دانلود رایگان مقاله چگونگی تکامل خرچنگ خزنده

Abstract

A new fossil lobster from the Cretaceous of Lebanon, Charbelicaris maronites gen. et sp. nov., is presented here, while the former species ‘Cancrinos’ libanensis is re-described as Paracancrinos libanensis comb. nov. P. libanensis is shown to be closer related to the contemporary slipper lobsters than to Cancrinos claviger (lithographic limestones, Jurassic, southern Germany). A finely-graded evolutionary scenario for the slipper-lobster morphotype is reconstructed based on these fossil species and extant forms. The evolutionary changes that gave rise to the current plate-like antennae of Scyllaridae, a key apomorphy of this group, are traced back through time. The antenna of what is considered the oldest slipper lobster became petaloid and consisted of about 20 fully articulated elements. For this group the name Scyllarida sensu lato tax. nov. is introduced. In a next evolutionary step, the proximal articles became conjoined and a lateral extension appeared on peduncle element 3. The entire distal petaloid region is conjoined already at the node of Verscyllarida tax. nov. In modern slipper lobsters, Neoscyllarida tax nov., the distal region is no longer petaloid in shape but asymmetrical. The study also emphasizes that exceptionally preserved fossils need to be documented with optimal documentation techniques to obtain all available information.

5. Conclusions and outlook

The here presented case supports that important evolutionary novelties in scyllarids occurred during the Jurassic and Cretaceous (Forster, 1973, 1984 € ). Due to the exceptional preservation of several Lagerst€ atten in the Jurassic and Cretaceous we have direct access to these evolutionary changes. In the days of evo-devo it is especially fortunate that such fossils, e.g. of achelate lobsters, even give insights into the ontogeny (Polz, 1971, 1972, 1973, 1987, 1995, 1996; Tanaka et al., 2009; Haug et al., 2011c, 2015; Audo and Charbonnier, 2012) and thus facilitate a palaeo-evo-devo approach (Haug et al., 2009a, 2013; Haug and Haug, 2013). More scyllarid and other achelatan fossils from the Mesozoic are currently worked up, and will likely provide new and additional insights. To summarise, our new finds on Mesozoic fossils demonstrate: - the importance of applying the right documentation method to exceptionally preserved fossils, - the step-wise evolution of the scyllarid morphotype, documented by these, - that fossils are extremely important to resolve the stepwise evolution of a distinct modern morphotype.