Vertebrate Paleontology

The large mammal and micromammal assemblages from Paleolithic cave sites in northwestern Croatia (Veternica, Velika peć ina, and Vindija) suggest the presence of relatively temperate environments without dramatic oscillations in faunal composition during MIS 3, and possibly also including MIS 2 and 4. Species such as woolly rhinoceros, arctic fox, varying hare, and saiga antelope were not present, and the micromammal assemblages show that all taxa are indicators of a temperate, continental climate characterized by somewhat less forested conditions than those present today. Nonetheless, the region does not appear to have served as a refuge for mammals whose distribution today is north of Croatia. The region appears to have had a fairly diverse and productive mammal fauna, which in turn could have supported significant hominin populations. Faunal composition did not dramatically change across the Middle-Upper Paleolithic transition (ca. 40 000-30 000 BP). The apparent stability in mammalian faunas could be owing to several factors: A) a depositional/preservational bias for warmer phases, B) dampered climatic oscillations in the region, C) faunal communities buffered from climatic oscillations owing to microclimate, topography, etc. Resolution of these factors requires further research.

Observation: Please note this is a major update with 11,468 entries (and corrections) from previous lists published online between July 2017 and January 2018.

This list include papers, conference papers, chapters, books, theses and dissertations - It does not include abstracts (but extended abstracts).

Please do not change the list or include any reference. Any inclusion (I'm sure there will be many) or correction, please forward me directly to the email
<[email protected]>

I also ask that, whenever you quote this list, please give the credit as follows:
De Luna P. 2018. South America Vertebrate Paleontology Reference List (1774-2018) (1774-2018) - version 20180325
DOI: 10.13140/RG.2.2.23993.06248
at
http://www.mediafire.com/file/1r8ki2kg0atkstx/VPSA_20180818_PDF_final.pdf

enjoy and share!

Pedro De Luna, Ph.D. (aka Peter Moon)
Post-doc fellow at the Biosciences Institute, Universidade de São Paulo São Paulo-SP Brazil

This map folio should be referenced as:
Scotese, C.R., 2013. Map Folio 70 Early Devonian (Emsian, 402.3 Ma), PALEOMAP PaleoAtlas for ArcGIS, volume 4, Late Paleozoic Paleogeographic, Paleoclimatic and Plate Tectonic Reconstructions, PALEOMAP Project, Evanston, IL.

Introduction
These maps (rectilinear projection) are from the PALEOMAP PaleoAtlas for ArcGIS (Scotese, 2013a-f).  This is a digital atlas of plate tectonic, paleogeographic, and paleoclimatic reconstructions designed for use with the GIS software, ArcMap (ESRI).  Table 1 lists the various types of maps that comprise the PALEOMAP PaleoAtlas.  The maps included in this folio are highlighted in bold text (Table 1).
The last map in each folio is a rectilinear graticule that can be overlain on the maps to provide a geographic reference frame.  A rectilinear projection was used because it can be easily georeferenced in ArcMap and transformed into a variety of other map projections.  The rectilinear map projection can also be directly “wrapped” onto a spherical projection, like the oneused by Google Earth. A set of Google Earth paleoglobes has made from the maps in this folio. These Google Earth paleoglobes can be downloaded at: www.globalgeology.com. 
If the map you need is missing, or if there doesn’t seem to be a map folio for the exact time interval of interest, please contact me ([email protected]). Table 2 lists all the time intervals that comprise the PALEOMAP PaleoAtlas for ArcGIS. The PaleoAtlas contains one map for every stage in the Phanerozoic, as well as 6 maps for the late Precambrian.  Eventually, Map Folios, like this one, will be published for every time interval in the PALEOMAP PaleoAtlas.  The following section is a brief description of the maps that makeup the Map Folio.

Recent discoveries in Asia have greatly increased our understanding of the evolution of dinosaurs' integumentary structures, revealing a previously unexpected diversity of "protofeathers" and feathers. However, all theropod dinosaurs with preserved feathers reported so far are coelurosaurs. Evidence for filaments or feathers in noncoelurosaurian theropods is circumstantial and debated.

Although fossils of Trionychidae are found as far back as the Early Cretaceous, their evolutionary history, including the origin of the crown clade, is poorly understood. Here, we use a microCT scan of the skull of ‘Trionyx’ kyrgyzensis from the late Early Cretaceous (Albian) of Kyrgyzstan as the basis for a thorough redescription of the cranial morphology of this species. New information includes the pattern of cranial circulation, which is comparable to all extant trionychids. A unique combination of cranial and postcranial characters of ‘Trionyx’ kyrgyzensis allows us to establish for it a new genus Petrochelys gen. nov. The data regarding Petrochelys kyrgyzensis are incorporated into a phylogenetic analysis. When Petrochelys kyrgyzensis is analysed without including additional, extinct taxa, it is placed in a highly derived position within the extant Nilssonia. However, the addition of five Cretaceous–Palaeogene taxa breaks up hypothesized long branches and results in more basal positions for Petrochelys kyrgyzensis within recovered trees. All results support the hypothesis that Petrochelys kyrgyzensis is a crown trionychid and a member of Trionychinae. Our findings highlight the importance of including multiple extinct taxa in phylogenetic analyses prior to using any of those taxa as calibration points in divergence dating estimates. http://zoobank.org/urn:lsid:zoobank.org:pub:592B98BF-87DF-48A8-8AA2-543AAD21FC95

The extinction of Ursus spelaeus remains controversial. In this paper, data from two archaeological sites from NE Iberian Peninsula are presented. Thus, the Middle-Upper Paleolithic term is thoroughly analysed by combining radiocarbon datings, palaeontological remains and archaeological findings.

The rate, timing, and pattern of change in different regions and paleoenvironments are critical for distinguishing among potential causes for the Permian-Triassic (P-T) extinction. Carbon isotopic stratigraphy can provide global chronostratigraphic control. We report a large δ13C excursion at the P-T boundary and no long-term Permian δ13C trends for samples from the interior of Pangea. Stratigraphic gaps between available samples limit the resolution of our δ13C curve, but the excursion is within a 15-m-thick zone of overlap between Permian and Triassic taxa. Sedimentological and taphonomic observations demonstrate that this 15 m interval does not represent geologically instantaneous deposition. Together these data support a rapid and globally synchronous P-T event, but suggest that it occurred over a geologically resolvable interval of time.

Four caves on the island of Tobago, three previously unrecorded, were explored, mapped and prospected for vertebrate paleontological resources. The caves and surface features, such as dry valleys and sink holes, suggest they were part of a single large cave system which we have designated the Crown Point Cave System. The largest, deepest, and most interesting cave is Amblypygid Cave. Archaeological resources of Effigy Cave and paleontological resources of Robinson Crusoe and Remnant Caves indicate all of these caves are valuable resources that should be protected.

We here report on the smallest-known, neonate-sized Tylosaurus specimen, FHSM VP-14845, recovered from the lower Santonian portion of the Niobrara Chalk exposed in Kansas, U.S.A. Lacking any associated adult-sized material, FHSM VP-14845 comprises fragmentary and associated cranial bones, here considered to represent a single neonatal individual with an estimated skull length of 30 cm. Despite its small size, a suite of cranial characters diagnoses FHSM VP-14845 as a species of Tylosaurus, including the elongate basisphenoid morphology. At the same time, FHSM VP-14845 unexpectedly lacks a conical predental rostrum on the premaxilla, generally regarded as diagnostic of this genus. Further, the first and the second premaxillary teeth are closely spaced, with the second set positioned posterolateral to the first, contributing to the overall shortness of the dentigerous premaxilla. Because a conical predental rostrum is already present in ontogenetically young specimens of T. nepaeolicus and T. proriger with respective skull lengths of approximately 40 and 60 cm, formation of such a rostrum must have taken place very early in postnatal ontogeny. Our recognition of a neonate-sized Tylosaurus specimen without an elongate predental rostrum of the premaxilla suggests hypermorphosis as a likely heterochronic process behind the evolution of this iconic tylosaurine feature.

The study of bone microstructure preserved in fossils provides substantial information about physiology, growth
gradients and strategies, and some ecological considerations. Paleohistology is a useful tool for understanding the biological
mechanisms of extinct animals. Presented here is the microstructure characterization of two Anhangueria pterosaurs. Thin
sections of the fi rst wing phalanx and metacarpal IV of MN 7060-V have been confectioned, as have sections of the radius,
ulna and fi rst wing phalanx of MPSC R2090. The histological analysis of bones of MN 7060-V revealed fi brolamellar tissue,
few osteocytes and vascular canals. Bones of MPSC R2090 showed a mixed plexiform-fi brolamellar tissue and histovariability,
showing that bones from the same individual grew in different patterns. The vascularization was high in the phalanx, intermediate
in the ulna and absent in the radius. The absence of canals in the radius may be related to biomechanical issues, due to torsion
resistance during fl ight. The histology and the absence of fused bones suggests that the specimens are not adults. Two distinct
moments of growth were established. MN 7060-V is a subadult, with presence of bone porosity and MPSC R2090 is a young
animal as determined by the high number of canals and plexiform-fi brolamellar tissues, which indicates fast growth. In this
work, we concluded that in the Anhangueria clade, the growth of bones is not compatible with the ontogenetic stage. Young
animals may present large proportions, whereas there were older individuals of smaller sizes in the same clade.

Terrestrial climatic data reflect variable and often conflicting responses to the global cooling event at the Eocene-Oligocene transition (ca. 34 Ma). Stable isotopic compositions of the tooth enamel of large, water-dependent, herbivorous terrestrial mammals are investigated here to better understand the European continental climate during the late Eoceneearly Oligocene. High d 18 O PO 4 and d 13 C values reflect a semiarid climate and ecosystem in the late Eocene. In the west-southwest region of Europe, these conditions prevailed until at least 33 Ma, after which it became more humid. A similar change was recorded north of the Alpine thrust, but it occurred 2 m.y. earlier. The north and west-southwest regions show a significant offset in d 18 O PO 4 composition between 35 and 31 Ma, indicating the influence of different air trajectories with different moisture sources (Atlantic versus Tethys). This also marks the presence of an orographic height in central Europe from the latest Eocene. After 31 Ma, a large drop in d 18 O PO 4 is registered, explained by altitude-induced fractionation on meteoric water isotopic composition. The related paleoaltitude change is estimated to be 1200 m, and the uplift could have taken place along the Alpine-Dinaridic orogenic system.

The palaeoecology of the primitive, limbed snake Pachyrhachis is reevaluated. Previously considered to have been preserved in a shallow bay with a nearby freshwater source, it is here demonstrated to have inhabited an inter‐reef basin. Evidence for this comes from the position of the nearest palaeoshoreline (450 km away), the finely laminated carbonate mudstones, and the absence of bioturba‐tion, alluvium, and unequivocally terrestrial or freshwater taxa. Marine adaptations of Pachyrhachis include the laterally compressed body and heavily ossified (pachyostotic) vertebrae and ribs. Hydrodynamic considerations indicate that it was a slow swimmer, and thus an ambush rather than pursuit predator. Morphology of the anterior vertebrae suggests that the strike muscles were well‐developed. The narrow head and neck might have been adaptations to reduce water resistance during rapid lunges, and/or to forage in burrows or tight crevices.

The exquisite transitional fossil Tetrapodophis e described as a stem-snake with four small legs from the Lower Cretaceous of Brazil e has been widely considered a burrowing animal, consistent with recent studies arguing that snakes had fossorial ancestors. We reevaluate the ecomorphology of this important taxon using a multivariate morphometric analysis and a reexamination of the limb anatomy. Our analysis shows that the body proportions are unusual and similar to both burrowing and surface-active squa-mates. We also show that it exhibits striking and compelling features of limb anatomy, including enlarged first metapodials and reduced tarsal/carpal ossification e that conversely are highly suggestive of aquatic habits, and are found in marine squamates. The morphology and inferred ecology of Tetra-podophis therefore does not clearly favour fossorial over aquatic origins of snakes.

A comprehensive analysis of early dinosaur relationships raised the possibility that the group may have originated in Laurasia (Northern Hemisphere), rather than Gondwana (Southern Hemisphere) as often thought. However, that study focused solely on morphology and phylogenetic relationships and did not quantitatively evaluate this issue. Here, we investigate dinosaur origins using a novel Bayesian framework uniting tip-dated phylogenetics with dynamic, time-sliced biogeographic methods, which explicitly account for the age and locality of fossils and the changing interconnections of areas through time due to tectonic and eustatic change. Our analysis finds strong support for a Gondwanan origin of Dinosauria, with 99 % probability for South America (83 % for southern South America). Parsimony analysis gives concordant results. Inclusion of time-sliced biogeographic information affects ancestral state reconstructions (e.g., high connectivity between two regions increases uncertainty over which is the ancestral area) and influences tree topology (disfavouring uniting fossil taxa from localities that were widely separated during the relevant time slice). Our approach directly integrates plate tectonics with phylogenetics and divergence dating, and in doing so reaffirms southern South America as the most likely area for the geographic origin of Dinosauria. Dinosaurs are one of the most charismatic and heavily studied groups of vertebrates (e.g., Sereno 1999), but despite ongoing work and many recent discoveries, certain aspects of early dinosaurian evolution remain unclear. A recent study of early dinosaur relationships presented a new phylogeny that departs radically from existing models, but forms a broader framework for inferring dinosaur evolutionary history than those that were previously available (Baron et al. 2017a). While that study was focused primarily on early dinosaurian anatomy and relationships, a general observation was made: based upon the geographic locations of key taxa in their phylogeny, a Laurasian setting for dinosaur origin may have been plausible. This proposal ran contrary to an established consensus based on earlier phylogenies that favoured a Gondwanan and, more specifically, South American setting for this event (Nesbitt et al. 2009; Brusatte et al. 2010; Langer et al. 2010; Sues et al. 2011; Boyd 2015). In particular, the European presence of silesaurids, a close outgroup to dinosaurs, and some early dinosaur taxa (e.g., Saltopus) hinted that northern Pangaea may have played an important role in the earliest stages of dinosaur diversification. However, given the space limitations associated with the original article, no quantitative analyses were carried out to evaluate this alternative hypothesis rigorously. Here, we test the alternative hypothesis implicit in Baron et al. (2017a) by analysing their early dinosaur dataset using a novel integration of time-sliced Bayesian biogeographic models (Landis 2016) and tip-dated Bayesian phylogenetics (Drummond et al. 2012; Bielejec et al. 2014; Gavryushkina et al. 2017). The current method simultaneously estimates phylogenetic relationships, divergence dates, evolutionary rates and biogeographic patterns. Biogeographical changes are inferred using models that account for the changing relationships of continents (and thus dispersal abilities) over time-a 'chronobiogeographical' paradigm (Hunn & Upchurch 2001)-and this information provides potentially critical information for improving estimates of tree topology and divergence dates. For comparison, we also perform analogous analyses using traditional biogeographic parsimony-based methods. Previous studies have advocated a similar approach to integrating phylogeny, stratigraphy, morphology and bio-geography in a parsimony framework (reviewed in Rossie & Seiffert 2006). However, that implementation was problematic: as parsimony trees lack an explicit time element, only very simple time-sliced biogeographic models were possible (e.g., three areas and three time slices) and tree topology and divergence dates had to be assessed manually. The analyses attempted here tackle this complex multidimensional problem more efficiently , using explicit Bayesian computational approaches.

Jacquemontia reclinata House (Convolvulaceae) is a federally listed endangered species endemic to coastal strand habitat of south-eastern Florida. In order to identify the closest relatives of J. reclinata, a phylogenetic reconstruction was performed based on nucleotide sequence data from the internal transcribed spacer region of nuclear ribosomal DNA and from the trnH-psbA intergenic spacer of chloroplast DNA. The three putative relatives of J. reclinata and the majority of Jacquemontia Choicy species known to occur in the Caribbean Islands were included. The strict consensus tree concurs with previous morphological studies, indicating that J. reclinata is closely related to the Caribbean species J. cayensis Britton, J. curtisii Hallier f., and J. havanensis (Jacq.) Urb. These three species and J. reclinata form an unresolved clade. Nucleotide divergence within this clade is low, suggesting that the group is recent, perhaps diversifying after the latest glacial period. These taxa need to be studied further using population-level DNA markers. Most species endemic to the Caribbean Basin form a strongly supported clade. Our phylogeny supports Convolvulus nodiflorus Desr. as part of Jacquemontia. In addition, J. ovalifolia (West) Hallier f. ssp. sandwicensis (A. Gray) K.R. Robertson is sister to the Antillean endemic J. solanifolia (L.) Hallier f. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 154, 443–454.

Palaeolama was a relatively rare camelid in North America during the Pleistocene. Here we report the first occurrence of P. mi- rifica in the Late Pleistocene of Puebla, central Mexico. This is the southernmost record of P. mirifica in North America, and fills in a geographic gap with a record of the species in Costa Rica. The fossil-bearing unit is composed of silt, fine sand, and scarce pebbles. This unit is partially correlative with the alluvial sequence of Axamilpa, Puebla, considered to be MIS 2 – 3 in age. Isotopic data and Mesowear III values indicate that P. mirifica from Barranca Xocoa was an intermediate feeder.

Mânzaţi is a worldwide famous locality due to the largest sized dinothere Deinotherium proavum (= D. gigantissimum) unearthed to the end of 19 th century. Recently, a partial rhinoceros skeleton was recovered from the uppermost Kersonian fluvial deposits exposed in the same locality, in the place named "La Nisipărie". The fossil belongs to a very large sized rhinoceros that we assign to a horned representative. Tentatively, we relate it to Dihoplus. The burial of the rhinoceros skeleton was rather fast, but before its ending, a part of the smaller and lighter bones as the phalanx and metacarpals were removed by fluvial streams. The cranium was partly damaged before the skeleton burial. This discovery brings new data about the rhinoceros that lived around the Kersonian/Meotian boundary in the so-called Siret-Bug land. The terrestrial sequence that yielded the rhinoceros fossils is very promising for further Upper Miocene mammal remains.

Abstract Sauropod dinosaurs were the largest terrestrial
herbivores and pushed at the limits of vertebrate biomechanics
and physiology. Sauropods exhibit high craniodental
diversity in ecosystems where numerous species coexisted,
leading to the hypothesis that this biodiversity is
linked to niche subdivision driven by ecological specialisation.
Here, we quantitatively investigate feeding behaviour
hypotheses for the iconic sauropod Diplodocus. Biomechanical
modelling, using finite element analysis, was used to
examine the performance of the Diplodocus skull. Three
feeding behaviours were modelled: muscle-driven static biting,
branch stripping and bark stripping. The skull was found to be
‘over engineered’ for static biting, overall experiencing low
stress with only the dentition enduring high stress. When
branch stripping, the skull, similarly, is under low stress, with
little appreciable difference between those models. When simulated for bark stripping, the skull experiences far greater
stresses, especially in the teeth and at the jaw joint. Therefore,
we refute the bark-stripping hypothesis, while the hypotheses
of branch stripping and/or precision biting are both
consistent with our findings, showing that branch stripping
is a biomechanically plausible feeding behaviour
for diplodocids. Interestingly, in all simulations, peak
stress is observed in the premaxillary–maxillary ‘lateral
plates’, supporting the hypothesis that these structures
evolved to dissipate stress induced while feeding. These
results lead us to conclude that the aberrant craniodental
form of Diplodocus was adapted for food procurement
rather than resisting high bite forces.

Recent discoveries from the Aptian–Albian Antlers (Oklahoma) and Cloverly (Montana, Wyoming) formations provide significant additions to the Early Cretaceous record of lizards in North America. The lizards from the Antlers Formation include two teiids (one named), an anguimorphan, and a series of fragmentary jaws with “paramacellodid”-like teeth. The lizards from the Cloverly Formation include a new species of Paramacellodus and many indeterminate jaw fragments. The apparent lack of shared lizard taxa between the two units calls into question their temporal equivalence, which is based on similarity of dinosaur taxa. Although apparently distinct, the lizard faunas of both units are very similar to that of the Late Jurassic Morrison Formation in being composed primarily of “para-macellodid” or “paramacellodid”-like taxa. It appears that there was a period of relative stasis in the evolution of lizards in North America between the Late Jurassic and Aptian–Albian, paralleling a similar trend in Europe between the Late Jurassic and the Barremian (or later). Reported lizards from the Aptian-Albian of Mongolia present a level of taxonomic diversity much different than that of the same time period in Oklahoma, Montana, and Wyoming, but more like that of the Late Cretaceous of North America, suggesting that taxonomic groups common to the Late Cretaceous and Tertiary occurred earlier in Asia than in North America.

A unique characteristic of mammals is a vertebral column with anatomically distinct regions, but when and how this trait evolved remains unknown. We reconstructed vertebral regions and their morphological disparity in the extinct forerunners of mammals, the nonmammalian synapsids, to elucidate the evolution of mammalian axial differentiation. Mapping patterns of regionalization and disparity (heterogeneity) across amniotes reveals that both traits increased during synapsid evolution. However, the onset of regionalization predates increased heterogeneity. On the basis of inferred homology patterns, we propose a " pectoral-first " hypothesis for region acquisition, whereby evolutionary shifts in forelimb function in nonmammalian therapsids drove increasing vertebral modularity prior to differentiation of the vertebral column for specialized functions in mammals.

The Valbro locality (Phosphorites du Quercy, France) has yielded a relatively diverse fauna of amphibians and squamate reptiles from the early Oligocene. Amphibians include two caudatans (the salamandrids cf. Megalotriton sp. and Salamandra sp.) and two anurans (an alytid of the 'Discoglossus group' and an indeterminate pelobatid). Squamates are more diverse, they comprise an agamid (Uromastyx europaeus), an indeterminate lacertid, an anguid (Dopasia sp.), a platynotan (Necrosaurus sp.), two amphisbaenians (an amphisbaenid and a blanid), an anilioid-grade snake (Eoanilius aff. E. oligocenicus), three boids and a colubrid (Coluber cadurci). The fauna includes taxa known also in the Eocene, i.e. which were already present in the Phosphorites before the Grande Coupure, and immigrants that entered western Europe after this event. The stratigraphic overlap of the holdovers Necrosaurus, 'boid C' and cf. Megalotriton sp., and of the newcomers U. europaeus, E. aff. E. oligocenicus and C. cadurci suggests a MP 22 (early Oligocene) age. This precise age was already inferred from mammals of the locality. Taxa indicative of arid environment and aquatic (in fresh water) forms are associated in this fauna, as is possible in karstic areas.

A total of 121 actinistian species belonging to 47 genera and 17 undetermined actinistians is reported from the literature. There are 69 valid speciesw ith fair assessmento f their phylogenetic position; 21 valid species with poor assessment of their phylogenetic position; 31 actinistian incertae sedis; and 18 taxa that had been identified incorrectly as actinistians or are nomen nuda. The fossil record of the actinistians covers a history of approximately 380 million years. The greatest diversity occurred during the Scythian (Early Triassic).

To cite this article: Dalla Vecchia F.M. (2020)-Raibliania calligarisi gen. n., sp. n., a new tanystropheid (Diapsida, Tanystropheidae) from the Upper Triassic (Carnian) of northeastern Italy. Riv. It. Paleontol. Strat., 126(1): 197-222. Abstract. Tetrapod remains are extremely rare in the early Carnian (Late Triassic) Calcare del Predil Formation on the Italian side of the Julian Alps (Friuli Venezia Giulia Autonomous Region), which yielded the Raibl fossil assemblage including the famous "Raibl ichthyofauna". A new tanystropheid archosauromorph, Raibliania calligarisi, is here named based on a partial skeleton found in this formation along the Prasnig Brook. The new taxon is similar to Tanystropheus, sharing with it the very elongated cervical vertebrae, but is characterized by the presence of relatively large button-like teeth; apex of the neural spines not transversely thickened; articular facets on the upper corners of the neural spines of the dorsal vertebrae; short and distally pointed pleurapophyses of the second and last 'lumbar' vertebra; ilium with a long preacetabular process bearing a robust and transversely thick tuberosity and a medial ridge bordering the entire ventral part of the iliac blade; and pubis with a cranial process. Tanystropheids lived in the present day Alps and Prealps of Friuli Venezia Giulia Region from the late Anisian to the mid-late Norian and were an important component of the coastal reptile faunas, although they were less common than eusauropterygians and placodonts during the early Carnian. Tanystropheids with extremely elongated cervical vertebrae are reported in this area from the upper Anisian to the lower Carnian.

Recent fossil discoveries of early cetaceans and sirenians document the functional transitions that occurred as each group adapted to a completely aquatic existence, but the timing and path of their ecological transition remain uncertain. We analyzed the stable-isotope composition of tooth enamel from several early members of each group to reconstruct the dietary, foraging, and habitat preferences of basal taxa. Carbon isotope (␦ 13 C) values provided evidence of foraging within freshwater, terrestrial, and marine environments, including seagrass beds, whereas oxygen isotope (␦ 18 O) variation was used as a measure of commitment to aquatic habitats. Enamel samples were collected from four regions (south Asia, north and west Africa, and southern Europe) spanning the late early Eocene (ca. 53.5 Ma) to the late Eocene (ca. 36 Ma). Sirenian and cetacean taxa included species that were likely capable of some terrestrial locomotion, and more specialized forms that were morphologically fully aquatic. Cetacean ␦ 13 C and ␦ 18 O values indicate that some early members of this group (some pakicetids) inhabited freshwater environments, but later members (e.g., remingtonocetids, protocetids, and basilosaurids) moved quickly into estuarine and marine environments. Low ␦ 18 O variation confirms that all of these early forms were primarily aquatic, but ␦ 13 C and ␦ 18 O values for early sirenians indicate an early transition to a marine seagrass diet without any evidence of an intermediate connection to freshwater habitats.