Fossil remains of extinct relatives of cephalopods are known to occur in Peruvian strata of Ordovician age (∼485–444 million years old) for a long time. However, they remain poorly known today. Here, we describe for the first time specimens that were collected from strata of the San José Formation of the Kimbiri and Inambari areas, southeastern Peru. The assemblage contains five species; one of them, Bactroceras cocafolium, is new to science. One other species is known from strata of the same age from elsewhere in the central Andes. The five species also show a relationship with cephalopod assemblages known from the old continents Gondwana and Avalonia.

The existence of Ordovician Peruvian cephalopods has been known since at least the 1910s. However, they have not been effectively documented previously with only a few described taxa listed in open nomenclature. Here, we describe a cephalopod assemblage at the finest taxonomic level possible. The specimens were collected from the Floian section (Baltograptus minutus graptolite Zone) of the San José Formation from the Kimbiri area, northwest of Cuzco (= Cusco), and from a section along the Inambari River, southeastern Peru. The dark mudstone-siltstone of the San José Formation was deposited within the Central Andean Basin. The assemblage contains five species of small orthoceracones belonging to four families and three orders, consisting of one indeterminate dissidocerid, one bathmoceratid (Saloceras sp.), one rioceratid (Rioceras? sp.), and two baltoceratids belonging to Annbactroceras grecicostatum (Kobayashi, 1937), and Bactroceras cocafolium new species. The dominance of small orthoceracones is typical for early Paleozoic pelagic cephalopod assemblages. One species, A. grecicostatum, is known from elsewhere in the Central Andean Basin. The other taxa indicate a peri-Gondwana-Avalonia paleogeographical relationship of the cephalopod fauna, which is consistent with previously published data from brachiopods and trilobites.