From the Art Daily website:
A set of 12 burials, inside basalt boxes, were discovered by archaeologists of the National Institute of Anthropology and History (INAH – Conaculta) in the southeast part of Nayarit. Given the great quantities of human bones that were contained in each burial, archaeologists consider this finding as a type of pre Hispanic cemetery about 1000 years old.
According to Lourdes Garcia Barajas and Jose Beltran Medina, archaeologists of the INAH Center in Nayarit, this funerary finding is unique since it’s the first one of its kind and because this is a mortuary tradition that had been unknown in the region, with the only related findings being shaft tombs or osseous remains cramped inside clay pots. Until this finding, never had they found osseous remains inside basalt boxes.
The experts detailed that they found complete skeletons both inside and around the mortuary containers –most of which were determined to have been burned given their black coloring– also, they found bones inside ceramic pots contained in the basalt boxes, which is why specialists haven’t been able to determine the total number of individuals that had been interred.