The trace fossils presented here belong to the category of animal behavior that Seilacher had defined and called “mortichnia.” However, Vallon and colleagues did not recommend the usage of this ethological category, because its recognition not only depends on trace fossil morphology, but also on tracemaker physiology and environmental interpretation. The two latter assumptions in particular cannot always be deduced correctly, rendering the whole interpretation false (especially when modern analogues of such environments or closely related organismal groups do not exist). Nevertheless, the category exists, and with the recently recovered specimens, a redefinition is attempted.
The specimens from Lebanon are all traces left by dying fish. At the beginning, the traces show the greatest physical strengths of the tracemakers, as their body movements were still relatively powerful. Over the course of the mortichnion, the traces reflect increasing exhaustion. The undulating movements of the tail fin decrease, and the resulting trail becomes more and more asymmetrical. Its depth becomes shallower. During last moments of the tracemakers' lives, their movement was reduced to barely discernible movements. Finally, the trail ends with the death and the preserved corpse of the tracemaker.
In our redefinition of mortichnia, we argue that trace fossils included in this ethological group must contain the fossilized corpse of the tracemaker. The corpse must ideally show signs of illness or predation (the tracemaker body fossil, however, is neither part of the trace fossil nor is it to be regarded as the actual trace fossil). Other trails or trackways, especially from non-fish tracemakers like Solemya at the Solnhofen Lagerstätte (Kimmeridgian–Tithonian; Germany), may show signs of loss of orientation, or the tracemakers might try to avoid certain areas that impose hostile living conditions (e.g., ripples, crests) if the environment is drying out and the tracemakers breath via gills.
Proper identification of behavioral patterns is an important prerequisite for the identification of any trace fossil and even more so for its interpretation. For the last 70 yr, the continually advancing state of ichnological knowledge has led to a gradual recognition of recurrent patterns of organismal behavior documented in the fossil record, which in turn gave rise to the ethological categories. “Mortichnia” was proposed for traces created during a death struggle of the tracemaker but has been reported only in a few cases. Fish mortichnia so far have only been reported in one specimen recovered from the Upper Jurassic Plattenkalk of Nusplingen (SW Germany). The category mortichnia is refined herein, but remains ambiguous. Eight newly discovered unique specimens of mortichnia from Upper Cretaceous marine sediments in central Lebanon (Haqil, En Nammoura) are preserved together with their tracemakers and described herein. In addition, 14 further incomplete specimens were collected where no tracemakers are present. However, morphology and close provenance allow them to be assigned to the same ichnotaxon.
The Lebanese mortichnia originate from fish that were subjected to significant environmental or individual stress leading to their deaths. During death convulsions, their bodies created sedimentary structures with a specific recurring morphology. The ichnogenus Pinnichnus n. igen. with ichnospecies P. haqilensis and P. emmae n. ispp. is proposed for these specimens.
