The largest fossil of the segmented spider Parvithele muelleri Wunderlich, 2017 (Mesothelae: Parvithelidae) from Cretaceous Burmese amber

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  The largest fossil of the segmented spider Parvithele muelleri Wunderlich, 2017 (Mesothelae: Parvithelidae) from Cretaceous Burmese amber Abstract A new specimen of the fossil spider Parvithele muelleri Wunderlich, 2017 (Araneae: Mesothelae) is described from the mid-Cretaceous (ca. 99 Ma) Burmese amber of Myanmar. Like the original holotype, the new specimen is a mature male, which clearly preserves a series of tibial macrospines, similar to the condition in the extant genus Liphistius Schiødte, 1849. Given that the single extant mesothele family, Liphistiidae, is predicted to have radiated ca. 39–58 million years ago, the occurrence of somewhat modern-looking male pedipalp spination in older fossil mesotheles is of considerable interest. The new specimen also shows spinnerets in a relatively posterior position, although variability observed in extant species suggests that this trait may be of limited systematic value. Of particular note is the presence of a large and well-dev...

Sexual dimorphism in bite force performance and cheliceral muscle morphology in a wandering spider (Araneae, Ctenidae)

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Sexual dimorphism in bite force performance and cheliceral muscle morphology in a wandering spider (Araneae, Ctenidae)

Abstract

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Bite force is a key performance trait in many animal taxa, directly influencing ecological and behavioral interactions such as predation, defense, and mating. In spiders, this trait could be modulated by both morphological and environmental factors, yet few studies have measured it directly. Here, we provide the first in vivo measurements of bite force in the wandering spider Phoneutria depilata and test the effects of sex, body size, diet, and predator-induced stress on bite force. We also investigate the volume and mechanical advantage of cheliceral muscles using μCT scans of male and female specimens. Our results show that females exhibit significantly higher bite forces than males, even after correcting for body size. This difference is primarily associated with sexual size dimorphism but is likely also influenced by the greater volume of specific adductor muscles (Anterior medial and Anterior medial outer). In contrast, neither dietary composition nor predator exposure had a significant impact on bite performance. These findings suggest that while environmental conditions may influence other traits, bite force in P. depilata is mainly determined by intrinsic morphological features. This study highlights the role of sexual dimorphism in shaping biomechanical traits and provides a basis for future research on functional performance in arachnids.

González-Gómez, J. C., Simone, Y., Herrel, A., Guevara, G., & F. Pérez, L. M. Sexual dimorphism in bite force performance and cheliceral muscle morphology in a wandering spider (Araneae, Ctenidae). Journal of Zoology. https://doi.org/10.1111/jzo.70106