Rougiertherium Tricuspes

Mammals of Late Cretaceous age are known from scattered sites in Brazil, Argentina, Bolivia, and Peru (figure 2.7, table 2.21). Collectively, these occurrences rank the Late Cretaceous mammal record from the South American continent as far superior to that of all other Gond-wanan landmasses combined. Yet we still lack sufficient evidence for a reasoned interpretation of mammalian bio-geography and faunal dynamics, both within South America and among the Gondwanan continents. It is especially important to recall that, aside from a few isolated occurrences, the pre-Maastrichtian record is limited to a single site in Patagonia. Then, as now, the continent spanned well over 50° of latitude south of the equator and presumably was characterized by great diversity in climate and habitat. It is conceivable, even likely, that major groups of mammals inhabited South America during the Late Cretaceous and remain unsampled in the existing record. Nonetheless, some significant new facts have emerged from this record—the cosmopolitan distribution of one group (Gondwanatheria, mentioned earlier) among several southern landmasses being a good example. Undoubtedly the most important insight that has emerged in recent years is that, prior to the Maastrichtian, at least, South America's mammal assemblage differed fundamentally from those of northern continents. By the Campan-ian, Laurasian assemblages were dominated by multi-tuberculates, eutherians, and (mainly in North America) marsupials. The pre-Maastrichtian record of South America, by contrast, reveals an extraordinary diversity of table 2.21. Late Cretaceous Mammals of South America (see figure 2.7; locality numbers do not correspond between map and table). Localities or local faunas: 1, Paraná Basin, Brazil (Adamantina Formation, Late Cretaceous); 2, Paso Córdoba, Río Negro Province, Argentina (Río Colorado Formation, Campanian-Maastrichtian); 3, Meseta de Somuncura, Chubut Province, Argentina (La Colonia Formation, Campanian-Maastrichtian); 4, Los Alamitos, Chubut Province, Argentina (Los Alamitos Formation, Campanian-Maastrichtian); 5, Fundo el Triunfo, Peru (Fundo el Triunfo Formation, Campanian-Maastrichtian);

6, Laguna Umayo, Peru (Vilquechico Group, Maastrichtian);

7, Paruro, Peru (Couches Rouges Formation, late Maastrichtian); 8, Pajcha Pata, Bolivia (El Molino Formation, middle Maastrichtian)

Mammalia incertae sedis (1, 2, 5, 6, 7, 8) ?Docodonta Reigitheriidae

Reigitherium bunodontum (3, 4) Eutriconodonta

Austrotriconodontidae

Austrotriconodon mckennai (4) Austrotriconodon sepulvedai (4) ?Multituberculata Family incertae sedis Gen. et sp. indet. (4) Archaic "symmetrodontans" Bondesiidae

Bondesius ferox (4) Stem Cladotheria ("eupantotherians") Dryolestidae

Groebertherium novasi (4) Groebertherium stipanicici (4) Leonardus cuspidatus (4) Gen. et sp. indet. (8) Mesungulatidae

Mesungulatum houssayi1 (4) Brandoniidae

Brandonia intermedia (4) ?Casamiquelia rionegrina (4) Marsupialia ?Peradectidae

Gen. et sp. indet. (6) ?Peradectes austrinum (6) ?"Pediomyidae"

Family incertae sedis

Perutherium altiplanense (6) Gen. et sp. indet. (8) Gondwanatheria Sudamericidae

Gondwanatherium patagonicum (4) Ferugliotheriidae

Ferugliotherium windhauseni (4)

'We consider Quirogatherium major to be a probable synonym of Mesungulatum houssayi (see chapter 10).

mammals (in some cases, highly derived) that appear to be members of archaic groups more common in the Jurassic of Laurasia—"triconodonts," "symmetrodontans," dryolestoid "eupantherianss," and (perhaps) "plagiaula-cidan" multituberculates and docodontans. Tribosphenic mammals, which clearly had an early (Berriasian) presence in northern Africa (Sigogneau-Russell, 1991a, 1992), radiated widely on northern continents through the entire Late Cretaceous. The limited evidence at hand suggests that marsupials and placentals, if they were ever present in South America prior to the Maastrichtian, were not very successful and were subordinate to the flourishing lineages of archaic therian groups.

There is clear evidence to suggest interchange of terrestrial vertebrates between the Americas in the latest Cretaceous and Early Tertiary. In North America, for example, the sauropod family Titanosauridae made a brief appearance in southwestern faunas of the Maastrichtian, presumably as immigrants from the south (Lucas and Hunt, 1989). Marsupials appeared in South America in the Late Cretaceous, and by the Early Tertiary they had achieved some diversity on the continent (Marshall, 1987; Muizon, 1991). Eutherians are also recorded in the Late Cretaceous of South America (Grambast et al., 1967; Gayet et al., 2001), though close resemblances between early Paleocene faunas of the two continents (Van Valen, 1988) suggest that some of the interchange, at least, may have occurred during the Tertiary. Late Cretaceous mammalian interchange among southern continents has only recently been documented (Krause, Prasad, et al., 1997). The Ornithorhynchidae (platypuses), a group long thought to be restricted to Australia (chapter 6), have been reported from the early Paleocene of Argentina (Pascual et al., 1992a), and it is possble that they were present in South America even earlier—perhaps much earlier.

Brazil

A mammal specimen was found by Christian de Muizon in the Paraná Basin (figure 2.7), Sao Paulo. The occurrence is in the Adamantina Formation, the age of which is not well constrained, other than the fact that it is Late Cretaceous. The specimen is a dentary fragment with several alveoli and a premolar (Bertini et al., 1993); it appears to belong to a tribosphenic mammal, but further identification is problematic.

Argentina

Three sites in Argentina, all in the southern part of the country (figure 2.7), have yielded Late Cretaceous mammals. A site at Paso Córdoba, Río Negro Province, lies in the Río Colorado Formation, which may be either Cam-panian or Maastrichtian in age. The single specimen from this site is a dentary fragment with alveoli for the last two molars, described as possibly belonging to a marsupial (Goin et al., 1986). The limited information presented by this specimen leaves its identity in doubt (Marshall and Muizon, 1988). Another Argentine occurrence with a single described Late Cretaceous mammal is at the locality of Meseta de Somuncura, Chubut Province. The site is in the middle part of the La Colonia Formation. The unit is not well constrained in terms of age: it may span Campanian (or pre-Campanian) to the Lower Tertiary; the site is believed to lie in the Campanian-Maastrichtian part of the sequence, which has also yielded remains of the bizarre theropod Carnotaurus. Pascual et al. (2000) report a jaw of Reigitherium bunodontum from Meseta de Somuncura. Reigitherium was initially described as a dryolestoid (Bonaparte, 1990). Pascual et al. (2000) consider it to be a member of Docodonta—a group that went extinct elsewhere by the Early Cretaceous. However, the relationships of Reigitherium remain uncertain (see chapter 5). An isolated mammalian petrosal described as "placental-like" has also been reported from Meseta de Somuncura (Pascual et al., 2000), but it has not yet been published.

The most diverse assemblage of Mesozoic mammals known from the South American continent is from Los Alamitos, Río Negro Province, a site discovered by José F. Bonaparte and colleagues. The site is in the Los Alamitos Formation, placed in the Campanian-Maastrichtian (Bonaparte, 1990; Pascual et al., 2000). The depositional environment is interpreted as predominantly lacustrine, with some brackish water influence (Andreis, 1987).

Some 14 mammals10 are known from Los Alamitos (Bonaparte and Soria, 1985; Bonaparte, 1986a,b, 1990, 1992), which is the basis for the "Alamitan" South American land-mammal age (Bonaparte et al., 1987). There are no tribosphenic mammals; rather, the assemblage includes "triconodonts," a ?multituberculate, "symmetro-dontans," the aforementioned Reigitherium, dryolestoid "eupantotherians," and a group of uncertain affinities (Gondwanatheria). Many of the included taxa are highly derived members of their respective groups, suggesting that the fauna is an endemic one, separated from Laur-asian assemblages since perhaps the Late Jurassic. The eutriconodontans (Austrotriconodon spp.) were initially placed in the Triconodontidae, but later referred to their own family, of enigmatic affinities (Bonaparte, 1992). Multituberculata may be represented at Los Alamitos by a dentary with p4 referred to originally as Ferugliotherium

10 Barberenia araujoae appears to be based on milk teeth of Brandonia intermedia (see Martin, 1999a), and there may be other such cases.

by Kielan-Jaworowska and Bonaparte (1996), and a few upper premolars, but now placed by us (see chapter 8) in Multituberculata incertae sedis. Other teeth, especially upper molars, referred to Ferugliotherium (e.g., Krause, Kielan-Jaworowska, and Bonaparte, 1992; Krause and Bonaparte, 1993) are now assigned to Gondwanatheria (see chapter 14). Upper molars of Ferugliotherium show striking similarities to those of the Late Cretaceous Gond-wanatherium and Paleocene Sudamerica, assigned to Gondwanatheria. The discovery by Pascual et al. (1999) of a dentary of Sudamerica with four molar loci precludes its assignment to Multituberculata (see also Pascual and Goin, 2001, and references therein, and chapter 14). At present, we can tentatively conclude that at least Gond-wanatherium is related to taxa from the Late Cretaceous of Madagascar and India (Krause, Prasad, et al., 1997). Most of the remaining taxa from Los Alamitos are "sym-metrodontans" and "eupantotherians" (six species). Three species are included in the Dryolestidae, which are rather common elements of Late Jurassic-earliest Cretaceous faunas of Laurasia, but which (with one exception) had become extinct elsewhere long before the onset of the Late Cretaceous. Mesungulatum houssayi, referred to its own monotypic family, is a relatively large species with rather bunodont molars that, interestingly, appear to be functionally convergent on those of "condylarth" eutheri-ans (Bonaparte, 1990). Three additional genera and species of dryolestoids ("Rougiertherium tricuspes,""Ala-mitherium bishopi," and "Paraungulatum rectangularis") from Los Alamitos were noted by Bonaparte (1999). Although they have not yet been formally described or illustrated and are therefore nomina nuda, they suggest a greater diversity of "eupantotherian" taxa from this site than currently recognized.

Peru

French teams, including Bernard Sige and colleagues, have recovered fossil mammals from several Late Cretaceous and/or Early Tertiary sites in the Peruvian Andes (figure 2.7). A tooth fragment belonging to an unidentified therian is known from Fundo el Triunfo south of Bagua in the Bagua syncline. The occurrence is in the basal Red Beds of the Fundo el Triunfo Formation, first estimated to be late Santonian to Campanian (Mourier et al., 1986), and later considered to be late Campanian to early Maastrichtian, based on charophytes and other evidence (Mourier et al., 1988). The associated fauna includes amphibians, turtles, and titanosaurid dinosaurs. Dinosaur eggshells have also been reported from this formation (Vianey-Liaud et al., 1995).

The most renowned mammal site in the Peruvian Andes is Laguna Umayo, Department of Puno. The site is in the Vilquechico Group (formerly called the Vilquechico Formation, see Jaillard et al., 1993). The Late Cretaceous age originally reported for Laguna Umayo (e.g., Grambast et al., 1967) has been disputed. Van Valen (1988), in particular, found the evidence presented by charophytes to be equivocal. Studies of dinosaur eggshell from Laguna Umayo (Kerourio and Sige, 1984; Vianey-Liaud et al., 1995) support a Late Cretaceous assignment. Jaillard et al. (1993) place the site in the upper part of the Vilquechico Group and, based on sedimentologic, lithologic, palyno-logic, and other paleontologic data, indicate it to be of probable Maastrichtian age.

At least five mammalian taxa, all represented by fragmentary remains, are known from the site. All are boreo-sphenidan mammals; one is a eutherian and at least three marsupials are represented. Initially, at least, the marsupials were compared favorably with those from the Late Cretaceous of North America (see chapter 12). A possible "pe-diomyid" was reported from Laguna Umayo (Sige, 1972). Another species was initially described as belonging to the North American genus Alphadon, as A. austrinum (see Sige, 1971), but later transferred to Peradectes (Crochet, 1980). Species referred to Peradectes are widespread, occurring in the Early Tertiary of North America, Europe (Crochet, 1980), and Africa. Given the limited nature of the evidence, the significance of this astonishingly broad distribution is difficult to interpret. The eutherian from Laguna Umayo is Perutherium altiplanense, known by a dentary fragment with parts of two molars (see chapter 13). Perutherium has sometimes been considered to be a "condylarth" (Grambast et al., 1967; Sige, 1972), even a member of the otherwise North American family Peripty-chidae (Van Valen, 1978; see summary by Cifelli, 1983). Alternatively, Perutherium may be an early member of one of South America's indigenous groups, the most likely being the Notoungulata (Marshall et al., 1983).

This variety of opinion serves to underscore the fact that there is presently insufficient evidence for definitive placement. Accepting the Maastrichtian age assessment for Laguna Umayo, we consider this faunule significant because it helps "bracket" the Cretaceous turnover in South American mammal faunas. Whatever the specific affinities of its included taxa, the faunule from Laguna Umayo is clearly of "modern" aspect; like later faunas of South America, it includes marsupials and, probably, an ungulate. In these respects, it is completely different from the somewhat older (Campanian-early Maastrichtian) fauna of Los Alamitos, Argentina, which is comprised exclusively of nontribosphenic mammals. We close our discussion of Laguna Umayo with brief mention of another site with which it has frequently been compared— Tiupampa in Bolivia.

A diverse, stunningly well-represented assemblage of mammals has been recovered from Tiupampa, including complete skulls and skeletons of marsupials (Muizon, 1994; Marshall and Sigogneau-Russell, 1995; Muizon et al., 1997). Tiupampa was initially placed in the El Molino Formation and considered to be Late Cretaceous in age (see, e.g., Marshall and Muizon, 1988). Later studies refer the site to the Santa Lucía Formation (see review by Gayet et al., 1991) and show it to be of early Paleocene age (Van Valen, 1988; Muizon, 1998).

Another Peruvian site of uncertain age is Chulpas, which lies in a microconglomerate in the upper sandstone levels of the Umayo Formation, some 200 m higher in the section than Laguna Umayo. There is no associated flora and as yet no constraint on the age of Chulpas, though the upper sandstones of the Umayo Formation are conformably overlain by volcanic rocks that might be datable (Crochet and Sigé, 1993). Eleven varieties of mammals are known from Chulpas (Crochet and Sigé, 1993, 1996). At least three of these are eutherians; two or more are noto-ungulates, and a proteutherian (sensu Romer, 1966), said to be similar to a Cimolestes-like taxon from Tiupampa (see Marshall and Muizon, 1988), are present. The remainder are marsupials. In addition to several unidentified didelphids, these include a representative of a new, mono-typic family of polydolopoids (Sillustaniidae), a caenoles-toid, and two caroloameghiniids. Interestingly, one of the marsupials of Chulpas (Chulpasia) may be closely related to Thylacotinga from the early Eocene of Australia, suggesting Early Tertiary dispersal between the continents (Sigé et al., 1995). Aware of the dangers of circular reasoning, we point out that the marsupial groups of Chulpas, like notoungulates, are generally considered to be characteristic of South America's Tertiary faunas. We herein consider Chulpas to be of Early Tertiary age—somewhat younger than the Cretaceous-Tertiary transition, where it is currently placed (Crochet and Sigé, 1993,1996).

A final possible occurrence of a Late Cretaceous mammal in Peru is based on footprints from the Couches Rouges Formation at Paruro, Cuzco. The tracks are described as "mammaloid" and rather large, the size of a dog or a cat (Leonardi, 1994). A variety of dinosaur tracks has been reported from this and other sites in the Cuzco-Sicuani Basin. The exact age of the tracks is unknown; the unit spans the Santonian-Paleocene, and the tracks are placed in the Cretaceous part of the section (Noblet et al., 1995).

Bolivia

A moderately diverse vertebrate assemblage, including mammals, has been reported from Pajcha Pata, near Cochabamba, Bolivia (Gayet et al., 2001). The fossils were recovered from the lower member of the El Molino Formation; combined geochronologic and fauna evidence points to a middle Maastrichtian age for the assemblage. Pajcha Pata is thus of great interest, as it is almost surely younger than Los Alamitos, Argentina (which contains an endemic mammalian fauna, comprised of highly derived members of archaic groups), and older than earliest Tertiary assemblages of South America (which are comprised of marsupials and placentals—groups that are presumed to have immigrated from North America sometime in the latest Cretaceous). Mammalian fossils known from Pajcha Pata include only two teeth and one tooth fragment. Nonetheless, they suggest a fauna comprised of both autochthonous and allochthonous elements: at least one dryolestid and one eutherian are represented.

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