International Journal of Molecular Evolution and Biodiversity 2024, Vol.14, No.4, 174-185 http://ecoevopublisher.com/index.php/ijmeb 175 a pair of legs. The mesothorax and metathorax also support the wings. Beetles possess two pairs of wings: the forewings, known as elytra, are hardened and serve as protective covers for the more delicate hind wings, which are used for flight (Cai et al., 2021). The variability in beetle morphology is immense, reflecting their adaptation to a wide range of ecological niches. For instance, the hind wings of dung beetles (Scarabaeinae) show significant variation in shape, which is linked to different selective pressures and ecological roles. Similarly, the exaggerated hind legs of certain scarab beetles from the Mesozoic era suggest adaptations for springing movements and fighting (Lu et al., 2023). The elytra themselves exhibit a range of modifications, from rigid connections to partial reductions, serving various functions such as protection, thermoregulation, and even acoustic communication (Asgari et al., 2020; Goczał and Beutel, 2023). 2.2 Morphological Adaptations Beetles have evolved a plethora of morphological adaptations that enable them to thrive in diverse habitats, diets, and behaviors. The conversion of forewings into elytra is a prime example of a morphological adaptation that has significantly contributed to the evolutionary success of beetles. Elytra provide mechanical protection, aid in water conservation, and facilitate various behaviors such as diving and burrowing (Linz et al., 2023). Adaptations related to habitat can be seen in the structural modifications of beetle wings. For example, the hind wings of dung beetles have evolved under different selective pressures, resulting in distinct morphological patterns that are linked to their ecological roles (Bai et al., 2012). Similarly, the robust and structured hind legs of certain Mesozoic scarab beetles suggest adaptations for specific behaviors like springing and fighting, which may have been crucial for their survival and reproductive success (Lu et al., 2023). Dietary adaptations are also evident in beetle morphology. The evolution of specialized herbivory in beetles, facilitated by the acquisition of plant cell wall-degrading enzymes through horizontal gene transfers, has led to the diversification of plant-feeding beetles. These enzymes enable the digestion of lignocellulose in plant cell walls, allowing beetles to exploit a variety of plant tissues and contributing to their adaptive radiation (Mckenna et al., 2019). Behavioral adaptations are reflected in the morphological traits of beetles as well. For instance, the development of neoteny in net-winged beetles (Lycidae) has led to body miniaturization and structural simplification, which are linked to their unique life histories and reproductive strategies (Kusy et al., 2019). Additionally, the presence of exaggerated morphological structures, such as horns and enlarged mandibles in stag beetles, is often associated with sexual selection and intraspecific competition (Kawano, 2020). 3 Fossil Records of Beetles 3.1 Historical Context Beetle fossils provide a rich source of information about the evolutionary history and palaeodiversity of the order Coleoptera, which is the most species-rich metazoan order with approximately 380 000 described species (Smith and Marcot, 2015). The discovery of beetle fossils has been crucial in understanding the evolutionary timeline and diversification of beetles. For instance, the study of Triassic beetles, such as those found in coprolites (Figure 1), has revealed well-preserved specimens that offer insights into early beetle evolution and their ecological interactions (Qvarnström et al., 2021). Additionally, the discovery of new beetle lineages in Eocene Baltic amber has shed light on the historical biogeography and diversification of specific beetle families. Several major fossil sites have significantly contributed to our understanding of beetle evolution. Amber deposits, particularly from the Eocene and Cretaceous periods, have preserved a diverse array of beetle species, providing detailed morphological data that are often not available from other types of fossilization (Hsiao et al., 2021). For example, the Mid-Cretaceous Burmese amber has yielded new species of soldier beetles, enhancing our understanding of their evolutionary history and biogeographical origins. Lacustrine deposits have also been important, preserving a wide range of beetle diversity and abundance, which has been instrumental in studying the macroevolutionary history of beetles.
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