What happened with the smaller ones? First comprehensive taphonomic analysis of microvertebrates from the Late Pleistocene of Rancho La Brea (Los Angeles, USA)

Abstract

Rancho La Brea (RLB) in Los Angeles, USA, is an iconic fossil locality, owing to the high number and diversity of Quaternary vertebrate remains and their excellent preservation. More than a century of study, focused predominantly on large mammals, has provided valuable information along different lines of research, including taxonomy, taphonomy, isotopic ecology, functional morphology, and paleopathology. In order to develop a better understanding of the formation of this site, we conducted a taphonomic study of the microvertebrates, using samples from asphalt seeps dating to before the Last Glacial Maximum. The taphonomic evidence suggests that direct entrapment is the most plausible process to explain the primary accumulation of the thousands of microvertebrate remains. Based on the absence of digestive corrosion and feeding marks, low percentages of juvenile individuals, relative abundance patterns, and anatomical indices (postcranial elements vs. cranial elements and distal vs. proximal limb elements), the activity of predators/scavengers is ruled out as a primary process in producing the assemblages, although other processes, such as water transport of skeletal elements from nearby areas, could also have played a role in the formation of the deposits. The occurrence of successive entrapments and episodes of fluvial transportation, combined with post‐depositional internal movement within the seeps, would have given rise to the development of time‐averaged assemblages produced through a complex interplay of factors.

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