It's time for the annual focus on the paleontology of a particular group in National Park Service lands. This year we turn from the felines to one of their prey items, the lagomorphs (rabbits, hares, and pikas). So, why bunnies and pikas? To be honest, most of us have probably never given more than a moment's thought to the fossil record of lagomorphs, and that moment probably involved one of three thoughts: a nodding recognition that fossil rabbits et al. must exist; goofy speculation ("prehistoric saber-toothed rabbits"); or providing some ancient carnivore an appropriate lunch for a drawing or story. Well, you know me: I love topics nobody else is talking about. (I get in fewer arguments that way.) Also, I come from a household that appreciates small mammals for what they are. In return, they seem to feel comfortable hanging around. (A Tamiasciurus hudsonicus deciding your yard is part of its territory provides entertainment value all winter; the little psychos will take on anything.) For the past couple of months a young rabbit has been a frequent visitor, so this is my tip of the cap.
As noted Lagomorpha includes the rabbits, hares, and pikas. Rabbits and hares are in the same family (Leporidae) and are generally similar except hares reach larger sizes and have longer ears. (In the U.S., most hares are known as jackrabbits, but they're all part of genus Lepus.) Pikas belong to the family Ochotonidae and look kind of like small rabbits with short round ears. In North America they prefer to live in scree accumulations in cool high-elevation areas (showing admirable preferences in climate and real-estate) and make adorable squeaking noises. Lagomorphs as a whole show up around the late Paleocene but don't arrive in North America until the Eocene, with leporids present in strata such as the upper Eocene Chadron Formation of the White River Badlands. Although often collectively called "rabbits" as shorthand, it should be noted that the early leporids were less "hop" and more "run". Pikas are today something of an afterthought in North America, being confined to the genus Ochotona, but were more diverse in the past. They were also not as geographically restricted; as recently as the Pleistocene pikas were present in the Appalachians, as shown by fissure and cave records (Mead and Grady 1996).
The shape of Lagomorpha through time (the stem forms are all from Asia).
Ge et al. (2013)
(CC BY 2.5).
The map is 32 parks deep; fossil lagomorphs may well be more abundant at the parks, just not as frequently recognized as other things. Most of the parks have only one lagomorphic unit. The exceptions are Badlands NP (Chadron and Brule Formations), Big Bend NP (Delaho Formation, Banta Shut-In Formation, and unnamed ?Pliocene alluvium), John Day Fossil Beds NM (John Day, Mascall, and Rattlesnake Formations); Joshua Tree NP (informal Pinto Formation and unnamed younger deposits), Niobrara NSR (Valentine Formation and Quaternary deposits), and Santa Monica Mountains NRA (early Hemingfordian pikas in the upper Sespe Formation and middle Hemingfordian rabbits in the Topanga Formation). Only 10 have pre-Quaternary lagomorphs, which makes for a fairly compact table and a fairly good spread:
Expand to see formation names. I cheated a bit with the John Day
Formation, as I don't have information on hand that would make the
spread more concise.
Twenty-three have Quaternary lagomorphs, of which the great majority (17) can be described as cave or alcove records. This is not to imply that the Pleistocene was populated by cave rabbits (scree-dwelling pikas are another story). Rather, many cave and alcove records are predator dens, or fissures that accumulated a little bit of everything, or packrat middens featuring whatever kind of decor a packrat fancied at the moment.
Nine of the 32 have pikas (Grand Teton NP, Great Basin NP, Mojave NPres, Potomac Heritage NST, Niobrara NSR, Santa Monica NRA, Valley Forge NHP, Wind Cave NP, and Yellowstone NP); Mojave is the only one with fossils of pikas only. The pika record is not quite as Quaternary-focused as the rabbits. Grand Teton, Mojave, Niobrara, and Santa Monica have Miocene records, and the two Eastern records (Potomac Heritage and Valley Forge) are not plain old Rancholabrean, corresponding to the early Middle Pleistocene Cumberland Bone Cave and Port Kennedy Bone Cave, respectively.
Six fossil lagomorphs are known to have been named from areas now in NPS
units, with a seventh possible. They are:
- Oreolagus colteri Barnosky (1986) from Grand Teton NP
- Praotherium palatinum Cope (1871) from Valley Forge NHP (now considered dubious)
- Alilepus vagus Gazin (1934) from Hagerman Fossil Beds NM
- Archaeolagus buangulus Dawson (in Stevens et al. 1969) from Big Bend NP
- Hypolagus gidleyi White (1987) from Hagerman
- Hypolagus limnetus Gazin (1934) from Hagerman (now considered a synonym of Hypolagus edensis)
- Palaeolagus haydeni Leidy (1856) possibly from Badlands NP
Unlike rodents, we aren't swarming with different genera and species. While
rabbits of course are quite accomplished at making more of their particular species, they don't seem to have
quite the evolutionary flexibility of rodents. A couple of park sites have
several taxa. The Norden Bridge quarry in Niobrara NSR boasts two pikas (Hesperolagomys fluviatilis
and Russellagus vonhofi) and two rabbits (Hypolagus parviplicatus
and H. cf. H. fontinalis) (Voorhies 1990). (I always enjoy a chance to cite the Norden Bridge site; it's one of the most diverse terrestrial vertebrate sites you could hope to find.) Cave sites of Great Basin NP dating to the late Quaternary are even more diverse, featuring the pika Ochotona (no longer present in the Snake Range), two extinct pygmy rabbits (Aztlanolagus agilis and Brachylagus coloradoensis) plus the extant B. idahoensis, jackrabbits, and desert cottontails (Bell et al. 2016).
Barnosky, A. D. 1986. Arikareean, Hemingfordian, and Barstovian mammals from
the Miocene Colter Formation, Jackson Hole, Teton County, Wyoming. Bulletin of
Carnegie Museum of Natural History 26:1–69.
Bell, G. L., Jr., J. S. Tweet, and V. L. Santucci. 2016. Great Basin National Park: Paleontological resource inventory. Natural Resource Report NPS/GRBA/NRR—2016/1285. National Park Service, Fort Collins, Colorado.
Cope, E. D. 1871. Preliminary report on the vertebrata discovered in the Port Kennedy Bone Cave. Proceedings of the American Philosophical Society 12:73–102.
Gazin, C. L. 1934. Fossil hares from the late Pliocene of southern Idaho. Proceedings of the U.S. National Museum 83:111–121.
Ge, D., Z. Wen, L. Xia, Z. Zhang, M. Erbajeva, C. Huang, and Q. Yang. 2013.
Evolutionary history of lagomorphs in response to global environmental
change. PLoS ONE 8(4): e59668. doi:10.1371/journal.pone.0059668.
Leidy, J. 1856. Notices of remains of extinct Mammalia, discovered by Dr. F. V. Hayden in Nebraska Territory. Proceedings of the Academy of Natural Sciences of Philadelphia 8:88–90.
Mead, J. I., and F. Grady. 1996. Ochotona (Lagomorpha) from late Quaternary cave deposits in eastern North America. Quaternary Research 45(1):93–101.
Stevens, M. S., J. B. Stevens, and M. R. Dawson. 1969. New early Miocene formation and vertebrate local fauna, Big Bend National Park, Brewster County, Texas. The Pearce-Sellards Series, Texas Memorial Museum 15.
Voorhies, M. R. 1990. Vertebrate paleontology of the proposed Norden Reservoir Area, Brown, Cherry, and Keya Paha counties, Nebraska. Division of Archeological Research, University of Nebraska, Lincoln, Nebraska. Technical Report 82-09.
White, J. A. 1987. The Archaeolaginae (Mammalia, Lagomorpha) of North America, excluding Archaeolagus and Panolax. Journal of Vertebrate Paleontology 7:425–450.