A new enigmatic lacustrine trackway in the upper Miocene of the Sierra de las Cabras (Jumilla, Murcia, Spain)

A new fossil trackway is described in the upper lacustrine Miocene in the Prebetic Zone of the Iberian Peninsula, in Jumilla town (Murcia region) called Aenigmatichnus jumillensis nov. ichnogen. nov. ichnosp. This trackway consists of a pattern made up of sets of three tracks or triads, which are subparallel to each other, arranged in alternate groups. Each track presents a depression formed by a central body that is three times as long as it is wide, with straight or slightly curved walls, with two shorter bodies placed at the ends, one of the ends being shorter and more pronounced than the opposite, which is longer and stretched. All the biomechanical possibilities compatible with an anatomical design that could leave the impression of three alternate triads of tracks are analysed. The supports are only from the extremities on one side of the organism (left or right), the displacement being by translation. It is concluded that it had to be a large arthropod (metre scale), with a hexapod or decapod (less probably octopod), which had to be dragged laterally by a current in a very shallow lake or wetland environment. To date, no fossil organism is known, nor its current equivalent, that corresponds to these characteristics.