New mid-Cretaceous macrothelids showing a similar living mode to extant Macrothelidae (Araneae: Mygalomorphae)

Five new spider species of the family Macrothelidae (Araneae:
Mygalomorphae) are described from mid-Cretaceous Kachin amber, Myanmar. A
new genus Acanthomacrothele gen. nov. is established for three new
species: A. pauciverrucae sp. nov., A. geminata sp. nov. and A.
longicaudata sp. nov. Both male and female specimens of A. pauciverrucae
sp. nov. are described, representing a rare case of a fossil spider with
both sexes known. We also describe an unidentified juvenile of
Macrothelidae to document different developmental stages of Cretaceous
species. To test the phylogenetic position of the new fossils, we
performed phylogenetic analyses using both topology-unconstrained and
topology-constrained methods. Our analyses supported the placement of
Acanthomacrothele gen. nov. in Macrothelidae, although its phylogenetic
relationship to other genera of Macrothelidae differed among different
analytical methods. The fossils documented here have elongated, widely
spaced posterior lateral spinnerets, compact rectangular group of eyes on
a tubercle and more spines on male tibia of anterior legs than female,
similar to extant macrothelids, suggesting that they probably have similar
retreat construction behavior, habitat preference and mating position to
their living relatives.