14.02.2010

New data on the taxonomy of the Myomiminae of Gargano

The late Miocene-Early Pliocene "Terre Rosse" vertebrate assemblages, found in the palaeokarst fissures fillings of the Apricena-Poggio Imperiale limestone quarries (North-Western side of the Gargano promontory, southern Italy), document a very long and complex history of endemic populations of a palaeoarchipelago. That history developed in at least four populating phases, which are characterised by changes in faunal diversity and include taxa with different degree of endemism.
They have been subject of several studies since the beginning of the 1970s and deserve a particular attention for their evolutionary and paleogeographical implications. The sampling of the "Terre Rosse" fissure fillings was carried on during successive field surveys from the Leiden Museum (1969-70) and from the Florence University (1980s). Until now, however, the two resulting collections have always been studied separately by different authors: this work is the first partial attempt to integrate the information derived from the two collections. A biochronological framework is proposed integrating the chronological succession of samples by Freudenthal in the scheme elaborated by De Giuli et al. However, some uncertainty remais in the details of the position of some fissures, in particular "Rinascita 1".

After the pioneering description of the gigantic dormouse Stertomys laticrestatus Daams & freudenthal 1985, the interest in the systematic of the Neogene Gargano glirids renewed just in the very last years.
Four species have been recently described: Stertomys daunius Freudenthal & martin-Suarez 2006, S. daamsi Freudenthal & Martin-Suarez 2006, Stertomys lyrifer Martin-Suarez & Freudenthal 2007, and Stertonys simplex Martin-Suarez & Freudenthal 2007.

In the present work the description of Stertomys from eleven further fissure fillings, documenting most of the whole succession of endemic population phases, is presented and discussed. The samples, for a total amount of 1696 dental elements, have been described by basic statistical parameter of measurements and frequency distribution of Daams´and Rinaldi´s morphotypes. Seven taxa have been identified: S. daunius, S. laticrestatus, S. aff. laticrestatus, S. ex gr. daamsi, S. degiulii nov. Sp., S. cf. degulii and S. aff. degulii.

The results of the analysis of the Stertomys species occurring in each fissure filling confirm the outline of the proposed biochronological framework and permit some improvement of the definition of the populating phases of the Gargano palaeoisland. Besides, they confirm the presence of some problems in arranging the details of the fissure succession of the oldest phase. Such uncertainties are possibly due to the frequent faunal exchanges among the islands of the palaeoerchipelago and with the mainland during the time documented by this earls phase. The results of the present contribution also suggest that an early radiation occurred in the palaeoarchipelago, producing at least five lineages. These lineages can be arranged in two main branchescharacterised by different size and morphology: large-sized Stertomys species, although closely related, cannot be considered as belonging to the same phyletic lineage. Among the small-sized taxa, S. daamsi and degiulii migth be arranged in a single phyletic lineage where a trend in reduction in size and an increase of the complexity of the pattern of connection amoung dental crests occur. S. simplex may be considered as a species with primitive morphology; very close to the ancestor of S. daamsi. Most of the evolutionary divergence is observed among the different lineages, while phyletic gradualistic changes are documented to a lesser extent.

Vengono presentati I risultati dell´analisi su reperti di Stertomys provenienti da undici fessure carsiche del Gargano selezionate in modo da essere rappresentative dell´intera successione delle fasi di popolamento endemico. L´analisi, di tipo morfo-dimensionale, é stata condotta sugli elementi dentari. Sono stati identificati sette taxa, S. daunius, S. laticrestatus, S. aff. laticrestatus, S. ex gr. daamsi, S. degiulii nov. sp., S. cf. degulii and S. aff. degulii, tra cui Stertomys degiulii viene descritto come nuova specie.
Da un punto di vista evolutiva le tre specie di taglia grande, benché correlate tra loro, non sembrano avere rapporti diretti di discendenza. Fra le specie di taglia piccola lo stesso si puó dire di S. daamsi e S. simplex. Per quanto riguarda S. daamsi e S. degiulii, invece, si puó ipotizzare una discendenza diretta. Lungo questa linea si nota un trend di diminuzione di taglia e una leggera complicazione del pattern dentale, sopratutto per quel che riguarda la connessione fra le creste.

Come riscontrato anche in altri taxa, le specie disperdono sull´isola giá diversificate e i cambiamenti riconducibili ad evoluzione filetica sono di minore entitá. Tale ricostruzione evidenzia quindi l´esistenza di minori cambiamenti gradualistici riconducibili ad evoluzione filetica, ma piú che altro é in accordo con le attese di un modello ed equilibri punteggiati, in cui la massima differenziazione avviene durante gli eventi cladogenetici.

BIBLIOGRAFIA:
RINALDI, P.M. & MASINI, F. (2009): New data on the taxonomy of the endemic Myomiminae (Gliridae, Rodentia) from the late Miocene-Early Pliocene of Gargano (southern Italy) with the description of the new species Stertomys degiulii. Bollettino della Societá Paleontologica Italiana 48(3): 189-233

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