Trace fossil evidence and behavioral reconstruction of Miocene avian courtship behavior

Here is your science article translated into English, with wording aligned to the terminology and interpretations used in the referenced paper:

Fossils do not only record the anatomy of organisms—they can also preserve their behavior. Traces such as footprints, trackways, burrows, and borings are known as trace fossils, representing the activities left behind by ancient organisms. By studying these traces, researchers can infer how animals moved, foraged, and even whether they exhibited social behavior or interactions. Although trace fossils are relatively rare and often difficult to interpret, comparisons with modern animals can help reconstruct the behavioral ecology of ancient ecosystems.

In the past, researchers have attempted to infer complex behaviors from fossil footprints, such as social activity, hunting strategies, and courtship behavior in dinosaurs. For example, some studies have suggested that large scrape marks found in Cretaceous deposits may represent courtship display arenas created by theropod dinosaurs—behaviors that are also observed in modern birds.

Location of the trace fossil site（Image source：Abbassi, N. (2025).，採用 CC BY-NC-ND 4.0 授權）

A 2025 study described a remarkable assemblage of bird trace fossils from a Miocene formation in northwestern Iran. The site contains more than 70 trackways and preserves evidence of seven distinct behavioral patterns, which are interpreted as being related to courtship display. This rare example of a fossilized bird mating dance provides a unique opportunity to glimpse the courtship behavior of ancient birds and compare it with that of modern species, offering further insight into the evolution of reproductive behavior.

At this trace fossil site, researchers identified a total of 70 trackways produced by small, tetradactyl birds. These trackways can be categorized into seven distinct behavioral types:

Yellow = walking; Red = high stepping; Orange = stomping in place; Gray = short-distance flight; Green = hopping; Purple = pecking; Blue = lateral leaping（Image source：Abbassi, N. (2025).，採用 CC BY-NC-ND 4.0 授權）

Walking:

Trackways form straight or slightly curved lines, with no clear change in direction. Footprints repeat in a regular pattern, accounting for approximately 29.5% of all behavioral states.

High stepping:

Characterized by dense, repetitive footprints in which each footprint overlaps the distal part of the previous one. This behavior closely resembles courtship displays observed in modern plovers and accounts for about 25.8%.

Stomping in place:

Occurs within small localized areas at the beginning, middle, or end of trackways. These zones contain numerous overlapping footprints along with irregular excavation and disturbance of the substrate. Some traces show paired symmetrical impressions. This behavior makes up about 19.8%.

Short-distance flying:

Identified by gaps within trackways where footprints are absent, interpreted as brief aerial movements interrupting walking. This behavior typically appears within high-stepping sequences and accounts for about 8.7%.

Hopping:

Recognized by paired footprints formed when both feet land simultaneously during bipedal hopping. This occurs during locomotion and represents about 7.9%.

Pecking:

Radially arranged scratch marks found at the beginning, end, or sides of trackways. These are interpreted as pecking traces associated with courtship behavior rather than feeding. They account for about 6.3%.

Lateral leaping:

Observed within high-stepping sequences, where the animal performs short sideways jumps before continuing forward movement. Footprints may occasionally be preserved during these motions.

From a to f: high stepping, stomping in place, short-distance flight, hopping, pecking, and lateral leaping, respectively（Image source：Abbassi, N. (2025).，採用 CC BY-NC-ND 4.0 授權）

Based on sedimentological context and footprint morphology, the trackmakers are interpreted as semi-aquatic birds inhabiting environments near rivers and lakes. Estimates of body size derived from footprint dimensions, combined with behavioral comparisons, suggest that these birds were likely members of the family Charadriidae, similar to modern plovers.

This Miocene bird mating site is particularly significant because it preserves most of the behavioral components seen in modern avian courtship displays. Comparisons with living birds show strong similarities in behaviors such as high stepping, pecking, hopping, and stomping. These traces were likely produced by adult individuals during the breeding season, probably in spring, when environmental conditions included clear seasonal variation.

Additionally, some high-stepping trackways occur in parallel arrangements, suggesting that multiple males may have been displaying simultaneously, possibly competing with one another. In modern birds, such behaviors are often accompanied by vocalizations and coordinated displays involving multiple individuals. Although vocal behavior cannot be directly confirmed from fossil evidence, researchers propose that these courtship displays were likely accompanied by sound. While inferring vocalization from footprints remains highly speculative, it opens new directions for future research into the evolution of avian behavior.

Trace fossils are crucial for understanding ancient animal behavior. Traditionally, they have been classified into five main behavioral categories: repichnia (locomotion), pascichnia (grazing/feeding), fodinichnia (deposit feeding), domichnia (dwelling), and cubichnia (resting). However, the behaviors documented in this study—related to courtship—do not fit within these categories. Therefore, the study proposes a new ethological class: Goshnichnia, defined as trace fossils associated with mating behavior. These traces typically reflect complex behavioral patterns and are often preserved in trackways.

（Author: Bai Leng）

Reference：

Abbassi, N. (2025). Reconstructing Miocene bird mating behavior from a fossil tracksite. Scientific Reports.