LAGOMORPHA, Brandt, 1855

Benton, MJ, Donoghue, PCJ, Vinther, J, Asher, RJ, Friedman, M & Near, TJ, 2015, Constraints on the timescale of animal evolutionary history, Palaeontologia Electronica (Florence, Italy) 15 (1), pp. 1-107 : 70

CROWN LAGOMORPHA (76)

Node Calibrated. The common ancestor of leporids (rabbits and hares) and ochotonids (pikas).

Fossil Taxon and Specimen. Our minimum estimate for crown Lagomorpha is based on the unnamed Indian leporid fossils (isolated calcaneus, GU/RSR/VAS 711, Garhwal University, Srinagar, India) described by Rose et al. (2008) from the Vastan mine, Cambay Shale, in West-Central India.

Phylogenetic Justification. Rose et al. (2008) identified these fossils as lagomorph on the basis of the occurrence of a calcaneal canal that passes diagonally through the bone, entering on the lateral side just inferior or proximal to the fibular facet and emerging just distal to the sustentacular facet and proximal to the cuboid facet. Further, in their cladistic analysis, Rose et al. (2008) assigned the Vastan ankle bones unequivocally to Leporidae , the hares, nested well within crown Lagomorpha .

Minimum Age. 47.6 Ma

Soft Maximum Age. 66 Ma

Age Justification. The Cambay Shale of West-Central India is dated as middle Ypresian based on the occurrence of foraminifera diagnostic of the Shallow Benthic Zone 10 and planktonic zone 6b

(Rose et al., 2008). The top of the Ypresian is dated at 47.8 Ma ± 0.2 Myr = 47.6 Ma ( Gradstein et al., 2012).

For the soft maximum divergence of crown lagomorphs we choose the K-Pg boundary at 66.04 Ma ± 0.4 Myr = 66 Ma, based on the occurrence of basal Glires such as Mimotona and Heomys (Dashzeveg and Russell, 1988; Li and Ting, 1993).

Discussion. There are many fossil Glires on the stem to Lagomorpha that long predate the first unambiguous occurrence of a leporid or ochotonid (Meng et al., 2003; Asher et al., 2005). None of these Paleocene Glires are members of Leporidae or Ochotonidae (Meng et al., 2003; Asher et al., 2005).

There are just under a dozen species of pikas ( Ochotonidae , Ochotona ), the oldest relative of which (to the exclusion of leporids) has been reported to be the late Eocene Asian form Desmatolagus (McKenna and Bell, 1997) . A yet older taxon, Decipomys from the early Eocene of central Asia, shows a pattern of enamel microstructure that could be a “structural predecessor” to that of modern ochotonids (Martin, 2004). The status of Decipomys as an ochotonid, or of Eocene palaeolagids as close relatives of rabbits and hares, would indicate a divergence within crown Lagomorpha by the early or middle Eocene, respectively. A recent analysis of isolated hindlimb elements from China and India (Rose et al., 2008) also indicates that leporids and ochotonids were distinct by the early Eocene. Although fragmentary, these elements are clearly diagnostic for the Leporidae . These identifications are consistent with the interpretation of the early Eocene Strenulagus and Gobiolagus from central Asia as leporids (Meng et al., 2005), although Lopatin and Averianov (2006) have more cautiously assigned them to “ Lagomorpha , Family Strengulidae ” without specifying a crown affiliation.