Author ORCID Identifier

https://orcid.org/0000-0001-7705-606X

Semester

Summer

Date of Graduation

2026

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Geology and Geography

Committee Chair

Jaime Toro

Committee Member

Amy Weislogel

Committee Member

Ivan L. F. Magalhaes

Abstract

The infraorder Mygalomorphae represents one of the earliest-diverging lineages of spiders, but its fossil record remains sparse relative to the modern diversity of the group. This is a reflection of both ecological and preservational biases, such as the predominantly fossorial habits of many mygalomorphs and the strong bias of the spider fossil record toward amber deposits. Compression fossils from rock deposits are therefore especially important for documenting the evolutionary history of the group. Here, two new mygalomorph fossils from the Lower Cretaceous Crato Formation, Araripe Basin (Brazil) are described. The first specimen is tentatively referred to ?Idiopidae based on male palpal morphology which includes an excavated tibia. The second specimen is interpreted as closely comparable to Pycnothelidae based on a combination of characters such as the absence of a rastellum, aspinose and scopulate tarsi and the presence of three tarsal claws with one reduced. This second specimen is also the largest spider fossil ever recorded, with a total length of 29.1 mm and a leg span of 87.5 mm. These fossils add two new fossorial morphotypes to the previously known Crato mygalomorph assemblage, which was dominated by long-spinneret diplurid-like forms. These new specimens suggest that Early Cretaceous mygalomorph communities in the Crato paleoecosystem were more morphologically and ecologically diverse than previously documented, and reinforce the relevance of Gondwanan deposits for understanding the early history of Mygalomorphae.

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