“Pegadas de mula”: An explanation for the occurrence of Mesozoic traces that resemble mule tracks

Abstract

Large semicircular traces and markings that resemble tracks made by horses or mules wearing horseshoes, have been a source of much confusion in the paleontological literature. Study of these traces has followed a convoluted trail from thirteenth century Portuguese folklore to purported Deinonychus tracks in Uzbekistan and China, to creationist preachings in North America. We show that these traces or markings, which occur in many Phanerozoic deposits, but especially in the Mesozoic, are in most cases examples of the well known burrow Rhizocorallium, or examples of current crescents.

Although these traces do bear a remarkable resemblance to tracks made by mules or horses (wearing “horseshoes"), such interpretations are obviously out of the question, for pre‐Cenozoic deposits, even though they have provided fuel for creationists. We herein show that the enigmatic trace fossil Gumatagichnus ungliformis from the Cenomanian of Uzbekistan is a Rhizocorallium burrow of invertebrate, not vertebrate, origin. Similar traces from the Upper Jurassic of Portugal and elsewhere, are also invertebrate in origin, even though they may occur in association with vertebrate tracks. The enigmatic Lower Jurassic trace fossil Hoplichnus, and similar Triassic markings/traces from terrestrial deposits have also been interpreted as Rhizocoralliumlike trace fossils, but may, in some cases, be inorganic sedimentary structures such as current crescents. The orientation and sedimentological/stratigraphic context of these traces/markings is important in distinguishing their origin.

Key words:

• horseshoe‐like tracings
• Rhizocorallium
• local legends
• creationists