Santa Cruz Formation Research Articles

Early Devonian non-trilobite arthropods from the Iberian Chains (North East, Spain)

ABSTRACT Slightly sclerotised arthropods are described from shales of the Early Devonian age of the Axial Depression of the Cámaras river in Northeast Spain. The oldest records represent eurypterid fragments assigned to indeterminate Pterygotidae. They have been found in the early Pragian Nogueras Formation associated with land plant remains and rare marine invertebrates. The other two correspond to the first report of the phyllocarid Nahecaris in Spain. Nahecaris carlsi n. sp. is represented by a single complete specimen from the Pragian Santa Cruz Formation and Nahecaris sp. by another specimen from the Emsian Mariposas Formation. Both are associated with a rich marine fauna of various invertebrate groups. Environmentally, these arthropods occupied different areas from marginal marine (Pterygotidae indet.) to more open marine conditions (Nahecaris). The discovery of slightly sclerotised arthropods in several levels informs about the potential of the area for such type of preservation.

Anurans from the Early–Middle Miocene Santa Cruz Formation at Río Chalía (Patagonia, Argentina), and a revision of the fossil Calyptocephalellidae (Anura: Australobatrachia)

A large number of vertebrate fossils has been collected from the outcrops of the Early–Middle Miocene Santa Cruz Formation (SCF) along the Río Chalía in southern Patagonia, Argentina. The analysis of the anuran components reveals the coexistence of two Calyptocephalella species as the only frog inhabitants of the Santacrucian fauna, one of them especially large and abundant. Amongst the hundreds of anuran fossil remains, many provided relevant anatomical data to identify new characters to emend the diagnosis of Calyptocephalella, and to reconsider the taxonomic status of the largely controversial ‘Gigantobatrachus’ parodii. The latter is herein definitively recognized as part of Calyptocephalella, C. parodii stat. rev. et comb. nov. Also, a new genus, Xerocephalella gen. nov., is erected to accommodate two species that were formerly included within Calyptocephalella but lack some characters of the temporal region in the skull, herein included in the diagnosis of this genus. The SCF was deposited during an interval that spans a climatic episode, the Miocene Climatic Optimum, and the fossil record reflects the faunal variations associated with climatic/environmental changes that occurred during this period. The sympatric presence of the anurans Calyptocephalella parodii stat. rev. et comb. nov. and C. cf. C. canqueli at the lower levels of the unit and the presence of only one of them in the uppermost levels suggests a declining trend of the lineage through the Miocene, a decline that resulted in the extinction of Calyptocephalella east of the Andes. https://zoobank.org/urn:lsid:zoobank.org:pub:E88E703A-FF2C-4981-B1E1-3B9D46FE8019

New metatherians from Collon Cura Formation at Cerro Zeballos (Middle Miocene), Chubut province, Argentina

ABSTRACT High latitude metatherians from the Middle Miocene of Patagonia (Argentina and Chile) are only known from medium-sized Sparassodonta, and undescribed taxa collected in several fossil localities of Collon Cura (Argentina) and Río Frías (Chile) Formations, although the latter has several species reported and mostly recognised for the slightly older Santa Cruz Formation. In this contribution we describe five new genera and six new species of metatherians from Collon Cura Formation at Cerro Zeballos, Chubut province (Argentina), based on 11 specimens that notably increased the diversity of Collon Cura Formation. The specimens were assigned to the orders Paucituberculata (Palaeothentoidea), Sparassodonta (Hathliacynidae), and Polydolopimorphia (Argyrolagidae), and are taxa of small size, including the smallest palaeothentoids known to date. Also, the Palaeothentoidea of Cerro Zeballos are amongst the youngest of the superfamily in Patagonia. The new specimens described herein show morphological differences with other metatherian associations already known, probably related to adaptive changes coincident with the Middle Miocene Climatic Transition and the beginning of a faunal turnover.

Tuff deposits as preservational context for a Miocene continental mammal assemblage from Patagonia, Argentina

Tuff deposits as preservational context for a Miocene continental mammal assemblage from Patagonia, Argentina

Highly siderophile element and Re-Os isotope systematics of a Neoproterozoic Iron Formation and its temporal relation to glaciation events

The Urucum iron- and manganese formation (IF-MnF) in the Santa Cruz Formation, Brazil, was deposited in a glacially influenced, late Neoproterozoic depositional environment. It has proven to be a reliable and robust archive for the late Neoproterozoic, allowing unique insights into the composition of seawater during an interval that is characterized by dramatic changes in the Earth’s litho-, hydros-, atmo-, and biosphere, including several episodes of low-latitude glaciations. Here we present highly siderophile element data of the Urucum IF-MnF to evaluate elemental sources that affected the Neoproterozoic seawater from which the Urucum IF-MnF precipitated. High uncertainties associated with current dating attempts of this formation overlapped with the Marinoan glaciation (∼650–635 Ma) as well as the Gaskiers glaciation event (∼580 Ma). A Re-Os regression line defined by iron-, manganese-, and chert-rich samples of the Urucum formation is interpreted as an isochron, yielding a refined age estimate of 577 ± 38 Ma and an initial 187Os/188Os ratio of 0.122 ± 0.003. The proposed depositional age overlaps with previous published age data of the Urucum IF-MnF, but relates the Urucum IF-MnF to the Ediacaran Gaskiers glaciation and overlaps with the age of the Shuram CIE (∼567 Ma). An initial 187Os/188Os ratio of 0.122 ± 0.003 is interpreted to represent pristine Neoproterozoic seawater and supports strong hydrothermal input, probably related to rifting, that promoted ferruginous conditions in the Urucum seawater.In an alternative scenario, Re-Os isotope data for the Urucum IF-MnF could also be interpreted in a multi-component mixing scenario, defined by hydrothermally influenced water masses that sourced most metals within the Urucum basin and a crustal component that entered the Urucum seawater either as detrital admixture or via riverine loads. Although none of the scenarios can be ruled out, we consider the isochron scenario as more plausible.

Systematic revision of the species of Protypotherium (Notoungulata: Interatheriidae) from the Santa Cruz Formation (Early–Middle Miocene), Argentinian Patagonia: a new phylogenetic hypothesis for the Interatheriidae

Abstract Protypotherium is one of the main genera of the Interatheriidae due to its species richness, abundance, and wide distribution from southern to middle latitudes of Argentina, Bolivia, Uruguay, and Chile. This genus is better known from the species founded by Florentino Ameghino during late 19th century from the prolific Santa Cruz Formation (Santacrucian South American Land Mammal Age (SALMA); Burdigalian–Early Langhian), Santa Cruz Province (Argentina). This contribution provides the taxonomic revision of the Santacrucian species of Protypotherium and the species erected by Florentino within this genus. We conclude that among the initial 21 species, Protypotherium antiquum, Protypotherium australe, Protypotherium praerutilum, Protypotherium compressidens, and Protypotherium claudum are valid, whereas Protypotherium obstructum is a Hegetotheriidae indet. We present a phylogenetic analysis that does not recover Protypotherium as a clade, due to the nesting of Juchuysillu and Caenophilus, and this assemblage appears as the sister taxon of the clade Progaleopithecus plus Archaeophylus. Finally, the interatheriines from the Santa Cruz Formation do not allow a subdivision of this unit, due to their wide geographic and temporal distribution, thus rejecting the biozones preliminary proposed by other authors. The Atlantic coast (east) and Río Santa Cruz (central) regions are similar in their interatheriine content, but both differ from the western area.

Systematic Revision of Interatherium and Icochilus (Interatheriidae, Notoungulata) from the Santa Cruz Formation (Early To Middle Miocene), Santa Cruz Province, Argentina

Systematic Revision of Interatherium and Icochilus (Interatheriidae, Notoungulata) from the Santa Cruz Formation (Early To Middle Miocene), Santa Cruz Province, Argentina

Tectonic evolution of the eastern margin of the Southern Patagonian Andes fold-thrust belt: U-Pb detrital zircon geochronology and kinematic-structural modelling

Tectonic evolution of the eastern margin of the Southern Patagonian Andes fold-thrust belt: U-Pb detrital zircon geochronology and kinematic-structural modelling

Cranial osteology of the basal megatherioid sloth Schismotherium (Mammalia, Xenarthra) and its taxonomic implications

ABSTRACT This study comprises a comparative description of the skull anatomy in the basal megatherioid sloth Schismotherium fractum, based on specimens from the Santa Cruz Formation (late early Miocene; Santacrucian SALMA) in southern Argentine Patagonia. We provide more detailed descriptions and illustrations of the skull bones and their sutural connections, as well as the cranial foramina and their contents, than have previously been available. The anatomy in S. fractum is compared to contemporaneous basal megatherioids from Santa Cruz, Hapalops elongatus and Pelecyodon cristatus. The latter is a close relative of S. fractum in several phylogenetic analyses, but given the high levels of anatomical variation and other taxonomic uncertainties that surround these sloths, previous authors have suggested that the two may not represent distinct taxa. Our observations demonstrate that although the skulls of S. fractum do indeed exhibit variation in a broad variety of features, there are invariant, apomorphic features that consistently distinguish Schismotherium and Pelecyodon from one another, including at least 17 features derived from virtually every region of the skull. While supporting the current taxonomic status of these important, basal-most megatherioids, the present study highlights the need for further anatomical and phylogenetic investigations of Santacrucian sloths.

Caviomorphs (Rodentia, Hystricognathi) from Pampa Castillo, Chile: new octodontoid records and biochronological implications

AbstractCaviomorph rodents have been diverse and abundant components of South American mammal communities since the late Eocene. We describe herein the octodontoids of Pampa Castillo, a Lower Miocene site in southern Chile (Aysén Region). Six genera and seven species of octodontoids are present, two of which are new: Dudumus berggreni sp. nov. and Caviocricetus guenekko sp. nov. The octodontoids from Pampa Castillo support assignment of this fauna to the Santacrucian South American Land Mammal Age (SALMA), which is consistent with previous studies. We conducted similarity analyses on 11 Early–Middle Miocene Patagonian rodent faunas using hierarchical clustering. Faunas generally fell into the three SALMAs to which they were traditionally assigned: Colhuehuapian, Santacrucian and ‘post‐Santacrucian’. The ‘Pinturan’ is a proposed biochronological interval between the Colhuehuapian and Santacrucian. At the genus level, Pampa Castillo clustered with ‘Pinturan’ faunas, while at the species level it clustered with the ‘typical’ faunas on which the Santacrucian SALMA is based (from outcrops of the Santa Cruz Formation along the Atlantic coast and Río Santa Cruz). The Pampa Castillo rodent fauna resembles both ‘Pinturan’ and ‘typical’ Santacrucian faunas in taxon distributions, reflecting complex temporal and palaeoenvironmental influences. Geochronological data indicate that some ‘Pinturan’ sites overlap temporally with Pampa Castillo and the upper Pinturas Formation, which both clustered with ‘typical’ Santacrucian faunas. These results indicate that the ‘Pinturan’ does not represent a distinct biochronological interval, but that the differences between it and ‘typical’ Santacrucian faunas are attributable to geographic or palaeoenvironmental differences.

Fossil vertebrates of the early-middle Miocene Cerro Boleadoras Formation, northwestern Santa Cruz Province, Patagonia, Argentina

The early-middle Miocene continental Cerro Boleadoras Formation (CBF) crops out in the area of Cerro Boleadoras and Cerro Plomo on the western slope of the Meseta del Lago Buenos Aires, northwestern Santa Cruz Province, Argentina. The lower levels of the CBF consist of laterally extensive medium to pebbly sandstone beds with trough cross-bedding, interpreted as fluvial channel deposits, interbedded with tabular fine-grained floodplain deposits. Recent fieldwork provided fossil vertebrates from these levels with an estimated age between ~16.5 Ma and 15.1 Ma (late Burdigalian-early Langhian). The studied section temporally overlaps with the middle or upper sections of the Santa Cruz Formation (SCF) in the Austral-Magallanes Basin of southern Patagonia, the Río Frías Formation in Chile, and the lower Collón Curá Formation of northern Patagonia. We compile an integrated faunal list for this locality, including specimens from previous collections, and discuss its chronological and paleoenvironmental implications. The taxa list includes most of the groups recorded in the SCF: one anuran, three birds, and at least 33 mammals (metatherians, xenarthrans, litopterns, notoungulate typotheres and caviomorph rodents), indicating a Santacrucian age sensu lato. We also recorded a testudine, which constitutes the southernmost record of tortoises in South America and worldwide. Faunal dissimilarities between the vertebrate fossil content of the CBF and the mentioned sections of the Santa Cruz, Río Frías and Collón Curá formations may reflect ecologic, climatic and geographic differences rather than temporal ones. The co-occurrence of arboreal or semiarboreal, browsing, frugivorous, and grazing mammals suggests the presence of both forested and open environments for the area occupied by the CBF rocks. However, it is not possible to discern whether these two environments coexisted or alternated, and whether one environment predominated over the other. Marker taxa, such as the chinchillid rodents Prolagostomus and Pliolagostomus, and the typothere Pachyrukhos indicate a trend to aridification during the Miocene in southern Patagonia, as previously reported for the upper part of the SCF along the Río Santa Cruz and south to the Río Coyle, along the Atlantic coast and the Río Gallegos.

Cavioids, Chinchilloids, and Erethizontoids (Hystricognathi, Rodentia, Mammalia) of the Early Miocene Pampa Castillo Fauna, Chile

Caviomorph rodents became important components of South American faunas after their Eocene arrival from Africa. Here we describe the cavioid, chinchilloid, and erethizontoid caviomorphs of the early Miocene Pampa Castillo fauna of southern Chile. This fauna's age and location make it key for resolving outstanding biostratigraphic questions concerning early Miocene Patagonian fossiliferous strata. Each of the four major caviomorph clades (“superfamilies”) is represented in the Pampa Castillo fauna, three whose members are detailed here: cavioids (3 genera; 3 species), chinchilloids (3 genera; 6 species), and erethizontoids (2 genera; 2 species). Abundantly represented taxa, e.g., Neoreomys australis, Perimys erutus, and Prolagostomus pusillus, corroborate previous work assigning the Pampa Castillo fauna to the Santacrucian South American Land Mammal “Age” (SALMA; inclusive of the “Pinturan”). Several taxa, including Eosteiromys, Perimys intermedius, and Perimys sp. nov.?, are also found in the lower and middle Pinturas Formation (lmPF) but not “core” Santacrucian faunas (from the Santa Cruz Formation [SCF] along the Río Santa Cruz and Atlantic coast), suggesting a distinctive resemblance between lmPF and Pampa Castillo rodents. Some authors consider the fauna from the lmPF to form the basis of a “Pinturan” SALMA or subage, considered to slightly predate core Santacrucian faunas, but which has yet to be formally recognized. The taxonomic composition of rodent fauna from Pampa Castillo, as well as relative abundance data, indicated a paleoenvironment intermediate between the closed forests of the lmPF and the mosaic of open and closed habitats of the core Santacrucian faunas from the SCF.

A New Humerus of Homunculus patagonicus, a Stem Platyrrhine from the Santa Cruz Formation (Late Early Miocene), Santa Cruz Province, Argentina

We describe a well-preserved humerus of Homunculus patagonicus, a stem platyrrhine from the late early Miocene of the Santa Cruz Formation, Santa Cruz Province, Argentina. The distal part of a humerus was collected by Carlos Ameghino and figured in the 19th Century, but is now lost. Other described postcranial elements, also collected by him include a femur and a partial radius. Comparative observations are made with living and extinct platyrrhines, Oligocene African anthropoids, and extant strepsirrhines. Homunculus patagonicus was a robustly built arboreal quadruped that weighed between 2.2 and 2.6 kg. There is no evidence that the elbow could be fully extended as in living suspensory platyrrhines like Ateles. The medial orientation of the epicondyle suggests that the finger and wrist flexors were not aligned with the long axis of the limb, a distinction from more cursorial monkeys (extant cercopithecoids and the Cuban Pleistocene fossil platyrrhine Paralouatta have retroflexed medial epicondyles). Overall, the morphology is typically platyrrhine although the bone is quite robust. The robustness of the humerus is most comparable to that of early anthropoids from Africa rather than any extant platyrrhine.

EL REGISTRO DEL TIPOTERIO PACHYRUKHOS (MAMMALIA, NOTOUNGULATA) Y EL CHINCHÍLLIDO PROLAGOSTOMUS (MAMMALIA, RODENTIA) EN LA FORMACIÓN SANTA CRUZ (MIOCENO TEMPRANO–MEDIO) AL SUR DEL RÍO COYLE, PATAGONIA, ARGENTINA

The continental early–middle Miocene Santa Cruz Formation (SCF) from Patagonia is one of the most important stratigraphic units of southern South America in terms of the terrestrial Neogene record. Its fossil content was pivotal for establishing the succession of Cenozoic faunas from Patagonia and formed the basis of the Santacrucian South American Land Mammal Age. Despite the updated knowledge recently achieved, the stratigraphic distribution of many taxa within the SCF remains to be clarified. That is the case with the typothere notoungulate Pachyrukhos and the chinchillid rodent Prolagostomus. New information on the stratigraphy of the SCF along the north bank of the Río Gallegos and Cabo Buen Tiempo (Santa Cruz Province), together with a detailed analysis of the provenance information of the specimens in the principal old museum collections, sheds light on the record of these taxa south to Río Coyle. Our results show that the first recorded occurrence of both taxa in the area was between ~17 Ma and 17.41 Ma, restricted to the upper part of the SCF, including the upper part of the Estancia La Costa Member at Cañadón Las Totoras-Monte Tigre, and the superimposed Estancia La Angelina Member along the Río Gallegos and Cabo Buen Tiempo. Their presence suggests a trend to aridification in the upper part of the SCF south to the Río Coyle. These results are consistent with recent information obtained from other locations of the SCF north to the Río Coyle.

Cryogenian glaciostatic and eustatic fluctuations and massive Marinoan-related deposition of Fe and Mn in the Urucum District, Brazil

Abstract Global Neoproterozoic glaciations are related to extreme environmental changes and the reprise of iron formation in the rock record. However, the lack of narrow age constraints on Cryogenian successions bearing iron-formation deposits prevents correlation and understanding of these deposits on a global scale. Our new multiproxy data reveal a long Cryogenian record for the Jacadigo Group (Urucum District, Brazil) spanning the Sturtian and Marinoan ice ages. Deposition of the basal sequence of the Urucum Formation was influenced by Sturtian continental glaciation and was followed by a transgressive interglacial record of >600 m of carbonates that terminates in a glacioeustatic unconformity. Overlying this, there are up to 500 m of shale and sandstone interpreted as coeval to global Marinoan glacial advance. Glacial outwash delta deposits at the top of the formation correlate with diamictite-filled paleovalleys and are covered by massive Fe and Mn deposits of the Santa Cruz Formation and local carbonate. This second transgression is related to Marinoan deglaciation. Detrital zircon provenance supports glaciostatic control on Cryogenian sedimentary yield at the margins of the Amazon craton. These findings reveal the sedimentary response to two marked events of glacioeustatic incision and transgression, culminating in massive banded iron deposition during the Marinoan cryochron.

A new species of Dryornis (Aves, Cathartiformes) from the Santa Cruz Formation (lower Miocene), Patagonia, Argentina

A new species of Dryornis (Aves, Cathartiformes) from the Santa Cruz Formation (lower Miocene), Patagonia, Argentina

A new genus of Interatheriinae (Interatheriidae, Notoungulata) from the Santa Cruz Formation (early–middle Miocene), Santa Cruz Province, Argentina, and the revision of the genus Cochilius Ameghino, 1902

ABSTRACT Interatheriinae is one of the most derived subfamilies of South American notoungulates. Several interatheriines have been described since the 19th century, but most of them have not been revised, or been formally re-examined, for more than a century. Most interatheriine taxa were erected based on materials collected from Argentinean Patagonia, particularly from the Santa Cruz Formation (early–middle Miocene), Santa Cruz Province. Within the framework of an exhaustive unpublished systematic revision of Interatheriinae (early Oligocene–late Miocene), we studied the holotype of Santacrucian Icochilus undulatus, leading to the recognition of a new monospecific genus, Neoicochilus gen. nov., and the new combination N. undulatus. In addition, we formalize the taxonomic revision of Cochilius, proposing the following: Paracochilius is the junior synonym of Cochilius; Cochilius consists of C. volvens, C. fumensis, and C. brevirostrus; Paracochilius chubutensis and Protypotherium minor are junior synonyms of Cochilius brevirostrus; Cochilius pendens is the junior synonym of Cochilius columnifer; and the holotype of Cochilius columnifer exhibits the diagnostic features of Protypotherium, so we propose the new combination Protypotherium columnifer, pending publication of our thorough taxonomic revision of Protypotherium. Our taxonomic scheme is supported by a cladistic analysis, which places Neoicochilus undulatus in a derived position within Interatheriinae, as the sister taxon of the monophyletic genus Cochilius, and the clade Neoicochilus plus Cochilius positioned as the sister taxon of Interatherium. Our phylogenetic results support the monophyly of Miocene interatheriines.

Insights on the controls on floodplain-dominated fluvial successions: a perspective from the Early–Middle Miocene Santa Cruz Formation in Río Chalía (Patagonia, Argentina)

The Santa Cruz Formation (SCF) in Río Chalía (Austral Basin, Patagonia, Argentina) is a well-exposed fluvial succession with abundant and diverse fossil vertebrates accumulated during the Miocene Climatic Optimum (MCO). Using facies analysis, characterization of stratigraphic architecture, U–Pb geochronology and vertebrate palaeontology, we assess the timing and interplay of controlling factors on the sedimentation, including tectonics, global sea level, climate and sediment supply. Throughout the succession, there occurred a constant aggradation of the floodplain-dominated fluvial system. Seven zircon U–Pb ages constrain the time of accumulation between c. 18 and 15.2 Ma, under a relatively constant sedimentation rate of 150 ± 50 m myr –1 . The large number of fossil vertebrates indicates a Santacrucian fauna, showing no recognizable changes through the section. The basin-scale, low-gradient anastomosed fluvial system of the SCF records a period of about 3 myr of relatively constant environmental conditions controlled by continuous basin subsidence and high sediment supply conditioned by explosive volcanism together with weathering of uplifting terrains in the Andes. In addition, the system was influenced by a temperate to warm and subhumid climate favoured by the MCO before the onset of the Andean rain shadow, together to high global sea levels. Supplementary material: Preliminary list of the taxa recorded in the SCF at Río Chalía, and LA-ICP-MS isotopic U–Pb data are available at https://doi.org/10.6084/m9.figshare.c.5324976

Paleoenvironments and paleoecology of the Santa Cruz Formation (early-middle Miocene) along the Río Santa Cruz, Patagonia (Argentina)

Paleoenvironments and paleoecology of the Santa Cruz Formation (early-middle Miocene) along the Río Santa Cruz, Patagonia (Argentina)

Patagonian Aridification at the Onset of the Mid‐Miocene Climatic Optimum

AbstractFossil‐rich sediments of the Santa Cruz Formation, Patagonia, Argentina, span the initiation of the Miocene Climatic Optimum (MCO), the most recent period of warm and wet conditions in the Cenozoic. These conditions drove the expansion of tropical and subtropical ecosystems to much higher latitudes, with the fossiliferous Santa Cruz Formation recording one of the southernmost examples. We collected new carbon and oxygen isotope compositions of herbivore tooth enamel from fossils ~17.4 to 16.4 Ma in age to investigate ecological and climatic changes across the initiation of the MCO. Enamel δ13C values are consistent with a C3‐dominated ecosystem with moderate precipitation and a mix of wooded and more open areas. Serially sampled teeth reveal little zoning in δ13C and δ18O values, suggesting little seasonal variation in water and plant isotope compositions or seasonal changes in diet. Carbon isotope‐based estimates of mean annual precipitation (MAP) are consistent with aridification, with MAP decreasing from ~1,000 ± 235 mm/yr at 17.4 Ma to ~525 ± 105 mm/yr at the start of the climatic optimum (~16.9 Ma). This decrease corresponds to increasing global temperatures, as indicated by marine proxy records, and was followed by a rebound to ~840 ± 270 mm/yr by ~16.4 Ma. In comparison to a modern mean annual temperature (MAT) in the region of ~8°C, oxygen isotopes indicate high MAT (at least 20°C) at the onset of the MCO at 16.9 Ma and a significant increase in MAT to ~25°C by 16.4 Ma.