The fish was in an odd place.
It was the fossil of a sabertooth salmon: a fanged, fearsome-looking creature that lived in the waning days of the dinosaurs.
But it was buried in the greenish New Jersey sediment known as glauconite - in a layer of earth thought to date from after the dinos' demise.
A Drexel University undergraduate named (no joke) Jesse Salmons made the curious, 65-million-year-old discovery April 30, in an old Gloucester County mine pit.
A few weeks later, along with a paleontologist from the New Jersey State Museum, some of his fellow students returned to tackle the aquatic puzzle: Just when did Enchodus ferox patrol the ocean?
The answer was a surprise.
The fish is one of at least six fossilized beasts unearthed recently by the students of Drexel's Ken Lacovara, an associate professor of biosciences. Also in the mix are bits of two sharks and three crocodiles, which will one day be housed in the newly renovated state museum.
A typical day's haul is a few shark teeth, or perhaps a bit of crocodile armor; the new batch of bones is one of the group's best in years. It will help scientists flesh out the picture of an age when the world was in flux.
New Jersey was a hot, swampy place back then, and much of it was underwater. The atmosphere was dense with heat-trapping greenhouse gases - far more so than today, although Lacovara says the era provides a valuable illustration of where the world might be headed:
"I like to quote something that Winston Churchill once said: 'The farther backward you can look, the farther forward you can see.' "
The mine pit is owned by Inversand Co., which asked that the exact location not be disclosed, to prevent passersby from climbing its steep, shifting hillsides. But the company welcomes the academic fossil-hunters.
It's a muddy but ideal place to dig for bones, as the miners' heavy equipment has exposed a veritable rainbow of New Jersey prehistory:
At the pit's bottom is the chocolate-brown Navesink formation, deposited more than 65 million years ago during the Cretaceous period. Then comes the Hornerstown layer of glauconite - sometimes called marl, as in nearby Marlton. After that the olive-drab Vincentown layer and the yellow-hued Kirkwood. On top, deposited within the last two million years, is the gravelly Pennsauken layer.
Salmons found his fish fossil - two pieces of jaw with intact smaller teeth and two longer fangs - in glauconite.
Scientists believe this dark-green sediment was deposited in the years after a meteor slammed into Earth, leading to a mass extinction. Yet all quality specimens of Enchodus - sometimes called a sabertooth herring instead of salmon, as it may be an ancestor of one or the other - had previously been dated to the Cretaceous.
This meant one of four things:
1. The species was around for a greater chunk of prehistory than previously thought - outlasting the dinosaurs.
2. This fish fossil really was from the Cretaceous, but ocean currents and other natural forces churned up the sediment after it died, so the bits of bone eventually came to rest in a higher, more recent layer of earth. (Team members discounted this option, though, as there were multiple intact bones from one animal in the same place.)
3. In this muddy New Jersey pit, perhaps the Cretaceous actually did not begin until after the sediment changed from brown to green.
4. The fish wasn't a sabertooth salmon after all.
Answering this question meant getting really dirty.
Jason Schein, a Drexel doctoral student and an assistant curator at the state museum in Trenton, helped dig out the fish on May 7. He was up almost to his waist in brown water.
Others stuck to drier ground, but got equally filthy. Glauconite feels like a mix of sand and clay - though in a strict geological sense, it is neither - and it readily adheres to boots and clothes.
Using a shovel and smaller tools, doctoral students Victoria Egerton and Jessica Battisto worked to expose one of the crocodiles and a shark.
The diggers left an earthen boundary around each specimen so as not to expose too much of the brownish, petrified bones. They then "jacketed" the mud-covered fossils with plaster-soaked strips of burlap, so that each could be safely lifted out for the trip to Philadelphia.
Professor Lacovara oversaw it all, darting from fossil to fossil to offer his students advice. He travels the world to dig up old bones - Egypt, Argentina, China - and knows how to say burlap and plaster in four languages.
But with an infant son at home, he likes digging less than a half-hour from his Drexel office. And Salmons, the undergrad who found the fish, likes the hands-on "classroom."
"It got me hooked really quick," he says.
The team took the plaster-coated fossils to the Academy of Natural Sciences. Fossil preparators began the painstaking work of clearing the remaining sediment from the bones, under the direction of lab manager Jason Poole.
As each fossil started to emerge, they dabbed on a chemical to harden the bone. Schein, who did his master's thesis on Enchodus, was sure that the new fish belonged to that species.
But why was it buried in glauconite?
So the Drexel students went back to the pit 12 days ago with Bill Gallagher, assistant curator at the state museum - an old hand at gauging the sediment of the Garden State. He has been trolling for fossils in glauconite pits since he was in junior high, in the 1960s.
Gallagher brought a Nikon hand level - a telescope with an air bubble that reveals when the device is being held precisely horizontal.
His goal was to see whether the fish had been found at the same depth as a fossil-rich layer they had discovered previously on the other side of the pit, more than 150 feet away.
That layer was known to be from the early Tertiary period - the beginning of the age of mammals. So if the fish was at the same depth, it belonged to the same moment in time.
But there was an obstacle in Gallagher's line of sight: a big ridge of mud that had been deposited by the miners' earth-moving equipment. So he had to break up the surveying into two parts, and later subtract the height of the ridge that was in his way.
When Gallagher finally aimed his scope at the opposite side of the pit, doctoral candidate Chris Coughenour clambered up the wall.
"Get back on the face," Gallagher called out across the void. "Yeah, that's it. Higher! Higher!"
Coughenour placed an orange flag in the dirt. Gallagher and Lacovara soon joined him, and the trio took turns digging down to the fossil-rich layer. Would it be at the same depth as where Salmons found his fanged fish?
After some vigorous digging, Gallagher's shovel struck something hard. It was a prehistoric clam. The beginning of the layer that contained fossils.
Lacovara pulled out his tape measure and determined that the clam was at just about the same depth as the fish and the other new fossils far across the pit.
The early Tertiary period. The species, it seemed, had outlasted the dinosaurs.
"This might be the first time that we can definitively identify Enchodus as a survivor of sorts," Gallagher says.
Drexel's Lacovara was cautious.
"I'd like to find a few more of them" before making any definitive judgment.
So he and Gallagher and the students will be back again, year after year, as long as the mine owners will have them.
"Science is a process of small, incremental steps," Gallagher says, "that we hope get closer and closer to the truth."