Holotype of Pachychirotherium gardenaensis
Photo: @ University La Sapienza of Roma.
One of the familiar refrains of creationism is that the fossil record contains no transitional forms. Yet transitions need not be preserved only in bones: sometimes, animals left evidence of evolutionary change in the footprints they made. A new study of ancient reptile tracks reveals a stepwise acquisition of features associated with upright locomotion — changes that helped establish the conditions for the later evolution of two-legged movement in dinosaurs and their close relatives.
The research, by Lorenzo Marchetti of the Museum für Naturkunde Berlin and Hendrik Klein of the Saurierwelt Paläontologisches Museum, is published in Palaeontology, concerns early archosauriforms, members of the wider evolutionary group that includes archosaurs — dinosaurs, pterosaurs, crocodilians and their relatives. Their history extends back into the Late Permian, more than 250 million years ago: already an insurmountable chronological problem for a literal reading of Genesis.
Marchetti and Klein re-examined footprints from the Val Gardena Sandstone Formation of northern Italy, including previously undescribed specimens, and recognised a distinctive track type, which they named Pachychirotherium gardenaensis. This is a name for the fossil traces, rather than a newly identified species of skeletal animal. Comparisons with fossil feet suggest that their makers were early archosauriforms with an anatomy resembling that of erythrosuchids.
The wider comparison with Permian and Triassic tracks is particularly revealing. Late Permian forms retain evidence consistent with sprawling locomotion; some Early Triassic forms show transitional characteristics; and a fully erect stance probably emerged during the Middle Triassic. Increasing reliance on the toes, changes in toe proportions and a reduction in the relative size of the forefoot impressions accompanied this evolutionary transition. These features were assembled progressively, rather than appearing together as a completed package.
This does not mean that the footprints identify an unbroken succession of direct ancestors leading to dinosaurs. They reveal something more defensible and scientifically useful: a sequence of changing anatomical and locomotor characteristics across related groups. Nor does an upright stance necessarily mean walking on two legs. Bringing the limbs beneath the body and reducing reliance on the forelimbs were distinct developments, with bipedality emerging later in some lineages.
For creationism, the difficulty is therefore twofold. These animals were walking the Earth hundreds of millions of years before the supposed “Creation Week”, and their tracks preserve evidence of the incremental changes that creationist rhetoric so often declares absent. For palaeontologists, meanwhile, the study shows how an incomplete skeletal record can be supplemented by another source of evidence: the impressions living animals left as they moved across an ancient landscape.
Faced with this evidence however, the standard response of creationists is to insist that the physical evidence they also assert their creator god created, is a forgery or otherwise unreliable because it conflicts with the claims in a book they also attribute to the same creator god. Given the choice allowing the evidence to change their fixed unchangeable minds, they will even condemn the god they purport to worship to the status of a celestial trickster who deliberately tries to mislead us. As Francis Collins points out in The Language Of God, this reflects the scientific and theological bankruptcy of creationism.
Fossilised Behaviour^ What Footprints Tell Us That Bones Cannot. A fossil skeleton preserves parts of an animal’s body. A fossil footprint preserves evidence of something that animal did: placing a foot on the ground. A succession of footprints — a trackway — can therefore supply information about movement that bones alone cannot provide. The study of these and other traces of biological activity is called ichnology.The paper in Palaeontology was accompanied by a news release from the Berlin museum:
Reading a Trackway
Researchers examine the shape, depth, spacing and orientation of footprints, together with the relationship between forefoot and hindfoot impressions. Several features can be informative:
Walking on Soles or Toes
- Trackway width: the distance between the left and right tracks can help constrain how the limbs were positioned during movement. It is a clue to posture, rather than a conclusive measurement on its own.
- Stride length:the distance between successive impressions of the same foot helps describe the animal’s gait. Combined with estimates of body dimensions, it can sometimes support an estimate of speed, although this involves assumptions.
- Foot contact: impressions may show whether much of the sole contacted the ground or whether support was concentrated on the digits.
- Forefoot and hindfoot relationships: their relative sizes and positions help researchers investigate differences in limb proportions and how the animal moved.
A plantigrade animal places much of the sole on the ground, as humans and bears do. A digitigrade animal walks on its digits with the heel raised, as cats and dogs do. These terms describe foot contact, rather than whether an animal walks on two legs or four.
In the archosauriform study, comparisons among Permian and Triassic footprints indicate a progressive acquisition of digitigrady, changes in toe proportions and a reduction in the relative size of the forefoot. Together with skeletal evidence, these changes help reconstruct the evolution of locomotion.
Upright Does Not Mean Two-legged
Posture and bipedality are different things. In a sprawling posture, the limbs extend substantially out to the sides. In an erect posture, they support the body more directly from underneath. An animal can have an erect posture while remaining quadrupedal: a horse is an obvious living example.
Consequently, the evolution of upright locomotion was not automatically the evolution of two-legged walking. The study identifies changes that preceded, and helped make possible, the later emergence of bipedality in some dinosaur-line relatives.
Why Give a Footprint Its Own Name?
The name Pachychirotherium gardenaensis identifies a distinctive type of fossil footprint — an ichnotaxon. It does not name a skeletal species whose identity has been established beyond doubt. Different animals with similar feet can leave similar tracks, while one animal can leave different-looking impressions as ground conditions or its movements change.
Matching tracks to their makers therefore requires comparisons with fossil anatomy. Researchers can sometimes identify a likely group of trackmakers without being able to identify a particular species.
Clues, Not Perfect Recordings
A footprint is the product of a foot interacting with a surface. Soft mud, firm sand, slipping, erosion and later deformation can all influence its appearance. An indistinct heel impression, for example, need not mean that the heel never touched the ground.
Reliable interpretations therefore depend on well-preserved specimens, repeated patterns and comparisons with other tracks and skeletal remains. Footprints complement bones: they can preserve evidence of animals and their behaviour even where suitable skeletal fossils have not been found.
Brief Glossary
- Trace fossil:
- preserved evidence of biological activity, such as a footprint, burrow or feeding mark.
- Ichnology:
- the study of traces made by organisms.
- Ichnotaxon:
- a named category of traces, classified by their characteristics.
- Manus:
- the hand or forefoot.
- Pes:
- the foot or hindfoot.
- Plantigrade:
- walking with much of the sole contacting the ground.
- Digitigrade:
- walking on the digits with the heel raised.
- Bipedal:
- moving on two limbs.
- Marchetti and Klein (2026), the stepwise evolution of archosauriform posture and locomotion, Palaeontology.
From Sprawling to Bipedalism: How Locomotion Evolved in Dinosaur Ancestors
A research team led by Dr. Lorenzo Marchetti of the Museum fur Naturkunde Berlin described the earliest archosauriform footprints (Pachychirotherium gardenaensis) from the GEOPARC Bletterbach - UNESCO World Heritage Dolomites, Italy. This study discovered that the transition from sprawling to erect locomotion was a stepwise process started in the late Permian and completed only by the Middle Triassic, leading shortly after to the acquisition of bipedality among the first dinosaurs and dinosaur relatives. This was published in the journal Palaeontology.
Archosaurs are iconic animals that ruled the Mesozoic, their most derived group being dinosaurs. Their direct ancestors, the archosauriforms, appeared during the late Permian. This was shortly before the catastrophic end-Permian extinction. However, their fossil record in the Permian is rather scattered. Additional information comes from their footprints, which have been first found in the GEOPARC Bletterbach - UNESCO World Heritage Dolomites, Italy. Until now, this material has been considered similar to Early Triassic archosauriform footprints such as Protochirotherium, known from Germany, Poland and Morocco. Also, it has been assumed that these footprints already indicated an erect stance while the animal walked.
In the frame of a research project on archosauriform footprints carried out at the Museum für Naturkunde Berlin , Dr. Lorenzo Marchetti, in collaboration with Hendrik Klein of Saurierwelt, re-analysed the material with the addition of some newly-described specimens. These footprints are now stored at the University "La Sapienza" of Rome and the Naturmuseum Südtirol of Bozen (Italy). The scientists concluded that these specimen belong to the ichnofamily Chirotheriidae and are taxonomically different from all other footprints belonging to this group. So they named these footprints Pachychirotherium gardenaensis, meaning "thick chirotheriid from Gardena".
A comparative study on Pachychirotherium and on the feet and hands of archosauriforms based on morphology and measurements allowed an attribution of these footprints to archosauriforms, and more specifically Erythrosuchidae or animals with a very similar limb morphology.
An additional analysis of archosauriform trackways from the Permian and Triassic revealed a stepwise transition from a sprawling posture (in the late Permian) to an erect posture (by the Middle Triassic) of these animals while walking. This happened together with an increase in cursoriality (so longer middle digits of the foot), digitigrady (so only the digits touched the ground) and a reduction in size of the hands. All of these features were essential for the later evolution of bipedality in dinosaurs and their close relatives.
It is amazing to see how many details on the biology and locomotion of archosauriforms are preserved in fossil footprints, and this becomes even more important when the skeletons are scarce. In fact, trace fossils are the only fossils to directly register the locomotion of living animals.
Dr. Lorenzo Marchetti, first author
Museum für Naturkunde Berlin, Berlin, Germany.
Holotype of Pachychirotherium gardenaensisPhoto: @ University La Sapienza of Roma.
Publication:
These footprints present creationism with the same familiar difficulties, this time impressed into ancient sediment. Their Late Permian and Triassic ages place them hundreds of millions of years before the supposed “Creation Week”, while their changing characteristics document the progressive acquisition of features associated with upright locomotion. The transition is not an imaginary sequence invented to fill a gap: it is an interpretation grounded in measurable differences between fossil traces, supported by comparisons with skeletal anatomy.
The Theory of Evolution is central to making sense of these findings. It provides the framework within which researchers compare related groups, recognise transitional combinations of characteristics and reconstruct how locomotion changed over time. There is no requirement that every trackmaker be a demonstrable direct ancestor of dinosaurs, nor any expectation that all relevant adaptations appeared simultaneously. A branching evolutionary history, in which different features emerged at different stages, is precisely what makes the evidence intelligible.
For those creationists who retreat to the claim that such evidence was planted to mislead us, the theological cost is considerable. If their creator deliberately manufactured the appearance of an ancient world and an evolutionary history that never happened, they are accusing the god they supposedly worship of being a cosmic trickster: one who supplies evidence of falsehoods and then expects us to reject the conclusions that evidence supports. That is no defence of divine truthfulness. It makes deception part of the proposed creation process, and is based on the absurd idea that a liar can be trusted when it writes its claims in a book, but not when it writes it in rocks.
Once again, palaeontologists have incidentally exposed the inadequacy of a literal reading of Genesis simply by investigating the natural world. Their purpose was to understand ancient animals and how they moved, not to refute a religious narrative. The conflict arises because the rocks preserve a history that the narrative cannot accommodate — a history in which evolutionary change left its evidence, quite literally, step by step.
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