Pliomerina Chugaeva, 1958, a characteristic element of the peri-Gondwanan Eokosovopeltis-Pliomerina Province, occurs in Llanvirn and Caradoc strata of the Argentine Precordillera. Three protaspid instars are present in the ontogeny of the Early Caradoc Pliomerina peripata new species. A species possibly representing Pliomerella is a rare element in Early Caradoc strata of the Las Aguaditas Formation. Prosopiscus is represented by a Llanvirn species with a first record of protaspid larvae for the enigmatic Family Prosopiscidae. Early growth stages support closest relations of prosopiscids to Phacopina. The presence of Pliomerina and Prosopiscus, along with the cheirurid Pateraspis, demonstrates a peri-Gondwanan influence on the Precordilleran fauna by the Llanvirn, and supports the proximity of the Precordillera terrane to the South American margin by that time.

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