Barry DiGregorio spent ten years as a Research Associate for Cardiff Centre of Astrobiology at CardiffUniversity in Wales from 1999 to 2010. From 2010 to 2016 DiGregorio was a writer for The American Society of Microbiology magazine MICROBE. In 2010 to 2018 Barry was made an Honorary Research Fellow for Buckingham University’s Centre for Astrobiology in the UK. Today he is retired and residesnear Lake Ontario in the state of New York.

On Earth, trace fossils (ichnofossils), are the trails, tracks and burrows left behind by ancient marine metazoans that are formally identified on the basis of their 3D morphology. On sol 1922 and 1923, of the Mars Science Laboratory (MSL) mission in Gale Crater, its microscope imager (MAHLI) returned to Earth over 84 images of a mudstone rock named Haroldswick.This rock had a number of dark-toned tube- like structures called “sticks” or crystals” by the MSL team (1). Haroldswick is part of a rock fragment group found near upper edge of Vera Rubin Ridge, once the site or shoreline of an ancient fresh water lake in Gale Crater 3.5 billion years ago (2).Although NASA has previously used photogrammetry and 3D printing to reconstruct a Martian meteorite imaged by the MER rover Opportunity (3), to date, they have not used this on Harorldswick and other rock fragments surrounding it. Because these unique features appear to be the first of their kind ever observed on Mars, we decided

to use a commercially available 3D photogrammetrybased imaging software program (4) to look at the features from various angles. Upon close inspection we identified over 20 key features that match established criteria used to identify terrestrial trace fossils (5).These features include burrows made up of galleries, tunnels, shafts, and chambers. An elongated and twisted metallic burrow-like feature only 10mm in length on Haroldswick clearly shows a shiny metallic aperture. A number of tube-like structures appear to meander in and out of their host rock just as terrestrial trace fossil burrows do.shoreline of an ancient fresh water lake in Gale Crater 3.5 billion years ago (2). Our work here shows the importance of using 3D photogrammetric analyses to reveal the full extent of delicate m o r p h o l o g i c a l textures and features found on rocks that may be of astrobiological significance. It is possible that the features we observed here may be evidence for metazoans that once existed in the ancient sediments of Gale Lake 3.5 billion years ago.