The 'Goldilocks' effect: preservation bias in vertebrate track assemblages

Area of Science:

• Paleontology
• Sedimentology
• Biomechanics

Background:

• The fossil record of vertebrate tracks (ichnology) is influenced by various factors.
• Body mass and substrate properties are hypothesized to create biases in track preservation.

Purpose of the Study:

• To investigate the bias in the ichnological fossil record attributable to dinosaur body mass.
• To assess the influence of substrate conditions on track formation and preservation.
• To enhance the use of vertebrate tracks as paleoenvironmental indicators.

Main Methods:

• Finite-element analysis was employed to simulate virtual dinosaur tracks.
• Four dinosaur taxa of varying sizes were modeled (Struthiomimus, Tyrannosaurus, Brachiosaurus, Edmontosaurus).
• Simulations were conducted across a range of substrate conditions, considering animal weight and limb loading.

Main Results:

• Ideal substrates showed a narrow 'Goldilocks' range of loads for track formation; small animals failed to indent, large animals became mired.
• Assuming a firm subsurface layer allowed for more track preservation, but with a strong bias towards larger, heavier animals.
• Track depths can indicate the thickness of mechanically distinct substrate layers during track formation.
• Simulated undertracks suggest that basal ridges may result from sediment displacement and pedal morphology, not necessarily limb kinematics.

Conclusions:

• Dinosaur body mass introduces significant bias into the ichnological fossil record.
• Track depth analysis offers valuable insights into substrate properties and paleoenvironmental conditions.
• Reinterpretations of undertrack features are proposed, decoupling them from limb kinematics.