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FOSSIL TRACKS OF THE CONNECTICUT VALLEY
Although
dinosaur footprints are the most abundant and well-known fossil tracks in the Connecticut
Valley, they are not the only traces of ancient life in southern New England.
Insects, fish, and other small animals of the Mesozoic also left their own
marks preserved in stone. There are dozens of different trace fossil species
from tiny animals throughout the Valley, a few of which are detailed below.
Bifurculapes
These
early Jurassic tracks consist of double rows of two scratch-like marks
(“furcula” means “forked”, and Bifurculapes trackway looks as if they were made
by the tips of two Y-shaped legs dragging through the mud). The tracks are
often found in association with ripple marks, suggesting that they were made by
aquatic insects crawling across the floor of a shallow playa lake. Several specimens
zig-zag, implying that the animals were being pushed off-course by a current
and repeatedly correcting their path. It’s not currently known what type of organisms made these traces, though the forked shaped of the tracks suggests at least some may have been made by crustaceans, which have biramous appendages.
Undichna
These
sinuous grooves were made by the tails and lower fins of fish as they swam near
the bottoms of shallow temporary pools. Specimens of Undichna are extremely
rare in the Connecticut Valley, although fossils of the primitive fishes that
made them- Semionotus or Redfieldius- are quite common. These shallow lakes
would have been prime fishing spots for the large theropod dinosaurs and
crocodilians that inhabited the Valley.
Batrachoides
In the 1850s geologist Edward Hitchcock discovered a curious fossil impression in Triassic sandstone near Hadley, Massachusetts. The rock slab was covered in what he described as “spheroidal cavities”. To a modern viewer, this unusual trace might look as if someone had pressed a large sheet of bubble wrap into the soft mud. Hitchcock interpreted this fossil as a collection of “tadpole nests”.
(I admit my illustration above came out a little weird for this one. Below are photos of the original fossils in the Edward Hitchcock Ichnological Cabinet at the Beneski Museum of Natural History.)
But what are tadpole nests, exactly? If you come across a temporary vernal pool in late spring, you’ll often find it swarming with hundreds of little black tadpoles clustered along the shallow edge. As the water slowly dries up, they excavate dimples or “nests” in the sediment by wiggling their tails and slowly rotating in circles, either to feed on the bottom or to escape the desiccating air. As the shore of the pool shrinks, the tadpoles move with it, continuously digging new nests until the bottom of the pool is covered in a shallow circular or hexagonal depressions.
There is some controversy about what made the Batrachoides impression. Some scientists have pointed out that similar patterns can be created by intersecting ripples. But the possibility that this unusual pattern was created by frog young is intriguing.
Currently known from a single specimen found at a private fossil site near Holyoke, Massachusetts. this unusual fossil is an almost complete body impression- including legs, abdomen, and head- made by a resting chelicerate, an animal from the group of Arthropods that includes spiders, scorpions, mites, ticks, and vinegaroons. Such creatures are distinguished by their mouthparts, called chelicerae, that move up and down rather than horizontally as insect mandibles do.
The outline of Cheliceratichnus, including the impressions of its two massive chelicerae, suggests that it was created by an organism closely related to the modern solifuges or sun spiders.
Cheliceratichnus was discovered at the end of a fossil trackway known as Acanthichnus cursorius, which shows feet impressions as well as drag marks from the tips of the creature’s heavy mouthparts. The sun spider created these tracks by walking backwards, a behavior found in many modern chelicerates.
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