THE EVOLUTIONARY AND ECOLOGICAL HISTORY OF THE FISH FAUNA OF THERIO LERMA.BASIN, MEXICO \
by Michael Leonalfd Smith
A dissertation sUbmitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Zoology) in. The University of Michigan . 1980
Doctoral Committee:
Professor Robert Rush Miller -Assistant Professor Susan Soltau Kilham Associate Professor Gerald R. Smith Associate Professor Bruce H. Wilkinsdin RULES REGARDING THE USE OF
MICROFILMED DISSERTATIONS
MicroWlmed or bound copies of 'doctoral-dissertations submitted to The University of Michigan and made available through University Micro- films International or The University of Michigan are open -for inspection, but they are to.b u ed only with due regard for the rights of the author.. Extensive copying of th dissertation or publication of material in excess of standard copyright limiAs, whether or not the dissertation has been • copyrighted, must have been approved by the author as well as by the Dean of the Graduate School. Proper, credit must be given to the author if "any material frO"-m„, the dissertation is used in subsequent written or published • work.
• . ACKNOWLEDGMENTS
am grateful to . Drs. Susan Soltau Kilham, Rohlert Rush Miller, Qerald R. Smith and Bruce H. Wilkinson for service on my doctoral clOmMittee and improvement of my dissertation and to John Vandermeer for p-articipAion in my oral examination. Dr. Miller has provided me with
much more than academic guidance; he Has taken considerable
care to see that I was provided with financial/aupport
while I Was a graduate student. My.graduate education
would not have been possible without his •stippor€.
I am grateful to Dr. Miller for various. research ' experiences including many field trips and to him 'arid Dr. Smith for opportunities to collaborate with them. It is also appropriate to thank Dr. Karl F. Lagler
who enriched my background' in tropical and marine environment!s. Dr. Reeve M. Bailey has given advic'e on nomenclature. • The staff and students of the nuseum.of Zoology
have Ilped me ing many ways. Peggy Lubahn, Mark Orser1„: and Kan a Steelqurst gave advice regarding layout, graphics, drawing and photography. Ellie Baker,.Koon and Marvel Parrington have proce'ssed much material and. helped me keep track of things .in general. When I was a
• beginnin graduate student groping for ideas, Clyde Barbour provided inspiration. I have benefitted from discussions with him and Betty Lou Brett, Barry Chernoff, Julian Humphries, Dolores Kingston and Phil Yant.- Ken Nicholls provided help in many aspects of
. production. Keary Campbell made the photographs in figures S, 7, 13, 18, 22 and 23. For assistance in the field I thank BarrysChernoff,
Robie Howard ZUlian. an Humphries, Ellie Baker Koon, Edie Marsh Robert Miller, David Sbltt and,BrUce
Turner. I especially acknowledge Ellie whose aLlity
to pick tiny bones from a screen . iias greatly added to knowledge of 'Mexican fossil fishes. I thank Frances
H. Miller for help.,in preparation for fied trips and , 'advice on logistiCS:' - This dissertation was enhanCed by teaching and
research appointments in the Division of Biological Sciences and research appointments under NSF grants 015829 and '01109 to R.R. Miller. A Scott Tuner
Award in carth Scidnce supported field .work. I acknowledge the cooperation of T. Downs and C. Swift,* Natural History Mtiseum of Los. Aneles County, in making material and notes available for studl',. W.I. Follett graciously allowed me to take over study of material in which he had a prior interest. - Special thanks are due to Drs. Jorge Carranza Fraser, iv Instituto Nacion'al de Pesca, and'Ismael Ferrusquia- Villafranca, instituto Nacional de Geologla, for arranging permission to conduct field work in.Mexico.
Field work was conducted under permit numbers 3616 and 6243.
,
•
PREFACr "Lack one lacks- both, and the-unseen is proYed by the seen, Till 'that becomes unseen, • and receives proof in its turn." -Walt Whitman, 1855 Leaves of-Grass -- --
An underlyina rationale.of this study is'that living organisms cannot 1;-e fully understood without reference to inferred past events. The basic'operational principle of- paleoecology is that an understanding of the ecology of fossil organisms can be derived from kndwledge of living plants and animals, but the converse may also be true.
It'should be possible to interpret many Ciaaracteristics of present biotas from' the fossil record. teatures of \ biotas, which we regard as - characteristic and which may have been recorded for a few hundred years, may seem , 0 • • , very fixed, but "the fossil record may suggest\that they are only passing phases which would not even be 'recorded in the rocks" .(Ager, 1963).
Paleontological data should be of interest to
, ecologists as a source of DerspeCtisves not otherwise, available. For example, paleontological data Occasionally provide insight into situations which have no modern analogues, such as revegetation of large, newly deglaciated recions far from seed sources. The most vi general perspective of paleontological data is that of - time. Ecological topics are dynamic and IRIVOLV". history which interplays with the present. Many ecological studies co id achie-7 a historical perspective by extension into past. Nonetheless, ecologists '
often hesitate to tilize paleontological data. Factors
contributing to thi situation include the uncertainties. of fossil ta'xonomy, the difficulties of working with fragmentary remains; and the tendency toward compartmentali'zation in science.- The third of these - factors may be the most' effective today; recent work
(reviewed, for example, by Miller, 1965;; Taylor, 1965:
Cooe,.,.l97OY has reduced the importance of the others. This study is concerned with ,a fish fauna. It 1 delves into the fossil history of the fauna not so much to learn what fish indicate about the past as to ledrn what the past can tell about fish.
VII TABLE OF CONTENTS''
DEDICATION- ...... ii ACKNOWLEDGMENTS - ...... , . . iii PREFACE ...... vi
LIST OF- TABLES ...... xi LIST OF. FIGURES ...... CHAPTER
'I. INTRODUCTI N - ... 1
Fossil Fish Collections and Localities Comparative Material Terminology and Abbreviations Theoretical Considerations Evolutionary Paleoetology Identification of Fossils — Paleontology of the Present Synthesis S • .
II. GEOLOGY OF THE FOSSIL LOCALITIES . . 28 Tectonic Setting Regional Geolog . The Western Mesa Central The Chapala Formation The -Atotonilco-Zatoalco Basin Santa Rosa. III. FOSSIL FISHES OF THE LERMA RIVER BASIN . . 49 Family 'Salmonidae // Genus Rhabdofario Cope Rhabdofario rugosus n. unidentified aalmonid TaMily Catostomidae. Genus Moxostoma Rafinesque. Moxostoma cf 1. robustum species group Moxostoma ammophilum,n. sp.'
VIII
- Family Cyprinidae Genus Yuriria Jordan.and Snyder YTIPITTg.alta 7 (Jordan). Yuriria elliana n. sp. Gents Algansea Girard , Algansea .tincella'(Valenciennes) Algansea milleri n. Algansea popoche (Jordan and Snyder) Family Ictaluridae Genus Ictalurus Rafinesque Ictalurus.spodius n. sp. Ictalurus dugesi Bean
• Family Goodeidae Genus Tapatia Alvarez and Arriola Tapatia occidentalis Alvarezi and Arriofa 'Genus Ameca Miller and Fitzsimons Ameca splendens Miller and. Fitzsimons Genus Chapalichthys Meek Chapalichthys encaustus (Jordan arid Snyder) •, • 'Genus Alloophorus Hubbs and Turner Alloophorus robustus (Bean)* Genus Goodea Jordan Goodva cf. C: atripinnis Jordan Genus Xenotoca Hubbs and:Turne Xenotoca sp. Goodeidae, incertae sedis Family Atherinidae Genus Chirostoma Swainson .Chirostoma cf. C. lucids Boulenger Chirostoma cf. C prome as Jordan and Snyder Chirostoma sp. • Chirostoma, indeterminate species Family Centrarchidae. Genus Micropterus1Lacepede Micropterus -relictus Cavender and - Smith
IV. DISCUSSION 150
Zbogeographic. Affinities of the Lerma4aun - Faunistic Assemblages-. Bioge6graphic Tracks . Pacific Coastal Track -WestPrn Mountp.An Track • Lerma-Rid Gralla4,Track Endemic Groups, Sequence of. Tracks Paleohydrography of the Western Mesa Central Climatic History
BIBLIOGRAPHY S 179
4
• s
dt, LIST OF TABLES
1. Generic groupirigs within the,family.Goodeidae based on the ovarian and trophotaenial characteristics of Hubbs and Turner (1939) ...... 104 2. .Zoogeographic affinities of fossil fishes ot the western Mesa Central...... 152
3. Matrix showing geographical occurrences of fossil fishes 'and their relatives in western Central Mexico...... 167
Z
XI 1.•
LIST OF FIGURES
1. The Lerma-Santi go- river system of Central Mexico . . . . . • •• ...... 2. Fossil fish localities in the western Mesa Central...... 1 .• ...... 6
3. Physiographic regions of Mexico ...... 32
4. Localities in the Chapala basin ...... 37
- 5. .Bones of Rhabdofario rugo'sus n. sp...... 53
6. catter diagram of maxillae of Mexican Moxostoma 59 * •7. Bones, of Mexican Moxostoma ...... 62 8... Bones. t of Moxostoma from Jocotepec Quarry . . 64. 9. Pharyngeal arches of Yuriiia ...... 71 10. Dentaries of Yuriria ...... 73
' 11. Cyprinid buries from Jocotepec Quarry ...... 20
.12. Dentaries of Algahsea ...... 87 13. Skulls of ICtalurus from the Chapala basin . . 95' 14. Bones of Ictalurus ...... 97 15. Palatopterygoid arch of Goodea atripinnis. . . 106. 16. Two types of jaws and jaw suspension in the Goodeidae ...... 109 17. Comparison of articular-angulars of Characodon and Goodea ...... 112 12. Taoatia-occidentalis ...... 116 '13. Bones of goodeids from the Chapala basin . . . 20. Bones of Chirostoma cf. C. lucius ...... 132 XII 21. JaW elements of Chirostoma sp...... 137 22. Bones of Chirostoma sp ...... 140 23. Bones of Micropterus relictus ...... 147 24.° Distribution of salmonids and lampreys in western North America V 155 V 25. Co-occurrences of western North American fish genera in Mexico ...... 158 26. Natural distributions of wastern North American genera in Mexico. 161 27. Outlines of eight hydrographic units in the western Mesa Central V 170
t • CHAPTER i INTRODUCTION The Lerma-Santiago river system (Fig. 1) is one of the most significant hydrographic featuies Of central:
Mexico. In common uSace,, the system is divided into two portions: the Rio Lerma which is the inlet of Lago de
Chapala and the Rio Grande de Santiago,• outlet of Lago de Chapala. This 'division is notentirely arbitrary as the two sections have'had different hydrographic and , faunistic 1-istories prior tO capture of the Lerma by the Santiago. The'Rio Lerma draIns. much cf the Mesa Central of Mexico, but, as Meek (1904Y flrst realized, it rlI st
have formerly , drained nearly all of this region as the distributions of its fishes correspond more closely., to the geological limits of the Mesa Central (Fig. 1) than to the present hvdrographic limits of the Rio Lerma and its tributaries,
The fish''fauna of the Rio Lerma. basin is of parti- ctilar interest because of its location in a reion where many fish taxa reach distributional limits (see Miller, 1976) and because of the distinctiveness of the -faUna. Endemism is so extensive (at the species through' / familial levels) that Regan (1906-08) recognized the • Figure 1. The\Lerma-Sa tiago river system of central Mexico. Geological limi\ts of the Mesa Central (after West, 1964) are \indica,ted by a dashed line.
• k
■ Figure 1
22
Rio •.% 20 \ • L Chapala \ ■ t ." ■ . • -,... • ‘ / / ... , ..... 8-
- N %
18 290
104 . 102 100 98 96
I • Lerma fauna aš one •of three sub-regIons of tha- iTea;ctic • Region. Although distinctive faunas - are usually
appealing to ichthyologists, the Lerma fauna has been
studied only sporaFlically. Early major contributions
are those of Jordan and Evermann (1896), Meek (1902,
1904) Regan (1906-08) and Hubbs and Turner (1939).
Not until the present decade have additional studies'
of major scope appeared (Alvarez., 1970; Fitzsimons,
1972; Barbour, 1973a,b; 1976; aarbcur and
Miller, 197E). The fossil fishes of the Lerna basin
were neglected until Alvarez (196C) described the first
known fosils of freshwater fishes from Mexico, but
this was followed by a series of accounts of fossil
fishes from.the western 'Mesa Central (Alvarez and
Artiola., 1072; Miller, 1972; Earbour, 19731:y; Alvarez,
1974; Smith et al., 1975).
This study treats the evolutionary and ecological
- • history of the LerMa fish fauna as inferred from
1 \ geological, paleontological and distributional data.
The fauna it sui:tabl'e for a study of this sort! because V it li'as,develped in place in an area of limited/aecr;raph-
ical extent where it has left abundant fossil remains.
Fossil Fish Collections and Localities
Freshwater fish fossils are now known frorr. atout.
14' .localities in :.!exico. Half of these are located in
the western Mesa Central (Fig. 2). The geology of Figure /. Fossil iish localities in the western Mesa Central, Jalisco, Mexico. (1) Santa Rosa. Miocene or Pliocene. (2) Atotonilco El Bajo. Late Pleistocene-. (3) Lake-bed deposits at the base of a butte, El Tecolote. . Late Pleistocene. (4) Exposed beds of Lago de Chapala - and Laguna de San Marcos Late Pleistocene. to'Recent(?). (5) Jocotepec Quarry. Pleistocene. (6).Lake-shOre deposits at Ajijic. Late Pleistocene; 47.) Chapala- Formation. Plio-Pleistocene. +VI
• .4 Figure ' 2
0 10 20
km
\-`ar--:- • 0- • 0
•-• Guadalajara * ' •
• Lago de Atertonilco a Lori"
Lago de San Marcos • ^ Laguna *de -Zacoalco Lago de Chapala these localities i given in Chapter- II and fish
material recovered from them' is listed under species
accounts in Chapter IqII.. Afl loCalities are in the' State of Jalisco:. \ •
- Santa Rosa.-'-A/varez and Arriola (1972) reported
the first known regains of the family'Goodeidae from
the Barranca d Santa-Rosa. The exposure is a 4 road7cut .13 km NE of the town of Amatitgn alksco, by
• ondary road frbm AmatitAn to-Presa Santa Rosa, a • --A- • . re'servoir on the Rio Grande de Santiago. Several
collections w,..re taken from the site in 1971 by Julio-
ArriolaLongOria, JOse Alvarez and Fdmundo Diaz Pardo.
Additional material 'as •collected in 1972 by:Robert R.
Mil1er, Frances H. Miller and Nancy A. Neff,and in 1975
by Michael L. Smith and Julian M. Eumphries.
Atotonilco El- Eajo.--Late Pleistocene vertebrate'i
fossils,.particularly mammal's and birds, are common in
superficial deposits inAhe area of •Laqo de Atotonilco.
Two small collections:of fish tones were made in this
area by J.R. Macdonald 1962. The collections
constitUte LoS Angel;e5T-County- usc -CLAC:l. localities
1235-6.
Ti- Tecolote.--Several'importa'ht collections, of
fish material have been recovered frcm Late Pleistbcene
lake-bed sediments at the base of 71 Tecolote, a butte
between Laco de San . Marcos and l acuna de Zacoalco, N of the town of Zacoalco, Jalisco; Included here are- LACM localities 1952, 1953 and 65191. Collections in this area were made by J.R. MaCdonald, Howard Smith and members of the Lake Chapala Natural Sciences Society in 1964 and M.L. Smith and Ellie baker Koon in 1977. Zacoalco-Chapala.--Diverse vertebrate fossils of , s.everal Ages were collected' by local people in the early 1950's when parts of the floors of lakes Chapala and Z'acoalco were exposed due to drainage and drought. Some •-- . of the material was taken to Federico.A. SolOrzano of Guadalajara and*was later donated to various institu- tions. Material from both lakes was combined without regard tb its origin, an unfortunate circumstance as the lakes occupy separate drainage basins. Portions of this colleCtion were described by Alvarez (1966, 1974);
additional material from the'same collection is included in Chapter III. Jocotepec Quarry.--Palmer (1926) reported the presence of fluvial sediments at the western end of
, Lago de Chapala. The site, here called Jocotepec 'Quarry, is a sand and gravel pit about 5 km W of the town of Jocotepec on Hwy 15 to Guadalajara. The abundant vertebrate fossils at Jocotepec Quarry were not discovered until the site was visited by Barbour and R.J. Douglass in 1969. A brief account of the remains was given by Barbour (1973b). Additional 9
• materialwas zolleCted by R.R. Miller and T.M. Cavender in 1971 and R.R. ililler, F.H. Miller, and N.A. Neff in 1972/. Smith et al. (1975) gave an account of all fish remains known from Jocotepec Quarry at that time. Subsequent _collections were made by M.L. Smith and
J.M. Humphries in 1976, M.L.S. and E.B. Koon in 1977;, . , and M.L.S., B.J. Turner, D.L. Soltz and R. Howard in 1977.
Ajijic.--Partial remains of a large salMonid were discovered uring construction of a ,house in Ajijic, a village on the northwestern shore of Lago de Chapala (P.R. Miller, pers..comM.). The remains were tal:en from superficial (presumably Late Pleistocene) lacustrine sediments and were associated with a bone of the centrarchid, Micropterus relictus. They were ultimately loaned to The University of Michigan Museum of
Paleontology and are under study 13v Cavender and. R.R. Miller. Chapala.--The type section of the Chapala Formation • (Palmer, 1926) is composed of dipping.lacustrin& beds A exposed in-a road-cut about.4 km N of the town of Chapala on the highway to Guadalajara., The beds hame yielded a.variety of vertebrate remains (Downs, 1958) including mammals which indicate an Early Pleistocene or Late Pliocene age. Fish bones were collected from • the Chapala type section by P.R. Miller and T.Y. , ii
A
. CATOSTOMIDAE
CAROIODES CARPIO: 179903-S, KENTUCKY; 202997-
Chihuahua. C. CYPRINUS: 182.022-S, MICHICAN. CATOSTOMUS • . ARDENS: 16A791: UTAH: C. BERNARDINI.: 182380-S, • CHIHUAHUA. C. CATOSTOMUS: 180452-S, WYOMING. C. CLARKI:
162817, ARIZONA. C. COLUIRBIANUS: _ 179588-S, 'IDAHO.
_C. COMMERSONI: 16906-S, MICHICAN. C. DISCOBOLUS:. 178686-S, ARIZONA. C. INSIGNIS: 162742-S, ARIZONA.
C. LUMEIVENTRIS. : 181667-S, CALIFORNIA. C. LATIPINNIS:
178689-S, ARIZONA. C. LUXATUS: 179364-S, OREGON.
C. MACRDCHEILUS: 179583-S, 194640=S, IDAHO.
C. .P_LATYRHYNCHUS: 1836'118-S, UTAH. C. TAHOT IS: 169022TS,
_ NEVADA. C. WARNERENSIS: 130509-S, OREGON. 'CHASMISTES
CULYS: 174436-S, NEVADA. CYCL&PTUS ELONGATUS: 176973-S,
TEXAS. ERIMX_7ON OBLONGUS: 2037E1-S,. MICHIGAN.
E. SUCETTA: 20339-S, MICHIGAN. LIZNENTELIUM NICRICANS:
LE94642-S, 'MICHICAN. ICTIOBUS, BUBALUS:, 197434-S; ILLTNOIS.
I. CYORIHELLUS: 197442-S ! ILLINOIS. I. NIGER,_ _ _ _169630-S,
TAMAULIPAS. MINVTREMA NL LANOPS: 194627-5, MICHIGAN.
MOXOSTOMA ANISUTUM: 203983-S, MICHICAN. M. AUSTRINUM:
203002-S, CHIHUAHUA; 161693-S,.173136, 175951, DURANAO:
172231, 178318-S, 179695-5, 197265, 192271, 192273, : - Jalisco, R. SANTIAGO; 172206, 178365, 192210, 192.532, '
JALISCO, TRIB. R. ARMERLA. M. BREVICENS: 179907-S, '
, KENTUCKY. M._ CARINATUM: 2E3990-S, Y:ICHICAN. M. CONGESTUM:- 192265-S, 192-271-S;-ZACATECAS, fossil and modern material. The material listed below . •is in The University tif Michigan Museum of Zoology and • • Museum of Paleontology., Catalogue numbers of . - . articulated and disartiCUlated- skeletons arendicated by the suffix -S, cleared. and stained specimens by the 'suffix. -CS, and fossils by the prefix V. Salmonfdae Hucho perryi: 187612-S, 187613-S, Japan.. 4corhynchus gofbuscha: 201722-S, Michigan. 0. keta:.172453-S, - - . 'Washipgton; 175915-S, Alaska. 0.'kis,utch:_ _ _ 186653-S; • Oregon; 186654-S, Washingi.an; 175912-S, Alaska; , . 190382-S, 1925.95-S, 2'01705-S, 187,925-A, Michigan. 2. nerka: 172452-S, 172453-S, 172454-S, tqashingtcn: . _ . -..,. • , . -. 175913-S, Alaska; 18E230-S, Coloraeo. O. rhodurus: 187609-S, Japan. O. salax, V62100, Glenns Ferry Formation, Idaho. O. tshawytscha: 178937-S, Washington; 201704-S, Michigan: 175914-S, Alaska. Salmo acuabonita: 189380-S, California. S. apachti: 193314-S, Arizona. S. clarki: 194655-S, 203829-S, Wyoming; -179560-S, New Mexico; 131723-S Nevada; 92A26-S Washington. S..gilae: 182405-S -New Mexico. Salvelinus namaycush: 172463- Michigan. 180.4647S; Coahuila; 97382, 19.2477, Nuevo Le8n. M. -duquesnei: -191775-S., Michigan. M. erythrurum:. 203934-2, Michigan. M. macrolepidotum: 197445-S, Illinois. M. mascotae: 17835§, 192199-S, Jalisco, R. Mascota; 172125, 173562, 178349, R. Ameca and tribs.
M. poecilurum: 161186-S 1 Mississippi. / M. robustum: .204199-S, N. Carolina. M. valenciennesi: 185206-S, , Michigan. ' Xyranchen texanus: 192559-S, Arizona. Cyprinidae Acrocheilus alutaceus: 179587-CS, Idaho. Agosia chrysogaster: 182407-CS, New Mexico. Alaande-aphariea:
178363-CS, 192196-05 A. Jalisco, R. Ayutla. A. barbata:
. 1941667C5, State ‘of Mexico, Ixtlahuaca. A. lacustris:
194165-CS, Michoacan, L. Pgtzcuaro. A s monticola avia: 172238-CS, 172Õ47-CS, 192188-CS, Nayarit, tribs. R. Grande de Santiago. . popoche, 167117-CS, 179704-S, Jalisco, L. Chapala. A. tincella: 172220-CS, Jalisco, R. TeuchitlLi; 179752-S, Jalisco,.R. TizapL; 189577-S; - Zan Luis Potosi, San Ysidro; 189608-CS, Michoacgn, Tocumbo; 189617-S, Michoacgn, Alvaro ObregOn. , Campostoma anpmalum: 184928-CS, New York. Couesius 4 plumbeus: 133303-CS, Michigan. Dionda dichroma: 189573-,CS, San Luis Potosi. D. episcopa: 189090-CS, Durango. Gila'alvordensis:. 1.86517-Si, Oregon. G.
atraria: 188958-S, Nevada. G. bicolor: 174438-,S, Nevada. G. nigrescens: 182401-S, Chihuallua. G. modesta: 13
186473-S, Coahuila. G. pandora: 177322-S, New Mexico.
G. pulchra: 182376-S, Chihuahua. G. purpurea: 157249-S,
Sonora. Hybopsis crameri: 166726-CS, Oregon.
H. gracilis: 159980-CS, Wyoming. H. rubrifrons: 158004-CS, Georgia. Hybognathus nuchalis: 132508-CS;
Alabama. Iotichthys phlegothontis: 141429-CS, Utah.
Moapa coriacea: 177086-CS. Nevada. Mylocheilus
cadrinus: 177108-S, Oregon. Milopharodon-.conocephalus:
179598, California. Nocomis biguttattth: 203942-S,
Michigan. N. biguttatus: 203942-S, Michigan. N.
micropogon: 203727-S, Michigan. Notropis aztecus:
172173-CS, 189622-CS, 192373-CS, State of Mexico.,- N.
boucardi: 178579-CS, Puebla. N. calientis: 192395-CS,
MichoacAn; 201540-S, Guanaivato.. N. lutrensis: 113359,
Oklahoma. N. nazas: 161725-CS, Durango. N. -sallei:
182346-CS, MichoacAn. Orthodon microlepidotus:
131620-CS, California. 15imepha1es notatus: 185143-CS,
Michigan. Pligopterus argentissimus: 124770-CS, Utah.
Ptychocheilus grangis:,179597-S, California. P. lucius:
182479-S, Utah. 1: e1ictus solitarius: 177095-S, Nevada. s Ainichthys osculus: 188961-S, Arizona. Semotilus
atromaculatus: 203944-S, Michigan. Yuriria alta: 124459-CS, 173532-CS, 179703-S, 191672-S, Jalisco, L.
Chapala; 178351-CS, Jalisco,. R. Atenguillo; 12203CS, Jalisco,,R. Ameca; 172328-CS, Jalisco, R. Verde; 192267-CS, Zacatecas, R. Juchipila;'192298-CS,_ Jalisco, 14
trib. R. Lerma; 189054-CS, Jalisco, San Luis Gonzaga. Ictaluridae Ictalurus sp.: 161697, Durango, R. Mezquital; 172017, 172051, Nayarit, trib.. Estero de San Bias. I. australis: 164711-S, San Luis Potosi. I. balsanus: 169854-S, Michoacgm. I. brunneus: 186257-S, Florida. I. catus: 186246-S, S. Carolina. I. dugesi: 178354-CS, 188987-S, R. Ameca and trib.; 179705-S, 179706-S, 179727-S, 179728-S, 188991-S, 191673=S, 192551-S, 193515-S, Jalisco, L. Chapala; 18$988-S, trib. R. Armeria; 201554-3, trib. R. Lerma. I. furcatus: 186270-S, Mississippi. I. lupus,: 203009-S, Chihuahua. I. melas: 193406-5, Michoac6n. I. natalis: 203766-S, Michigan. I. nebulosus: 197451-S, Ohio. I. platycephalus: 186245-S, S. Carolina. I. pricei: 178258-S, Sonora. I. pdhctatus: 1862i9-S, Virginia. I. serracanthus: 186258-S, Florida:, Goodeidae Allodontichthys sp.: 199002-CS, Jalisco, R. Pola. A. tamazulae: 190892-CS, Jalisco, R. TamaZula; 192250-CS, Jalisco, R. Tuxn6n. A. hubbsi: 172158-CS, Jalisco, R. San Rafael; 191682-CS, Jalisco, R. Terrero. A. zonistius: 189593-CS, Colima, R. Comala. Alloophorus robustus: 172180-CS,.189618-S&CS, 198826-S, 198951-S, MichoacSn. Allotoca maculata: 173553, jalisco, trib. L. Magdalena. A. dugesi: 178586-CS, 198814-CS, 15
• Michoacgn. Ameca splendens: 172229-CS, Jalisco, R. Teuchitlgn. Ataeniobius toweri: 172191-CS, 192513-CS, San Luis Potosi. Chapalichthys encaustus: 18b650-CS, - Jalisco, R. Grande de Santiago; 1916757S, Jalisco, L. Chapala.. C. pardalis: 191684-CS, Michoacgn. Characodon lateralis: 160880-CS, 161689-CS, 192459-CS, Durango. Girardinichthys viyiparus: 108622-CS, 192375-CS, State ' of Mexico. G. multiradiatus: 172174-C 192375-CS, r-*\ '. State of Mexico. Goodea sp.: 189026-CS, San Luig Potosi. G. atripinnis: 189609-S, 198826-S, Michoacgn;'173680-CS, Jalisco, trib. R. Lerma; I67720-CS, Jalisco, L. Chapala. 189680-CS, trib. R. Ameca; 179759-CS, Jalisco, R. Aguascalientes/Hubbsina turneri: 178584-CS, 1.92618-CS, Michoacgn. Iyodon furcidens: 198845-CS, Jalisco, Presa Santa Rosa; 189595-CS, Colima, R. Comala; 178358-CS, Jalisco, R. Mascota; 189586-CS, Jalisco, R. de la Pola; 145307-CS, Jalisco, R. Tuxpgn; 172160-CS, Jalisco, R. San Rafael. I. xantusi: 169841-CS, Michoacgn; 172132-CS, Colima, Arroyo Puenlo Nuevo; 189594-CS, Colima, R. Comala; 198840-CS, Jalisco, R. Terrero. I. whitei: I896127S, 192423-CS, Michoacgn. Neoophorus catarinae: 198817-CS, Michoacgn. N. diazi: 173510-CS, Michoacgn. N. meeki: 198816-CS, Michoacan. Skiffia bilineata: 172187-CS, Michoacgn. S. lermae: 173507-CS, 173962-CS, Michoacgn. S. multipunctata: 172169-CS, Michoacgn; 172223:-CS, Jalisco, R. Teuchitlgn. Xenotoca eiseni: , 16
172243-CS, Nayarit; 192252-CS, Jalisco, R. Tuxpgn.
X. melanosoma: 186292-CS, 189079-CS, Jalisco, R.
Tamazula; 192240-CS, Jalisco, L. Atotoriilco. X.
variata: 172188-CS, Michoacgn; 172200-CS, Jalisco, trib. R. Verde; ,179760-CS, Jalisco, R. Aguascalientss; 192325-CS, Guanajuato, R. Turbio. Xenoophorus captivus: \, \ 108556-CS, 118120-CS, 186283-CS, 192272-CS, 8an Luis\
Potosi. Xenotaenia resolanae: 186293-CS,' 192216-CS,
Jalisco. Zoogoneticus quitzeoensis: 172171-CS,
Michoacan. Atherinidae
Chirostoma arge: 179762-CS, Jalisco, R. Aguascalientes.
C. ,chapalae: 191677-S, Jalisco, L. Chapala; 197612-CS, Jalisco, R. Grande de Santiago. C. consocium: 179720-CS,
179730-S, Jalisco. C. estor: 197650-CS, Michoacan. C.
jordani: 197602-CS, Jalisco, L. Chapala. C. labarcae: 193463-CS, Jalisco, I" Chapala. •C. lucius: 179707-S,
179717-CS, 179729-S, 1 '8990-S, f91676-S, Jalisco, L.
Chapala. C. promelas: 193465-CS, Jalisco, L. Chapala.- C. sphyrabna:'179708-S, 186203-CS, Jalisco, L. Chapala. Centrarchidae
Ambloplites rupestris: 65815-CS, Michigan. Lepomis gibbosus: 98449-CS, Michigan. L. marginatus: 88445-CS,
Georgia. L. megalotis: 60240-CS, Michigan. L. microlophus: 113252-CS,.Florida. Micropterus coosae: ' 168593-CS, Alabama. M. dolomieui: 81758-CS, 97760-CS, 17
189334-S, 194618-S, Michigan. M. punctulatus: 114888-S 1
Kansas; 119548-CS, W. Virginia. M. salmoides: 69904-CS,
105985-S, 182062-S, Michigan; 179863-S, Coahuila. M. treculi: 136852-S, Texas.
Terminology and Abbreviations
The names of bones used in this study are those of
Weitzman (1962) whenever possible. the articular of
Weitzman or angular of Haines (1937) is here called the articular-angular and the angular of Weitzman is termed the retroarticular. Osteological terms used in illustra- tions are abbreviated as follows: AF, allterior fontanelle; AR, articular-angular; DE, dentary; EB, epiphyseal bar; EC, ectopterygoid; EN, entopterygoid;
FC, frontal crest; HY, hyomandibular; IO, interopercle;
LE, lateral ethmoid; MA, maxilla; OP, opercle; PA, palatine; PF, posterior fontanelle; PM, premaxilla; PO, preopercle; TT, pterotic; QU, quadrate; SE, supraethmoid;,
SO, subopercle; SU, supraoccipitalf SY, symplectic.
Hydrographic place names in Mexico are confusing because many lakes and streams have more than one' local name and streams often have different names in different stretches. For thepurpose of standardization, the hydrographic names used here are those of Tamayo and
West (1964), even though these names sometimes differ from common usage. I. The institutions which provided material for this 18
itudy are abbreviated as follows: Museum of Paleontology,
Institute of Geology, University of Mexico (IGUM);
Los Angeles County Museum (LACM); Universitý of Michigan
Museum .of Paleontology (UMMP); and University o
Michigan Museum of Zoology (unmz).
Theoretical Considerations
Uniform Ecological Response.
• Whenever inferences are made about events which occur beyond the limits of observation, an induction must be applied which ,bridges the hiatus of logic between the observed and the unobservable. The most general such induction is the assertion,, that "nature is uniform." This is'a nonfalsifiable proposition,, and its validity has therefore been of interest to philosophers
(Hume, 1748; Keynes, 1921; Mill, 1930; Russell, 19.48) as well as to scientists confronted with the necessity of applying It- (Lyell, 1837; Cloud, 1959, Scott, 1963). Ultimately the -concept must be accepted not because it 1 as/ been shown to be valid, but because we cannot proceed
without it.
As a general proposition, the uniformity of ure
is a fundamental operational principle of many sZentific
disciplines. Therefore it is often paraphrased/in ways
suited to its different applications. In paleoecologic
contexts, the term uniformitarianism is usually restricted
to the assertion that the ecological response of a species 19
is uniform in time (Scott, 1963; Ager, 1963). - A generar methodology in paleoecologic studies is .to: deduce fossil environments from ana1ogie8 .between fossil species and living species whose ecological relationships are known. The underlying assumotion,.as stated by . Scott (1963), is "that the relation between a given ,species and its present habitat is uniformly applicdOle - to fossil occurrences of that species."- The impact 6f this assumption is noteworthy begaise of its widespread and apparently successful application, particularly in Pleistocene studies, and also because it,is not - consistent with evolutionary thought.
Paleoecoiogic interpretatiOns involving living . species are usually accepted with unqualified confidence (Scott, 1963). Most Pleistocene species are strikingly similar to Recent species, and in the case of nohmarine mollusks and insects, differences in morphology are
' usually insignifiCant.(Taylor, 1965; Coope, 1970). Taylor (1965) was fully aware of the limitations of uniform ecological response,'. but he recognized that. '"Quaternary shells are\so like those of liVing mollusks
that interpretation of the past in'terms of the present has seemed a commonplace'.". The assumption of uniform ecological response is clearly in conflict with th'e idea that species evolve. Ecological uniformity has its' origiTs in Lvell's (1837) .20
uniformitarianism:which antedates ,Darwin's (1859) thebry Of :evolution 'by natural selection. The .cohtinue.d accep- tance of tlie ass,umtion after 1859 is an important comment on compartmentalized thinking in biology. The
_ comment is most relevant to"Pleistocene studies which ire; . primarily ecological, rather than to studies'of earlier - Segments of time, which are primarily evolutionary. As Deevey (1965) pointed out; the distinction between • ecological and evolutionary studies' is one of emphasis, ' for "the subjects are not sharply separable, but ecologists and evolutionists usually have different questidns in mind. Similar or' identical data---the . ' occurrence of fossil in geological settings--lead them to different .inferences about the history of environ- ments -on the one hand, and about the phyletic histo4, of organisms on the other." The continued acceptance of ecological uniformity may partly arise from its use:in near synonymy with uniformitarianism (usually by implication, but sometimes explicitly; Ageri 1963)/: Uniformity shbuld be applied at a general level, that of physical and • bio ical laws, rathen than at the level of particular biologi al relations, fdr these are known'to 'change- consider the biotic impact of the appearance of grasses irfthe Mesozoic, or the demise of dinosaurs in the Cretaceous. We must assume the "uniformity of nature" AS_AN OPERATIONAL PRINCIPLE, BUT UNIFORM ECOLOGICAL
RESPONSE IS ONLY A PARTICULAR ,STATEMENT OF THAT
PRINCIPLE.
EVOLUTIONARY PALEOECCYY - • I IF THE ECOLOGY OF organisms is not .UNIFQRM,IN TIME,
IS IT POSSIBLE TO DRAW DEDUCTIONS FRDM ANALOGIES BETWEEN
FOSSIL AND LIVING SPECIES? THE SUCCESS OF DEDUCTLONS'
FROM SUCH DATA IS EVIDENCED BY THEIR CONTRIBUTION TO A
COHERENT PICTURE OF PAST ENVIRONMENTS, _PARTICULARLY OF THE
QUATERNARY, WHICH IS IN ACCORD WITH INDEPEND4NT PHYSICAL
AND GEOLOGICAL LINES OF,EVIDENCE. - THIS PICTURE SO FAR
IS VERY GENERAL. IF DETAILS ARE TO BE ADDED, MORE
RIGOROUS METHODOLOGIES MUST BE DEVELOPED BASED ON SOUND
° THEORETICAL PRINCIPLES. A 'REFINED BASIS FOR DEDUCTION
FROM ECOLOGICAL ANALOGIES, CONSISTENT WITH NEO-DARWINIAN
LTHEORY, IS EMERGING.
IT IS SOMETIMES ASSUMED THAT CHANGES IN MORPHOLOGY •
AND ECOLOGICAL RESPONSE OCCUR AT AOPROXIMATELY THE SAME
RATE, WHEN VIEWED OVER EVOLUTIONARILY SIGNIFICANT PERIODS
BF TIME, SO THAT THE AMOUNT OF MORPHOLOGICAL CHANGE in A
SPECIES MAY E USE AS AN. ESTIMATOR OF THE AMOUNT OF
CHANGE IN ECOLOGICAL RESPONSES (SMITH ET AL, 1975).
THERE ARE SEVERAL REASONS TO EXPECT THIS. THE MOST
STRAIGHTFORWARD IS THAT A MORPHOLOGICAL CHARACTER MAY BE
DIRECTLY INVOL*ED IN AN ECOLOGICAL RELATIONSHIP (E.2.,
GILL-RAKER MORPHOLOGY IN THE FOSSIL SALMON ONCORHYNCHUS' 22
salax indicates a planktivorous habit; Smith, 1975).. When this relation holds, qualitative changes in ecological response may be deduced directly.fiom changes in morphology. Less direct, but perhaps I mOre pervasive, are the effects of pleiottopy. Single genes often exhibit multiple phenotypes so that •chahge in a given character may be associa€ed with changes in other (not necessarily related) characters. It may therefore be unlikely that significant changes in genetically based ecological .characters could accumulate without some change appearing in morphology. • Little evidence is so far available to support the assumption that ecological change can be estimatedby morphological change. However, a few examples from records of fossil foraminfera have been documented by Kennett (1968a, 1968b, 1970). He found that latitudinal changes occur in ratios of left and right coiling individuals of Globigerina pachyderma Kennett (1968a, 1970). The ratios are indicative of oceanographtc conditions in living populations and are in accord with similar'paleo-oceanographic conditions deduced from associations of other foraminifera in deep-sea cores. In another foraminiferal species, Globorotalia truncatulinoides, the average width-height ratio of individuals decreases as average surface water temperature increases (Kennett, '1968b). Patterns 23
• observed in living populations have been documented in-the fossil record, arrd it-has been possible to trace
the Southward spread of the species from,Aequatorial
waters, where it originalli'appeared about 2x106 yr B.P.
(before p ent), into subantarctic waters, where it
appeared 200,000 yr B:15.'-.N(Kennett, 1970). , - The fact of evolution places a qualification-on
analogies between fossil and living species: the
uncertainties of deductive extrapolation increase with
time. Cloud (1959) referred to this assertion as the
"rule of exponential uncertainty." The uncertainty of
deductions is reduced, however, when 4they are based on
comparisons of-assemblages of species rather than on
single species. Recurrence of similar habitats is the
simplest explanation for recurrent assemblages. For
example, Smith (1954) described a fossil fish fauna from
the Illinoian age Berends'fauna of Oklahoma. The fa
comprised ten species, extant today,- and two unidentified
species. He inferred that the climate of the Berends
fauna was similar to that of present Wisconsin, the
center of the area of sympatry -of the living species. -
It is a feature of many ch studies, however, that when
a large number of diverse .faunal and floristic elements
are compared, a residue of irreconciliable elements
remains. If uniform ecological response has been
assumed, such conflicts of evidence are difficult to 24 .
.resolve, and ads,hoc reasoning is often employed. In
explaining anomalous associations of deeper-Water
invertebrates with shallow-water species ,Emerson (1956)
and Valentine (1958) invoked - dpwelling, transport by .
stoi'm waves, and climatic change. Likewise', Natland
(1957) resolved conflicting evidence-by hypothesizing
fortuitous transport. The necessity of ad hdc reasoning • is eliminated'by recognizing the posSibility of evolu-
tionary change in some elements of the assemblage. .
Identification of Fossils.
When deductions about ecology are dawn from
comparison of foSSil and living populatibns, it is
assumed that they represent the same or similar species.
However, the criteria for the identification'of fossil.
and living organisms are not the same. Except for some
microfossils, complete organisms are rarely preserved.
The characters which form the basis for the taxonomy of •
Recent species are often not fossilized. However, even :41
.1.,, disarticulated or fri entary skeletal elements usually
bear adequate diagnoStic features for identification by
comparison to modern material. The: paleontological
concept of species assumes that if significant changes
.accumulate'in any part of the gnome, tiley will be
; associated with changes in hard parts. This asSumption
is not supported by evidence and will remain suspect
until the relationship iš rigorously specified and 25
DOCUMENTED. VIR
AN ADEQUA'TE TAXONOMIC UNDERSTANAING OF - FOSSIL • • MATERIAL HAS ONLY RECENTLY BEEN%ATTAINED - FOR SOME GROUPS,
SPECIFICALLY FISHES (MILLER; 1965), NONMARINE MOLLUSKS
•
(TAYLOR, 1965).1 AND INSECS (COOPE r 1970). THE TAXONOMY
OF LIVING MOLLUSKS HAS LAGGED, SO FAR THAT MANY LIVING,
SPECIES WEREOORIGINALLY DESCRIBED AS FOSSILS (TAYLOR,
1965). MILLER (1965) HAS POINTED OUT THAT MUCH EARLY.
WORK ON .FOSSIL FISHES SHOULD BE SCRUTINIZED, BECAUSE „
EARLY IDENTIFICATIONS-OF FISH FOSSILS CANNOT BE ACCEPTED
AT FACE VALUE IN LICIFFT OF RECENT.ADVANCES.IN FOSSFT
TAXONOMIC KNOWLEDGE OF THE COMPARATIVE OSTEOLOGYOF
MAJOR FISH GROUPS HAS BEEN LIMITED IN THE áST, BUT IS • .
CURRENTLY-BEING EXPANDED.
. PALEONTOLOGI OF THEPRESENT
INTERPRETATIONS OF THE PAST IN TERMS OF THE PRESENT
'ASSUME THAT THE PRESENT IS WELL UNDERSTOOD.' DEDUCTIONS "'
FRBM ANALOGIES'BETWEEN FOSSIL AND LIVING ORGANISMS ARE
• ISOMETIMES LLMITED BY THE -SPARSE ECOLOGICAL INFORMATION
AVAILABLE FOR MODERN SPECIES. ,REVIEWS OF PROGRESS IN
PALEOECOLOGY OFTEN CALL FOR RESEARCH ON THE ECOLOGY OF
'MODERN ORGANISMS ( WRIGHT. AND FRY, 1965). MANY WORKERS '
NOW APPROACH ECOLOGICAL STUDIES BY INTEGRATING
PALEONTOLOGY WITH NEONTOLOGICALCDATA. MARTIN AND
MEHRINGER (1965) INTERPRET FOSSIL POLLEN ASSEMBLAGES
IN THE SOUTHWE S T IN THE LIGHT OF MODERN POLLEN RAIN IN. . V.1 . 26 . /-„." •
. different habitats. . Covich (1970) studied a molluscan
comMaity in the Yucatameninsula. . by extending Observations on the modern fauna ino Sediments of the
• last 28,000 years. Kennett's (1970) interpretation of
foraminiferal biostratigraphy is"based partly' on studies 6 o_f todern 'oceanographic r'elat.,,ions. •
\ Interpretations Of fossils are enhanced by a know- , ledge of the-processes of preservation. The.study of , these processes has been called "the paleontology of the s , 13 esent"'-(Ager, 1963). The chief roponent- - of this' - -'3T7
' approach was , Rudolf Richter (1928) who 'Studied thqr
structures built by marine organisms in modern sediments • and compared them with structure in older rocks. The
work of Richter and otheis using a similar approach has --
- been surveyed- by Schafer (1962).L
SyntheSis.
Uniform ecological response has been:vieWed aš a .
- necessary,. assumption of deductions baSed on analogies between fossil an living populations (COope et al., 1971, p.88; Lamb, 1971,.p. 127;-Frenzel, 1973,p 40) * This assumption is neither necessary nor justifiable,. Recognition of evolutionary change in ecological
response introduces uncertainty. 'into specific statements
about supposed temperatures depths,- ete. of ancient
environments. However, allows' the recogmition of .
those inferences in which confid4nCe is justified. . These 1 27 •
'situations occur when (1) deductions are based on large and diverse assemblages rather than smaller assemblages or sinle species, (2) all floristic or faunistic elements can be reconciled, (3) organisms show little or no morphological change, (4) identifications of fossil and living species are based on the same criteria, and (5) deductions are based on an understanding of the relation between the ecology of living organisms and
the remains they are likely to leave.
41. CHAPTER II
GEOLOGY OF THE FOSSIL LOCALITIES
The geological historyrof the Mesa Central provides • importiint data which bear on fish ecology.and evolution.
The criti al background for interpretation of the fish fauna includes 1) the development of high relief,
2) 1.11 ,ographic compartmentalization of the area, and .
3) depositional evidence -of the environments in which fossiliferous sediments were deposited.
Tectonic Setting
The tectonic and igneous activity which has dominated the development of the present surface configuration of central Mexico can be related to crustal plate interac- tions most clearly documented in adjacent sections of the Caribbean and Pacific basins. It appears "...that the Caribbean and East Pacific [Cocos and Nazca] plates formed .a single unit prior to the Eocene" (Malfait and
Dinkelman; 1972).. These lithospheric units separated during the Eocene or early Oligocene and, subsequently, were further subdivided. The relative%motion of plates was reoriented during this time (Ibid.) resulting in a complex system of fracture Zones and faults in the eastern
Pacific basin, some of which presumably extend into ceritral Mexico (Menard, 1960).
28 29
Four major fracture zones have been traced on- the
Pacific floor off western North America (Menard,q955).
One of thes7e4; the Clarion fracture, zone, is in line with
the lieovolcanic Axis of Mexico (Maldonado-Koerdell,
1964:Fig. 11) and has been genetically related to volcan-
ism in the Mesa Central (Menard, 1955). To the north of
this axis, an east-west trending fault which passes
through the Chapala basin (the Chapala-Acambay fault of
Gierioff-Emden, 1970) is continuous with the San Andreas
fault zone' of southern California and the Gulf of
California (Maldonado-Koerdell, 1964; Mooser, 1968). This
pattern shows clearly, in the tectonic maps of Mexico
(de Cserna, 1961) and North America (King, 1968). A
fault lying beneath the Quaternary volcanic rocks of the
.kans-Mexican volcanic belt has been inferred by Gastil
and Jensky (1973) from offsets in the structural
lineament of the Sierra Madre Occidental, petrographiC
and K/An belts in western Mexico, Mexican silve'r bel€s,
and the west Mexican gravity gradient. Gastil and Jensky -, - (1973)- inferred that approxiliately 175 km of movement,
occurred along this fault in late Cretaceous or early
Tertiary time followed by an additional 260 km of
similar movement in Miocene or Pliocene time. This \ fault system passes through the Chapala basin which is a \ graben bounded by\east-west trending structures (Palmer,
1926) which parallel the Chapala-Acambay fault. It is 30
events which have occurred along these faults during and
since Miocene time which have primarily determined the
surface features of the present terma basin.
Regional Geology
The region of concern in interpretation of the
Lerma fish fauna is the Mexican Plateau and the three
mountain systems which define its limits (Eqg 3). The
Sierra Madre Oriental, which bounds the plateau on the
east, is a result of an early Eocene epilode of hplift
and deformation which constitutes the Hidalgoan onigeny
(de Cserna, 1960). Erosion' of these mountains produced
the detritus which composes the present Gulf Coastal
Plain of eastern Mexico. The major river systems of the
eastern slope of Mexico which contributed to the -V construction of the coastal plain rriay have become estab-
lished,,ingeneral f rm, at about-this time (cf. de Cserna,
1975). On the western side. of the mountains, erosion
••••4 ,debris accumulated in the TasIn and Range Province. (of
Raisz, 1959), the Mesa Central, and the Balsas-Mexcala
basin (de Cserna, 1975), 'contributing the first sediments
in the build-up of the Central Plateau. The thick
accumulation of sediments suggests that, even-at this
early time, the plateau area was a region of endorheic
basins.
Volcanic activity of the Oligocene and Miocene
built up a thick volcanic pile, the Sierra Madre- 31
•
Figure 3. Physiographic regions of Mexico as discussed in the text. The Central Plateau consists of two units, the Mesa del Norte" and the Mesa Central.
'1
32 . r : 33
Occidental (R.E. King, 1939;P.B. King, 1942; de Cserna,
1960; Eardley, 1962), which forms the western limit of
the plateau. Products of this activity accumulated
between the eastern and western m untains further
. contributing to the development o the Cen al Plateau.
Uplift of the mountains and plate u has occurred •
inte:r61 /tent1y-into the Quaternar (King, - 1939; Eardley,
19.62), so that the formation of m dern drainage patterns
on the western slope may not hay taken place until the
Vleistocene:
At the southern end of the sentral Plateau, a line
of volcanoes began to develop in the Miocene, producing
lava flows and associated volcan clastics which accumu-
lated to an average maximum thic ness of 1.000 m by the
'end of th.d Pleistocene (de Csern .1975). Although
volcanism in this area reached i s greatest intensity
during the Pleistocene, it conti ues today, new volcanic
structures having developed in t e area in historical
times (Termer, 1952; Wilcox, 195 , Williams, 1945, 1950).
The intense tectonic and volcanic activity of the
Mesa Central is associated with instability of drainag s.
A series of endorheic basins spans central Mexico,at 0 approximately 20 N latitude, coinciding with the
Neovolcanic Axis. Tamayo and West (1964) believe thi
system of isolated basins was formed when exterior
drainage was disrupted by volcanic activitx,
44"."445i. 34
example, Lago de'Zirahuen has been dammed by a lava flow.
- However, the extensive playas of the Magdalena and Sayula
basins suggest that piracy of tributaries and increasing
aridity have also been involved, at least in the western
basins.
The Western Mesa Central
According to Palmer (1926) the volcanics of the
Mesa Central are underlain by shales and limestone which
bear marine foraminifera and rudistids. If Palmer was
correct in assigning these deposits to the Turonian and
Cenomanian, they could have be laid down by a marine
transgression, the Balsas Portal, which connected the
Pacific Ocean with the Mexican Geosyncline during the
late Mesozoic (Maldonado-Koerdell, 1964:Fig. 6). Remains
of sharks of Cretaceous age have also been reported from
this area (Silva-Barcenas, 1969).
Clements (1963) questioned whether the Chapala basin
•HY is underlain by:Cretaceous sediments as he found no
-rocks'-of that age in the Chapala basin itself. Recent
veologic maps of Mexico (e.g., de Cserna, 1961) show
only Cenozoic .volcanics and alluvium in the area.
Palmer's (1926) opinion was apparently based on exposures
in the states of Morelos and Hidalgo 'and at Zopbtiltic,
, Jalisco: about 50 km south of Lago de Chapala. About
10.00 feet of limestone is exposed at zopotiltic. - , 35
Palmer (1926) described two basalts in the Chapala
-- basin. The older Tizapgn basalt is exposed on the southern
edge of the lake and at Jiquilpin (Fig. 4). This basalt, was
considered Teriary,(possibly Miocene) in , age. Palmer reported that the Chapala beds rest on the TizapAn-
basalt in the vicinity of Jiquil n. The Chapala beds
are overlain by the Pleistocene Estancia asal.t. at,
ConcepciOn de Los Buenos Aires, west of Jiquilpgn, and
near Las Caleras (Palmer,'op. l cit.). Cl ents (1963)
recognized only one basalt which- he co si ered to be
Pleistocene in age. A'series of.older basalts are exposed. . . in the canyon of the Rio Grande de Santiago, north of
Lago de Chapala. _Potassium-argon analyses, of a. section
in the canyon wall north .of Guadalajara indicate two
volcanic episodes, one from c. 4.6 to 5.5 rft.y. And
another from 8.7 to 9.5 m.y. before.present (Watkins
et al., 1971).
The Chapala Formation
Lacustrine sediments.--Although most .of the Mesa
Central is dominated by volcanic featurs, lacustrine
sediments are widespread in the Chapala area. Palmer
(1926) referred to the sediments as the "Chapala Beds,"
basing the name on the extensive exposures around the 0 town of Chapala'on the northern shore of the present
lake: Within this designation:he included the beds at
• Chapala and "...elevated lake- and swamp-deposits..." at TizapSn, Las Caleras and La Palma, on the southern 36
Figure 4. Localities of the Chapala basin mentioned in the text. Dots indicate cities and towns; stars indicate ' fossil sites.
41. .e:
_ .r 37
•
•Guadalajara,.
El Molino • Chapala type section Jocotepec Quarry *4/ Jocotepec • 0 • 40, • c?
• • Tizapan Las Caleras
• , • Concepcion de Los BuenoS Aires JiquilpAn
• Zopotiltic
,
2,0 • km
Figure 4 '38
of the lake, and at ConcepciOn de Los. BuenOs
Aires, C. 40-km south_Of the lakl. Downs (1158) 'referred ,
to the beds as, the Chapala Formation, and Cleffients (1963)
expanded the2d4tinition to include lacustrine sediments
whiCh o crop on the Chapala-Guadalaaf.a highway, north
- - ,pf"the volcanid ridge• which forms the present northern-
limit of(Nphe Chapala basin. Both Palmer and Clemes
referred to deposits of tuff and pumice in,-their
- descriptions of the Chapala Formatio thereby including
deposits of fluviatile sedimen s at Jocotepec QuarrY.
Clemen (1963) described a thick conglomerate.overlain
by ash and pumice north of the lake in the pas% followed
by Highway 15. His description matches the upper exposures
-'at Jocotepec Quarry. Palmer (1923) mentioned-"...exten-
sive tuft and pumice beds in the upper part of the Chapala
formation." Such deposits are.--known only at Jocotepec*
Quarry.
Palmer (1923) des4ribed the beds near the town of
Chapala as "...loose, or slightly consolidated, very .
light-gray and white clays, marls gnd_fine sands, - together With an occasional bea,-di coarse sandstone.
• and fine arkose conglomerate. There are also extensive
beds of white, diatQmaceous earth, carrying /fresh-water diatoms and - liany thin beds of pumice. In this locality
the section is several hundred feet, thick, and well- bedded,- and has a'general dip to the northeast of
20 degrees." .-39
Palmer.s description is most closely matched by a
section exposed in a roadcut on the Chapala-Guadalajaia
highway, c. 4 km north of Chapala. Remains of fishes
from this locality are described in Chapter III.
Repti1.es, identified by T.R. Van Devender and J.B. ,
Iverson, include a turtle in,the genus Pseudemys and a
crocodilian, CrocodYlus sp. Two species of birds recorded
from Joeotepec Quarry (Alvarez, 1977). ate based on Material
which actually came from the Chapala roadcut (UMMP V61086).
.They , te a:sandpiper, Calidris fusicollis (Vieiliot),
and a meadowlark; Sturnella(?) sp. Downs (1958) reported
a probable Mexican cormorant and flamingo from. tlie Same
beds. -Mammals from the Chapala section are. Cuvieronius
sp., Equus sp., Nannippus sp., and a ;arge peccay.'.
= series of diatom-smples from the 'Chapala.roadcut are St • - being examined by 1J.P. Bradbury.'
In 1977 Several new sections in the Chapala 7 . . / Formatisi.m had been exPosed_by-constr 'tion of a roads
from the Chapala,-Guadalaiara highw y north of ChapAla // . to the town of A4400.c (Fig. 4). The sediments in these
exposures resemble those of/the'ttype'Chapala.section,
consisting of diatomac' 9.ús earth, clays, poorley
CONSOLIDATED INUDSTON , fine sand and fine volcanic ash.
The diatomite is oft, light gray to ochreous stone
with no obvious bedding 'STRUCTURE. It occurs in layers
from one to ten meters thick which mayanclude small 40
lenses of fine sand. Clay and mudstone occur An beds i usually less than one meter thick/with many fine" horizontal . ,/ • 7' . , /, laminations. -Lenses of sand thay, be as much as two meters
- thick, but they are of limited lateral extent (-usually
less than--I5 m), The sand- and ash are frequently
cross-bedded. There as no consistent trend in clagt size
,-IroM the bottom to tOp of the deposits, hut volCanic. ash
is more common in the upper part of the section. •
The beds in the Chapala type section are tilted tb
the vprth at an angle of 21.'3 . Afong the new road to. . z te4 ,-'Ajijic, the beds are highly folded and fractured ift
several places, presumably as a consequence of having 144 been uplifted.
Fluviatile-sediments.--The deposits ap JocotePec- , Quarry provide a distinct contrast to the rained, / well sorted deposits which`are wide-spread AlihZ4hapala ' basin. Although a few lenses of diatOmite and
sand do occur at Jocotepec Quarry, -tile sediments — ts‘ •*,
largely consist of pumice particles, .cobbles and SoupAer4 nollP••••le • .
4r: which are generally well rounded and sugge4ptive of-curie
action. / 411.• ./' • •••■■
The Jocotepec Quarry is an active sand and gravel • • •
pit 'being used as a source of con6truc.Eion materials. • When it was visited by Barf?our and Douglass in 1969 mid
Miller and Cavender in.1971, it - Consisted of two pits', described in a geologic section by Smith et al. '(19751. In p1976 the quarry had been greatly altered, the lower '
pit being more extensive and much deeper.
The stratigraphicaily lowest deposits in the Jocotepec- -% section are a series of alternating beds of mudstone, -
diatomite and fine gray sand which vary in thickness
from a.few centimeters to c. 3 ,m. . A total thickness of 10 m of such sediments is exposed. The mudstone and
diatomite are poorly consolidated and exhibit nd'bedding
• -•• structure. They are very similar to sediments of the
Chapala type section to which they may be stratigraphically ,
equivalent.. However, the lenses of sand included in
these ..bedsare thicker and more common than at Chapala; \ they are cross-bedded and bear abundant remains of /^\ suckers, minnows and catfish which are not known from
• the Chapala type section. Similar beds of fie ' sediments
and some finely laminated shales occur in other parts of
the Jocotepec section, but they are thinner (less than
30 cm thick) and less common toward the top of the
section.
The fine-grained sediments in the base of the
section are overlain by layers of coarse cross-bedded
sand and water-rounded cobble. Boulders •(to 2 m in
diameter) occur in parts of the section. The larger
clasts (gravel to boulders) are composed of basalt
probably derived from a steep volcanic ridge which • forms the eastern wall of the pass at Jocotepec Quarry. 42
• In the upper part of the settion the san s and
• gravels are replaced by progressively thicker beds of
, water-laid ash and cross-bedded particles of pumice.
The most extensive deposit at the quarry is a cross-
beddrel, fractured pumice-conglomerate at the top of the
section which is greater than 6 m in thickness.
Bedding structure is not well marked in the fine 1 sediments of the lower,part of the section, except in
occasional thin beds of horizontallYi laminated shale.
Most of the coarser sediments are srongly cross-bedded,
most often indicating deposition by water moving to the
west oninorthwest.
Several Of the beds containing larger clasts are
• poorly sorted and have an open matrix. They contain
angular boulders and appear to be the result of mass movement of alluvium from the eastern wall of the pats. Vertebrate fossils are extremely abundant at
Jocotepec Quarry. The remains of nineteen, species of
fishes have been recovered from this locality (see
Chapter III). Reptiles include the turtles Kinosternon
hirtipes, K. integrum, Terrepene culturatus and two
snakes, Thamnophis sp., and Trimorphodon tau (Smith,
'Van Devender and Iverson, in prep.). The twelve species
of water birds described from Jocotepec Quarry by
Alvarez (1977) include grebes, cormorants, ducks and
an anhinga. Most mammalian material from the quarry - 43
has not yet been identified; the remains include rodents,
horses, a peccary, an armadillo and a mammoth. Portion6
of the mammalian,material are being examined by R.M.
Wetzel and L.L. Jacobs.
Age.--The unusual association of fossiliferous
sediments with volcanic materials in the Chapala area
should eventually allow precise dating of the fossils.
However, paleomagnetic and potassium-argon analyses
have so far been made at only one lodalitY (Watkins et al.,
"7-1971) which doesliIot-bear on the Chapala Formation.
Most vertebrate fossils from_the Chapala area are
considered-to be late Pleistocene in age . (Ferrusquia- Villafranca, 1978), but there has been confusion, about
the source of the mderial on which this age is based.
Much of the material in institutional collectibns was
taken from reworked lake-bottom sediments and probably
representg%3 mixed fauna. Downs (1958) considered this
material to be characteristic of the late 'Pleistocene.
Fossils taken from the Chapala type section seem to be
correlative with the lake-floor fauna, with exception
of the genus Nannippus (Ibid.). This small .horse is
well documented from the late Pliocene of North
America (Ferrusqula-Villafranca, 1978), although
Pleistocene records are also known 4Romer, 1966). The
presence of the Pliocene grebe, Pliolymbus, col-roborates the determination of the Chapala beds as PlioT-Pleistocene 44
(Howard, 1969). This is taken to be the maximum age. of the Chapala Formation.
. The deposits at Jocotepec Quarry are positioned stratigraphically above the Chapala type section and Q IF - bear a much younger fauna. On the basis of fossils-of'''
Sigmodon and Neotoma, C.W. Hibbard consisdered the eatina . to be Pleistocene, but older than Sangamon or Wisc6nsini
1 )ICT - 41%1/4 (letter to C.D. Barbotlr-, 1969). ' X "R
Sedimentary environment.--The well sorted, E4V • t fine-grained N,sediments which are widespread in the NN Chapala basin were most likely laid d9wn by a single lake which waS .1a;ger than the one which occupies the basin tbday (Palmer, 1926, Clement, 1963). The fossiliferous sediments expose ..ar the towns of - Chapala, Ajijic and Jocotepec may Ii4:ye been near the margin of the former Lake as they contan.. beds of . - cross,-bedded sand, and remains of wading ,birds and terrestrial animals. The thickness of the deposits suggests prolonged, uniform conditions, although volcanic activity occurred iptermittently nearby as indicated by layers of fine volcanic ash. The beds were probably deposited at a lower elevation and were subsequently uplifted, as they have been fractured and tilted.
This inference is .corroborated by the presence of a crocodile. and flamingo which are not preS-OfffY known from elevations as illigh as in the Chapala basin (c. 1600 m). 45 •
Clements (1963) reported lake-shore terraces at
levels 200, 150 and 100 in above the present lake,'and 41. attempted to correlate the terraces with pluvial events
doctimented elsewhere in North America. Subsequent
investigators have failed to locate terraces in the
Chapala basin, and topographic maps show that a lake at
the levels mentioned cOuld not have been contained by
present topography. However, occasional extension of'
lacustrine conditions is indicated by the occurrence
of diatomite and finery laminated shales at Jocotepec
Quarry. ... . The deposits at Jocotepec Quarry were apparently
id down by a former westward-flowing outlet of the
\\\1aCha\p basin (Smith et al., 1975). The abundance
of coars material including large boulders indicates
'high relief. This coarse material might not be expected -; in the outlet of large sedimentary basin, "but it could
have been delved loc lly in the 'pass itself.
..The Atotonilco-Zacoalco Basin
Fine-rained, water-laid sediments are widespread in
the Atotonilco-Zacoalco basin, an endorheic basin which trN ! lies just west of Lago de Chapala. These sediments
have yielded many late Pleistocene vertebrate fossils
including fish material from three sites (Fig. 2:
Localities 2-4). Howard (1969) recorded remains of nine species of birds from basin, but the large 46
mammalian fauna has not yet been reported.
The shallow lakes which now occupy the basin
(Atotonilco, Zacoalco and San Ma;,eos)- fluctute greatly
in size, and bne of them, Lago de San' Marcos, is
A , seasonally dry. Lacustrine sediments extend far
beyond the maximum limits of the present lakes to
form an interconnected system of. playas which occupy
'the larger part of the basin. It appears that much of
the basin was once inundated by a large lake. This
could have occurred when the Chapala basin was drained
from its western end by the outlet which left the
deposits of Jocotepec Quarry. This outlet probably
flowed about 8 km northwestward to El Molino (Fig. 4)i
wher4e it cut a gorge through a series of basalts and
entered the Atotonilco==Zacoalco basin. This connection
is supported by zoogeographic evidence (Chapter IV).
Mammals and birds from the floor of Lago de San
Marcos agree,with the concept of a late Pleistocene
age for the deposits (Howard, 1969).
Santa Rosa'
'After leaving the Chapala basin, the Rio Grande
de Santiago flows northwestward, cutting a deep canyon
through primarily igneous rocks. In the single section
where detailed petrologic studies have been made, tuffs and thick flat-lying ignimbrite sheets are dominant; in upper exposures; they are intercalated with.flows 47
of basalt or bAsaltic andesite (Watkins et al., 1971).
In a.separate section.,:at Santa Rosa, c. 35 km to the ,
west, the canyon exposes a series of fine sands and'
lacustrrne-shales between two basalt flows.
Most.oT the deposits at Santa Rosa are not
fossiliferous, but well preserved remains of goodeids
have been recovered from some of the fine-grained shales
-which are delicately laminated. The preservation of
delicate laminations requires that lake-bottom sediments
not be disturbed by turbulence or biological activity..
Such conditions occur in thermally and chemically
stratified lakes in which only anaerobic bacteria are
present below the hypolimnion (Bradley, 1929, 1931., 1948;
Hulsemann and Emery, 1961; Van Houten, 1964).. The
preservation of delicate skeletons in articulated form,
as in Fig. 18, also supports the inferende of anaerobic
conditions in a stratified lake. Such Conditions are
probably rare in small freshwater lakes (Wilson, 1974).
‘It is therefore possible that the laminated shales at
Santa Rosa were-laid down by a rather large body of
stratified water.
Alvarez and Arriola (1972) assigned the Santa Rosa
fossils to the Pliocene, partly on the basis of a
geologicl map showing Pliocene rocks in the Santiago,.:
- canyon. They also noted that rocks in the canyon 35 km to the east were of two , age groups, about five - 48
and nine million years old (Watkins et al., 1971). 4 . It, is likely but not certain that the flat-lying beds
samPled by Watkins and coworkers extend as far as. 1 Sana Rosa as geology in the area is not complex
(Watkins, pers. comm.). 'However, even if the absolute ages of the Santiago basaltt are being used correctly, -
.a Miocene designation would be more appropriate, as the
-Pliocene is now taken as extending only between 1.6
and 5.5 million years (Berggren and Van Couvering, 1974).
•
.;- CHAPTER III
FOSSIL-FISHES OF THE RIO LERMA BASIN
The 'following species accounts provide a cata- • te":".... logue and description of the known fossil remains.of. ., • fishes from the Lerma Basin and its inferre ormer parts'in western Mexico. 'Synonymies are l' ited to fossil records, even in the cases of taxa still extant.
.Diagnoses and descriptions aie osteological and empha- size characters useful in determining fossil material.
Remarks on Recent,fish distributions are based on field work, collection records at the University_of
Michigan Museum of Zoology, and published records
(where cited). Material which is listed without catalogue numbers will be deposited in the Museum of
Paleontology, Institute of Geology, University of
Mexico (IGUM),.
FAMIIY Salmonidae
Genus Rhabdofario Cope
Characteristics of Rhabdofario are discussed by
qope (1870), Cavender and Miller (1972), and G. R. '1
Smith (1975). The latter reference includes an 49 • s ' 1.
extensive'diagnosisl of the genus and type species, , -
R. lacustris. •
Rhabdofario rugosus new 'species
(Figure '5) % ' Holotype.--LACM uncat.: an.incomplete right -3A
articular-angular lacking part of the anterior ramus;,
total len4th 20.7 mm.
Horizon and type locality.-- LACM locality 65191:-„I
lake tied deposits on the east slide of El Tecolote in ; Laguna de San Marcos, 5 km N and 1.5 km -E of Zacoatco,
. Jalisco, Mexico. Unnamed formation, late Pleistocene
(Howard, 1969). •04 . - T Material.--LACM Incat.: 4 caudal vertebrae from type locality. - Diagnosis.--A salmonine assigned' to Rhabdofario on
the basis of the high coronoid process of the articular-'
angular, dorsal process vertical above the retroarti-
cular, and articular fOssa wiae and strongly slanted.
-yentromesially with only 3 slightly produced lip, at its
anterior border. The species is distinct from other
Rhabdofario in having an articular-angular with: a
small sensory canal pore in the lateral surface of the
dorsal process, well defined endosteal process separat-
ed from the base of the coronoid process by a large pit
in its dorsal surface, and more extensive exostosis
at the posterior end of the mandible. 51
Description.--The angle of the coronoid process of
/ the articular-angular (Fig. 5) is 49° from the axis of
the endosteal process. This compares to .26-42° for
living North American Oncorhynchus and 49-57° for
, other. Rhabdofario. The lateral surface orthe articular-
angular is marked by extensive iugose exostosis eXtending
onto the dorsal process and,base of the coronoid"pro-
cess; pores and fine striations emanate from the area
beneath the dorsal process toward the margins of the . q„ bone. The articular fossa is wider than long and
weakly bilobate; thedorsal process rises behind the
lateral lobe, vertically above the retroarticular. The
dorsal process is as broad as high and is perforated on
its lateral surface by a relatively sMall foramen for
the acoustico-lateralis canal. The well defined
endosteal process rises as a riage on the mesial surface
of the bone; it is separated from the coronoid process
by a deep, oblong forameil in its dorsal surface. The
groove for Meckei's cartilage is dee5-3M stops short
of the articular facet, at a point even with the anter-
ior end of the endosteal process.
The centra of the four caliaal vertebrae (Fig. 5)
measure as follows (length/horizontal diameter, mm):
4.8/7.5, 4.8/7.6, 4.7/7.5, 4.8/7.5. The neurar and hemal spines are broken off just above their base.' The sides of the centra are ornamented with 'fine perfor- 52
Figure 5. Bones of Rhabdofario rugosus, n. sp. (A) Lateral and (B) mesial views of right articular-angular, LACM uncat., holotype, 20.7 mm. (C) Lateral and (D) mesial views of caudal vertebra, LACM uncat., 7.5 mm in horizontal diameter. • 53
Figure 5 54
c-- ations over which a network of horizontal ridges-Xs superimposed.
Remarks.--The similar dimensions of the four cen- tra suggest that they are from the same fish. They have about the same diameter as caudal pentra fr.m an •
Oncorhynchus kisutch which was 527 mm in standard' length. The articular-angular is probably-from a dif- ferent, slightly larger fish. '
The' lateral perforations of the walls, of the centra are similar to those of Salmo clarki, as pointed out by
Miller (1972). However, thei unusual horizontal' ridges - are most similar to striations in Rhabdofario carinaus.
Weaker striationscan be seen in large centra of
R. lacustris, but material similar in size to that of , R. rugosus is not available for comparison.
The bones of R. rugosus were taken from fine- grained sediments; like other members of the genus, it appears to have been a lake-dwelling species. -I.ts re- mains were associated with bones of a minnow, Yuriria elliana, and a large catfish, Ictalurus. The catfish, remains were most abundant. • Etymology.--The name of the new species is taken from the Latin ruga, wrinkle, in reference to the ridged l ral surface of the articular-angular. It is • .:, given as.a masculine adjective in the nominative singu- ; lar. 55
Unidentified Salmdnidae
Remains of, an additional salmon-like fish have
been recovered from 'a' late Pleistocene deposit near the
• present shore of Lago de Chapala at Ajijic,
Other remains of the same species were collected from ,
the lake bottom at Ajijic; they were associated with
Pleistocene mammalian fossils. The bones suggest a
large salmon, nearly one meter in total length. The
is being described by T.M. Cavender and R.R. species • Miller.
Family CatostoMidae
Genus Moxostoma Rafinesque
The disarticulated remains of two sucker spe-
cies occur' together at JOcotepec. They are assigned
to Moxostoma on the basis of maxillary and opercular
characters. Members of the genus are distinct from
other catostomids in having the anteromedian process of
' the maxilla thick and blunt rather than elongate and
sPatulate. The maxilla is robust with at least moder-
ately developed dorsal and ventral keels and a thick
neck. The opercle is natrow, its height more than twice
its upper width (Nelson, 1949). The anterior opercular
margin is concave anteriorly, and the ventral carina of
the interopercle is confined to the anterior* two-thirds . of the bone or less.
■•••■■ •,. 56"
Moxostoma cf. M. robustum species group (Figs. 7-8) ' Moxostoma sp.--Smithet al., 1975. , - Material, localities and horizons.-Chapala Forma-
tion, Jocotepec Member. Pleistocene. UMMP V62544, par7 tial hyomandibular; V62545, fratments of cleithra and
opercles; V62546, partial opercle; V72713, interoper-
cles; V72714, metapterygoid, quadrate, dentary,.der- . methmoid; V72715, maxillae. IGUM, uncatalogued, dermeth-
. moids, metapterygoids, opercles, intexopercles, premax-
illae, maxillae, hyomandibular.
Identification.--Three species of redhorse suckers
are present in Mexico today, M. congestum,.M. austrinum, and M. mascotae, Together with M. robustum of south-
eastern United States, they constitute the M. robustum
species group (Rbbins and Raney; 1957). Although the ' Mexican species differ in head morphology and charaAtert of the Weberian apparatus (Robins and Raney, 1957),
they are difficult to separate osteologically, Max- - • illae, which have generally been found to be diagrioitic
to the species of catostomids (e.g., Miller and Smith;' 1967), are not so useful in distinguishing'members of the M. robuttum 'species group. G.R. Smith (1975) used principal components analysis as A method of sorting trends in variance among fossil,maxillae of Catostomus /* from Lake-Idaho. A similar approach was used here in 57
an effort to find distinctions among the maxillae of the M. robustum species group. Seventy-three maxillae representing all species and subspecies of Mexican Moxostoma (and including six 'fossil specimens) were scored for twelve measurements
(length and diameters of processes and distances-be-
tween insertions of muscles and ligaments). Principal
components (Sneath and Sokal, 1975) were calculated
from the correlation matrix in separate analyses of un-
transformedLand_log-transformed data. Pair-wise and
overall comparisons of.\ all taxa and unknowns were made, and bivariate scatter diagrams were analyzed. No axes
were found/ capable of separati maxillae of the Recent
taxa. ,FosIsil maxillae were distinct to various degrees
(Fig. 6). One of them, repre enting the new species de-
scribed below, assumed an iso4ted position in most scatter diagrams. Five remaining fossils formed a clus-
ter incoMpletely distinct from living taxa, but this was
due to their stores on the first principal component
which primarily reflects their greater size.
To test the possibility that the nominal taxa do not constitute good species, principal components anal- ysis was also performed on'31 meristic And morphomet- • ric characters of 114 alcoholic specimens representing all Recent taxa. The-species and subspecies recognized by Robins and Raney (1957) were found to be porphologic- ..• • 1,4•
Figure 6. Scatter diagram of maxillae of Mexican Moxostoma on principal components I and II. Circles, M. austrinum; open squares, M. congestum; solid , squares, M. mascotae; open star, M. ammophilum; solid stars, fossils from Jocotepec Quarry (cf. M. robustum species group).
.••••
••• • 59 60
ally distinct (Smith, manuscript in preparation).
Osteological characters OF the FOSSIL material are
given below. The only consistent_distinction between
O the FOSSILS and Recent material is the greater size OF
the FOSSILS. The largest maxilla is from a fish about • 0.5 m SL, based on extrapolations from Recent skeletons. Description.--The metapterygoid (Fig. 7) bears a
mesial crest on its ventral limb which is better devel-
oped than in Recent material. The sympletic process is
slanted posteroventrally. A crest on the posterior mar-
- gin of the bone receives the anterior margin of the ven-
trallimb o'f the hyomandibular. The ventrar and mesial
planes of the metapterygoid meet at an obtuse angle.
The dorsal keel of the maxilla is moderate with a
straight anterior edge (Fig. 7). The anterodorsal pro-
cess is vertical to the long axis of the maxilla and is more than half as high as - the premaxillary process.
The premaxillary process is drum-shaped, very roust •
and curved anteroventrally. The crest for inde tion of
the palatomaxillary ligament' is complex, situated at
the base of the anterodorsal process. Insertions of the
maxillaris muscles are well defined. The premaxilla has a straight or slightly curved biting edge; the dor- sal limb is slightly longer than the lateral limb (Fig. 8). The dentary has a. short and broad gnathip ramus 61
Figure 7. Bones of Mexican Moxostoma. (A) Lateral and (B) mesial aspects of.right maxillary of M. ammophilum, IGUM uncat., holotype, 22.0. mm total length. (C) Mesial and (D) lateral views of left maxillary of cf. M. robustum' species group, UMMP V72715, 21.9 mm total length. (E) Mesial. view of left opercle of cf. M. robustum species group, IGUM uncat., 22.9 mm greatest length. (F) Mesial view of right opercle of M. ammophilum,.UMMP V62543, 31.7 mm greatest length.
_
I? 62 t.
FIGURE 7 vst
63
Figure,8. Bones of Moxostoma from Jocotepec Quarry. (A) Mesial, dorsal and lateral views of dentary of Moxostoma cf. 'M. robust= species group, UMNP V72714; (B) Dorsal view of dermethmoid of M. ammoOilum, IGUM uncatalogued. (C) Lateral view of right interopercle, UMMP V72713, and (D) right gremaxilla, IGUM uncatalogued of Moxostoma cf. M. robustum species group. Scales indicate 1 cm.
4 64
•
• 65
■ \ without a well-developed groove for the labial carti- lage (Fig. 8). The gnathic forameh-and crest for Meckel's cartilage are 'clo§e together at the base of
the gnathic limb, about even with the anterior edge of
the coronoid process. The articular fossa of the opercle is nearly
round; it is reinforced by thickening- of the opercle at
its base, but not'by well-developed struts (Pig. 7).
The interopercle iselongate with a well-develeped ven-
tral keel; the posterior ramus is more than one-third
' the length of the bone (Fig. 8).
Remarks.--Bones of Moxostoma were most abundant
in a bed of coarse cross-bedded sana where they were associated with Ictalurus. They occurred occasionally
in lacustrine beds with Ictalurus, Chirostoma and
Micropterus.
Moxostoma ammoohilum new species
(Figures 7-8)
Moxostoma sp.—Smith et al., 1975.'
a.complete right maxilla col- , lected '3 June L977 by M.L. Smith. Measurements (mm): - tbtal-lengh 22.0, greatest depth between keels 10.9, least depth posterior to keels 3.6, 'least deptli anter- ior to keels 2.7. • Horizon and type locality.-- Jocotepec Quarry. - Chapala Formation, Pleistocene. \ 66
. Material. -UMMP V72712, V62543, partial operclei with dorsal processes and articular fossae. IGUM, der- - methmoid, opercles. All from Jocotepec Quarry.
Diagnosis.--A Mexican Moxostoma with a deep-bodied maxilla; the dorsal keel very high with a strongly curved anterior margin; ventral keel moderate; premax- illary process blurit, slanted only slight1I'ventrally; anterodorsal process very thick and short, only about half as long as the premaxillary process; crest for insertion of palatomaxillary ligament broad, Situated in the center of the head of the makilla-,-
Descriptiofi.-.-Maxilla.as above (Fig. 7). A der- methmoid was collected with the holotype, but it seems to represent a slightly larger individual. Its dorsal surface is flat and twice' as wide as long; the lateral edges curve toward the frontal contact which.is little more than half ai.wide as the anterior margin (Fig. 4.
The anterior process is short, about as broad as long.
A sensory foramen is present near the anterior margin of both rateral wings.
Four opercles are tentatively assigned to this spe- cies. They differ from those of the robustum group in having an oblong, rather than round, articular fossa' which extends onto the dorsal proCess and a complex
pattern of Struts.and 15erforations_ at the base of the
articular lacqt,(Fig. 7). • 67
Comparisons.--M 'ammophilum does not appear to be _L closely related to the subgenus Scartomyzon, in' which
the maxilla is elongate and has only a moderate 'dorsal
keel with a straight anterioi margin. The maxilla of
, M. ammophilum is more_similir to that of M. carinatum
in general shape, but differs in having the anterodor-
sal process slanted posteriorly at an acute angle. The
insertions for the maxillary muscles are less well-de-
fined in ammophilum than in most Moxostoma.
This species also differs from the robustum group
in having a*trapezoidal rather than rectangular dermeth-
moid, if that bone is..dorrectly associated with the hol-
otype.
Remarks.--All sucker bones from jocotepec which
are in agreement with the robustum species group have
been assigned to it.. Some bones of ammophilum may
therefore have been assigned to the robustum group, if
there are elements in which it is not distint from
that-group.
Etymology.--The name ammoPhilum is given as an ad-
jective in the nominative singular.. It is taken from
the Greek ammos, sand, and philia, love, in reference
.to the occurrence of the known remains in sandy sedi-
ments. 68
FAMILY CYPRINIDAE
Although minnows of the family Cyprinidae, consti-
tute_a_dominant element of the fish.fauna of most of
North America, the diversity of cyprinid taxa becomes -
progressively lower as one travels southward from the . 4 Rio Grande basin. Only three genera, Notropsis,
Algansea and Yuriria, are found in the Lerma basin to-
day, and only, the latter two are known as fossils from -
the basin. Cyprinid bones occur at all:localities ex-
cept Santa Rosa, but they are nowhere common. -1
Genus Yuriria Jordan and Evermann
Tho nomenclatural history- of Yuriria has been re-
viewed by Miller (1576). Jordan et al. (19n) first
treated Yuriria as a full genus, an action which is
supported by the present study. Characters diagnoping
Yuriria were given by Smith et al. (1975) and Miller
(1976). Members of the genus are recognized osteolog-
ically by the numerous, large and closely spaced pores . in the cephalic sensory canals; supraorbital sensory
canal extending onto the parietal; pharyngeal arch with
- a single row of robust, conical teeth; and preopercle
with vertical and horizontal limbs of equal length.
alta (Jordan)
(Figures 9,10) . . 4 Falcularius chapalae.--Alvarez, 1974. Yuriria alta.--Alvarez, 1974. 69
Diagnosis.--A cyprinid with-.a moderately heavy
pharyngeal arch (Fig; 9) Toihich.has anterior and poster-
ior limbs less robust than in Y. elliana, its only con-
gener. The anterior, limb'is not as wide as the base of
the second tooth (iir mesia1 view); it tapers to its mid-
point and then expands into,kflattened distal end.
The dorso-ventrally expanded wing of the dorsal limb is
not as wide as in elliana.v The'dentary (Fig. 10) IL
long ana nearly straight ‘zith a slender anterior ramus • which tapers into - a marked, constriction before expand-- , ing into a -distinctive symphyseal end. The gnathic
surfAce is 4 to 4.5 times as long as wide. Sensory ca-
nal pores are numerous on the dentary (6 or 7, counted •■• • anterior- to the mid-base of the coronoid process) and
• . -Nkre larger than in any Other North American id cypr?"'., examir40. The distance from the sensory'aanil to the
ventral margin ofethe dentary Is eqUal to or less than
• the width of the largest pore.
• Discussion.--Alvarez (19.74) recorded Falcularius
chapalae'and Yuriria alia from bottom sediments of Lake
Chapala and Zacoalco. He assigned vertebrae and var-
ious head bones to the two nomirial forms without charac- terizing them. Pharyngeal arches were distinguished on
.the basis of the lateral perforations and lamellae,: _ however, these characters show great variation, some-
tunes differing considerably between the two arches in 70
Figure 9. Mesial and dorsal views of pharyngeal arches of Yuriria. (A,B) Y. elliana, LACM 9070, lake—floor sediments in Laguna de Zacoalco, 17.2 mm greatest length. (C,D) Y.,elliana, UMMP M72717, Jocotepec Quarry, l8.7 mm. (E,F), Y. alta, UMMZ 179703, Lago de Chapala, 157 mm!
/ • 72
Figure 10. Lateral, dorsal and mesial views of'dentaries. of Yuriria.. GPO, -Y.- alta,- UMMZ 179703-S#1, Lago de . Chapala. (B)‘ Y. 61137.Ta, holotype, IGUM, Jocotepec Quarry. (C) Y. eirriFITT UMMP V72716, Chapala type section. Scales indicate1 cm. 73 •
.Figure 10 • , 74 1‹
the same individual. I find no consistent osteological
'differences between the two forms in Recent material. f: The genera were originally distinguished on the - . "basis of a barbel present in Yuriria, but thought to be
lacking in Falcularius. The barbel actually occurs in
both (though variably) and they represent the same spe-
cies (Miller, 1976).
Distribution and ecology.--Y. alta'is known today
from the Lerma basin, the upper Rio Grande de Santiago
including those tributaries which drain parts of the
Mesa Central, and the upper parts of the Ameca system.'
. It occurs in most aquatic habitats in this range, from
large lakes (including Lago de Chapala) and rivers to
very small 'streams. The speCies occurs over a variety
of bottom types and its presence cannot be taken to in-
dicate any particular habitat.
The fossils of this species discussed by Alvarez
(1974) are from the Zacoaico-Chapala- collection of
Federico SolorzanO. Since the collection includes
bones from two separate drainages which were combined , without regard to their origin, it is not possible to'.
determine whether the Yuriria fossils came from one or
'both lakes. Y. alta is not known from the Zacoalco . ba-
sin today, but is common in Lago-de*Chapala. However,
it is reasonable that it once occurred in Lago de Za-
coalco, since it now occurs in the Rio Ameca which is ' ' inferred to have served as. the former outlet of that '
lake (see, Smith ind Miller, in press). Yuriria elliana new species
- (Figures 9-11f
Yuriria alta.--Smith et al. „1975. -
polotype.--A complete right .dentary (Fig. 1G) A collected 6 June 1977 by M.L. Smith. Measurements (mm):
- total length 19.9, length gnathic ramus 11.5, greatest
width gnathic surface 3.6, length coronoid process
' Horizon and type locality.--Lacustrine bed in SW'
f Jocotepec 2uarry. Chapala Formation, JocotepeC
Pleistocene.
terial, localities and horizons.--7C,hWpa1a -Forma-
tion. apala type section and local faAna. Plio-
Pleistocene- . (Downs, 1958). UMM V72716, pharyngeal , arches maxilla, preopercle, dentary.
JocotePec local fauna. Pleistocene. UMMP V6/538,
c pharyngeal arches; UMMI;'V62539,.pharyngeal arches, bas.-
ioccipitals; UMMP V62540, cleithra, quadrate, pharyn-
geal arches, dentary;. UMMP V62541, basioccipitals, phar-
Yngeal arch; UMMP V72717, baaioccipitals, cleithra,
• , opercles, preopercles, dentaries', articular, frontals, haryngeal teeth and arches; IGUM, eight collections
containing h4sioccipita1s, cleithra, preopercles,'oper-
cles, cientaries, articulars, frontals, Pharyngeal teeth I .and arches. , tl Zacoalco local fauna. Lake bed deposit in Laguna
de Zacoalco on W side of 'El Tepolote, a butte between
Lagunas de Zacoalco and San Marcos, Jalisco. Late
Pleistocene. LACM 9079 complete left pharyngeal arch . with teeth.
Lake bed deposit in Laguna de San Marcos on E side
of-El Tecolote: Late Pleistocene.. LACM uncat., cleithra,%
opercles. IGUM, ceratohyal, dentary, opercle% UMMP
V72718, dentary. . . • Diagnosis.--A large 'species of Yuriria reaching a
maximum size of ca. 300 mm SL, based on extrapolatipn
from pharyngeal bones. The pharyngeal teeth are short
and thick with slight to moderate hooks at their tips. The pharyngeal arch is more robust than an other central
Mexican cyprinids.'. The numerous sensory canal pores on
, bones df the head are neither as large nor as closely
spaced as in Recent'material or*Y. alta. The dentary
is shorter and more robust than in Y. alta.. Length of
, ,the gnathic limb is 2.7 to , 3.5 times the greatest width
- of the gnathic surface (n=7). r ' Description.--Yuriria elliana is known only from No* disarticulate4 remains. Diverse.skeletal elementi are .tv assigned to the new species on the basis of their
association with dentaries.
The anterior limb of the pharyngeal arch is"°. slightlY shorter than the tooth row and is more robust , 77 •
than in Y. alta, about as wide (in mesial view) as the
lase of the second tooth (Fig. 9). -The anterior limb
iš straight or nearly so (in dorsal view) and bears no
distinct.carina. The dorsal limb is longer than 'the -todth row and massive; it is laterally compressed and
expanded dorsoventrall§l to form a wing 1.ihich is broader
than in the living species. Pharyngeal teeth are ro-
• bust and conical. The two anterior teeth are.usually
unhooked and swollen at mid-point; their grinding sur-
faces are poorly developed. The posterior teeth are
slightly compressed and Moderately hooked with narrow,
oval grinding surfaces.
The pharyngeal plate of the basioccipital is five-
sided; itš greatest width equals 60-75% of its length.
The lateral walls of the pharyngeal plate are low and
rounded, not pointed as in Y. alta. The masticatory
surface is concave and smooth. The plate ends in a pos-
terior process which is laterally compressed, expanded 2 •dorsoventrally to form a broad paddle and about equal
to the pharyngeal plate in length. .The process lies in
a plane nearly parallel to that of the basioccipital.
The robust dentary (Fig. 10) curves mesially at its
anterior end; it is 'not' ventrally. The gnath-
ic surface is broad and flares outward'to,form a dis- , '.tinct lateral'crest. The interior limb tapers anterior- .1Y and ends in. a dorseventrally expanded symphyseal 78
knob; it is not much constric ed posterior to the Om-
physis as in alta. The sensory canal follows thelyen-
tral edge of the dentary'at a distance 1 tO 4 times as
great as the largest pore, and opens to the surface- through 5 or 6"pores.(counted anterior to the mid-base
of the coronoid grocess). The porei are about equal to
the- width .of the spaces separating them, but . are not as - wide as in Y..alta.
PreOpercles of Y.-elliana are distinguished by an
adductor_ridge running in front of the sensory canal
pores (Fig. 11). The laminar part of the bone is re-
cessed anterior to the ridge. Sensory canal pores are
numerous and about as wide as the spaces separating
them. The dorsal margin of the opercle is nearly
straight or slightly convex. The ascending process is
directed anterodorsally and is reinforced, on its mesi- al surface by a strut from the opercular cotyla * (Fig. 11).1. The supraorbital margin of the frontal is broadly 'concave (Fig. 11). The - sensory canal is covered by ,a
thin roof of bone which rises above the rest of the sur-
face of the frontal. Variation.--5AVaries referred to this spe es , _ are variable in4he-1ength and robustness of the gnath- ic limb, amount of constriction Of the gnathic 1 mb- pos- terior to the symphyseal knob, breadth and defle tion 79
Figure 11. 'Cyprinid bones frot Jocotepec Quarry. (A) Algansea milleri, UMMP V72719, dorsal/and mesial views of left maxilla lacking the rostral process. (B) A. milleri, UMMP V62532, dorsal- view of right phar7ng-ea-1--iTa lacking. the first tooth and the anterior and dorsal limbs. (C) A. milleri, IGUM, lateral view of right preopercleT (D) Yuriria elliana, UMMP V72717, lateral views of partial faTTTe-opercles. (E) A. milleri, IGUM, mesial view of partial left •' opercle. (F) Y. elliana, UMMP V72717, mesial view of partial right opercle. (G) Y. elliana, UMMP 72717, dorsal view of left frontal.— Scales indicate1 cm.' 80
s Figure 11 81.e ‘
4 of the gnathic surface, and orientation of the coronoid
process. However, they all share the distinctive size
and position of sensory canal pores with Y. elliana.'
The single cyprinid dentary known from the Chapala type
section (Fig. 10) is particularly short and heavy with
the coronoid process at a right angle to the gnathic
limb. Other cyprinid bones with which it is associated
(pharyngeal arches, preopercle, and maxilla) •are typi-
cal of Y. elliana. A specimen froM Jocotepec Quarry is
unusual in the shortness and breadth of the gnathic sur-
face and placement of the mental foramen adjacent to
the crest for Meckel's cartilage rather, than posterior
to it. These bones may represent extreme variants of
Y. elliana or possible new taxa closely related to it.
Relationships.--Although Yuriria has generally
been regarded as a form of Hybopsis, several osteologi-
• cal traits distinguish it from that genus'an'd suggest
that it is actually related to cyprinids from western
rather than eastern-United States (Smith et al.0 19754 Miller, 1976).. The supraorbital sensory canal extends , onto the parietal (as in Gila, Mylopharodon,-Myloch- - eilus and other western genera) % here it erids i;r1 a
pore. Thqtlarge number of sensory canal pores on the
head and the complete supratemporal'canal also suggest
• relationships to western genera (see Illick, 1956).
The new species is closely allied to Y. alta with 82
which it 'shares many'osteological traits. The most
readily apparent distinction' between the two species is
the size and lOcation of the mandibulai sensory canal
pores. The large pores placed near the ventral border
of the dentary of Y. alta are unique among the North
American cyprinids examined. The size of the pores in
i Y. elliana approaches that of Y..alta, but their loca-
tion farther from the margin of the dentary is more Nice'
that of Gila. This state is inferred to be.primitive
because of -its occurrence in many western genera.
Distribution and ecology.--Y. elliana is the most'.
widespread fossil minnow on the Mesa Central. Its re-
mains occur in fine-grained sediments of the Chapala
section and Zacoalco Basin and are most abundant in the -
lower-most lacustrine bedsTht Jocoteped Quarry. It is _ „ usually rare. in coarse sediments, but disarticulated
teeth are abundant in one deposit of cross-bedded sand
at Jocotepec Quarry. Its most frequent associates are
. Micropterus and Ictalurus.
Etymology.--The species epithet is an adjedtive
made from the name of Ellie Baker Koon who collected
much of the material of this study. -
Algansea -Girard „ DiagnoSis.--Mexican cyprinid fiShes with a single r row of four-teeth in each pharyngeal arch. The teeth
are long laterallj compressed, slightly hooked or not,:
\ '
83
. 'IN • • • - and clogely.crowded at the posterior end of the bone; the grinding surfaces are lacking or weak on the first
tooth, but mode4.6 to well-developed on •the remaining teeth. The pharyngeal arch is delicate with slender
limbs. The dentary is elongateand has a few small • sensory canal pores. The plate-like d iMosphenotic
is wider than long. , Algansea tincella (Valenciennes )
(Figure 12)
Algansea rubescens.--Alvarez, 1974.
Diagnosis.--An Algansea wit1a relatively short
pharyngeal arch, the anterior limb shorter and more ro-
bust than in A. popoche. The pharyngeal teeth are,
neither as compressed nor as crowded as in A. popoche.
The gnathic ramug of the dentary is short and robust;
the crest for Meckel's cartilage is in the posterior sis one-third of the gnathic / us, beneath the gnathi:C.for-
Amen; Pores of the acoustico-lateralis system few on
the dentary, only 2 or. 3 in advance of the mid-base of the coronoid process.
Discussion.--Remains of this species were re- ported by Alvarez (1974) from the SolOrzano collection from lakes Zacoalco and Chapala. The species occurs in
. both of those basins today as well as the Ameca,'Magda- lend and upper Panuco basins and the Valley of Mexico. 'Alvarez's material, was not re-examined. 84
• Algansea milleri new species
(Figures 11, 12) Alqansea tincella.--Smith et al. 1975. Holotype.--A complete left dentary collected 3
June 1977 by M.L. Smith. Measurements (mm): total length'14.2, length gnathic ramus 9.4, greatest width • gnathIc surface 2.1, length coronoid process 5.0.
Horizon and type locality.=-Lacustrine bed in SW'
wall of Jocotepec Quarry. Chapala Fortation, Jocotepec
Member. Pleistocene.
Material, localities and horizons.--Chapala Forma-
tion. Chapala type section and local fauna, Plio-Pleis-
tope'ne: IGUM, partial pharyngeal arch, ceratohyal. Jocotepec local fauna, Pleistocene. UMMP V62532, pharyngeal arches, basioccipital,,partial dentary; UMMP
V72719, maxilla, hyomandibular, Opercle; UMMP V62530,
dentary; IGUM/ pharyngeal'arches and teeth, dentaries, maxillae, and basioccipitals. Taxonopy.--Limited material of this species was assigiied to A. tincella by Smith et al.- (1975), al- though difference's were noted between fossil and Recent material in robustness of the pharyngeal teeth. The
• subsequent collection of additional material demon-
strates the fossil sDeCiles to be distinct in many as' s of its osteology. Diagnosis.--An Algnsea with a robust. dentary., the •I 85 ■••,"
•
gnathic ramus longer than in .tincella but not attenuate
as in .eppoche; gnathic surface broad with a sharp later- al edge; crest for'Meckel's cartilage near mid-point
of gnathic ramus-, well in advance of the gnathic fora-
men; sensory canal pores small and many, 5 'or 6 anter-
ior to mid-base of the coronoid process.
Description;--Dentary as in diagnosis (Fig. 12),
The anterior limb of the pharyngeal arch is distinctly
longer than the tooth, row; it curves gently lateral and
bears a moderate dorsal or mesial carina. The'anterior
limb iš not drawn to a point as in popoche, but is ex-
pande'd distally. The dorsal limb is slightly longer
than- the tooth row. It is very narrow longitudinally - and flattened on its lateral surface, but otherwise
round. All teeth (Fig. 11) bear distinct grinding sur-
faces which are long and narrow, ending in slight to moderate hooks.
The pharyngeal plate is as wide as or slightly wi- der than the c6ntrtm of the basioccipital. The poster-
ior pharyngeal process descends slightl from the plane'
of the basioccipital. It is Moderately compressed and
exceeds the pharyngeal plate in length. The maxilla (Fig. 11) is short and stout with long
palatiAe and ascending Processes. ' The depth of the bone at the midpoint of the ascending process equals one- 'third its' length. The posterior limb about equals the 86
Figure 12. Mesial, dorsal and lateral views of dentaries of Algansea. (A) A. tincella, UMMZ 189577-S#3, Lago de Chapala. (B) A. milleri, holotype, IGUM, Jocotepec Quarry. (C) A. popoche, UMMZ 179704-S#2, Lago de Chapala. (D) A. popoche, IGUM, Jccotepec Quarry. Scales. indicate 1 cm.— ' 37
f470—
• ,
• s
•
Figure 12 88
depth at the ascending process. The rostral process is about three times the length of the premaxillary pro- cess.
Comparisons.--In most aspects of its known anatomy,
A. milleri seems closest to A. tincella. These speciiis share a fairly robust pharyngeal arch in which the .111. tenor limb is not much longer than the tooth row. In the 40.mited material available, the ,-anterior two phar- yngeal teeth are more robust in milleri.
Bones\ of the mandible and upper jaw show consider- able variation in Algansea- (Barbour and Miller, 1978).
In general form, the dentary of milleri resembles that 4 4-1 11 of tincella, though the gnathic ramus is less robust. 1176 A. milleri shares two characters of the dentary with
22poche: the greater number of sensory pores and the advanced positiOn of the crest for Meckel's cartilage. The wide coronoid process of the dentary is unique in the genus.
Distribution.--Most of the material of this species was taken from a single lacustrine bed near the bottom of the section at Jocotepec Quarry. The same bed yielded remains of Alcansea popoche, Yuriria elliana, Micropterus relictus, and Ictalurus spodius. Occasional bones of A. milleri were taken from lenses of cross- bedded pumice.
Etymology.--It is appropriate to name this species 89 -
for'Ro-bert R. Miller who initiated the study of fish
remains from Jocotepec Quarry.
Algansea popoche (Jordan and Snyder)
(Figures 11, 12)
XistroSus popoche.--Alvarez, 1974.
Material, localities and horizons.--Chapala
Formation, Jocotepec local fauna l - Pleistocene. IGUM;: basioCcipitals, preopercle, dentary.
Diagnosis.--An Algansea with a'distinctly elongate
dentary, the gnathic ramus attenuate and ending in a
small symphyseal knob. The gnathic surface is moderate toJoroad with the edge extending into a lateral wing; at
its posterior end it may flare outward from the dentary,
leaving an open space between the gnathic foramen and
the base of the coronoid process. The crest for
.Meckel's cartilage is well in advance of the gnathic , foramen. Sensory canal pores are numerous on the mandi-
ble, 5 or 6 in advance of the mid-base of the coronoid
process. Description.--Dentary as in diagnosis and Fig. 12.
The masticatory plate of the basi ccipital is five-
sided with lateral corners curvi ventrally. The plate is about as:I wide as the centrum of the basioccip- - ital. The slightly , concave masticatory surface may be rugase or porous. The pdsterior Pflaryngeal process . is about equal to the pharyngeal plate in length; it descends ventrally f m the pl-algLoi'tiie basioccipital'. - I A preopercle (Fig. 11') is assigned to this' species because of its numerous sensory pores (12 compared to
8-10 for Recent tincelia'and 10-13 for Recent popoche).
Remarks.--A. popoche is distinctive in.a number of
trophic specializations, (Barbour and Miller, 1978),
. notably the elongation Of mouth bones. The dentary
here asigned to pepoche\is elongate, though it is not
as de1icat o narrow anteiiorly. The sensory canal is
damaged but appea&to haVe the high number cif pores \ of popoche. 'The posteriot\part of the gnathic surface
forms a free wing in the fossil, a condition which
occurs in a majority of specimens of Recent popoche.
Family Ictaluridae
The occurrence of fossil\catfishes in Mexico has been mentioned by Downs (1958)\, Miller (1965), Alvarez 1.' (1966), Barbour (1973), and Smith et 'al'. (1975). The extensive Cenozoic record of No th American catfishes-
north of Mexico was reviewed by undberg (1975).7
Genus Ictalurus Rafi esque
Ictalurus spodius new s ecies
,(Figures 13,14Y Cf. Ictalutus.sp.--Downs, 1958. r Ictalurus (close to I. duqesi.i) --Miller, 1965. o Ictalurus dugesi.--Smith et al.,: \f975. Holotype.--UMMP V62528, a nearly complete'skull (Fig. 13) collected 15 July 1969 by C.D'. Barbour and_
R.J. Douglass. 1 Measurements(mm): total length 90.0,
least supraethmoid width 7.5, greatest lateral-ethmoid I • width 36.7, least width across frontals 14.4.
Horizon and type locall.--Chapala Formation 4 Jocotepec Member. Pleistocene. • .•
Material, localities and horizons.--Chapala Form-
. ation. Jocotepec local fi4na. Pleistocene. UMMP
V62501, mandibles; V62502, pectoral spines; V62503,
• supraoccipitals; V6250\4, cleithra; V62505, supraeth-
moids, dentaries, articular-angulars, cleithra; V62506,
articular-angulars; V62507, supraethmoids; V62508,
• dorsal spines, cleithra, vertebrae; V62509, hyoid bars, fragments of suspensoria; V62510, cleithra; V62511,”
Weberian complexes; V62512, pectoral spines; V62513,
Weberian complexes; V62514, hyoid bars, quadrates;
V62515, fragments of suspensoria; V62516, supraethmoids;
V62517, pectoral spines; V625i8, opercle, sUpracleith-
rum', cleithrum, hyomandibular, basioccipitai, vertebrae;
V62519, dentaries, articular-angulars; V62520, verte-
brae, pectoral spines, supraethmoid; V62521, pectoral spine, basioccipital, supraethmoid, dentary; V62521,
supraethmoid, pectoral spine, dentary; V62522 pectoral spines; V62523, supraoccipital, supracleithra, leithra,
bisioccipital, pectoral spine; V62524, vertebrae V62525, Weberian apparatus; V62526, suspensoria, 92
o; TO'T P Opercle; V62527, mandibles; V62529., pectoral/:Spines;
- V62530, pectoral spines, articular-angulars; V62531,
supraethmoids, suspensoria, cleithra, supraoccipitals;
V72721, skull, Weberian complexes, supraethmoids,
mandibles, cleithra, suspensoria, dorsal and pectoral
fin spines. IGUM, several collections including all
elements listed above.
Zacoalco local fauna. Lake bed deposit in Laguna
de San Marcos, Jalisco. Late Pleistocene. LACM 16003,
vertebrae, dorsal spine. Lake bed deposit at Atotonilco
el Bajo, Jalisco. Late Pleistocene. LACM 115406,
supraethmoid, pectoral spine, vertebrae; LACM 115404,
pectoral spine. , Locality indeterminate'lZacoalco/Chapala collection
of Federico Sol8rzano). LACM 115405, dorsal and
pectoral spines, vertebrae. LACM uncatalogued, vertebrae, supraethmoid, basioccipitals, supraoccipital, dentaries, articular-angulars, ceratohyals, suspensoria.
Diagnosis.--An extinct Ictalurus of the subgeAus
Ictalurus which reached a large size, nearly ,one meter
standard length, based on extrapolations from mandibles.
The new species is distinguished from the subgenus
Amiurus by the broad band of teeth on the mandible,
high coronoid process, absence of a ventral keel on the
mandible, restricted hyomandibular-metapterygoid
contact, and development of an extensive ventral keel 93
- on the coracoid. It is distinguished from I. furcatus
And balsanus by the wider supraoccipital process and abbence of ornamentation on the frontaN. It differs
from Other Mexican Ictalurus, including several unde-
scribed forms, in the closure of the posterior fontanelle of the skull roof, development of the high mid-dorsal
supraoccipital crest, and a more extensive crest for
insertion of the levaor arcus palatini muscle.
Description.--The collection of a series of neuro-
crania in 1977 makes known almost the complete skull
anatomy of this species. The dorsal surface of the skull
is,illustratdd in Fig. 13. The supraethmoid is long and
moderately road; the cornua are robust with slight
mesial pro'esses and a convex anterior margin (Fig:14).
The laterai-ethmoid wing is pointed; its posterior border
is at about a right angle to the long axis of the skull. •
The anterior fontanelle is open btit the posterior one is elimin ted by fusion of the longitudinal supraoccipital crests into a sharp mid-dorsal keel extending to the supr occipital process. The latter'process is broad and'
fla ; its dorsal surface is deeply etched with ridges
an grooves. /The suspensorium is typical of the subgenus
ctdlurus (Fig. 14). Hyomandibular-metapterygoid contact is reduced, and the hyomandibular and quadrate are separated by a space for cartilage. The crest of the 94
Skull of Ictalurus spodius, Fig. 13A, facing page.
Figure 13. Dorsal views of skulls of IctalUrus from - tha Chapala basin. (A) I. spodius, holotype, .upoo V62528, 90.0 mm total length, - from Jocotepec Quarry. (B) I. dugesi, UMMZ 179705-S116,/1 92.8 mm total length of skull, from Lago de Chapala. 95
Figure 13 96 '
Figure..14. Bones of tctalurus. (A) I. spodius, UMMP V72721, lateral aspect of susperisorium, anterior to right. (B) I. spodiUs, UMMP V7272I, dorsal aspect of supraethmoid. Ventral aspects of left pectoral spines of (C) I; spodius, UMMP 72721, juvenile; (D) I. dugesi, UMMZ 192551-S#1, juvenile; (E) I. spodius,- UMMP 72721, adult; (F) I. dugesi, UMMZ 179705-S#5, adult. All times 2.75.
:?tet
• •• • tr` • ;•• 97
• , •
r:
1:••••-•
, .•
•••••.- • 98
levator arcus palatini muscle is more extensive than in other IctalUrus; it extends anteriorly as a winged pro- cess. The anterior process of the hyomandibular is flattened, not well distinguished from.the dorsal hyomandibular crest. The interopercle is flatten‹, and expanded posterior to the sensory canal.
The mandible (Smith et al., 1975:Fig. 3) is robust and apparently large. The coronoid process is high, equal to 43-57Vof total length of the articular- angular (n=41). The pymphysis is broad, flattened dorsoventrally, amd without processes. Teeth are in 'a broad band which extends onto the lateral surface 4E:o the mandible.
The postventral process of the cleithrum is/.101T4 and heavy; its lateral surface is ornamented with a pattern of ridges which are sometimes reticulated and sometimes broken into coarse tubercles. The coracoid bears a long ventral keel.
The strong pectoral spine (Fig. 14) is usually straight over its entire length. Distal serrae and anterior dentations are weak or, more often, absent. Posterior dentations are numerous (8-26, n=39),
usually retrorse, and occur in both distal and prox-
. o imal halves of the spine. 99 '
Variation.--Lundberg (1970) noted that Mexican species of the subgenus Ictalurus share a tendency to change the shape of skeletal parts with the attainment of sexual maturity,. In particular, the lower jaw broadens and turns inward. This developmental pattern appears to apply to I. spodius which exhibits a broad, range of variation in the mandible (a variant is illustrated in Smith et al., 1975). Supraethmoids are highly variable in the size and shape of the cornua and the cleft between them. In A few instances, pectoral spines from Jocotepec Quarry bear multifid posterior dentations And strong anterior serrations. These spines may represent an additional species (they'resemble spines of I. furcatus) t other elements with which they are associated_do not suggest the presence of two taxa. They are here regarded as extreme variants of I. spodius. Remarks.--The high supraoccipital keel and conse- auent closure of the posterior foramen are unique in the subgenus and probably apomorphic. The development of a keel may be related to increased musctilature of the nape. The much expanded crest for insertion of the evator arcus palatini muscle also indicates increased musculature in this region. The new species is apparently close to I. dugesi x 100
with which it has been fused. The two can be diag-
nosed on the basis of pectoral spines, in addition to
the cranial characters discussed above esi,
the posterior dentations of the p ctotal s ine are absent or weak. When present in adults, the dentatio s I . are reduced to a series of wavy bumps (Fig. 14)4 The - • • dentations are sometimes dlstirect i n juveniles, tend- ,4 4 ing to obsoles with growth: In both juveniles and
adults of . duge i, the dentations number six or fewer,
and t y are usually confined to the di'stal half of the ne. The posterior dentations are probably secondarily
reduced in 'I. dugesi, as they occur in all other members
of the subgenus. This condition could be derived from
I. spodius which has pectoral spines similar to those
of dugesi in all 'Other respects.
Distribution and ecology.--The Mlaterial from the Zacoalco basin is assigned to this species on the basis
of hyomandibulars, pectoral spines and a partial neuio-
cranium. I. spodius has been collected at several lo-
' ,calities in the Zacoalco basin; at the San Marcos site,
it was associat'ed with Rhabdofario rugosus and Yuriria elliana in fine-grained sediments. The bones of I. spodius are the most abundant of all remains at Jocotepec Quarry. They occur throughout the section in nearly every bed (including lacustrine 101
and fluvial deposits) where fish bones were found::
spodius is the ddminant and sometimes only species in.
coarse-grained and cross-bedded sediments. It is most
often associated with the larger species, Moxostoma
and Micropterus.
The absence of I. spodius from the Chapala type
section is notable in view of its abundance elsewhere.
It is probably not absent for ecologicaTik-reasems, as it
occurs in lacustrine beds at Jocotepec and Zacdalco.
It therefore seems likely that Ictalurus did not arrive
• in the basin until after the Chapala sediments were
laid down in late Pliocene or early Pleistocene time.
Etymology.--The species name is a masculine adY§c-
tive in the nominative singular made from the Greek V 4 spodos, ashes, in reference to the abundant volcanic
ash at the type locality.
Ictalurus dugesi Bean
(Figure 13)
Remarks.--Alvarez (1966) recorded this species
from Late Pleistocene deposits of Lakes Zacoalco and
Chapala. His material, from the Solorzano collection,
was not re-examined. However, other material from the
same collection (LACM 115405) is I. spodius, based on
pectoral-spine dentations. Alvarez remarked on the di-
verse states of mineralization of his material, some of
which is apparently Recent. It is therefore possible 102.
, //Alr-r4 .41 w that his sample includes both I. spodius and_g dugeii,
The latter species is not known from the Zacoalco basin
today. -
Family Goodeidae
The Lerma fish fauna is dominated by the .
cypr4n6dontOid_family Goodeidae. It comprises 35-40
viviparous sivecies whose known history and 'aigtribution are largely confined to the Mesa Central and its periph-
ery. Within this compact range, members of the family
6 occupy virtually all permanent aquatic habitats
accessible to fishes.
Early classifications of the family (Jordan and
Evermann, 1896-1900; Meek, 190,1904) were based primarily on trophic structures. Being diverse in
dentition and jaw morphology, the genera then known were
distributed among various cyprinodontoid groups which
now constitute separate families.
Regan (1906-8) first assembled a monophyletic
group, the Characondontinae, as 'a subfamily of the
Poeciliidae. It was elevated to family status by Hubbs
(1924) who corrected the name to Goodeidae. The family as now constituted is defined by "viviparity coupled with a shortening rather than an elongation of the anterior anal rays in the male" (Hubbs and Turner, 1939) . In the only comprehensive revision of the family, 103
Hubbs and Turner (1939) erected four subfamilies (Table 1) on the basis of olarian anatomy of females „or and the histology and morphology of trophotaeniae (rec-
tal'processes of embryos presumably involved in nutri-
tion). The value of these structures in the inference of relationships was first questioned by Mendoza (1965) and later by Miller and Fitzsimons (1971) and
Fitzsimons (1972, 1979). They found intraspecific vari-
ation to be greater than was apparent in the limited
material available to Hubbs and Turner. Additional
difficulties have been encountered in the placement of
new taxa which have tended to stretch or bri'.ege the
earlier definitions subfamilies (de "Wen, 1941; .
Mendoza, 1956; MillçÅ and Fitzsimons, 1971).
A survels, of goodeid osteologli was undertaken as the
necessary background for the identification of,fossil remains. Osteological characters suggest generic
' groupings which do not conform to those based on ovaries
and trophotaeniae, The following account, based on 32
species including some undescribed (see Material), is
preliminary, but will serve as an introduction to t1ie osteology of the family.
Diagnosis.--The Goodeidae differ from all other atheriniforms in having the anterior seven anal rays of
• ■■• males shortened, bunched together and variably separated from the following rays by a notch. The first Table 1. Generid■groupings within the family Goodeidae based on the ovarian and trophotaenial characters of Hubbs and Turner (1939). Members of the Goodea group are indicated by an asterisk.
GOODEINAE CHARACODONTINAE GIRARDINICHTHyINAE ATAENIOBIINAE
Allodontichthys Characodon Girardiniihthys Ataeniobius* Chapalichthys Ilyodon* Alloophorus Goodea* Xenotoca Zoogoneticus Ailotoca Neoophorus POSITION UNCERTAIN Xenoophorus* Xenotaenia Hubbsind Ameca Tapatia •/
• I j t, 74, vet •
I 105
anal ray is reduced to a small splint, particularly in males, which has often been overlooked (Miller and .
Fitzsimons, 1971). The anterior hemal spines of males
are not modified to form a ligastyle and gonapophyses nor are the actinosts thickened and lengthened. The
basal segments òf9 the sixth and seventh anal rays of females:- are ankylesed; their fused bases are longer
'than in rays 2 through 5. The lower end of the pre-
maxilla is trapezoidal, iituated between the maxilla
and the articular-angular.' The upper and lower
hypural plates are completely fused to form a'single
symmetrical plate. The ectopterygoid is small but
distinct; the entopterygoid is very much reduced (relative to the atherinoid and exocoetoid condition)
to form a thin sheet of bone attached to the quadrate
and autopalatine.
Jaw mechanism.--The suSpensorium of goodeids
involves a palato-pterygoid . complex which has undergone reduction and fusion'of elements (Fig. 15). The -
ectopterygoid is small and partially fused to the
autopalatine. The entopterygoid is reduced to a thin bone at the posterior edge of tlile palatopterygoid arch; it does not extend beneath the orbit. An anterior lobe
of the entopterygoid fits into a pocket on the mesial surface of the quadrate. As pointed out by Rosen (1964), the angle of the 106
PALATINE
ECTOPTERYGOID
ECTOPTERYGOID
QUADRATE
/'
Fig. 15. Mesial aspect of left palatopterygoid arch of Goodea atripinnis, UMMZ.173680-CS. Anterior to right. 107
palatine is related to the degree of protrusibility of .
the jaws. In atheriniforms \ with non-protrusile pre-
maxillae, the symplectic is short and the palatine is
consequently inclined forward. In species with pro-
trusile premaxillae, the symplectic is long and the pal-
atine is nearly vertical. Both of these conditions
occur, among goodeids (Fig. 16). Because groups defined -
on the basis of jaw suspension do not correspond to ex-
isting generic groupings, I will refer to them by the
vernacular names Characodon group (non-protrusile pre- maxillae) and Goodea group (protrusile premaxillae).
The members of each are indicated in Table 1.
The Characodon and Goodea groups can be further
diagnosed by a number of suspensorial characters. In
Characodon lateralis (Fig. 16) and similar goodeids,
the jaws are large, usually greater than 23% of head
length. The palatoquadrate is inclined and forms an
even U-shaped curve with the hyomandibular, which is
nearly vertical. The Quadrate is large and the process
for the articular-angular does not extend much beyond
the anterior edge of the palatopterygoid complex. Goodea atripinnis and similar goodeids differ in - several respects. The symplectic and hyomandibular are elongate, and the hyomandibular slants forward at its .ventral end. The position of the quadrate is conse- quently advanced relative to the auto2alatine; the Figure 16. Two types of jaws and jaw suspension in he Goodeidae. Lateral views of (A) Characodon lateralis, UMMZ 192459-CS, and (B) Goodea atripinris, UMMZ 1-67720-CS. Drawings have been partially spread apart to show details, but natural orientation of bones has been maintained. •
c- 109 110
• articular-angular process of the quadrate is produced far-forward of the palatine. The anterior position of the quadrate and elongation of its articular-angular process allow the mandible to swing through a greatei arc in the Goodea group.
-.- In all goodeidb, the lower end of the premaxilla is'_attached.by ligaments to the lateral surface of the dorsal process of the articular-angular; it is pulled forward as the dorsal process moves to a verticle posi- tion. Protusibility of the premaxilla is therefore limited by the length of the arc through which the dor- sal process moves as the mouth opens. In the
Characodon 'group, the dorsal process of the articular- angular is at nearly a right angle to the anterior pro- cess, which lies in the plane of the mandible (Fig. 17). -1% This is inferred to be the plesiomorphic state because ' it is widespread among other cyprinodontoid taxa including primitive groups . such as *Profundulus: In the
Goodea group, the dorsal process is reflexed over and behind the quadrate articulation so that its axis is almost parallel to that of the anterior process
(Fig. 17). The'dorsal process therefore moves through
a much greater arc than in the Characodon group. These 4
characters of the articular-Angular are unique to the Goodea group and presumablr-apomorphic. 111
• Figure 17. Comparison of left articular-angulars of W Characodon lateralis, UMMZ 192459-CS, and (B)., GOodea atripinnis, UMMZ 167720-CS. Mesial aspect, anter- ior to right. Scales indicate 2 mm.
•=5
• 112 113
Genus Tapatia Alvarez and Arriola .. . Tapatia occidentalis Alvarez and Arriola
(Figure-18)*
Tapatia occidentalis.--Alvarez and Arriola, 1972.
Locality and material.--Road-cat in'wall of
Barranca de Santa Rosa, 7 km NE of Amatitgn, State of
Jalisco, Mexico (20°53'N, 103°40'W). .Laminated shale,
Upper Miocene or Pliocene. UMMP V72722 and V72723,
fragmentary to complete skeletons imbedded'in matrix...... Diagnosis.--An extinct goodeid .. fish with fewer •
total vertebrae (usually 28 or 29) tharvany-ather mem-
ber of the family. The conic, slightly rdcurved teeth are arranged in a single series. Dorsal-fin rays.
15-20; anal-fin rays 15-20; pectoral-fin rays 12-25;
maximum standard length 20 mm.
Description.-- Alvarez and Arriola (1972) give
morphometric data for the holotype and meristiCs for
• . several additional specimens. Their meristic data, in-
cluded in the diagnosis above, has been modified to con-
form to published data for living goodeids: one verte-
bra.is added to their counts (for the hypural complex
which they did not include) and one ray is subtracted
from their dorsal- and anal-fin ray counts .( as the last
two closely approximated rays are usually counted as
one; Miller and Fitzsimons, 1972)% Additional material
is described below. 114
Tapatia occidentalisis known from skeletal im- pressions in finely laminated shale (Fig. 18). The fins and axial skeleton are often clearly preserved, but bones of the head are usually pressed closely together so that individual elements are not easily discernible.
. The dorsal fin originates just behind the pelvic- fin insertion, midway between the snout and end of the hypural plate or slightly nearer the latter. The anal- fin insertion lies beneath the anterior half of the dorsal-fin base. The dorsal and anal fins are long, the longest rays almost equal to the basal length of the fin. The seven anterior anal rays of males are only / slightly shorter than the rays that follow. Dorsal-tin rays 16 (in 1 specimen), 17(1), 20(1). Anal-fin rays
16(1), 17(3), 18(1), 20(2). Pectoral-fin rays Total vertebrae 25(1), 31(2). The longest caudal-fin ray equals 23-27% SL.
The dentary is robust. Outer-row teeth are conic and slightly recurved as A Allotoca and Neoophorus: inner-row teeth cannot be detected. The dorsal and anterior processes of the articular-angular form a right angle at the quadrate articulation; the anterior process is longer than the dorsal process and bears a deep groove for Meckel's cartilage. The retroarticular is excluded from the quadrate articulation. The 115
Figure 18. Tapatia occidentalis, UMMI0 V72723, 15.4 mm total length, from Santa Rosa, Jalisco.
4.4,21 .. .1, Figure 18 17
.pharyngobranchial plate is narrow, with about four rows
of teeth at its mid-point.
Comparisons.--On the basisoof its articular-
'angular, T. occidentalis falls into the large Characodon group, but its' affinities within the group
are unclear. The conic, recurved teeth of Tapatia
resemble those of Alloophorus, Allotoca, Hubbsina,
Neoophorus and Zoogoneticus. Teeth are variably conic
to bifid in Girardinichthys. .,While these genera are , - very similar in dentition,Vthe resemblance may not in-
dicate close relationships, as conic teeth seem to be
primitive in atheriniforms.
Alvarez and Arriola (1972)Tobserved that the range of ddrsar-ray numbers of Tapatia (15-20) approaches the
range of Girardinichthys (18-31; Miller and Fitzsimons,
1971), but it is actually more Similar to some species of Neoophorus and Allotoca (e.g., N. diazi, 15-19).
Tapatia also more closely resembles the latter genera
in total number of vertebrae: Taoatia, 26-31; Neoophorus, 33-36; Allotoca, 31-35; Girardinichthys,
34-40. The range for Tapatia is the lowest in the
family; that for Girardinichthys is among the highest (R.R. Miller, pers. comm.).
‘"? 118
-Ecology --The remains of T. occidentalis are known only from fine-grained lacustrine..sediments, apparently 7 deposited in a large lake (see p. 47) 1" In life, however, the species may have been associated with coarser sediments. Each skeleton includes several coarse grains of sand, usually in the abdominal region, which were apparently part of the gut contents. Such . grains are otherwise rare in the fossil-bearing shales.
Fine-grained sediments are usually expected near the centers of lakes, while coarser sediments occur in belts toward the lake margins (Twenhofel, 1932;
Reineck and Singh, 1975). On the basis of gut contents, it is inferred that T. occidentaiis lived along or near the margins of a lake where sand could be ingested.
Ameca Miller and Fitzsimons
Ameca splendens Miller and Fitzsimons
(Figures 19-21)
Material, localities and horizons.--Chapala
Formation. Jocotepec local fauna. Pleistocene. UMMP
V72724, opercleS; UMMP . V72725, premaxillae, dentary;
UMMP V72726, premaxilla; IGUM, opercles, premaxillae, dentaries. Diagnosis.--A goodeid of the Characodon group with a small mouth, the gnathal bones correspondingly shortened. The bifid outer-row teeth arise from the upper third of the anterior face of the dentary: their 119
Figure 19: Bones of goodeids from the Chapala basin. (A) Goodeidae, incertae sedis, UMMP V72730, mesial and" ventral aspects-FE-Fig-Et premaxilla. (B) Alloophorus robustus, UMMZ 189618-S#1, mesial and ventral asp,edts of right premaxilla. (C) Ameca splendens, UMMP V72726, mesial and ventral aspects of left premaxilla. (D) Goodea cf G. atripinnis, IGUM uncat., mesial and ventral aspects of left premaxilla. CE) Ameca sPlendens, UMMP V72724, mesial view of right preoiETFre. (F) Chapalichthys encaustus, UMMP V62536, right preopercle. (G) Allookthorus robustus, IGUM uncat., right preopercle. Scales indicate 0.5 mm.
123
.„ 121
bases are laterally compressed. Theconic or bifid inner row teeth are closely set in a broad band extending onto the postdorsal ramus. Bones of both jaws have well-developed gnathic limbs and reduced posterior limbs.
Description.--The dentary is robust (Fig. 19); its gnathic ramus is short and deep with a broad oval symphysis and weak ventral keel. The gnathic surface is produced posteriorly as a ridge which extends onto the postdorsal process. The latter process is reduced and displaced dorsally to leave a broad cleft for the anterior limb of the articular-angular.
The posterior end of the premaxilla is short and deep (Fig. 19). Its dorsal and ventral surfaces are nearly parallel. In both the premaxilla and dentary, the posterior limbs are set at a right angle to the gnathic ramus.
The anterior process of the articular-angular is deep and triangular rather than rod-like; it is equal to or shorter than the dorsal process. The sesamoid bone usually forms part of the dorsal margin where the anterior and dorsal processes meet. The articular- angular is concave laterally.
The opercle is sub-triangular with a straight anterior edge (Fig. 19). It is reinforced on its mesial surface by a strut from the hyomandibular articulation 122
running parallel to the dorsal margin. This strut is
longer than in any other member of the Characodon group.
The dorsal process of the opercle is short and not
distinctly set off •from the dorsal margin'.
Relationships.--In describing Ameca splendens,
Miller and Fizsimons (1971) noted the distinctiveness
of the species in karyology, biochemistry and characters-..
of the ovary and trophotaeniae. The latter characters
indicate that A. splendens is close to the subfamily
Goodeinae of Hubbs and Turner, but the species could
not be assigned to any of the phyletic lines within that
subfamily. Osteological characters show Ameca to be
very similar to Xenotoca and Chapalichthys. These
genera share robust gnathal bones; laterally compressed
bases for the bifid outer row teeth; placement of the
outer-row teeth on the upper, anterior face of the
dentary; and reinforcement of the opercle with a dorsal -
supporting strut.
Distribution and ecology.--Ameca splendens is known
from two localities in the Ameca basin (Miller and
.•,.. Fitzsimons, 1971): the mainstream of the Rio Ameca and
- the upper reaches of a tributary, the Rio Teuchitl.;.n. The latter locality is a system of pools and large
springs that coalesce to form a small stream (c. 6 m
wide). Ameca is found in most habitats of the Rio
Teuchitlan, including sections of stream with sand and 123
gravel substrates, but it is most common in the still
water of pools over mud or silt bottoms.
Chapalichthys Meek
Chapalichthys encaustus (Jordan and Snyder)
(Figure 19)
Chapalichthys encaustus.--Smith et al., 1975..
Materi'iL, loc ies and horizons.--Chapala. Forma- tion. Jocotepec local fauna. Pleistocene. UMHP
V62536, opercle; UMMP V62537, frontal; UMMP V72727, articular-angular, dentary; IGUM, opercles, frontals, articular-angulars, dentaries.
Diagnosis.--A goodeid with gnathal bones similar to those of Ameca, but less robust. The gnathic ramus
'Of the dentary is deep, shorter than the posterior rami,
with a broad symphysis:- Inner row teeth do not extend
appreciably onto the postdor'sal ramus.
Description.--Dentary as above. The anterior
process of the articular-angular (Fig. 19) is longer
than the dorsal process (measured from the quadrate
articukation). The dorsal process is wide, laterally
deflected at its distal end, and ends in an'anterodorsal
point.
The dorsal process of the dpercle (Fig. 19) is
sauare-shaped and higher than the dorsal crest from
which it is distinctly separated. The articulating
cotyla iš- supported by a dorsal strut which is strong- '124
at its proximal end, but Short (about one-third the length of the opercle). Distribution and 'Ecology.--C. encaustus is known only from Lago de Chapala and nearby reaches of its in- let and outlet. The species is abundant in sballow bays, along beaches and in quiet backwaters of streams.
It is found over firm bottoms usually composed of sand or fine gravel. The remains at Jocotepec Quarry wee taken from diatomite and fine water-laid volcanic as114.-
Alloophorus Hubbs and Turner
Alloophorus robustus (Bean)
(Figure 19) ,
Material, localities and horizons.--Chapala-Forma- tion. Jocotepec local fauna. Pleistocene. UMMP
172728, articular-angular, dentary; UMMP V72729, opercle; IGUM, articular-angulars, dentaries, opercles, premaxilla.
Diagnosis.--Among goodeids, Alloophorus is unique
in having attenuate gnathic bones adapted for pisci- ., vorous feeding.' The trapezoidal lower end of the
premaxilla is distinctively shallow and elongate with
the dorsal and ventral margins. parallel. The gn.;.thic
limbs of both.upper and lower jaw bones are elongate
and evenly curved, bearing an outer row of large conical teeth with robUst bases and a narrow band of
smaller innef teeth. 115
Description.--The posterior processes of the
dentary are elongate and expanded into thin wings of
bone; the coronoid process is curved laterally at its
posterior end. The gnathic ramus is slender with only „. a weak ventral keel (Fig. 19). The gnathic ramus of the
premaxilla is very long, accounting for more than 50%
' of the total length of the bone (Fig. 19). It expands
dorsally to form a keel which is produced near the
symphysis into a prominent ascending process. The
maxilla is evenly curved in its anterior half and bears
a reduced premaxillary process.
The anterior process of the articular-angular is
slender (Fig. 19), Measured from the quadrate articula-
tion, it is three times the length of the endosteal
process, twice the length of thedorsal process.
The operCle (Fig.19 s nearly ,triangular. * although the auricular 'corner may be truncate. The
dorsal process is moderately developed and usually set
off from the dorsal margin by a notch. The articulating
cotyla is supported by a postdorsal strut which is
strong but short, crossing only one-third of the opercle.
Remarks.--Alloophorus, which is monotypic,
resembles .7■Teoophorus and Allotoca in shape of the
articular-angular, dentition, and placement of teeth on
the dorsal surface of the .dentary and ventral surface
of the premaxilla, rather than on the antero-lateral 126. ,
surfaces of those bones. Alloophorus is distinctive in specializations related to piscivory (e.g.,
elongation of gnathic bones) and large size (143 mm SL)
in Recent material).
A. robustus is. not common but is widely distributed
- in the lower Lerma basin above the canyon of the Rio . Grande de Santiago,. It also occurs in the interior
basins of MichoacSn. The species has beeh46st •
frequently taken in lakes, but is also known from the
slower'stretches of large streams. Its remains at Jocotepec are associated with coarse sand.
Goodea Jordan
Goodea cf. G. atripinnis Jordan (Figure 19)
Material, localities and horizons.--Chapala
Formation. Jocotepec local fauna. Pleistocene. IGUM, premaxilla, hyomandibular.
Remarks.--Although the above bones are in agreement
with G. atripinnis, the determination is qualified because the material is limited and fragmentary, and
because the systematics of living members of the genus is uncertain. Goodea is distinguished from other goodeids (except Ataeniobius) by the posterior end of
the premaxilla (Fig. 19) which is shortened and much
expanded ventrally. In G. atripinnis •the dorsal and ventral margins of the expanded portion are not 127
parallel; the posterior process descends obliquely
from the main axis of the bone. The gnathic ramus is set at an obtuse angle (105-120°) to the posterior_
limb. Tooth sockets (which' are produced as a delicate
anterior extensidn of the gnathic- ramus in Recent
material) are lacking in the fossils. The hyomandi-
bular bears a lateral crest which is higher than in
other goodeids. In G. atripinnis it extends onto the
anterodorsal process.
Xenotoca Hubbs and Turner
Xenotoca sp.
- Material, localities and horizons".--Chapala
Formation, Jocotepec Member. Pleistocene. UMMP V72732, - premaxilla; UMMP V72731, articular-angulars; IGUM, premaxilla, artictilar-angulars.
Remarks.--The premaxillae are assigned to Xenotoca • on the basis of the shape of the expanded posterior end of the bone. Assignment to species is not possible because the gnathic rami are missing in all specimens. , The fossil articular-angulars resemble those of
X. variata (Bean) and X. meIanosoma Fitzsimons, but these species cannot be reliably separated on the basis of articular-angulars. The fossil material is dis- tinguished from X. eiseni (Rutter) and Amecas'splendens by the less,robust anterior process of the articular- angular, the longer dorsal process, and the narrower 128
margin between the endosteal process and dorsal margin
- of the bone.'
Goodeidae, incertae sedis
Two premaxillae from Jocotepec Quarry (UMMP V72730,
IGUM uncat.) belong to a group of cone-toothed goodeids
which includes Allotoca maculata Smith and Miller,
A. dugesi (Bean), Neoophorus catarinae De Buen, N. diazi
(Meek), and N. meeki Alvarez. The two genera can be dis-
tinguished on the basis of ovarian and trciphotaenial
characters (Hubbs and Turner, 1939), but corresponding' C osteological distinctions are unknown.
In Allotoca, Neoophorus and the Jocotepec fossils
(Fig. 19), the trapezoidal lower end of the premaxilla
is short and deep with a truncate anteroventral process.
The gnathic limb is shot and -heavy with a prominent ,)
ascending process at the symphysis. Outer-row teeth • arise from the ventral, rather than lateral, surface of
the gnathic limb.
Family Atherinidae
Genus ChirOstoma Swainson
The genus Chirostoma parallels the family Goodeidae
in number of species, distribution and importance in the
modern fauna of the Lerma basin. The systematics and
biogeographic history of the genus have beeny,eXamined,
by Barbour (1973a,b). • . . Figure 20. Bones of Chirostoma cf. C. lucius, UMMP V72733. (A) Ventral and (B) dorsal aspects a*right maxilla, 24f.7 mm greatest length. (C) Lateral and (D) 'mesial aspects of right pnamocilla, 26.0 mm. (E) Mesial and (F) lateral aspects of left dentary, 34.5 mm. (G) Lateral aspect of left articular-angular! 28.3 mm. 132
'Figure 20 133
specimen with a more attenuate gnathic ramus resembles C. sphyraena but bears smaller alveoli in wider bands
than is typical of that species. The jaw bones 'of C. sphyraena and:C. lucius, which are subject to extreme allometric growth, are variable in Recent material and show some overlap in dentition. The fossil material more closely resembles C. lucius. Chirostoma cf. C. promelas Jordan and Snyder
Material, localities and horizons.--Chapala Formation,
Jocotepec local fauna. Pleistocene. UMMP V72735, partial dentaries, articular-angulars, maxilla; IGUM uncatalogued, partial dentaries, articular-angulars, maxilla. Description.--Fragments of dentaries include ganthic rami with dentigerous surfaces and sensory pores. The gnathic ramus is deep with widely spaced pores of the acoustico-lateralis system. The mandibular foramen opens above the third or fourth pore. The tooth band is narrow .with only two or three small alveoli at its widest
..; .point. Alveoli are of uniform size throughout the band. The articular-angular is deep with a moderately broad ventral process; the ascending process tapers gradually to the end of the anterior limb, thus forming a distinctive, thin dorsal carina. The maxilla is only moderately curved. The premaxillary processes extend ventrad without the mesial 134 •";
curve of most Chirostoma; they are not much expanded
longitudinally.
Comparisons and discussion.--The fossil dentaries
esemble those of C. ip omelas, C. chapalae and C. consocium in having a narrow dentigerous surface with
small alveoli of uniform size throughout the band.
However, sensory pores in the fossils are notas large .
as in C. chapalae and C. consocium. The placement of
A sensory pores and the mandibular foramen is the same aS-
in C. promelas, and it is on this basis that the fossil s _‹: material is tentatively assigned to that species.
The short and straight premaxillary processes of the
maxilla and the dorsal carina of the articular-angular *
are shared with C._ promelas and C. consocium. It is possible that bones of either or both of these species have been inciuded here.
Chiro9toma sp:
(Figures 21-22) Material, localities and horizons.--Chapala Formation,
Jocotepec local fauna. Pleistocene., UMMP V72732,
dentaries, articular-angulars maxillae, premaxillae,
hyomandibulars, opercleg, pharyngeal tooth plates, frontals; IGUM uncatalogued, dentaries, articualr-angulars, maxillae, premaxillae, hyomandibulars, opercles, pharyngeal tooth plates, frontals. 135
Diagnosis--An inland Mexican silverside of moderate ,..
size, about 140 mm max. SL, based on extrapolation from
articular-angulars. The species is distniguished from Chirostoma 'ordani by the position of the mandibular
foramen over the fourth, rather than second, pore of the
acoustico-lateralis system op,the dentary, the smaller
sensory pores on the dentary, and-the longer -band of
teeth. It differs from Chirostoma other than 'ordani
in the fewer sensory pores on the dentary; development
of a prominent ventral process at the symphysis of the dentary; greater robustness of the gnathal bones;
steep angle and small size of the ascending process. of the articular-angular; and very long and broad ventral process of the articular-angular.
Description.--The dentary (Fig. 21) is deep with a
much expanded coronoid process and broad postventral
process. The robust gnathic ramus curveS sharply mesiad and ends in a distinctive Symphyseal nob which bears a
' prominent ventral process. The acoustico-lateralis
canal on the dentary opens to the surface through
5 pores (n=6) which are not as large as the interspaces
between them. The mandibular foramen bpens above the
fourth pore ot the interspace preceding it.
The dentary Sand premaxilla each bear a band of alveoli wide enough for 3 or 4 teeth which were small or minute. Alveoli extend onto the mesial surface of 136.
Figure 21. Jaw elements-of_Chirostoma sp., UMMP V72732. (A) Dorsal and (B) ventral aspects of left maxilla, 8.1 mm greatest length. (C) Lateral and (D) mesial 'aspects of right premaxilla l 12.4 mm. (E) Lateral and ( F) mesial aspects of right dentary, 13.8 mm. 17.7
A 401K... 00 411.4--
Figure 21 138 -
both bones and are directed posteriorly. The outer-row tooth sockets on the dentary form a pronounced lateral shelf; theesarresponding shelf of the premaxilla is less well-developed.- The dentigerous surface of the dentary ends•,_1 above the fourth acoustico-lateralit pore or the • inteitspac following it
The:gnathic ramus of the,premaxilla (Fig. 21) is attenuate; it does not change in thickness. at the base of the ascending process. .The ascending process is short and directed posteriorad. The Rremaxillary processes of the maxilla (Fig. 21), which are also short, descend slightly ventrad and then curve mesially.
The inferior tooth plate (Fig. 22) is elongate and bears a band of irregularly spaced alveoli wi:44enough for 8 teeth at its widest point. Alveoli are mostly: , small, but there are sockets for 4 or 5 much lar4ei . t4Oth on the lateral edge of the tooth band. The ventral carina of the tooth plate is moderately developed.
The articular-angular (Fig. 22) is robust with a thick and relatively short anterior limb. The process is small and rises from the quadrate articulation at a steep angle. The ventral process is extremely broad and long, 54-63% as long as the anterior limb.
The ventral process bears a prominent lateral tube for the acoustico-lateralis system. The short posterior process rises dorsally behind the quadrate articulation 139
Figure 22. Bones of Chirostoma sp., UMMP V72732. (A) Lateral and (B) mesial views of right articular-angular, ' 11.9 mm greatest length. (C) Lateral view of left opercle,. 16.0 mm. (D) Dorsal and (E) ventral views of pharyngo- " branchial plate, 9.8 mm. 143
Figure 22 141
and is laterally twisted. The sesamoid articular
(present in a single specimen), is longer than the endosteal process which it largely covers; it fills nearly all the space between the endosteal process and the base of the ascending process.
Comparisons-and discussion.--Among the silversides - t 1 of the Chapala bagin (p. 129) the fossil material most closely resembles C. 'ordani. The two species share the distinctive articular- angular which bears a much expanded ventral process; the number of sensory pores on the dentary; and shape of the gnathal bones. These characters are arsoshared by_ some members of the genus Menidia. Generic p1acement-16'f the fossil material is therefore provisional. The fos'sil material differs from available material of C. 'ordani (from the Rio TurbioY in characters given in the diagnosis (above).
:.-~..p hirostoma, Indeterminate Species
The following material can be referred to the genus
Chirostotha, but assignment to species is not possible, because the specimens are fragmentary or lack diagnostic characters: 1) Material, Localities and horizons.--Chapala
Formation, Jocotepec local fauna. Pleistocene. IGUM uncatalogued, partial left dentary including the dentigerous surface and anterior sensory pores. 14Z
The specimen has the destinctive gnathic ramus and' symphyseal nob of C. larbarcae. The ventral end of the symphysis projects forward'of e anterior end of/the tooth band. However, the:alveoii are •.smaller and arranged in a wider band than in lab.arcae, and the sensory pores are less closely spaced. The mandibular foramen-is reduced to a narrow slit above the fourth sensory
pore., •,;• 2) Material, localities and horiidns.--Chapala
Formation. jocotepec local fauna. tleistocene. UMMP
V72734, partial dentaries; - IGUM uncatalogued, partial dentaries.
The specimens have the narrow dentiglerous surface and large sensory pores of C. estor or- C.\cha0.1ae, 1 but are too fragmentary to be designated with confidence.
3) Material, localities and horizons.--Chapala Formation, Chapala type section . Plio-Pleistocene.
IGUM uncatalogued, fragments of premaxillae ind opercles.
Family Centrarchidae
Genus Micr terus Lacepede
. Micropterus relictus Cavender and Smith
(Figure 23)
Micropterus n. sp.--Miller, 1974.
Micropterus relictus.--Smith et al., 1975. Material, localities and horizons.--Chapala Formation. Chapala type section. P110-Pleistocene. 143
UMMP V62469, maxilla; UMMP V62474, dentary; UMMP V62480,
dentary.
Jocotepec local fauna. Pleistocene. UMMP V62470,
supracleithrum; V62471, quadrate; V62472, ar icular-
angular,, dentary, premaxilla; V62473, maxi ; V62475,
dentaries, articular-angular; V62476, preoperculai;
V6247-7, parasphenoids; V62478, fiontals,; V62481,
dentaries; V62482, quadrate; V62483, premaxillae, dent-
axles; V62484, hyomandibular; V62485, epihyal; V62486,
a:rti,culat -angular; V62488, ceratohyal; V62489, dentaries,
arUcular-angular; V62490, premaxilla; V62491, dentaries;
V62492, maxillae; V62493, parasphenoid; V62494, atlas;
V62495, frontals; V62496, supracleithrum; V62497,
P mikllae; V62498, articular-angular;-V62499, dentary
(holotype), V62500, premaxilla; V72736, preopercle. IGUM
, uncatalogued, maxillae, premaxillae, dentaries, articular- 'angulars, quadrates, hyamandibulars, ceratohyals, epihyals,
parasphenoids vomers, vertebrae, supracleithra, frontals.
- Locality. indeterminate (Zacoalco-Chapala collection „ of FedercarSolorzaho). UMMP V62462, vertebrae; V62463, premaxillae; V62464; parasphenoid; V62466, vomer; V62467, premaxiala; V62468, vertebrae, maxillae, premaxillae.
, Lacustrine sediments on northwestern shore of Lag&
de Chapala at Ajijic. UMMP'V62465, hyomandibular, ,parasphenoid. 144
Diagnosis.--An extinct centrarchid assigned to
Micropterus on the basis of its elongate jaw bones, -4 - villiform jaw teeth in broad bands which are expanded
anteriorly on the derltary and- premaxilla, subtriangular
tooth patch on the vomer, perforation of the ceratohyal
by a' slit-like fenestra, and relatively small diameter of
the cephalic sensory canals and pores. M. relictus
s is distinguished from itscongeners bý the orientation of the adductor ridge perpendicular to the lateral
surface of the hyomandibular; presence of a pronounced
oval sulcus at the mandibular nerve foramen of the
dentary; heavy construction of the' quadrate and bones of
the hyoid arch; lateral placement of the articular facets
of the atlas vertebra; and presence of a pore on the
commissural branch of the supraorbital canal. Other
diagnostic characters are giveri'by Smith et al. (1975).
Description.--The type specimen is an incomplete dentary (UMMP V62499), 33 mrri long. The gnathic ramus is
intact, including most of the dentigerous surface, three
anterior sensory-canal pores, and the mandibular nerve
foramen. Many additional dentaries are now known. The
toothed area is broad -and expanded at its anterior end to form a lobe on the mesial.surface of the dentary behind the symphysis. The gnathic ramus (Fig. 23) is
/ deeper and more robust than in most extant Micropterus, l abut the same as in M. aalmOides. Pores of the sensory 145
Figure 23. Bones of Micropterus relictus. (A) Lateral. and (B) mesial views of right preFairrg7 IGUM uncat., 27.8 mm greatest length. (C) Mesial.land (D) lateral views of left dentary, IGUM uncat., 31.5 znm. (E) Mesial and (F) lateral views of left articular-angular, UMMP V62475, 34.5 mm. 14 6
..
Figure 23 147
canal are large.for Micropterus; the second and third
pores are nearly as wide as the interspace between
,them. The three anterior-most canal pores and the
mandibular foramen are closely spaced on the anterior
end of the dentary, a distinction from M. salmoides.
A shallow groove runs longitudinally below the, lateral
edge of the .tooth band, as in M. dolomieui. A deep
oval sulcus lies beneath the lateral shelf of the
toOthband, above the interspace between the third and
fourth sensory-canal pores. The articular-angular
i- (Fig. 23) is short and deep l suggesting jaw proportions
as in M. dolomieui. The coronoid process rises at a
steep angle to the axis of the articular process. The premaxilla (Fig. 23) is known from fragments
usually lacking the post-maxillary process and
. posterior end of the bone. The articular process is
unusually broad, its basal width equal to its height.
The ascending process rises at a right angle from
• the gnathic limb; it bears a deep sulcus in its anterior surface which becOmes extreme with increasing size.
The maxilla is greatly expanded at its posterior end,
its greatest width equal to about one-third 'its. 'length. The quadrate (Fig. 23) is similar in shape to that of M. dolomieui, but is thicker and heavier than in any extant species. The ventral and anterior edges meet at a broad angle as in'M. dolomieui. The 148
posterior edge_ii straight or convex rather than
concave. a in tlie extant species. The ceratohyal is a bibbed bone with a thin dorsal'
carina between the two lobes; the base of the carina is
perforated by a lOngitudinal slit-like opening. The
epihyal is heavy with a broad posterior apex as in
M. dolomieui and M. treculi.
Remarks.--While a perforated ceratoIal is found -;
commonly among centrarchids, the slit-like fenestra
of Micropterus is distinctive. An oval or round
fenestra occurs in Acantharchus, Archoplites,
„Chaenobryttus and some Lepomis. Reduction of the
ing to a longitudinal slit may be a specialization
of Micropterus, since a perforated ceratohyal has
been regarded as primitive for the Acanthopterygii • ( tosen and Patterson, 1969). An additional specializ-
ation supporting the placement of relictus in the genus
Micropterus is the small diameter of the cephalic ' sensory canals (cf. Branson and Moore, 19621:
It is difficult to determine the relationships of
M. relictus to other blackbasses becluse the known
anatomy of the fossil species involves apparently primitive states. These include orientation of the ascending process of the premaxilla and flexure of the parasphenoid and shaft of the yomer, as discussed by Smith et al. (1975). The. prominent lateral sulcus
A.. 149 4
at the base of the coronoid process of the dentarr is
found in M. relictus and most centrarchids except the
'six extant species of Micropterus..
Distribution and ecology.--M. relictus is the most
abundant species in lacustrine sediments at the base of
the Jocotepec section. It is also known from late
Pleistocene lake-shore deposits at Ajijic where two
, bones'were found in association with a salmonid skull.
The oldest known remains of the species*Eire from tile
type Chapala section here it is rare.
The remains of M. relictus are strongly associated
with lake deposits. The only exception is a collection from a layer of water-rounded cobble at Jo‘Aepec
Quarry. The same bed produced very large - bones of
the catfish, Ictalurus spodius.
• CHAPTER IV
mollet DISCUSSION Zoogeographic Affinities of the Lerma Fauna
Faunistic Assemblages.
, Relative to other assemblages of fishes in North
America, the living fauna of the Mesa Central is depauperate and highly endemic (Turner, 1946; Miller and Fitzsimons, 1971; Barbour, 1973a; Barbour and Brown,
1974). These characteristics are generally taken to b the result of long-term inaccessibility of the Mesa
Central to fishes from other areas. Meek (1904) and
Regan (1906-08) emphasized the sharp transition in species composition between Central Mexico and neigh- boring regions by erecting a discrete faunistic unit for the fishes of the Lerma basin and its former parts.
Regan (op. cit.) recognized four such units-in/ Mexico: mestern Notth American fishes found west of/the conti- .// nental divide from southern Canada to the northwestern coast of Mexico; eastern North American fishes from
Alaska, Canada and the eastern sloPe of the continent south. to Central Mexico; neotropical fishes from Central America northward to southern Mexico; and Lerma fishes
within the geological limits of the Mesa Central.
150 151
Regan's zoogeographic regions are reasonably
discrete in terms of Recent species, but his faunistic
boundaries 'tend to be compromisedsby late CenOzoic
fishes. Data bearing on this problem inclIge- range extensions and new insights into relationships based on fossil material. Zoogeographic implications of the
late Cenozoic - Lerma fishes are summarized in Table 2
and discussed below. •
• Biogeographic Tracks.
When the distributions of different organisms ctincide, it may be hypothesized that the separate
, distributions are historically related to the same
- geographic events. When this relationship holds, it
is possible to deduce biogeographic history from a
knowledge of the distribution of taxa and their sister
groups. Confidence that a general distributional
p.ittern has a geographic basis increases with the number •
, of monophyletic groups which exhibit the same pattern,
or biogeographic track (Croizat et al., 1974; Platnick
and Nelson, 1978; Rosen, 1978). With varying degrees
of confidence, three biogeographic tracks can be recognized involving fossil and living fishes of the Lerma basin.
Pacific coastal track.--Salmon and trout are a- conspicuous element of the western North American fish fauna. Recent work sh6ws the family to have been - , 152
•
•
Table 2. Zoogeographic'ailfinities of fossil fishes of the Western Mesa Central.
Location of Fossil Occurrence Related Taxa
c •ri cn co ci ca cci , U 0 .f-I •r4 8 S4 $.4 ,-.1 W W M >4 O W 0 g Pq U 1.4 0 N . 4-) .B .2 r_i I Cy C.) $4 )4 it ✓ cl) • 0 0 1-i C.) U m z z 4.) ,-.1 w c
Ropa ..-i _ cl. irs 0 0 w c w 0 .--1 $4 s-I U O 4-) •f-I 11:1 W W 4-) 0 'in C1 4-) 4) RI • O 0 -r-I rt) I* U) u) •rn .4 CD 4-) 01- M 0) SANTA 4 3 4 U
. Rhabdofario X X -. undescribed salmonid X X MOxostoma X X Yuriria X X ? X Algansea ? X X X Ictalurus X X X TaPatia , X X Ameca X X Chapalichthys X X Alloophorus X X Goodea x X Xenotoca X X. Chirostoma X X Micropterus X x X X 153
widespread and diverse during th late Cenozoic (Cavender
and Miller, 1972; Kimmel, 1975; Smith, 1975).
Nonetheless, the two late Pleistocenesalmon7like fishes" 4 from San Marcos and Ajijic are the least expected
elements in the Lerma fossil assemblage.
Inferences about the biology of the fossil. species , are admittedly weak. However, the salmon from Ajijic
is a member of the genus Oncorhynchus (Miller, pers.
comm..), a .group of anadromous fishes of the North Pacific
Ocean. In North America, the genus reaches its present
southern limit off the coast of northern Baja California
(Fig. 24) (Castro-Aguirre, 1978). Origin from a sea-run
stock is a iikely explanation for the presence of a
salmon at Ajijic. This implies a past depression of
pa-surface temperatures (see Climatic History, below) , and southward extension of the range of the genus to
include the former outlet of the Lerma basin. This .¼ inference is supported by the present occurrence of
two endemic lhmpreys on the Mesa Central; the southern coastal limit of this family of primarily anadromous
fishes is also off northern Baja California (Fig. 24). The known material of the other fossil salmon, Rhabdofario, rugosus, is inadequate to allow determination
.of its relationships in a cladistic sense. Its g zieric placement is based on phenetic resemblance tb "the two other members of the genus from the Miocene- 154
Figure 24. Distribution of some salmonids and lampreys in western North America. Southern coastal limits are shown for (A)+Oncorhynchus gorbuscha, from Hubbs (1946); _(3) Oncorhynchus kisutch, from Scofield (1937); and (C) Entosphenus tridentatus, from Hubbs (1967). Inland localities are shown for (.l) Rhabdofario carinatus from the Miocene-
Pliocene of Oregon (Kimmel, 1975); (2) R. lacustris from the Pliocene of Idaho (Smith, 1975); (3) R. rugosus and an unidentified salmonid from the late Pleistocene of Mexico; and (4) two relict living lampreys from Mexico (Alvarez, (1970).
11•-• 155
112 104 -
Figure 24 156
Pliocene,of Oregon (Kimmel, 1975) and the Pliocene of
Idaho (Smith, 1975). The species of Rhabdofario appear to have been carnivores in large lakes. There/ is little evidence for i nadromy in the genus, except that it may be related to Oncorhynchus. While R. rugosus cleaily has affinities to fishes in western North America, it is unclear whether it represents a coastal or inland track.
Western mountain track.--The two cyprinid genera known as fossils from the Mesa Central are related to fishes of northwestern Mexico and western United States.
Yuriria has been treated as a form of the eastern genus
Hybopsis, but several characters indicate that its relationships actually involve Western fishes (Chapter
III). Barbour and Miller (1978) presented evidence of similar relationships for the genus Algansea. It appears to' bethe sister group of five species of Gila
including G. ditaenia, G. purpurea and G. pulchra of northwestern Mexico.
- A *track along the present Sierra Madre Occidental
(Fig. 25) is cOrroborated by the distribution of
additional species of Gila, trouts of - the.genus Salmo (Needham and Gard, 1959), and mountain suckers of the suhcerms Rantasts cenus Catnstaraus (Smith. Lerma-Rio Grande track.--Slickers of the genus Moxostoma are widely distributed in eastern North Figure 25. Co-occurrences of western North American fish ð. genera in Mexico: (A) Gila, (B) Catostomus, (C) Salmo,
(D) Yuriria, and (E) Algansea. • 159
America from Hudson Bay southward into the Rio Grande ;.- basin. In Mexico, they are also known from disjunct
populations in the Sierra Madre Occidental, Mesa Central,
and peripheral streams south of the Mesa Central.
The three living Mexican species constitute a monophyletic
, group (Robins and Raney, 1957), the range of which can
be taken to define a biogeographic track from the Rio
Grande to the Rio Lerma (Fig. 26): The extinct species
from Jocotepec Quarry, M. ammophilum, provides independent
confirmation of this track because it is apparently nOt
part of the monophyletic group defined above but it
also has affinities with fishes of eastern North America.
The natural distribution of basses of the genus
Micropterus closely coincides with that of Moxostoma.
They aredistributed from southeastern Canada through.
the eastern United States into northern Mexico. ' The
occurrence of a fossil Micropterus in the Lerma basin.,
significantly extends'the range of the genus (and
family Centrarchidae) and increases the degree of
coincidence'between the ranges of 1,4icropterus and
Moxostoma (Fig. 26).
The North American catfish genus, Ictalurus,
occurs throughout most of eastern North .America and
Mexico southward into Guatemala. The species in the
Lerma basin, I.,spOdius and I. dugesi, are part of a
tonophyletic group which includes other species of
160
• Figure 26. Natural distributions of three eastern North
. American genera, Micropterus, Moxostoma and Ictalurus, in
4 Xexico. All thpe genera are known as _fossils from the • terma basin (star).
' T 162
the Central Plateau and I. punctatus of the Rio Grande' basin and eastern United States. If the silverside genus Chirostoma includes derivatives of ai Menidia-like stock as hypothesized by Barbour (1973a), then part of Chirostoma, the jordani species group, may also be interpreted as an element in the Lerma-Rio Grande track. Menidia now occurs along the Atlantic and Gulf slopes including streams in Texas and northeastern Mexico (Chernoff et al., in press). The
'ordani group includes a form in the headwaters of the Rio Mezquital, a former tributary of the Rio Gfande. , Endemic groups.--As far as can be determined from distribution and the known fossil record, the evolutionary history of the family Goodeidae has been confined to the Mesa Central and nearby streams. This group range is _ unusually compact in view of the diversity within the family. With about 40 species, the Goodeidae is nearly as diverse as the Ictaluridae, the largest endemic North American fish family (43 living species; Lundberg, 1975). But whereas the range of the Ictaluridae spans nearly half the conti ent, that'of the Goodeidae is limited to an area that is ti ip omparison. The compactness and , diversity of the Goodeidae ggest a long history in isolation. The fossil record reveals only that goodeids were present in the area of the present Mesa Central in
the Miocene, that their'• unique reproductive specializations 163
had been developed by that time, and that several living
species show little detectable morphological change since
the Pleistocene. The ultimate origins of the family
will be detectable when its relationships within the '
Cyprinodontoidei become known.
The silverside genus Chirostoma is the other large
endemic group on the Mesa Central. As mentioned earlier,
part of the genus, the jordani group, may be interpreted
as part of the Lerma-Rio Grande track. Silversides in the 4'
arge group may be derived from a Melaniris-like stock
(Barbour, 1973a). Melaniris now occurs along both' coasts
of Mexico. It is possible that the origin of the arge
group in Central Mexico involves the marine transgression,'
the former Ralsas Portal (Barbou 1973b).
Sequence of tracks.--The vicariance concept of
biogeography assumes dispersal of ancestral biotas and
subsequent allopatric speciation events which result in
highly sub.divided distributions (Rosen, 1978). The
fact that generalized tracks overlap (that is, organisms
occur in sympatry), as is the case for fishes of the
Lerma basin, is itself evidence that dispersal has
occurred. The temporal sequence of tracks can-be estimated
by the following driteria (Smith, 1975): (1) the earliest .
fossil occurrendes of the-taxa'involved, particularly, in
the basins of concern, (2) the relative strength of each '
'track in numbers of specie's, and (3) the relative diver- 164
gence of the species representing the tracks. The first freshwater fishes in the area of the
present Mesa Central'appear to have been the goodeids.,
They were already present in the Miocene, and they have
diverged from other cyprinodontoid families to the extent that their relationhips are obscure.
, 7 4 Both the western mountain track and the Lerma-Rio
Grande track have left remnants in the Plio-Pleistocene
Chapala section (Table 2)). The minnows of the western
- mountain pattern (Yuriria and Algansea) are more distinct • from their northern sister groups than are the species of
the Lerma- Grande pattern. Those fishes (Micropterus
relictus, Ictalurus spodiuš and Moxostoma spp.) each have a congener in the Rio Grande basin. They may
represent a former iinage of the Central Plateau which
was tributary to the .Rio Grande during the Pleistocene and perhaps. as early as the Plio-Pleistocene. The
Pacific coastal track is indicated only by latp Pleisto-
cene and living-fishes and may be the youngest of the
patterns involving the Lerma fauna.
It is noteworthy that the Lerma fauna has very
limited affinities to the neotropical fauna touth of the Mesa Central. The poeciliid genus Poeciliopsis rom streams along the west coast of 'Mexico Central America and a small part of the Gulf of Mexico coast. A single species, P. infans, has 165
entered the Ameca, Santiago, Magdalena and Lerma basins. 1 Two characteristic Aeotropical families, the Cichlidae
and Characidae, extend from South America through Central - America and northward along both coasts of Mexico. r T Although both families now occur in the lower Rio Grande
.ts basin, niether is known from the Mesa Central. This
implies 'that (1) habitats of the Mesa Central are ecolog-
ically unsuitable to cichlids and characins, or (2)
. there have been no hydrographic connections available
to them since their arrival in the area. The first * alternative seems unlikely in view of the broad ecological
amplitude of these fishes, particularly of the characin,
Astyanax fasciatus. The second alternative seems compatible with other biogeographic patterns. Characins and cichlids
may not have been present in southern North America until
the late Pliocene when a terrestrial connection was estab-
lished between North. and South America (Ferrusquia-Villa- franca, 1978). The mountains which delimit the Central
Plateau had already been uplifted by that time. Hydro-
graphic exchanges since the late Pliocene have been from
the plateau to coastal drainages which are eroding
headward into the plateau.
PaleohydrograpWy of the Western Mesa Central The present surface configuration of Central Mexico ' is- largely the result of intense tectonic and igneous activity. Geological instability has been. associated with 16'6
iepeated compartmentalization of surface drainages as indicated by flat-floored valleys with thick Lacustrine sediments in many parts of the Lerma basin (Tamayo and
West, 1964). The hydrographic limits of an ancestral drainage can be taken to correspond to tfie aeological boundary of the Mesa,Central (Fig. 1, p. 3). Excluding headwaters of coastal streams, this area is now divided into ten separate hydrographic units: the Lerma and Ameca . rivers and eight endorheic basins (Tamayo and West, 19641'
Fig. 4). It appears that the Mesa Central has been drained by a system which flowed westward through the ancestral
Chapala basin utilizing the Rios CoaRtiayana, Ameca or
Rio Grande de Santiago as exits, but the exact course and extent of the system are unknown (Palmer, 1926; Clements,
1963; Tamayo and West, 1964; Barbour, 1973b).
Some aspects of the surface history of the western
Mesa Central are revealed by the distribution of its fossil fishes and their known relatives. Occurrences of these fishes are plotted against drainages in Table 3.
The fossil species and their relatives are distributed among eight hydrographic units in the western Mesa Central (Fig. 27). These units are defined on the basis of hydrographic limits or geological boundaries. The
Lerma basin is taken to include Lago de Chapala, all of its tributaries, and its outlet as far as the falls at JuanacatlAn'. The Rio Grande de Santiago is taken
167
tZb // Table 3. Matrix showing geographical occurrences of fossil fishes and their relatives in western Central Mexico. Hydrographic units correspond to the basins of .Fig. Occurrences.are inditated as Repent (R) e Pleistocqne (P) or Plio-PleiStecene ,(I).. The ranges of some taxa extend beyon'ae"BiasiA -Included here.
0- UI (I NI . R-I •RI -,--1 0 4I 04 0 Z .4-4 f-4 CL) C.) 0 O 0 - M C C, I M -R4 W a) 0 ‘1•1 CL) RA (‚3 T—I 0 )4 1 IM Z C.) MI RL CD 1:11 M CD R0 •RL E
1 M CD A. 1.71 0 .4 COAHUAYANA x .6)" S o o o o a.) %pi %,4 • 4.) ••-i
1-1 P4 C4 1-1 - GG C4 Rio • 07 Rhabdofario rugosus P- undescribed salmonid' Moxostoma.rohiustum group PR• R R R Moxodtoma ammophilum
Algansea aphanea • R R Alganseetincella
mAlgansea millei± Allansea popOche Algansea.monticola. ° R Yurirta altt R R Yurria elilana IP 1,4 , - Yuriria sp. • tont.
-1 •
1
Table 3. Continued.
m .-1 .,-1 0 04 0 , / H 4 M / 0 0 • / Z. 0 I-) M M N C C I 0 .,-I W W WI-7 0 •H M M H. 0 3-1 M 43 r-4 0 M 0 r0 .H 5 LT C / m '• m , o 4 z .4) 0 0 0 E %.,.4 • 4.) ..,..1 0 g 4 4 a I 0 ICtalurus dugesi R R R .:1 Ictalurus spodius P P Xenotoca: melanosoma ,R R R R R ...,2 Xenotoca eiseni 'R R R R r Xenotoca variata R R Xenotoca sp. P Goodea atripinnis PR R R R R . Ameca splendens P R Chapalichfhys encaustus ' PR Alloophoeus robustus PR ChiAlstoma'lucius , PR' Chirostoma promelas -,PR t • Chirostoma 'ordani R R R R R Chirostoma sp. P Micropterus relictus IP 169
Figure 27. Outlines of eight hydr6araPhic units in the western Mesa Central. Rio Ameca, AM; Rfo Armerfa, AR; Atotonirco-Zacoalco basin, AZ; Rio CoahUayana, 'CO; Rio Lerma, LE; Laguna de Magdalena, MA; Rio Grande, de' Santiago, SA; Rios Verde and Juchipila, VJ.
•
--t \ / ..- / \ \ ,..• \ / \ ,- ;.--- \. . ‘ t ■ / \ \ \ 1 r \-- ‘ . \ 1 wi / \ -0 ; \ , -. / I \ .. › _ , ,...... / / 0 \ 0 ,.--. SA / % -T, I mA\ ■ \ 6 \ • ... % - ■ .■ .. __. is - k % \ .,. AM \ I ■ ' . ■ 1 % „...." l .../ I ...... (i ,k LE t 1 tt 1 I ■ N.... 1• / % i k ■ .... / -‘, ....--.... \ k .. _, , ■ 4 ..0. ' : ■ AR r ..... _._ -- -- ■ ■ 1 . ■ 0 ■ / ■ ■ 0 . - I / 0 1 ■ % 7 - i 1 t , '2 1 , . \ I / / ( .,,, . \ 1 / / ■ CO / // / .• ■ - '- Figure 27, 171
TO INCLUDE ONLY , THE PORTION BELOW JUANACATLAN. TWO
PRESENT TRIBUTARIES OF THE SANTIAGO, THE RIOS VERDE AND
JUCHIPILA, DRAIN A PORTION OF THE MESA CENTRAL AND ARE
REGARDED AS A UNIT SEPARATE FROM THE SANITAAGO.
• THE RIO GRANDE DE SANTIAGO IS ERODING HEADWARD INTO
THE MESA- .CENTRAL. iÆ HAS CUT A DEEP CANYON INTO THE .
THE PLATEAU IT IS INFERRED TO HAVE CAPTURED THE RIOS
VERDE AND JUCHIPILA WHICH HAVE- FAUNISTIC AFFINITIES TO
THE RIO. LERMA. INSPECTION OF TABLE .3 REVEALS THAT THE
CANYON OF THE SANTIAGO CONSTITUTES A DISJUNCTION IN THE
RANGES OF FIVE SPECIES COMMON TO THE VERDE, JUCHIPILA
AND LERMA RIVERS. THE SANTIAGO ALSO APPEARS TO HAVE
CAPTURED A PORTION OF THE ANCESTRAL CHAPALA BASIN, RESULT-
ING IN A DROP IN LAKE LEVEL AND LOSS OF THE OUTLET THROUGH
THE PASS AT JOCOTEPEC QUARRY. THE INFERENCE THAT AN „ AN TRAL LAKE EXTENDED N&RTHWARD INTO THE AREA NOW DRAINED •
BLE"THE 'UPLFRE-F- SANTLAG-6- ABOVE THE FALLS IS BASED .9N CLEMENTS
(1963) REPORT O'F . LACUSTRINE DEPOSITS SIMILAR TO THOSE OF
THE CHAPALA FORMATION NORTH. OF THE PRESENT BASIN.
' A HY,AROGRAPHIC CONNECTION BETWEEN THE CHAPALA,AND •
ATOTONILCD-ZACOALCO.BASINS IS INFERRED ON THE BASIS OF # GEOLOGICAL EVIDENCE FOR A FORMER OUTLET FROM THE WESTETH
• END OF THE CHAPA4.1 BASIN AND A FORMERLY MORE EXTENXIVE
LACUSTRINE SYSTEFRLIN THE ATOTONILCO-Z-ACOALCO BASIN
( PP. 45-46). - THIS INFERENCE IS SUPP6RTED BY BIOGEOGRAPHIC
DATA. A LARGE, LATE PLEISTOCENE LAKE FILLED MUCH OF THE basin and supported a lacustrine fish fauna which '
Included Rhabdofario rugosus; Algansea milleri, Yuriria
elliana and Ictalurus spodius. Of these fishes, only
R. rugosus is unicflue to the basin; material of the others cannot be distinguished from remains from Jocotepec
'Quarry.
Diversion of the Lerma system due to stream capture
by the Santiago resulted in loss of the tributary through
the Jocotepec pass to the Atotonilco-Zacoalco basin. The 1
lake which had nearly filled its catchment basin (based '
on widespread lacustrine sediments) was reduced to the
present shallow playa lakes, and exterior drainage wass
lost. The lacustrine fish fauna, which formerly included the large top carnivore.R. rugosus, was reduced to a
' simpler fauna of small ipshes.
On the basis of unspecified geological evidence, Palmer
(1926) hypothesized that the Mesa Central was once drained
by a southern outlet which passed through the basin of
the present klo Coahuayana (Fig. 27). The two species
of Xenotoca shared by the Coahuayana and Atotonilco- ' Zacoalco basins (Table 3), rit y support a Pleistocene
outlet or indicate headwater capture. A 'former wesLrn outlet of the Mesa, Central through
tie basin of the pre6ent Rio Ameca was hypothesized by Smith and Millpr (1980) on the basis of distributions of Redent fishes. It appears that the presently 9nd6rheic 173
Laguna de Magdalena was more extensive, and was also
drained by the Rio AmeCa (Ibid.). A western oCitlet is
supported by paleontological. evidence. The fossil species
common tO the Lerma and Atotonilco-Zacoalco basins are
represented by living congeners in those basins and the
Rio Ameca. One fossil goodeid from Jocotepec Quarry,
Ameca splendehs, is known today only from the headwaters
of the Rio Ameca.
A former drainage in the western Mesa Central
appears to be .defined by the ranges of Algansea tincellal Goodea atripinnis, and Chirostoma 'ordani (Table 3). Occurrences of these and other fishes suggest that the
Rios Verde and Juchipila have been tributaries of the
Rio Lerma which flowed westward through the Chakala,
Atotonilco-Zacoalco and Ameca basins to the Pacifid.
4guna de Magdalena drained into the lower pat of this
system., - a Climatic History
Regional events.--During the Quaternary of the
Southwestern United States and Mexico north of the Mesa
Central, floras and faunas were repeatedly displaced
both altitudinally and latitudinally in response to changes in climate (Wells, 1966, 1978; .Van Devender, 1976, 1977; Miller, 1977; Metcalf) 1978; Van Devender and
Worthington, 1978; Axelrod, ■9-79). .Climatic fluctUations have also been inferred from geomoi.phological data; for . .174
example, past pluvial episodes are indicatOd by abandoned beacheS and wave-cut terraces in the Basin and Range Province of northern Mexico (Reeves, 1969).
The evidence indicatgo a general trend toward increasing aridity in northern Mexico which, although interrupted during pluvial'episodes, has resulted in a dry climate which is presently more severe than at any earlie'r time '
(Axelrod, 1979).
Quaternary climatic events are also reflected in the present hydrography of the Mexican tentral Plateau.
The streams of the Mesa del Norte (Fig. 3) hav,e been tributaries of the Rio Grande system, as'indicat by their fish faunas (Meek, 1902,1904; Miller, 1976,1978). With the development of desert climate in the past
11,500 years (Wells, 1978) and presumably between late
Cenozoic pluvial episodes, the volume of flow in these # streams has been reduced to thee7xtent that many of them no longer achieve exterior drainage. Much of the area is now drained by, ephemeral streams which flow through • 11 Indefinite courses (ramayo and West, 1964). A1thol.*1 piracy of headwaters may account for reduction of flow.
In some streams Ce:g. the _Rio Nazas; Albritton, 1958), rain-shadow effects cASequent to upliftsof the, Sierra' • t.ladre Occidental are certainly also involved. It is controversial whether the climatic events recorded in .northern Mexico can be extended southwai'd 175
as far as the Mesa/1Centra1. Clements (1963) inferred
pluvial. stages of Lago de Chapala on the basiS of wave— cut terraces. These *strtictures have not been relocated,
but If they do exist they could 'beplausibly explained by the drainage changes ' erred above without invoking pluvial episodes.
Extension of glaciers on the high peaks around the
Valley of Mexico has been inferred from moraines (White,
1954, 1956, 1962), but it does not appear that these minor glacial. advances are asso&ated with significant climatic changes below c. 3000m in elevation. Based on mid to late Pleistocene diatom stratigraphy n the
Valley of Mexico, Bradbury. (1971) concluded that "climatic changes known to have occurred in more northerly latitudes
do not seem to have been reflected in this region of,
Mexico." The remarkable persistence of many diatom
species throughout the sediments examined and thir
common distribution in the basin today suggest that truly
pluvial conditions did not reach the Valley of Mexico (Ibid.). . Lago de ChapaV, At. 20°15' N latitude, is about
100 km north of the 1titdé of the Valley of Mexico.
Faunal shifts:7-A1thOugh the Mesa.Central may not have experienced pluvial episodes or periods of aridity
comparable to those of northern Mexico, some degree of , climatic fluctuation is indicated by the'former occurrence • • OF SALMONIDS AND: A CEHTRARCHID ON THE MESA' CENTRA.1. 176
BASED ON COMPAILSONS OF SUCCESSFUL AND UNSUCCESSFUL
INTRODUCTIONS OF OLIEORHYNCHUS BEYONDTHE PRESENT NATURAL
RANGE OF THE GENUSE=TEVIDSON AND.-HUTCHINSON (1938)' CON- ' • , CLUDED THAT BOTH OCEANITEMPERATURES AND ACCESSIBILITY OF
SUITABLE SPAYPING STREAMS WERE LIMITING FACTORS IN THE - -/ • DISTRIBUTION AF'THE GENUS. HUBBS (1948) DEMONSTRATED
THAT DISPLACEMENT OF SALMONIDS AND OTHER FISHES OFF
WESTERN NORTH AMERICA IN HISTORIC 'TIMESIS CORRELATED
WITH CHANGES IN OCEAN TEMPERATURES. THAT OCEAN TEMPERA-
TURES HAVE UNDERGORLE MAJOR PLEISTOCENE FLUCTUATIONS OFF
CALIFORNIA AND MEXICO IS INDICATED BY SOUTHWARD
DISPLACEMENT OF LATE PLEISTOCENE MOLLUSCAN FAUNAS
(ADDICOTT, 1966) AND ISOLATION OF NORTHERN FISHES IN
THE SOUTH-OPENING GULF OF MEXICO (FREY, 1965).
THE PRESENT SOUTHERN COASTAL LIMIT OF ONCORHYNCHUS
IN NORTH AMERICA IS AT ABOUT 31° N LATITUDE (FIG. 24).
THE SCRILTHERNNIOST NATURAL. INLAND LOCALITY APPEARS TO HAVE
BEEN THE SAN LORENZO RIVER, 37° N,LATITUDE (SCOFIELD,
1916). SEA-RUN TROUT, SALMO GAIRDNERI, OCCUR OFF THE
COAST OF SOUTHERN CALIFORNIA AND SPAWN IN STREAMS AS '
FAR SOUTH AS - THE RIO SANTO DOMINGO, BAJA CALIFORNIA
( HUBBS, 1946). LAMPREYS OCCUR OFF THE WEST COAST AS
0 FAR SOUTH AS 29 N LATITUDE ( FIG. 24).. EXCEPT FOR TWO $. RELICT SPECIES ENDEMIC TO THE MESA CENTRAL (ALVAREZ,
1G701, THE SOUTHERNMOST INLAND LOCALITY FOR THE FAMILY
APPEARS TO BE THE Los ANGELES BASIN, CALIFORNIA (HUBBS, 177
19671. '
If the fossil salmonids and living lampfeys of the
_Mesa Central are of a sea-run origin, they suggest a southward displacement of the ranges of both families to include the former outlet of the Mesa Central, probably the Rio Ameca. This displacement, or a similar one at an earlier time, may explain the presence of a trout, Salmo chrysogaster,'in coastal streams along the Gulf of
California.
The presence of the extinct bass, Micropterus r'Xictus, in the Chapala basin does, not necessarily , imply climatic conditions different from those of today.
Many centrarchids have been successfully introduced into the Lerma system, including Micropterus salmoides in the Chapala basin.
Eight of the fossil species known from the Mesa Central are now extinct. Of these, four are still represented 'in the area by living relatives which include possible ',descendent forms. These species, followed by their living reIaives, ard: Algansea milleri, A tincelIa; 4 a Yuriria elliana, Y. alta; Ictalurus spodius, I. dugesi;
ChIros-eoma sp., C. jordani. The extinct species not represented by close living
relatives in the Chapala basin are Micropterus relictus, Moxostoma.ammophilunt, Rhabdofario rugosus and the salmonid from Ajijic. Except'for the sucker, these species were 178
large top carnivores associated with lacustrine
sediments. Their'extinction between the,late Pleis-
tocene and present may indicate a reduction in the
volume of aquatic habitat. Reduction of the previOusly
extensive lacustrine system may have resulted in part
from changing drainage patterns. However, drainage
changes would not account for the reduction of Laguna
de Magdalena which occupies a basin in a divide (Smith
and Miller, 1980) where there could not have been
significant former tributaries. It is possible that
some degree of climatic change is also involved.
( 180
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