The Santa Cruz Formation is a geological formation in the Magallanes/Austral Basin in southern Patagonia in Argentina and adjacent areas of Chile. It dates to the late Early Miocene epoch, and is contemporaneous with the eponymous Santacrucian age of the SALMA (South American land mammal age) timescale. The Santa Cruz Formation is known for its abundance of vertebrate fossils, including South American native ungulates (astrapotheres, litopterns, notoungulates), as well as rodents, xenarthrans (armadillos, sloths, anteaters), and metatherians.
The formation extends from the Andes to the Atlantic coast. In its coastal section it is divided into two members, the lower, fossil rich Estancia La Costa Member, which consists predominately of tuffaceous deposits and fine grained mudrock, and the upper fossil-poor Estancia La Angelina Member, which consists of sedimentary rock, primarily mudrock, and sandstone. The environment of deposition was mostly fluvial, with the lowermost part of the Estancia La Costa Member being transitional between fluvial and marine conditions. The environment of the Estancia La Costa Member is thought to have been relatively warm and humid, but likely became somewhat cooler and drier towards the end of the sequence.
Stratigraphy The Santa Cruz Formation is exposed in isolated outcrops across the Magallanes/Austral Basin extending from the Atlantic coast to the Andes, especially along the Santa Cruz River, as well as along the southern coastline of Santa Cruz Province. While primarily located in Argentina, small outcrops are also found in Chile.Raúl Ugalde, Enrique Bostelmann, Karina E. Buldrini, and José Luis Oyarzún Lithofacies, architecture, and depositional environments of the Santa Cruz Formation in Chilean Patagonia (2015) XIV Congreso Geológico Chileno The base of the formation is defined by a marine regression event transitioning from the marine environment of the underlying Monte Léon Formation, which formed when large areas of Patagonia were submerged as a part of the Patagoniense Transgression.
The main source of sediment input to the basin was from the Andean orogeny to the west. The formation reaches a maximum thickness of over 295 meters, though the total thickness of the formation is strongly controlled by subsequent erosion and the 295 meters likely does not represent a complete sequence. The formation primarily consists of floodplain deposits. The lower parts of the formation have an abundance of tuffs and tuffaceous sediments. These likely originated from distant eruptions that were transported into the basin by aerial fallout, wind and/or river transport. The formation likely spans an approximately 3 million year interval in the late Early Miocene around 18 to 15.2 million years ago, during the Burdigalian and Langhian stages.
Paleoenvironment The environment of the Santa Cruz Formation is thought to have been relatively warm and humid, including a mix of open savanna, gallery forests and semi-deciduous forests. Permanent bodies of water such as lakes, ponds and streams are likely to have been present.
Paleoflora Name Species Locality Material Notes ImageNothofagusIndeterminateRincón del Buque, Punta SurLeaves, woodAraucariaIndeterminatePunta SurTwigMorphologically similar to A. marensii from the Eocene of AntarcticaLauraceaeIndeterminatePunta SurWoodAssigned to form genus Laurinoxylon MyrceugeniaM. chubutensePunta SurWoodA member of the family MyrtaceaeEucryphiaceoxylonE. eucryphioidesPunta SurWoodWood probably belonging to the genus EucryphiaFaboideaeIndeterminatePunta SurWoodPossible affinities to Sophora (Fabaceae) DoroteoxylonD. vicenti-pereziiPunta SurWoodWood with affinities to the subfamily CaesalpinioideaeAkanioxylonA. santacrucensisPunta SurWoodA member of the family Akaniaceae ChloridoideaeIndeterminatePhytolithsGrassPanicoideaeDanthonioideaePooideae
Paleofauna Invertebrates Name Species Material Notes ImageCrassostreaC. orbignyiNumerous individuals in large beds at the base of the formationA marine true oysterDiplodonD. cf. colhuapiensisA freshwater bivalve belonging to HyriidaeStephadiscusIndeterminateA terrestrial gastropod belonging to CharopidaeGastrocoptaG.patagonica A terrestrial gastropod belonging to Vertiginidae ?Scolodonta IndeterminateA terrestrial gastropod belonging to Scolodontidae PunctumP. patagonicumA terrestrial gastropod belonging to Punctidae ZilchogyraZ. miocenica A terrestrial gastropod belonging to CharopidaePatagocharopaP. enigmaticaA terrestrial gastropod of uncertain affinities, possibly a member of Charopidae PoriferaUnspecifiedSpiculesFreshwater spongeBacillariophyceaeUnspecifiedFrustules Freshwater diatomsChrysophyceaeUnspecifiedFreshwater algae
Amphibians Name Species Locality Material Notes ImageCalyptocephalellaC. parodiiRincón del BuqueA calyptocephalellid frogC. cf. C. canqueliCañadón de las VacasNeobatrachiaIndeterminateEstancia La CostaSkull fragments and presacral vertebrateA frog originally assigned to "Leptodactylidae", but requires further investigation
Birds Name Species Locality Material Notes ImageAnisolornisA. excavatusA bird of uncertain affinities, authors have varyingly suggested affinities to trumpeters or limpkinsAnkonettaA. larriestraiPartial tarsometatarsusA basal member of AnatidaeBadiostesB. patagonicusA member of the family FalconidaeBrontornisB. burmeisteriControversial taxonomic position, either considered a terror bird or an anserimorphDryornisD. pampeanusD. hatcheriTwo partial left humerusA New World vulture.EutelornisE. patagonicus
E. australisLimb fragmentsA member of Anseriformes, relationships of the species to each other or to other Ansiferiformes is uncertainLiptornisL. hesternusA member of AnhingidaeMacranhingaIndeterminateA member of AnhingidaeMiocariamaJorge I. Noriega; Gerald Mayr (2017). "The systematic affinities of the putative seriema Noriegavis santacrucensis (Noriega et al., 2009) from the Miocene of Argentina". Contribuciones del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia". 7: 133–139.M. santacrucensisPartial cranium and tibiotarsi fragmentsA seriemaNothurinae2 Indeterminate speciesTinamouOpisthodactylusO. patagonicusLimb, vertebra and skull fragmentsA member of RheidaePatagornis P. marshiA terror birdPhorusrhacosP. longissimusPartial skullsA terror birdProtibisP. cnemialisdistal end of tibiotarsusPotentially a spoonbillPsilopterusP. lemoinei
P. bachmanniA terror birdThegornisT. musculosus
T. debilisA member of the family FalconidaeArchaeopsophiaA. aoniA member of the family Psophiidae (trumpeters)ChehueniaC. facongrandeiA rollerKaikeniaK. mourerchauvireaAn anatid belonging to the subfamily TadorninaePeioaP. australisA member of Anseriformes.
Squamates Name Species Locality Material Notes ImagePristidactylusIndeterminateLa CuevaFragmentary jaw bonesOriginally assigned to the dubious genus "Erichosaurus"PleurodontaTupinambisMonte LeónFragmentary dentaries and maxillaA teiid lizardColubridaeCerro ObservatorioPartial trunk vertebraeA snake
Mammals Meridiungulates
Astrapotheres Name Species Locality Material Notes ImageAstrapotheriumA. magnum A. nanum
A. sp.An astrapotheriid
Litopterns Name Species Locality Material Notes ImageAdianthusA. bucatusAn adianthid litopternAnisolophusA. australis A. floweriA proterotheriid litopternDiadiaphorusD. majusculus D. sanctaecrucis
D. sp.A proterotheriid litopternTetramerorhinusT. cingulatum T. fleaglei
T. mixtum
T. lucarius
T. prosistens
T. sp.Estancia La Costa MemberA proterotheriid litopternTheosodonT. fontanae T. garretorum
T. gracilis
T. karaikensis
T. lydekkeri
T. patagonicumEstancia La Costa MemberA macraucheniid litopternThoatheriumT. minisculum T. sp.Estancia La Costa MemberA proterotheriid litoptern
Notoungulates Name Species Locality Material Notes ImageAdinotheriumA. ovinum A. robustum
A. sp.A toxodontid notoungulateCochiliusC. sp.An interatheriid notoungulateHegetotheriumH. mirabile H. sp.A hegetotheriid notoungulateHomalodotheriumH. cunninghamiA homalodotheriid notoungulateInteratheriumI. anguliferum I. brevifrons
I. dentatum
I. interruptum
I. robustum
I. rodens
I. supernumAn interatheriid notoungulateNeoicochilusN. undulatusAn interatheriid notoungulateNesodonN. imbricatusA toxodontid notoungulateNotohippusN. toxodontoidesA notohippid notoungulatePachyrukhosP. moyaniA hegetotheriid notoungulatePatriarchusP. palmidensAn interatheriid notoungulateProtypotheriumP. attenuatum P. australe
P. praerutilum
P. sp.An interatheriid notoungulate
Xenarthrans
Pilosa Name Species Locality Material Notes ImageAnalcimorphusA. giganteus A. inversusEstancia La Costa MemberA basal megatherioid slothAnalcitheriumA. antarcticumEstancia La Costa MemberA scelidotheriid sloth EucholoeopsE. fronto E. ingens
E. litoralis
E. titansEstancia La Costa MemberA megalonychid ground slothHapalopsH. longiceps
H. elongatus
H. indifferens
H. angustipalatus
H. platycephalus
H. ponderosus
H. rectangularisA ground sloth belonging to MegatherioideaHyperleptusIndeterminateA megatherioid ground sloth of uncertain affinitiesMegalonychotheriumM. atavusA megalonychid ground slothMylodontidaeIndeterminateNematheriumN. angulatumA ground sloth belonging to Mylodontoidea PelecyodonP. cristatusA ground slothPlanopsP. magnus A megatheriid ground slothProtamanduaP. rothiAn anteaterPrepotheriumP. potens P. filholiA ground slothMegalonychidae IndeterminateA ground slothSchismotheriumS. fractumA ground slothXyophorusX. atlanticus X. latirostrisA nothrotheriid ground sloth
Cingulata NameSpeciesLocalityMaterialNotesImageAnantiosodonA. rarusAn armadillocf. Asterostemmacf. A. depressaA glyptodontCochlopsC. muricatusA glyptodontEucinepeltusE. petesatusA glyptodontMetopotoxusM. laevatusA glyptodontParutaetusP. sp.An armadilloPeltephilusP. ferox
P. giganteus
P. nanus
P. pumilus
P. strepensA horned armadilloProeutatusP. carinatus P. deleo
P. lagena
P. oenophorus
P. robustusAn armadilloPropalaehoplophorusP. australis P. incisivus P. minusA glyptodontProzaedyus P. exilis P. proximusAn armadilloStenotatusS. patagonicusAn armadilloStegotheriumS. tauberi S. tessellatumAn armadilloVeteliaV. punctaAn armadillo
Metatherians Name Species Locality Material Notes ImageAbderitesA. meridionalisA member of Abderitidae (Paucituberculata)AcdestisA. owenii A. lemaireiA member of Palaeothentidae (Paucituberculata)AcrocyonA. sectoriusA borhyaenid sparassodontAcyonA. tricuspidatusA hathliacynid sparassodontArctodictisA. muniziA borhyaenid sparassodontBorhyaenaB. tuberataA borhyaenid sparassodontCladosictisC. patagoniaA sparassodontLycopsisL. torresiA sparassodontMicrobiotherium M. acicula
M. patagonicum
M. gallegosense
M. tehuelchumA member of Microbiotheriidae (Microbiotheria)PalaeothentesP. aratae
P. minutus
P. intermedius
P. lemoinei
P. pascualiA member of Palaeothentidae (Paucituberculata) Perathereutes P. pungensA hathliacynid sparassodontPhonocdromusP. gracilisA member of Pichipilidae (Paucituberculata) ProthylacinusP. patagonicusA sparassodontPseudonotictisP. pusillusA hathliacynid sparassodontSipalocyonS. gracilis
S. obustaA hathliacynid sparassodontStilotheriumS. dissimile A member of Caenolestidae (Paucituberculata)
Rodents Name Species Locality Material Notes ImageAcarechimysA. minutus A. minutissmus
A. constans
A. gracilisA member of OctodontoideaAcaremysA. murinus
A. messorA member of Acaremyidae (Octodontoidea)AdelphomysA. candidusA member of OctodontoideaDudumusIndeterminate, potentially new speciesA member of OctodontoideaEocardiaE. montana
"E". excavata
"E". fissaA member of CavioideaNeoreomysN. australisA member of CavioideaPerimysP. erutus
P. onustus
P. incavatusA member of ChinchilloideaPhanomysP. mixtus