With the oldest known record dating to the Sinemurian age of the Early Jurassic, and possible species surviving into the Cenomanian stage of the Late Cretaceous, Pseudastacus has a long temporal range and was a widespread taxon.

[1] A year later, Münster described several fossils from the Solnhofen Limestone he believed to represent isopods, and erected the genus Alvis to contain the single species A. octopus, naming it after the dwarf Alvíss from Norse mythology.

[4] The name Pseudastacus combines the Greek word ψεύδος (pseudos, meaning "false") and Astacus, referencing its resemblance to the modern crayfish genus.

His analysis also found that the specimen named as Alvis octopus by Münster was not an isopod, but essentially identical to P. pustulosus, and therefore synonymized the two species.

[6][21][22] In 2013, Karasawa and colleagues recovered Pseudastacus as the sister taxon to Stenochirus, making Chilenophoberidae a paraphyletic group.

In addition, they noted that in fossil glypheids and the extant Neoglyphea inopinata, the females possess longer clawed limbs than the males.

Based on this, they declared P. muensteri as a junior synonym of P. pustulosus, and actually represents a female specimen of this species which was sexually dimorphic.

[6] The type series of P. lemovices consists of five individuals preserved together in a single limestone slab, possibly indicating that the species exhibited gregarious behaviour, with this group being killed in a mass mortality event (perhaps caused by temperature changes or lack of oxygen).

All known remains of this species were collected from the Solnhofen Limestone of Bavaria, Germany, which dates to the Tithonian age of the Late Jurassic period, between 149.2 and 145 million years ago.

During the time of deposition, the European continent was partly inundated, forming a dry, tropical archipelago at the edge of the Tethys Ocean.

[26] A coastal habitat is further confirmed by the fossil content of the area, which includes numerous marine species that P. pustulosus would have lived alongside.

[30][31][32] Remains of terrestrial animals, though rarer, are also present and represent species that would have lived on the islands surrounded by the lagoons, including dinosaurs (such as Archaeopteryx and Compsognathus),[33] lizards (such as Ardeosaurus, Bavarisaurus and Schoenesmahl),[34] and pterosaurs (such as Rhamphorhynchus, Aurorazhdarcho, Pterodactylus, Germanodactylus, Ctenochasma and Scaphognathus).

[35][36] Two Pseudastacus species, P. mucronatus and P. minor, originate from deposits dating to the Cretaceous period, though their assignment to this genus remains uncertain.

Known remains of P. mucronatus have been collected from the Speeton Clay Formation in England, which extends from the Berriasian to Aptian ages of the Early Cretaceous (145 to 113 million years ago).

[39] Ammonites, crustaceans, and the teeth of sharks and rays (including Cretorectolobus, Spathobatis, Dasyatis and Synechodus) are also commonly recorded from these deposits.

[8][40][41] Known from a single (currently missing) specimen from the Cenomanian-aged (between 100.5 and 93.9 million-year-old) marine deposits of Lebanon, P. minor would be the geologically youngest species of Pseudastacus, assuming it does belong to the genus.

[43] The paleontological sites of Lebanon have yielded many well-preserved fossils, including a wide variety of fish, crustaceans and even octopuses.