Journal of South American Earth Sciences - Duke University
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Journal of South American Earth Sciences 109 (2021) 103296
Contents lists available at ScienceDirect
Journal of South American Earth Sciences
journal homepage: www.elsevier.com/locate/jsames
Paleoenvironments and paleoecology of the Santa Cruz Formation
(early-middle Miocene) along the Río Santa Cruz, Patagonia (Argentina)
Richard F. Kay a, *, Sergio F. Vizcaíno b, c, M. Susana Bargo b, d, Jackson P. Spradley e,
José I. Cuitiño f
a
Department of Evolutionary Anthropology and Division of Earth and Ocean Sciences, Duke University, Durham, NC, 27708, USA
b
División Paleontología Vertebrados, Facultad de Ciencias Naturales y Museo, Unidades de Investigación, Anexo Museo, Av. 60 y 122, 1900, La Plata, Argentina
c
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
d
Comisión de Investigaciones Científicas, Provincia de Buenos Aires (CICPBA), Argentina
e
North Carolina State University - College of Veterinary Medicine, Department of Molecular Biomedical Sciences. Raleigh, NC, USA
f
Instituto Patagónico de Geología y Paleontología Centro Nacional Patagónico, Puerto Madryn (U9120), Argentina
A R T I C L E I N F O A B S T R A C T
Keywords: The continental early-middle Miocene Santa Cruz Formation (SCF) in Austral Patagonia contains the best record
Ecometrics of South American mammalian faunas prior to the Great American Biotic Interchange (GABI) and is of particular
Paleobiology interest because it is the best preserved high-latitude continental biotic record in the Southern Hemisphere
Paleoclimate
spanning the mid-Miocene Climatic Optimum. Through intensive fieldwork we recovered numerous fossil ver
Mammals
Neogene
tebrates, mostly mammals, from the SCF along the Río Santa Cruz (RSC), the type area for the formation and its
South America fauna. We examine whether the SCF fauna differed among three distinct temporal intervals of the SCF spanning,
Frugivore problem from the oldest to youngest, the Atlantic coastal suite of localities Fossil Levels (FL) 1–7, at about 17.4 Ma,
through localities in the RSC Barrancas Blancas (BB), between ~17.2 and ~16.3 Ma, and Segundas Barrancas
Blancas (SBB), between ~16.5 and ~15.6 Ma. With the objective of reconstructing paleoenvironmental and
community structure of these RSC faunas, we compared them with 55 extant lowland mammalian localities
across South America from 8◦ N to 55◦ S latitude representing a wide range of seasonality and, annual rainfall
and temperature, as well as canopy height and net primary productivity, sampling communities ranging from
tropical rainforest to semi-arid steppe. Extant nonvolant mammalian genera at each locality were assigned a
body size interval and niche parameters reflecting diet and substrate use, from behavioral data in the literature.
Extinct genera were assigned similar niche metrics on the basis of their morphology. From the generic niche
parameters, we compiled indices and ratios that express vectors of the community structure of each fauna,
including the total number of genera, the pervasiveness of arboreality, frugivory, and browsing, and the relative
richness of predators to their prey. The community structure variables were used to model community structure
of the fossil localities based on uniformitarian principles. The fossil sample includes 44 genera of mammals from
FL 1–7, 38 genera from BB, and 44 genera from SBB. The Simpson Coefficients of faunal similarity among the
fossil localities are no greater than expected on the basis of the geographic distances among them, and do not
suggest any apparent climatic differences. Based on the models we obtained no significant differences in MAP
(Mean Annual Precipitation) for FL 1–7, BB and SBB, with mean estimates of 1635 mm, 1451 mm, and 1504 mm,
with the confidence intervals for the estimates overlapping widely. MAT (Mean Annual Temperature) estimates
are between ~21 ◦ C and ~22 ◦ C for FL 1–7 and SBB, possibly lower at 16 ◦ C for BB, but with a wide and
overlapping range of estimates. Temperature seasonality is modest (3 ◦ C to 4 ◦ C) and similar for all localities.
Canopy heights exceed 20 m for all sites. Despite these geographic and inferred climatic similarities, the presence
of certain key taxa (e.g., the caviomorph rodent Prolagostomus and the typothere Pachyrukhos) together with an
increased overall abundance and richness of rodents with ever-growing cheek teeth suggests a trend to aridifi
cation in the upper part of the SCF at SBB compared with FL 1–7 and BB. Taken together, we propose that the SCF
paleoenvironment consisted largely of semi-deciduous forests ranging into savannas with gallery-forest com
ponents. This range of habitats occurs today where the mesic inland Atlantic forests of Southern Brazil,
* Corresponding author.
E-mail addresses: richard.kay@duke.edu (R.F. Kay), vizcaino@fcnym.unlp.edu.ar (S.F. Vizcaíno), msbargo@fcnym.unlp.edu.ar (M.S. Bargo), jpspradl@ncsu.edu
(J.P. Spradley), jcuitino@cenpat-conicet.gob.ar (J.I. Cuitiño).
https://doi.org/10.1016/j.jsames.2021.103296
Received 9 December 2020; Received in revised form 23 March 2021; Accepted 23 March 2021
Available online 29 March 2021
0895-9811/© 2021 Elsevier Ltd. All rights reserved.
R.F. Kay et al. Journal of South American Earth Sciences 109 (2021) 103296
northeastern Argentina and eastern Paraguay give way northwestward into the more xeric Paraguayan Gran
Chaco. These interpretations are in general agreement with other sources of evidence from sedimentology,
paleosols, isotopes, paleobotany and other faunal elements. We highlight the value of focusing paleoenvir
onmental and paleocological studies of the SFC on stratigraphically and geographically confined samples instead
of on the entire temporal and geographic distribution of the SCF based on historical collections with limited
provenance. The Santacrucian can be considered a model to the study of South American faunas after the arrival
of hystricomorph rodents and anthropoid primates but before GABI.
1. Introduction a renewed background and vision.
From a paleoecological perspective, in the last decade there have
The continental early-middle Miocene (Burdigalian-early Langhian) been two different approaches for the understanding of the biota and
fossil record of the Santa Cruz Formation (SCF) from Austral Patagonia, environments of the SCF: either considering stratigraphically and
represents the biota that has most impacted historically and conceptu geographically restricted samples obtained through exhaustive field
ally the understanding of the Cenozoic biotic evolution of South America work efforts (Kay et al., 2012; Vizcaíno et al., 2010) or globally along the
prior to the Great American Biotic Interchange (GABI), when South entire temporal and geographic distribution of the formation based on
America was mostly isolated from other Continents . Moreover, the SCF bibliography and historical collections (Croft, 2013).
contains the best preserved high-latitude continental biotic record in the The approach by Vizcaíno et al. (2010) and Kay et al. (2012) was
Southern Hemisphere providing further insights into mid-Miocene based on fossils collected from geographically and stratigraphically
temperature and precipitation. It is well known that floras and faunas restricted sets of localities of the Atlantic Coast outcrops, which are often
dependent on warm, wet conditions expanded to higher latitudes in in an excellent state of preservation, including partial or complete ar
South America at that time (Frenguelli, 1953; Ortiz-Jaureguizar and ticulated skeletons, offering a unique opportunity to perform paleobio
Cladera, 2006; Pascual and Odreman Rivas, 1971; Pascual and logical studies based on a form-function approach (Vizcaíno et al.,
Ortiz-Jaureguizar, 1990). The analysis of Hinojosa (2005) of early and 2012d). For these authors, the fact that many taxa come from certain
middle Miocene floras at 33–34◦ S latitude between 21 and 13 Ma, levels deposited in a restricted time frame provides a narrow temporal
suggests an increase in mean annual temperatures (MATs) from the late window that allows reliable paleoecological analysis (Kay et al., 2012;
Oligocene-early Miocene from 16–17 ◦ C to MATs exceeding 22 ◦ C. Perkins et al., 2012). Vizcaíno et al. (2010) used the relationship be
Likewise, at the beginning of the Miocene, the floras indicate an even tween population density and body size for estimating the on-crop
more abrupt rise in rainfall, which culminated in values exceeding 1000 biomass (in kg/km2) of the species of these paleocommunities and
mm. During the middle and late Miocene, rainfall subsided, reaching calculated their metabolic requirements. Kay et al. (2012) reconstructed
minimum values of ~440 mm by around 10 Ma (Hinojosa, 2005). The the niche structure by identifying the number of species present, the
expanded faunal samples and precise dating of our early-middle body size, locomotion, and diet of the mammalian genera at the suite of
Miocene SCF localities (Trayler et al., 2020b) make them ideal candi localities FL 1–7 compared with similar kinds of data for extant faunas of
dates for evaluating Patagonian climate and biota nearly 20◦ farther South America; using that data they interpreted the paleoclimate and
south that Hinojosa’s localities, practically at the southern end of the paleoenvironment of FL 1–7. The FL 1–7 fauna was later studied by
continent. Spradley et al. (2019) updating the approach of Kay et al. (2012) to
Historically, the record from the Río Santa Cruz (RSC) represents the derive paleoecological predictive models for the same Atlantic Coast
first systematic and exhaustive effort for collecting and studying verte fauna and the Miocene La Venta fauna of Colombia. Finally, Rodrí
brate fossils from Patagonia, planned by Francisco P. Moreno and guez-Gómez et al. (2020) estimated the biomass of the primary and
executed by Carlos and Florentino Ameghino in 1887 (Brinkman and secondary consumers of the paleoecosystem to assess if the resources
Vizcaíno, 2014; Fernicola et al., 2014, 2019b; Vizcaíno et al., 2013). For available would satisfy the nutritional requirements of all species of
the following three or four decades, the material and intellectual results secondary consumers.
of this first and subsequent expeditions undertaken by Carlos and pub The results of the foundational work by Kay et al. (2012) were pre
lished by Florentino stimulated important academic institutions of the sented as the concluding chapter of a volume on the paleobiology of the
world to obtain their own collections of fossils from the SCF (Vizcaíno Santacrucian biota recorded on the Atlantic Coast edited by some of the
et al., 2013, 2016, 2017b). Especially during that period, the Santa Cruz authors of this contribution (Vizcaíno et al., 2012a). When considering
fossils became an inescapable reference for comparing other vertebrate the future direction of their research program, Vizcaíno et al. (2012d)
continental faunas, either older or younger. proposed to expand this approach to a more complete geographic and
Conceptually, the Ameghino collections were crucial for under chronologic range of the SCF, recording the different assemblages at
standing and setting the succession of Cenozoic faunas from Patagonia different levels and evaluating the ecological changes that occurred
(Ameghino, 1906) and constituted the basis for the establishment of the during the time of deposition of the formation in different areas. The
Santacrucian South American Land Mammal Age (SALMA) (Pascual aforementioned update of the RSC stratigraphy and fossil record pro
et al., 1965). With the addition of fossils from other SCF localities, vides an invaluable opportunity to achieve that undertaking in the his
especially those from the Atlantic coast outcrops, their abundance and torically and scientifically most significant location of the SCF and its
quality makes them the best material for interpreting the taxonomic fossil record.
richness and biological diversity of mammals in Patagonia after the The main goal of this contribution is to reconstruct the paleoecology
mid-Cenozoic arrival of primates and rodents, but before the arrival of (paleoclimate and paleoenvironment) of two temporally-restricted and
North American immigrants as part of the Great American Biotic distinct, mostly non-overlapping fossil faunas recovered by us along the
Interchange (GABI) (Vizcaíno et al., 2012d). Recent intensive fieldwork RSC compared with the temporally constrained and slightly older FL 1–7
has refined the stratigraphy and the vertebrate fossil record of the SCF fauna of the Atlantic coast presented in Kay et al. (2012). We examine
from the right bank of the RSC compiled in a volume edited by Fernicola whether the SCF fauna differed among three distinct temporal intervals
et al. (2019a). In that volume, Fernicola et al. (2019b) proposed that the of the SCF spanning, from the oldest in the Atlantic coast FL 1–7, at
exposures along the RSC should be considered the type area for the SCF about 17.4 Ma (Trayler et al., 2020b), to the youngest localities in the
and its fauna. The work constitutes a starting point for comparisons with RSC Barrancas Blancas, between ~17.2 and ~16.3 Ma, and Segundas
other early and middle Miocene exposures and faunas in Patagonia with Barrancas Blancas, between ~16.5 and ~15.6 Ma (Cuitiño et al., 2016,
2
R.F. Kay et al. Journal of South American Earth Sciences 109 (2021) 103296
2019a). The SCF is superbly exposed along coastal cliffs and wave-cut plat
forms south of Río Coyle, including sites such as Anfiteatro, Estancia La
2. Background Costa, Cañadón Silva and Puesto Estancia La Costa (Fig. 1). In this area,
the SCF is lithologicaly similar to that of the RSC, including thicknesses
2.1. Geological setting of a maximum of 100 m (Matheos and Raigemborn, 2012; Tauber,
1997a). Fossil levels (FL) 1 to 7 were defined in laterally continuous
The SCF is an early to middle Miocene lithostratigraphic unit widely package about 35 m thick of exposures in the Estancia La Costa Member,
distributed in the Austral Basin and mostly composed of fine-grained (Kay et al., 2012; Tauber, 1997a). The age of this composite level is
fluvial sediments, showing thickness variations from about 500 m based on the age of two radiometrically dated tuffs that bracket it: the
close to the Andean foothills to about 200 m at the Atlantic coast. In CO tuff of Perkins et al. (2012), and the CV-13 tuff of Trayler et al.
terms of stratigraphy and sedimentology, the best known localities are (2020b). The former as refined by high-precision U–Pb age modeling is
along the Atlantic coast between Río Coyle and Río Gallegos (Matheos 17.31 Ma and the latter is 17.62 Ma (Trayler et al., 2020b).
and Raigemborn, 2012; Tauber, 1997a, 1997b; Trayler et al., 2020b;
Zapata, 2018), inland along Río Santa Cruz and Río Chalía (Cuitiño
et al., 2016, 2019a, 2021; Fernicola et al., 2014), and in the Andes south 2.2. Santacrucian fauna
of Lago Posadas (Cuitiño et al., 2019b) (Fig. 1). Age assignments for the
SCF in western (Andean) localities suggest a time of accumulation be In addition to what was mentioned above, the fossils of the SCF are
tween 18.5 and 14 Ma (Blisniuk et al., 2005), whereas in the eastern part the best record for interpreting the biological diversity of mammals in
of the basin this time span is restricted between 18 and 15 Ma (Cuitiño the southern part of South America (Patagonia) prior to the GABI
et al., 2016, 2021; Perkins et al., 2012; Trayler et al., 2020b). (Vizcaíno et al., 2012d). As noted by Simpson (1980) this fauna is
The SCF crops out in several localities along the escarpments of the particularly important for understanding a phase in the history in which
east-west oriented valley of the RSC. Most of the best exposures are the communities of South American mammals consisted of a complex
located along the southern margin of this valley, from which recent mixture of descendants of ancient lineages of the continent (meta
surveys provided novel sedimentologic, geochronologic and paleonto therians, xenarthrans, astrapotheres, notoungulates and litopterns) and
logic data (Fernicola et al., 2019a). Following the original nomenclature new immigrants (primates and rodents) from other land masses (prob
of Carlos Ameghino, these localities are known from east to west as ably Africa) (Antoine et al., 2012; Arnal et al., 2020; Boivin et al., 2017;
Barrancas Blancas (BB), Segundas Barrancas Blancas (SBB) and Yatén Bond et al., 2015; Kay, 2015a, 2015b; Lavocat, 1976; Seiffert et al.,
Huageno (YH) (Fernicola et al., 2014). In BB the SCF lies transitionally 2020). Fossil mammals include small paucituberculatans and caenoles
above the early Miocene shallow marine deposits of the Monte León tids, medium to large carnivorous sparassodonts (Metatheria), several
Formation, while its base is covered in western localities. In turn, the armadillos, some medium-sized glyptodonts, a large diversity of me
SCF is overlaid everywhere by fluvial terrace conglomerates of late dium to large-bodied sloths, and one small anteater (Xenarthra), a large
Miocene-Pliocene age showing a sharp, regionally extensive erosional astrapothere (Astrapotheria), several small typotheres, two medium to
surface. large toxodontids, a large homalodothere (Notoungulata), some pro
In the RSC valley, the SCF is mostly composed of partly pedogenized terotheriids and a medium-sized macraucheniid (Litopterna), as well as
fine-grained fluvial deposits accumulated on fluvial floodplains. Sparse many caviomorph rodents (Rodentia), and a medium-sized platyrrhine
lenticular sandstones represent accumulation within fluvial channels. monkey (Primates).
Tabular, fine-grained tuff and tuffaceous horizons are also common There is also a rich assemblage of birds (Rheiformes, Tinamiformes,
(Fig. 2). Zircon U–Pb ages from these tuffs, in combination to calculation Gruiformes, Anseriformes, Pelecaniformes, Ciconiiformes, Falconi
of sedimentation rates, constrain the time span of the SCF to between formes, and Cariamiformes) (Degrange et al., 2012; Diederle and Nor
~17.2 and ~16.3 Ma for Barrancas Blancas, and between ~16.5 and iega, 2019). Unaccountably, no crocodilians and turtles are recorded,
~15.6 Ma for Segundas Barrancas Blancas (Cuitiño et al., 2016, 2019a). but among the herpetofauna there are anurans and several squamates,
including a tupinambine teiid and some iguanians and colubrids (Albino
Fig. 1. Map of the southern region of Santa Cruz Province showing the distribution of the Santa Cruz Formation (in yellow) and the localities studied. On the Atlantic
coast, FL 1–7 refers to the penecontemporaneus localities Anfiteatro (1), Estancia La Costa (2), Cañadón Silva (3), and Puesto Estancia La Costa (4) (Kay et al., 2012).
In the Río Santa Cruz, Barrancas Blancas (BB), Segundas Barrancas Blancas (SBB) and Yatén Huageno (YH). (For interpretation of the references to color in this figure
legend, the reader is referred to the Web version of this article.)
3
R.F. Kay et al. Journal of South American Earth Sciences 109 (2021) 103296
Regarding the fossil mammals recently collected in the RSC, Ferni
cola et al. (2019c) reported 1828 specimens from the three localities
(540 specimens in Barrancas Blancas, 1267 in Segundas Barrancas
Blancas, and 21 in Yatén Huageno), comprising 64 species: 10 species of
metatherians (four Sparassodonta, five Paucituberculata, and one
Microbiotheria), 12 species of xenarthrans (five Folivora and seven
Cingulata), one astrapothere, nine notoungulates (three Toxodontia and
six Typotheria), seven litopterns (six Proterotheriidae and one
Macraucheniidae), 24 rodents (11 Octodontoidea, two Erethizontoidea,
five Cavioidea, and six Chinchilloidea), and one new species of primate
(Homunculidae) (Fig. 3). Combining the list of species of the new
collection with other species previously reported for the RSC and
recognized by the specialists in Fernicola et al. (2019a) the taxonomic
richness rises to 95 taxa (16 species of metatherians, 22 xenarthrans, two
astrapotheres, 16 notoungulates, 7 litopterns, 31 rodents, and one pri
mate (see Appendix 2 in Fernicola et al., 2019c). Following the work of
Fernández (2020), in gthe present contribution we identify three species
not reported by Fernicola et al. (2019c): the typotheres Protypotherium
compressidens Ameghino (1891), Interatherium rodens Ameghino (1887)
and I. extensus Ameghino, 1895.
3. Materials and methods
3.1. Selection of samples, localities, and levels
Fossil faunas. The study presented here is based on fossil vertebrate
collections recovered during fieldwork by the authors and their team
during 2013 and 2014 in the RSC at BB, and SBB. The RSC collection
includes more than 1900 specimens that are cataloged in the permanent
collections of the Museo Regional Provincial Padre M.J. Molina (MPM-
PV), Río Gallegos, Santa Cruz Province, Argentina. In the results section
we tabulate the number of specimens broken down by taxon. Most of
these specimens were reported in the volume edited by Fernicola et al.
(2019a). As in Kay et al. (2012), we based our analysis solely on the
collection made by us (i.e. not considering the old collections of un
certain provenance and stratigraphic level).
Additional faunal comparisons are based on specimen records from
our collecting expeditions in the SCF at FL 1–7 in Vizcaíno et al. (2012a).
The FL 1–7 fauna is a composite of specimens collected at pene
contemporaneous localities (Anfiteatro, Estancia La Costa, Cañadón
Silva, Puesto Estancia La Costa; Fig. 1) from the Estancia La Costa
Member of the SCF on the Atlantic coast south of Río Coyle, between 51◦
03′ and 51◦ 11’ S (Vizcaíno et al., 2012d). The fossil species lists are
updated from those reported by Vizcaíno et al. (2012a) and Kay et al.
(2012) based on systematic revisions and fieldwork work undertaken
since the collecting season of 2011.
Each fauna samples a different non-overlapping age range: FL 1–7 is
younger than a tuff designated CV-13 dated at 17.62 Ma and older than
the CO tuff (17.31 Ma) (Trayler et al., 2020b); BB is dated at between 17
Fig. 2. Age-correlated sedimentary sections of the Santa Cruz Formation at
Ma and 16.5 Ma, and SBB between 16.3 Ma and 15.6 Ma. A brief interval
Barrancas Blancas and Segundas Barrancas Blancas localities at the Río Santa
Cruz. Each section represents the integration from several closely-spaced partial of temporal overlap between BB and SBB contains no fossils (Fig. 2).
sections reported by (Cuitiño et al., 2019a). Zircon U–Pb ages from tuffs are For each fauna we present taxonomic identifications (genera and
indicated in red; all other ages are estimated upon sedimentation rates (Cuitiño species presence or absence), and the stratigraphic ranges at BB and SBB
et al., 2016, 2019a). (For interpretation of the references to color in this figure (Supplementary document S1). Stratigraphic ranges are adjusted by
legend, the reader is referred to the Web version of this article.) correlation based on reported radiometric ages, supplemented by
depositional rates.
et al., 2017; Fernicola and Albino, 2012; Muzzopappa, 2019). Our reports of absolute and relative abundance are based on spec
The 1887 expedition of Carlos Ameghino to the RSC produced more imen records in the MPM-PV collection catalogs. Species abundances are
than 2000 fossil specimens, on the basis of which his brother Florentino roughly comparable between most components of the fauna (meta
erected 110 new species of mammals (Ameghino, 1887), dramatically therians, notoungulates, primates, litopterns) because the identifiable
increasing the number of Santacrucian taxa from the 12 described parts are mainly dentitions, but xenarthran records are not comparable
earlier (see references in Fernicola et al., 2019b). Between 1887 and because they are based on other anatomical parts. This is especially the
1894, approximately 500 added taxa from the SCF were proposed by case for armored taxa for which the identification is based on dermal
Ameghino and Mercerat, of which about 120 type specimens came from scutes.
the RSC (Fernicola et al., 2019b). Extant Faunas. For the analysis of extant mammalian faunas, we used
a subset of 55 of the 85 faunas enumerated by Spradley et al. (2019)
4
R.F. Kay et al. Journal of South American Earth Sciences 109 (2021) 103296
Fig. 3. Exposures of the SCF at the Río Santa Cruz. A view of the river and exposures. B, Barrancas Blancas, and C, Segundas Barrancas Blancas. Life reconstructions
of some of the genera recorded at the Río Santa Cruz. Taxa >5 kg are approximately scaled and those < 5 kg (Abderites, Palaeothentes, Pachyrukhos and Homunculus)
are not. Modified from Chapters 10, 11, 12, 13, 14, 15 and 16 of Vizcaíno et al. (2012a,b,c,d).
from localities with restricted geographic areas across South America tropics and high latitudes (Ojeda and Mares, 1989; Patterson et al.,
(Fig. 4). We consider only the faunas of low elevation because the SCF’s 1998).
depositional environment indicates a lowland with little topographic The list of extant localities in Appendix A provides some of the
relief (Cuitiño et al., 2019a; Raigemborn et al., 2015, 2018a) and accompanying information about elevation above sea level, mean
because faunal composition is affected by altitude. Our upper-limit annual precipitation (MAP), mean annual temperature (MAT), as well as
cutoff is based conservatively on data for elevational gradients of summaries of niche metrics for modern and Santacrucian localities (see
vegetation, which are particularly significant above our cutoff elevation, below). Other data, including precipitation and temperature season
although the elevation at which the changes occur differs between the ality, canopy height, and net primary productivity are provided in
5
R.F. Kay et al. Journal of South American Earth Sciences 109 (2021) 103296
Fig. 4. The South American continent with
the position of the localities evaluated. Black
dots are extant faunas listed in Appendix A.
Three overlapping red stars are the Miocene
localities of the Santa Cruz Formation. The
four panels represent the mean annual tem
perature (◦ C), temperature seasonality (◦ C),
mean annual precipitation (mm), and pre
cipitation seasonality (Coefficient of Varia
tion of monthly rainfall). Data from NOAA
Physical Sciences Laboratory (PSL) (https://
psl.noaa.gov/data/gridded/data.UDel_Air
T_Precip.html). (For interpretation of the
references to color in this figure legend, the
reader is referred to the Web version of this
article.)
Supplementary document S2. The full list of 208 genera of extant non- Global Land Analysis and Discovery group of the University of Maryland
volant mammalian genera is found in Supplementary document S3. A (https://glad.umd.edu/dataset/gedi). Spatial maps of 30 arc-seconds
few updates were made to Spradley et al.’s faunal lists and based on resolution for MAP, MAT, and temperature seasonality and a resolu
other highly corroborated and complete lists in the literature (see notes tion of 30 arc-minutes for canopy height were then uploaded into QGIS®
in SD S1). The most significant difference between the lists reported here (QGIS.org, 2021). In order to extract the data for each locality. The
and those in Spradley et al. (2019) is that we count genera, not species sampling areas of the extant faunas represent a wide range of mean
(see Section 3.2). While it is likely that a few taxa go unrecorded in annual rainfall and the faunas range in latitude from 10◦ N to 55◦ S. Both
Spradley’s list and ours, this procedure provides a more reliable repre floral diversity and the complexity of vegetation in the lowland tropics is
sentation of any given fauna at a locality than does the use of distribu strongly correlated with annual rainfall (Gentry, 1988). At one extreme,
tion maps (Spradley et al., 2015). at Río Caura, Estado Bolívar, Venezuela, rainfall exceeds 3.5 m per year
MAP, MAT, and temperature seasonality data for all localities were with no appreciable dry season. At the other extreme at Parque Nacional
obtained through the online database WorldClim.org (https://www.wor Bosques Petrificados de Jaramillo, Santa Cruz Province, Patagonia,
ldclim.org/data/bioclim.html) as high-resolution spatial data. MAP is Argentina, with rainfall ~200 mm per annum and dry the year around.
defined as the sum annual precipitation in millimeters averaged over the Mean annual temperature for the extant ranges from ~28 ◦ C at Puerto
course of a thirty-year span (1970–2000) (O’Donnell and Ignizio, 2012). Páez, Estado Apure, Venezuela to ~4 ◦ C at Parque Nacional Tierra del
MAT is defined as the annual mean temperature in degrees Celsius as Fuego, Provincia de Tierra del Fuego, Argentina. In environments where
calculated from the mean monthly temperatures for a given year. rainfall exceeds 2000 mm/year and a dry season lasts fewer than 4
Temperature seasonality is defined by O’Donnell and Ignizio (2012) as months, evergreen rainforest predominates. In regions with less than
“the amount of temperature variation over a given year (or averaged 1000 mm of rainfall and dry intervals longer than 6 months, the domi
years) based on the standard deviation (variation) of monthly temper nant vegetation is drought-resistant and deciduous. Areas of interme
ature averages”, and is also measured in degrees Celsius. Precipitation diate rainfall between 1000 and 2000 mm/year with 4–6 months of dry
seasonality (expressed as a percentage) is the coefficient of variation of season tend to exhibit semideciduous forests, often as riparian gallery
the monthly total precipitation to the mean monthly total precipitation. forests with interspersed savannas.
Spatial data for canopy height (in meters) were downloaded from the
6
R.F. Kay et al. Journal of South American Earth Sciences 109 (2021) 103296
3.1.1. Use of genus as the level of interest Basic ecological information for each extant genus was compiled
Kay et al. (2012) analyzed the SCF fauna at the generic level whereas from the literature (Supplemental Document S3). These include cate
Spradley et al. (2019) used species rather than genera as the unit of gorical variables for average body mass, primary diet, and preferred
comparison. We have transformed Spradley’s dataset into one that uses locomotion, which, in combination, permit a general evaluation of the
genera. In choosing the generic level for our analysis, we recognize that role of the genus in niche space (Vermillion et al., 2018), as described in
we may be sacrificing sensitivity in detecting differences in community Table 1. The niche structure of the fossil mammalian genera from FL
structure but this choice is made for several reasons. First is the problem 1–7, BB, and SBB given in Appendix B, is based upon ecomorphological
of detection bias. The likelihood of recovering a high percentage of the reconstructions presented in Vizcaíno et al. (2012a) with updates
species present in a fossil community must be far lower than that for the (Álvarez and Arnal, 2015; Álvarez and Pérez, 2019; Arnal and Vucetich,
recovery of most of its genera. 2015b; Cassini, 2013; Muñoz et al., 2019; Toledo, 2016; Toledo et al.,
Second, the recognition of fossil species is much more problematic 2014).
than the recognition of genera. Hapalops Ameghino, 1887 is a classic To evaluate the community structure of the extant faunas, we use
example (Bargo et al., 2019; Kay et al., 2012). Ameghino (1887, 1891, total generic richness or total herbivore richness, and the indices devised
1894) named a vast number of species. Scott (1903–1904) recognized 22 by Kay and Madden (1997a; 1997b) to express the number of genera
species of Ameghino’s as likely valid and listed another 15 for which he within a guild (that is, with a particular niche specialization or within a
“could arrive at no definite conclusion (page 258)”. Bargo et al. (2019) body size range) relative to total number of genera.
would further reduce the number of Hapalops species at BB and SBB to
one, with certainty, and an uncertain number of others for which there is 1. Frugivore Index expresses the proportion of frugivorous and seed-
insufficient information. Such uncertainly would render any effort to eating species to the total number of plant-eating species in the
reconstruct paleoecology based on species numbers problematic fauna:
whereas the number of genera is more stable.
Third, morphologically-defined genera sensu Mayr (1950) 1 have 100*(F(I) + S + F(L))/(F(I) + S + F(L) + L + G + Sc (Tu) + Sc(L))
been used with success as the primary analytical units for a wide range
of large-scale paleontological analyses in paleoecology. The justification 2. Browsing Index expresses the proportion of browsing or leaf-eating
is that analyses of genus-level operational units generally capture (i.e., shrub and tree leaves and forbs) species to the total number of
species-level patterns (Jablonski and Finarelli, 2009). The genus taxon grazing and browsing species in the fauna:
also was preferred by for an analysis on the evolution of body size in 100*(L)/ (L + G)
Cenozoic mammalian herbivores from South America “because they are
discrete taxonomic units accepted by most paleontologists, and they are
less affected by the problems of evaluating intraspecific variation in
fossils” (pg. 82 in Vizcaíno et al., 2012b). Table 1
Definitions of the ecological categories used in this study. Each genus is assigned
3.1.2. Should we limit the analysis to taxa greater than 500 g? a number from each variable. Locomotion/substrate preference (six categories)
following Fleming (1973) and Andrews et al. (1979).
Often, comparison among faunas for the purpose of assessing
paleoecology, paleoclimate or the driving factors of mammalian biodi Body Definition Locomotor Definition Dietary Definition
versity restrict their comparisons to species that exceed 500 g in body Mass Category Category
Category
size because data for smaller taxa are sensitive to detection bias (Reed,
1998; Robinson et al., 2017; Rowan et al., 2016, 2020). We include these 1 (I) 10–100 g 1: LT large 1: Vert vertebrate
terrestrial prey
smaller taxa for two reasons: as already noted, using genera rather than
(>1 kg)
species should compensate for detection bias. Second, at least in the 2 (II 100 g-1 2: ST small 2: Sc(I) scavenging
Neotropics, species (and generic) richness of small mammal taxa (pri kg terrestrial and insects
mates, small rodents, metatherians) varies from place to place whereas (500 kg 6: T(F) fossorial 6: I(F) insects (with
(including some fruit or
For reconstructing the niche structure of all faunas, we identify the semi- nectar)
number of genera present at the modern localities and fossil sites, the fossorial)
body size, substrate preference and use, and diet of the taxa, as deter 7: F(I) fruit (or
gum), with
mined by behavioral studies of the living genera and as inferred from some animal
ecomorphology in the case of the fossil genera. protein
8: S small seeds
of grasses
1 (and other
Morphologically-defined genera (morphogenera) are defined by Mayr
plants or
(1950) as: “… one [or several] species of common ancestry, which differ in a insects)
pronounced manner from other groups of species and are separated from them 9: F(L) fruit with
by a decided morphological gap,” Genera are considered by Mayr to occupy leaves
adaptive plateaus “based on a more fundamental difference in ecology than that 10: L leaves
between the ecological niches of species.” To this is sometimes added the caveat (browse)
that paraphyletic taxa are inadmissible (Wood and Collard, 1999). In any event, 11: G stems and
as noted by Jablonski and Finarelli (2009), a significant percentage of mor leaves of
grasses
phogenera are monophyletic (Jablonski and Finarelli 2009) and species and
(graze)
genus-level diversification dynamics are comparable (Liow and Finarelli, 2014).
7
R.F. Kay et al. Journal of South American Earth Sciences 109 (2021) 103296
3. Arboreality Index is used to express the proportion of arboreal The Simpson Coefficient of faunal similarity is 76.3% between FL 1–7
species to the total number of non-volant species: and BB, 81.6% between FL 1–7 and SBB, and 92.1% between BB and
SBB.
100*(A + 0.5*A(T)/ (sum of all locomotor categories)
To interpret the comparison of SI between the fossil localities, we
examined a cluster of seven extant localities: Reserva de la Biosfera y
4. Predator/prey ratio expresses the proportion of secondary
Estación Biológica del Beni, Bolivia, Parque Nacional Madidi, Bolivia,
consumers Parque Nacional Noel Kempff Mercado, Bolivia, Estación Biológica
Cocha Cashu, Peru, Reserva Nacional Tambopata, Peru, Parque Nacio
100*((Vert + Sc(I) + Sc(Tu) + Sc(L) + MYR + I(F))/all herbivores nal del Manú, Peru, Otishi National Park, Peru, and Manaus, Brazil
(Appendix A). These localities are at low elevation (less than 600 masl),
5. Size Index: expresses the proportion of species in size classes II and between 2.5◦ and 14.6◦ S, separate by an average of 184 km, and have an
III relative to those in class IV an V where the size classes are II = average rainfall of 2142 ± 561 mm. There are 28 pairwise comparisons
100–1000 g; III = 1–10 kg; IV = 10–500 kg; V = >500 Kg: possible among these localities. They have an average Simpson’s Index
of 67% with a range of 34%–90%. There is significant correlation be
100*(Class II + Class III)/ Class IV + Class V tween SI and distance between the localities in this sample (R2 = 0.70, P
< 0.0001). On the other hand, SI and rainfall are not correlated signif
In comparing the rodents of the three fossil faunas we present a
icantly between the localities (R2 = 0.010, P = 0.62). The SI values of the
discrete variable for cheek-tooth crown height (hypsodonty). Hyp
three SCF localities, separated by a maximum of 125 km, fall within the
sodonty is based on the relationship between the height of the crown and
range expected for such a distance. In other words, in terms of faunal
the anteroposterior length of the crown of the lower molars (Janis and
similarity, the three SCF faunas, despite their temporal separation, do
Fortelius, 1988). Arnal (2011) evaluated the grade of hypsodonty as
not differ more than would be expected for localities with similar
follows: brachydont: ratio of mesiodistal length/crown height < 0.5;
geographic distance of separation.
mesodont: ratio < 1.0; protohypsodont ratio >1.0 but forming a root;
euhypsodont (rootless crown). From this we derive a hypsodonty score
4.1.1. Meridiolestida
(HS), HS is the percentage of specimens of each crown height weighted
The early Miocene meridiolestidan Necrolestes (Rougier et al., 2012;
by crown height with euhypsodont taxa counting for 3: protohypsodont,
Wible and Rougier, 2017) has been recorded in the SCF, but it is un
2: mesodont, 1: and brachydont, 0. The total score is divided by the
common. All remains come from coastal SCF. The type specimen is from
maximum possible score if all taxa were euhypsodont, i.e., 300, and is
Monte Observación (Ameghino, 1891) and the specimens from Prince
expressed as a percentage. If all specimens are euhypsodont, the score is
ton University/Yale Peabody Museum Collection (YPM-VPPU; JB
100%; if all are brachydont the weighted score is 0%.
Hatcher’s old collections) are from south of Río Coyle along the Atlantic
The Simpson Coefficient of faunal similarity (SI) (Simpson, 1943) is
coast and Killik Aike Norte on the Río Gallegos. We have recovered three
used to compare some of the faunas. SI is 100*(C/N1) where C is the
specimens of Necrolestes (cranial and mandibular remains) in FL 1–7,
number of taxa in common between two faunas and N1 is the total
one in Cañadón de las Vacas and one in Rincón del Buque (Fig. 1), but
number of taxa in the smaller sample.
have not recorded it so far in the RSC localities.
Necrolestes has anatomical specializations found in extant subterra
3.3. Statistical analyses nean mammals. Recent studies proposed that it was as a head-lift digger,
by analogy with extant African golden moles and Australian marsupial
Least-squares regressions using linear and second degree polynomial moles; analysis of the ear region supports the inference that it was
models and Principal Components analysis (using a correlation matrix) adapted for subterranean habits (Wible and Rougier, 2017).
were carried out with JMP® Pro 15.0.0 for Mac.
We also estimated environmental parameters using two machine- 4.1.2. Metatheria
learning models, random forest (RF) and Gaussian process regression Metatherians (Sparassodonta and Paucituberculata) are relatively
(GPR), previously used in paleoenvironmental reconstruction by infrequent elements of the SCF. We identified 95 metatherian specimens
Spradley et al. (2019). These machine-learning models take advantage in our collections from FL 1–7, BB, and SBB: 43, 15, and 37, respectively.
of the same multivariate approach as a linear regression, while also At FL 1–7, 11 genera and 14 species are recorded; at BB, there are 5
incorporating relationships between geographically closely related data genera and 7 species and; at SBB, 8 genera and 10 species (Table 2).
points in order to model even non-linear relationships between variables There seems to be a taphonomic bias in the collections made at the
(see Spradley et al., 2019 for further explanation of RF and GPR and different localities. Sparassodonts (45 records) are clearly more abun
their utility in paleoenvironmental reconstruction). The models were dant in FL 1–7 (where more complete and articulated specimens appear)
derived from the ecological indices discussed above, and were used to than in the RSC localities: 31 in FL 1–7, 4 in BB, and 10 in SBB. We
estimate mean annual precipitation (MAP), mean annual temperature recorded 8 genera and 8 species in FL 1–7, 2 genera and species in BB
(MAT), temperature seasonality, and canopy height at FL 1–7, BB, and and 4 genera and species in SBB. Borhyaena and Sypalocion are present in
SBB. As demonstrated in Spradley et al. (2019), these machine learning the three localities; Cladosictis and Perathereutes appear in the coast and
models have the ability to effectively estimate temperature seasonality SBB, and Prothylacynus, Lycopsis and Acrocyon are recorded only in FL
and canopy height, in addition to MAP and MAT, in an extant 1–7. However in the old collections of RSC, there are records of Acyon,
species-level dataset from Australia as well as South America. Error es Acrocyon, and Lycopsis (Fernicola et al., 2019c). This highlights the need
timates are presented as mean absolute error (MAE). to use caution when evaluating predator-prey ratios in these faunas.
Sparassodonts were part of the predator guild, being mainly hyper
4. Results carnivores. They exhibited different locomotor abilities (from scansorial
to terrestrial) and a wide range of body masses, from 1 kg to ~40 kg).
4.1. Review of mammalian occurrences Prevosti et al. (2012) reconstructed the Santacrucian predator guild and
suggested that there was a good niche partition within these
Our sample of fossil mammals includes 44 genera from FL 1–7, 38 sparassodonts.
genera from BB, and 44 genera from SBB (Appendix B). These faunas are Paucituberculatans (50 records) are more abundant in the RSC,
very similar to one another at the generic level. FL 1–7 and BB share 29 particularly in SBB (12 in FL 1–7; 11 in BB; 27 in SBB), where fossils are
genera; FL 1–7 and BB share 31 genera and BB and SBB share 35 genera. more fragmentary and more small remains are found. At FL 1–7 we
8
R.F. Kay et al. Journal of South American Earth Sciences 109 (2021) 103296
Table 2
Occurrence and frequency of metatherian specimens at FL 1–7, Barrancas Blancas, and Segundas Barrancas Blancas.
Taxon FL 1-7 Barrancas Blancas (BB) Segundas Barrancas Blancas (SBB)
a b a b
Higher level classification Genus P/A N sp◦
N Freq. (%) P/A N sp.
◦
N Freq. (%) P/A N◦ sp. Na Freq. (%)b
SPARASSODONTA
Hathliacynidae Cladosictis 1 1 8 28.6 0 0 0.0 1 1 4 40.0
Sipalocyon 1 1 4 14.3 1 1 3 75.0 1 1 2 20.0
Perathereutes 1 1 1 3.6 0 0 0.0 1 1 1 10.0
Prothylacynus 1 1 2 7.1 0 0 0.0 0 0 0.0
Hathliacynidae indet. 5 17.9 0 0.0 0 0.0
Borhyaenidae Borhyaena 1 1 8 28.6 1 1 1 25.0 1 1 1 10.0
Lycopsis 1 1 1 3.6 0 0 0 0.0 0 0 0 0.0
Arctodictis 1 1 1 3.6 0 0 0.0 0 0 0.0
Acrocyon 1 1 1 3.6 0 0 0.0 0 0 0.0
Borhyaenidae indet. 0 0.0 0 0.0 2 20.0
Summary 8 8 31 2 2 4 4 4 10
PAUCITUBERCULATA
Palaeothentiidae Palaeothentes 1 4 10 90.9 1 3 9 81.8 1 3 22 81.5
Acdestis 1 1 1 9.1 1 1 1 9.1 1 1 2 7.4
Microbiotheriidae Microbiotherium 1 1 1 0 0 0.0 1 1 2 7.4
Abderitidae Abderites 0 0 0.0 1 1 1 9.1 1 1 1 3.7
Summary 3 6 12 3 5 11 4 6 27
SUMMARY ALL TAXA 11 14 43 5 7 15 8 10 37
a
number of catalog entries.
b
Frequency of occurrence (number of subordinal records) divided by the total records at this locality. P/A, presence/absence; Freq., frequency.
recorded 3 genera and 6 species, 3 genera and 5 species in BB, and 4 features in the specimens we collected (Fernicola and Vizcaíno, 2019).
genera and 6 species in SBB (Table 2). Santacrucian glyptodonts are moderately large (up to 120 kg) and
Palaeothentes is, by far, the most abundantly recorded everywhere. ambulatory selective feeders in relatively closed to strictly closed hab
Palaeothentes recorded at RSC are medium to large-sized curso-saltato itats (Vizcaíno et al., 2011, 2012c).
rial insectivorous species ranging from ~80 g to 900 g; (Abello et al., The armadillos Proeutatus and Prozaedyus are the most abundant and
2012); the larger, more frugivorous Palaeothentes aratae (Strait et al., frequent cingulates at all localities, while Stenotatus is more frequent/
1990) was not identified at the RSC. The medium-sized insectivore- abundant in the Río Santa Cruz. Peltephilines are more common in the
frugivore Acdestis oweni and the frugivorous/scansorial Abderites mer coastal localities than in the RSC, but they are less frequent than the
idionalis were both recorded at BB and SBB (Chornogubsky et al., 2019). other three taxa. We did not record Stegotherium at FL 1–7, and in the
We have no records of Stilotherium, which is found in the old collections RSC we found only three osteoderms at BB, suggesting that it was quite
at RSC (Fernicola et al., 2019c). Stilotherium likely had an insectivorous rare. All Santacrucian armadillos were diggers and the variation of the
diet based on the morphology of its cheek teeth illustrated by Abello masticatory apparatus shows a broad range of specializations from
et al. (2021). herbivory and strict myrmecophagy. The taxonomic richness and di
versity of armadillos supports the environmental interpretation of a
4.1.3. Xenarthra mixture of open and relatively closed vegetation in relatively dry con
Among xenarthrans, Cingulata and Folivora are disparately repre ditions (Vizcaíno et al., 2012c).
sented among the moderate to large mammals of the SCF. We recorded Folivora (sloths) are also abundant elements of the SCF. However, as
550 specimens of xenarthrans in our collections (129 in FL 1–7, 191 in with cingulates, skeletal remains such as skull and mandibles are rare
BB, and 230 in SBB; Table 3). At FL1-7 we recorded 13 genera and 15 and postcranial elements are particularly abundant, which makes
species, 9 genera and 9 species at BB, and 10 genera and 10 species at taxonomic allocations difficult (Bargo et al., 2019). We recorded 123
SBB. specimens of sloths (57 in FL 1–7, 20 in BB and 46 in SBB). At FL 1–7 we
Cingulates (armadillos and glyptodonts) remains are probably the recorded 6 genera and 8 species, one genus and species in BB and 5
most frequently found in the field, due to the more than 1000 osteo genera and species in SBB. The most common sloth remains are un
derms that constitute an individual carapace. Other skeletal remains are identifiable postcranial elements of Megatherioidea indet. (FL1-7: 53%,
uncommon, especially skulls, mandibles, and teeth. Particularly for the BB: 80% and SBB: 67%, Table 3). Hapalops is the only genus recorded in
glyptodonts, precise specific or even generic allocation of osteoderms the three localities, with the highest abundance, and Schismotherium and
may depend on the association with cranial remains (Fernicola and Nematherium are recorded on the coast and at SBB. While Pelecyodon,
Vizcaíno, 2019). Beyond those specimens with carapace associated with Hyperleptus and Eucholoeops record only in the coast, Xyophorus records
endoskeleton, our collecting strategy for cingulates was to collect a few are only in the RSC (SBB). Remarkably, we recorded megatheriids only
osteoderms from each locality and level to document taxon pre in the highest levels of the RSC (at SBB), but they are not recorded so far
sence/absence. We recorded 426 specimens or lots of osteoderms: 121 BB or FL1-7. The Planopinae indet at Segundas Barrancas Blancas is
glyptodonts (13 in FL 1–7, 48 in BB and 60 in SBB), and 305 armadillos either Planops or Prepotherium, see Bargo et al. (2012). Planopinae are
(58 in FL 1–7, 123 in BB, and 124 in SBB). At FL 1–7 and BB two genera the largest of the Santacrucian sloths (100–120 kg (Toledo et al.,
and species of glyptodonts were recorded, while in SBB only one. 2014);). Megatherioid sloths have body masses from ~40 to 80 kg, while
Armadillos are represented by four genera and species at FL 1–7, 5 in BB, mylodontids reached ~80–90 kg. According to Toledo (2016) the
and 4 in SBB (Table 3). mid-sized sloths (Hapalops, Pelecyodon, Schismotherium, Hyperleptus and
Glyptodonts (Propalaehoplophoridae) are very common components Eucholoeops) are members of the arboreal folivore paleoguild. The
of the SCF. mylodontid Nematherium may have been semiarboreal consumers of
Cochlops and Eucinepeltus are recorded in the three localities. The leaves, fruits and tubers due to their digging capabilities, while
absence of Propalaehoplophorus in our collections but present in the old megatheriids were the most terrestrial sloths, and folivores.
collections at RSC may be an artifact due to the lack of diagnostic Vermilingua (anteaters) are poorly represented in the SCF (Bargo
9
R.F. Kay et al. Journal of South American Earth Sciences 109 (2021) 103296
Table 3
Occurrence and frequency of xenarthran specimens at FL 1–7, Barrancas Blancas, and Segundas Barrancas Blancas.
Taxon FL 1-7 Barrancas Blancas (BB) Segundas Barrancas Blancas (SBB)
a b a b
Higher level classification Genus P/A N sp.
◦
N Freq. (%) P/A N sp.
◦
N Freq. (%) P/A N◦ sp. Na Freq. (%)b
CINGULATA
Propalaehoplophoridae Cochlops 1 1 2 15.4 1 1 12 25.0 0 0 0 0.0
Eucinepeltus 0 0 0 0.0 1 1 2 4.2 1 1 11 18.3
Propalaehoplophorus 1 1 4 30.8 0 0 0 0.0 0 0 0 0.0
Propalaehoplophori- dae indet. 7 53.8 34 70.8 49 81.7
Summary 2 2 13 2 2 48 1 1 60
Peltephilidae Peltephilus 1 1 12 20.7 1 1 7 5.7 1 1 7 5.6
Dasypodidae Proeutatus 1 1 26 44.8 1 1 42 34.1 1 1 43 34.7
Stenotatus 1 1 2 3.4 1 1 26 21.1 1 1 22 17.7
Prozaedyus 1 1 15 25.9 1 1 47 38.2 1 1 52 41.9
Stegotherium 0 0 0 0.0 1 1 1 0.8 0 0 0 0.0
Dasypodidae indet 3 5.2 0.0 0.0
Summary 4 4 58 5 5 123 4 4 124
VERMILINGUA
Myrmecophagidae Protamandua 1 1 1 100.0
Summary 1 1 1 0 0 0 0 0 0
FOLIVORA
Megatherioidea Hapalops 1 2 12 21.1 1 1 3 15.0 1 1 6 13.0
Pelecyodon 1 1 2 3.5 0 0 0 0.0 0 0 0 0.0
Hyperleptus 1 1 1 1.8 0 0 0 0.0 0 0 0 0.0
Schismotherium 1 1 3 5.3 0 0 0 0.0 1 1 1 2.2
Xyophorus 0 0 0 0,0 0 0 0 0,0 1 1 1 2,2
Megatherioidea indet. 30 52.6 16 80.0 31 67.4
Megatheriidae Planopinae indet. 0 0 0 0.0 0 0 0 0.0 1 1 2 4.3
Megatheriidae indet. 0.0 0.0 4 8.7
Megalonychidae Eucholoeops 1 2 6 10.5 0 0 0 0.0 0 0 0 0.0
Mylodontidae Nematherium 1 1 2 3.5 0 0 0 0.0 1 1 1 2.2
Mylodontidae indet. 1 1.8 1 5.0 0.0
Summary 6 8 57 1 1 20 5 5 46
SUMMARY ALL TAXA 13 15 129 9 9 191 10 10 230
a
Number of catalog entries.
b
Frequency of occurrence (number of subordinal records) divided by the total records at this locality. P/A, presence/absence; Freq., frequency.
Table 4
Occurrence and frequency of typothere, toxodont, astrapothere and litoptern specimens at FL 1–7, Barrancas Blancas, and Segundas Barrancas Blancas.
Taxon FL 1-7 Barrancas Blancas (BB) Segundas Barrancas Blancas (SBB)
Higher level classification Genus P/ N◦ of sp. Na Freq. (%)b P/ N◦ of sp. Na Freq. (%)b P/ N◦ of sp. Na Freq. (%)b
A A A
TYPOTHERIA
Hegetotheriidae Hegetotherium 1 1 40 23.3 1 1 11 22.4 1 1 10 3.6
Pachyrukhos 0 0 0 0.0 0 0 0 0 1 1 86 30.8
Interatheriidae Interatheriun 1 2 70 40.7 1 2 17 34.7 1 2 59 21.1
Protypotherium 1 3 62 36.0 1 3 21 42.9 1 4 124 44.4
Interatheriidae indet. 10 5.8 0 0
Summary 3 6 182 4 7 49 4 8 279
TOXODONTIA
Toxodontidae Nesodon 1 1 14 31.1 1 1 12 31.6 1 1 18 39.1
Adinotherium 1 1 30 66.7 1 1 24 63.2 1 1 18 39.1
Toxodontidae indet. 11 24.4 0 0
Homolodotheriidae Homalodotherium 1 1 1 2.2 1 1 2 5.3 1 1 10 21.7
Summary 3 3 56 3 3 38 3 3 46
ASTRAPOTHERIA
Astrapotheriidae Astrapotherium 1 1 8 100.0 1 1 4 100.0 1 1 12 100.0
LITOPTERNA
Proterotheriidae Anisolophus 0 0 0 0 1 1 1 7.7 1 1 15 51.7
Diadiaphorus 1 1 4 22.2 1 1 3 23.1 1 1 1 3.4
Thoatherium 1 1 8 44.4 1 1 4 30.8 1 1 6 20.7
Tetramerorhinus 1 1 2 11.1 1 2 3 23.1 1 2 3 10.3
Proterotheriidae indet. 13 72.2 0 0.0 1 3 10.3
Macraucheniidae Theosodon 1 1 4 22.2 1 1 2 15.4 1 1 1 3.4
Summary 4 4 31 5 6 13 6 6 29
SUMMARY ALL TAXA 11 14 277 13 17 104 14 18 366
a
Number of catalog entries.
b
Frequency of occurrence (number of subordinal records) divided by the total records at this locality. P/A. presence/absence; Freq.. frequency.
10R.F. Kay et al. Journal of South American Earth Sciences 109 (2021) 103296
et al., 2012). They are only recorded at FL1-7 by one specimen of Pro toxodontids. Homalodotherium is large (about 400 kg) brachyodont
tamandua, and there are no records at the RSC. clawed “ungulate” that may have been a browser that inhabited rela
tively closed habitats (Elissamburu, 2010).
4.1.4. Astrapotheria
Astrapotheres, the largest South American native ungulates, were 4.1.7. Litopterna
represented in the SCF by only one genus. We identified only 12 speci Litopterns are much less abundant than notoungulates in the SCF. We
mens as belonging to Astrapotherium: 8 in FL1-7, 4 in BB and 12 in SBB identified 73 specimens in our collections: 31 from FL 1–7, 13 from BB,
(Table 4. Fig. 5). Astrapotherium was a one-ton browser that inhabited and 29 from SBB (Table 4). Only 7 of them correspond to the macrau
closed habitats (Cassini, 2013). cheniid Theosodon (FL 1–7: 4 from, BB: 2, SBB: 1). We recorded 3 genera
and species of protherotheriids from FL 1–7, 4 genera and 5 species from
4.1.5. Typotheria both BB and SBB.
Typotheres are common elements of the SCF. We identified 510 According to Cassini et al. (2012) litopterns are brachyodont
typothere specimens in our collections from FL 1–7, BB, and SBB: 182, mixed-feeders (Theosodon; 100–150 kg) or browsers (protherotheriids;
49, and 279, respectively (Table 4). At FL 1–7, 3 genera are recorded 25–50 kg) in closed habitats.
(exact species counts are pending revisions). At BB, there are 3 genera
and 6 typothere species; at SBB 4 genera and 8 species. The composite 4.1.8. Rodentia
stratigraphic ranges for typothere genera are depicted in Fig. 5. Caviomorph rodents are by far the most abundant mammals in the
Most of the taxa are represented in similar abundances at FL 1–7 and SCF. We recovered more than 900 identifiable specimens from FL 1–7,
BB. Interatherium and Protypotherium have similar abundances and BB, and SBB: 250, 173, and 507, respectively. At FL 1–7, nine genera are
Hegetotherium is common but less abundant than the other two. The recorded (species identifications are pending revisions); at BB, there are
situation at SBB is quite different. While Interatherium and Protypothe 14 genera and 19 species; at SBB, 17 genera and 23 species (Table 5,
rium remain common, Hegetotherium declines in abundance with 4% of Fig. 6).
all typothere records versus 23% and 22% at FL 1–7 and BB. The likelihood of recording a taxon at a particular locality may
The clearest difference in typothere abundance is seen in Pachyr depend on its rarity, and be a consequence of sampling probability. In
ukhos. This taxon is at least very rare (but more probably absent) in our such cases, one cannot say with any certainty that a taxon would not also
material from FL 1–7 (one possible record out of 183 typothere speci have occurred at the other localities had we collected a sufficient
mens), nor does (Tauber, 1997a) record this taxon in the Ea. La Costa number of specimens. For example, we record one specimen of Dudumus
Member of coastal SCF, whereas it does occur in the overlying Ea. La at SBB (0.2%) but none occur at either FL 1–7 or BB. The same is true of
Angelina Member, and is common in some places, e.g., at Killik Aike Acaremys (none at FL 1–7, 1.2% at BB, 0.4% at SBB), "Eocardia" excavata
Norte2; more details are provided in (Vizcaíno et al., 2021). Pachyrukhos (0.4%, 2.9%, 0.8%), Schistomys (0%, 0% and 0.6%), Scleromys (0.8%,
is absent at BB but is by far the most common typothere at SBB (44%). 4.2%, 0.8%), and Prospaniomys (0%, 0.6%, 0.4%). Befitting their rarity,
As all the typotheres are characterized by euhypsodont cheek teeth, either Dudumus nor Prospaniomys were recorded in the old collections of
there is no evident trend in this respect. The appearance of Pachyrukhos RSC while Adelphomys, Pseudoacaremys are found in the old collections
in SBB is notable. This species is usually depicted as having been capable but not in our samples (Fernicola et al., 2019c). The more common ro
of moving rapidly using saltatorial locomotion. It had a short tail, limbs dent taxa (at least 5% of specimens occur at least in one locality) are
arranged in a parasagittal orientation; a long hindlimb with the prox represented in Fig. 6. In these commonly occurring taxa we may be on
imal segment much shorter than the distal all suggesting that it could safer ground to infer that the absence, or presence at a different level of
move rapidly using saltatorial locomotion (Cassini et al., 2012; Sinclair, frequency may indicate some difference in community structure.
1908). Its presence at SBB has been interpreted as indicative of more Most of the more common taxa are represented in similar abundance
open areas in comparison with BB, FL 1–7 and BB (Fernández and at all three localities. These include Sciamys (5.2% at Fl 1–7, 5.2% at BB,
Muñoz, 2019). 3.0% at SBB), Spaniomys (6.4%, 11.0%, 8.8%), Steiromys (2.0%, 6.9%,
1.6%). Eocardia has abundances as 15.4% at FL 1–7, 11.6% at BB, and
4.1.6. Toxodontia 11.4% at SBB.
Toxodontia are the most common large ungulates (around 100 kg or In a number of cases, a genus at SBB occurs far more frequently than
more) and probably mammals of the SCF but its two main groups at FL 1–7 or BB. Acarechimys, a brachydont taxon, appears 8.0% of the
(toxodontids and homalodotheriids) are very disparately represented. time at SBB but only 2.0% at FL 1–7 and 1.7% at BB. The common
We identified 140 Toxodontia specimens in our collections from FL 1–7, euhysodont taxon Prolagostomus accounts for 26.2% of all rodent records
BB, and SBB: 56, 38, and 46, respectively (Table 4, Fig. 5). at SBB (131 specimens) but we have no records at FL 1–7 and only 2
Among toxodontids, two genera and two species are represented in specimens at BB. Pliolagostomus is absent at FL 1–7 and BB whereas at
the three localities. The remains of the Adinotherium are twofold those of SBB it is quite common (7.6%). Stichomys shows a gradual increase in
Nesodon in the FL 1–7 and BB, but both are equally recorded at SBB. Both abundance (absent at FL 1–7, 4.1% at BB, 9.2% at SBB).
are considered ambulatory grazing ungulates of moderate (Adinotherium Several taxa decrease in numbers, especially Perimys (19.0%, 11.6%,
about 100 kg) to large size (Nesodon, about 500 kg) (Cassini et al., 2012). 6.8%), and Neoreomys (46.8%, 28% 14%). Respecting Perimys, there are
Another toxodont Hyperotoxodon is recorded from the old collections of also a difference in body size of the species (Arnal et al., 2019). Perimys
RSC but Fernández and Muñoz (2019) did not report it from our erutus (a small species) and Perimys onustus (a larger species) both occur
collections. at BB and SBB but the former is more common is more common at BB (11
Homalodotheriids are represented by a single genus and species specimens to 1 specimen) and the latter is more abundant at SBB (1
usually quite rare, at least at FL 1–7 (1 specimen) and BB (2 specimens). specimen to 23 specimens).
We identified more remains from SBB (10), but still far fewer than Table 6 lists the niche characteristics of commonly occurring rodents
in the Santa Cruz Formation at FL 1–7, BB, and SBB. Among the more
common rodent taxa, there are no discernible trends in body size other
2 than in species of Perimys. Locomotor habits are poorly documented but
Killik Aike Norte (formerly Felton’s Estancia) on the north shore of the
estuary of Río Gallegos was previously suggested to be temporally equivalent to no obvious trends are apparent—the more common rodent taxa were
FL 1–7 (Ea. La Costa Member) (Tejedor et al., 2006) but reevaluation of the ground-dwellers (Muñoz et al., 2019). The one possibly scansorial
tephra indicate a much younger age and allocation to the upper levels of the (semi-arboreal) taxon Steiromys remains stable in numbers. Acarechimys,
coastal SCF (Trayler et al., 2020b). with some fossorial tendencies, increases in abundance at SBB Perimys,
11You can also read
