( Ciencias da Terra (UNL),<i~ I' Lisboa _I N° 14 pp. 323-334 . I , 2000... .16 Figs . 1"< -0:. :~.)

Miocene marine mammals from PortugalPaleogeographical and paleoecological significance

Mario Estevens

Centrode &ludoa Gcol6gicos, Faculoaie de Ci&lcia!l e Tecnologia,Quinta ca TOfTe, P-l 825-I !4 Capariea, Portugal

Pbonc: (35I) 212948573, Fax: (35 I) 212948556, E-mail:alcYcns@mlliLfcLwd.pI:

ABSTRACT

Key words: Marine manvnals; Miocene; Portugal; geographicand stratigraphic distriburion;correlation with environmc:ntal changes;paleogeognphical and paleoecological significance.

Neogenemarine mammals arestill incompletely knownin Portugal. However, a general overviewofthe geographic and stratigraphicdistribution of marine mammal localities in the Miocene of Portugal is already possible. An attempt of correlation between thetrends shown by these distributions and the horizontal and vertical environmental shifts is presented In general, sirenians occur indeposits representing shallow, warm. low energy aquatic environments; while cetaceans are more frequent in more open, deep andtemperate marine environments.

RESUMO

Palavras-chave: Mamlferos marinhos; Miocenico; Portugal; d istribui~o geografica e esrratigraflca; conetacsc com variaccesambienlais, significado paleogeografico e paleoecologico.

o conhecimento dos mamiferos marinhos neogenicos e ainda incompleto em Portugal. Ccnrudc, e pcssivel delinear a disrribuiegogeografica e estratignifica das jazidas de mamiferos marinhos' do MiocCnico de Portugal. Tentou-se, igualmente, relacionar astendencies cxibidas par estes distribuilj'Oes com varialj'Oes horizontais e verticals das condi¢es paleoambicntais. Demodo geral, csSirenia ocorrem em ambientes pouco profundos, de aguas quentes e fraca energia; enquanto que os Cetacea sio mais frequentes emambicntes marinhos eberros, de maier profundidade e aguas mais tempcradas.

INTRO DUCTIO N

This paper is an updated vers ion of a preliminary re­port on the same subject (Estevens, 1998a). It includesnew data on the collections of the "Museu Nac ional deHist6ria Natural da ljniversidade de Lisboa" (NationalMuseum of Natural History of the University of Lisbon) .Th e co llections of the " lns tituto Geol6gico e Mineiro"(Geo logical and Mining Institute) were reevaluated, andsome new specimens were added to the collections de­posi ted at the "Departamento de Ciencias da Terra daFaculdade de Ciencies eTecnologia da Universidade Novade Lisboa" (Department of Eanh Sciences of the Facultyof Sciences and Technology of the New University ofLisbon).

Although long known in Portugal (Escbwege, 183 1),Miocene marin e mammals have not been mucb studied inthis country (Antunes, 1984). Only a few sbort descrip­tive notes have been published (Vandelli, 1831 ; Kellogg.1938-40; Zbyszewski, 1944, 1953, 1954; Antunes, 1959,1979; Mata, 1963; Jonet, 1980-81). A considerab le numberof undescribed specimens can be found in Portuguesecollec tions.

Th e systematic study of the Neogene marin e mam­mals ofPortugal wasresumedby the author at the "Centrode Es tudos Geol6gicos da Faculda de de Ci encias eTecnologie", under the supe rvision ofProf. Miguel TellesAntunes . The first results about a sma ll assemblage ofodontocetes from the Lower Tagus Basin Miocene willsoon be present ed. Meanwhile, based on published data

323

The grea t majo rity (85,7%) of the 56 localities arelocated in the distal region of the Lower Tagus Basin(LTB ). This incl udes Lisbon region (LR) and SetubalPeninsula (SP), located respectively north and south ofTagus River (Fig. 2). Few localities can be found southwardsofthis area: only 5 in the vast region encompassing Atcacerdo Sal, the littoral ofAlentejo andAlvalade Basin (Fig . 3),and a mere 3 in Algarve (Fig. 4). A single additional record(not disc ussed here), concerns the Santa Maria Island, inthe Azores Archipelago (Cotter, 1888-92).

The predomi nance ofmarine mammal localities in theLTB results largely from the fact that this basin conta insthe most complete Miocene mar ine seri es in Portugal(Antunes et aI., 1996). As a consequence, the LTB hasbeen both the most studied and the one from where morefossils were collected. Barnes (1976: 338) noted that forthe eastern Nort h Pacific fossil cetacean assemblages abiased collecting might be part ly on the origin of suchdiversity or abundance trends.A more detailed prospectionof the other Tertiary Portuguese basins may lead to thediscovery of new localities. However, this wou ld j ustatt enu ate the observ ed geographic t rend wi thoutprodu cing any dramatic changes . The LTB will certainlyremain the most importan t area in Por tugal in whatconcerns Miocene fauna in general, and marine mammalsin particular.

A significant geographic segregation can be observedbetween Sircnia and Cetacea locali ties within the distalregion of the LTB (Fig. 2).

10 Congresso sabre 0 Cenozoico de Portugal

and on the inventory of specimens from collections, it isalready possible to present a list of Portuguese Mioceneloca lities where marine mammal remains were registered .Pliocene records are scarce and somewhat dubious (seebelow). At this point, only the presence of Cetacea, Sireniaor "Pi nnipedia" will be acknowledged for each locality,with no indication of subordinal assignment. Such a listallows to outline the geographic and stratigraphic distri­bution of each group, focusing on the main differencesbetween them. The paleogeographical and paleoecologicalsignificance of such differenc es was evaluated by corre­lating the detected trends with horizontal and vertica lchanges of the paleoenvironmental conditions .

The conc lusions herein presented were hampered bysome difficulties concerning both the published data andthe inventoried collections.

Pub lished records of marine mammals are not alwaysreliable in what concerns systematics, even at an ordinallevel. Many older references of cetaceans for the EarlyMiocene of Lisbon probably concern sirenians (pa rticu­larly those in Cotte r, 1956 and Choffat, 1950a). Anotherexample is a record for the Burdigalian of Foz da Fonte(48), originally reported to Cetacea (Zbyszewski et al.,1965) and later reassigned to Sirenia (Zbyszewski, 1967).As most ofthesc records correspond to fragmentary materialnot always collected, it is difficult to determi ne their truetaxonomic nature. Nevert heless , the scarce bibliographi creferences for which a positive corres pondence could beestablished with material deposited in the studied collec­tions ind ica te that mos t (i f not all) Early Miocenepublished records of marine mammals corres pond in factto sirenians (as noted by Antunes, 1959, 1969-70, 1984).The systematic nature of some references, however, couldnot be definitely asce rtained. In these cases, the taxonomicuncertainty will be indicated either by a broken outline ofthe symbols representing each marine mammal order (inFigs. 2 and 5), either by hatched areas (in Fig. 6).

The inverse prob lem was found when proceeding tothe inventory offossil marine mammals in Portuguese col­lections. In this case it was not the systematic assignmentof the specime ns that constituted a problem (at least forthe majority of them), but rather the definition of theirprovenance. A large part of'the collections of the "InstituteGeologico e Minciro" raised too many problems in th isrespect. Many undescribed specimens are not labeled, andeven for those sitting in labeled trays there is a strongpossibi lity of having been misplaced. l f for some it is stillpossible to deduce their original locality of provenance(through the adhering matrix or their relatio n to otherwell-known specimens), for others this was impossib le.

Therefore, the list of localities presented and theconclusions therefrom derived arc based only on thoserec or ds for whic h the geograp hic and stratigraphicoccurrence could be safely determined.

GEOGRAPHIC DISTRIBUTION

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324

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Ciencias da Terra (UNL) , 14

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325

10 Congressc scbre 0 Cenczcico de Portugal

Sirenia localities arc almost exclusively located in LR,many of them within the limits of Lisbon. There are onlytwo localities to the west (S - Barreiro da Maruja and 10 ­Praia de Carcavelos) and another two near the northernoutskirts (8 - Casal dos Cucos and 13 -Arecirode s Fctais).Santa lria da Azcia(23) could constitute the northernmostreco rd of Sirenia for the Portuguese Miocene, but see be­low discussion on uncertain taxonomic ass ignme nt of re­mains therein found. Sirenians are scan t south of TagusRiver, occ urring only at Pene do Sui (47) and Foz daFonte (48).

Cetaceans, on the other hand, predominate in SP(86,7% of marine mamm al localities in this area) . Thoseloc ated north of Fagu s Ri ver are co nc entrated ineasternm ost Lisbon. Tune! do Rossie (1) would constitutethe exception, hut the reader is aga in re ferred to thediscussion on uncertain taxonomic assignments below.

The single "p inniped" record consists of phocid re­mains from Penedo Norte (46) (Antunes et af., 1995).

In the Alvalade Basin (Fig. 3), marine mammals wererecorded at the three localities that have produced the rich­est fossil assemblages of this region (Antunes et al., 1986).

GEOLOGY Of AL CA CIEA 00 SAL RIEGION.LnTOflAL O f ALlNTl~O AND ALVALADE S ASIN

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326

Cunctas da Terra (UNL), 14

Fig. 4 • Geogra phic distri bution of Miocene marine mammallocalities in the Algarve. Geology adapted from Oliveira et al.

( 1992 ), revised by J. Pais.

Only cetaceans were found at Esbarro ndadoiro (52), whilstthere were only sirenians at Vale de Zebro (53 ). Accordingto a personal communication from J. Pais, sirenia n ribfragments arc to be added to Santa Margarida do Sado(5 1), fro m where only cetacean rema ins were known(Estevens, 1998a ). T he latte r thus becomes one ofthe fewPortuguese loca lities where fossils of these two groupsoccur simultaneously.

Marine mamm als were also recorded at Cerrado daPedra (49) (Sirenia in Antunes & Mein, 1983), located inthe southeastern extension o f the LTB (Alcacer do Sal re­gion), and in Melides (50) (Cetacea in Zbyszewski, 1954).

Only one loca lity in Algarve (Fig. 4) had so far beenreferred in the literature as yielding marine mammal remains:Olhos de Agua (55), from where both Sirenia and Cetaceawere described (Antunes, 1979). T his and Santa Margaridado Sado are the only Portuguese localities where sireniansand cetaceans were simultaneously recorded. The inven­tory of the Port uguese collections revea led fur therundescribed specimens of cetaceans from the Miocene o fAlgarve, collected at Cerro das Mos (54) and Cacela (56) .

STRATIGRAPHIC DISTRIBUTION

T he stratigraphic distri bution of the 56 Neogenelocalities where marine mammals were recorded issummarized in Fig. 5.

Marine mammals occur in almost every PortugueseMiocene marine unit, from the earli est ones at the distalregion of the LTB (Aquitanian DS A I) , to the latest onesat the Alvalade Basin (la te Messinian, EsbarrondadoiroFor mation ). Inversely, only the littoral marine sands atOlhos de Ag ue (55), in Algarve, could be referred to thePliocene, according to a recent 87S r~6Sr isotopic datationof a mollusk bed located just above the sands (An tunes etaI., 2000b). T he vertebr ates found in a lower stratigrap hiclevel ( a~ng which the marine mamm als), seem howeverto indicate a Middle to Late Miocene age (Antunes, 1979).These may thus constitut e a redeposited association(Antunes , personal communicatio n).

Fig. 5 also shows signi fica nt differenc es between thegrou ps o f mari ne mam ma ls in what concern s theirstratigraphic distri bution .

Within the distal region o f the LTB , sirenians arcfrequent in LR from the Aquitanian to the Langhian, nearlydisappearing afterwards (Antunes, 1984). The few mid­d le Serravallian records (Esteve ns, 1998a) are now con­side red too doubtful and were consequently disregarded.Only two sirenian records are known for SP, both of themBurdigalian (localities 47 - Penedo Sui and 48 - Foz daFonte) . A rib fragment collected at Santa Ida da Azoia(23) was questionably ascribed to Cetacea (Choffat, 1950a:120). Th e fragment see ms to indicate a sirenian instead,and in that case it would cons titute the latest record of thegrou p (early Serravallian) for the distal region of the LTB.Conversely, in the southeas tern extension of this samebasin (Alcacer do Sal region), sirenians occur later (la teSerravallian) at Ccrrado da Pedra (49) (Antunes & Mein,1983). Further to the south, in the Alvalade Basin, they

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occur even later (Messinian) at Santa Margarida do Sado(51) and Vale de Zebro (53). The only sirenian record inAlgarve is from Olhos de Agua (55) (Antunes, 1979),supposedly of Pliocene age (see Antunes et al., 2000b andabove) but probably older (Middle to Late Miocene) andredeposited.

Inversely to sirenians, cetaceans only became commonfrom the Langhian-Serravallian boundary upwards.At theLTB they occ ur mostly in the Serravallian and earlyTortonian (Antunes, 1984). Outside this basin, there is onerecord for Melides (50) (Zbyszewski, 1954), correlativeof the most modem well-dated levels of the LTB. On theother hand, cetaceans are known from latest Miocene bedsat the Alvalade Basin (Messinian localities 51 - SantaMargarida do Sado and 52 - Esbarrondadoiro) (Antuneset al., 1986), and Algarve (late Tortonian ofCacela - 56).Also in Algarve , ce tacea ns were found at Olhos deAgua (55) (Antunes, 1979) and Cerro das M6s (54). Thelatter (on a small hill near Lagos) is now recognizedto be Serravallian in age, according to recent isotopicdatations of nearby correlative deposits (Antunes et al.,2000b).

So far, the only Early Miocene locality that unques­tionably yielded cetacean remains is Palcnce de Baixo (36)(middle Burdigalian) , in SP (LTB). There is a doubtfulrecord for the Aquitanian ofTunel do Rossio (1) by Choffat( 1889: 40): "os de grand e taille, incomplet, peraissantappartenir aun crane de Cetace". As no specimens possi­bly related to this occurrence were found, it must be hereheld questionable.

The "pinniped " fro m Penedo Norte (46) is la teSerravallian in age (Antunes et al., 1995).

PALEOGEOGRAPII ICAL ANDPALEOECOLOGICAL SIGNIFIC ANCE

The geographic and stratigraphic trends summarizedabove can be correlated to environmental changes welldocumented in the literature.

The most striking case concerns the marine mammalrecord of the LTB Miocene, which was already the objectof general considerations (Estevens, 1998b). Fig. 6 showsthe e lose correla tion between va r iati ons of thepaleoecological conditions (namely sea temperature anddepth) and the number of Sirenia and Cetacea localitiesfor the distal region ofthe LTB.

Sirenia occur from the earliest Mioeene (Aquitanian)to the early Middle Miocene (Langhian), when sea tem­peratures stayed over :::::24°C (ranging from tropical to sub­tropical environments according to Antunes & Pais, 1984).Sirenia are present whene ver very shallow near-shoreenviron ments are co ncerned, and ab sent wheneverenvironments became slightly deeper (never attaining thecircalittora l stage). The maximum abundance of Sireniaoccurred during the Langhian, when temperatures werehighest in shallow, ncar-shore to fluvial tropical environ­ments (Antunes & Pais, 1984, Antunes et al., 1996).Afterthe Langhian, a marked drop in temperature and increasein depth led to the disappearance of sirenians.

Cunctas da Terra (UNL), 14

This change of envirorunental conditions turned thebalance to the Cetacea favor. Cetaceans became frequentand reach maximum abundance at events of greater depth(circa or ncar-circalittoral stages) during the Scrravallianand early Tortonian. It is noteworthy that the only EarlyMiocene Cetacea occurrence corresponds to the apogeeof the Burdigalian transgression, another maximum depthevent. The number of localities that yielded cetaceanremains became much reduced at the late Serravallian.

The stratigr aphic near-excl usion of sirenians andcetaceans in the distal region ofthe LTB is thus a result ofimportant environmental changes that took place duringthe Langhian (Antunes & Pais, 1984). The subtropical totropical climate and shallow, protected marine gulfs thatprevailed from the Early to early Middle Miocene (Antuneset al., 1996) were an idea l habitat for sirenians (Domning,1976, 1978). The more tempe rate and deeper marineenvirorunents that followed (Antunes et al., 1996, 2000a),were instead more favorable to the occurrence ofcetaceans(Barnes, 1976; Fordyce et al, 1994) .

The geograp hic distribution of marine mammals in thedistal region of the LTB is also co ntro lled by thesepaleoecological factors. The prevailing occurrence ofsiren ians in LR and cetaceans in SP is related to thepredominance of esse ntia lly Early Miocene shallowerdeposits in the former, in contrast to the deeper marineMiddle to Late Miocene sediments that cover most of thelatter (Antunes et al., 1996). The occurrence of a phocidin Penedo Norte (SP) agrees with these assumptions.

The scarce representation of Miocene marine mam­mals outside the distal region of the LTB is related to thelesser development of marine units.

The permanence of sirenians in the Alcacer do Salregion and Alvalade Basin (until the Late Miocene in thelatter) is an indication of the persistence of shallowprotected gulfs and moderately warm waters (Antunes,1983; Antunes et al.; 1986). This took place well after theincrease in depth and coo ling verified by the end of theLanghian in the distal region of the LTB, that eventuallyled to the disappearance of sirenians from this area. Thesouthwards withdrawal of Sireni a in the PortugueseMiocene is in agreement with the accentuation of the ther­mal latitudinal gradient recognized for the northwesternAtlantic during this epoch (Lauriat-Rage et al., 1993).

The cetacean record of Melides (50) is compatible withthe mar ked ly op en and litt oral marine env ironmentrecognized for both these deposits (Prates & Carvalho,1983-85) and their correlatives in the LTB.

In the Alvalade Basin, the contemporaneous occur­rence of open marine environments (either shallower asin Santa Margarida do Sado, either relatively deeper as inEsbarrondadoiro) with the restricted inner gulf of Vale deZebro (Antunes et al ., 1986), made possible for cetaceansand sirenians to occur simultaneously during the lateMessinian.

Few paleogeographical or paleoecological inferencescan be made from the scarce Miocene marine mammaloccurrences in Algarve. The Lagos-Portimao Formation,where Cerro das Mas (54) is included, presents a "warmtemperate" carbonate shelf facies according to Antunes et

329

1° Congresso sobre 6 Cenoz6ico de Portugal

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2000a) and LLU for locallithostratigraphic units (Cotte r, 1904).

01. (2000b). Vertebrates found in the same deposits pointout. however, to near-tropical cond itions (Antunes et 01.,1981 ). Cacela (56) co rrespo nds to a littora l marineenvironment (Antunes et 01., 1981), and Olhos de Agua(55) to a shallow coastal environment witha nearby estuary(Antunes et al., 2000b) .

In conclusion, the.distribution of marine mammals inthe Portuguese Miocene is closely controlled by ecologi­cal restrictions. Sirenia occur mostly in shallow, warm,low energy aquatic environments (a s postulated byDomning, 197.6, 1978). while cetaceans are more frequent

in more open, deep and temperate marine environments(as recognized by Barnes, 1976 and Fordyce et al.,1994).The paleogeographical and paleoecological sig­nificance of marine mammals, and their utility in thereconstitution ofmarine paleoenvironments, is thus re­asserted by the present study.

ACKNOWLEDGMENTS

First and foremost to Prof. Miguel Telles Antunes,who from the beginning of this study has provided all

330

the oppo rtunities and ongoi ng support, as well as athorough review of this manuscript. Also to Doctor M.Magalhaes Ramalho (Vic e-Presi dent of the " InstituteGeo l6gic o e M ineiro" ) and Prof. A. M. Galop im deCarvalho (Director of the "Museu Nacional de HistoriaNatural da Universidade de Lisboa") , who have grantedaccess to the fossil collections under their care.

'REFERENCES

Cunaos da Terra (UNL) , 14

Partofthe researchwas stilldeveloped during the PRAXISXXI Proj ect 2!2.lICTN106/94 "Necgenico e Quaternarioda margem atlantica da Iberia e transformacoes globais",when the author was benefiting from a "Bolsa de IniciacaoaInvesrigacao Cientifica", gran ted by the "Pundecso paraa Ciencie e Tecnologia " under the "Sub-Programa Cienciee Tecnologia do 20 Quadro Comunitirio de Apoio" .

Almeida, F.M. (coord.) (1980) - Carta Geologica de Portugal na escala 1:50 000. Folha 34-C (Cascais) . ServoGeo!.Portugal

Antunes, M.T. (1959) - Nota sobre um mamifero do Aquitaniano de Campo de Ouri que (Lisboa). Bol. Soc. Port.Cunc. Nat., 2- ser., 7 (3): 129-137.

Antunes, M.T. (1969-70) - Mamiferos nao marinhos do Miocenico de Lisboa: ecologia e estratigra fia (nota preliminar).Bol. Soc. Geal. Portugal, 17 (1): 75-85.

Antunes, M.T. (1979) - Vertebrados miocenicos de Olhos de Agua (Algarve), interesse estratigrafi co. Bol. Mus. Lab.Min. Geot. Fac. Cienc. Univ: Lisboa, 16 (1): 343-352 .

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