The taphonomy and palaeoecology of the early Miocene (Burdigalian) vertebrate assemblage
of Ullujaya (East Pisco Basin, Peru) is here described. Vertebrate remains are concentrated
in marine facies (Ct1a association) of the exposed Chilcatay Formation (dated 19-18
Ma) deposited within a 30-40 m deep, semi-enclosed, offshore environment. Coupled
with ichnological observations, the size distribution of pyrite framboid relics reveals
fluctuation of euxinic and oxic-dysoxic conditions at the seafloor. The assemblage
is dominated by toothed cetaceans (kentriodontids, squalodelphinids, physeteroids,
and the eurhinodelphinid-like Chilcacetus), together with a large dermochelyid turtle,
some bony fish, and diverse elasmobranchs, mostly juveniles of Carcharhinus brachyurus
and Cosmopolitodus hastalis. The vertebrate assemblage comprises a coastal community,
dominated by mesopredators, representative of a warm-temperate, sheltered embayment
connected with riverine and open ocean environments. Vertebrate skeletons are typically
disarticulated and incomplete, and some bone elements display shark bite marks. Microborings
are observed at the bone surface. Bones exhibit a good degree of apatite mineralisation
and bone cavities are locally filled by Ca-Mg carbonates. Our taphonomic observations
suggest prolonged flotation of carcasses during which they were subject to biogenic
and physical processes of partial destruction (including scavenging by sharks), before
final deposition on a soft compact substrate. Preservation was favoured by the oxygen-deficient
bottom conditions that inhibited the action of benthic macro-scavengers.
