Discovery of Paleodictyon in the Indian Ocean

Northernmost (Subarctic) and deepest record of Paleodictyon: paleoecological and biological implications

“…The density of Paleodictyon in the study area was considerably lower than the maximum densities (45 indiv./m 2 )found at the MAR 5 or along the Indian Ridge (9.7 indiv./m 2 ), where patchy distributions were observed 9 . Also, the densities in the Aleutian area were three orders of magnitude lower than the average values reported for the CCZ (0.3 indiv./m 2 in Durden et al 7 ; and 0.2 indiv./m 2 in Boehringer et al 8 ) but higher than those reported in the DISCOL Experimental Area (DEA) in the Southeastern Pacific (0.0033 indiv./m 2 in Boehringer et al 8 ).…”

“…Since 32 fossil ichnospecies of Paleodictyon have been distinguished based on different sizes and morphologies 3 , modern analogues might be expected to display high diversity as well. In fact, the majority of described specimens have been assigned to the relatively large ichnospecies Paleodictyon nodosum , which reaches a size of up to 7.5 cm 5 , 7 , 9 . The recent study of Boehringer et al 8 is the only one to distinguish two types of modern Paleodictyon and analyze them separately.…”

“…Also, the densities in the Aleutian area were three orders of magnitude lower than the average values reported for the CCZ (0.3 indiv./m 2 in Durden et al 7 ; and 0.2 indiv./m 2 in Boehringer et al 8 ) but higher than those reported in the DISCOL Experimental Area (DEA) in the Southeastern Pacific (0.0033 indiv./m 2 in Boehringer et al 8 ). Mesh sizes (usually referred as diameter) reported in the literature span from 1.8 to 7.5 cm, with the average size always being more than 2.5 cm 5 – 9 . The Aleutian examples are considerably smaller than the previously published examples, except for some specimens from the DEA (Fig.…”

“…Preferentially the net is preserved” 2 (emended diagnosis by Uchman 3 ). Regular nets of Paleodictyon first appear in the Early Cambrian 4 and are found in modern oceans 5 – 9 . Mesh size and tunnel diameter, the basic ichnotaxobases used for distinguishing ichnospecies of Paleodictyon , show different size trends from the Paleozoic to the Neogene 10 .…”

“…1 in Gerdes et al, 2021). They are reported in the North Atlantic along the Mid-Atlantic Ridge (MAR) 5 , 12 , in the South Atlantic 14 , and in the Pacific along the Australian margin 6 , as well as in western 15 and equatorial regions (Clarion Clipperton Fracture Zone [CCZ]) 7 and recently on the southern central Indian Ridge and the Southeast Indian Ridge 9 . All these records are from tropical or subtropical areas close to the Tropics of Cancer (23.5°N) and Capricorn (23.5°S), and there are no published records from beyond 50°N and 50°S.…”