The Cova des Pas de Vallgornera is the longest cave of Mallorca (Balearic Islands, Western Mediterranean) and one of the 30 longest caves in the world. The exploration of one of the galleries allowed the discovery of a fossiliferous deposit of vertebrate remains in a remarkable preservation state. The fossil faunal complex found in this gallery is composed of up to 5 mammalian species (Myotragus aff. kopperi, Hypnomys onicensis, Nesiotites aff. ponsi, Rhinolophus aff. mehelyi and Pipistrellus sp.), at least 14 bird species (among them two Mallorcan endemic taxa: Pica mourerae and Athene vallgornerensis), one reptile (Podarcis aff. lilfordi) and one amphibian (Discoglossus sp.). This faunal composition is similar to the one recorded in the Pedrera de s’Ònix, a well known deposit from the Early Pleistocene of Mallorca, and shared morphological characteristics between taxa of both deposits suggest that the chronology of the Cova des Pas de Vallgornera should be considered Early Pleistocene as well. Both taxonomical analysis and chronology of this fauna furnished information on some speleological aspects of the cave.

The data set presented in this paper includes the fossil fauna collected in the cave named Cova des Pas de Vallgornera (CPV), located on the southern coast of Mallorca (Balearic Islands, Spain). It holds 1481 catalogued items, 97.5% identified at species level. Mammalia, Aves, Reptilia, and Amphibia are represented in the Database. The fauna collected in the cave includes the three endemic mammals present on Mallorca during the Early Pleistocene (Myotragus aff. kopperi, Hypnomys onicensis, and Nesiotites aff. ponsi). There are also represented two taxa of Chiroptera (Rhinolophus aff. mehelyi and Pipistrellus sp.), 16 taxa of birds (6 of them identified at species level), one Reptilian taxon (Podarcis sp.) and one Amphibian taxon (Discoglossus sp.). Most of fossils were collected during a single excavation campaign of 3 days (28-30th May, 2010). A few remains were obtained in two previous visits to the cave, in 2006 and 2009. All the specimens are curated and documented at the Vertebrate Collection of the IMEDEA [Institut Mediterrani d'Estudis Avançats (CSIC-UIB)]. The assemblage of CPV fossils is a part of the paleontological collection IMEDEA-PALEOVERT, included at the GBIF portal.

A growing number of studies suggest that cave formation by deep-seated groundwater  (hypogene) is a more common process of subsurface water-rock interaction than previously  thought. Fossil hypogene caves are identified by a characteristic suite of morphological  features on different spatial scales. In addition, mineral deposits (speleothems) may provide  clues about the chemical composition of the paleowater, which range from CO2-rich to  sulfuric acid-bearing waters. This is one of the first studies to examine hypogene cave  formation in dolomite. Kozak Cave is a fossil cave near the Periadriatic Lineament, an area  known for its abundance of CO2-rich springs. The cave displays a number of macro-, mesoand  micromorphological elements found also in other hypogene caves hosted in limestone,  marble or gypsum, including cupolas, cusps, Laughöhle-type chambers and notches. The  existance of cupolas and cusps suggests a thermal gradient capable of sustaining free  convection during a first phase of speleogenesis, while triangular cross sections (Laughöhle  morphology) indicate subsequent density-driven convection close to the paleowater table Notches mark the final emergence of the cave due to continued rock uplift and valley  incision. Very narrow shafts near the end of the cave may be part of the initial feeder system,  but an epigene (vadose) overprint cannot be ruled out. Vadose speleothems indicate that the  phreatic phase ended at least about half a million years ago. Drill cores show no evidence of  carbon or oxygen isotope alteration of the wall rock. This is in contrast to similar studies in  limestone caves, and highlights the need for further wall-rock studies of caves hosted in  limestone and dolomite