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We study the foundations for the development of optimal randomization in mixed strategy games. We consider a population of children and adolescents (7 to 16 years old) and study in the laboratory their behavior in a nonzero sum, hide‐and‐seek game with a unique interior mixed strategy equilibrium where each location has a known but different value. The vast majority of participants favor the high‐value location not only as seekers (as predicted by theory) but also as hiders (in contradiction with theory). The behavior is extremely similar across all ages, and also similar to that of the college students control adult group. We also study the use of cheap talk (potentially deceptive) messages in this game. Hiders are excessively truthful in the messages they send while seekers have a slight tendency to (correctly) believe hiders. In general, however, messages have a small impact on outcomes. The results point to a powerful (erroneous) heuristic thinking in two‐person randomization settings that does not get corrected, even partially, with age.

Amazonian environments are being degraded by modern industrial and agricultural activities at a pace far above anything previously known, imperiling its vast biodiversity reserves and globally important ecosystem services. The most substantial threats come from regional deforestation, because of export market demands, and global climate change. The Amazon is currently perched to transition rapidly from a largely forested to a nonforested landscape. These changes are happening much too rapidly for Amazonian species, peoples, and ecosystems to respond adaptively. Policies to prevent the worst outcomes are known and must be enacted immediately. We now need political will and leadership to act on this information. To fail the Amazon is to fail the biosphere, and we fail to act at our peril.

Madagascar’s biota is hyperdiverse and includes exceptional levels of endemicity. We review the current state of knowledge on Madagascar’s past and current terrestrial and freshwater biodiversity by compiling and presenting comprehensive data on species diversity, endemism, and rates of species description and human uses, in addition to presenting an updated and simplified map of vegetation types. We report a substantial increase of records and species new to science in recent years; however, the diversity and evolution of many groups remain practically unknown (e.g., fungi and most invertebrates). Digitization efforts are increasing the resolution of species richness patterns and we highlight the crucial role of field- and collections-based research for advancing biodiversity knowledge and identifying gaps in our understanding, particularly as species richness corresponds closely to collection effort. Phylogenetic diversity patterns mirror that of species richness and endemism in most of the analyzed groups. We highlight humid forests as centers of diversity and endemism because of their role as refugia and centers of recent and rapid radiations. However, the distinct endemism of other areas, such as the grassland-woodland mosaic of the Central Highlands and the spiny forest of the southwest, is also biologically important despite lower species richness. The documented uses of Malagasy biodiversity are manifold, with much potential for the uncovering of new useful traits for food, medicine, and climate mitigation. The data presented here showcase Madagascar as a unique “living laboratory” for our understanding of evolution and the complex interactions between people and nature. The gathering and analysis of biodiversity data must continue and accelerate if we are to fully understand and safeguard this unique subset of Earth’s biodiversity.

We use a laboratory experiment to test the dynamic formation of networks in a six-subject game where link formation requires mutual consent. First, the game tends to converge to the pairwise-Nash stable (PNS) network when it exists, and to not converge but remain in the closed cycle when no PNS network exists. When two Pareto-rankable PNS networks exist, subjects often coordinate on the high-payoff one. Second, the analysis of single decisions indicates the predominance of myopic rational choices, but it also highlights interesting systematic deviations, especially when actions are more easily reversible and when they involve smaller marginal losses. Third, behavior is heterogeneous across subjects, with varying degrees of sophistication.

We develop a novel graphical paradigm of a strict-dominance-solvable game to study the developmental trajectory of steps of reasoning between 8 years old and adulthood. Most participants play the e...

La biota de la Amazonía se ha producido durante millones de años, a través de una combinación diná-mica de procesos geológicos, climáticos y evolutivos. Su singular historia produjo paisajes heterogé-neos en múltiples escalas geográficas, generó hábitats diversos, alteró las conexiones geográficas y genéticas entre las poblaciones e impactó las tasas de adaptación, especiación y extinción. Su biota ecológicamente diversa, a su vez, promovió una mayor diversificación, la coexistencia de especies y la coevolución, aumentando la biodiversidad con el tiempo.

Barter and commodity markets have been ubiquitous throughout history, suggesting that humans are good at exploiting profitable exchange opportunities. This paper studies our ability to trade through a developmental approach. We present a market experiment involving children who have not yet fully developed trading habits and are relatively unfamiliar with the concept of money. Namely, we ask 117 children aged 5 to 8 to trade in situations in which efficient market outcomes can either be achieved through simple barter or else necessitate the endogenous emergence of commodity money (trade requires transitory bookkeeping losses). We find that equilibrium outcomes are frequent (74% to 82% of subgroups depending on the treatment). Pareto efficient equilibrium outcomes occur in 82% of barter economies and 53% of commodity markets. Finally, 47% of children always trade efficiently. The results indicate that many young children can engage in profitable market exchanges.

We investigate iterative reasoning in children from pre-kindergarten to first grade (4–7 years old). We consider two-person games that have a unique Trembling Hand Perfect Equilibrium but vary in three key features: iterative complexity (the number of iterations required to reach the equilibrium), perspective requirement (the identity of the player with whom the iteration should start) and action symmetry. The beliefs of participants regarding the decision of their partners are elicited either before or after their own choices are made. We obtain the following findings. (1) Iterative complexity is not necessarily a cause of equilibrium failure. (2) Games where the equilibrium action is the same for both players are correctly solved more often. (3) Starting a recursion by solving the problem of a different player is non-intuitive in all our age groups but it can be overcome by asking participants to think about their partner’s decision before making their own choices. (4) Such ex-ante belief elicitation can, however, be detrimental in complex asymmetric games. We discuss these results in the context of the development of logical abilities and theory of mind abilities.

Significance The biological interchange between North and South America associated with the formation of the Isthmus of Panama is key to defining current gradients of species diversity. A major gap in our understanding of the interchange is its asymmetry, where mammals of North American origin attained higher diversity in South America than vice versa. The prevailing view is that this asymmetry resulted from higher origination of immigrant mammals in South America. In contrast, we find that asymmetry results from high extinction of native mammals in South America, which reduced the diversity of native mammals available to disperse northwards. These results shed light on the legacy of the biotic interchange to understand the current patterns of species diversity across the Americas., The interchange between the previously disconnected faunas of North and South America was a massive experiment in biological invasion. A major gap in our understanding of this invasion is why there was a drastic increase in the proportion of mammals of North American origin found in South America. Four nonmutually exclusive mechanisms may explain this asymmetry: 1) Higher dispersal rate of North American mammals toward the south, 2) higher origination of North American immigrants in South America, 3) higher extinction of mammals with South American origin, and 4) similar dispersal rate but a larger pool of native taxa in North versus South America. We test among these mechanisms by analyzing ∼20,000 fossil occurrences with Bayesian methods to infer dispersal and diversification rates and taxonomic selectivity of immigrants. We find no differences in the dispersal and origination rates of immigrants. In contrast, native South American mammals show higher extinction. We also find that two clades with North American origin (Carnivora and Artiodactyla) had significantly more immigrants in South America than other clades. Altogether, the asymmetry of the interchange was not due to higher origination of immigrants in South America as previously suggested, but resulted from higher extinction of native taxa in southern South America. These results from one of the greatest biological invasions highlight how biogeographic processes and biotic interactions can shape continental diversity.

We develop a graphical, non-analytical version of the two-person beauty contest game to study the developmental trajectory of instinctive behavior and learning from kindergarten to adulthood. These are captured by observing behavior when the game is played in two consecutive trials. We find that equilibrium behavior in the first trial increases significantly between 5 and 10 years of age (from 17.9% to 61.4%) and stabilizes afterwards. Children of all ages learn to play the equilibrium, especially when they observe an equilibrium choice by the rival. Our younger children are the weakest learners mainly because they are less frequently paired with rivals who play at equilibrium. Finally, the choice process data suggests that participants who play at equilibrium in the second trial are also performing fewer steps before reaching a decision, indicating that they are less hesitant about their strategy.

Madagascar’s unique biota is heavily affected by human activity and is under intense threat. Here, we review the current state of knowledge on the conservation status of Madagascar’s terrestrial and freshwater biodiversity by presenting data and analyses on documented and predicted species-level conservation statuses, the most prevalent and relevant threats, ex situ collections and programs, and the coverage and comprehensiveness of protected areas. The existing terrestrial protected area network in Madagascar covers 10.4% of its land area and includes at least part of the range of the majority of described native species of vertebrates with known distributions (97.1% of freshwater fishes, amphibians, reptiles, birds, and mammals combined) and plants (67.7%). The overall figures are higher for threatened species (97.7% of threatened vertebrates and 79.6% of threatened plants occurring within at least one protected area). International Union for Conservation of Nature (IUCN) Red List assessments and Bayesian neural network analyses for plants identify overexploitation of biological resources and unsustainable agriculture as the most prominent threats to biodiversity. We highlight five opportunities for action at multiple levels to ensure that conservation and ecological restoration objectives, programs, and activities take account of complex underlying and interacting factors and produce tangible benefits for the biodiversity and people of Madagascar.

This chapter reviews the evolutionary history of the Amazon’s terrestrial and riverine ecosystems, involving geological and climatic events operating over millions of years and across the whole of continental South America. The chapter discusses the important roles of geographic barriers, habitat heterogeneity, climate change, and species interactions in generating and maintaining the most biodiverse ecosystems on Earth. This unique history produced heterogeneous environments and diverse habitats at multiple geographic scales, which altered the connections between populations and allowed for the accumulation of the most diverse biota on Earth.

How does value-based reasoning develop and how different this development is from one domain to another? We propose a novel experimental design where children 5 to 11 years old make pairwise choices in the Goods (toys), Social (sharing between self and other), and Risk (lotteries) domains, and we evaluate the consistency of their choices. The development of consistency across domains cannot be fully accounted for by existing developmental paradigms such as transitive reasoning, attentional control and centration. We show that choice consistency is related to self-knowledge of preferences which develops gradually and differentially across domains. The Goods domain offers a developmental template: children become more consistent over time because they learn what they like most and least. In the Social domain, children gradually learn what they like most, while in the Risk domain they gradually learn what they like least. These asymmetric developments give rise to asymmetric patterns of consistency.

In this laboratory experiment, children and teenagers learn the composition of balls in an urn through sampling with replacement. We find significant aggregate departures from optimal Bayesian learning across all ages, but also important developmental trajectories. Two inference-based and two heuristic-based strategies capture the behavior of 65% to 90% of participants. Many of the youngest children (K to 2nd grade) base their decisions only on the last piece of information and use evolutionary heuristics (such as the “Win-Stay, Lose-Switch” strategy) to guide their choices. Older children and teenagers are gradually able to condition their decisions on all previous information but they often fall prey of the gambler’s fallacy. Only the oldest participants display optimal Bayesian reasoning. These results are modulated by task complexity, and Bayesian reasoning is evidenced earlier when inferences are simpler.

We develop a theory of dishonesty based on neurophysiological evidence that supports the idea of a two-step process in the decision to cheat. Formally, decisions can be processed via a costless “honest” channel that generates truthful behavior or via a costly “dishonest” channel that requires attentional resources to trade-off costs and benefits of cheating. In the first step, a decision between these two channels is made based on ex-ante information regarding the expected benefits of cheating. In the second step, decisions are based on the channel that has been selected and, when applicable, the realized benefit of cheating. The model makes novel predictions relative to existing behavioral theories. First, adding external complexity to the decision-making problem (e.g., in the form of multi-tasking) deprives the individual from attentional resources and consequently decreases the propensity to engage in dishonest behavior. Second, higher expectations about the benefits of cheating results in a higher frequency of trial-by-trial cheating for any realized benefit level. Third, multiplicity of equilibria (characterized by different levels of cheating) emerges naturally in the context of illegal markets, in which expected benefits are endogenous.

Employing a variant of GARP, we study consistency in aging by comparing the choices of younger adults (YA) and older adults (OA) in a “simple”, two-good and a “complex” three-good condition. We find that OA perform worse than YA in the complex condition but similar to YA in the simple condition, both in terms of the number and severity of GARP violations. Working memory and IQ scores correlate significantly with consistency levels, but only in the complex treatment. Our findings suggest that the age-related deterioration of neural faculties responsible for working memory and fluid intelligence is an obstacle for consistent decision-making.

The Pliocene–Pleistocene transition in the Neotropics is poorly understood despite the major climatic changes that occurred at the onset of the Quaternary. The San Gregorio Formation, the younger unit of the Urumaco Sequence, preserves a fauna that documents this critical transition. We report stingrays, freshwater bony fishes, amphibians, crocodiles, lizards, snakes, aquatic and terrestrial turtles, and mammals. A total of 49 taxa are reported from the Vergel Member (late Pliocene) and nine taxa from the Cocuiza Member (Early Pleistocene), with 28 and 18 taxa reported for the first time in the Urumaco sequence and Venezuela, respectively. Our findings include the first fossil record of the freshwater fishes Megaleporinus, Schizodon, Amblydoras, Scorpiodoras, and the pipesnake Anilius scytale, all from Pliocene strata. The late Pliocene and Early Pleistocene ages proposed here for the Vergel and Cocuiza members, respectively, are supported by their stratigraphic position, palynology, nannoplankton, and 86Sr/88Sr dating. Mammals from the Vergel Member are associated with the first major pulse of the Great American Biotic Interchange. In contrast to the dry conditions prevailing today, the San Gregorio Formation documents mixed open grassland/forest areas surrounding permanent freshwater systems, following the isolation of the northern South American basin from western Amazonia. These findings support the hypothesis that range contraction of many taxa to their current distribution in northern South America occurred rapidly during at least the last 1.5 million years.

We study in the laboratory three-, four- and six-player, dominance solvable games of complete information. We consider sequential and simultaneous versions of games that have the same, unique Nash equilibrium, and we use mousetracking to understand the decision making process of subjects. We find more equilibrium choices in the sequential version than in the simultaneous version of the game and we highlight the importance of attentional measures. Indeed, depending on the treatment, equilibrium behavior is 30 to 80 percentage points higher for subjects who look at all the payoffs necessary to compute the Nash equilibrium and for those who look at payoffs in the order predicted by the sequential elimination of dominated strategies than for subjects who do not. Finally, the sequence of lookups reveals that subjects have an easier time finding the player with a dominant strategy in the sequential timing than in the simultaneous timing. However, once this player is found, the unraveling logic of iterated elimination of dominated strategies is performed (equally) fast and efficiently under both timings.

Psychophysics studies suggest that our perception of time is different from the objective passage of time. Economics research emphasizes that the value of a reward depends on the delay involved. In this paper, we combine both strands and estimate time perception and time discounting functions at the individual level in an incentivized controlled laboratory environment. We find a negative and statistically significant correlation between time perception and time discounting: subjects who overestimate objective time intervals are less willing to delay gratification. The result suggests that our ability to delay consumption is related to our mental representation of time delays.

We investigated self-awareness in time perception using three time production tasks with different reward structures, and collected self-assessments of performance. Participants had monetary incentives to target the true time in the first (baseline) task, not to exceed the true time in the second task and not to fall below the true time in the third task. We found that participants overestimated time in all tasks but responded correctly to incentives: they decreased their estimates in the second task and increased them in the third. Participants’ self-assessment in the baseline task was in line with their time perception biases, and their behavior in the other tasks was consistent with their (correct) beliefs. Self-perceived over-estimators decreased their estimates in the second task significantly more relative to self-perceived under-estimators, while in the third task they increased their estimates significantly less. Last, we explored the effect of physiological stress by having half of our population complete the Cold Pressure Task and found no significant effect.

We develop a theory based on the evidence reported in Hare et al. (2009) to explain consumption of goods that feature a low-order attribute (e.g., taste) and a high-order attribute (e.g., health). One brain system with access to the low-order attribute computes the goal value of consumption while another brain system can modulate this value, at a cost, by transmitting information regarding the high-order attribute. We determine the optimal modulation and consumption strategy as a function of the cost of information transmission and the environment. We show that in healthy environments, modulation is used to signal surprisingly unhealthy goods so as to trigger abstinence when consumption would ordinarily occur. Conversely, in unhealthy environments, modulation is used to signal surprisingly healthy choices so as to trigger consumption when abstinence would ordinarily occur. From an outside perspective, individuals may appear to under-regulate their choices (self-indulgence) but also to over-regulate them (self-restraint). Both modulation and decisions are affected by factors orthogonal to the decision problem. In particular, taxing executive functions results in less modulation and more inefficient behavior. Finally, the model can shed light on issues related to eating disorders, present-biased preferences, habit formation and compulsive behavior.

We characterize the pricing structure in a model of platform competition in which two firms offer horizontally differentiated platforms and two sets of complementors offer products that are exclusive to each platform, respectively. We highlight the presence of indirect network effects: platforms and complementors benefit from the quality and number of firms in their group and suffer from the quality and number of firms in the rival’s group through their effects on prices and market share. We then determine the incentives of platforms to subsidize the independent complementors in an equilibrium. We further analyze the incentives of each platform to form a strategic alliance with complementors through contractual exclusivity or technological compatibility, or to integrate with the complementors. Finally, we discuss the welfare consequences of these strategies.

We conduct a laboratory experiment of second-price sealed bid auctions of a common value good with two bidders. Bidders face three different types of information: common uncertainty (unknown information), private information (known by one bidder) and public information (known by both bidders), and auctions differ on the relative importance of these three types of information. We find that subjects barely differentiate between private and public information and deviate from the theoretical predictions with respect to all three types of information. There is under-reaction to both private and public information and systematic overbidding in all auctions above and beyond the standard winner’s curse. The Cursed Equilibrium and Level-k models successfully account for some features of the data but others remain largely unexplained.

We study experimentally the decision of an individual to steal or pay for an object that is produced at a cost by another individual. We consider two conditions. In the first condition, subjects caught stealing are sanctioned with a nominal fee. In the second condition, the sanction is increased by making the identity of the individual public (shaming). We also collect skin conductance responses to better understand the emotional arousal conducive to choices. Behaviorally, we show that stealing decreases significantly when shaming is introduced. More importantly, the emotional response at the time of decision strongly correlates with behavior. In particular, subjects who are more aroused are more likely to steal in the first condition, and also more likely to stop stealing in the second condition. Based on this physiological evidence, we develop a theoretical model where current decisions contribute to a “moral stock”, which in turns affects the future cost of stealing and therefore the future decisions. The structural estimation of this model provides a good fit while capturing the heterogeneity across individuals.

We propose a theory of “optimal memory management” that unveils causal relationships between memory systems and the characteristics of the information retrieved. Our model shows that if the declarative memory is more accurate but also more costly than the procedural memory, then it is optimal to retrieve exceptional experiences with the former and average experiences with the latter. The theory provides other testable predictions: (i) decisions are closer to original experiences when the declarative memory is invoked, and (ii) the declarative memory is more likely to be invoked when the importance of recalling information accurately increases.

We report on intraspecific and interspecific morphological variation in the cranium, mandible and teeth along the ontogenetic trajectories of the two species of the largest living rodent, the capybara. A three dimensional geometric morphometrics approach was used to compare 171 Hydrochoerus hydrochaeris and 44 Hydrochoerus isthmius specimens ranging from newborn to adult. The specimens were assigned to seven different age classes according to cranial suture closure. The species can be differentiated in the morphospace occupation. They differ in the angle between the braincase and rostrum—H. hydrochaeris displays a straight transition whereas the snout of H. isthmius is inclined ventrally. The males in both species are bigger than the females, but no shape differences were detected. The youngest two age classes (up to 0.5 months and 0.5–10 months; before reaching sexual maturity) can be morphologically differentiated from the older age classes. Shape changes during growth are similar in both species: with increasing age, the round neurocranium flattens and the proportionally short snout elongates. Moreover, both species follow similar ontogenetic trajectories. H. hydrochaeris and H. isthmius can be differentiated by size and shape; the shape differences may indicate differences in diet and habitat. This study illustrates the relevance of an ontogenetic perspective to characterize species and examine the bases of disparity in adults. Furthermore, variation recorded in dental features serves to evaluate taxonomic and evolutionary aspects in fossil capybaras.

We study in the laboratory a variant of the house allocation with existing tenants problem where subjects are partitioned into tiers with hierarchical privileges, and they know their position in the priority queue before making their decision. We evaluate the performance of the modified versions of three well-known mechanisms: Top Trading Cycle (TTC), Gale-Shapley, and Random Serial Dictatorship (RSD) with Squatting Rights. For all three mechanisms, we find low rates of participation (around 40%), high rates of truth-telling conditional on participation (around 90%), high proportions of fair allocations (above 90%), and significant efficiency losses. We also observe differences across mechanisms: RSD is ranked highest in efficiency and TTC is ranked lowest in fairness. We then show that position in the queue has a positive and significant impact on participation whereas tier has little effect on behavior. Finally, the individual analysis reveals that the majority of subjects who do not play according to the theory still follow discernible patterns of participation and preference revelation.

We conduct a dictator experiment with children (7–16 years old) and adults to study the development of the underlying motivations for other-regarding behavior. Prior to choosing the sharing rule, our participants can manipulate their access to information and remain strategically ignorant of the payoffs associated with some or all of the alternatives. We find that information avoidance is infrequent (11.2% of the trials) and occurs for two opposite motives: some participants –mostly adults– look only at their payoffs and maximize them whereas some other participants –mostly school age children– look only at the other person’s payoffs and maximize them. Among fully informed participants, sharing depends on age but it is also nuanced by the opportunity cost of giving.

South America was isolated during most of the Cenozoic, and it was home to an endemic fauna. The South American Native Ungulates (SANUs) exhibited high taxonomical, morphological, and ecological diversity and were widely distributed on the continent. However, most SANU fossil records come from high latitudes. This sampling bias challenges the study of their diversity dynamics and biogeography during important tectonic and biotic events, such as the Great American Biotic Interchange, the faunal exchange between North and South America after the formation of the Isthmus of Panama. We describe new SANU remains from the Neogene of the Cocinetas (northern Colombia) and Falcon (northwestern Venezuela) Basins. In the Cocinetas Basin, the middle Miocene fauna of the Castilletes Formation includes Hilarcotherium miyou sp. nov. (Astrapotheriidae), cf. Huilatherium (Leontiniidae), and Lambdaconus cf. L. colombianus (Proterotheriidae). The late Pliocene fauna of the Ware Formation includes a Toxodontinae indet. and the putative oldest record of Camelidae in South America. In the Falcon Basin, the Pliocene/Pleistocene faunas of the Codore and San Gregorio Formations include Falcontoxodon aguilerai gen. et sp. nov. and Proterotheriidae indet. We provide a phylogenetic analysis for Astrapotheriidae and Toxodontidae. The new data document a low-latitude provinciality within some SANU clades (e.g., Astrapotheriidae, Leontiniidae) during the middle Miocene. This contrasts with the wide latitudinal distribution of clades of other mammals recorded in the fauna, including the sparassodont Lycopsis padillai, the sloth Hyperleptus?, and the proterotheriid Lambdaconus cf. L. colombianus. The Pliocene/Pleistocene tropical faunas from northern South America are characterized by the predominance of native taxa despite their proximity to the Isthmus of Panama (fully emerged by that time). Only one North American ungulate herbivore immigrant is present, a cf. Camelidae indet. The Pliocene and early Pleistocene faunas suggest that environmental changes and biotic interactions affected the diversity dynamics and biogeographic patterns of SANUs during the Great American Biotic Interchange.

Strategic thinking is an essential component of rational decision-making. However, little is known about its developmental aspects. Here we show that preschoolers can reason strategically in simple individual decisions that require anticipating a limited number of future decisions. This ability is transferred only partially to solve more complex individual decision problems and to efficiently interact with others. This ability is also more developed among older children in the classroom. Results indicate that while preschoolers potentially have the capacity to think strategically, it does not always translate into the ability to behave strategically.

We study in the laboratory a series of first price sealed bid auctions of a common value good. Bidders face three types of information: private information, public information and common uncertainty. Auctions are characterized by the relative size of these three information elements. Only half of our subjects bid differently depending on whether the last piece of information obtained is private or public but they do not react to each type of information as predicted by theory. The other half of the subjects do not distinguish between private and public information and either consistently underbid or consistently overbid.

We describe one of the oldest notoungulate skeletons with associated craniodental and postcranial elements: Thomashuxleya externa (Isotemnidae) from Canadon Vaca in Patagonia, Argentina (Vacan subage of the Casamayoran SALMA, middle Eocene). We provide body mass estimates given by different elements of the skeleton, describe the bone histology, and study its phylogenetic position. We note differences in the scapulae, humerii, ulnae, and radii of the new specimen in comparison with other specimens previously referred to this taxon. We estimate a body mass of 84 ± 24.2 kg, showing that notoungulates had acquired a large body mass by the middle Eocene. Bone histology shows that the new specimen was skeletally mature. The new material supports the placement of Thomashuxleya as an early, divergent member of Toxodontia. Among placentals, our phylogenetic analysis of a combined DNA, collagen, and morphology matrix favor only a limited number of possible phylogenetic relationships, but cannot yet arbitrate between potential affinities with Afrotheria or Laurasiatheria. With no constraint, maximum parsimony supports Thomashuxleya and Carodnia with Afrotheria. With Notoungulata and Litopterna constrained as monophyletic (including Macrauchenia and Toxodon known for collagens), these clades are reconstructed on the stem to Euungulata (i.e., Perissodactyla and Artiodactyla). Unconstrained, Bayesian analysis weakly supports the possibility that Thomashuxleya is a stem xenarthran; with Notoungulata and Litopterna constrained as monophyletic, the two clades are recovered as sister to Perissodactyla. Anatomical data sampled thus far for Thomashuxleya, combined with collagen amino acids for Pleistocene meridiungulates, substantially limit the number of possible affinities for endemic South American species among mammals, although ambiguity still remains.

Brain modularity is a key concept in neuroscience. It challenges the common view of the single coherent self adopted in many disciplines, including economics. Multi-process theories of decision-making rely on the existence of several brain systems interacting with each other to revisit standard paradigms of choice, propose choices that fit the behavioral data better, and offer testable predictions. In this paper, we present a selective review of our recent research in this area. We focus on constrained optimization models rather than the computational models extensively used in neuroscience.

To understand the thinking process in private information games, we use “Mousetracking” to record which payoffs subjects attend to. The games have three information states and vary in strategic complexity. Subjects consistently deviate from Nash equilibrium choices and often fail to look at payoffs which they need to in order to compute an equilibrium response. Choices and lookups are similar when stakes are higher. When cluster analysis is used to group subjects according to lookup patterns and choices, three clusters appear to correspond approximately to level-3, level-2, and level-1 thinking in level-k models, and a fourth cluster is consistent with inferential mistakes (as, for example, in QRE or Cursed Equilibrium theories). Deviations from Nash play are associated with failure to look at the necessary payoffs. The time durations of looking at key payoffs can predict choices, to some extent, at the individual level and at the trial-by-trial level.

One of the most striking components of the modern assemblage of South American mammals is the semiaquatic capybara (Caviidae, Hydrochoerinae), the biggest rodent in the world. The large hydrochoerines are recorded from the middle Miocene to the present, mainly in high latitudes of South America. Although less known, they are also recorded in low latitudes of South America, and in Central and North America. We report the first record of capybaras from the late Pliocene of Colombia, found in deposits of the Ware Formation, Guajira Peninsula in northeastern Colombia. We analyze the phylogenetic position within Caviidae, the possible environmental changes in the Guajira Peninsula, and the implications of this finding for the understanding of the Great American Biotic Interchange. The morphological and phylogenetic analyses indicate that the hydrochoerine of the Guajira Peninsula is a new species, ?Hydrochoeropsis wayuu, and this genus is most closely related to Phugatherium. According to the latest phylogenetic results, this clade is the sister group of the lineage of the recent capybaras (Neochoerus and Hydrochoerus). ?Hydrochoeropsis wayuu is the northernmost South American Pliocene hydrochoerine record and the nearest to the Panamanian bridge. The presence of this hydrochoerine, together with the fluvio-deltaic environment of the Ware Formation, suggests that during the late Pliocene, the environment that dominated the Guajira Peninsula was more humid and with permanent water bodies, in contrast with its modern desert habitats. Fil: Pérez, María Encarnación. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Associate Researcher At The Field Museum; Estados Unidos Fil: Vallejo Pareja, María C.. Smithsonian Tropical Research Institute; Panamá. Sam Houston State University; Estados Unidos Fil: Carrillo, Juan D.. Universitat Zurich; Suiza Fil: Jaramillo, Carlos. Smithsonian Tropical Research Institute; Panamá

We conduct a controlled laboratory experiment in which subjects dynamically choose to allocate their portfolio between (i) a safe asset, (ii) a risky asset and (iii) a skewed asset with negative expected value (a \bet"), in an environment where they can sometimes choose to acquire some information about the performance of their peers. We nd three distinct groups of individuals: 16% of subjects never buy the bet, 29% of subjects learn not to buy the bet and 55% subjects persist purchasing the bet throughout the experiment. Among the latter group, purchases are most frequent when subjects are rich and when it is their last opportunity. Our subjects are also interested in the wealth of others, especially relative to theirs. Indeed, a subject with low, medium and high wealth has a preference for nding out what is the minimum, average and maximum wealth in the session, respectively. We also nd that subjects buy more bets when they are richer and (unexpectedly) learn that their peers outperform them.

We build on research from neurobiology to model the process through which the brain maps outside evidence into decisions. The sensory system encodes information through cell-firing. Cell-firing is measured against a threshold, and an action is triggered depending on whether the threshold is surpassed. The decision system modulates the threshold. We show that the (constrained) optimal threshold is set in a way that existing beliefs are likely to be confirmed. We then derive behavioral implications. Our mechanism can explain in a unified framework a number of ‘anomalies’ noted in psychology and economics: (i) belief anchoring (the order in which evidence is received affects beliefs and choices); (ii) polarization (individuals with opposite priors may polarize their opinions after receiving identical evidence); (iii) payoff-dependence of beliefs and (iv) belief disagreement (individuals with identical priors who receive the same evidence may end up with different posterior beliefs).

We consider a model where two adversaries can spend resources in acquiring public information about the unknown state of the world in order to influence the choice of a decision maker. We characterize the sampling strategies of the adversaries in the equilibrium of the game.We show that as the cost of information acquisition for one adversary increases, that person collects less evidence whereas the other adversary collects more evidence. We then test the results in a controlled laboratory setting. The behavior of subjects is close to the theoretical predictions. Mistakes are relatively infrequent (15%). They occur in both directions, with a higher rate of over-sampling (39%) than under-sampling (8%). The main difference with the theory is the smooth decline in sampling around the theoretical equilibrium. Comparative statics are also consistent with the theory, with adversaries sampling more when their own cost is low and when the other adversary’s cost is high. Finally, there is little evidence of learning over the 40 matches of the experiment.

We present the first comprehensive review of the present and past shark and ray diversity in marine waters of Tropical America, examining the patterns of distribution in the Eastern Central Pacific (EP) and Western Central Atlantic (WA) realms. We identified the major regions of diversity and of endemism, and explored the relations to physical variables. We found a strong relationship between shark and ray diversity with area and coastal length of each province. The Tropical Northwestern Atlantic Province is characterized by high diversity and greater occurrence of endemic species, suggesting this province as the hotspot of sharks and rays in Tropical America. The historical background for the current biogeography is explored and analyzed. Referential data from 67 geological units in 17 countries, from both shallow and deep-water habitats, across five time-clusters from the Miocene to the Pleistocene were studied. New data include 20 new assemblages from six countries. The most diverse Neogene and extant groups of shark and ray are Carcharhiniformes and Myliobatiformes, respectively. The differentiation between Pacific and Atlantic faunas goes to at least the middle Miocene, probably related with the increasing closure of the Central American Seaway acting as a barrier. The highest faunal similarity between the assemblages from the EP and the WA at the early Miocene could be related to the lack of a barrier back then, but increased sampling is needed to substantiate this hypothesis.

This paper presents a model where individuals have imperfect information and there is an opportunity cost of learning. It shows that the endogenous decision to collect costly information before taking an action has a systematic effect on choices. More precisely, consider two alternatives with ex ante identical expected payoff but different variances. The model predicts that, after the learning process is stopped, a majority of individuals will select the alternative with largest payoff-variance. The result persists when agents have multiple sources of information. Applications to entrepreneurial investments, composition of advisory committees, and judicial decision-making are discussed.