BIOGEOGRAPHY, BIODIVERSITY, AND ENVIRONMENTAL PREFERENCE OF HOMOLOIDEA (BRACHYURA) FROM THE LATE JURASSIC TO THE PRESENT

The superfamily Homoloidea comprises both extinct and extant crab taxa, with records ranging from the Tithonian (Jurassic) to the modern. Examination of both fossil and contemporary occurrence records for this clade—compiled using published literature and the Ocean Biodiversity Information System (OBIS), respectively—provides insight into the biogeography, biodiversity, and environmental preference of the homoloid crabs over time.

Based solely on the fossil record, the diversity of Homoloidea peaked in the uppermost Cretaceous and declined toward the present, with the most recent fossils of the group known from the lower Miocene. The majority of homoloid fossils known are those of the family Homolidae, which are global in their distribution. The other homoloid families of Tithonohomolidae, Mithracitidae, Poupiniidae, and Latreilliidae are known from much sparser records. Fossil occurrences of all homoloid taxa most commonly occur in carbonate deposits followed by fine, mixed, and coarse siliciclastics. There are a few extant genera to which fossil species have been attributed, however, the degree to which these fossil occurrences overlap with the ranges of their modern genera varies.

The contemporary biodiversity of Homoloidea is particularly high in the tropical Indo-Pacific, with all 17 extant genera present in the Indian Ocean and/or Pacific Ocean—compared to only five genera present in the Atlantic Ocean. Contemporary occurrences are absent from a few notable areas, including the polar regions and the Pacific coast of the Americas. The lack of Homoloidea in polar regions may indicate that temperature is a limiting factor in the distribution of these taxa. The absence of modern homoloids along the Pacific American coast is curious given the robust fossil record of the clade in this region (particularly the temperate northeast Pacific). In terms of depth, the greatest abundance and diversity of modern homoloids occurs at roughly 50-550 meters deep, however, there exists variation in depth between taxa.

Certain patterns and trends, such as these, appear when the fossil and contemporary records of Homoloidea are compared and assessed, findings that may have important implications for future study of this clade, particularly in relation to dispersal/turnover events and environmental constraints.