BPOUBITLA vp opun vue, ‘doays ‘ozo ‘Xoprmeq ‘so0q -Byod ‘ouro BSNS *U04}O9 ‘STRAOULTY Sy TUL -WINS JB RLOY PUB RUNG 9U0Z oyRod -wo} padopadsgp [pea ‘suourmndod }loasop YIM sodo[s puke spurpAorT MOT Aypensn ‘sodojs uo Arp ‘afc 2A [peyurey, UW1ojSe A, Pus Uo A Jo sppey t UL SUISWE BARI) OYPY “BquaRqn.ay) Srulindy ‘oquiey, ‘ormyuryy Sony SPINS 78 Sppoey yor iseduued pueydn osuey YIU ‘Mo| “9G SNOPLATPVVIB ‘SoBLOT JOALL YBa) $29F OOOOT OF OOOG OULAOL [BUI “OT OSE op OM19S) jo Opuny uorendod osardg }SalOJ [Bol -doiy, “wequiny “u04400 Sreqqnyy Ajlep qysouye “Yysry [peyurey, BZR Seq “RUOLOTY ‘OdEN ‘PeABOL] olng “eonypenyy ‘uouReyy o[ppyy PABA\YSBo pudoaty :syvod TOYS MOF YF YQOO GF dn sure, | -unour ouros ‘ured pooy Ayysopy J9J COOST OF ODE OOULAOL JSBOU]}.LO NT 3) stern Cordillera popiqeyur Aur} 1oyyey a9 ]JOO “NU ALOAT “U0Z}O9 “WOO,) JSBo O} YSULUUTpP SULTRY -UNOW SE PABA JSRoyJIOU BUISvoLo -ur uoNRydiwotd oYyy ‘SuOsBas Aap pue Jom poyteur [peu popu] Sole} “NL snozidioord “ytoys ‘snorownu QM OStyURg pur UoUTIRyYy SON, puoly PABMYSKOYPIOU SOBIOG JOA YBotr) 499} OOOST OF OOOT DUTAOL | [RAPWILY YON “CT BURJUOTY OL, SUaNY TVUL BALLOTS OUT, Western Cordillera a Western Cordiller: Western Cordillera ayo Jo 4Pq opera ul Suyeuruty, SuIZznas SuURy LoTR A, SAOT[BA poyYBSLUT pu sureyUNOUT Loysry 10J ydooxo J.losap ssoyureyy | “oqo “TERY, 5 OWOS YILM SBoIR “OCUIe T, + [[ByUre. pupydn A IATL [jets MOOT Ppeyoesstp Youur “Spy BAB pues syvod oluwojoA AUBUTUOpotg | 199} NOOGL 0} foray Bag WULAOA W19}SAMYPNOY */) SUOLBULLOJ OLUBIJOA OF ASURYY 9Y} PUB ‘ORUIT[O SLOLLEE, | | 9URD IeSNs ‘U0}}00 ‘ouRNS | ‘solloysy = ouLet Song NOL | SAO[[BA UL OfT] SOT SAO][BA payRaLur pue sureyUNoUL Yysty 1of ydaoxe yAosop sso[Urey | Eats) QL BULB, “CIOT[Ip.10F) W194S89 \\ Jo SpPyAous Ul Susi ‘yuoueULtod ‘SMAALL PoZIs-pOOd Mo} B JO UOLGIY, pe}oes sip Ajdeap ‘uolyBAvo }BaLs Jo surequnour snoytdioatd APOU ING, }99J NOOIT OF [PA0] BOS | oUTAOAg WIOYSO Ay [BUI “ET eorsayd uBbyy Aoyyed oOlpeuatpo Auepunog poyiqeyur Aposedg [lO SsSopesl] ALON SUTBJUNOUL UL ydooxo uMouyun JSOUW[B [peyarey, ‘oqo Sonbodoyonbos ALL BINT StBoA ay} JO 4SOUL Aap {Uo} UT “Los SUMBAL}S UOL}VAO[a JUS “SULLY -UNOU [BYSBOD U9AeEg ‘suLByd pooy juotouR ‘surerd 4yes ‘sounp purg }99F QOS OF [A] BS DULAOA JSOMYLON VW Stor oy, ) AO TAONG WOIHdAVADOUDOOT “TW TAVL \ vn Pacific Oce Pacific (cean
42 FISHES OF WESTERN SOUTH AMERICA of the Eastern range cast a broad rainshadow upon the valleys giving rise to great variation in the amounts of precipitation received in various sections. Climbing southeastward by the Urubamba and its tributary the Vilcanota river, we come out upon the southern intercordilleran bridge, the Nudo de Vilcanota, where, at La Raya, 14153 feet, we see the mingling of the waters of the Atlantic-bound Vilecanota with the headwaters of streams of the Titicaca basin. Here we enter the south-central region (F).
The same impenetrable Western Cordillera here forms the barrier toward the Pacific, but from here well down into Chile the outlines of the sedimentary formations are blotted out by volcanoes and volcanic formations, while the Eastern ranges, the Cordillera Real, have climbed to their highest elevations, and to the most elevated and most youthful portion of the entire Andean system. The snowcapped Sierra Nevadas fringing Lake Titicaca and attaining to heights of 20000— 22000 feet, culminating in Sorata and Ilimani, the crowning glory of the continent, are granitic intrusions which have disrupted and upended the adjacent sedimentary formations of the region. Thus the Region F is unlike any other in being bounded by voleanic formations on the one hand and by igneous on the other. In this region the Central Cordillera had long been regarded as missing, but now its outlines are thought to be discernible in the alluvial plains of the Poop6o basin as a series of low hills rising abruptly from the level pampa, partly lost by reason of their diminishing height, and partly by the burial of much of it through the processes of aggradation. Elsewhere the erosive action of streams has kept pace with the uplift of the mountains, creating the gorges and water gaps draining to the Atlantic. But in this section, no stream has done so. In the southern direction, toward the streams of Argentina, the most logical outlet, the intercordilleran valleys have been cut off, not by another bridge or Nudo, but by a series of volcanic formations. Hence the story of the Titicaca-Poop6é basin has been, despite its great altitude, one of aggradation. One stream alone, the Rio La Paz, has actually penetrated the highest portion of the Cordillera Real and at this geological period is in the act of pirating the glacial waters of the western slopes which belong to the Titicaca drainage, escaping to the Atlantic side by way of an abrupt arroyo 1300 feet deep in the detritus of the pampa and a canyon 7000 feet deep through the cordillera.
The northern section of this area with its moderate precipitation drains through a number of small rivers entering the lake from north, west, and east. It is a terrain of moderate relief above the 12500 feet of the lake, rolling and mature. Titicaca itself occupies a constricted middle portion of its basin, and is bordered by alternating hills and aggraded valleys becoming marshy on much of the lake shore at the north and west. Its great depth with its contours unlike the surrounding aggraded terrain encourage the belief that it may have been formed by block faulting. In various places I have observed the sedimentary formations near its shores, much distorted and displaced, often standing on edge, and rising many feet above the pampa. This is especially noteworthy at the northeast and southwestcorners.
DISTRIBUTION OF THE FISHES 43 Lake Poop6, the recipient of the waters of Titicaca through the Desaguadero, in turn spills over into the flat salt marshes of Coipasa where there is sufficient area to provide for the evaporation of the excess.
Region G, the northernmost one of the Montana extends from the crest of the Eastern Cordillera. It may be characterized by the great size and number of its network of streams, a plexus of active and backwater rivers, channels, oxbowlakes, ete. All the eastern rivers of the region trend northward to the Maranon, parallel to the cordilleras, while those of Oriental Ecuador enter the same river from the northwest, spread out fanwise. It is a region of high rainfall, high humidity, and high temperature. Except for good-sized areas of grassland such as the Pampa de Sacramento, it is a tropical forest. Navigation is practicable to good-sized steamers for many hundreds of miles of the Maranon, Huallaga, and Ucayali.
Region H is the least explored, consisting of rather broken terrain about the headwaters of the Jurua, the Purus, etc., and except for the eastward slopes of the cordillera is tropical lowland forest. It is difficult of access by trail, and very remote from bases in Brazil for approach by river.
Region I consists of the Atlantic slopes of the Eastern Cordillera in Bolivia, very rugged terrain, but largely explored for minerals. The summits are often more mature and are used, together with the limited hillside lands and valley floors for agriculture. Rough trails follow the precipitous streams to the lowlands. This area was explored for fishes by N. E. Pearson on the Mulford Expedition. (1924.)
The barriers separating the oriental regions are slight, and not effective for land forms. In fact the climatic zones follow vertical cleavage much more sharply than horizontal. All three of the Atlantic provinces are sparsely populated. Cotton, ivory nut, and rubber are typical products of the lowlands; coca, balsa-wood, sugar-cane and quinine of higher terrain.
FAUNAL LISTS OF THE PRINCIPAL RIVER SYSTEMS LOWER MARANON PONGO DE MANSERICHE TO TABATINGA Bunocephalus aleuropsis Pimelodella puruensis z melas a lateristriga 21 haggini “ buekleyi * coracoideus . hasemani Callophysus macropterus cristata Pimelodina flavipinnis os cyanostigma Microglanis zonatus Pimelodus pictus Zungaro zungaro jivaro Chasmocranus peruanus ee clarias Rhamdia quelen Goeldiella eques 8 bathyura Pseudoplatystoma fasciatum _ humilis Phractocephalus hemiliopterus “c dorsalis Sciades marmoratus
44 FISHES OF WESTERN SOUTH AMERICA Brac hyplatystoma juruense goeldu Sorubim lima Platystomatichthys sturio Hemisorubim platyrhynchos Sorubimichthys planiceps Perugia agassizil Centromochlus heckelii s steindachneri eyrinus Trachycorystes galeatus =f isacanthus brevibarbus coracoideus Auchenipterus nuchalis z brachyurus? Epapterus dispilurus Megalodoras irwini Centrodoras brachiatus Pterodoras granulosus Platydoras costatus Agamyxis pectinifrons ‘““ ~ flavopictus Amblydoras hancocki e monitor Anadoras grypus “ nauticus Hypodoras forficulatus Physopyxis lyra Pseudodoras niger Trachydoras nattereri atripes Hemidoras stenopeltis motrisl Opsodoras parallelus humeralis orthacanthus Ageneiosus ucayalensis - brevifilis Tympanopleura nigricollis iL alta Hypophthalmus edentatus Hemicetopsis candiru Pseudocetopsis ventralis Pariolius armillatus Pareiodon microps Henonemus punctatus Pseudostegophilus nemurus Apomatoceros alleni Urinophilus diabolicus y erythrurus Tridens melanops vc a3 ims oe Callichthys callichthys Hoplosternum littorale : thoracatum melampterum Decapogon adspersum Corydoras ambiacus te acutus amphibelus paleatus episcopl Dianema longibarbis Brochis coeruleus Chaenothorax bicarinatus ie semiscutatus Osteogaster splendens Canthopomus agassizil Hypostomus emarginatus Hemiancistrus arenarius Pterygoplichthys gibbiceps multiradiatus Lasiancistrus heteracanthus Chaetostoma sericea oe variola Xenocara latifrons Ancistrus hoplogenys Hypoptopoma gulare thoracatum Otocinclus vestitus x macrospilus Loricaria acuta s brunnea konopickyi maculata evansil nudirostris punctata macromystax cataphracta ims ‘ ce ce Hemiodontichthys acipenserinus Harttia microps ‘ brevirostris Sturisoma rostrata a giintheri Farlowella smithi Acrobrycon iIpanquianus Phenacogaster pectinatus Astyanax asymmetricus A bimaculatus maximus fasciatus abramis