516
Journal of Paleontology 92(3):506–522
Table 3. Results of body mass estimation (in grams) by postcranial element. IC-L=lower interval of confidence, IC-U=upper interval of confidence, N=number of specimens measured, x̄=arithmetic mean.
Bone Femur Tibia Humerus Measurement
proximal transversal diameter distal transversal diameter distal anteroposterior diameter length
FTDp FTDd
proximal anteroposterior diameter proximal transversal diameter distal transversal diameter distal anteroposterior diameter distal transversal diameter
FAPDd FL
TAPDp TTDp TTDd
HAPDd HTDd
PR3 pattern of p3 in leporines was derived from PR1 through the morphocline PR1→PR2→PR3 (i.e., Alilepus→Nekrolagus Hibbard, 1939b→Lepus morphotypes; sensu Averianov and Tesakov, 1997), Corbet (1983) regarded as more probable a direct derivation of the PR3 pattern from PR0 (i.e., Hypolagus morphotype; sensu Averianov and Tesakov, 1997) by the elongation of a shallow hypoflexid. This conclusion was prob- ably preferred, invoking the parsimony principle, because it requires fewer transformations and is supported by an analogy with p4-m2. Corbet’s model was rejected by Averianov and Tesakov (1997). They argued that such a model is not supported by fossil evidence and does not fulfil the parsimony principle because the choice of the hypothesis implying fewer transfor- mations must be done among hypotheses equally supported by facts. We agree that Hibbard´s hypothesis is supported by paleontological evidence, however, in our opinion, the lower probability of Corbet’s hypothesis does not exclude its possi- bility, also because Hibbard’s model can not be looked upon as a general phenomenon in all leporine lineages. In fact, Averianov and Tesakov (1997) themselves and Čermák et al. (2015) demonstrated the limited validity of Hibbard’s hypothesis. Indeed, it is well documented, particularly in the late Cenozoic North American populations of the lineage Hypolagus parviplicatus Dawson, 1958–Alilepus hibbardi White, 1991– Nekrolagus progressus (Hibbard, 1939a)–Lepus ssp./Sylvilagus ssp. Averianov and Tesakov (1997) suggested at least two independent parallel developments to explain the origin of the long p3 hypoflexid of advanced leporines: from Nekrolagus and from Trischizolagus Radulesco and Samson, 1967. The current fossil record of leporines suggests that the
above-mentioned morphodynamic gradients (both continuous and discontinuous ones) took place independently and, most probably, with a different “trigger” (cf., different evolutionary stages of reentrants in Hypolagus species limited exclusively to the PR0 p3 morphotype or variable flexa coupled with PR0-PR1-PR2 morphotypes). The length/morphological evolution of p3/P2 reentrants, particularly the anterior ones, seems to be more conditioned by environmental selection pressures than by the basic p3 patterns (PR0–4). Generally, in lagomorphs, the anterior part of tooth row (i.e., P2 and p3) supports a large part of masticatory stress (see the application of Greaves, 1978 schemes to the ochotonid Prolagus in Mazza and Zafonte [1987, p. 228, fig. 5], in which p3 is the tooth where the highest muscle resultant is applied). Changes in environmental conditions are steadily and swiftly reflected in these teeth, and because evolutionary pressure should have similar “intensity” in the same part of tooth row, we theoretically expect similar
N
2 3 2 1 4 4 6
10 10
x̄
1119.50 –– 1394.86 1581.38 1599.25 1626.22 1722.29
1944.69 1616.30 2241.94
1657.92 1524.78 1801.88
1275.48 1447.97 1460.11 1523.30 1609.39
IC-L IC-U
2231.46 1707.82 2682.00
1514.24 1714.80 1738.38 1729.14 1835.19
evolutionary degrees in P2 and p3. In fact, fossil and recent species of Oryctolagus and Lepus possess p3 of PR3/A1 pattern, and concordantly well-developed p3 anteroflexid and P2 hypo-/ mesoflexa. The continental endemic extant leporid Lepus cas- troviejoi Palacios, 1977 deserves a special mention; in this species, p3/P2 with advanced morphotypes coexist with p3/P2 with “regressed” characters (Palacios and López Martínez, 1980). However, the concordance seems to be important, at least considering the population in its entirety. The reason why in Sardolagus n. gen. a PR3 p3 with
well-developed anteroflexid is coupled with a simple P2 with shallow/absent hypo-/mesoflexa for the moment remains unclear. Such dramatic discrepancy in the evolutionary degrees of p3 and P2 in Sardolagus can not be related to insular endemism. In fact, in other western Mediterranean fossil lepor- ids, the concordance of the evolutionary degrees of P2 and p3 is important: (1) in Nuralagus rex, the degree of anterior reentrants
development in P2/p3 is concordant; in fact in p3 the antero- flexid is missing; in P2 the hypoflexus is missing and the mesoflexus is incipient (it is worth noting, though, that among PR0–PR1/A0 p3, the anteroconid of N. rex is relatively advanced [morphotypes III–V sensu Fladerer and Reiner, 1996; see Quintana et al., 2011, fig. 6]); (2)H. balearicus has the same (concordance of reentrants development in P2/p3) as in Nuralagus rex, however H. balearicus dental pattern appears slightly more primitive, showing a PR0/A0 p3 with anteroconid of morphotype III (instead of III–V, as in N. rex); and (3) in H. peregrinus, the degree of anterior reentrant development in P2/p3 is concordant, but with more advanced, shallow anterior reentrants (Fladerer and Fiore, 2003, fig. 2).
The BM of Sardolagus obscurus in the context of western Mediterranean lagomorphs.—In insular environments mam- mals largely undergo Foster’s rule: small mammals increase their BM, whereas large ones undergo the opposite destiny (Foster, 1964; Van Valen, 1973). At present, the reasons for these BM shifts have not been fully clarified (see Lomolino et al., 2012). The response of middle-sized mammals as lago- morphs is not as clear as Foster (1964) suggested: extant leporids show a BMshift mostly directed to a reduction of size, but extant ochotonids are not represented in islands and their pattern is unknown (Lawlor, 1982; Lomolino, 1985). Assessing the fossil lagomorphs of western Mediterranean islands, we can shed light on this particular biological trend. Indeed some extinct insular ochotonids of the Mediterranean area appear quite large with respect to continental congeneric taxa (Moncunill et al., 2015, 2016a, b). However, the authors could
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194 |
Page 195 |
Page 196 |
Page 197 |
Page 198 |
Page 199 |
Page 200 |
Page 201 |
Page 202 |
Page 203 |
Page 204 |
Page 205 |
Page 206 |
Page 207 |
Page 208 |
Page 209 |
Page 210 |
Page 211 |
Page 212 |
Page 213 |
Page 214 |
Page 215 |
Page 216 |
Page 217 |
Page 218 |
Page 219 |
Page 220
