

Therefore, in this work, three simple criteria were incorporated to facilitate the ichnospecific assignment through this morphometric approach. Taking into account this material and previous works where Asteriacites were analysed, we observed that some problems arise in the ichnospecific assignment when applying the methodology of Knaust and Neumann (2016). New Asteriacites-bearing levels from different localities are described, and specimens that were previously assigned to A. In this work, ichnotaxonomic tools are discussed through the analysis of trace fossils assigned to this ichnogenus from the Mulichinco Formation (Valanginian) of the Neuquén Basin, northern Patagonia. The last review of Asteriacites (Knaust and Neumann 2016) dismissed sculpture as an ichnotaxobase for this ichnogenus and used simple morphometric parameters to differentiate the ichnospecies, reducing them to three: A. quinquefolius were similar in shape to the striations produced by movement of tube feet of living ophiuroids and asteroids, respectively. The striations of Asteriacites lumbricalis and A. Since the asteroids crawled raising the other four arms by their tube feet which produced rough and deep striations, the wide and shallow striations remained only in a half of each arm depression. When the asteroids started to move again, they bulldozed the substratum under the one preceding arm, where the striations were erased. Similarly, asteroids also produced wide and shallow striations perpendicular to the arm axis by tube-feet movement. The one backward arm erased the striations, and parallel fine striations remained in four arm depressions. When the ophiuroids resumed crawling, they raised their disc and four arms above the substratum and dragged one arm backward. The oral tube-feet produce fine, radial striations in the central depression. The basal-arm tube-feet produce well spaced, fine, parallel striations that are perpendicular to the arm axis. When ophiuroids stopped crawling, they buried themselves shallowly in the substratum, removing substratum under their arms and discs by using their tube-feet. To clarify the process of producing the striations in the trace fossil Asteriacites, we observed the behavior of living ophiuroids and asteroids in aquariums. These studies show that there are important differences in the morphology and in the production of asteroid and ophiuroid traces. The producers were observed to move from the resting position in the opposite direction of an ill-defined depression remained.

The size and shape of trace fossils suggest that the producers may belong to an ophiuroid species found from the Late Jurassic around Ried. The resting traces of living ophiuroids (four well preserved depressions and an ill-defined one) were much wider than the producing animals. On the other hand, Asteriacites lumbricalis is interpreted to originate from ophiuroids based on the previous experimental study of living ophiuroids. Asteriacites quinquefolius was very similar to these resting traces of living asteroids, and its producer is suggested to be an asteroid. The producers were observed to move from the resting position in the direction of the indistinct depression. The sizes of traces were more or less the same as the producing animals. Similar shaped resting traces were also observed on the deep-sea floor. Consequently, a star-shaped like depression was left behind with four radiating wider and sub-triangular arm furrows tapering toward the tip and one straight or indistinct sub-triangular depression left by the bulldozing starfish. When it moved from the resting position, the three front arms of the moving asteroid bulldozed the substrate in front of these arms. scoparius buried itself shallowly, keeping its arms in a pentamerous symmetrical position. quinquefolius and to examine the producing process, resting traces of living asteroids, Astropecten scoparius and some deep-sea starfishes were observed in an aquarium and in situ, respectively.

The large and small traces were assigned to Asteriacites quinquefolius and Asteriacites lumbricalis, respectively. Two different size star-shaped trace fossils are described from the Upper Jurassic Hienheim Formation in Germany.
