New hypotheses concerning the earliest brachyurans (Crustacea, Decapoda, Brachyura)

Abstract

All Jurassic brachyuran taxa known to date are based solely upon dorsal carapaces, and only a limited number of Early and mid-Cretaceous crabs retain ventral parts. Therefore, all Jurassic taxa and many forms from the first half of the Cretaceous are carapace-based entities. All of them are considered to be "dromiaceans", podotremes to be precise. The recent discovery of an exceptionally well-preserved male crab from the Upper Cretaceous (lower Cenomanian) of Chiapas (Mexico), Archaeochiapasa mardoqueoi Guinot, Carbot-Chanona & Vega, 2019, at first sight of a podotreme nature, has allowed a detailed description of its thoracic sternum and pleon, which revealed that it was actually a typical eubrachyuran, in need of a new family, Archaeochiapasidae Guinot, Carbot-Chanona & Vega, 2019. This has brought back to life one of my earlier ideas about the possible non-podotreme nature of certain enigmatic Late Jurassic and Cretaceous Brachyura previously placed in various "dromiacean" (i.e., podotreme) families and superfamilies. My investigations have led the me to formulate the present hypothesis that the extinct families Bucculentidae Schweitzer & Feldmann, 2009 (currently assigned to the Homolodromioidea Al-

Systematics and convergent evolution of multiple reef-associated Jurassic and Cretaceous crabs (Decapoda, Brachyura)

“…For the most part, the classification system for Mesozoic Brachyura in Schweitzer et al (2010) was used. However, during the peer review of process of this paper, a new classification was proposed by Guinot (2019). It is outside the scope of this paper to evaluate both hypotheses and we choose not to support or reject one hypothesis at this stage.…”

“…It is outside the scope of this paper to evaluate both hypotheses and we choose not to support or reject one hypothesis at this stage. We have evaluated some of the taxa in detail as suggested by Guinot (2019), but much more research on other taxa is needed. Institutional abbreviations for specimens referred to herein: I-F/MP=Museum of the Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Cracow, Poland; LPBIII art=Laboratory of Paleontology, Department of Geology and Paleontology, University of Bucharest, Bucharest, Romania; MAB k=Oertijdmuseum, Boxtel, The Netherlands; MGSB=Museo Geológico del Seminario de Barcelona, Barcelona, Spain; MGUP=Museo Geologico G.G.…”

“…Recently, Schweitzer et al 2018erected Prosopon barbulescuae based on two specimens from the Tithonian of Romania, mentioned to differ mainly from congenerics by having its widest point at the epibranchial regions rather than at the confluent meso-/metabranchial regions, which was also noted by Guinot (2019). However, the specimens of this taxon are smaller compared to figured coeval specimens of E. aculeatum (=E.…”

“…Despite attempts to reveal the orbits, we did not find a single orbital cavity in 28 specimens of Nodoprosopon ornatum, from which we conclude that this cavity is likely to have been poorly developed and/or lightly calcified. Guinot (2019) opined that Nodoprosopon may be close to Bucculentidae. There are multiple similarities including the overall regional definition, but differences also exist such as the orbits and the hepatic region of Bucculentum Schweitzer and Feldmann, 2009d, which is much more swollen, so that the carapace of bucculentids is more rectangular in shape than in Nodoprosopon (Guinot, 2019; pers.…”

“…Subsequently, Klompmaker et al (2011) included Rathbunopon in Prosopidae again based on its close similarity to what is now known as Europrosopon, a fit with the diagnosis of Prosopidae in Schweitzer and Feldmann (2009d), and the presence of an augenrest in Rathbunopon, a feature that would be characteristic of prosopids (but see some species of Laeviprosopon). Subsequent papers by Guinot (2019) and Collins et al (2020) kept Rathbunopon in Glaessneropsidae, but others favored placement in Prosopidae (González-León et al, 2016;Ossó et al, 2018). Schweitzer et al (2012bSchweitzer et al ( , 2018 maintained placement in Glaessneropsidae and provided a more detailed explanation providing only differences in orbital characters.…”