The family Equidae in Anza-Borrego State Park is currently represented
by seven taxa (Fossil Treasures Appendix, Table 3). The following section will
provide an overview of some of them as they are presently understood, and
in general is confined to those fossils that have been assigned to species.
The naming and classification of each of them has been accompanied by
vigorous scientific debate, not only over the identification of individual
specimens, but also about how the various equids are to be organized into
a system that includes them all.
The geologically oldest equid fossils known from Anza-Borrego are a
right upper last molar from the Deguynos Formation (early Pliocene), three isolated
upper molars from the “Imperial Group - Palm Spring Group transitional
formations” (early Pliocene), and a partial mandible (jawbone) (Fossil Treasures Figures 15.4,
15.6) from the Hueso Formation (middle to later Pliocene) (Downs and Miller,
1994). They have been assigned to cf. Dinohippus sp.
Is there a zebra-like Equid found in Anza-Borrego?
Three fossils resembling Equus simplicidens have been identified from Anza-Borrego. The partial mandible assigned to cf.
Dinohippus sp. by Downs and Miller (1994) and described above, could equally reasonably be referred to Equus sp. cf. E. simplicidens, and is roughly contemporaneous with other fossils of Equus sp. cf. E. simplicidens from Anza-Borrego. Another specimen, an excellently preserved skull with associated lower cheek teeth (Fossil Treasures Figures 15.7, 15.8), is from the lower Hueso Formation, and is late Pliocene in age. Additionally, a partial skull, probably female, also assigned to Equus sp. cf. E. simplicidens, was recovered from the Arroyo Diablo Formation, and is mid-Pliocene in age. A most significant find from Anza-Borrego, Equus enormis (Downs and Miller, 1994), was initially considered to be plesippine (zebra-like) in nature. The holotype specimen, a partial cranium with associated right and left dentaries and assorted postcranial material, was recovered from the late Pliocene part of the
Hueso Formation. The new species was named for its large size, and indeed, the cheek teeth of this fossil are massive (Fossil Treasures Figures 15.9, 15.10). However, metapodial measurements showed that E. enormis was really no larger than (and in some cases smaller than) other extinct horse species from North America. Other fossils assigned to the new species, including skulls, teeth and jaws and a pelvis, were found in both the Hueso Formation and the Ocotillo Conglomerate, implying an age for E. enormis of between 2.1 million and approximately 500,000 years.
👉 Read Fossil Treasures (searchable PDF)
by seven taxa (Fossil Treasures Appendix, Table 3). The following section will
provide an overview of some of them as they are presently understood, and
in general is confined to those fossils that have been assigned to species.
The naming and classification of each of them has been accompanied by
vigorous scientific debate, not only over the identification of individual
specimens, but also about how the various equids are to be organized into
a system that includes them all.
The geologically oldest equid fossils known from Anza-Borrego are a
right upper last molar from the Deguynos Formation (early Pliocene), three isolated
upper molars from the “Imperial Group - Palm Spring Group transitional
formations” (early Pliocene), and a partial mandible (jawbone) (Fossil Treasures Figures 15.4,
15.6) from the Hueso Formation (middle to later Pliocene) (Downs and Miller,
1994). They have been assigned to cf. Dinohippus sp.
Is there a zebra-like Equid found in Anza-Borrego?
Three fossils resembling Equus simplicidens have been identified from Anza-Borrego. The partial mandible assigned to cf.
Dinohippus sp. by Downs and Miller (1994) and described above, could equally reasonably be referred to Equus sp. cf. E. simplicidens, and is roughly contemporaneous with other fossils of Equus sp. cf. E. simplicidens from Anza-Borrego. Another specimen, an excellently preserved skull with associated lower cheek teeth (Fossil Treasures Figures 15.7, 15.8), is from the lower Hueso Formation, and is late Pliocene in age. Additionally, a partial skull, probably female, also assigned to Equus sp. cf. E. simplicidens, was recovered from the Arroyo Diablo Formation, and is mid-Pliocene in age. A most significant find from Anza-Borrego, Equus enormis (Downs and Miller, 1994), was initially considered to be plesippine (zebra-like) in nature. The holotype specimen, a partial cranium with associated right and left dentaries and assorted postcranial material, was recovered from the late Pliocene part of the
Hueso Formation. The new species was named for its large size, and indeed, the cheek teeth of this fossil are massive (Fossil Treasures Figures 15.9, 15.10). However, metapodial measurements showed that E. enormis was really no larger than (and in some cases smaller than) other extinct horse species from North America. Other fossils assigned to the new species, including skulls, teeth and jaws and a pelvis, were found in both the Hueso Formation and the Ocotillo Conglomerate, implying an age for E. enormis of between 2.1 million and approximately 500,000 years.
👉 Read Fossil Treasures (searchable PDF)
