Angelone et al.—A new endemic leporid from the early Pleistocene of Sardinia
the arrival of the ancestor of Sardolagus in Sardinia at 2.9 Ma and in all later migration events recorded up to now. Most probably the ancestor of Sardolagus n. gen. arrived in Sardinia between ~8 Ma and ~3.6 Ma.
Conclusions
After a century of paleontological studies, the report of a fossil leporid in the first years of the twenty-first century (Rook et al., 2003) represented a novelty for the vertebrate paleobiodiversity of Sardinia. The remains were provisionally ascribed to the genus Oryctolagus. However, our analyses indicated a com- pletely new perspective about its taxonomy, which made the erection of the endemic insular taxon Sardolagus obscurus n. gen. n. sp. necessary. The analyzed material was recovered from a few fissure fillings of the Monte Tuttavista karst complex (E Sardinia), referable to the Capo Figari/Orosei 1 FSC and to the Orosei 2 FSC (early Pleistocene, ~2.1–1.1 Ma or ~1.9–1.1 Ma, following either Palombo, 2009, or Palombo and Rozzi, 2014, respectively). Additional leporid remains have been found also in other Monte Tuttavista infillings. If such remains pertain to Sardolagus obscurus n. gen. n. sp., following the biochronological schemes proposed by Palombo (2009) and Palombo and Rozzi (2014), the youngest record of Sardolagus obscurus n. gen. n. sp. should be at ~0.8 Ma. A peculiar combination of advanced and primitive features
characterizes Sardolagus obscurus n. gen. n. sp. A quite primitive P2 lacking deep flexa (predominance of morphotypes LL II and BMR A, after Fladerer and Reiner, 1996) similar to the P2 of Alilepus and Hypolagus, is coupled with a p3 showing an advanced morphology (PR3 after Čermák et al., 2015) comparable to extant Lepus and Oryctolagus. The discrepancy in the evolutionary degrees of P2/p3 differentiates Sardolagus obscurus n. gen. n. sp. from continental leporids of the Miocene–Pleistocene of Europe and from the other insular endemic leporids of western Mediterranean islands (e.g., Nuralagus rex, Hypolagus balearicus, H. peregrinus), all characterized by a concordant pattern. Sardolagus obscurus n. gen. n. sp. differs from other leporids from western Mediterra- nean islands also by its smaller p3 size, with the exception of H. balearicus. An interesting character shared by Sardolagus obscurus n. gen. n. sp. and other leporids from western Medi- terranean islands, in contrast to continental genera (except for Pliopentalagus), is the elongated p3. Unique to the new taxon is the p3 with very variable anteroflexid and unusually, among the PR3 motphotype, short hypoflexid without anterior tip. The size of p3 is not directly correlated with BM, as high-
lighted by the study of other insular endemic fossil lagomorphs (Moncunill-Solé et al., 2016b). It is possible to compare theBM of Sardolagus obscurus n. gen. n. sp. (average BM: ~1650 g) with other two insular endemic leporids: N. rex, which is noticeably larger (Quintana et al., 2005, 2011; Moncunill-Solé et al., 2015), and H. balearicus, for which the BM range includes that of S. obscurus (Quintana and Moncunill- Solé, 2014a). The mix of archaic and modern features observed in
Sardolagus obscurus n. gen. n. sp. may have been attained in two ways: (1) after convergent evolution, which led to an
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independent origin of PR3 pattern of p3 from an archaeolagine/ leporine ancestor bearing a PR0/1 p3; or (2) after a selective reversal morphocline from an Oryctolagus-like leporine with advanced P2 and p3 morphotypes. However, given the present state of knowledge, neither hypothesis can be conclusively rejected.
Given the taxonomic framework, it is quite difficult to
identify the continental ancestor of Sardolagus obscurus n. gen. n. sp. and the moment of its arrival in Sardinia. Crossing the European leporid record and evidence of migrations to Sardinia, we identified three possible moments between ~8Ma and ~3.6Ma in which the ancestor of Sardolagus obscurus n. gen. n. sp. may have arrived in the Island.
(1) ~8 Ma: Indeed the appearance of modern leporids in Europe marks a biochronological event at ~8Ma (“Leporid Datum”; Flynn et al., 2014), which is the same age of a major migrational event to the Tusco-Sardinian PB (Van der Made, 2008). In this case, the ancestor for Sardolagus obscurus n. gen. n. sp. should be sought among the most ancient “true” leporids of Europe.
(2) Messinian: The arrival of the ancestor of Sardolagus obscurus n. gen. n. sp. during the Messinian would imply its relationship to Alilepus or Hypolagus stock (whose presence in continental Europe is certain since MN12 and MN13, respectively). Unfortunately, there is no trace of leporids in Sardinian assemblages up to Capo Mannu D1 (MN15/M16 boundary, Angelone et al., 2015) to support this hypothesis.
(3) Early/late Pliocene regression: If the absence of leporids up to Capo Mannu D1 is an actual datum and not the consequence of the extreme scantiness of the Sardinian fossil record in pre-Pleistocene times, we may postulate an alternative hypothesis about the arrival in correspondence of the early/late Pliocene regression. In this case, the ancestor of Sardolagus obscurus n. gen. n. sp. would be among the earliest forms of Oryctolagus and imply a reversal of P2 and p3 morphoclines.
In fact, “true” Oryctolagus is known from early MN16
(~3.5 Ma). In this context, the relationship of Sardolagus obscurus n. gen. n. sp. with the fragment of a tooth referred to Leporidae indet. collected in Capo Mannu D1 (early/late Pliocene boundary; Angelone et al., 2015) is, for the moment, impossible to unravel. The most parsimonious hypothesis would be an ancestor-descendant relationship.
Acknowledgments
We would like to thank the firms that perform quarrying activ- ities at Monte Tuttavista for their kind collaboration; M. Asole, P. Catte, A. Fancello, G. Mercuriu, G. Puligheddu, and A. Useli for the careful work of preparation of the analyzed fossils; and the Superintendents F. Lo Schiavo, F. Nicosia, and M.A. Fadda of the Soprintendenza Archeologia, Belle Arti e Paesaggio per le prov. di Sassari, Olbia-Tempio e Nuoro, who allowed the study of the material here analyzed. We thank also two anonymous reviewers for constructive criticism and H.-D. Sues for careful editorial
work.CAhas been supported by the Agencia Estatal de
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