Introduction to the study of Northamerican collections

During the conference and at several other occasions, I had the possibility to observe, measure, and take pictures of many skulls from various equids of different ages, in the New York, Chicago, Lincoln, and Riverside collections. It seemed a pity not to publish them as they are, without any pretension to achieve correct systematics, but with the hope that the raw information, at least, will be useful. I had no time between the New York Conference and today to follow up the progresses and read the relevant literature devoided to the subject and had no intention to become involved again. As I proceeded, however, I felt that several points (some of them briefly discussed in Eisenmann et al. 1987 59.Is horse phylogeny becoming a playfield in the game of theoretical evolution ? ), may help to discriminate several ’groups’. Recently, I tried to catch up, at least with the chronology (PNAS chronology and M. Woodburne abstract of "Phyletic diversification of the Cormohipparion occidentale complex...", BAMNH 2007, on the web), but I am afraid that many blunders may still persist.
Incidentally, I was happy to discover that the ages of many Northamerican sites are now considered older than what I understood at the time of the Conference : it suppressed the discrepancies with the estimated ages of Old World Hipparions.

The collections references were quite a problem : the letters preceding the numbers are variable and not always clear (in the Field Museum of Chicago collections, there may be ’P’ or ‘PM’) ; some specimens may be borrowed from other collections (a few skulls in Chicago bear the sigles FAM or UC) ; there may be casts, and a double numerotation (UNSM 1353 = FAM 107596) ; a double numerotation may also exist for the same skull in the same collection (CRO 50-1281 = FAM 73940). I have done my best to resolve these issues but decided to omit the initials in my catalogues, tables, etc., and also to omit ‘Quarry’ or abbreviate it as ‘Q.’

Almost all studied skulls belong to the Frick collection (and bear the initials FAM). Morris Skinner has grouped some of the skulls under the following unformal generic names :
– Anchipparion : Boulder Q. 69511
– Atavippus : Echo Q. 71101, 71103, 71108 ; MacAdams Q. 10835 ; Tesuque 98-64.
– Fortihippus : Devil’s Gulch 69607 ; Loup Fork 8347
– Griphippus : Burge Q. 70005 ; Devil’s Gulch 60810 ; Jonas Wilson Q. 70708
– Lakotahippus : Ash Hollow 60300 ; Boulder Q. 18312
– Leurohippus : 71018
– Scaphohippus : Big Springs CRO 66-700 ; E. Sand 87301
– Trinihippus : Boulder Q. 69561.
The photographs are classified in part according to these names. But the ratio diagrams refer some of these to other morphs most of which belong to « Group A  » and « Group B  ».

Two catalogues give lists of :
– photographs (skulls, upper cheek teeth, muzzles, mandibles, lower cheek teeth, symphyses)
– ratio diagrams groups
– brief description of the characters and nature of specimens
– collections
– sites and individual ages of specimens (if juvenile or very old)
– names written on specimens or labels
– accession numbers.
The first is ordered by accession numbers (Table 1) ; the second by ratio diagram groups (Table 2).