Santa Cruz formation

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Coordinates: 51 ° 10 ′ 0 ″  S , 69 ° 10 ′ 0 ″  W.

Coastal region in the Monte León National Park in the province of Santa Cruz

The Santa Cruz Formation is a lithostratigraphic unit that is distributed over large parts of Patagonia and is to be placed in the transition from the Lower to the Middle Miocene about 16 to 18 million years ago. It is mainly composed of fine-grained sand and clay / siltstone layers , which are interposed by volcanic deposits. It is particularly rich in fossils in the lower area, some of which are complete skeletal remains . These mainly include birds and mammals , but there are alsoReptiles and amphibians . Due to its abundance, the Santa Cruz Formation represents one of the most important areas of discovery from this geological epoch worldwide. The discovered fauna community, consisting of large ratites and water birds as well as large herbivorous mammals, allows a landscape to be reconstructed with gallery forests and open habitats . Fossil-rich outcrops are mainly located on the Atlantic coast of Argentina , but there are also significant sites in the interior known. Exploration of the Santa Cruz Formation began as early as the mid-19th century. The investigations were intensified again from 2003.

The first fossils were discovered in the Santa Cruz Formation in 1845 and brought to England. The following year, described Richard Owen with Nesodon , a representative of the extinct South American hoofed animals , the first kind from the rock unit. A major phase of research began at the end of the 19th century, when the brothers Carlos and Florentino Ameghino documented and published finds in the region for several years. Florentino Ameghino also gave the name "Santa Cruz Formation", which he first used in 1889. In the succession of the Ameghinos, various scientists from Princeton University were mainly active in the fossil record, which lasted until the early 1930s. It was not until the end of the 20th century that the Santa Cruz Formation moved closer to the focus of international research.

Geographical location

Santa Cruz Formation fossil sites

The Santa Cruz Formation is a fossil-bearing rock unit that is widespread in southern South America , mainly in Patagonia east of the Andes , and extends in the north from Lago Buenos Aires at 46 ° south to the Río Turbio at 51.6 ° south latitude . The most fossil-rich outcrops are mainly on the steep east coast in the Argentine province of Santa Cruz at about 51 ° south latitude between the mouths of the Río Coyle and the Río Gallegos about 70 km further south in the Atlantic Ocean , about 100 km north of the Strait of Magellan . So far, bone and tooth remnants have been unearthed in almost a dozen different places, important sites can be found from Punta Sur in the north via Amfiteatro , Puesto Estancia La Costa , Monte Tigre to Cabo Buen Tiempo in the south. Some of these sites have only recently been discovered. However, outcrops of the same formation can also be found up to 90 km further north along the coast, such as the sites of Monte Observación and Monte León . The fossil sites are partially exposed to the tides and are affected by severe erosion , with the tidal range of the Atlantic reaching up to 12.8 m, one of the largest in the world. Additional points of discovery could also be documented on the steep banks of the two rivers mentioned further inland or at deep cuts in other rivers such as the Río Santa Cruz , which flows further north, and its tributary Río Bote . Fossil- rich sites on the Río Santa Cruz include Barrancas Blancas , Segundas Barrancas Blancas and Yaten Huageno . In addition, the deposits of this formation have been proven with the help of boreholes in areas further from the coast. Outcrops in the deep interior of the country include the upper reaches of the Río Bandurrias south of the village of Calafate near the border with Chile .

Geological structure

Geological structure of the Santa Cruz Formation in the area of ​​the Atlantic coast

The Santa Cruz Formation is spread over large parts of Patagonia. It consists of terrestrial sediments and is located in the east on the Monte León formation, which has been shaped by the effects of the sea . In the west in the area of ​​the foot of the Andes it becomes over 800 m to 1500 m thick, here the Estancia de 25 Mayo formation , which is also influenced by marine life, forms the basis. There are numerous outcrops, especially in the region around Lake Argentino , and the Santa Cruz Formation was first detected here in 1972. In the area of ​​the northwestern occurrence up to 480 m thick outcrops southwest of the Lago Posadas in geographical proximity to the Lago Pueyrredón are documented. The find area is narrowed by the Río Furioso in the west and the Río Tarde in the east. The deposits here consist largely of sandstones , but the relatively uniform layer package can be subdivided into at least three different facies units. Fossil finds come from three sections of the profile, two of them in the lower part and one in the middle. Here, too, the basis of the sequence is formed by marine sediments, in this case the El Chacay Formation . Outcrops have also been reported from the eastern Andes. In its northern range, the Santa Cruz Formation has between 270 and 380 m thick sediment layers, with the thickness decreasing from west to east. The Monte León formation is found in the lying position . Fine-grained, less solidified sediments with numerous biogenic disturbances that can be traced back to various flooding events predominate. Coarse clastic sandstones with some cross-stratification can, however, be interpreted as river deposits. Individual tufa layers are included in the sediment sequence . Fossil-bearing areas are often found in the middle to upper sections of the rock unit. Equally important are the up to 295 m thick outcrops on the Río Chalía, which flows a little further north .

To the east to the Atlantic coast, the Santa Cruz formation thins out significantly. On the steep cliffs of the east coast of Patagonia, it reaches an average thickness of around 200 to 240 m. Here it comprises two almost equally powerful stratigraphic units, at the bottom there is the Estancia-La-Costa-stratum and above the Estancia-La-Angelina-stratum . The lower deposit unit consists largely of a sequence of mostly green colored clay stones , between which thinner layers of pyroclastic sediments and clay / silt stones are embedded. Basically, there is a larger proportion of bioclastic rocks that belong to a transition facies from marine to terrestrial conditions. At the beginning of the sedimentation of the Santa Cruz Formation, the area represented a wide estuary under the influence of the tides , this influence gradually decreasing and finally ending in a flood plain. In the higher sections of the Estancia La Costa strata , old soil formations then also appear. The upper series of sediments, on the other hand, is made up of bleached sandstones with thin-layer clay and siltstones that are also interposed. A total of 27 fossil-bearing strata can be identified within the sequence of deposits, 23 of which belong to the lower Estancia La Costa strata and which alone contain 96% of the extensive find material. The formation of the entire formation took place in the end of the Lower Miocene , its origin is related to the folding of the Andes , whose debris it partially represents.

Finds

The Santa Cruz Formation is the most fossil-rich rock formation of the Cenozoic in all of South America , with especially the bird and mammal fauna being very extensive. As a result, the finds are very numerous and in the thousands, since 2003 alone over 1,600 objects have been discovered, mostly from mammals, from the 1990s more than 500 are known, during several expeditions between 1900 and 1923 hundreds of fossil finds of at least 32 Genera had been discovered. Most of them come from vertebrates , mainly birds and mammals . The preservation is very good, and in many cases no superficial weathering of the bones can be observed. It is noteworthy that, especially in mammals, often complete skeletons or skeletal parts are found in association, predominantly skulls with postcranial skeletal parts , which allow better reconstruction and taxonomic and phylogenetic classification. More fragmented material occurs mainly in the northern outcrops. Different processes of decay of the individual fossil finds and sometimes articulated skeletal parts are often due to the influence of water in the former flood plains and to biological processes such as the action of scavengers . It is generally assumed that the carcasses only stayed on the surface for a relatively short time and were embedded relatively quickly. Investigations at the Amfiteatro site revealed a relatively dense find situation with 148 objects found on an area of ​​123 m². 96% of the pieces were made up of mammalian remains, with birds and coprolites as a subordinate part . The total vertebrate fossil material of the Santa Cruz Formation consists of 84% mammals, 13% birds, 2% reptiles and 1% amphibians .

flora

Remnants of the plant world are rather rare and occur largely in the basal areas of the Santa Cruz Formation. They include microfossils such as sponges , golden brown algae and diatoms, and phytolites . The latter are silicate deposits of plant and represents, due to the form of representatives of Panicoideae , chloridoideae and Pooideae from the family of grasses are assigned. Others, in turn, represent pseudo-beeches , legumes or myrtle plants and thus represent arboreal components of the flora community. In addition, macro remains of plants are known with fossilized wood. These can be placed with similar tree shapes, but there are also araucaria , laurel and silver tree plants . In addition, Akanioxylon from the Akaniaceae family was found , the family is only found in Southeast Asia and Australia today. Other, but very rare, macro remains include leaf prints. Due to the shape, the serrations and the architecture of the vascular bundles, they all belong to the false beeches, more precise assignments are not yet available.

fauna

Invertebrates

Invertebrates have hardly been observed so far, but are quite often documented from the underlying Monte León Formation , which, however, formed under marine conditions. Shells of Crassostrea , a mussel from the group of oysters, come from the lower 40 m in the base area of ​​the Santa Cruz Formation . They sometimes form bed-like layers. The representatives of the genus preferred marginal sea areas with soft or hard soils and tolerated a wide range of different salt contents as well as partially subaeric conditions. All other mussel finds are due to their strong rolling traces to be regarded as processing residue of the Monte León formation, when today's Patagonia was covered by the sea. From somewhat higher altitudes, however, a collection of different snails , mostly land snails , was found. These include diaper snails such as Gastrocopta , point snails such as Punctum and representatives of the Charopidae such as Zilchogyra , Patagocharopa and Stephacharopa . Some of the snail forms are still present in South America today, but occur in more northern regions. Others no longer perform in America. Different cases of the freshwater mussel Diplodon from outcrops of the Río Santa Cruz refer to waters in the landscapes of that time.

Amphibians and reptiles

There are only sparse remains of amphibians and reptiles . The frog Calyptocephalella has been identified through several remains of the lower jaw and skull fragments, which are ornamented on the outside by numerous small bumps . The total of 8.2 cm long lower jaw suggests an animal up to 25 cm long. Calyptocephalella gayi is the only present-day representative of the genus in central Chile . Tupinambis represents the rail lizards and is also passed down through remains of the jaw. However, with a body length of 60 cm, it was significantly smaller than today's representatives of the real Tejus. Further fossil finds can be assigned to the iguanas , for example the genus Pristidactylus from the family of the big head iguanas , which occurs with several upper and lower jaw remains. Presumably it is a very primitive form of the genus that still exists in South America today, but has a somewhat more northern distribution area. Likewise, snakes represented, but so far discovered vortex allow only generally an assignment to the snakes .

Birds

Skull of Phorusrhacos
Skull of Noriegavis (A) compared to the Schwarzfußseriema (C) and the Rotfußseriema (B, D)

From the group of birds alone, 15 species have been identified, and the finds are among the most important fossil records in all of South America. The palaeognathae represents among other Opisthodactylus , one the rheas related party animal. Individual leg bones were found from him, which point to a bird weighing around 57 kg. There are also remains of cocoon relatives . All other birds in the Santa Cruz formation can be assigned to the new jaw birds . The finds of the predominantly ground-dwelling and most likely carnivorous Phorusrhacidae ("terror birds"), which occur in a very wide range of forms, are to be emphasized . So the small, about 80 cm high comes Psilopterus before that can show including several complete skulls and kg with about 5 weight was slightly larger than an average-sized Seriema AGENT,, the closest living relatives of "terror birds". May have been Psilopterus enabled due to the rather delicate physique to gliding flights of several hundred meters distance. On the other hand, Phorusrhacos , which was described in 1887 on the basis of a lower jaw from the Santa Cruz Formation, with a height of about 240 cm and an assumed body weight of 110 to 160 kg is one of the largest members of this group of birds. Other finds are from the medium-sized Patagornis and from Noriegavis , the latter has been proven to have a complete skull including a well-preserved partial skeleton and, as a fossil representative, is particularly close to the two today's Seriema species, originally it was also included in their genus.

The largest bird that occurs is Brontornis , an animal over 280 cm tall and weighing up to 380 kg, which originally also belonged to the "terror birds", but is now placed at the base of the geese birds . For this huge bird, which moves slowly due to the structure of its legs, both a scavenging and a herbivorous way of life are considered, but it is only proven by individual leg bones and highly fragmented skull material. More geese birds with Eoneornis , Eutelornis and Ankonetta handed, the latter was about medium height due to the found forearm and hand bones and is a close relative of today's Whistling Ducks represent. The Anhinga birds some remains of the humerus must be made and the genus are Macranhinga assigned. Ultimately, representatives of the birds of prey could also be documented with Badiostes and Thegornis , among others . Thegornis is known to have an almost complete skeleton from the lower part of the Santa Cruz Formation. It represents a relative of the laughing falcon and, like the laughing falcon , was probably specialized in snakes as food due to its short-toed feet .

Mammals

The extensive mammal fauna is represented by over 60 species from more than two dozen families. The marsupials are very versatile . In particular, the Microbiotheria and Paucituberculata mainly only include animals of small body size. Microbiotherium , which has four species alone, was one of the smallest mammal representatives of the Santa Cruz Formation with 20 to 147 g. The animals related to today's Chiloé opossum mostly fed on insects . Palaeothentes is also extensive with five species. These are close to the mouse opossums and reached a body weight of between 82 and 860 g and, due to their characteristic body skeleton, moved mainly hopping. More occurring marsupials Abderites and Phonocdromus . The Sparassodonta , which, in addition to the "terror birds", are the main predators of the Santa Cruz Formation, became significantly larger . They encompass 11 genera and represent hypercarnivore hunters who are highly specialized in meat nutrition . These predatory pouches have been handed down through numerous well-preserved skulls and postcranial skeletal material. The Borhyaenidae represent the largest marsupials in the Santa Cruz Formation. Arctodictis reached a body weight of up to 51 kg, while Borhyaena still weighed around 36 kg. At the other end of the scale are the representatives of the Hathliacynidae . Here Perathereutes and Pseudonotictis were waiting with a body weight of only 1 kg each. Other forms such as Cladosictis had a more intermediate character with regard to their height. According to analyzes, the individual Sparassodont genera occupied different ecological niches, ranging from tree-dwelling in smaller forms to purely terrestrial in the large representatives. A special feature is the only 15 cm long and 80 to 120 g heavy Necrolestes , an animal that lived underground and, according to reconstructions, was equipped with a cylindrical body with strong, grave-shovel-like forefeet and a short neck. On its pointed, ascending muzzle, it possibly had a leathery nose pad that represented a robust grave organ. Necrolestes was initially compared to the African gold mole , with whom it shares the development of a third forearm bone, the so-called "flexor" bone. Later analyzes put it in the vicinity of the marsupials, but a relationship with the Meridiolestida is more likely . This primeval group of mammals was considered to have died out during the transition from the Cretaceous to the Paleocene , making Necrolestes a Lazarus taxon and surviving its relatives until the beginning of the Neogene .

Remnants of armor from Stegotherium

Among the higher mammals , especially the representatives of the secondary articulated animals are documented in larger numbers. The armadillos appear in many ways . Prozaedyus belongs to the family group of the dwarf armadillo and the six-banded armadillo and is preserved with two largely complete skeletons including the back armor. Vetelia appears rather rarely , of which only individual bone platelets have so far been found. The form probably belongs to the same line of development of euphractine armadillos as Prozaedyus . With Proeutatus , handed down among other things via a nearly complete skeleton, there is a somewhat extensive relative that weighed around 15 kg, while Stegotherium stands near today's long-nosed armadillos and weighed 11 kg reconstructed. Furthermore, there is at least one skull of Peltephilus , an extinct distant relative of the armadillos from the Peltephilidae group . He wore two horn-like bone scales of head armor on his nose. The Glyptodontidae , which are also closely related to the armadillos and are characterized by a rigid shell, have been identified with several genera. All found representatives belong to the Propalaehoplophorinae , a rather primitive line, and were significantly smaller than their later descendants from the Pleistocene . Thus achieved Cochlops approximately 80 kg body weight, Eucinepeltus brought up to 115 kilos. The latter is proven, among other things, by a complete, 18 cm long and at the zygomatic arches 13 cm wide skull. The head armor, which was composed of eleven bone plates, was still attached to it. An exception to these early glyptodons are armor plates, which were found in an otherwise fossil-free area near Estancia La Peninsula in the western area of ​​the Santa Cruz Formation. They belong to a member of the Neuryurus line of ancestors and thus to the group of Hoplophorinae . The typical physique of the Glyptodontidae did not enable them to a burrowing way of life, as is the case with the armadillos, so they represent pure land dwellers. Conspicuous with the armored articulated animals, which are present with almost two dozen different species in the Santa Cruz Formation are, is a decreasing wealth of forms from east to west, which may be due to regional ecological gradations in connection with the beginning of the folding of the Andes .

Skull remains from Nematherium

Sloths comprise a total of 11 genera. They, too, lag far behind the huge proportions of their future relatives. This includes Eucholoeops from the relationship of the Megalonychidae , which is documented, among other things, on the basis of a skull with an associated skeleton and which in some cases weighed almost 100 kg. Nematherium , an early member of the Mylodontidae, was similar in size . The surviving finds of the genus, including two partial skeletons, largely come from outcrops on the coast, but an almost complete skull was also found far inland near the Argentine-Chilean border. For Prepotherium as one of the largest representatives of the group, a weight of around 123 kg is estimated. This represents a member of the Megatheriidae , whereby a so far not exactly identified representative of this sloth line from the deposits of the Santa Cruz formation could have weighed up to 200 kg. Hapalops , a genus with little known relationships but possible closer relationships to the Megatheria, is still passed down with at least six species, the size of which varied between 15 and 85 kg. Like Hapalops , Schismotherium and Xyophorus are also to be understood as basal megatherioid sloths. For both forms, various remains of the Río Santa Cruz have been described. A large part of the sloths of the Santa Cruz Formation specialized in leafy food, as could be reconstructed, among other things, based on the structure of the lower jaw and the attachment points of the chewing muscles in Eucholoeops . Some forms such as Analcitherium and Nematherium preferred harder and more fibrous plant material due to their skull anatomy, as is typical of the later Mylodontidae. According to the construction of the limbs, most of the sloths lived partly tree-dwelling, whereby due to the strong and short front legs a locomotion deviating from today's forms was exercised in the trees, which is more reminiscent of that of the tree-climbing anteaters or pangolins . However, the design of the musculoskeletal system, such as the elongated upper joint of the ulna or the short and wide forefeet, also indicates a burrowing way of life, which is not known in recent sloths. Similar interpretations are possible due to the structure of the hind legs, which enable the reconstruction of massive muscles. Exceptions are probably the large megatheria, which were too heavy to climb trees, their musculoskeletal system speaks for a purely terrestrial way of life. Protamandua is one of the rare fossil records of the anteater and one of the oldest . The found skull and parts of the body skeleton indicate an animal weighing about 6 kg that was well adapted to an arboreal (tree-dwelling) life.

Astrapotherium skull

The South American ungulates , which exist in more than a dozen genera, are among the largest known mammals of the Santa Cruz Formation . Astrapotherium alone , an externally tapir -like animal with a trunk from the extensive group of Astrapotheria , weighed over 1 t. Passed down on several skull and lower jaw remains, it represented an animal that was largely adapted to a soft vegetable diet that lived on the banks of rivers and lakes and had a short trunk and strong canine teeth. The Notoungulata are an extremely diverse group of South American ungulates . Here Nesodon grew into a huge animal with a body weight of a good 630 kg, Adinotherium was significantly smaller at 120 kg. Both animals are classified as Toxodontia within the Notoungulata . Due to their high-crowned teeth, they were often considered to eat grass, but recent studies have shown that they mainly fed on leaves and bark, possibly depending on the availability of mixed vegetable food. A partial skull of the Río Bote , a tributary of the Río Santa Cruz in the western distribution area of ​​the Santa Cruz Formation, was described in 2019 from the little studied, but stratigraphically important Notohippus . Previously, the shape from the rock unit was only known from a few individual teeth. The medium-sized representative with relatively high-crowned teeth was the inspiration for the name of the older section of the formation period of the rock unit ( Étage Notohippidéen ). The Typotheria , which also belonged to the Notoungulata , did not reach the dimensions of the Toxodontia, but were significantly smaller. Interatherium and Protypotherium only weighed around 2 to 7 kg and are among the smallest South American ungulates. A complete skeleton of each has been excavated. They resembled modern rodents in their appearance , the structure of their front legs could indicate a burrowing way of life, which, however, was not quite as pronounced in comparison to other animals living in this way. Patriarchus is closely associated with both genres . So far only a single lower jaw from the Río Bote is available. The Litopterna form another large group within the South American ungulates. Therein Diaidiaphorus belongs to the group of Proterotheriidae . The animals are somewhat reminiscent of today's horses , as they only had one toe per limb like these. Thoatherium had a similar feature, but it was significantly smaller than Diadiaphorus . Both of them most likely inhabited more open landscapes. Theosodon from the line of the camel-like Macraucheniidae is related to them . In contrast to the more well-known Pleistocene representatives of the Macraucheniidae, the nasal bone in this basal form was not so far backward that there was probably no trunk. Compared to the Proterotheriidae, the Macraucheniidae are rarely recorded in the find report.

Several skulls, lower jaws, isolated teeth and remains of the body skeleton have been found by Homunculus , an early representative of the New World monkeys with an ambiguous relationship. Also outstanding is the almost complete skull of a young animal, which is one of the oldest such fossil remains of an extinct New World monkey. The fully grown animal, weighing 1.9 to 3.4 kg, lived arboreally and was adapted to both soft fruit and hard-shelled seed food, which it probably collected during the day due to its relatively small eyes. Another genus of primate, Killikaike , which has been described using a skull, is controversial in its systematic independence. Ultimately, rodents from the group of guinea pig relatives were also discovered. Perimys , a representative of the chinchilla-like and the guinea- pig- like Eocardia , remained quite small in their body dimensions and weighed between 500 g and almost 3 kg. On the other hand, the latter closely related and extremely common Neoreomys could reach over 7 kg and thus exceeded its current relatives, the Agoutis and Acouchis . All three genera are identified on the basis of numerous skull remains and parts of the body skeleton. The largest member of the rodents at around 14 kg, Steiromys from the tree prickly area , is only rarely documented in the fossil record. The highest diversity among the rodents of the Santa Cruz Formation, however, had the truss rat- like, which include forms such as Spaniomys , Stichomys , Acarechimys and Sciamys . The structure of the musculoskeletal system shows very different adaptations for the individual rodents. So were Eocardia and Neoreomys probably due to its stable arm of the few sideways movements admitted soil inhabiting. The former genus can be regarded as a good runner, the latter had a more agile hand and possibly lived a long migratory life. Perimys and Steiromys , on the other hand, had rotatable arms. Further anatomical details indicate that Perimys tended to dig, while Steiromys probably climbed. These different habitat uses indicate a high ecological diversity for the rodents of the Santa Cruz Formation. Another peculiarity of the rodents from the Santa Cruz Formation is that for the first time forms with euhypsodontic , i.e. extremely high and rootless tooth crowns appear.

Ichnofossils

Trace fossils have been observed in great numbers. In addition to the root ducts of plants, there are also often grave traces of animals. These can be assigned to different animals due to their different sizes and shapes, but the actual cause is unknown. Individual smaller ones measuring only 0.6 to 1.3 cm in diameter can be traced back to worms or insects , larger ones to crabs or crabs . Most of these tracks are deepened in what used to be soft soil. Several millimeters long, cylindrical or oval shaped structures with rounded or flat ends refer to solitary digger wasps . They are predominantly assigned to the Celliforma trace genus . Some of these structures still contain organic residues that are interpreted as food pulp for the larvae . Another, horizontally stored, larger cavity up to 7 cm high and 12 cm long suggests a mammal . Other trace fossils consist of coprolites from predators and birds.

Age position

Stratigraphic position of the Santa Cruz Formation within the Miocene

Several radiometric age dating was carried out mainly at the coastal discovery sites, including at Monte Observación in the northern distribution area of ​​the Santa Cruz Formation. Here, in the lower third of the sediment sequence in activated volcanic deposits, an age of 16.18 to 16.58 million years could be determined with the help of argon-argon dating , which falls in the outgoing Lower and beginning Middle Miocene . Corresponding dates from the underlying Monte León Formation on outcrops of the eponymous Monte León showed an age of 19.33 million years. Comparable age values ​​could already be obtained with similar methods in the mid-1980s. Further radiometric data from the region confirm these age data and are between 16 and 18 million years old. In the western hinterland, on the other hand, a longer time range must be expected, since older sediment layers may have survived here that no longer occur in the coastal outcrops. Here, the data extends over 18 million years, for example from the Karaiken site near Lake Argentino. At Lago Posadas, data for the lowest sections of the Santa Cruz Formation were obtained around 18.15 million years ago. A new, fossil-rich site on the southern flank of the Cerro Cono in the Sierra Baguales in Chile showed an age of 18.23 million years with the help of uranium-lead dating . Radiometric dates published in 2016, the basis of which were various outcrops along the Río Santa Cruz, showed that sedimentation in the western area of ​​the Santa Cruz Formation began 18.8 million years ago, while in the eastern part it began around 1 million years later, around 17.7 million years ago.

From a biostratigraphic point of view, the faunistic remains are placed in the chronostratigraphic level Santacruzium , for whose name the Santa Cruz formation was the inspiration due to its fossil richness. The Santacruzian is a phase in the development of the South American Land Mammal Ages (SALMA) and dates between 16.3 and 17.5 million years, but individual areas in the interior can also be dated to more than 18 million years. At least two biozones could be distinguished within this stage, which are characterized by the exchange of the notoungulate Protypotherium attenuatum in the lower find horizons by Protypotherium australe in the upper ones.

Landscape reconstruction

The southern part of Patagonia between 46 ° and 51 ° southern latitude is today a dry and cold region in the lee of the Andes , which is one of the windiest in the world. The average annual temperature is around 12 ° C and annual precipitation fluctuates from 125 mm in the east to 500 mm in the west, with this being concentrated on the cold season. These climatic conditions result in open steppes and grass-bush landscapes. Forests exist only in the western part in the transition to the Andes, where the rainfall is higher.

The Santa Cruz Formation was formed in the foothills of the Andes, its deposits mostly represent accumulations in the lowlands. When it was formed, Patagonia was at about the same latitude as it is today. Above all the primate Homunculus , which has the southernmost record of all primates in South America, and some rodent representatives led to the view that the landscape at that time was densely forested and existed under a rather warm, humid climate. The predominantly leaf-eating diet of the large Notoungulata was also a sign of this. However, the sediments of the Santa Cruz Formation also showed some indications of significantly drier conditions, for example due to the presence of switched-in gypsum crystals or fractures in the rather fine-grained deposits. Investigations into plant communities of the early Miocene, which, however, were not carried out directly on the basis of finds from the Santa Cruz Formation, showed that both closed and open landscapes occurred and that shrubbery and herbaceous plants were dominant at that time , in contrast to the previously predominant closed forests in the Oligocene . The plant remains of the Santa Cruz Formation itself also show similar results.

Today it is assumed that forests mainly existed as floodplain or gallery forest on the banks of rivers and were inhabited by sloths , primates , anteaters and arboreal marsupials . The wider landscape outside the river basins was interspersed with bush and savanna vegetation , in which the large flightless birds and armadillos and some larger ungulates may have dominated. In comparison with similar landscapes today, an annual precipitation of 1000 to 1500 mm is assumed with an annual average temperature of around 19.3 ° C. The relatively warm to subtropical climate indicates evidence of the real Tejus , the primate Homunculus and the anteater Protamandua , among other things . Calcified root canals, which occur in some soil formations, suggest seasonal precipitation, with most falling during the cooler season. Since the Andes were not so high up during the transition from the Lower to the Middle Miocene - the main unfolding only began in the Middle Miocene about 15 million years ago - they did not yet act as a blockade for westerly winds, so that moist air currents from the Pacific also did could reach the Atlantic coast . However, in the upper sites of the Santa Cruz Formation there is also a tendency towards further opening of the habitats and aridization of the climate. Due to the southern geographical position of this landscape at that time, it was subject, as it is today, to a strongly fluctuating duration of daylight times over the year.

The abundant herbivore community found in the Santa Cruz Formation, consisting of the South American ungulates, glyptodons, sloths and various rodents, spanned animals weighing just a few kilograms, such as Steiromys , to giant forms that weighed a good 1 t, such as Astrapotherium . These also attracted a diverse group of predators divided into marsupials and large birds. The available biomass is estimated at around 672 to 864 kg per square kilometer and year. Most of the predators specialized in small to medium-sized prey animals weighing between 10 and 45 kg, for which there was more intense competition than larger herbivores. Presumably only a few predators of the Santa Cruz Formation were able to kill massive herbivores weighing several hundred kilograms. These include above all Phorusrhacos from the group of "terror birds" as well as Borhyaena and Arctodictis from the group of Sparassodonta. For all three, however, a more scavenging lifestyle is also being discussed.

Comparison references

The classic sites of the Santa Cruz Formation on the Atlantic coast contrast with some older ones of the same rock unit in the interior. The Cerro Cono in the Sierra Baguales in southern Chile is important , where at 1100 to 1200 m elevation in a 90 m thick outcrop of the Santa Cruz Formation, consisting of clayey and silty rocks, a mammal fauna comprising more than 20 taxa emerged . The composition of the finds is similar to that of the sites on the Atlantic coast, including Perimys and Adelphomys , two guinea pigs , among the small mammals . Among the ungulates are Paramacrauchenia , Nesodon and Astrapothericulus . An extensive community of secondary animals was also documented. The largely small-sized fossil material dates back to around 18.23 million years. In the northern distribution area of ​​the Santa Cruz Formation, south of the Lago Buenos Aires in Chilean territory (here the lake Lago General Carrera is called) is another important site of the Santacruzium with Pampa Castillo and with an altitude of almost 1350 m one of the highest in the southern part of South America. The deposits attributed to the locally occurring Río-Zeballos Formation have so far contained around three dozen mammalian taxa, a third of which are rodents . Among them are, in addition to the known guinea pig relatives, Prolagostomus and Pliolagostomus from the group of chinchillas or stingomys and acarechimys from the group of stingomys continue also Sciamys from the relationship of octodontidae . Some of the rodent species found were previously only known from the fossil-rich Pinturas Formation and indicate a somewhat older age for Pampa Castillo. The Pinturas Formation is distributed in the northwestern part of the Argentine province of Santa Cruz on the Río Pinturas and correlates to the lower sections of the Santa Cruz Formation.

Research history

First discoveries

Bartholomew James Sulivan , 1896

The exploration of the Santa Cruz formation began as early as 1845 when the British captain Bartholomew James Sulivan discovered the first fossils during an expedition with the HMS Philomel to the Falkland Islands near the Río Gallegos . As a former shipmate of Charles Darwin on his voyage with the HMS Beagle from 1831 to 1835, Sulivan had been instructed in finding fossils. He was enthusiastic about the spectacular steep cliffs at the mouth of the Río Gallegos and landed about 20 km inland, where he picked up individual larger and smaller bones. He sent these to Darwin, who in turn passed them on to Richard Owen at the Royal College of Surgeons in London. Owen, one of the most important anatomists of his time and at that time busy processing the finds from Darwin's expedition, described a fossil as Nesodon the following year . This mammal, which belongs to the South American ungulates, is one of the most frequently found genera in the Santa Cruz Formation and is also the first scientifically named taxon from this rock unit. It was also one of the oldest known fossil forms from South America. Charles Darwin later commented on these finds, noting that he himself had visited individual outcrops in Patagonia in 1832 on his journey with the HMS Beagle , but had not collected any fossils. After his return to England, Sulivan tried in vain for a while to convince the British Admiralty of a new expedition to the Río Gallegos and returned there on his own between 1848 and 1851, where he hid more fossils. It was not until 1863 that the British Admiralty approved another trip, which Sulivan undertook together with his son James YF Sulivan and the naturalist Robert Oliver Cunningham . The finds recovered in the process came into the hands of William Henry Flower , Owen's successor at the Royal College of Surgeons, who described Homalodotherium from this collection, among other things .

The Ameghinos

Florentino Ameghino named the Santa Cruz Formation in 1889

After these early discoveries, the Santa Cruz Formation was not revisited by researchers until 1877, who also found some fossil remains. Francisco Moreno also carried out the first geological investigations. He also reached the Río Santa Cruz on his expedition to Lake Argentino . An important period of exploration began ten years later when the brothers Carlos and Florentino Ameghino discovered and described other fossils there and conducted studies of the geological structure of the formation, which brought the Santa Cruz Formation back into the spotlight. It was mainly Carlos who carried out the work there, while his brother Florentino largely processed the results. Carlos' first expedition to the region took him up the Río Santa Cruz to Lake Argentino in 1887, which took the time from February 27 to April 3 there and back. During the first expedition, Carlos collected over 2000 fossils, which his brother published in a preliminary report that same year. A first comprehensive monograph appeared in 1889 under the title Contribución al conocimiento de los mamíferos fósiles de la República Argentina . In this important publication, Florentino first mentioned the term “Santa Cruz Formation” ( Formación Santacruceña ) as well as the chronostratigraphic stage “Santacruzium” ( Piso Santacruceño ), which he later divided into two sub-units, the older Notohippidéen and the younger Étage Santacrucienne . In the years that followed, other larger monographic treatises were to follow. Carlos Florentino returned a total of five times to the outcrops of the Santa Cruz Formation by 1893. In 1888 and 1889, he visited the region around the Río Chubut , in 1890 the Río Deseado and from 1891 to 1893 the coastal region twice. Most of the finds are now in the Museo de La Plata in La Plata .

The turn from the 19th to the 20th century

John Bell Hatcher conducted several expeditions between 1896 and 1899

Around the same time as the Ameghinos, Theodor Allemann, a Swiss electrical engineer who worked in Argentina in the 1880s and 1890s, amassed a large collection of fossil remains from the Santa Cruz Formation. It includes the teeth and skull parts of a wide variety of mammals such as marsupials, articulated animals, South American ungulates and rodents, but also of birds and amphibians. It is unclear whether Allemann collected on site himself or bought the finds. The approximately 1,100 objects are now in the Palaeontological Museum of the University of Zurich . From 1896 to 1899, the American researcher John Bell Hatcher led a total of three expeditions to the Santa Cruz Formation, which he carried out on behalf of Princeton University . During this time he examined, among other things, the areas around the Río Gallegos , Lake Pueyrredón (Lago Posadas) and the coastal areas, such as around Cape Fairweather . The last expedition took place together with the American Museum of Natural History , from whose side Barnum Brown was involved. Hatcher handed the finds to Princeton University, where most of them are still kept today. Princeton University's research was presented in 15 voluminous monographs , largely edited by William Berryman Scott . At around the same time as Hatcher, André Tournouër from the Muséum national d'histoire naturelle in Paris visited various sites in Patagonia. During several trips between 1898 and 1904 he collected in the Santa Cruz Formation, among other things, outcrops of the Río Coyle and on Monte León . He found numerous vertebrate bones, including many remains of birds that are now in the Paris Natural History Museum. In a short essay on the geology of Patagonia from 1903 Tournouër also gave an age estimate for the Santa Cruz Formation, which came very close to today's knowledge.

Another high phase of exploration was between 1900 and 1923. It comprised several expeditions from different universities, partly in continuation of the work of Hatcher. The first expedition in 1904, led by Handel T. Martin from the University of Kansas , lasted several months, with the most fossil-rich outcrops being documented at Cape Fairweather. Martin also visited Florentino Ameghino and viewed his collection, which he took up extensively. The results of the expedition were never processed, only a short essay appeared in the same year under Martin's name. Martin sold some of the 400 or so finds to various museums, most of which are now kept at the University of Kansas. In the 1920s, Elmar S. Riggs led several trips to South America that were sponsored by Marshall Field . The first of these trips from November 1922 to May 1923 focused on the Santa Cruz Formation, in which Riggs largely followed Hatcher's footsteps. The trip yielded over 280 fossil remains, including more than 170 skull finds. Riggs gave an overview of his travels in a short essay in 1928. Most of the finds are stored in the Field Museum in Chicago.

Modern research

Until the 1990s, there was only a little on-site research. In the mid-1970s, Larry G. Marshall of the University of California was doing some on-site work. He was followed in the early 1980s by Rosendo Pascual from the Museo de La Plata with several field studies. A joint expedition of Stony Brook University in New York and the Museo Argentino de Ciencias Naturales Bernardino Rivadavia in Buenos Aires under the direction of John Fleagle and Miguel Soria took place in 1988. The main focus of interest was the Monte Observación site north of the Río Coyle. During the same period, Adán A. Tauber from the Universidad de Córdoba carried out on-site investigations, while an independent research group was on the way to Antarctica for a day excursion in Killik Aike Norte and discovered, among other things, the facial skull of a primate. Only Adán A. Tauber continued his research over a longer period of time. He was not only able to identify several old sites, but also amassed a collection of around 250 fossil finds. Since 2003, an international group of researchers from Argentina, the USA and Uruguay under the joint direction of Duke University and the Museo de La Plata have been carrying out more intensive research on the outcrops of the Santa Cruz Formation with annual field investigations; the analysis of the findings continues to this day. While the coastal regions were initially the focus of the scientists, since 2009 more and more excavation activities have been carried out inland.

literature

  • William Berryman Scott: Reports of the Princeton University Expeditions to Patagonia, 1896-1899. Princeton, Stuttgart, 1901–1932 ( [10] )
  • Juan C. Fernicola, M. Susana Bargo, Sergio F. Vizcaíno and Richard F. Kay (eds.): Early-Middle Miocene Paleontology in the Río Santa Cruz, Southern Patagonia, Argentina. 130 years since Ameghino, 1887. Publicación Electrónica de la Asociación Paleontológica Argentina 19 (2), 2019
  • Sergio F. Vizcaíno, M. Susana Bargo, Richard F. Kay, Richard A. Fariña, Mariana Di Giacomo, Jonathan MG Perry, Francisco J. Prevosti, Néstor Toledo, Guillermo H. Cassini and Juan C. Fernicola: A baseline paleoecological study for the Santa Cruz Formation (late-early Miocene) on the Atlantic coast of Patagonia, Argentina. Palaeogeography, Palaeoclimatology, Palaeoecology 292, 2010, pp. 507-519
  • Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (Eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York 2012

Individual evidence

  1. ↑ a b c d e f g h Sergio F. Vizcaíno, M. Susana Bargo, Richard F. Kay, Richard A. Fariña, Mariana Di Giacomo, Jonathan MG Perry, Francisco J. Prevosti, Néstor Toledo, Guillermo H. Cassini and Juan C. Fernicola: A baseline paleoecological study for the Santa Cruz Formation (late – early Miocene) at the Atlantic coast of Patagonia, Argentina. Palaeogeography, Palaeoclimatology, Palaeoecology 292, 2010, pp. 507-519
  2. ^ A b Richard F. Kay, Sergio F. Vizcaíno, M. Susana Bargo, Jonathan MG Perry, Francisco J. Prevosti and Juan Carlos Fernicola: Two new fossil vertebrate localities in the Santa Cruz Formation (late early - early middle Miocene, Argentina ), ≈51 ° South latitude. Journal of South American Earth Sciences 25, 2008, pp. 187-195
  3. ^ A b Juan Carlos Fernicola, José I. Cuitiño, Sergio F. Vizcaíno, M. Susana Bargo and Richard F. Kay: Fossil localities of the Santa Cruz Formation (Early Miocene, Patagonia) prospected by Carlos Ameghino in 1887 revisited and the location of the Notohippidian. Journal of South American Earth Sciences 52, 2014, pp. 94-107
  4. ^ A b Santiago Hernández Del Pino, Mercedes Fernández, Esperanza Cerdeño and Juan C. Fernicola: Anatomy and systematics of Notohippus toxodontoides Ameghino, 1891 (Mammalia, Notoungulata), from the Miocene of Santa Cruz Province, Argentina. Journal of Vertebrate Paleontology 39 (1), 2019, p. E1577870, doi: 10.1080 / 02724634.2019.1577870
  5. ↑ a b c d Juan Carlos Fernicola, M. Susana Bargo, Sergio F. Vizcaíno and Richard F. Kay: Historical background for a revision of the paleontology of the Santa Cruz Formation (Early-Middle Miocene) along the Río Santa Cruz, Patagonia , Argentina. Publicación Electrónica de la Asociación Paleontológica Argentina 19 (2), 2019, pp. 1-13
  6. ^ A b Marcos Martin Cenizo and Federico L. Agnolin: The southernmost records of Anhingidae and a new basal species of Anatidae (Aves) from the lower-middle Miocene of Patagonia, Argentina. Alcheringa: an Australasian Journal of Palaeontology 34, 2010, pp. 1-22
  7. ^ A b Sergio D. Matheos and M. Sol Raigenborn: Sedimentology and paleoenvironment of the Santa Cruz Formation. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 59-82
  8. ↑ José I. Cuitiño and Roberto A. Scasso: Sedimentología y paleoambientes del Patagonio y su transicion a la Formación Santa Cruz al sur del Lago Argentino, Patagonia Austral. Revista de la Asociación Geológica Argentina 66 (3), 2010, pp. 406-417
  9. ↑ a b c d José I. Cuitiño, Sergio F. Vizcaíno, M. Susana Bargo and Inés Aramendía: Sedimentology and fossil vertebrates of the Santa Cruz Formation (early Miocene) in Lago Posadas, southwestern Patagonia, Argentina. Andean Geology 46 (2), 2019, pp. 383-420, doi: 10.5027 / andgeoV46n2-3128
  10. ↑ a b c J. Enrique Bostelmann, Jacobus P. Le Roux, Ana Vásquez, Néstor M. Gutiérrez, José Luis Oyarzún, Catalina Carreño, Teresa Torres, Rodrigo Otero, Andrea Llanos, C. Mark Fanning and Francisco Hervé: Burdigalian deposits of the Santa Cruz Formation in the Sierra Baguales, Austral (Magallanes) Basin: Age, depositional environment and vertebrate fossils. Andean Geology 40 (3), 2013, pp. 458-489, doi: 10.5027 / andgeoV40n3-a04
  11. ↑ a b José I. Cuitiño, Juan C. Fernicola, M. Sol Raigemborn and Verónica Krapovickas: Stratigraphy and depositional environments of the Santa Cruz Formation (Early-Middle Miocene) along the Río Santa Cruz, Southern Patagonia, Argentina. Publicación Electrónica de la Asociación Paleontológica Argentina 19 (2), 2019, pp. 14–33
  12. ↑ Juan C. Fernicola, Sergio F. Vizcaíno, M. Susana Bargo, Richard F. Kay and José I. Cuitiño: Analysis of the Early-Middle Miocene mammal associations at the Río Santa Cruz (Patagonia, Argentina). Publicación Electrónica de la Asociación Paleontológica Argentina 19 (2), 2019, 239–259
  13. ↑ Sergio F. Vizcaíno, M. Susana Bargo, José I. Cuitiño, ME Pérez, MA Muñoz, I. Aramendía, RL Tomassini and Richard F. Kay: The outstanding Río Chalía (= Sehuén) outcrops of the Santa Cruz Formation (Early Miocene, Burdigalian) and is fossil vertebrate content. Publicación Electrónica de la Asociación Paleontológica Argentina 19 (1 suppl.), 2019, p. R85
  14. ↑ a b c d e f g h Larry G. Marshall: Fossil localities for Santacrucian (early Miocene) mammals, Santa Cruz Province, southern Patagonia, Argentina. Journal of Paleontology 50, 1976, pp. 1129-1142
  15. ↑ M. Sol Raigemborn, Sergio D. Matheos, Verónica Krapovickas, Sergio F. Vizcaíno, M. Susana Bargoe, Richard F. Kay, Juan C. Fernicola and Luciano Zapata: Paleoenvironmental reconstruction of the coastal Monte Leon and Santa Cruz formations (Early Miocene) at Rinc on del Buque, Southern Patagonia: A revisited locality. Journal of South American Earth Sciences 60, 2015, pp. 31-55
  16. ↑ a b c d Darin A. Croft: What Constitutes a Fossil Mammal Community in the Early Miocene Santa Cruz Formation? Journal of Vertebrate Paleontology 33 (2), 2013, pp. 401-409
  17. ^ A b Marcos D. Ercoli & Francisco J. Prevosti and Analía M. Forasiepi: The Structure of the Mammalian Predator Guild in the Santa Cruz Formation (Late Early Miocene). Journal of Mammal Evolution 2013, doi: 10.1007 / s10914-013-9243-4
  18. ↑ a b c Gerardo De Iuliis, François Pujos, Néstor Toledo, M. Susana Bargo and Sergio F. Vizcaíno: EucholoeopsAmeghino, 1887 (Xenarthra, Tardigrada, Megalonychidae) from the Santa Cruz Formation, Argentine Patagonia: implications for the systematics of Santacrucian . Geodiversitas 36 (2), 2014, pp. 209–255
  19. ↑ a b c Adán A. Tauber: Paleoecología de la Formación Santa Cruz (Mioceno inferior) en el extremo sudeste de la Patagonia. Ameghiniana 34, 1997, pp. 517-529
  20. ^ A b Claudia I. Montalvo, M. Sol Raigemborn, Rodrigo L. Tomassini, Luciano Zapata, M. Susana Bargo, M. Celeste Martínez Uncal and Sergio F. Viszcaíno: Floodplain taphonomic mode of Early Miocene vertebrates of Southern Patagonia, Argentina. Palaios 34, 2019, pp. 105-120
  21. ^ A b Juan C. Fernicola and Adriana Albino: Amphibians and squamata reptiles from the Santa Cruz Formation (late Early Miocene), Santa Cruz Province, Argentinia: paleoenvironmental and paleobiological considerations. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (Eds.): Early Miocene Paleobiology in Patagonia: High Latitude Palaeocommunities of the Santa Cruz Formation. Cambridge University Press, New York 2012, pp. 129-137
  22. ^ A b Mariana Brea, Alejandro F. Zucol, M. Susana Bargo, Juan Carlos Fernicola and Sergio F. Vizcaíno: First Miocene record of Akaniaceae in Patagonia (Argentina): a fossil wood from the early Miocene Santa Cruz formation and its palaeobiogeographical implications . Botanical Journal of the Linnean Society 183, 2017, pp. 334-347
  23. ^ A b Mariana Brea, Alejandro F. Zucol and Ari Iglesias: Fossil plant studies from late Early Miocene of the Santa Cruz Formation: paleoecology and paleoclimatology at the passive margin of Patagonia, Argentina. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (Eds.): Early Miocene Paleobiology in Patagonia: High Latitude Palaeocommunities of the Santa Cruz Formation. Cambridge University Press, New York 2012, pp. 104-128
  24. ↑ Miguel Griffin and Ana Parras: Oysters from the base of the Santa Cruz Formation (late Early Miocene) of Patagonia. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (Eds.): Early Miocene Paleobiology in Patagonia: High Latitude Palaeocommunities of the Santa Cruz Formation. Cambridge University Press, New York 2012, pp. 83-90
  25. ↑ Pablo E. Rodriguez, Sergio E. Miquel, Asán A. Tauber and Jerónimo M. Krapovickas: First record of land gastropods province (Mollusca, Pulmonata, Charopidae) in the earlymiddle Miocene from Santa Cruz, Austral Patagonia, Argentina. Archiv für Molluskenkunde 141, 2012, pp. 57–66
  26. ↑ Sergio E. Miquel and Pablo E. Rodriguez: A novel late Early Miocene assemblage of terrestrial gastropods from Santa Cruz (Patagonia, Argentina). Journal of Paleontology 89 (5), 2015, pp. 748-761
  27. ↑ Leandro M. Pérez, José I. Cuitiño, Augusto N. Varela and Nahuel A. Muñoz: Diplodon cf. Colhuapiensis (Bivalvia, Hyriidae) in the Santa Cruz Formation (Early Middle Miocene) at the Río Santa Cruz, Patagonia, Argentina . Stratigraphic and paleoenvironmental considerations. Publicación Electrónica de la Asociación Paleontológica Argentina 19 (2), 2019, pp. 34–47
  28. ↑ Santiago Brizuela and Adriana M. Albino: Re-evaluation of the Type Material of “Diasemosaurus occidentalis” Ameghino and “Dibolosodon typicus” Ameghino (Squamata: Teiidae) from the Miocene of Argentina. Journal of Vertebrate Paleontology 28 (1), 2008, pp. 253-257
  29. ↑ Paula Muzzopappa: Calyptocephalella (Anura, Australobatrachia) remains from Río Santa Cruz (Early Middle Miocene, Santa Cruz Formation), Santa Cruz Province, Argentina. Publicación Electrónica de la Asociación Paleontológica Argentina 19 (2), 2019, pp. 48–54
  30. ^ Adriana Albino, Santiago Brizuela and Sergio Vizcaíno: The southernmost fossil record of Squamates. Amphibia-Reptilia 38, 2017, pp. 15-30
  31. ↑ a b c Federico J. Degrange, Jorge I. Noriega and Juan I. Areta: Diversity and paleobiology of the Santacrucian birds. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 138-155
  32. ↑ a b Juan M. Diederle and Jorge I. Noriega: New records of birds from the Santa Cruz Formation (Early-Middle Miocene) at the Río Santa Cruz valley, Patagonia, Argentina. Publicación Electrónica de la Asociación Paleontológica Argentina 19 (2), 2019, pp. 55-61
  33. ↑ Herculano MF Alvarenga and Elizabeth Höfling: Systematic revision of the Phorusrhacidae (Aves: Ralliformes). Papéis Avulsos de Zoologia 43, 2003, pp. 51-91
  34. ↑ Gerald Mayr and Jorge I. Noriega: A well-preserved partial skeleton of the poorly known early Miocene seriema Noriegavis santacrucensis (Aves, Cariamidae). Acta Palaeontologica Polonica 2013
  35. ↑ Jorge I. Noriega, Sergio F. Vizcaíno and M. Susana Bargo: First Record and a New Species of Seriema (Aves: Ralliformes: Cariamidae) from Santacrucian (Early-Middle Miocene) Beds of Patagonia. Journal of Vertebrate Paleontology, 29 (2), 2009, pp. 620-626
  36. ^ A b Claudia P. Tambussi: Palaeoenvironmental and faunal inferences based on the avian fossil record of Patagonia and Pampa: what works and what does not. Biological Journal of the Linnean Society 103, 2011, pp. 458-474
  37. ^ A b Claudia P. Tambussi and Federico J. Degrange: Neogene Birds of South America. In: Claudia P. Tambussi and Federico J. Degrange (Eds.): South American and Antarctic Continental Cenozoic Birds. Paleobiogeographic Affinities and Disparities. SpringerBriefs in Earth System Sciences, 2013, pp. 59–86 (pp. 59–65)
  38. ↑ Federico L. Agnolin: Brontornis burmeisteri Moreno & Mercerat, un Anseriformes (Aves) gigante del Mioceno Medio de Patagonia, Argentina. Revista del Museo Argentino de Ciencias Naturales Nueva Series 9, 2007, pp. 15-25
  39. ↑ Jorge I. Noriega, Juan I. Areta, Sergio F. Vizcaíno and M. Susana Bargo: Phylogeny and taxonomy of the Patagonian Miocene falcon Thegornis musculosus Ameghino 1895 (Aves, Falconidae). Journal of Paleontology 85 (6), 2011, pp. 1089-1104
  40. ↑ María Alejandra Abello, Edgardo Ortiz-Jaureguizar and Adriana M. Candela: Paleoecology of the Paucituberculata and Microbiotheria (Mammalia, Marsupialia) from the late Early Miocene of Patagonia. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 156-172
  41. ^ Francisco J. Prevosti, Analía M. Forasiepi, Marcos D. Ercoli and Guillermo F. ​​Turazzini: Paleoecology of themammalian carnivores (Metatheria, Sparassodonta) of the Santa Cruz Formation (late early Miocene). In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 173-193
  42. ↑ Laura Chornogubsky, María A. Abello and Germán D. Barmak: The Metatheria from the Río Santa Cruz (Santa Cruz Formation, Early-Middle Miocene, Argentina): History and new records. Publicación Electrónica de la Asociación Paleontológica Argentina 19 (2), 2019, 62–84
  43. ^ William Berryman Scott: Reports of the Princeton University Expeditions to Patagonia, 1896-1899. Volume 5: Palaeontology Princeton, Stuttgart, 1903–1905, pp. 1–490 (pp. 365–383) ( [1] )
  44. ↑ Robert J. Asher, Inés Horovitz, Thomas Martin and Marcelo R. Sánchez-Villagra: Neither arodent nor a platypus: a reexamination of Necrolestes patagonensis Ameghino. American Museum Novitates 3546, 2007, pp. 1-40
  45. ↑ Guillermo W. Rougier, John R. Wible, Robin MD Beck and Sebastian Apesteguía: The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America. PNAS 109 (49), 2012, pp. 20053-20058
  46. ↑ Nicolás R. Chimento, Federico L. Agnolin and Fernando E. Novas: The Patagonian fossil mammal Necrolestes: A Neogene survivor of Dryolestoidea. Revista del Museo Argentino de Ciencias Naturales 14 (2), 2012, pp. 261-306
  47. ↑ John R. Wible and Guillermo W. Rougier: Craniomandibular Anatomy of the Subterranean Meridiolestidan Necrolestes patagonensis Ameghino, 1891 (Mammalia, Cladotheria) from the Early Miocene of Patagonia. Annals of Carnegie Museum 84 (3), 2017, pp. 183-252
  48. ↑ Juan C. Fernicola, Sergio F. Vizcaíno and M. Susana Bargo: Primer registro de Vetelia puncto (Xenarthra, Cingulata) en la Formación Santa Cruz (Mioceno temprano) de la costa atlántica de la provincia de Santa Cruz, Argentina. Ameghiniana 46 (4) suppl.), 2009, p. 77R
  49. ↑ Sergio F. Vizcaíno, M. Susana Bargo, Richard F. Kay and Nick Milne: The armadillos (Mammalia, Xenarthra, Dasypodidae) of the Santa Cruz Formation (early-middle Miocene): An approach to their paleobiology. Palaeogeography, Palaeoclimatology, Palaeoecology 237, 2006, pp. 255-269
  50. ↑ Laureano Raúl González and Gustavo Juan Scillato-Yané: Una nueva especie de Stegotherium Ameghino (Xenarthra, Dasypodidae, Stegotheriini) del Mioceno de la provincia de Santa Cruz (Argentina). Ameghiniana 45 (4), 2008, pp. 641-648
  51. ↑ Barnum Brown: A new species of fossil edentate from the Santa Cruz Formation of Patagonia. Bulletin of the American Museum of Natural History 19, 1903, pp. 453-457
  52. Jump up ↑ Laureano Raúl Gonzáles Ruiz, Alfredo Eduardo Zurita, John Fleagle, Gustavo Juan Scillato-Yané, María Teresa Dozo and Martín Zamorano: The southernmost record of a Neuryurini Hoffstetter, 1958 (Mammalia, Xenarthra, Glyptodontidae). Paläontologische Zeitschrift 85, 2011, pp. 155–161
  53. ↑ Sergio F. Vizcaíno, Juan C. Fernicola and M. Susana Bargo: Paleobiology of Santacrucian glyptodonts and armadillos (Cenarthra, Cingulata). In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 194-215
  54. ↑ Juan C. Fernicola and Sergio F. Vizcaíno: Cingulates (Mammalia, Xenarthra) of the Santa Cruz Formation (Early Middle Miocene) from the Río Santa Cruz, Argentine Patagonia. Publicación Electrónica de la Asociación Paleontológica Argentina 19 (2), 2019, 85–101
  55. ^ George Gaylord Simpson: A Miocene sloth from southern Chile. American Museum Novitates 1156, 1941, pp. 1-6
  56. ^ Néstor Toledo, Guillermo Hernán Cassini, Sergio F. Vizcaíno and M. Susana Bargo: Mass estimation of Santacrucian sloths from the Early Miocene Santa Cruz Formation of Patagonia, Argentina. Acta Palaeontologica Polonica 59 (2), 2014, pp. 267-280
  57. ↑ M. Susana Bargo, Gerardo de Iuliis and Néstor Toledo: Early Miocene sloths (Xenarthra, Folivora) from the Río Santa Cruz valley (Southern Patagonia, Argentina). Ameghino, revisited 1887. Publicación Electrónica de la Asociación Paleontológica Argentina 19 (2), 2019, 102-137
  58. ↑ M. Susana Bargo, Sergio F. Vizcaíno and Richard F. Kay: Predominance of orthal masticatory movements in the Early Miocene Eucholaeops (Mammalia, Xenarthra, Tardigrada, Megalonychidae) and other megatherioid sloths. Journal of Vertebrate Paleontology 29 (3), 2009, pp. 870-880
  59. ^ Néstor Toledo, M. Susana Bargo, GH Cassini and Sergio F. Vizcaíno: The Forelimb of Early Miocene Sloths (Mammalia, Xenarthra, Folivora): Morphometrics and Functional Implications for Substrate Preferences. Journal of Mammalian Evolution 19, 2012, pp. 185-198
  60. ^ Néstor Toledo, M. Susana Bargo and Sergio F. Vizcaíno: Muscular Reconstruction and Functional Morphology of the Forelimb of Early Miocene Sloths (Xenarthra, Folivora) of Patagonia. The Anatomical Record 296, 2013, pp. 305-325
  61. ^ Néstor Toledo, Susana M. Bargo and Sergio F. Vizcaíno: Muscular Reconstruction and Functional Morphology of the Hind Limb of Santacrucian (Early Miocene) Sloths (Xenarthra, Folivora) of Patagonia. The Anatomical Record 298, 2015, pp. 842-864
  62. ^ M. Susana Bargo, Néstor Toledo and Sergio F. Vizcaíno: Paleobiology of Santacrucian sloths and anteaters (Cenarthra, Pilosa). In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 216-242
  63. ↑ Guillermo H. Cassini: Skull Geometric Morphometrics and Paleoecology of Santacrucian (Late Early Miocene; Patagonia) Native Ungulates (Astrapotheria, Litopterna, and Notoungulata). Ameghiniana 50 (2), 2013, pp. 193-216
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  65. ↑ Guillermo H. Cassini, Manuel Mendoza, Sergio F. Vizcaíno and M. Susana Bargo: Inferring habitat and feeding behavior of early Miocene notoungulates from Patagonia. Lethaia 44, 2011, pp. 153-165
  66. ↑ Mercedes Fernández, Juan C. Fernicola, and Esperanza Cerdeño: The genus Patriarchus Ameghino, 1889 (Mammalia, Notoungulata, Typotheria), from the Santa Cruz Formation, Santa Cruz Province, Argentina. Journal of Vertebrate Paleontology 39 (2), 2019, p. E1613416, doi: 10.1080 / 02724634.2019.1613416
  67. ↑ Mercedes Fernández and Nahuel A. Muñoz: Notoungulata and Astrapotheria (Mammalia, Meridiungulata) of the Santa Cruz Formation (Early Middle Miocene) along the Río Santa Cruz, Argentine Patagonia. Publicación Electrónica de la Asociación Paleontológica Argentina 19 (2), 2019, 138–169
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  69. ↑ Guillermo H. Cassini, Esperanza Cerdeño, Amalia L. Villafaño and Nahuel A. Muñoz: Paleobiology of Santacrucian native ungulates (Meridiungulata: Astrapotheria, Litopterna and Notoungulata). In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 243-286
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  78. ↑ Luciano Zapata, Verónica Krapovickas, M. Sol Raigembom and Sergio D. Matheos: Bee cell trace fossils associations on paleosols from the Santa Cruz Formation: Palaeoenvironmental and palaeobiological implications. Palaeogeography, Palaeoclimatology, Palaeoecology 459, 2016, pp. 153-169
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  80. ↑ Larry G. Marshall, Robert E. Drake, Garniss H. Curtis, Robert F. Butler, Kathy M. Flanagan and Charles W. Naeser: Geochronology of Type Santacrucian (Middle Tertiary) Land Mammal Age, Patagonia, Argentina. Journal of Geology 94, 1986, pp. 449-457
  81. ↑ a b Michael E. Perkins, John G. Fleagle, Matthew T. Heitzler, Barbara Nash, Thomas M. Bown, Adán A. Tauber and Maria T. Dozo: Tephrochronology of the Miocene Santa Cruz and Pinturas Formations, Argentinia. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 23-40
  82. ↑ José I. Cuitiño, Roberto Ventura Santos, Pablo J. Alonso Muruaga and Roberto A. Scasso: Sr-stratigraphy and sedimentary evolution of early Miocene marine foreland deposits in the northern Austral (Magallanes) Basin, Argentina. Andean Geology 42 (3), 2015, pp. 364-385, doi: 10.5027 / andgeoV42n3-a05
  83. ↑ José I. Cuitiño, Juan Carlos Fernicola, Matthew J. Kohn, Robin Trayler, Maximiliano Naipauere, M. Susana Bargo, Richard F. Kay and Sergio F. Vizcaíno: U-Pb geochronology of the Santa Cruz Formation (early Miocene) at the Río Bote and Río Santa Cruz (southernmost Patagonia, Argentina): Implications for the correlation of fossil vertebrate localities. Journal of South American Earth Sciences 70, 2016, pp. 198-210
  84. ↑ a b c d e f g h Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo: Background for a paleoecological study of the Santa Cruz Formation (late Early Miocene) on the Atlantic Coast of Patagonia. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 1-22
  85. ↑ Viviana Barreda and Louis Palazzesi: Patagonian vegetation turnovers during the Paleogene-Early Neogene: origin of arid-adapted floras. The Botanical Review 73, 2007, pp. 31-50
  86. ↑ Darin A. Croft and KE Beth Townsend: Inferring habitat for the late early Miocene Santa Cruz Fauna (Santa Cruz Province, Argentina) using ecological diversity analysis. Society of Vertebrate Paleontology, Journal of Vertebrate Paleontology, Program and Abstracts Book 2005, p. 48A
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  88. ↑ M. Sol Raigemborn, Verónica Krapovickas, Elisa Beilinson, Lucía E. Gómez Peral, Alejandro F. Zucol, Luciano Zapata, M. Richard F. Kay, M. Susana Bargo, Sergio F. Vizcaíno and Alcides N. Sial: Multiproxy studies of Early Miocene pedogenic calcretes in the Santa Cruz Formation of southern Patagonia, Argentina indicate the existence of a temperate warm vegetation adapted to afluctuating water table. Palaeogeography, Palaeoclimatology, Palaeoecology 500, 2018, pp. 1-23
  89. ↑ Guillermo Rodríguez-Gómez, Guillermo H. Cassini, Paul Palmqvist, M. Susana Bargo, Néstor Toledo, Jesús A. Martín-González, Nahuel A. Muñoz, Richard F. Kay and Sergio F. Vizcaíno: Testing the hypothesis of an impoverished predator guild in the Early Miocene ecosystems of Patagonia: An analysis of meat availability and competition intensity among carnivores. Palaeogeography, Palaeoclimatology, Palaeoecology. 554, 2020, p. 109805, doi: 10.1016 / j.palaeo.2020.109805
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  103. ↑ Nelson M. Novo, Marcelo F. Tejedor and Laureano R. González-Ruiz: Previously unknown fossil platyrrhines (Primates) of Patagonia from the Tournouër collection at the Muséum national d'Histoire naturelle, Paris. Geodiversitas 40 (22), 2018, pp. 529-535
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