First known trace fossil of a nesting iguana (Pleistocene), The Bahamas

Abstract

Most species of modern iguanas (Iguania, Iguanidae) dig burrows for dwelling and nesting, yet neither type of burrow has been interpreted as trace fossils in the geologic record. Here we describe and diagnose the first known fossil example of an iguana nesting burrow, preserved in the Grotto Beach Formation (Early Late Pleistocene, ~115 kya) on San Salvador Island, The Bahamas. The trace fossil, located directly below a protosol, is exposed in a vertical section of a cross-bedded oolitic eolianite. Abundant root traces, a probable land-crab burrow, and lack of ghost-crab burrows further indicate a vegetated inland dune as the paleoenvironmental setting. The trace fossil matches dimensions and overall forms of burrows made by modern iguanas, and internal structures indicate active backfilling consistent with modern iguana nesting burrows. The trace fossil is also located on an island with a modern native species of rock iguana (Cyclura riyeli riyeli), suggesting a presence of iguanas on San Salvador since the Late Pleistocene. This nesting burrow may provide a search image for more fossil iguana burrows in The Bahamas and other places with long-established iguana species and favorable geological conditions for preserving their burrows.

The skull of the Turks and Caicos rock iguana, Cyclura carinata (Squamata: Iguanidae)

“…Many fossils of Cyclura have been collected from the Greater Antilles, and a better understanding of the cranial osteology of extant species would be highly useful for rigorous identifications of these fossils. Known fossils of Cyclura include cranial and appendicular elements ( Etheridge, 1965 ; Olson, Pregill & Hilgartner, 1990 ; Pregill, 1982 ) and even nesting trace fossils ( Martin et al, 2020 ) from the Bahamas, and cranial and potentially appendicular fossils from Turks and Caicos and the Cayman Islands ( O’Day, 2002 ; Morgan & Albury, 2013 ). Most fossils of Cyclura were reported in faunal lists rather than formal descriptions.…”

Defaunation and species introductions alter long-term functional trait diversity in insular reptiles

“…Reptiles are one such group that play important, albeit understudied, roles in ecosystem function, including seed dispersal, pollination, ecosystem engineering ( 2 – 4 ), and nutrient cycling ( 5 ). Whereas mammals and birds are widely recognized as important pollinators and seed dispersers, turtles and lizards also contribute to these services.…”