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Journal of Paleontology 92(3):506–522
Figure 7. Average body mass (= BM, solid gray horizontal line) and interval of confidence (= IC, delimited by dotted gray lines) of Sardolagus obscurus n. gen. n. sp. BM estimations (average BM, indicated by the black diamond, and IC, indicated by the vertical solid line) based on different postcranial measurement are reported above each estimator (x axis). The numbers below or above estimations indicate the sample size of each measurement. FAPDd=distal femoral anteroposterior diameter, FL=femur length, FTDd=distal femoral transversal diameter, FTDp=proximal femoral transversal diameter, g=grams, HAPDd=distal humeral anteroposterior diameter, HTDd=distal humeral transversal diameter, TAPDp=proximal tibia anteroposterior diameter, TTDd=distal tibia transversal diameter, TTDp=proximal tibia transversal diameter.
obscurus falls in the lower range of extant Oryctolagus cuniculus (OR of L xW=1.57–2.09 x 2.74–3.96, N=17).
BM estimation.—The BM of the Sardinian leporid is estimated ~1650g (IC=1443–1856g; Table 3, Fig. 7). BM estimations extrapolated from measurements performed on tibiae and humeri are quite consistent with this interval, whereas those extrapolated from femora are more erratic. The small sample size (N) of femora (1–3 specimens, depending on themeasurement; Table 3) is likely to have biased the results, giving a wider IC. Considering humeri and tibiae, a distal humeral transversal diameter is the measurement that estimated the highest BM. In previous studies of BM estimations of insular leporids, Moncunill-Solé et al. (2015) noticed that in Nuralagus rex the distal humeral trans- versal diameter also overestimated the BM of this species.
Discussion
Temporal and geographical distribution of Sardolagus obscurus.—To date, Sardolagus obscurus n. gen. n. sp. has been reported only from a few fissure fillings of the Monte Tuttavista karst complex, thus its distribution seems limited to central eastern Sardinia. This could be due to the extreme scarcity of pre-Middle Pleistocene fossil assemblages in Sardinia and Corsica. However, leporids are unknown even in the well- studied, long-known Capo Figari infillings (see Van der Made, 1999 and references therein), the age of which partly overlaps with the Monte Tuttavista ones. The material of Sardolagus obscurus analyzed in this
paper covers the Capo Figari/Orosei 1 FSC of the Nesogoral FC and the Orosei 2 FSC of the Microtus (Tyrrhenicola) FC (e.g.,
the early Pleistocene) (Fig. 1). Additional material not taken into consideration here (see Abbazzi et al., 2004) is referable to the same FSCs. We lack a quantitative age datum to define the exact age of the fissures. Biochronological considerations based on fossil mammals seem to point out that every single infilling of Monte Tuttavista karst complex was accumulated in a relatively short time span, with a few exceptions (Angelone et al., 2008). This evidence allowed determination of a relative chronological arrangement of the infillings by interpolating the results obtained from several papers mainly centered on single taxa (Palombo, 2009). Single taxa, in fact, may not follow the general trend. For example, according to Palombo (2009), IVm should be younger than X4, whereas preliminary data in Angelone et al. (2009) provide the opposite result (i.e., IVm older than X4, a hypothesis tentatively followed also by Palombo and Rozzi, 2014). If we follow Palombo (2009), the time span covered by the
findings of Sardolagus here analyzed is of ~1 Ma (~2.1–1.1 Ma), whereas it is slightly shorter (~1.9–1.1 Ma) if we follow Palombo and Rozzi (2014). If the additional, unpublished leporid remains reported from other Monte Tuttavista infillings (Abbazzi et al., 2004) should pertain to Sardolagus obscurus n. gen. n. sp., the youngest record of S. obscurus could be at ~0.8 Ma. Similarly, if the undetermined leporid from Capo Mannu D1 (Angelone et al., 2015) could be related to Sardolagus obscurus n. gen. n. sp., its first report could be backdated to the earliest late Pliocene (~3.6 Ma) and its known temporal dis- tribution could be extended to western central Sardinia.
significantly discrepant evolutionary degree between p3 and P2 has been observed in Sardolagus obscurus n. gen. n. sp. This implies two possible alternative hypotheses: (H1) Sardolagus obscurus n. gen. n. sp. developed from an ancestor bearing a primitive dental pattern and maintained a primitive P2 mor- photype (LL-II / BMR-A) typical of Archaeolaginae Dice, 1929 and primitive Leporinae, and independently developed a p3 of PR3 type; or (H2) the ancestor of Sardolagus obscurus n. gen. n. sp. was a leporine with advanced P2 and p3 morphotypes (e.g., as in Oryctolagus), which underwent a selective reverse morphocline that led to the shortening of P2 flexa and of p3 hypoflexid. In the case of a selective “reversal morphocline” of some
Peculiarities of the dental pattern of Sardolagus obscurus. —The main evolutionary changes of leporine teeth take place in the anterior parts of their tooth rows, and can be very well observed in the occlusal surface of p3 and/or P2. These changes are formed predominantly by: (1) a selection in tooth structural clusters among the phylogenetic morphoclines leading to a presence of discontinuous p3 patterns (i.e., PR0–4 morpho- types), and (2) a continuous development of morphologies between two morphological states of particular tooth parts (e.g., lengths of flexids/flexa). An effect of the above phenomena on P2 and p3 is generally different, but an overall evolutionary degree of both tooth positions is more or less concordant in the vast majority of leporid taxa. However, as highlighted in the taxonomic discussion, a
characters (hypothesis H2), one may expect in the relatively large sample under study, the occurrence (though in limited percentage) of specimens of Sardolagus n. gen. showing the
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