A paper published in 2011 introduced the chelonian community to a new species of tortoise that has actually been roaming the bajadas of the southwestern United States and northern Mexico from time immemorial.
Written by Robert W. Murphy, Kristin H. Berry, Taylor Edwards, Alan E. Leviton, Amy Lathrop & J. Daren Riedle, the paper is entitled “The dazed and confused identity of Agassiz’s land tortoise, Gopherus agassizii (Testudines, Testudinidae) with the description of a new species, and its consequences for conservation.” It was published in the peer-reviewed, open-source journal ZooKeys in June 2011.
In this important paper, the authors make the case for a division of the desert tortoise species Gopherus agassizii into two distinct species. The Mojave Desert population retains the scientific name Gopherus agassizii and gains the common name Agassiz’s desert tortoise. The Sonora Desert population acquires the scientific name Gopherus morafkai and the common name Morafka’s desert tortoise. The authors’ argument in favor of the G. agassizii split has been widely accepted by the scientific community.
Biologists had believed for quite some time that more than one species of desert tortoise existed in the deserts of North America. For more than twenty years, scientists and resource managers had known about differences in shell shape, differences in behavior in habitat, and differences in DNA data among individual desert tortoises. As additional research was conducted, it became apparent that the Colorado River formed a natural border between two distinct populations of desert tortoises.
A team of six scientists headed by Dr. Robert W. Murphy of the Centre for Biodiversity and Conservation Biology, Department of Natural History of the Royal Ontario Museum in Toronto, Canada began conducting an investigation into the physical, behavioral and genetic differences between populations of “desert tortoises.” Their inquiry added a new member to the chelonian family of tortoises, the Testudinidae. G. morafkai was named in honor and memory of Dr. David J. Morafka, the late desert ecologist and professor from California State University Dominguez Hills.
A Shroud of Mystery
Many aspects of the desert tortoise’s identity were shrouded in mystery as the current investigation began. The very date of publication of the species description, as well as the location of the three original cotypes, were uncertain.
James G. Cooper, MD presented the discovery of the new tortoise species and genus, Xerobates agassizii, the Agassiz Land-Tortoise, at a meeting of the California Academy of Natural Sciences held on July 7, 1861. The new species description was published in a collected Proceedings of the Academy, a publication that included issues from 1859 to 1862. The collected Proceedings was closed and printed with a title page dated 1863. For decades thereafter, 1863 was cited as the date of publication of the description of X. agassizii.
The individual issues, known as signatures, that comprise the collected Proceedings were published at intervals during the period from 1859-62. Publication of signature 8, the issue containing Dr. Cooper’s description of the newly discovered tortoise, likely took place shortly after his presentation in 1861. Based on this conclusion, Murphy et al. propose the official date of publication as July 25, 1861.
Three cotypes (a set of type specimens) of the newly discovered tortoise were collected by Dr. Cooper, but the locations of collection and the locations of the cotypes themselves were sources of confusion.
The type locality of the type specimens is unclear. Dr. Cooper traveled to the Army’s Fort Mojave on the east bank of the Colorado River in late 1860. The description of the collection site is vague, “the mountains of California, near Fort Mojave,” and has been credited to several specific locations throughout the years.
Dr. Cooper sent one cotype to the Smithsonian Institution sometime after 1861 and it remains in the Smithsonian’s collections today. This specimen was assigned the identification “USNM 7888,” for United States National Museum #7888. The exact location at which this specimen was collected remains a mystery, as Dr. Cooper’s notes from his travels have not survived. Murphy et al. determined that Soda Valley, CA aka Soda Playa, is probably the type locality at which the Smithsonian’s cotype specimen (USNM 7888) was collected.
The circumstances of the remaining two cotypes may never be conclusively determined. Most of the records kept by the California Academy of Sciences, and possibly the two cotypes themselves, were destroyed in the 1906 San Francisco earthquake and the fire that followed.
A Change in Classification
The genus name Xerobates that was assigned to the new tortoise species by Dr. Cooper in 1861 was derived from two Greek root words: xero-, meaning dry, and -bates, meaning one that walks, treads or haunts.
Leonhard Hess Stejneger, a Norwegian-born scientist, became Curator of Reptiles for the Smithsonian Institution in 1889. In 1893, Stejneger suggested that a taxonomic (i.e., classification) change for the species X. agassizii was necessary. He concluded that the species belonged to “the North American genus “Gopherus Rafinesque 1832, as G. agassizii (Cooper)” (Murphy et al. 2011). His assignment of the desert tortoise to the genus Gopherus was widely accepted by the scientific community and remained fixed for over a century.
A Scaly-headed Desert Tortoise
In 1989 a “new” species of Gopherus tortoise was described by Ottley and Velasquez Solis. Known by the common names of the scaly-headed, or Sierra Madre tortoise, Gopherus lepidocephalus was discovered in the Cape Region of Baja California Sur, Mexico. Reports indicated that it lived in hillside environments, in rock crevices on slopes and hilltops rather than in burrows. This way of life corresponded to the desert tortoise populations of the Sonoran Desert.
There was skepticism regarding the validity of this new species among some wildlife biologists, who called G. lepidochelys a junior synonym of G. agassizii. In zoological classification, a junior synonym is defined as a subordinate synonym of an established taxon (classification group). The type specimen of G. lepidochelys became part of the DNA testing done by Murphy et al. in the course of their investigation.
A Case for Multiple Species
The journal Chelonian Conservation and Biology published an article in 2002 co-authored by Drs. Kristin H. Berry, David J. Morafka and Robert W. Murphy entitled “Defining the Desert Tortoise(s): Our First Priority for a Coherent Conservation Strategy.” The article presented an overview of the evidence for multiple species of “desert tortoises.”
The evidence cited in the 2002 article included differences in microsatellite DNA2, differences in mitochondrial DNA3, and “behavioral and ecological differences,” among other differences. The examination of this evidence resulted in the authors’ conclusion that “G. agassizii is best viewed as a composite of at least two and possibly as many as four species” (Murphy et al. 2011).