Angelone et al.—A new endemic leporid from the early Pleistocene of Sardinia
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Table 1. Dental measurements (mm) of Sardolagus obscurus n. gen. n. sp. CV=coefficient of variation (%), l=width of antero–posteroloph isthmus, L=length, N=number of specimens measured, OR=observed range,W=width, Want=anteroloph width, Wpost=posteroloph width, Wtal=talonid width, Wtrig=trigonid width, x̄=arithmetic mean.
Lower teeth Nx̄
i1 L2 – W2 – L
p3 p4-m2 m3
Wtrig Wtal L
Wtrig Wtal
W 14 L
14 27
27 27 5 5 5
3.40 2.68 2.87 2.75 2.70 1.92 1.76 1.17
OR
1.65, 1.79 3.26, 3.46 3.12–3.76 2.49–2.92 2.62–3.22 2.41–3.04 2.20–3.01 1.70–2.15 1.60–1.90 1.00–1.25
CV –
11.15 6.36 8.89
5.35 4.93 5.75 6.44 7.22
N P3-M2
W L
7 7
Upper teeth x̄
– W1 – P2
I1 L1 – L
Want
M3 L1 – –
Wpost l
W
35 35 35 35
1
1.73 2.73 2.29 3.34 3.58 1.05
OR
1.57–1.83 2.53–3.01 1.98–2.50 2.85–3.70 2.65–4.20 0.80–1.35 0.82 1.56
1.69 3.42
CV –
–
5.38 6.34 5.72 5.87
10.03 13.14 – –
Table 2. Mandibular and cranial measurements (mm) of Sardolagus obscurus n. gen. n. sp. CV=coefficient of variation (%), N=number of specimens measured, OR=observed range, x̄=arithmetic mean.
Nx̄
Alveolar length of p3-m3 Length of diastema
Lingual height of mandibular body at p3 5 11.03 10.35–12.28 6.87 Lingual height of mandibular body at m3 2 Width of mandibular body at p3/p4 Width of mandibular body at m2/m3 Length of mandibular ramus Width of articular head
Total height of mandible 1
Height of cranium at occipital condyle Width of cranium at auditory bulae Alveolar length of P2-M3
1 1 1
3 19.06 15.51–20.84 – – – –
2 1
23.58 31.95 16.03
34.00 –
4 5.29 4.92–5.54 4.97 –
13.28, 14.00 4.79, 4.89 4.08
– – –
– – – – –
hypothetical “original” advanced morphology (see Palacios and López-Martínez, 1980; Averianov and Tesakov, 1997), but this does not occur. This means that the P2 of Sardolagus obscurus n. gen. n. sp. shows no trace of the morphology of a hypothetical advanced leporine supposed to be its ancestor. Contrarily, the available P2 phenotype implies an affinity to Archaeolaginae or primitive Leporinae, such as Hypolagus or Alilepus. The posi- tion of the incisor pocket of Sardolagus n. gen. reinforces a possible affinity with Archaeolaginae. Such considerations fit with hypothesis (H1). The presence of morphologically simplified teeth is often
explained by paedomorphosis, which is a common evolutionary strategy in lagomorph. The phenomenon is well manifested and described in the extant taxa Nesolagus Forsyth-Major, 1899 and Brachylagus Miller, 1900 (Averianov et al., 2000). Their dentitions are highly paedomorphic along the entire tooth rows, both upper and lower. In particular, we note a PR4 morphotype of p3 lacking anteroflexid, a reduced P2 with one reentrant, and P3-M2 with very short and simple hypoflexus (see Averianov et al., 2000). In contrast to that, Sardolagus n. gen.: (1) exclu- sively has p3 with “non-paedomorphic” PR3 morphotype; and (2) does not bear any paedomorphic traits of simplification and/ or shortening of reentrants in upper and lower teeth. The relevant question is whether the simple morphology of
P2 in Sardolagus n. gen. may be explained merely by its small size. In P2, the relationship between size and morphological complexity is very important because genus/species differences are established on the continuous elongation of hypo- and mesoflexus and not on the presence of discontinuous patterns, as
OR CV
4 16.21 15.55–16.78 3.12 6 16.02 14.68–17.74 6.77 –
mostly in p3 (i.e., PR0–4 morphotypes). Simplified occlusal morphology of P2 with relatively less-developed reentrants is often present in juvenile specimens with a conical tooth shaft where the small-sized simplified occlusal outline differs from the one visible on the root side and disappears during ontogeny (=ontogenetically dependent changes). However, this is not the case for the Sardolagus n. gen. material. All analyzed P2s are represented by small-sized prismatic teeth with stable mor- phology along the entire tooth shaft and belong to adult speci- mens. So we explored the morpho-dimensional variability and differences among adult P2s pertaining to selected extinct and extant leporid taxa (Fig. 6). The morphology (LL+BMR morphotypes) of prismatic P2 plotted against the tooth size (length multiplied by width) clearly shows that complexity of adult P2 does not depend on size, neither within species nor across species. P2 with a simple pattern increases its size across ancient species in a sequence (from smallest to largest): Alilepus laskarevi, A. turolensis, Sardolagus obscurus n. gen. n. sp., Hypolagus balearicus (all four are of comparable P2 size), H. petenyii, Nuralagus rex (Fig. 6.1). On the other hand, in the comparably small-sized species Serengetilagus praecapensis and Pliopentalagus dietrichi, the P2 is significantly more advanced (Fig. 6.1). Analyzed recent species Oryctolagus cuniculus, Lepus europaeus, and L. timidus possess comparably advanced P2, but significantly more advanced than in Sardolagus; this is also true for all fossil species of Oryctolagus (Fig. 6.2). The difference between Oryctolagus and Lepus is expressed particularly in their P2 size: the P2 of Oryctolagus is smaller than in Lepus, and dimensionally close to Sardolagus n. gen. It is thus evident that in all the analyzed species represented by more abundant material, within intras- pecific variability, a degree of P2 complexity is not dependent on its size. An interesting feature observed in the p3 of Sardolagus
obscurus n. gen. n. sp. is the lack of the hypoflexid anterior tip, coupled with a relatively shallow hypoflexid. This is quite unusual for a PR3-type leporid, and it is not a secondary detail. It may imply either: (h1) a secondary simplification that follows the above-mentioned paedomorphosis pattern, or (h2) a differ- ent genesis for PR3 morphotype in Sardolagus n. gen. (i.e., the lingual elongation of a short hypoflexid). The latter evolutionary hypothesis (h2) about the origin of
PR3 pattern in Leporidae has already been formulated by Corbet (1983). In contrast to Hibbard (1963), who hypothesized that the
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