Agomphus tardus

Cretaceous Turtle from Inversand

April 9, 2011

The following background information on Inversand is from an unpublished document from the New Jersey State Museum;
"The greensand “marl” mines of central New Jersey have been economically important for well over 150 years, but their significance to the geological and paleontological sciences over the same period cannot be underestimated. In terms of quality, quantity, and continuous productivity of vertebrate fossil remains of both known and new species these sediments have few, if any, equals. Fossils are common throughout most of the sediments exposed at the Inversand Mine. However, the greatest accumulation of vertebrate remains is concentrated in a thin (~20 cm) layer at the contact between the latest Cretaceous Navesink Formation and the overlying earliest Paleocene Hornerstown Formation. This bone bed is commonly referred to as the “Main Fossiliferous Layer”, or the MFL, and is renowned for both the abundance and quality of preservation of the remains it contains"
The turtle was found in the MFL and was identified in the field as Agomphus tardus by Dave Parris, curator of the New Jersey State Museum. A. tardus is thought to be a land turtle and considered a rare find. After piecing the fragments back together I contacted Dave who was excited about the find. While this turtle is far from complete, almost all the pieces I found are missing from the museums existing specimen.

Authors note: While turtle fragments are probably the most common bone found in New Jersey these are normally just isolated bits and pieces. Finds such as this one are considered very uncommon and should be reported to the New Jersey State Museum.

The "Badlands" of New Jersey.
The Inversand marl pit.

Agomphus tardus pieced back together.
The specimen consisted of 7 costals (side), 1 peripheral (edge) and a significant
portion of the plastron (bottom)
I estimate that this little critter was about 1 foot long.
This specimen was donated to the New Jersey State Museum.

The plastron or bottom of the turtle.
This is in excellent condition and should prove useful in the additional
research planned for this species.

Two views of the same complete costal.
There is a distinctive "ridge" that runs along the top.
Other characteristics include a weak rib structure and an "erosion" like ornamentation on the shell.

New Jersey fossil turtles seem to explode of their own accord.
Even when found in situ they tend to be fragile.
Prepping consisted of simply rinsing off the fragments and piecing them back
together. The heavy shell of this species made the task of reassembly easier
than normal.

The first piece that came out had a fresh break which was my clue to stop
digging and feel around for more. The rest was removed by hand.

Left - from left to right Robert Badger and Dave Parris from the New Jersey State Museum
Right - This photo of me was taken right after the hole collapsed

With any donation comes the paperwork.
Rod Pellegrini, registrar for the museum made sure all was in order
and we had the opportunity to chat for awhile.