Hatcherichnus

Hatcherichnus is a name for a type of fossil footprint, or ichnogenus. It is not the name of a crocodile species discovered from a skeleton. The original tracks came from the Late Jurassic Morrison Formation of Utah; later examples from Asturias, Spain, broadened the record to another coastal landscape. The trace fossil is listed in the ancient crocodylomorph catalogue because its makers are interpreted as crocodylomorph-like.

Footprints preserve contact between an animal and soft ground. Their shape can reveal which digits touched the sediment and how successive steps were placed, but the maker's precise identity is harder to infer. In the case of Hatcherichnus, a crocodile relative is plausible while a genus-level attribution remains unproven.

Quick facts

A footprint name, not a body-fossil genus

Trace fossils are named independently from the bodies that produced them. A trackway can be diagnosed and compared even when the animal that made it left no bones nearby. Lockley and Foster introduced Hatcherichnus in 1997 for Late Jurassic footprints from Utah. The name therefore attaches to the preserved trace and its defining pattern, not to a reconstructed animal as though a skeleton had been found.

The type material comes from the Salt Wash Member of the Morrison Formation. The tracks preserve impressions attributed to the hind feet and, in the type series, fore-foot marks with fewer visible digits. Sediment can hide toes, collapse around a print or preserve only part of a step. A digit absent from the impression may simply have failed to register.

What the Spanish tracks preserve

Avanzini and colleagues described Hatcherichnus tracks from the Upper Jurassic Lastres Formation of Asturias in 2010. The Kimmeridgian deposits formed in a coastal plain with deltaic and shallow-water environments. Track surfaces at localities including Villaverde, Argüero and Tazones preserve prints made on damp sediment before burial.

Some impressions show claw traces, and a few have been discussed as possibly webbed. These details are not equally secure in every print. Water saturation, erosion and the angle at which a foot entered the mud all affect the visible outline. A footprint is a mold of pressure and sediment response, not a clean anatomical stamp.

The Spanish trackways include manus and pes impressions. Their relative sizes and placement can help distinguish a walking pattern from isolated marks, although an incomplete sequence limits stride calculations. The trackmaker crossed a surface in a particular way; the trackway does not tell us how it behaved during the rest of its life.

Reading gait without overreading behaviour

Trackway geometry can reveal direction of travel, step sequence and approximate pace. The distance between successive prints is measured on the preserved surface, while the animal's hip height and speed must be estimated through comparative models. Such estimates are sensitive to whether the trackmaker walked, trotted, slipped or moved over a yielding substrate.

Some Lastres prints have been interpreted as evidence that an animal was partly buoyant or swimming while its feet intermittently contacted the bottom. That is a possible reading of shallow, irregular impressions, not a direct observation of swimming. A changing water level, soft mud or incomplete preservation can produce related patterns. The most secure information is the contact sequence itself.

Who made Hatcherichnus?

The prints are compatible with a crocodylomorph-like animal. Their arrangement and digit impressions have been compared with the feet of early crocodile relatives, including goniopholidids and possible teleosaurids. Neither family can be identified solely from a generic resemblance in footprints. The tracks do not preserve the skull, teeth or other characters that distinguish those lineages.

Track names and skeletal names answer different questions. A named body fossil can be placed in a family using a suite of anatomical characters; a track may preserve only the shape and motion of a foot. No associated skeleton currently links the Utah or Asturias Hatcherichnus material to a particular named genus. The animal behind the tracks may remain unknown even if the footprint type is recognizable.

A long, well-preserved trackway can also reveal whether the left and right steps form a consistent sequence. Where only isolated prints remain, researchers cannot confidently infer stride length or estimate the trackmaker's height. These limits are especially important when comparing tracks formed on very different substrates.Trackways can also preserve changes in direction or spacing within a short distance. These may record acceleration, a turn, a change in substrate firmness or simply a difference in how well each step registered. Without a long, continuous trail, it is unsafe to turn a few prints into a detailed story of pursuit or escape.

That limit does not make the trackway uninformative. The Utah and Spanish surfaces show that crocodile relatives walked across Jurassic landscapes and occasionally left a record where bones did not. In the catalogue, Hatcherichnus represents evidence of activity rather than a complete biological profile.