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GSA 2020 Connects Online, 2020

The 84th Annual Meeting of the American Association of Physical Anthropologists, St. Louis, MO, 2015

The 86th Annual Meeting of the American Association of Physical Anthropologists, New Orleans, 2017

PLOS ONE, Sep 10, 2013

Specialized acrobatic leaping has been recognized as a key adaptive trait tied to the origin and ... more Specialized acrobatic leaping has been recognized as a key adaptive trait tied to the origin and subsequent radiation of euprimates based on its observed frequency in extant primates and inferred frequency in extinct early euprimates. Hypothesized skeletal correlates include elongated tarsal elements, which would be expected to aid leaping by allowing for increased rates and durations of propulsive acceleration at takeoff. Alternatively, authors of a recent study argued that pronounced distal calcaneal elongation of euprimates (compared to other mammalian taxa) was related primarily to specialized pedal grasping. Testing for correlations between calcaneal elongation and leaping versus grasping is complicated by body size differences and associated allometric affects. We reassess allometric constraints on, and the functional significance of, calcaneal elongation using phylogenetic comparative methods, and present an evolutionary hypothesis for the evolution of calcaneal elongation in primates using a Bayesian approach to ancestral state reconstruction (ASR). Results show that among all primates, logged ratios of distal calcaneal length to total calcaneal length are inversely correlated with logged body mass proxies derived from the area of the calcaneal facet for the cuboid. Results from phylogenetic ANOVA on residuals from this allometric line suggest that deviations are explained by degree of leaping specialization in prosimians, but not anthropoids. Results from ASR suggest that non-allometric increases in calcaneal elongation began in the primate stem lineage and continued independently in haplorhines and strepsirrhines. Anthropoid and lorisid lineages show stasis and decreasing elongation, respectively. Initial increases in calcaneal elongation in primate evolution may be related to either development of hallucal-grasping or a combination of grasping and more specialized leaping behaviors. As has been previously suggested, subsequent increases in calcaneal elongation are likely adaptations for more effective acrobatic leaping, highlighting the importance of this behavior in early euprimate evolution.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2017

Quantifying the relationship between carbon cycle perturbations and the hydrologic cycle in the g... more Quantifying the relationship between carbon cycle perturbations and the hydrologic cycle in the geologic past is crucial to accurately modeling how future anthropogenic carbon emissions and resulting radiative forcing might affect the hydrologic cycle. Interpreting changes in proxy records for insight into paleohydrologic change is complex, and documented records of paleohydrologic response to past global warming are rare. We use the relationship between two independent proxy records, the stable isotope ratios of hydrogen in n-alkanes and oxygen in tooth enamel of Coryphodon, to examine paleohydrologic change in the continental interior of North America during the Paleocene-Eocene Thermal Maximum (PETM) hyperthermal~56 Ma. The Coryphodon δ 18 O record allows us to infer shifts in surface water isotope values through time by applying an empirical relationship between tooth enamel and precipitation δ 18 O values. Precipitation δ 18 O values increase by~4‰ during the PETM, but nalkane hydrogen isotope ratios show no directional change during the PETM. We explore multiple hypotheses that could explain the differences between the isotope records, including a change in apparent fractionation as a result of plant community change, a shift in the slope of the local meteoric water line, a change in the season of rainfall, or a shift in the season of lipid production. We model the changes that would be required to reconcile the isotope records for each hypothesis and evaluate the likelihood of each of the scenarios. We posit that the most likely hypothesis for the observed differences between the isotope records is a change in either the season of rainfall or the season of lipid production during the PETM.

Journal of Human Evolution, Jul 1, 2007

Biology Letters, 2015

Small-bodied, insectivorous Nyctitheriidae are known in the Palaeogene fossil record almost exclu... more Small-bodied, insectivorous Nyctitheriidae are known in the Palaeogene fossil record almost exclusively from teeth and fragmentary jaws and have been referred to Eulipotyphla (shrews, moles and hedgehogs) based on dental similarities. By contrast, isolated postcrania attributed to the group suggest arboreality and a relationship to Euarchonta (primates, treeshrews and colugos). Cretaceous-Palaeocene adapisoriculid insectivores have also been proposed as early euarchontans based on postcranial similarities. We describe the first known dentally associated nyctitheriid auditory regions and postcrania, and use them to test the proposed relationship to Euarchonta with cladistic analyses of 415 dental, cranial and postcranial characteristics scored for 92 fossil and extant mammalian taxa. Although nyctitheriid postcrania share similarities with euarchontans likely related to arboreality, results of cladistic analyses suggest that nyctitheriids are closely related to Eulipotyphla. Adapisoriculidae is found to be outside of crown Placentalia. These results suggest that similarities in postcranial morphology among nyctitheriids, adapisoriculids and euarchontans represent separate instances of convergence or primitive retention of climbing capabilities.

Springer eBooks, 2007

There are five major scenarios that have been advanced to account for the early events in the ori... more There are five major scenarios that have been advanced to account for the early events in the origination of the order Primates: a transition from terrestriality to arboreality, the adoption of a grasp-leaping mode of locomotion, the evolution of features for visual predation, an adaptation to terminal branch feeding occurring during angiosperm diversification, or a combination involving terminal branch feeding followed by visual predation. These hypotheses are assessed using both neontological and fossil data. Of the five scenarios, the angiosperm diversification hypothesis is not contradicted by modern data and is found to be the most consistent with the fossil record. In particular, the evolution of features for manual grasping and dental processing of fruit in the earliest primates (primitive plesiadapiforms), and the subsequent development of features for better grasping and more intense frugivory in the common ancestor of Euprimates and Plesiadapoidea, is consistent with a close relationship between early primate and angiosperm evolution. All the other scenarios are less consistent with the pattern of trait acquisition through time observed in the fossil record. Consideration of non-euprimates (e.g., scandentians and plesiadapiforms) is found to be essential to viewing primate origins as an evolutionary process rather than as an event.

Cambridge University Press eBooks, Sep 1, 2010

Springer eBooks, 2013

ABSTRACT There are five major scenarios that have been advanced to account for the early events i... more ABSTRACT There are five major scenarios that have been advanced to account for the early events in the origination of the order Primates: a transition from terrestriality to arboreality, the adoption of a grasp-leaping mode of locomotion, the evolution of features for visual predation, an adaptation to terminal branch feeding occurring during angiosperm diversification, or a combination involving terminal branch feeding followed by visual predation. These hypotheses are assessed using both neontological and fossil data. Of the five scenarios, the angiosperm diversification hypothesis is not contradicted by modern data and is found to be the most consistent with the fossil record. In particular, the evolution of features for manual grasping and dental processing of fruit in the earliest primates (primitive plesiadapiforms), and the subsequent development of features for better grasping and more intense frugivory in the common ancestor of Euprimates and Plesiadapoidea, is consistent with a close relationship between early primate and angiosperm evolution. All the other scenarios are less consistent with the pattern of trait acquisition through time observed in the fossil record. Consideration of non-euprimates (e.g., scandentians and plesiadapiforms) is found to be essential to viewing primate origins as an evolutionary process rather than as an event.

Special publication, 2014

Journal of Human Evolution, Mar 1, 2019

Omomyiform primates are among the most basal fossil haplorhines, with the oldest classified in th... more Omomyiform primates are among the most basal fossil haplorhines, with the oldest classified in the genus Teilhardina and known contemporaneously from Asia, Europe, and North America during the PaleoceneeEocene Thermal Maximum (PETM)~56 mya. Characterization of morphology in this genus has been limited by small sample sizes and fragmentary fossils. A new dental sample (n ¼ 163) of the North American species Teilhardina brandti from PETM strata of the Bighorn Basin, Wyoming, documents previously unknown morphology and variation, prompting the need for a systematic revision of the genus. The P 4 of T. brandti expresses a range of variation that encompasses that of the recently named, slightly younger North American species 'Teilhardina gingerichi,' which is here synonymized with T. brandti. A new partial dentary preserving the alveoli for P 1-2 demonstrates that T. brandti variably expresses an unreduced, centrally-located P 1 , and in this regard is similar to that of T. asiatica from China. This observation, coupled with further documentation of variability in P 1 alveolar size, position, and presence in the European type species T. belgica, indicates that the original diagnosis of T. asiatica is insufficient at distinguishing this species from either T. belgica or T. brandti. Likewise, the basal omomyiform 'Archicebus achilles' requires revision to be distinguished from Teilhardina. Results from a phylogenetic analysis of 1890 characters scored for omomyiforms, adapiforms, and other euarchontan mammals produces a novel clade including T. magnoliana, T. brandti, T. asiatica, and T. belgica to the exclusion of two species previously referred to Teilhardina, which are here classified in a new genus (Bownomomys americanus and Bownomomys crassidens). While hypotheses of relationships and inferred biogeographic patterns among species of Teilhardina could change with the discovery of more complete fossils, the results of these analyses indicate a similar probability that the genus originated in either Asia or North America.

Journal of Human Evolution, Feb 1, 2023

The 86th Annual Meeting of the American Association of Physical Anthropologists, New Orleans, 2017

Paleobiology, Mar 19, 2021

Interpreting the impact of climate change on vertebrates in the fossil record can be complicated ... more Interpreting the impact of climate change on vertebrates in the fossil record can be complicated by the effects of potential biotic drivers on morphological patterns observed in taxa. One promising area where this impact can be assessed is a high-resolution terrestrial record from the Bighorn Basin, Wyoming, that corresponds to the Paleocene-Eocene thermal maximum (PETM), a geologically rapid (∼170 kyr) interval of sustained temperature and aridity shifts about 56 Ma. The PETM has been extensively studied, but different lines of research have not yet been brought together to compare the timing of shifts in abiotic drivers that include temperature and aridity proxies and those of biotic drivers, measured through changes in floral and faunal assemblages, to the timing of morphological change within mammalian species lineages. We used a suite of morphometric tools to document morphological changes in molar crown morphology of three lineages of stem erinaceid eulipotyphlans. We then compared the timing of morphological change to that of both abiotic and other biotic records through the PETM. In all three species lineages, we failed to recover any significant changes in tooth crown shape or size within the PETM. These results contrast with those documented previously for lineages of medium-sized mammals, which show significant dwarfing within the PETM. Our results suggest that biotic drivers such as shifts in community composition may have also played an important role in shaping species-level patterns during this dynamic interval in Earth history.

The 86th Annual Meeting of the American Association of Physical Anthropologists, New Orleans, 2017

Cambridge University Press eBooks, Jun 12, 2008

GSA 2020 Connects Online, 2020

The 84th Annual Meeting of the American Association of Physical Anthropologists, St. Louis, MO, 2015

The 86th Annual Meeting of the American Association of Physical Anthropologists, New Orleans, 2017

PLOS ONE, Sep 10, 2013

Palaeogeography, Palaeoclimatology, Palaeoecology, 2017

Journal of Human Evolution, Jul 1, 2007

Biology Letters, 2015

Springer eBooks, 2007

Cambridge University Press eBooks, Sep 1, 2010

Springer eBooks, 2013

Special publication, 2014

Journal of Human Evolution, Mar 1, 2019

Journal of Human Evolution, Feb 1, 2023

The 86th Annual Meeting of the American Association of Physical Anthropologists, New Orleans, 2017

Paleobiology, Mar 19, 2021

The 86th Annual Meeting of the American Association of Physical Anthropologists, New Orleans, 2017

Cambridge University Press eBooks, Jun 12, 2008

72nd Annual Meeting of the Society of vertebrate Paleontology. Program and Abstracts, 2012:108. ... more 72nd Annual Meeting of the Society of vertebrate Paleontology. Program and Abstracts, 2012:108.

Titanoboa cerrejonensis from the Cerrejón Formation (middle to late Paleocene; 58-60 My) of Colombia, is the largest known snake. The taxon was originally diagnosed, assigned to the clade Boinae, and estimated to be approximately 12.8 m (±2.18 m) in total body length on the basis of precloacal vertebral morphology and size, but the absence of cranial remains prohibited a more precise size estimate and robust phylogenetic hypothesis. Recent fieldwork in the type locality has resulted in the recovery of several new specimens of Titanoboa including parts of the cranium and mandible (maxillae, palatine, pterygoid, quadrate, dentary, and compound elements) associated with partial axial skeletons. We estimate skull length from cranial elements to be 40 cm, corresponding to a total body length of 14.3 m (±1.28 m) based on the scaling relationship of head length to body length in the extant boine Eunectes. Phylogenetic analyses of Titanoboa and extant macrostomatan snakes using cranial and postcranial osteology, and including analyses incorporating a molecular scaffold for extant taxa, supports boine affinities of Titanoboa, based on the extreme reduction of the palatine choanal and posteromedial processes as well as vertebral anatomy. Within Boinae, Titanoboa shares a close relationship with Pacific Island-Madagascan taxa. These results are the first historical evidence linking Neotropical and Old World boines, and constrain divergence timing of the clades to no younger than 58 My. Cranial elements of Titanoboa possess unique features relative to other boids, including high palatal and marginal tooth position counts, low-angled quadrate orientation, and reduced palatine-pterygoid and pterygoid-quadrate articulations. These characters, combined with weakly ankylosed teeth in Titanoboa, are characteristic of piscivorous feeding ecology in extant caenophidian snakes. Preservation in the large-scale fluvial depositional environments of the Cerrejón Formation, combined with the recovery of associated fossils of large dipnoan and osteoglossomorph fishes, also suggests a dominantly piscivorous feeding ecology for Titanoboa, which is unique among living and fossil boids.

The Paleocene-Eocene Thermal Maximum (PETM) presents an opportunity to characterize continental h... more The Paleocene-Eocene Thermal Maximum (PETM) presents an opportunity to characterize continental hydrologic changes during rapid and extreme global warming. The Bighorn Basin, Wyoming, USA, has long been recognized for the PETM sequences preserved there and sits in an ideal location for recording hydrologic changes in the interior of North America. The southeast Bighorn Basin is of particular interest because it contains not only alluvial paleosols and vertebrate fossils, but also macrofloral remains from the PETM. The carbon isotope excursion associated with this event is preserved in this part of the Basin in leaf wax lipids, tooth enamel, and bulk organic matter. To characterize the hydrologic changes that occurred during the PETM we are applying a suite of isotopic, paleobotanical and paleopedological approaches to sections in the southeast Bighorn Basin. Reported here are results from the combined hydrogen and oxygen isotope analysis aimed at reconstructing relative humidity. Oxygen isotope ratios (δ18O) of biogenic apatite from mammalian tooth enamel and fish scales vary with environment, physiology and diet. Because mammals are homeothermic, they primarily track surface water values with predictable physiological offsets. Hydrogen isotope ratios (δD) of leaf-wax lipids (long-chain n-alkanes) reflect both meteoric water δD values and additional D-enrichment caused by evapotranspiration. The enrichment factor between water δD and n-alkane δD can therefore be used as a proxy for relative humidity (RH). In this study, δ18O of surface water is estimated using the δ18O of Coryphodon tooth enamel. We use these δ18O values to estimate surface water δD values using the Global Meteoric Water Line (δD = 8δ18O + 10). We then calculate relative humidity from n-alkane δD values using a Craig-Gordon type isotopic model for D-enrichment caused by transpiration from leaves. Results of the combined hydrogen-oxygen isotope paleohygrometer indicate a general rise in relative humidity during the first half of the PETM followed by a decline during the second half of the event. The rise is punctuated by at least one small drop in relative humidity. Other proxies for available soil moisture (soil weathering indices) and mean annual precipitation (leaf physiognomy) suggest an initial drying at the onset of the PETM followed by subsequent periods of wetter and dryer conditions in the southeastern Bighorn Basin. In contrast, the isotope results presented here suggest that the onset of the PETM was marked by an increase in relative humidity. This discrepancy might indicate increased seasonality during the PETM. Leaf wax hydrogen isotope values are likely biased to record primarily the growing season, which may have become more humid, while soil and plant proxies could reflect an overall decrease in available moisture as a result of increased seasonality of precipitation.

The modern northern Neotropics possesses some of the highest diversity among extant squamates, but the sparse fossil record from this region has previously limited the ability to reconstruct their evolutionary histories. New discoveries from the early Paleogene of northern South America reveal biogeographic patterns and paleoecology of modern clades. Squamates have been recovered as components of vertebrate faunas from the late Paleocene Cerrejón Formation and late Paleocene- early Eocene Bogotá Formation of Colombia. The Cerrejón Formation represents large-scale fluvial deposits with associated rainforest flora and herpetofauna. The squamate record consists of snakes, including multiple individuals of the giant aquatic boid Titanoboa cerrejonensis and a single, poorly preserved precloacal vertebra assigned to Anilioidea on the basis of extreme reduction of the neural spine, broadly concave dorsal margin of the neural arch and comparatively narrow zygosphene. The presence of a fossorial to leaf-litter specialist provides the first the first terrestrial component to the reptile record and indicates geographic proximity of the aquatic record to rainforest habitats within the Cerrejón Formation. The Muchelo Creek locality in the Bogotá Formation is dated to just before the Early Eocene Climatic Optimum (EECO). It represents smaller scale fluvial deposition, and preserves a diverse squamate fauna consisting of iguanians, including the fossil record of hoplocercines, and boine, caenophidian, and ungaliophiine snakes. Modern members of these clades include arboreal taxa, and the Bogotá squamate record represents a forest herpetofauna. Extant tropical forest squamates undergo thermal stress at high ambient temperatures, and inferred thermal tolerances of the Bogotá squamate record may constrain temperature estimates at the beginning of the equatorial EECO.

The Colombian squamate record indicates that the continental-scale biogeographic zonation of the modern northern Neotropics was established no later than the middle Eocene. Both the Bogotá and Cerrejón formations include representatives of extant clades that are either endemic or predominately South America (“anilioids”) or whose Central American distributions are limited or represent more recent immigration from South America (hoplocercines, boines). These records additionally indicate that the biogeographic events that initially assembled Neotropical squamate faunas, including New World immigration of iguanians and first occurrence of South American boines, were likely late Mesozoic in age.

New continental sections representing the Paleocene-Eocene Thermal Maximum (PETM) have been disco... more New continental sections representing the Paleocene-Eocene Thermal Maximum (PETM) have been discovered in the southern Bighorn Basin, Wyoming. Three localities preserving leaves and fruits are the first megafossil record of plants from this geologically short (about 150ky) period of intense warming. The localities produce fossil pollen and spores as well. The plant remains are in sections that preserve vertebrate fossils

ABSTRACT The modern northern Neotropics possesses some of the highest diversity among extant squa... more ABSTRACT The modern northern Neotropics possesses some of the highest diversity among extant squamates, but the sparse fossil record from this region has previously limited the ability to reconstruct their evolutionary histories. New discoveries from the early Paleogene of northern South America reveal biogeographic patterns and paleoecology of modern clades. Squamates have been recovered as components of vertebrate faunas from the late Paleocene Cerrejón Formation and late Paleocene- early Eocene Bogotá Formation of Colombia. The Cerrejón Formation represents large-scale fluvial deposits with associated rainforest flora and herpetofauna. The squamate record consists of snakes, including multiple individuals of the giant aquatic boid Titanoboa cerrejonensis and a single, poorly preserved precloacal vertebra assigned to Anilioidea on the basis of extreme reduction of the neural spine, broadly concave dorsal margin of the neural arch and comparatively narrow zygosphene. The presence of a fossorial to leaf-litter specialist provides the first the first terrestrial component to the reptile record and indicates geographic proximity of the aquatic record to rainforest habitats within the Cerrejón Formation. The Muchelo Creek locality in the Bogotá Formation is dated to just before the Early Eocene Climatic Optimum (EECO). It represents smaller scale fluvial deposition, and preserves a diverse squamate fauna consisting of iguanians, including the fossil record of hoplocercines, and boine, caenophidian, and ungaliophiine snakes. Modern members of these clades include arboreal taxa, and the Bogotá squamate record represents a forest herpetofauna. Extant tropical forest squamates undergo thermal stress at high ambient temperatures, and inferred thermal tolerances of the Bogotá squamate record may constrain temperature estimates at the beginning of the equatorial EECO. The Colombian squamate record indicates that the continental-scale biogeographic zonation of the modern northern Neotropics was established no later than the middle Eocene. Both the Bogotá and Cerrejón formations include representatives of extant clades that are either endemic or predominately South America (“anilioids”) or whose Central American distributions are limited or represent more recent immigration from South America (hoplocercines, boines). These records additionally indicate that the biogeographic events that initially assembled Neotropical squamate faunas, including New World immigration of iguanians and first occurrence of South American boines, were likely late Mesozoic in age.

The Arctocyonidae are a family of extinct "condylarth" mammals that were abundant and speciose du... more The Arctocyonidae are a family of extinct "condylarth" mammals that were abundant and speciose during the Paleocene and declined in diversity and number during the early Eocene in North America, Europe, and Asia. Arctocyonids have been reconstructed as primitive omnivorous condylarths and may be the sister group to Artiodactyla. This study focuses on arctocyonids within the Paleocene-Eocene Thermal Maximum (PETM), ~56 Ma, when global temperatures increased by ~5-10° C. Three species were initially identified in the PETM faunal zone Wasatchian-0: (1) Thryptacodon barae, characterized by a centralized paraconid equal in size to the metaconid on M2 and a distinct hypoconulid on the lower molars; (2) Chriacus badgleyi, characterized by the absence of a metaconid on the P4, an anteriorly placed molar paraconid, and a highly reduced hypoconulid; and (3) Princetonia yalensis, characterized by a lingual molar paraconid and a low, shallow, anteroposteriorly compressed trigonid with rounded cusps and crests compared to Chriacus. The latter two species have been difficult to distinguish in part because the holotype of C. badgleyi contains only C1, P2-P4, whereas the holotype of P. yalensis contains only M2-M3. These species were recently synonymized under the name C. badgleyi (based primarily on a poorly-preserved specimen). We report a large collection of arctocyonid specimens from the PETM, collected in the southern Bighorn Basin, Wyoming. The number of specimens includes ~100 molars, numerous premolars, and deciduous teeth. It also includes the most complete specimen of a PETM arctocyonid known: a partial dentary of C. badgleyi with alveoli for C1-P2, crowns of P3-M3, and a preserved ascending ramus and mandibular condyle. The measurements and morphology documented in this sample clearly separate specimens of Thryptacodon, while supporting a second morphological group (Chriacus) in which body size range exceeds that normally observed in extant mammal species. When placed in stratigraphic context, C. badgleyi body size is found to correspond well with inferred temperature during the PETM, similar to recent findings for the earliest equid Sifrhippus. These results support the classification of two species: the less abundant T. barae (in contrast with the northern Bighorn Basin), and C. badgleyi. While the morphotype described for P. yalensis is present in the collection, it is rare and observed only in worn specimens. These findings, coupled with a lack of discrete tooth dimensions in the temporal series, suggest that the P. yalensis morphotype results from wear to the molars of C. badgleyi and support the synonymy of these taxa.

wetter southeastern US. Furthermore, δ13C values were greater in the southwestern US in all categ... more wetter southeastern US. Furthermore, δ13C values were greater in the southwestern US in all categories and overall; however, there is no correlation between δ13C values and δ18O values. Thus, while C4 recourses may have been more abundant in the southwest, environmental sensitivity does not appear to be related to dietary feeding strategies. Collectively, this meta-analysis helps clarify regional climatic differences and identifies taxa that may be useful for quantifying changes in aridity over time.

Cingulates have dermal armor composed of osteoderms that protect the torso, tail, and head. The c... more Cingulates have dermal armor composed of osteoderms that protect the torso, tail, and head. The cephalic shield of cingulates is a structure comprised of sutured osteoderms that is highly variable in overall shape and number of osteoderms across the different taxa. The cephalic shields of the extinct giant armadillos (pampatheres) have not been previously described. The late Blancan Haile 7G locality in north-central Florida has produced the largest known assemblage of pampatheres from a single site; over 40 individuals of the species Holmesina floridanus represented by partial to nearly complete skeletons. Of these, 11 preserved the skull, of which three were recovered with nearly complete, articulated cephalic shields. The cephalic shield of H. floridanus comprises ~78 cephalic osteoderms and is very broad, only slightly longer than wide. The shield is bilaterally symmetrical, with the widest point in the middle at a protuberance along the posterior orbital margin, and narrows ant...

The Paleocene-Eocene Thermal Maximum (PETM) was a brief period of significant global climate chan... more The Paleocene-Eocene Thermal Maximum (PETM) was a brief period of significant global climate change that occurred ~56 Ma, with a rapid increase in temperature of ~5-10° C, followed by a return to pre-PETM temperatures. One major biotic effect of the PETM was dwarfing in mammal lineages that then increased in size after the PETM. Our study utilized fossils from a well-constrained stratigraphic sequence that allows for evaluation of morphological trends over the course of the PETM. We asked: 1) how tightly correlated are body size shifts in mammal lineages, and 2) do we see differences in tooth development patterns in lineages as they shift from smaller to larger body size? We first measured linear dimensions of M1 in specimens of two ecomorphologically similar genera that experienced dwarfing in the PETM and body size increase thereafter: the phenacodontid Ectocion (n=65), and the equid Sifrhippus (n=49). The smallest specimens in both lineages occur at the same stratigraphic level and are closely followed by larger specimens. A moving window log-rate-interval analysis found a significant decrease in size in both lineages during the PETM, a significant increase in size in Ectocion after the PETM, and constrained the termination of the decrease in size in both lineages to a 50 kyr interval. These findings suggest that body size change in these lineages is tightly correlated. To test our second question we compared relative sizes of molars in dentaries between small-sized species from the PETM-E. parvus (n=25) and S. sandrae (n=12)-and large-sized species that followed the PETM-E. osbornianus (n=103) and S. grangeri (n=84). Bootstrap analyses and ANCOVA of log-corrected molar areas found significant differences in relative tooth sizes. S. grangeri showed a higher ratio of M2/M1 area and M3/M2 area, but no change in slope from S. sandrae. Under an inhibitory cascade model of tooth development, this is consistent with decreased anterior molar inhibition leading to expanded posterior tooth size in S. grangeri. E. osbornianus showed no change in the ratio or slope of M2/M1 from E. parvus. Yet, the M3/M2 ratio was increased and had a significantly different slope, indicating that development in the M3 was altered without a concurrent effect on the anterior molars and suggesting different dental developmental integration in Ectocion. Data from modern taxa suggest that feeding ecology may be an important control on the activator/inhibitor ratio during dental development. We infer that climate-induced changes in feeding ecology invoked different evolutionary pathways of tooth development in these taxa. Geometric morphometric analyses of occlusal morphology are underway to detect potential functional shape changes associated with the altered developmental processes.

Titanoboa cerrejonensis from the Cerrejón Formation (middle to late Paleocene; 58-60 My) of Colom... more Titanoboa cerrejonensis from the Cerrejón Formation (middle to late Paleocene; 58-60 My) of Colombia, is the largest known snake. The taxon was originally diagnosed, assigned to the clade Boinae, and estimated to be approximately 12.8 m (±2.18 m) in total body length on the basis of precloacal vertebral morphology and size, but the absence of cranial remains prohibited a more precise size estimate and robust phylogenetic hypothesis. Recent fieldwork in the type locality has resulted in the recovery of several new specimens of Titanoboa including parts of the cranium and mandible (maxillae, palatine, pterygoid, quadrate, dentary, and compound elements) associated with partial axial skeletons. We estimate skull length from cranial elements to be 40 cm, corresponding to a total body length of 14.3 m (±1.28 m) based on the scaling relationship of head length to body length in the extant boine Eunectes. Phylogenetic analyses of Titanoboa and extant macrostomatan snakes using cranial and ...

Expansion of the Panama Canal that began in 2008 has resulted in renewed focus on geological and ... more Expansion of the Panama Canal that began in 2008 has resulted in renewed focus on geological and paleontological research. New exposures of outcrops have resulted in recovery of many additional vertebrate fossils from the previously known early Miocene Cucaracha Formation (Centenario Fauna). Here we report the first known mammals from the underlying late Oligocene/early Miocene Las Cascadas Formation, a volcanoclastic and tuffaceous sequence outcropping in the southern part of the Panama Canal. The faunal assemblage includes the oldest records of carnivores, rodents, peccaries, equids, anthracotheres, protoceratids, and camelids from the Panama Canal. The new camelids, represented by two partial dentaries and isolated lower teeth, can be attributed to Floridatragulinae based on the following characteristics: 1) a complete lower dental formula, 2) brachydont lower molars, 3) an unusual elongated jaw with 2 caniniform teeth (C/1-P/1) well separated by a diastema; 4) a long and narrow ...