Neoichnology of mygalomorph spiders: Improving the recognition of spider burrows in the geological record

Author(s)

Nascimento, Diego Luciano ^{[1, 2]} ; Netto, Renata Guimaraes ^[3] ; Indicatti, Rafael Prezzi ^{[4, 5]}

Affiliation

^[1] Univ Estadual Campinas, Inst Geosci, BR-13083855 Campinas, SP - Brazil

^[2] Sao Paulo State Univ Julio de Mesquita Filho, Inst Geosci & Exact Sci, Ave 24-A, 1515, BR-13506900 Rio Claro, SP - Brazil

^[3] Unisinos Univ, Geol Grad Program, Ave Unisinos 950, BR-93022750 Sao Leopoldo, RS - Brazil

^[4] Univ Estadual Paulista, Inst Biociencias, Dept Zool, Rio Claro, SP - Brazil

^[5] Inst Butantan, Lab Colecoes Zool, Sao Paulo, SP - Brazil

• Document type: Journal article
• Source: Journal of South American Earth Sciences; v. 108, JUN 2021.
• Web of Science Citations: 0

Abstract

The female Mygalomorphae spiders are sedentary and long-lived organisms that spend most of their lives inside their burrows. Neoichnological studies provide relevant information that can help the recognition of these structures in paleosols. Body fossils of spiders are known since the Carboniferous and burrowing is a primitive behavior in Mygalomorphae spiders. However, trace fossils attributable to ground-dwelling spiders are still poorly documented in the geological record. In this work, we examine the burrows and burrowing behavior of Rachias intermedius Soares, 1944 (Araneae: Mygalomorphae: Nemesiidae) in its natural environment and discuss the characteristics that can be used as ichnotaxobases for recognition of fossil spider burrows. Three major architectures, straight shaft with a terminal ovoid chamber, J-shaped winding shaft with the terminal chamber, and Y-shaped with a terminal teardrop-shaped chamber, are described and compared to morphologically similar ichnogenera, like Capayanichnus, Loloichnus, Macanopsis, and Psilonichnus. Differences in burrow shape and architecture are linked with the spider's sex and ontogenetic stage. Pedipalps, chelicerae, and fangs are used for soil excavation, forming a variety of burrow wall ornaments represented by delicate sub-horizontal parallel ridges, irregular knobby micro-relief surface with soil structures attached to the wall, rounded pits, and millimeter-scale vertical striations along the burrow length. A thick inorganic clay lining covers the inner burrow wall, a feature that has not been described for spider burrows yet. These characteristics allow distinguishing spider burrows from burrows produced by other soil-dwelling arthropods. They should be used for spider burrow recognition in paleosols, mainly the millimeter-scale vertical striations that had not been documented before. The data discussed herein improve the knowledge about spider burrowing behavior and the mechanism that play the main role in preserving these burrows' features in the fossil record. (AU)

• FAPESP's process: 17/11985-9 - Morphological and molecular systematics and biogeography of Mygalomorph spiders of Atlantic Forest
• Grantee: José Paulo Leite Guadanucci
• Support Opportunities: BIOTA-FAPESP Program - Young Investigators Grants
• FAPESP's process: 15/17632-5 - Sedimentation and pedogenesis in Cretaceous continental sequences of the Bauru, Sanfranciscana, Parecis and Neuquén basins.
• Grantee: Alessandro Batezelli
• Support Opportunities: Regular Research Grants
• FAPESP's process: 12/18287-1 - Systematics of the Neotropical Nemesiidae genera (Araneae, Mygalomorphae)
• Grantee: Rafael Prezzi Indicatti
• Support Opportunities: Scholarships in Brazil - Post-Doctoral