15 research outputs found
Dental histology of late Miocene hipparionins compared with extant Equus, and its implications for Equidae life history
Hipparionins were a dominant element of the late Miocene faunas of Europe; however, their biology and ecology remain incompletely understood. In this paper, we explore the pace of life history of different-sized hipparionin horses, using dental histology, and compare it with extant equids. In doing so we consider (i) the size diversity of hipparionins, (ii) their generally smaller size compared to extant equids, and (iii) the allometric coupling between size and life history. In particular, we reconstruct the dental growth in lower first/second molars and in later-formed lower third molars for three hipparionin taxa: two dwarf species (Hipparion periafricanum and H. gromovae), and a larger species (H. concudense). We also analyze dental growth in an extant zebra (Equus quagga) for comparative purposes. Our results reveal that, within each species, there are differences in enamel growth parameters between the first/second molars and third molars. These results illustrate the differences in the developmental timing of these teeth and the existence of a relationship between dental growth parameters with somatic growth. We also find that hipparionin teeth grow at slower rates and tend to erupt later in time than in extant Equus. Dwarf hipparionins, moreover, exhibit lower enamel extension rates than the larger species, but similar formation and eruption times. Considering the link between dental development and life history, these results suggest a slower pace of growth of selected hipparionins compared to extant equids, and a further slower life history than expected for their size in the two dwarf forms
Life history and ecology of late Miocene hipparionins from the circum-Mediterranean area /
Departament responsable de la tesi: Departament de Biologia Animal, de Biologia Vegetal i d'Ecologia.A portada: Institut Català de Paleontologia Miquel Crusafont.Els hipparionins eren uns èquids tridà ctils molt diversificats durant el Miocè superior a l'à rea circummediterrà nia, on alguns van esdevenir nans. Per la seva abundà ncia, aquests són un grup clau en la recerca paleoecològica i l'anà lisi de patrons evolutius, tot i que encara cal conèixer millor la seva ecologia. Un dels aspectes més importants de la biologia d'un organisme és la seva història de vida, la qual pot ser reconstruïda a partir de la microestructura òssia i dental, i ens proporciona informació sobre el context ambiental. Aixà mateix, la dieta, una altra caracterÃstica de la biologia d'un organisme i un important vincle amb l'ambient, es pot inferir a través del microdesgast dental. En aquesta tesi, l'objectiu principal és dilucidar les condicions ecològiques i els mecanismes relacionats amb la disminució de mida que van patir alguns hipparionins de l'est i oest del Mediterrani. Amb aquesta finalitat, es (i) reconstrueixen els patrons de creixement de metà podes i molars d'hipparionins de diferent mida, (ii) s'infereixen les seves històries de vida, i (iii) s'exploren les seves dietes a través del microdesgast per testar les inferències ecològiques obtingudes de l'anà lisi de les històries vitals. L'estudi de la histologia dels metà podes permet reconstruir el creixement ontogenètic i establir l'assoliment d'una maduresa relativa. La identificació de diferents edats de maduració, doncs, evidencia diferents estratègies de creixement en els hipparionins analitzats. L'estudi de laminacions dià ries en l'esmalt revela, per primer cop en ungulats, taxes de creixement en primeres/segones molars més elevades que en terceres molars de formació més tardana, suggerint un vincle entre el desenvolupament dental i el somà tic. AixÃ, les taxes de creixement dental més lentes i les erupcions relativament posteriors (correlacionades amb trets d'història de vida) indiquen ritmes de creixement més lents en hipparionins comparat amb Equus. Això contrasta amb la idea d'històries de vida rà pides en hipparionins pel fet de ser generalment més petits. A més, els hipparionins nans occidentals mostren un desenvolupament dental més lent que el de les formes grans i una maduresa relativament tardana, indicant també una història vital més lenta de l'esperada per la seva mida. D'acord amb la teoria de les històries de vida, això assenyala que la menor disponibilitat de recursos és la causa del nanisme en aquests hipparionins. Per contra, les formes petites orientals mostren una maduresa relativa avançada, el que suggereix que la disminució de mida va ser causada per una major mortalitat extrÃnseca (depredació). Diferències paleoambientals explicarien les pressions ecològiques contraposades: ambients més tancats a l'oest del Mediterrani proporcionaven més cobertura contra la depredació però menys recursos pels hipparionins, mentre a l'est els hà bitats més oberts eren arriscats però rics en recursos. L'anà lisi del microdesgast dental indica un tipus d'alimentació mixta i oportunista en la majoria dels hipparionins, encara que algunes formes occidentals grans pasturaven. D'altra banda, els hipparionins occidentals nans tenien espectres tròfics més amplis i brostejaven, el que avala que habitessin ambients més boscosos i/o tinguessin recursos més limitats. En canvi, els hipparionins orientals petits no difereixen dels grans en les seves textures de microdesgast, suggerint dietes similars en un entorn ric en recursos que evitaria la necessitat del seu repartiment. Contrà riament al que s'esperaria en ambients més oberts, els hipparionins orientals menjaven menys gramÃnies que els occidentals, cosa que es podria relacionar amb canvis de dieta durant sequeres i/o la presència de sorra alterant la textura del microdesgast. En resum, aquesta tesi proporciona evidències que els processos de disminució de mida i els mecanismes infrajacents no són uniformes sinó que depenen del context ecològic. Els resultats presentats suposen un pas més per entendre les històries de vida i ecologies d'èquids extints.Los hipparioninos eran unos équidos tridáctilos muy diversificados durante el Mioceno superior en el área circunmediterránea, donde algunos decrecieron en tamaño. Debido a su abundancia, estos constituyen un elemento clave en estudios paleoecológicos y de patrones evolutivos, aunque todavÃa queda mucho por conocer sobre su ecologÃa. Uno de los aspectos más importantes en la biologÃa de un organismo es su historia de vida, la cual puede ser reconstruida a partir de la microestructura ósea y dental, y nos proporciona información sobre el contexto ambiental. Asimismo, la dieta, otra caracterÃstica de la biologÃa de un organismo y un importante vÃnculo con el ambiente, se puede inferir a través del microdesgaste dental. En esta tesis, el objetivo principal es dilucidar las condiciones ecológicas y los mecanismos relacionados con la disminución de tamaño de algunos hipparioninos del este y oeste del Mediterráneo. Con esta finalidad, se (i) reconstruyen los patrones de crecimiento de metápodos y molares de hipparioninos de diferentes tamaños, (ii) se infieren sus historias de vida y (iii) se exploran sus dietas a través del microdesgaste para testar las inferencias ecológicas obtenidas del análisis de las historias vitales. El estudio de la histologÃa de los metápodos permite reconstruir el crecimiento ontogenético y establecer una madurez relativa. La identificación de distintas edades de maduración ha permitido distinguir diferentes estrategias de crecimiento entre los hipparioninos analizados. El estudio de laminaciones diarias en el esmalte revela, por primera vez en ungulados, tasas de crecimiento en primeras/segundas molares más elevadas que en terceras molares de formación más tardÃa, sugiriendo un vÃnculo entre el desarrollo dental y el somático. AsÃ, las tasas de crecimiento dental más lentas y las erupciones posteriores (correlacionadas con rasgos de historia de vida) indican ritmos de crecimiento lentos en hipparioninos en comparación con Equus. Esto contrasta con la idea de historias de vida rápidas en hipparioninos por ser generalmente más pequeños. Además, los hipparioninos enanos occidentales muestran un desarrollo dental más lento que el de las formas grandes y una madurez relativamente tardÃa, indicando también una historia vital más lenta de la esperada por su tamaño. De acuerdo con la teorÃa de las historias de vida, esto sugiere que una menor disponibilidad de recursos fue la causa del enanismo en estas formas. Por el contrario, los hipparioninos pequeños orientales muestran una madurez relativa avanzada que sugiere que la disminución de tamaño fue debida a una mayor mortalidad extrÃnseca (depredación). Diferencias paleoambientales explicarÃan las presiones ecológicas contrapuestas: ambientes más cerrados al oeste del Mediterráneo proporcionaban más cobertura contra la depredación, pero menos recursos para los hipparioninos, mientras que al este los hábitats más abiertos eran arriesgados pero ricos en recursos. El análisis del microdesgaste dental indica un tipo de alimentación mixta y oportunista en la mayorÃa de los hipparioninos, aunque algunas formas occidentales grandes pastaban. Por otra parte, los hipparioninos occidentales enanos tenÃan espectros tróficos más amplios y ramoneaban, lo que avala que habitasen ambientes boscosos y/o dispusieran de recursos más limitados. En cambio, los hipparioninos orientales pequeños no difieren de los grandes en las texturas de microdesgaste, indicando dietas similares en un entorno rico en recursos que evitarÃa la necesidad su repartimiento. Contrariamente a lo que se esperarÃa en ambientes más abiertos, los hipparioninos orientales comÃan menos gramÃneas que los occidentales, lo que se podrÃa relacionar con cambios de dieta durante sequÃas y/o la presencia de arena alterando el microdesgaste. En resumen, esta tesis proporciona evidencias de que los procesos de disminución de tamaño no son uniformes, sino que dependen del contexto ecológico. Los resultados presentados suponen un paso más para entender las historias de vida y ecologÃas de équidos extintos.Hipparionins are a clade of tridactyl equids that greatly diversified during the late Miocene throughout the circum-Mediterranean area, with some taxa undergoing dwarfing. Due to their abundance, they have been the subject of several paleoecological studies and constitute a key mammalian group for exploring evolutionary patterns, although more research is necessary to better understand their ecology. One central aspect of an organism's biology is its life history, which can be inferred from the analysis of bone and dental microstructure. In addition, since a species' life history evolves relative to ecological conditions, its study can provide environmental information. Feeding ecology, another feature of an organism's biology and an important link to its environment, can be inferred from dental microwear. With this in mind, the central aim of this thesis is to elucidate the ecological conditions and mechanisms that accompanied dwarfing in western and eastern Mediterranean hipparionins. Therefore, I (i) reconstruct the growth patterns of metapodials and molars in different-sized hipparionins using bone and dental histology, (ii) make inferences regarding their life histories, and (iii) examine their diets by studying dental microwear textures to test the ecological inferences obtained from life history analyses. Metapodial histology confirms the usefulness of metapodials for reconstructing the entire ontogenetic growth and establishing a relative maturity attainment. Therefore, the identification of different timings of metapodial growth cessation demonstrate distinct growth strategies within the hipparionins analyzed. For the first time among ungulates, the analysis of daily enamel laminations reveals higher growth rates in first/second molars compared to later-formed third molars, which suggests a link between dental development and somatic growth. Thus, the slower dental growth rates and the relatively late eruption timings (correlated with life history traits) in hipparionins indicate slower paces of life compared to Equus. This challenges previous assumptions that hipparionins have faster life histories due to their generally smaller body size. Western dwarf hipparionins, moreover, show an even slower dental development than larger forms, and a relatively late skeletal maturity, pointing to a slower life history than expected for their size. Conforming with life history theory, this evidences that dwarfing in these western hipparionins was led by lower resource availability. Conversely, the eastern small-sized form shows an advanced relative maturity, which indicates that its size decrease was triggered by higher extrinsic mortalities (predation). This scheme suggests that paleoenvironmental differences accounted for the distinct ecological pressures inferred: forested habitats in the western Mediterranean likely provided increased cover against predation but less resources for the hipparionins, while the more open habitats further east were riskier, but richer in resources. Dietary reconstructions reveal mixed-feeding diets and opportunistic feeding behaviors in most hipparionins, although some western large-sized forms were grazers. Dental microwear textures of western hipparionins, therefore, provide evidence of distinct diets between the size classes. In this case, dwarfs had broader browse-dominated feeding spectra supporting the idea that they dwelt in more forested habitats and/or that their resources were more limited. Conversely, eastern hipparionins do not show significantly different microwear textures, thus indicating similar dietary preferences in a resource-rich environment that precluded resource partitioning. Contrary to expectations for more open habitats, eastern hipparionins seem to have included less grass in their diets than western forms, which could be related to a higher consumption of browse during droughts and/or the presence of grit affecting microwear texture. In summary, this thesis provides evidence that the dwarfing process and the mechanisms behind it are not uniform, but that they depend on the specific ecological context. The results represent a further step toward the understanding of the life histories and ecologies of extinct equids
The life history of European Middle Pleistocene equids : first insights from bone histology
Evolutionary trends in body size are a central issue of study in Palaeontology. However, and despite body size being one of the most important life history traits of an animal, iconic size-decrease trends such as the one experienced by Equus during the European Pleistocene have never been analysed under a life history framework. Here, we studied the metapodial bone histology of two large Middle Pleistocene species (Equus mosbachensis and Equus steinheimensis) to reconstruct key life history traits that correlate with body size (e.g. size at birth, growth rate), and compare them with that of smaller extant Equus (Equus grevyi, Equus quagga, Equus zebra and Equus hemionus). Our results show that neonatal size of these Middle Pleistocene equids fits predictions from body mass scaling. We estimate a similar age of epiphyseal fusion for the metapodia of E. mosbachensis and E. steinheimensis and that of extant equids. Our findings also reveal that extinct equids grew at higher rates than extant Equus. This result conforms to the predictions of life history theory on environments with different levels of resource availability and provides a new framework of study for body size shifts on European Pleistocene equids
Bone histology provides insights into the life history mechanisms underlying dwarfing in hipparionins
Size shifts may be a by-product of alterations in life history traits driven by natural selection. Although this approach has been proposed for islands, it has not yet been explored in continental faunas. The trends towards size decrease experienced by some hipparionins constitute a good case study for the application of a life history framework to understand the size shifts on the continent. Here, we analysed bone microstructure to reconstruct the growth of some different-sized hipparionins from Greece and Spain. The two dwarfed lineages studied show different growth strategies. The Greek hipparions ceased growth early at a small size thus advancing maturity, whilst the slower-growing Spanish hipparion matured later at a small size. Based on predictive life history models, we suggest that high adult mortality was the likely selective force behind early maturity and associated size decrease in the Greek lineage. Conversely, we infer that resource limitation accompanied by high juvenile mortality triggered decrease in growth rate and a relative late maturity in the Spanish lineage. Our results provide evidence that different selective pressures can precipitate different changes in life history that lead to similar size shifts
Publisher Correction : Bone histology provides insights into the life history mechanisms underlying dwarfing in hipparionins
Aquesta és una correcció a l'article 10.1038/s41598-018-35347-
Reconstructing molar growth from enamel histology in extant and extinct Equus
Abstract The way teeth grow is recorded in dental enamel as incremental marks. Detailed analysis of tooth growth is known to provide valuable insights into the growth and the pace of life of vertebrates. Here, we study the growth pattern of the first lower molar in several extant and extinct species of Equus and explore its relationship with life history events. Our histological analysis shows that enamel extends beyond the molar’s cervix in these mammals. We identified three different crown developmental stages (CDS) in the first lower molars of equids characterised by different growth rates and likely to be related to structural and ontogenetic modifications of the tooth. Enamel extension rate, which ranges from ≈400 μm/d at the beginning of crown development to rates of ≈30 μm/d near the root, and daily secretion rate (≈17 μm/d) have been shown to be very conservative within the genus. From our results, we also inferred data of molar wear rate for these equids that suggest higher wear rates at early ontogenetic stages (13 mm/y) than commonly assumed. The results obtained here provide a basis for future studies of equid dentition in different scientific areas, involving isotope, demographic and dietary studies
Reconstructing molar growth from enamel histology in extant and extinct Equus
The way teeth grow is recorded in dental enamel as incremental marks. Detailed analysis of tooth growth is known to provide valuable insights into the growth and the pace of life of vertebrates. Here, we study the growth pattern of the frst lower molar in several extant and extinct species of Equus and explore its relationship with life history events. Our histological analysis shows that enamel extends beyond the molar's cervix in these mammals. We identifed three diferent crown developmental stages (CDS) in the frst lower molars of equids characterised by diferent growth rates and likely to be related to structural and ontogenetic modifcations of the tooth. Enamel extension rate, which ranges from ≈400 μm/d at the beginning of crown development to rates of ≈30 μm/d near the root, and daily secretion rate (≈17 μm/d) have been shown to be very conservative within the genus. From our results, we also inferred data of molar wear rate for these equids that suggest higher wear rates at early ontogenetic stages (13mm/y) than commonly assumed. The results obtained here provide a basis for future studies of equid dentition in diferent scientifc areas, involving isotope, demographic and dietary studies
Dental histology of late Miocene hipparionins compared with extant Equus, and its implications for Equidae life history
Hipparionins were a dominant element of the late Miocene faunas of Europe; however, their biology and ecology remain incompletely understood. In this paper, we explore the pace of life history of different-sized hipparionin horses, using dental histology, and compare it with extant equids. In doing so we consider (i) the size diversity of hipparionins, (ii) their generally smaller size compared to extant equids, and (iii) the allometric coupling between size and life history. In particular, we reconstruct the dental growth in lower first/second molars and in later-formed lower third molars for three hipparionin taxa: two dwarf species (Hipparion periafricanum and H. gromovae), and a larger species (H. concudense). We also analyze dental growth in an extant zebra (Equus quagga) for comparative purposes. Our results reveal that, within each species, there are differences in enamel growth parameters between the first/second molars and third molars. These results illustrate the differences in the developmental timing of these teeth and the existence of a relationship between dental growth parameters with somatic growth. We also find that hipparionin teeth grow at slower rates and tend to erupt later in time than in extant Equus. Dwarf hipparionins, moreover, exhibit lower enamel extension rates than the larger species, but similar formation and eruption times. Considering the link between dental development and life history, these results suggest a slower pace of growth of selected hipparionins compared to extant equids, and a further slower life history than expected for their size in the two dwarf forms