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Like for the first phalanges, I received from John Howe copies of his data on second phalanges (Ph2) on separated (10) sheets. A few data were redundant, in that cases I used their mean noted ’-X’. In Table 1, you may find the original data, in Table 2 - the ones I used, and in Table 3 - the same after sorting the anterior Ph2 from the posterior.
Uusually a scatter diagram of distal articular width (6) versus maximal length (1) separates easily the anterior Ph2 (shorter and wider) from the posterior. In this case, I used the sum of minimal width (3) and distal articular width (6) versus maximal length (Fig.1).
This scatter diagram shows a bulk of slender Ph2 with little overlap and one uncertain specimen. Besides, a few phalanges seem rather large ; three rather small.
The remaining specimens are too large and/or too robust to belong with the precedent group.
Middle-sized slender Ph2 (A. cf. pseudaltidens)
Statistics (Table 4) on 87 supposed anterior Ph2 are compatible with a single form. Size and shape are similar to extant E. hemionus onager apart a smaller proximal depth (5). The corresponding bone by bone Simpson’s diagram is in Fig.2.
Statistics on supposed 80 posterior Ph2 are also compatible with a single form, not very different from the extant E. hemious onager (Table 5). The corresponding bone by bone Simpson’s diagram is in Fig.3.
Large slender Ph2
There are eight of them (Fig.4). I suppose that they come from a different level of Natural Trap.
Small slender Ph2
I do not know what to make of these three small specimens (Fig.5). The posterior, extremely slender, may be a juvenile ?
Five anterior and seven posterior are close in size and proportions (Fig.6). to extant E. przewalskii or Mongolian horses Ph2.
A. leoni-like Ph2
I refer to A. conversidens two anterior Ph2. Although I have no data on A. leoni Ph2, this is a logical assumption in the context of other fossils of Natural Trap. One Ph2 of an extant E. africanus is smaller but otherwise not very different (Fig.7).
Fig.1 Natural Trap gracile Ph2, Scatter diagram (3+6) versus 1 Fig.2 Natural Trap gracile Ph2 Ant, Simpson’s diagrams
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Fig.3 Natural Trap gracile Ph2 Post, Simpson’s diagrams
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Fig.4 Natural Trap large and gracile Ph2 Ant, Simpson’s diagrams
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Fig.5 Natural Trap large and gracile Ph2 Post, Simpson’s diagrams
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Fig.6 Natural Trap Caballine Ph2, Simpson’s diagrams
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Fig.7 Natural Trap A. conversidens Ph2 Ant, Simpson’s diagrams
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Table 1. Natural Trap Ph1 Data, sheets
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Table 2. Natural Trap Ph1 Data used, by numbers
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Table 3. Natural Trap Ph1 Ant/Post Data used, by numbers
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Table 4. Natural Trap A. cf. pseudaltidens Ph1 Ant, Statistics
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Table 5. Natural Trap A. cf. pseudaltidens Ph1 Post, Statistics
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