José Ignacio Valenzuela-Ríos

Bio: José Ignacio Valenzuela-Ríos is an academic researcher from University of Valencia. The author has contributed to research in topics: Conodont & Devonian. The author has an hindex of 11, co-authored 40 publications receiving 401 citations. Previous affiliations of José Ignacio Valenzuela-Ríos include University of California, Davis.

New Lower Devonian Polygnathids (Conodonta) from the Spanish Central Pyrenees, with comments on the early radiation of the group

Abstract: The comprehensive study of six Pragian-lower Emsian (Lower Devonian) sections from the Spanish Central Pyrenees has yielded a rich assemblage of conodont faunas, highlighting an important succession of Polygnathus species. Among them, the presence of the biostrati­graphical markers P. pireneae , P. kitabicus, P. excavatus excavatus and P. exc. 114 stands out. This conodont succession allows the identification of the Pragian/Emsian boundary and the early Emsian zones and subzones: the kitabicus Zone and the Lower and Middle excavatus subzones. It is also remarkable the presence of three new polygnathid species: P. aragonensis n. sp., P. carlsi n. sp. and P. ramoni n. sp. Additionally, P. pannonicus and P. sokolovi are also reported for first time in the Iberian Peninsula. According to all these records, the abundance and diversity of these species suggest that during this time interval an evolutionary radiation of the group took place, identifying two pulses during the early radiation of the group. The first one during the pireneae-kitabicus Zone, and a second one during the Lower excavatus Zone. The new data presented herein increase considerably the known paleobiodiversity of the genus dur­ing the Pragian-early Emsian interval in the Spanish Central Pyrenees and corroborates the presences of the most important early Emsian conodont markers used in other regions such us Europe, North Africa, Central Asia, Australia, and North America. ozonas Dc, E y F asociados al evento de enfriamiento global del Mioceno medio.

Tooth replacement rates in early chondrichthyans: a qualitative approach

Abstract: The continuous replacement of teeth throughout their lifetime is a common characteristic of most chondrichthyans. This process was already present in the earliest representatives of the group. It has been well established that different species of extant sharks show rapid tooth replacement rates; however, some authors have suggested that in early chondrichthyans this rate might have been much slower. Here we present a qualitative approach to analyse tooth replacement rates in the Early Devonian shark Leonodus carlsi, the earliest tooth-bearing shark known to date. For this, we have examined 1,103 isolated teeth from Celtiberia, Spain. Our study provides strong evidences of an extremely slow dental replacement in this primitive chondrichthyan based on three independents analyses: (1) statistical analysis of the wear degree, demonstrating that teeth remain functional for a long period of time; (2) analysis of both the histological and the morphological features of the teeth cusps suggests that this chondrichthyan used a maturation process that optimizes its function, thus worn teeth show an efficient working shape that implies their teeth remained functional for a long time after being modelled by use; and (3) estimations of size increments between teeth (Δs) of the same dental family for some recent sharks whose rates of replacement were known prove that Δs is inversely proportional to the rate of replacement (R2 = 0.8327). The estimated values of tooth replacement rates obtained from Δs for L. carlsi and for some Late Devonian cladoselachian sharks are significatively slower than those observed in current sharks.

Early Pragian conodont‐based correlations between the Barrandian area and the Spanish Central Pyrenees

Abstract: Occurrences and distribution of extremely scarce eognathodontids do not facilitate reliable correlation across the European regions. The correlation of the traditional early Pragian of the Prague Synform (a part of the classical Barrandian area) and the Spanish Central Pyrenees (section Segre 1) is based on conodont taxa of the Icriodus steinachensis and the Pelekysgnathus serratus stocks. This correlation has the potential to be extended to other peri-Gondwanan regions where this scarcity of eognathodontid faunas exists as well. Application of the morphotype subdivision in I. steinachensis enables approximation of the beginning of the Pragian in the Pyrenees. It is based on the entry of I. steinachensis beta morphotype; it enters together with early eognathodontid taxa in the Barrandian sections. These correlations show that routine application of certain zonal concepts can lead to misleading conclusions. Copyright © 2007 John Wiley & Sons, Ltd.

The Silurian Period

Abstract: The Silurian Period (443.1–419.0 Ma) was a time of general convergence of continental plates, strong fluctuations in global sea level, and the early stages of colonization of land. The base of the Silurian System is defined at the level of the first appearance of the graptolite species Akidograptus ascensus at Dob’s Linn, Scotland. Silurian time can be finely resolved using integrated graptolite, conodont, and isotope biochemostratigraphy. The Silurian time scale is based on a CONOP9 composite of graptolite range data derived from 837 stratigraphic sections and 2651 graptolite taxa, with interpolated radioisotope dates, spanning the Ordovician into the Lower Devonian. There is a succession of at least seven globally recognizable positive carbon-isotope excursions, most of which are associated with important bioevents and environmental changes indicated by other geochemical proxies. These data show that the Silurian was a time of dramatic changes in climate, ocean chemistry, and biodiversity.