Archeological Finds at Meadowcroft Rock Shelter Turned Back the Clock on Humankind’s First Migration to the New World.

Miller Projectile Point

Unearthed from a woodchuck hole inside Meadowcroft Rock Shelter in 1972 the twelve-thousand year-old Miller Projectile Point was named for the site’s discoverer, a gentleman farmer named Albert Miller. Photo credit: David Scofield

By Tom Imerito

Twelve thousand years ago a Native American hunter left a flint spear point at a campsite beneath a rock overhang along the banks of Cross Creek, a tributary of the Ohio River some 29 miles southwest of Pittsburgh. The three-inch by one-inch point was a re-sharpened remnant of a larger point that had been hand crafted by striking a piece of flint with another stone, a process called flint-knapping. In all likelihood, the point had been crafted by the hunter himself and would have been bound to a spear or arrow shaft with animal sinew or vegetable cordage. But the wear and tear of the hunt had necessitated re-sharpening the point to a shorter length, probably more than once. In its current diminutive state, the point was close to the end of its useful life. It may have been left in the carcass of the animal that served as that evening’s stone-age supper. It may have been misplaced. Perhaps it was discarded. Nobody knows for sure. Surely, nobody cared for 12,000 years. Eventually, however, it would push back the date of the first human migration to the New World by thousands of years.

Remembering Rural Life

In the interim, the rock overhang under which our prehistoric friend slept that evening continued to serve as a refuge from the elements for all who passed through the Cross Creek watershed, whether hunting, trapping, trading, fighting, prospecting or simply traversing the interior of the continent. In recent times, the site came to be known as Meadowcroft Rock Shelter. Located in Avella, PA, less than an hour from Pittsburgh, the rock shelter is part of The Historical Society of Western Pennsylvania’s Meadowcroft Village, a collection of architectural and cultural artifacts representative of human life in North America through the ages. The village is home to a one-room schoolhouse from the 1840s, a fully functional blacksmith shop, a covered bridge, a nineteenth century wooden church, a museum of rural life, and a sixteenth century Indian village, complete with a palisade enclosure, wigwams, a sustainable garden and an atlatl throwing range. Originally, the Meadowcroft property was owned by two brothers, Albert and Delvin Miller whose family had farmed the property since the late 1700s. The pair held an abiding reverence for the preservation of rural American culture. Prior to Meadowcroft’s ascendancy to a position of archeological importance, they began to relocate and reassemble a collection of nineteenth-century buildings on the plateau above the Shelter. In 1993, the village merged with the Historical Society of Western Pennsylvania. Today the Miller brothers’ collection constitutes much of Meadowcroft Village.

Interior if Meadowcroft Rock Shelter

Visitors view the original Meadowcroft excavation from a platform inside the new structure. Photo credit: Ed Massery


Best Practices in Archeology

But the charm of the village serves as an adornment to Meadowcroft’s main attraction, the Rock Shelter, which serves as a showcase for some of archeology’s most important discoveries in North America as well as a demonstration project for the best excavation and documentation practices in the world. No longer a mere refuge from the elements, no longer an archeological dig covered with plywood, two-by-fours and tar paper, today the shelter is protected by an exquisitely designed steel and wooden structure fitted sensitively and elegantly around the excavation. A wooden and steel stairway comprised of sixty- five low-rise steps ascends from the parking lot alongside Cross Creek, up the hillside to a wooden observation deck. There visitors stand out of the weather to view the excavation, the locations of ancient fire pits, mollusk shells, animal bones, the original steel survey stakes laying out the site’s grid, and innumerable white, button-like tags on the excavation’s vertical profiles marking precise coordinates within 11 distinct strata. A plank roof atop steel beams anchored in the Rock Shelter’s 28-foot limestone rear wall as tour guides explain the dig’s features in concert with automated ceiling lights that shine upon the exhibit of the moment. Completed in 2008, the $2 million structure was designed by Pfaffman and Associates and constructed by F.J. Busse Company, Inc., both of Pittsburgh.

Geology of the Shelter

Put simply, the Rock Shelter itself can be described as a hillside terrace beneath a large rock overhang about 30 feet above. The shelter’s openness combined with its orientation to the prevailing winds would have made it comfortable for humans by discouraging insects and dispersing campfire smoke. As with virtually all such geologic features, over time large pieces of the overhang broke off from time to time. Some tumbled into Cross Creek, others crashed into the floor of the shelter, making the roof smaller and reducing the size of the protected area. At least three calamitous roof falls have been identified by radio carbon dating of massive slabs of rock in and around the shelter. One massive 23,000 year-old slab rests in the bed of Cross Creek. Inside the shelter, a 12,000 year old piece, known as the Old Roof Fall measures roughly ten by eighteen feet across and ten feet deep. Another, known as the New Roof fall, occurred between 300 and 600 AD. Extending through the roof of the new site enclosure, the fifteen foot thick stone is partially buried in the earthen floor which still shows signs of deformation at the point of impact.

The shelter was formed millions of years ago, when Cross Creek flowed about forty-five feet higher than today. Over thousands of years the creek scoured a vein of soft sandstone away from its bank, leaving behind a harder layer of rock above which became the shelter’s roof. Fortuitously for the million-plus Meadowcroft artifacts, each day the roof rock sheds an infinitesimal quantity of rock dust from its surface. Through the shelter’s history, this continual “rain” of rock dust served to very gradually blanket anything left behind – seeds, husks, shells, fibers, bones, stone tools… and our prehistoric friend’s forgotten spear point. Thanks to the roof dust, the Meadowcroft artifacts remained safe and sound year after year, century after century, millennium after millennium.

It Started in a Woodchuck Hole

Then, on November 12, 1955, one of Meadowcroft’s owners, Albert Miller, who was both a gentleman farmer and an amateur archeologist, noticed several charred bone fragments at the mouth of a woodchuck hole near the rear wall of the shelter. His interest piqued, Miller excavated the hole to a depth of thirty inches where he found a stone knife. Recognizing the significance of his find and wary of looters, he kept his discovery to himself and began a search for a qualified archeologist. His search went on until 1972 when Professor James Adovasio came to the University of Pittsburgh to establish an archeological field school. Meadowcroft proved to be ideal. Albert Miller’s seventeen-year search for a professional archeologist to excavate the Meadowcroft Rock Shelter in a manner commensurate with its promise was over.

Meadowcroft Rockshelter Before Excavation

Meadowcroft Rockshelter before archeological excavation which began in the early 1970s.

Archeology Field School

Beginning in 1972, scores of students and researchers from around the world began coming to Meadowcroft each summer to teach, learn and undergo field training in Adovasio’s rigorous excavation and documentation techniques. As the diggers dug their way through what would become a sixteen-foot-deep excavation, they came upon retrospective evidence of thousands of years of human habitation. In the topmost strata metal beer cans and hypodermic syringes mixed among campfire ashes evinced the activities of modern day revelers. Deeper layers bore primitive cutting tools knapped by Native Americans from the glass shards of Revolutionary War gin bottles followed by thousands of charred small animal bones, nut shells, seed husks and the waste remnants of stone tool manufacture.

The First Major Find

Then in July of 1974, the long-forgotten spear point left or lost by our Stone Age hunter emerged from its ancient resting place. On one sunny morning, a Temple University archeology undergraduate named Joe Yedlowski, working in the deepest section of the dig, uncovered what appeared to be yet another one of many pieces of flake debitage, the waste material chipped from larger pieces of stone during the shaping of implements. Over the course of the morning, as Joe gingerly removed more soil, first with a six-inch mason’s trowel, then with a single-edged razor blade, and finally with a paintbrush, it became clear that the sides of the artifact were symmetrically curved to form a point and chipped to a sharp edge on both sides to form what archeologists call a bifaced projectile point, but most people would call an arrowhead.


As the point’s significance became more apparent, the dig began to buzz in anticipation of a momentous find. “By the time it was exposed we realized it was like nothing anybody had ever seen before,” Dr. Adovasio said. By late in the day, after several hours of mapping, documenting and photographing the point in its ancient state of repose, Joe gingerly lifted it from its resting place with his bare hands and handed it over to Adovasio, who after finding a place for its safe keeping, phoned the local watering hole to assess its preparedness for a celebration of momentous proportions. By all accounts, the bar was adequately provisioned, ten kegs of beer were consumed by the hundred-odd members of the digging crew, and the celebration was one not to be forgotten.


But elation soon gave way to controversy. The “Miller Lanceolate Projectile Point,” as the 1974 discovery came to be called in honor of the site’s discoverer, was but the first in a series of finds that would become a proverbial shot heard round the world of archeology. Although radio carbon dates indicated that the strata in which the Miller projectile point was found fell within the conventionally accepted timeframe of human habitation of the New World, subsequent finds at deeper levels pushed the date back by at least three thousand years, and possibly as many as six thousand. The oldest stone implement, a knife blade, was found in a layer that dated back 16,000 years. Even older was a 19,000 year-old piece of charred bark. The evidence suggested it was not a permanent settlement, but a transient campsite. Nonetheless, almost overnight Meadowcroft became the earliest known site of human habitation in the New World.

Not unlike many breakthrough discoveries in which new knowledge contradicts conventional wisdom, the finds precipitated a storm of disciplinary skirmishes within the archeology community that came to be known as The Clovis Wars. Prior to the Meadowcroft discoveries, the accepted date of the first human migration to North America had been set at 13,000 years ago by the discovery of a projectile point near the town of Clovis, New Mexico in 1936. The discovery of 16,000 year-old artifacts at Meadowcroft bumped the Clovis date out of first place on the Migration-to-the-Americas timeline and threw the field of archeology into a disciplinary tizzy.

The Clovis Wars were waged between two sets of professional archeologists: On one side were those whose minds were sufficiently open to allow new evidence to change their position about the date of human habitation of the New World; On the other, the Clovis Firsters had invested their careers in the Clovis date and were disinclined to change their view of when humans first came to the Americas. Some never changed their minds, despite increasing evidence of Meadowcroft’s validity.

“We weren’t looking for anything this different,” Adovasio said. “The Miller projectile point was the inadvertent lightening rod for all the flack about the site that emerged ever since. I underestimated the tenacity of people in terms of their retention of contrarian ideas. I didn’t think it would take a generation for them to alter their mindset.”

Meadowcroft Rock Shelter Visitor Center Today

Today, thousands visit the excavation at Meadowcroft Rockshelter under the protection of a new $2 million visitor center. The center gives visitors an unobstructed view of the original dig at the same time it protects the site from foot traffic that might impede future excavations.

The Clovis Firsters had two basic arguments against Meadowcroft’s antiquity: First, they claimed the two-mile thick Laurentian ice sheet, which extended as far south as Moraine State Park, less than an hour’s drive from Pittsburgh, would have made human habitation at Meadowcroft impossible sixteen thousand years ago and; Second, that the carbon samples must have been contaminated, which would have made the radio carbon dates wrong. However, the sheer wealth of Meadowcroft finds, which includes 20,000 human-made artifacts, 95,000 animal remains, and 1,400,000 plant remains, in combination with the exquisitely precise excavation and documentation techniques for which Adovasio has become renowned, gives the site uncommon status in the field of archeology. Additionally, 52 radio carbon dates, ranging from 30,000 years ago to the time of the Revolutionary War all correlate technically and chronologically with artifacts found at other sites. What is more, since the time of the initial Meadowcroft finds, numerous other discoveries of pre-Clovis habitation throughout the North and South America have corroborated the site’s age.


World renowned author and expert on the habitation of the New World, Dr. Brian Fagan, said, “Meadowcroft is the single most complex archaeological excavation I have ever seen. It’s a classic example of the very best in stratigraphic observation and meticulous recording in the field. The superb excavation methods give one great confidence in the important evidence for the first Americans found in the bottom layers of the site.”

In 1990, Adovasio accepted an offer from Mercyhurst College in Erie to establish a world class archeology program at the school. With the University of Pittsburgh’s blessing, he relocated the Meadowcroft collection and much of its staff to Mercyhurst where he began in earnest to build the new program. Today, he serves as Mercyhurst’s provost, dean of science and mathematics, and director of the Mercyhurst Archeological Institute. Active in archeological digs around the world, Adovasio travels to Meadowcroft several times a year to lecture visitors on the site’s history and its impact on the field of archeology.

Still associated with Adovasio today, Joe Yedlowski, who uncovered the Miller Projectile Point, directs Mercyhurst’s Summer Field Training Program in Prehistoric Archaeology.

Meadowcroft Village is open Wednesday through Sunday afternoons from Memorial Day to Labor Day; weekend afternoons in May, September and October; closed during the winter months. For details go to or call (724) 587-3412


Tom Imerito is president of Science Communications, a Pittsburgh technology communications consultancy. He can be reached at 412-892-9640 or To learn more about Science Communications, please visit

This article first ran in Pittsburgh Quarterly Magazine. You can read it here:

Researchers Quantify Tissue Networks at McGowan Institute.

Dr. William Wagner (left), director of the McGowan Institute for Regenerative Medicine, reviews scanning electron microscope images of synthetic tissue scaffolds with researcher Antonio D’Amore.

By Tom Imerito

At their weekly meeting, Doctors William Wagner and Antonio D’Amore are reviewing progress on D’Amore’s efforts to transform images of biological tissue into mathematical data.

D’Amore’s work will be instrumental in engineering synthetic materials for implantation in patients suffering from tissue and organ insufficiencies.   For Wagner, who was named director of the McGowan Institute for Regenerative Medicine earlier this year, meeting with D’Amore is just one of a multitude of administrative tasks associated with managing the Institute as well as serving as lead investigator for his own group of a dozen-or-so researchers.

D’Amore shows his boss a skeleton-like map of a tissue fiber network detailing each fiber segment’s size, shape, position, angle, intersections, and overlaps along with their corresponding mathematical values.  He has produced the map by running a scanning electron microscope image through software filters he has developed.  The process is not only more accurate than human measurement – at three minutes per image it is forty times faster than the two hours of manpower it took previously.

D’Amore’s innovation comes at a perfect time.  Recently the focus of tissue engineering has shifted toward smaller components of the tissue generation mechanism, including D’Amore’s area of interest – the mechanical properties of the non-cellular collagen scaffolds, called extracellular matrices – into which cells implant themselves and multiply to form organs.

A native of Palermo, Italy, with a PhD in biomechanics and tissue engineering, D’Amore is also a fellow of The Ri.MED Foundation, an international partnership between the Italian Government, the Region of Sicily, the University of Pittsburgh, and UPMC.  He gravitated to McGowan as a result of its renown as a Mecca for regenerative medicine.  Similarly, twenty years earlier Wagner had gravitated to Pittsburgh for precisely the same reason.  UPMC and its academic partner, the University of Pittsburgh, had, and still has, all the essential ingredients for the continuously emerging field – transplant surgeons, medical specialists, research scientists, and engineers of every ilk – all of which attract an abundance of patients.  The only missing ingredient was, and continues to be, a sufficient supply of donor organs, which serves as the driving force behind McGowan’s three-pillar, patient-centric approach to the problem of replacing failed tissues and organs.

The first of the pillars is made up of intermediary assistive devices, such as heart pumps and artificial lungs, which are designed to keep patients alive while they wait for donor organs.  Next, the field of tissue engineering – D’Amore’s area of expertise – attempts to remedy tissue and organ deficiencies with both natural and synthetic substitutes.  Finally, stem cell therapy has emerged as a viable option due to the discovery of ways to coax adult stem cells to differentiate into a variety of organ cells.  But, rather than looking for ideal solutions for any one of these areas at some point in the future, McGowan mixes and matches all of them to improve the lives of individual patients today.

Click to expand

Scanning electron microscope images of biological extracellular matrix tissue scaffolds and synthetic electrospun polyester urethane urea tissue scaffolds.
Top: Fiber network and diameters detected by the algorithm, A) isotropic elastomeric scaffold, B) anisotropic elastomeric scaffold. Fiber network and diameters manually detected, C) isotropic elastomeric scaffold, D) anisotropic elastomeric scaffold.
Bottom: Detected fiber networks for A) isotropic elastomeric scaffold, B) anisotropic elastomeric scaffold, C) Rabbit MSC seeded collagen gel, D) Decellularized rat carotid arteries. (Click image for full size)

This eclectic, solution-focused approach is exemplified in an epiphany D’Amore had when he first arrived in Pittsburgh last year.   An astute amateur photographer, D’Amore was photographing a tree next to Pitt’s Cathedral of Learning when an unexpected connection between the structure of the tree and that of the fiber networks he was studying at work occurred to him.  While observing the tree’s branches against the sky, D’Amore realized that he was mentally defining the tree’s geometry by successively identifying the boundaries, intersections, sizes and directions of its branches.  It struck him that, using the same method his brain naturally used to define the tree, he could write a computer program to mathematically map tissue fiber networks much faster than any human could.  It wasn’t long before D’Amore’s work was published in the field’s leading journal, Biomaterials.

In an amazing feat of mathematical gymnastics, D’Amore extracts digital values from analog microscope images of biological tissue and converts them into computer control input values for a synthetic tissue scaffold fabrication system.  The fabrication process entails precisely depositing electrically atomized strands of a synthetic plastic called polyester urethane urea on a spinning cylinder at varying angles and directions to simulate the forms and performance characteristics of living tissue networks.  The resulting ES-PEUU scaffold (electrospun polyester urethane urea) can be seeded with stem cells during manufacture, ready for implantation and growth in a biological system.  Once inside a body the stem cells divide and populate the scaffold to produce new functioning organ tissue.  When the cells fully populate the scaffold, the synthetic material is absorbed by the body and eliminated.

Although the process is promising, it is still in the laboratory.  And although D’Amore’s innovation represents progress, the field of tissue engineering is still fraught with many more questions than answers.  But in the quest to improve human lives, nobody is looking more intently for solutions than Drs. Wagner, D’Amore and their colleagues at the McGowan Institute for Regenerative Medicine.


Tom Imerito is president of Science Communications, a Pittsburgh technology public relations consultancy.  He can be reached at 412-892-9640 or  To learn more about Science Communications, please visit

An abridged version of this article first ran in TEQ magazine. You can read it here: