International Journal of Molecular Evolution and Biodiversity 2024, Vol.14, No.4, 174-185 http://ecoevopublisher.com/index.php/ijmeb 178 4.2 Major Morphological Changes Over Time Key evolutionary events have significantly impacted beetle morphology. The diversification of beetles during the Mesozoic era, particularly the Jurassic and Cretaceous periods, coincided with the rise of angiosperms, leading to the co-evolution of beetles and flowering plants. This period saw the emergence of specialized herbivory, facilitated by the horizontal transfer of plant cell wall-degrading enzymes (PCWDEs) from bacteria and fungi, which enabled beetles to efficiently digest plant tissues (Mckenna et al., 2019). This adaptation was crucial for the diversification of herbivorous beetles and their subsequent radiation. Significant morphological transformations include the development of exaggerated structures, such as the robust hind legs of Antiqusolidus maculatus, which likely supported unique behaviors like springing movements. Another example is the evolution of neoteny in net-winged beetles (Lycidae), where female neoteny evolved multiple times, leading to body miniaturization and structural simplification (Kusy et al., 2019). These changes reflect the diverse evolutionary pressures and ecological niches that beetles have adapted to over time. 4.3 Adaptive Radiation and Diversification Environmental changes have played a crucial role in promoting morphological diversity among beetles. The Cretaceous Terrestrial Revolution, marked by the widespread emergence of flowering plants, provided new ecological opportunities that spurred the adaptive radiation of beetles. The codiversification of beetles and angiosperms is a prime example, where the evolution of plant-feeding habits in beetles was closely linked to the availability of new plant resources (Wang et al., 2013). Case studies of adaptive radiation in beetle lineages include the diversification of the Chrysomeloidea superfamily, which saw the emergence of longhorn beetles (Cerambycidae) and leaf beetles, among others. The earliest known longhorn beetle, Cretoprionus liutiaogouensis, from the Lower Cretaceous, exhibits features characteristic of the Prioninae subfamily, indicating an early adaptation to specific ecological niches (Wang et al., 2014). Similarly, the evolutionary history of Carabid beetles (Carabidae) shows how changes in thoracic structure and locomotory adaptations have allowed them to exploit various habitats and prey types, contributing to their extensive diversification (Brandmayr, 2020). 5 Insights from Fossil Records 5.1 Patterns of Morphological Evolution The fossil record provides a wealth of information on the evolutionary trends in beetle morphology, particularly in terms of size, shape, and structural complexity. One of the most significant morphological adaptations in beetles is the development of the elytra, or hardened forewings, which serve multiple functions including protection, thermoregulation, and aiding in flight. The evolution of elytra is believed to have occurred early in the Coleoptera lineage, likely during the Carboniferous period, through a gradual process of forewing sclerotization and the formation of inward-directed epipleura and a secluded sub-elytral space (Kusy et al., 2019; Goczał and Beutel, 2023). In terms of size and shape, beetles exhibit a wide range of morphological adaptations. For instance, the Cetoniinae subfamily shows significant variation in body weight, which is accommodated by both size-invariant and size-dependent features in their elytra. These adaptations include chemical compositions, layered-fibrous architectures, and graded motifs that maintain biomechanical functionality across different sizes. Additionally, the reduction and modification of elytra have been observed in various beetle lineages, such as the ship-timber beetles (Lymexylidae), where fossil evidence shows a trend towards shortened elytra and exposed hindwings, dating back to the mid-Cretaceous period (Yamamoto, 2019). Specialized morphological features such as mandibles and sensory structures have also evolved in response to ecological and behavioral pressures. For example, in the broad-horned flour beetle (Gnatocerus cornutus), the enlargement of mandibles for fighting has led to correlated changes in body morphology, including the reduction of elytra length (Okada and Miyatake, 2009). Similarly, the evolution of campaniform sensilla in the elytra of
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