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Palaeontological studies on exosqueletal disarticulated remains of chondrichthyans have focused on teeth and only less interest has been paid to scales due their limited taxonomic and systematic significance. However, classical works linking the morphology and the function of the squamation in extant sharks suggest that, despite their limited taxonomic value, the study of isolated scales can be a useful tool for palaeoenvironmental and palaeoecological inferences. Following this idea, we have analyzed the fossil record of shark scales from two Middle Triassic sections of the Iberian Chain (Spain), identifying different functional types by means of a morphometric discriminant analysis. From a total of 1136 isolated chondrichthyan scales, 25% were identified as abrasion resistant scales, 62% as drag reduction scales and 13% as scales of generalized functions. The elevated proportion of abrasion resistant scales suggests that this chondrichthyan palaeocommunity was highly dominated by benthic sharks that lived over a hard sea floor. However, one of the stratigraphical levels studied (He-20), presents statistically significant differences from the others, showing a lower percentage of abrasion resistant scales and a larger percentage of drag reduction scales. This level can be linked with storm episodes that could introduce remains of bentho-pelagic or pelagic forms in the inner platform.. Finally, partial correlation analysis between relative abundances of functional scale types and tooth-based taxa from the same sections provide positive correlation between teeth of Hybodus and Pseudodalatias and drag reduction scales, and teeth of Prolatodon and abrasion strength scales.Keywords: Triassic, Chondrichthyes, scales, teeth, Iberian Chain Resumen Los estudios paleontológicos de restos desarticulados de condrictios se han centrado en los dientes, no prestando prácticamente interés al estudio de sus escamas debido a su limitada importancia taxonómica y sistemática. Sin embargo, algunos trabajos clásicos que han relacionado su morfología y función en base al estudio de la escamación de tiburones actuales, sugieren que, a pesar de su limitado valor taxonómico, el estudio de las escamas aisladas puede ser una herramienta útil para obtener inferencias paleoambientales y paleoecológicas. Siguiendo estas ideas, se ha analizado el registro fósil de escamas de tiburón de dos secciones del Triásico Medio de la Cordillera Ibérica (España), identificando diferentes tipos funcionales por medio de un análisis morfométrico discriminante. De un total de 1.136 escamas aisladas de condrictios, el 25% de ellas fueron identificadas como escamas resistentes a la abrasión, el 62% como de reducción de la fricción con el agua y el 13% de las escamas como de función generalizada. La elevada proporción de las escamas resistentes a la abrasión sugiere que esta paleocomunidad de condrictios estaba claramente dominada por tiburones bentónicos que habitaban sobre un sustrato rocoso. Sin embargo, uno de los niveles estratigráficos estudiados...

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The enameloid microstucture of chondrichthyan teeth has been studied for decades and it has proven to be a useful taxonomic tool. Changes in enameloid organization have been related to the emergence of new trophic strategies and Mesozoic radiation of the neoselachian crown group. However, in contrast to the abundance of these data on tooth enameloid, descriptions of chondrichthyan scale enameloid are almost nonexistent. The topology and microstructure of scale enameloid in particular euselachian groups: fossil Mesozoic Hybodontiformes and living neoselachians, including batoids and sharks, are described. It is shown that a thick layer of single crystallite enameloid (SCE) covers all studied scales. Although the enameloid of scales clearly does not reach high levels of microstructural differentiation present in the dental enameloid of some neoselachians, we found some degree of organization, such as oriented crystallites, differentiation into sublayers, and the presence of poorly structured sets of densely arranged parallel crystallites. As scales lack feeding functions of teeth, we suggest that the emergence of microstructural organization/differentiation of chondrichthyan enameloid can be understood as consequence of a self organizing process rather than adap tive pressure.

Purpose.-In the present study, we described, for first time, the chondrichthyan fauna from several Middle-Late Triassic sections in the Betic Domain and compare it with other recent described coeval faunas from the Iberian Ranges.Methods.-Specimens were retrieved after the dissolution (with 10% acetic acid) of carbonate rocks.Results.-The assemblage comprises of seven species belonging to six genera (Hybodus plicatilis, Omanoselache bucheri comb. nov., Omanoselache contrarius comb. nov., Lonchidion derenzii, Lissodus aff. L. lepagei and cf. Rhomaleodus budurovi), most of them non-nesoselachian. Chondrichthyans remains occur in levels dating from Ladinian to Carnian according with bivalves, ammonoids and conodonts.Conclusions.-The findings are comparable, in taxonomical terms, to the chondrichthyan fauna from the Ladinian of the Iberian Range that was recently described, although chondrichthyans seems noticeably less abundant in the Betic Domain. Most of the species found occur also in the Iberian Range, with the exception of Lonchidion 2 derenzii and cf Rhomaleodus. budurovi, which occur in the Boyar Section, dated as Carnian. The small size of all teeth recovered, belonging probably to young specimens, suggest that the very shallow epicontinental environments recorded in Middle-Upper Triassic rocks from the Betic Domain could be used as nursery areas.