Digging Holes


Painted Desert of Petrified Forest National Park in Arizona.  The distant skies are filled with virgas, rain that evaporates before it reaches the ground.  Image credit: Curious Sengi.

This post is part of a series commemorating the 150th anniversary of the Yale Peabody Museum of Natural History.  You can read about the first specimen to enter the Vertebrate Paleontology collection here.  This story is about the most recent fossils to enter the collections — specimens that were collected just over a month ago in May and June 2016 during a field expedition to the Triassic rocks of Petrified Forest National Park, Arizona.   

Our dig site is marked by a dark blue tarp, a faint pinprick of artificial color in the Painted Desert.  At this point, we had already trudged over a mile through the trackless desert:  picking our way between the low scrub, avoiding rattlesnakes, and using a distant red-lipped hill as our only bearing.  Now we stood at the edge of badlands, where the fossils are.  The heat of the day is rising.  And that blue tarp is still painfully far away.

No sane human being would be out here.


The black arrow marks the location of the blue tarp that covers one of the multiple dig sites worked during the 2016 field expedition.  Image credit: Curious Sengi.

In our heat-addled hallucinations, we see the dreamscape of the desert, where gypsum erupts from the red earth like misshapen white molars or glittering panes of broken glass.  Millions of years of sediment deposition stand out in vivid colors, much too reminiscent of seven-layer dip and Neapolitan ice cream — trivial pleasures in an endless panorama.  Fat horny toads blink their stoic welcome.  Small lizards eye us suspiciously and make their challenge with jerky little push-ups before losing their nerve and diving for cover.  Lanky jackrabbits flash across the hills and disappear like omens.  Vampiric winds suck the moisture from our lips.  Dust devils gather.  When it stops, the cedar gnats come.  Bone chips weathering out of a hillside metamorphose into wishful thinking with the changing light.  Black zigzag lines on a pale potsherd is a startling reminder that we were not the first to venture out here.  But we are here now, driven by the hope of finding ancient beasts beyond all imagining.


Colorful layered sediments. Image credit: Curious Sengi.


Native American potsherd discovered while hiking. All archaeological artifacts found in the park are photographed, given GPS coordinates, and reported to park officials. The artifacts themselves are left untouched. Image credit: Curious Sengi.

The desert is a ravishing world that simultaneously destroys and restores.  For those moments of absolute beauty and discovery, we gladly welcome all the associated abuses it renders upon us.  After all, we are far away from the annoyances of home and office.  These are the few precious weeks out of every year we have in order to collect.  Collecting fossils is, of course, always a grand adventure of luck, sharp eyes, and digging holes.  But each expedition is just a beginning, the very first unfolding of multiple layers of discovery.

It starts with your eye catching something a little different, something a bit unusual and curious.  Perhaps it is the color or texture or shape — even just a feeling — that draws you to a piece of bone on the ground surface.  Other times, it is stunningly obvious:  a tooth with glossy enamel shining on the surface of rock pulled out from a quarry.  But for the most part, all you can know is that this is a fossil.


A little spot of homemade shade is a respite from a full day in the sun and wind. Image credit: Curious Sengi.


Life under the tarp.  Fossil preparator Christina Lutz works on undercutting a plaster jacket. Image credit: Curious Sengi.


Big bone weathering out the side of a hill. Image credit: Curious Sengi.


Yale Peabody Museum’s chief fossil preparator, Marilyn Fox, puzzles over the big bone. After brushing away the dirt and layer of bone weathered into dust, some shapes begin to take form.  Even so, the identity of the fossil remains a mystery.  Image credit: Curious Sengi.

Our priority in the field is to bring fossils back safely to the museum.  The care and preservation of specimens begins out there under the sun and blowing dust.  A touch of archival glue might help consolidate fragile pieces together.  Loose specimens are wrapped in packets of toilet paper and aluminum foil.   Larger specimens or bone embedded in the matrix are given a generous buffer of surrounding rock before being encased in hard protective plaster jackets.  Everything is meticulously labelled with field numbers and recorded with good locality data.  Always, good locality data.


Some of the treasures brought back from the expedition. These plaster field jackets cover and stabilize fossils that remain embedded in rock. Collectors mark approximate areas where bone is located in the block. Image credit: Curious Sengi.

These bundles return to the museum, often with very little idea of what the bone is or what kind of animal it belonged to.  That second moment of discovery comes when the fossils are prepared out of the rock, unveiling the extent of their shape and identity.  It takes skill and patience to prepare fossils, so this moment might be delayed by months or even years.  Even then, careful preparation might only reveal that an unidentifiable bone shard is just an unidentifiable bone shard.  Stunning or not, all of these specimens will eventually be accessioned into museum records and properly housed to ensure their long-term preservation.

The next moments of discovery are potentially infinite.  What can we learn from this specimen?  What does it say about anatomy or ecology or geological processes?  This moment could come from an observation waiting to be made tomorrow.  It could also stretch off into the future as generations of researchers find new questions to ask and innovate better ways of extracting information.  The vertebrate paleontology collections at the Yale Peabody Museum have the benefit of a long history — specimens that were discovered over a century ago have not exhausted their scientific value and are now being investigated using novel technologies, such as microCT scanning, that were beyond the wildest dreams of their original collectors.


Some dig sites contained bone encrusted in an unknown material similar to oxidized iron. Preparator Christina Lutz is experimenting with chemical methods to remove this layer. Research in museums also includes discovering better ways to prepare, conserve, and preserve specimens. Image credit: Curious Sengi.


Specimens fresh from the field. Image credit: Curious Sengi.

We have now returned as collectors ourselves.  Even at our desks and computers, we feel a fellowship with all those who experienced the beauty and brutality of the desert in search of fossils.  We also feel a certainty that those long-dead collectors would be as grateful as we are, to know that our contributions will endure in the hands of dedicated museum staff and curious minds yet to arrive.  These specimens will be here, waiting for their many moments of discovery to unfold.

And we also wait here, watching the calendar for the next time we can step out into field.


The joys of camp. Some of the field crew prepare dinner. Members of our expedition came from all backgrounds and experience levels. The team included undergraduate students, volunteers, museum professionals, and academics. Image credit: Curious Sengi.


Until next time. . . . . Image credit: Curious Sengi.

Special thanks to Marilyn Fox and Christina Lutz for their help in preparing this post.


Blood in the Desert: Phrynosoma spp.


Greater Short-Horned Lizard (Phrynosoma hernandesi) spotted in Petrified Forest National Park, Arizona.  Image credit: Curious Sengi.

Unlike your typical desert lizard that skitters away at the slightest movement, the horny toad — or rather, horny lizard — usually just sits there, looking rather overstuffed and grumpy.

It is a charming grumpy, however.

Horny toads (Phrynosoma spp.) are characterized by having flat, squat bodies, a frill of horns on the head, and a stumpy little tail that makes these lizards look more like their amphibian namesakes.  The genus is widely distributed from western Canada down to Guatemala, though the horny toad seems to have particularly captured the imagination of the American Southwest and Texas.


The short, stumpy tail and squat body makes this lizard look rather toad-like.  In fact, the genus name, Phrynosoma, means “toad” or “frog-bodied.”  P. hernandesi.  Image credit: Curious Sengi.


There something eccentric and wonderful about horny toads that have made this reptile a favorite character of the American desert.  Their image has been shaped into representatives of a classic motorcycle brand, household novelty items, team mascot for Texas Christian University, and soft plush toys.  Everyone loves horny toads!  Image credit (clockwise from top left): Thunderpress T-Shirt Shop, Rivers Edge Products, Wikipedia Commons, FluffEngine Etsy shop.

These oddly charismatic lizards can afford to be unhurried in the the face of danger.  Their cryptic coloration allows them to be camouflaged against the desert dirt, rocks, and vegetation.  But if they are discovered and charging would-be attackers with lowered horns and open mouth, or puffing out is not enough of a deterrent, horny toads can unleash a surprising defense:  squirting a stream of blood from their eyes.

Squirting Phrynosoma

Some species of horny toad can eject an impressive directed jet of blood as a defensive measure.  Image credit:  New Scientist via Tag the Bird.

Scientists, naturalists, and inquisitive children had long noted the discharge of red fluid from these lizards.  Oliver Perry Hay (1816 – 1930), an American paleontologist who spent much of his life on fossil turtles, was finally able to confirm that the ejecta was not some glandular secretion but indeed blood.  In his 1892 report:

Near my desk there was a specimen of Phrynosoma coronatum [sic] which had been sent from California by a member of Dr. Merriam’s exploring party.  About the 1st of August it was shedding its outer skin, and the process appeared to be a difficult one, since the skin was dried and adhered closely.  One day it occurred to me that it might facilitate matters if I should give the animal a wetting; so, taking it up, I carried it to a wash-basin of water near by and suddenly tossed the lizard into the water.  The first surprise was probably experienced by the Phrynosoma, but the next surprise was my own, for on one side of the basin there suddenly appeared a number of spots of red fluid, which resembled blood. . . . . I concluded that this was a good time to settle the question whether this fluid was blood or not.  A microscope was soon procured and an examination was made, which immediately showed that the matter ejected was really blood.

The affair now became very interesting.  Just where the blood came from I could not determine with certainty, the whole thing having happened so suddenly and unexpectedly. . . . There appeared to be a considerable quantity of the blood, since on the sides of the vessel and on the wall near it I counted ninety of the little splotches.  A consultation was had with Mr. Stejneger the next day with regard to the propriety of dashing the animal into the water again to discover, if possible, where the blood came from.  It was thought, however, that such blood-lettings must be somewhat exhausting, and that it would be better to allow the animal a day to recuperate.  While talking I picked up the lizard and was holding it between my thumb and middle finger, and stroking its horns with my fore-finger.  All at once a quantity of blood was thrown out against my fingers, and a portion of it ran down the animal’s neck; and this blood came directly out of the right eye.  It was shot backward and appeared to issue from the outer canthus.  It was impossible to determine just how much there was of the blood, but it seemed that there must have been a quarter of a teaspoonful.  I went so far as to taste a small quantity of it, but all that I could detect was a slight musky flavor.

Phrynosoma solare bloody face

The bloody aftermath.  P. solare.  Image caption: John Cancalosi / NPL via BBC.

So blood it is.  But what was the mechanism behind this alarming feat?  Blood-squirting horny toads have a large orbital sinus — a pocket rich with venous blood — in the space between the eyeball and eyesocket, wrapping around to the inner wall of the eyelid.  Observers have noted that when harassed, the eyes of the horny toad took on a puffy, swollen appearance which quickly deflated if the animal was then left alone.  Scientists suspected that a rise in blood pressure was responsible for rupturing the thin walls of the orbital sinus.  An anatomical study by Henry L. Bruner revealed a minute, sphincter-like muscle specialized to pinch off the internal jugular vein (m. constrictor venae jugularis internae).  Though Bruner found this muscle in many of the reptiles he studied and hypothesized that it generated a “swell mechanism” associated with skin shedding, this anatomical feature could have been co-opted in horny toads to increase cranial blood pressure enough to squirt a stream of blood at least 3 ft away (0.9 m; reports of ejections 6 ft away have also been reported but not substantiated).


The horny toad’s preferred line of defense is blending in.  P. hernandesi hanging out at the margin of dried grasses and low scrub in Petrified Forest National Park, Arizona.  Image credit: Curious Sengi.

Hay’s well-intentioned effort to help the horny toad on his desk shed its skin by plopping it into a basin of water might be a clue into what motivates it to squirt blood.  Squirting does not seem to be a response to all threatening situations.  Some have noted the prevalence of this behavior during the perilous molting season.  But most curious of all, horny toads preferentially squirt when harassed by canines.

Even though horny toad predators include roadrunners (Geococcyx spp.) and grasshopper mice (Onychomys spp.), these encounters elicit opening of the mouth, head-down charging, and puffing up, but rarely (if at all) result in a squirt of blood.  Instead, this context-dependent defense was reserved for canid predators such as coyotes (Canis latrans), kit foxes (Vulpes macrotis), and even dogs (C. familiaris).  In order the understand this specificity, Middendorf and Sherbrooke (1992) staged a series of predator-prey encounters between horny toads that included supervised interactions with a “2-3 year-old female, yellow Labrador retriever” named Dusty.  After “. . . .attacks [involving] barking, pawing, gentle biting, nibbling, and picking up and tossing of the lizard” all 10 out of 10 lizards squirted blood.  On the other hand, humans mimicking dogs with “. . . .one of us on all fours, barked at, approached, chased, and physically manipulated the lizard (WCS touched, stroked, tapped, picked up, and tossed but did not bite)” only resulted in 20% responding.  Middendorf and Sherbrooke concluded that while tactile cues were important in inducing blood squirting, they have yet to pinpoint what is actually triggering this behavior.

Phrynosoma skulls

There are over a dozen recognized species of horny toad distributed all throughout western North and Central America.  The horns are bony outgrowths of the parietal and squamosal bones of the skull.  Another defensive tactic is for the lizard to charge at attackers, head down and horns at the ready.  Note that skulls are not to scale.  Image credit: Digimorph.

Taking a slightly different tack from using pets and researchers simulating dog attacks, Sherbrooke and Mason (2005) focused on the effect of blood squirting on potential canine predators.  It seemed remarkable that the blood ejected from the eyes was not a frantic spray, but a directed jet that targeted the eyes, nose, and mouth.  Hay’s 1892 account of tasting the blood only led him to comment on its “musky” taste, though he did quote a man who experienced eye irritation.  Another study found no difference in blood chemistry between ejected blood and blood circulating in the body.  However, compared to other lizards, horny toads did possess an unnamed compound in the blood related to the animal’s ability to detoxify venom from their preferred food, seed harvester ants (Pogonomyrmex maricopa).

Sherbrooke and Mason used captive coyotes to test which sensory system was targeted by horny toad blood.  Feeding coyotes whole lizard carcasses resulted in regurgitation.  One particular coyote was determined to keep down its meal:  “. . . . the coyote regurgitated (<1 min) a food bolus containing the remains of the lizard.  Then the coyote went through 3 series of reingestion-regurgitation episodes with the same bolus.”  It is not known if this pattern of repeated ingestion is normal, but both coyotes and foxes have been found the horny toad remains in their stomachs.  The researchers then used five test fluids (saline control, blood plasma and whole blood from horny toad, blood plasma and whole blood of a Sceloporus lizard) and squirted them into the eyes, nose, and mouth of their perhaps not-wholly-willing test subjects.  The most pronounced response was from the introduction of horny toad blood into the nose and mouth — the coyotes opened and closed their mouths and shook their heads in what appeared to be efforts to get rid of the distasteful substance.  So even though horny toads certainly fall prey to canine hunters, the targeted blood squirting defense might provide enough of a distraction to potential predators for the horny toad to scurry away and blend back into the dirt and vegetation.

Phrynsoma phylogeny

Phylogenetic tree reconstructed for the genus Phrynosoma based on mitochondrial and nuclear DNA.  Note the black bars crossing the branches.  ABS (antipredator blood squirting is present at the very base of the tree, suggesting that this ability is ancestral to all horny toads.  This phylogeny hypothesizes four independent losses of blood squirting (marked as “ABS loss”).  Image credit: Leache & McGuire 2006.

Despite the iconic image of blood streaming from the eye of the horny toad, not all members of this genus squirt.  A molecular-based phylogeny indicate loss of blood-squirting in at least four groups of horny toad species that are not directly related to each other.  It is not clear if these animals simply do not exhibit the behavior, or if they have lost some key anatomical feature necessary for the process.  The study’s authors readily admit that reconstructing the horny toad family tree is challenging and it is unclear how many times blood squirting ability was lost.  But we can conclude from their results that blood squirting is part of the essence of horny-toadness and appears at the base of the Phrynosoma tree as the ancestral state.


This sweet little P. hernandesi is just chilling.  No need for blood squirting here.  Image credit:  Curious Sengi.


Bruner, Henry L.  1907.  “On the cephalic veins and sinuses of reptiles, with description of a mechanism for raising the venous blood-pressure in the head.”  American Journal of Anatomy 7 (1):  1 – 117.

Burleson, Gretchen Lyon.  1942.  “The Source of the Blood Ejected from the Eye by Horned Toads.”  Copeia 1942 (4):  246 – 248.

Hay, Oliver P.  1892.  “On the Ejection of Blood from the Eyes of Horned Toads.”  Proceedings of the United States National Museum 15 (907):  375 – 378.

Leaché, Adam D. & Jimmy A. McGuire.  2006.  “Phylogenetic relationships of horned lizards (Phrynosoma) based on nuclear and mitochondrial data:  Evidence for a misleading mitochondrial gene tree.”  Molecular Phylogenetics & Evolution 39 (3):  628 – 644.

Middendorf III, George A. & Wade C. Sherbrooke.  1992.  “Canid Elicitation of Blood-Squirting in a Horned Lizard (Phrynosoma cornutum).”  Copeia 1992 (2):  519 – 527.

Middendorf III, George A, Wade C. Sherbrooke, & Eldon J. Braun.  2001.  “Comparison of Blood Squirted from the Circumorbital Sinus and Systemic Blood in a Horned Lizard, Phrynosoma cornutum.”  The Southwestern Naturalist 46 (3):  384 – 387.

Sherbrooke, Wade C. & J. Russell Mason.  2005.  “Sensory Modality Used by Coyotes in Responding to Antipredatory Compounds in the Blood of Texas Horned Lizards.”  The Southwestern Naturalist 50 (2):  216 – 222.

Winton. W.M.  1916.  “Habits and Behavior of the Texas Horned Lizard, Phrynosoma cornutum, Harlan.”  Copeia 36:  81 – 84.

Hidden Beauty: Crotalus viridis


Western, or Prairie, Rattlesnake (Crotalus viridis) coiled up in a footprint we left earlier in the day.  Image credit: Curious Sengi.



This particular individual was a youngster, about 1 ft (approx. 30.5 cm) long. Adults typically grow to around 3 ft (approx. 91.5 cm).  C. viridis is one of the most common rattlesnakes of the American Southwest. Image credit: Curious Sengi.



Like most venomous snakes, rattlers rarely bite without extreme provocation. This little fellow clearly had enough of the photography and decided to head into the brush, rattling its tail with no particular urgency and no particular agenda except to maintain good form. Image credit: Curious Sengi.