Cricetodon

A new species of Cricetodontini (Cricetidae, Rodentia, Mammalia), Cricetodon nievei sp. nov. from the Toril section
(Toril 3A, Toril 3B, Toril 2) and Las Planas 5H is described. All this sites belong to the local biozone G3 (late Aragonian,
late middle Miocene) from the Calatayud-Daroca Basin (Zaragoza, Spain). The new species displays a mosaic pattern
consisting in a combination of primitive and derived characters: the upper molars have a basal Cricetodon-like pattern –
short and not complete ectolophs –, whereas the lower molars share several derived features with the older representatives
of Hispanomys – absence of metalophulid II. The generic assignation of the new taxon is further discussed and it is
compared with all the species of Cricetodon and Hispanomys described until date. This mosaic evolutionary pattern of
dental characters is also recognized in other species of Cricetodontini from Europe during the late Aragonian, although
involving different combination of morphological characters. At this time, the diversity of the tribe increases, including
species with complex morphology and higher intraspecific variability than the older representatives. The new species
proposed here is morphologically close to Cricetodontini recorded outside the Calatayud-Daroca Basin, especially
C. albanensis and H. decedens from France. Finally, the palaeoecological context of the new species is discussed; the
stratigraphical distribution of Cricetodon nievei sp. nov. coevals changes in the faunal assemblages which are possibly
related to an increase of humidity detected in the Calatayud-Daroca Basin

This work is focused on the study of 1870 fossil dental remains of two Cricetodontini
genera, Cricetodon and Hispanomys from the Toril-Nombrevilla section (Calatayud-
Daroca Basin). This section is situated in the northeastern part of Spain and comprises
11 micromammal sites: Toril 2, 3A & 3B, Nombrevilla 2, 3, 4, 9, 10, 14, the classical
Nombrevilla (1) and Pedregueras 2A. The stratigraphical superposition of the fossiliferous
levels and their richness and abundance of fossil remains make this section especially
interesting for the analysis of rodent faunas evolution from the Late Aragonian to
Early Vallesian, In addition, Cricetodon and Hispanomys have biochronological and
biostratigraphical relevance within this interval.
One of the first results of this study is the unexpected high diversity and turnover shown by
Cricetodon and Hispanomys in this basin. The taxa recorded are the following: Cricetodon
aff. jotae in TOR 2, 3A and 3B; Hispanomys aguirrei and H. lavocati in NOM 2, 3 and 4 ; H.
nombrevillae in NOM 9, 1 and 10; and H. aragonensis in NOM 14 and PED 2A. One of the
most relevant conclusions of this study is that the replacement of Cricetodon by Hispanomys
took place (NOM 2) long before the first appearance of Hipparion (NOM 1); this fact has
important consequences for the local biozonation. On the other hand, in the localities NOM
2, 3 and 4 two taxa have been found for the first time in the Calatayud-Daroca Basin, H.
aguirrei and H. lavocati. These species have been described before in the Duero and the
Vallés-Penedés basins respectively. The presence of two different species of Hispanomys
in the same fossiliferous level is unusual but an analogous situation has been described on
the Vallès-Penedès Basin. Our preliminary results suggest that probably these three basins
(Calatayud-Daroca, Duero and Vallès-Penedès) had periods of higher faunal exchanges than
previously thought.