Several notes to the functional morphology of remopleurid and ellipsotaphrid trilobites of the Prague Basin
Abstract
The general body morphology of remopleurid and ellipsotaphrid trilobites of the Prague Basin suggests that these trilobites belong to active nektobenthic to nektic swimmers. Several life strategies are supposed in different evolutionary lineages: Amphitryon Hawle & Corda, 1847 and possibly also Apatokephalus Brogger, 1896 were, very probably, rather nektobenthic animals.
Flat ventral side of the exoskeleton as well as flat free cheeks (with long narrower genal spines in Apatokephalus) and the visual surface of eyes forming relatively narrow strip oriented especially frontally, laterally and posteriorly but not ventrally. Glabella together with palpebral lobes and eyes form steeply delimited platform enable an excellent outlook for the animal, even in these benthtic to nektobenthic forms.
In contrast, Girvanopyge Kobayashi, 1960 (= Cremastoglottos Whittard, 1961 fide Fortey and Owens, 1987, = Gamops Šnajdr, 1976 fide Vaněk and Valíček, 2001), Ellipsotaphrus Whittard, 1952 and Sculptaspis Nikolaisen, 1982 are considered as distinctly better swimmers with possibly nektic mode of life. Their general morphology is supposed to represent a distinct convergence to the cyclopygid trilobites (many authors consider Girvanopyge for cyclopygid up to now).
The free cheeks are reduced (especially anteriorly), the cephalon is more vaulted and the visual surface of the eyes covers, at least partially, even the ventral cephalic surface. Our opinion fits well with the concept of Shiino et al. (2012 and pers. com. 2012) supposing differences in the life habits within different groups of remopleuridids.
Only Apatokephalus and Amphitryon occurred as common elements, meanwhile the other representatives belong to very rare taxa in the Prague Basin