sounds like an Earle Stanley Gardner mystery story but happens to be an
account of sleuthing in a non-fiction science mystery. All of the elements
of a mystery are present - a missing link, unidentified people, unknown
localities, incomplete bits of information and an exotic setting. "A
detective story!" is the comment made by friends who have heard it. Will the
hypothesis prove correct? Will the lizard be found? This uncertainty makes
mysteries exciting and is what makes science exciting. Maybe this is the
reason so many biological scientists find that their vocation is also their
The missing clue in this mystery
was Ditmars' horned lizard, last seen alive in 1898.
Most of the lizards along our
borders are well known. Of 136 species from the United States listed in
Hobart Smith's Handbook of Lizards, all but three are well documented. One
of the three is the smooth-necked alligator lizard, Gerrhonotus levicollis
levicollis (Stejneger), from western and southern Chihuahua and recorded
originally from the "Mexican Boundary", but has not been found along the
Arizona and New Mexico-Mexico borders since. Another is Bipes sp., a
soft-bodied two-legged worm lizard. The nearest distribution of this genus
is represented by Bipes biporus at the tip of Baja California where the
habitat is damp sandy soil. In spite of rumors reported by Smith, it is
doubtful that it ever was found in the mountains of southern Arizona because
there is almost no damp sandy soil in this area. There have been many
reports of two-legged lizards in the Chiricahua Mountains in Southeastern
Arizona, but they consistently turn out to be the local alligator lizard, G.
kingi (Gray), a slender lizard with tiny legs and a snake-like movement.
The mystery involving the third,
Ditmars' horned lizard, could not be solved so easily. Two collections of ''ditmarsi''
were made in 1890 and 1897, for a total of three specimens and none had been
found since, in spite of the efforts of many professional and amateur
herpetologists, including myself. Trips through back country in Sonora in my
well-traveled pickup Camper ''El Ghosto Blanco" produced nothing more than a
few specimens of the regal horned lizard, Phrynosoma solare, along the
valley roads. But the quiet old towns, each with its central plaza, church
and adobe houses, looking as they did when missions were first established
in the late 1600s, made the trips worthwhile.
The country is relatively
unexplored by biologists and ditmarsi could occur anywhere. The roads, all
narrow, winding, gravel or merely two ruts, skirted vast canyons, cottonwood
lined rivers, outcrops of rhyolite and volcanic plugs standing stark above
the landscape. They wound through narrow canyons with jungle-like foliage
and bright-plumed trogons, up dry washes and over rocky mesas. Some places
required a second run to get up the hilly roads, even in compound low.
In broad, sycamore-shaded
Guadalupe Canyon, at the junction of the three states of Arizona, New Mexico
and Sonora, I visited with John Magoffin, a local cattle rancher. He assured
he had never seen a horned lizard in Guadalupe Canyon, nor in the adjacent
Sierra San Luis.
From the Trail Dust Zoo near
Bisbee, Arizona, came rumors that ditmarsi had been found by someone from
California. Mr. Howard Hamm, a talented western artist and curator of the
zoo who has a "green thumb" when it comes to animals (all his animals seem
friendly!) assured me he had seen ditmarsi among the lizards brought to him.
But later, when my hopes were raised, he decided that actually he hadn't
seen any. While looking over the wide range in color of the douglassi in his
cages, an onlooker commented, "You seem to know something about lizards." I
admitted a moderate knowledge. "Well, I've seen one like that," he said,
pointing at a douglassi, "reddish and flat, but with no horns. My boy picked
it up at the Sunnyside Church in Douglas a few years ago."
This was exciting news, but when
reconsidered and a second look taken at Douglas, it was discarded. Douglas
lacked the necessary habitat.
Tim Walker, an amateur
herpetologist from Paradise, Arizona, had made many hiking trips in the
mountains below the border insearch of snakes and lizards. When it comes to
locating snakes, Tim is one of the best and most persistent of the
herpetologists, but he had had no succcss in locating the elusive ditmarsi.
He and I spent many hours speculating on the habitat of ditmarsi, and came
to the conclusion that it must he on one of the isolated mountain ranges -
but which one?
Dr. Charles H. Lowe, a well-known
herpetologist of the University of Arizona at Tucson. has been on the
lookout for ditmarsi since the l950's. He obtained a large collection of
horned lizards from a mining engineer, Arthur Ruff from Cananea, Sonora, but
they were all the mountain short-horned species, P. douglassi (Bell).
During the 1890-91 Lumholtz
Archaeological Expedition, sponsored by the American Museum of Natural
History (AMNH), F. Robinette collected the first specimen of ditmarsi, which
languished for many years unidentified and with no locality in the AMNH
herpetological collections. In 1968, a graduate student of Lowe's, Mike
Robinson, began an analysis of the first part of the Lumholtz expedition,
and in 1969 received a grant from the Arizona-Sonora Desert Museum to aid
his search for the missing lizard. During his visits to the Southwestem
Research Station (SWRS), we shared information accumulated separately and
speculated whether ditmarsi was a valid species or might even be extinct.
Mike tried following the guessed-at route of the Lumholtz expedition without
success in finding the lizard.
The problem has been that the
exact route of the expedition from Bisbee to Fronteras was not indicated by
Lumholtz in any of his articles. His field notes were not on file at the
AMNH and local newspapers of the 1890s didn't record the arrival and
departure of the expedition. After searching through published reports it
was possible to piece together some localities and dates given by J. A.
Allen in his list of mammals and birds collected on the expedition. Although
there were some errors in those records, a tentative route was established.
The expedition left Bisbee on
September 6 and headed southwest to Greenbush Ranch (the present-day
Stevenson Ranch) near Palominos, Arizona, crossed the Mexican border
September 15 at the San Pedro River to the Mexican Aduana (Customs Station
at San Pedro just south of Palomitas), and then turned east along the border
where they stopped at Trincheras (September 20), Santa Barbara (September
2l) and Leoncita (September 23). These small villages are uninhabited today
and not on recent maps.
They probably stopped at Ojo de
Agua at the north end of the Sierra de los Ajos and passed through the
mountains. After reaching the "Fronteras Highway" they traveled south,
arriving in Fronteras on September 23, and in Oputo (also spelled Opoto) on
October 22. Although the lizard collected by Robinette had no locality nor a
date available we speculated that ''Northern Sonora" would indicate all area
north of Oputo, especially since the expedition didn't leave there until
November 25 or so. late for horned lizards to be active.
The second and third specimens
collected in 1897 had been turned over by a "Mr Eustace" to Raymond L.
Ditmars, then Curator of Reptiles in the New York Zoological Park. Ditmars
kept one specimen alive for about a year and commented on its peculiar
habits in a letter to Dr Leonhard Stejneger, Curator in the Division of
Reptiles and Batrachians at the United States National Museum (USNM). This
letter of October 12, 1905 was located in the USNM archives by Dr. George
Zug, Assistant Curator of the Division of Reptiles and Amphibians. Ditmars
wrote, "This little creature used to jump clear off the ground in most
clown-like fashion when annoyed, emitting a series of hisses like miniature
The lizards were preserved and
later forwarded to Dr. Stejneger for identification, and he subsequently
described them in 1906 as Phrynosoma ditmarsi Stejneger, naming them after
his colleague Raymond Ditmars. In his letter to Stejneger, Ditmars wrote.
"the most definite locality I can give you for this specimen is 'Northern
Sonora, Mexico'." Stejneger gave the type locality as ''State of Sonora,
Mexico, not far from the boundary of Arizona," elaborating slightly on the
My attempts to locate Mr.
Eustace, or information about him or his descendants failed. A letter to the
Douglas Dispatch directed towards old timers, and searches through the
Bisbee, Naco and Tombstone newspapers of the 1890s, and through the Arizona
Historical Society files, and even telephone directories, produced no
mention of his name.
At this point it became obvious
that additional information was necessary before the species could be
recovered. So far all efforts had produced only frustration, stronger leg
muscles and worn out vehicles. For such a scarce lizard, it was impractical
to search over so wide a country. Even in the Chiricahua Mountains, its
relative the short-horned lizard, P. douglassi, was not easily found.
Because of the similarity of the two species, Mike Robinson and I
conjectured that it might be a mountain species rather than a low-land
species like the Texas horned lizard, P. cornutum, or the regal horned
lizard, P. solare.
After Mike and I had almost given
up hope of finding the lizard, another possibility arose. While identifying
the stomach contents of some local lizards for a student, Carol Simon, the
solution to finding ditmarsi became apparent to me. The stomach contents of
the three preserved specimens of ditmarsi could be studied to identify the
insects upon which the lizards fed, determine their habitats and known
distribution and then a summary of the data would identify the type of
habitat and locality of ditmarsi .
The search was becoming more
In May 1970 an airmail request
was sent to Dr. Richard G. Zweifel, head of the Department of Herpetology at
the AMNH, for the stomach and large and small intestines of their specimen
of ditmarsi (AMNH 557). They arrived by return mail.
The stomach contents were
removed. washed repeatedly in alcohol and screened into various sizes. I
then sorted them microscopically using progressively higher magnification.
Many of the specimens were partially digested and in pieces, but a total of
eighteen different items were separated: pebbles of andesite, seeds of three
species of grasses, and fourteen insects.
This approach was so successful
that I sent an immediate request to Dr. Zug at the USNM for the stomachs of
the other two lizards. One of the two had been kept in captivity for a year,
so only one stomach would be of value. Imagine the concern and consternation
when Dr. Zug replied that one lizard had been eviscerated! The other lizard
was being sent by return mail. The question immediately arose - would Mr.
Eustace have removed the stomach of the lizard that had died? Or would
Ditmars have eviscerated a lizard that died in the laboratory? The question
was pondered apprehensively since one specimen would be useless, the other
of great value.
When the specimen arrived by
registered mail, excitement charged the laboratory as I opened the package
and one of the three known specimens in the world was unveiled. And as the
cheesecloth shroud was unfolded, unveiled it was! Such an insignificant
animal, alcohol soaked, gray, dead over seventy years, the tips of many
tubercles rubbed off, the short horns just as Stejneger had described. With
some trepidation. the lizard was opened by Ralph Luetke, a volunteer
assistant at the Station, and the stomach and intestines removed.
We held our collective breaths as
the first slit was made, and out popped gramma grass seeds, Bouteloua sp.,
and Apache harvester ant heads, Pogonomyrmex apache Wheeler, the same seed
and species of ant as found in the AMNH specimens. The stomach contents were
from the Southwest and not laboratory food. We were on the right track.
Then began the process of sorting
and identifying. I made the initial identifications and then made the
specimens available to specialists, writing almost fifty letters and making
an equal number of personal contacts. For instance, the weevils were taken
to Karl Stephan, an amateur coleopterist (specialist in beetles) in Tucson,
then sent to a specialist on weevils for a generic identification, and then
on to a person who specialized on the specific genus. Everyone cooperated
enthusiastically and, caught up in the spirit of the search, remarked, "Let
me know if you are successful."
When sorting was finished, there
were thirty different items the lizards had ingested, and of special
importance, eight species of ants in one stomach. There were pebbles picked
up accidentally by the horned lizard, indicating it had fed upon the ants as
they carried pebbles from their nest. There were gramma grass seeds, almost
one seed for each harvester ant! The lizard obviously was also feeding upon
ants returning to the nest.
No specific identifications were
available for the seeds, but several grass specialists hazarded guesses. I
spent a day in the University of Arizona Herbarium comparing seeds and
narrowed the possibilities to several gramma grasses of one type and to
bullgrass, Muhlenbergia sp. Roy Snelling of the Los Angeles County Museum
studied the ants and returned a summary of the habitats of the eight
species. Later, other species were sent to additional ant specialists. Among
them was one unique reticulated thorax and part of an abdomen of a ponerine
ant, Gnamptogenys regularis Mayr, previously known only from Tepic, Nayarit,
Mexico. Were we wrong in assuming that ditmarsi came from near the border of
Thc next bit of information also
directed our attention southward. Dr. Ann Howden of Ontario, Canada
recognized the three weevils as identical to an undescribed species of
Pandeletius collected a few years before by her husband in the southern part
of Sonora at Yecora, on a juniper at 7,000 feet.
Each time an identification was
obtained, it meant searches through the literature and of the University ot
Arizona insect collection for distribution records. Gradually information
came in, and a pattern slowly developed. The distribution of most of the
specimens showed an affinity for the mountains of southern Arizona or
Other weevils, tiphid wasps, a
male scale, jumping spiders, true bugs and grasshoppers were identified.
Once of the grasshoppers was Barytettix h. humphreysii (Thomas) upon which
Dr. Ted Cohn of San Diego State College was working at the time. Its
distribution is west of Agua Prieta and Sierra San Jose near Naco, whereas
the distribution of a related species, B. h. cochesei Gurney occurs east of
Agua Prieta. One extremely unusual insect, a true bug with short wings,
lateral thoracic horns, and a dorsal scutellar horn, was represented by only
a few parts. After almost giving up attempts to identify it, I assembled the
parts like a jigsaw puzzle, made a composite drawing and sent it to Dr. R.
C. Froeschner of the USNM in Washington D.C.
Dr. Froeschner replied
immeddiately that it was very close to a South American genus of largid bug,
Thaumastaneis, known only from Bolivia and Brazil! It is similar to a local
ant-mimicking, brachypterous (short-winged) true bug, Arhaphe cicindeloides
Walker (which lacks the dorsal spines), a very common largid bug among the
dead leaves in oak stands in the Chiricahua Mountains.
In another field, several
geologists and petrologists suggested that the tiny pebbles were not
adequate for a specific determination. However, the pebbles were described
by W. H. Pierce of the Arizona Bureau or Mines as "a finely crystalline
igneous rock characterized by plates or tables of plagioclase feldspar and a
dark to red brown ferromagnesian mineral of undetermined species. A small
amount of magnetic and other unidentified material was present. Quartz was
not observed. Based upon spotty evidence. I would suggest that the material
is diorite in composition."
Mr. Sidney Williams of the Phelps
Dodge Corporation at Douglas, Arizona, felt that these mineral specimens
were andesite, a close relative of diorite. He knew the areas below the
border, and suggested that two mountain ranges be investigated, Sierra
Manzanal, south of Cananea, and Sierra San Luis, near the Chihuahuan border,
both of which had extensive deposits of andesite. We were able to eliminate
Sierra San Luis because it was east of Agua Prieta and out of the range of
the Barytettix grasshopper.
It was time to summarize the
data. After many hours of discussion over meals, in my office and
laboratory, over campfires, retelling the story of the missing lizard to
anyone who would listen, and then sifting through their ideas, suggestions,
and speculations, plans for the future evolved. Looking over the data, it
was possible to come to the following conclusions:
The lizards had been collected in
the fall of the year as evidenced by the expedition collections from
northenr Sonora and probably in the month of September. The seeds,
grasshoppers and jumping spiders found in the stomachs had been mature,
reconfirming the time of year. The presence of gramma grass seeds, Apache
harvester ants, andesitic pebbles in both stomachs indicated that the
lizards were collected in the same area. The soil would probably be sandy
red as Ditmars described the color of the live lizard; horned lizards
normally blend well with the substrate. The specific habitat had been
described by Snelling as ''a canyon habitat with a small stream, rocky
slopes, grass, oak-juniper, possibly with sycamores on the canyon floor. It
looked to me like the lizard was foraging above the streams, between the
stream and the sides of the canyon."
Then I realized there had been
extensive change in the habitats over the past seventy years - lower
rainfall and over-grazing in many areas. Was I studying lizards taken from
the extreme edge of their habitat? There were still so many variables that
at times I was ready to give up.
The Changing Mile by Hastings and
Turner describing climatic changes of southeastern Arizona during the late
1800s and early 1900s showed some significant transformations in the
vegetation. If similar changes took place south of the border, insect (and
lizard) life may have been altered significantly and marginal species such
as the horned largid bug, Gnamptogenys ant, and the Pandeleteius weevil, as
well as ditmarsi, may have been pushed further south.
While the identifications of the
plants, insects and spiders were being obtained, extensive collections of
ants were made in the Chiricahua Mountain area at elevations ol 4160 to
a1most 10,000 feet to determine the altitudinal distribution and habitat
preference for the species found in the lizards' stomachs. Most of these
species occured sympatrically within 4,800 to 5,400 feet on dry hillsides
often adjacent to riperian situations.
The key items to locate were the
andesite (its magnetic properties made it especially valuable), grasses
(conspicuous in the fall), Barytettix grasshoppers, Apache harvester ants,
Gnamptogenys ant, largid bugs, and Pandeleteius weevils. With the time of
year determined, knowledge of the general area in Mexico and its habitats,
and an idea of the mineral make-up of the area, we started serious searches
in the field in mid-summer of 1970. The best possibility appeared to be the
Sierra Manzanal. One of the two ranges below the border with known deposits
of andesite. The mountains at Cananea, nearby, had produced only douglassi,
and to the east Sierra de los Ajos had been searched briefly with no
success. We made several insect collecting trips into northern Sonora for
samples of the organisms and pebbles found in the lizards' stomachs. The
habitat in which most of the species occurred would likely be the place
where ditmarsi would be found.
These trips with friends and
volunteers from the SWRS required crossing the border with all the hassles
involved with Mexican officials over papers for the pickup truck, birth
certificates or lack of them, temporary visas, below-age students without
written permission from parents, a neat beard (''He's a heepie!"), a German
passport, and the often expected mordida (the extra pay for "extra
The first stop in Mexico would be
the panaderia for a bag of birotes, the tasty, hard Mexican rolls, some
small but flavorful Mexican bananas, tamarindos, dried seed pods with a
citrus-acid like flavor, limes for hot limeade or for squeezing over fresh
mangos, and bars of panocha, a raw sugar for energy food. Then through Agua
Prieta, typically lacking direction signs, past the cemetery to the checking
station, and then abruptly out into the backcountry - wide open vistas, no
power or telephone lines, no billboards, and little fencing.
Maps from the American
Geographical Society, U. S. Coast and Geodetic Survey (Aeronautical Charts)
and the Secretaria de Agricultura y Ganaderia, Direccion y Meterologia from
Mexico City gave little help. They were consistent only in their
inconsistencies. Localities on one map were missing or spelled differently
on another, altitudes varied considerably in the mountain ranges which never
seemed to be in the same place. Roads which didn't exist were depicted with
heavy lines, and good roads not even indicated! Still, the maps were of some
Our first destination was the
west side of the mounta range we thought was Sierra Manzanal. On a back
trail, while we were lunching on birotes and mangos a truck bounced out of
the mountains with a load of copper ore. We flagged it down and found we
were not in the Sierra Manzanal, but in the Sierra de los Ajos. So back up
the road to Cananea, a relatively American-looking mining town, and then
south on a different road to our goal.
We checked out each road into the
Sierra Manzanal, most of them never having seen a grader or bulldozer, so it
meant a slow, rough trip. Five or ten miles per hour is considered good
progress. After an hour or so on one narrow road gouged out of the steep
mountain side we came to a small cluster of brown corrugated-paper-clad
shacks with the usual half-dozen or more small children and their pregnant
mothers. We asked about the road and about horned lizards. The road went on
for a couple of miles, but as for the lizards, they knew of none in the
area. One relaxed fellow said they could be found at Sierra San Antonio to
the west, but were very rare. Later a look at the map showed no mountain by
A couple of miles up the road we
parked at a deserted mine and looked over the area. The habitat didn't
appear promising except for many of the ants we were looking for. Soon dark
clouds, lightning and rain in the distance cut short our stay. Being caught
in a cloudburst in this country can mean an unexpected stay of a few days if
the roads turn into rivers or quagmires. We returned to Canon de Evans in
the Sierra de los Ajos and drove five miles up a sycamore and oak-lined wash
to make camp.
The area was still promising with
the type of habitat described by Snelling and with many of the insects we
were seeking, but no andesite. On our way home we stopped in Douglas to see
Sidney Williams, a geologist who knows northern Sonora well, and he gave us
the directions we needed to get into the Sierra Manzanal.
Our next trip into Mexico took us
deep into this mountain range because we picked up a Mexican who was heading
for his ranch and showed us new roads. He seemed to know nothing about
horned lizards and again we wondered if we could be in the right mountain
range. After we dropped him off we located a small stream, cooled off in the
water and took a siesta (when in Mexico, do as the Mexicans do). Some
collecting in the area again showed a few of the insects in which we were
interested, also some red rock similar to what we were looking for, but no
lizards. That evening we camped beneath an old oak and had our usual dinner
of potatoes wrapped in aluminum foil and baked in hot coals, birotes and
fresh cantaloupes. Debris nearby indicated that many years ago this had been
the site of a large mining camp. We wondered if Mr. Eustace had been a
mining engineer and collected the lizards right here. On a nearby hill we
saw and heard a drilling rig, indicating current drilling activity.
That night horizontal streaks of
lightning broke into fingers of light and then ended in balls of fire . . .
one of the greatest displays ot lightning I have ever seen. With the
thunder, then came rain, and later a herd of curious burros. It was hard to
sleep under my plastic ground cover. After a breakfast of corn pancakes,
bananas and hot chocolate, we explored some nearby mine shafts, searched for
horned lizards and then climbed the hill to investigate the drilling
operation. ,We found an engineer, Hector Lopez, in charge, and with the help
of my daughter, Susie, who had spent some time in Mexico, we communicated
fairly well. ,After the usual. "What are you doina up here?'' from both
sides, we got down to business.
"Any homed lizards? we asked.
''Si!" His children had been
playing with them last week in the brush around the drilling rig. He drew a
reasonable facsimile of a horned lizard then then cinched it by saying it
squirted blood out of its eye, characteristic only of horned lizards.
I offered a reward of 100 pesos
(about $10) to anyone who would get a specimen for me that turned out to be
ditmarsi. With this agreement, we left with a promise to return soon.
Over two weeks passed before we
could return and then we found that Senor Lopez had left for Mexico City
where his wife was having a baby. In the meantime, we had studied the
material taken on the previous trip and believed that we were in the right
area, but intensive searches around the drilling rig produced no horned
lizards. A new engineer. this time an American, Paul Geiger, was at the rig
and communication was easy. He promised to obtain a lizard for us if
possible. Other searches in the area produced no more likely place for
ditmarsi. We returned to Canon de Evans to Camp and once again decided that
the Sierra de los Ajos couldn't be the right locality.
Almost two weeks later a call
came from Cananea. It was Paul Geiger asking if I could meet him in Douglas
the following morning. He had a lizard! At the Station the excitement was at
high pitch and everyone wanted to go to town immediately. We arrived early
at the appointed spot and waited. As he drove in, we dashed up and were
handed a small box. We cracked open the lid slightly and out peered a very
spiny horned lizard. Our hopes died. ''A douglassi!" was all I could say at
first, but then added. "It's a good record anyway." We sent a few dollars
along for the collector as a consolation prize, and went home wondering
where we would look next. At the Station the specimen was turned over to
Chuck Lowe, who peered through a hole in the box and agreed it was a
The next day a call came from
Chuck. "Mike and I are coming down tomorrow." Just a flat statement, no
reason, no nothing. Something was in the wind. They arrived the next morning
with the electrifying news, the lizard had been identified by its abdominal
keeled scales as ditmarsi! There still was a slight question in Chuck's
mind, but in the meantime the type of the species had been requested for
comparison. More specimens were needed for confirmations so it was back to
This time, accompanied by Chuck
and Mike, we decided to check out the road along the border to Rio San Pedro
and possibly locate some of the Lumholtz Expedition tracks. The road was
unproductive for lizards, but a picnic site along the river had a record
sized wild grape vine a foot in diameter near the base. The back road
eventually led along the river, across farm lands, through grasslands and
ejidos to Cananea. We located none of Lumholtz's route.
We drove into the Sierra Manzanal
and up a narrow mining road where we had to back up to make one turn on the
precipitous mountain side to the drilling rig. I introduced Paul to Chuck
and Mike and we made arrangements to obtain additional specimens of
We looked carefully for lizards,
found none, but took notes on this habitat. It was similar but not identical
to the habitat we expected because it was on top of a rocky oak-covered hill
with sandy red soil rather than in a canyon. Without a doubt we were near,
but not necessarily at the type locality.
The rest of the tale was
anticlimactic . . . we obtained more specimens, the identity of the 1izard
was confirmed, and the rediscovery was written up (Lowe, Robinson and Roth
1971). Stomach contents provided additional information on the food habits
of these lizards (Roth 1971). The search was over . . . and successful. All
that remained was to tell the story again and again to interested biologists
and herpetologists who almost invariably replied, "Sounds like a detective
story" - which it was!
Acknowledgements. - Many thanks
to David Hardy, Sr. and Karen Hayes who typed and repeatedly improved this
Allen, J.A. 1893. List of mammals
and birds collected in northeastern Sonora and northwestern Chihuahua,
Mexico, on the Lumholtz Archaeological Expedition 1890-92. Bulletin American
Museum of Natural History Article III, Vol. 5:27-42.
Ditmars, R.L. 1930. The Reptile
Book. Doubleday, Doran and Co., Garden City, NewYork, 472 pp.
Hastings, J.R., and R.M. Turner.
1965. The Changing Mile. University of Arizona Press, Tucson. 317 pp.
Lowe, C.H., M.D. Robinson and V.D.
Roth. 1971. A population of Phrynosoma ditmarsi from Sonora, Mexico. J.
Arizona Acad. Sci. 6:275-277.
Roth, V.D. 1971. Food habits of
Ditmars' horned lizard with speculations on its type locality. J. Arizona
Acad. Sci. 6:278-281.
Smith, H.M. 1946. Handbook of
Lizards. Comstock Publishing Co., Ithaca, New York.
Stejneger, L. 1906. A new lizard
of the genus Phrynosoma from Mexico. Proc. U.S. Nat. Mus. 29:575-567.
* From an unpublished manuscript
written in 1972
** Former Resident Director, Southwestern Research Station of
the American Museum of Natural History, Portal, Arizona