# Description of Bird Tracks from the Kitadani Formation (Aptian), Katsuyama, Fukui, Japan with Three-Dimensional Imaging Techniques

> In the Early Cretaceous, birds walked across the muddy banks of a river in what is now Fukui, Japan. Using handheld 3D scanners, researchers described two of their footprints, one with a small web between the toes, and showed how they told these bird tracks apart from those of small dinosaurs. The tracks may come from two medium-sized kinds of bird, adding to the little that is known about Early Cretaceous birds in Japan.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/2018-imai-tsukiji-description-bird-tracks-kitadani/

## Citation and access

- **Authors:** Takuya Imai, Yuta Tsukiji and Yoichi Azuma
- **Year published:** 2018
- **Journal or source:** Memoir of the Fukui Prefectural Dinosaur Museum
- **Full citation:** Imai, T., Tsukiji, Y. and Azuma, Y. 2018. Description of bird tracks from the Kitadani Formation (Aptian), Katsuyama, Fukui, Japan with three-dimensional imaging techniques. Memoir of the Fukui Prefectural Dinosaur Museum 17: 1–8.
- **Access status:** Hosted (freely available elsewhere)
- **PDF:** https://www.originalwisdom.com/wp-content/uploads/2026/11/2018_Imai_and_Tsukiji_etal_description-of-bird-tracks-with-three-dimensional-imaging-techniques.pdf

## Tags

- **Species:** Birds
- **Region:** Asia > Japan
- **Tracking:** Track measurements; Tracking; Tracks; Tracks and signs identification
- **Data type:** Existing data; New field data
- **Observer qualification:** Not reported
- **Discipline:** Ichnology
- **Year published:** 2018

## Detailed keywords

- **Species:** Studied: fossil birds known only from their footprints, from the Early Cretaceous. Two tracks: FPDM-F-74, assigned to cf. Aquatilavipes ichnosp., and FPDM-F-75, assigned to cf. Gyeongsangornipes ichnosp. (an ichnotaxon is a name given to a type of fossil track, not to the animal that made it). Compared with: published tracks of small non-avian theropod dinosaurs and Early Cretaceous bird tracks from China, South Korea, Canada, the United States and Spain (Table 2), including Gyeongsangornipes lockleyi, Sarjeantopodus semipalmatus, Dongyangornipes sinensis, Shandongornipes muxiai, Limiavipes curriei and Wupus agilis. Living birds mentioned: great blue heron (Ardea herodias, scientific name only in the paper), grouse and some domesticated Galliformes (which have small webs between their toes). Other tracks at the same level of the quarry: possible amphibians, pterosaurs and non-avian theropod dinosaurs.
- **Location and habitat:** Kitadani Dinosaur Quarry, on the left bank of the Sugiyama River, northern Katsuyama, Fukui, central Honshu, Japan. Kitadani Formation (Aptian, Early Cretaceous), uppermost Akaiwa Subgroup, Tetori Group. The tracks were in alternating fine sandstone and mudstone laid down by a meandering river, interpreted as a channel-fill deposit.
- **Topics:** ichnology (fossil tracks); fossil bird tracks; telling bird tracks from small dinosaur tracks; total divarication (spread) angle between digits II and IV; webbed (semipalmate) bird tracks; claw traces; digital pads; heel impression; absent hallux (back toe) trace; natural casts; preservation affecting track shape; variation within one species; isolated tracks versus trackways; Early Cretaceous birds of East Asia; three-dimensional (3D) imaging of tracks.
- **Statistics or models:** Measurements after Leonardi (1987): track length (TL), track width (TW), TL/TW ratio, free digit length, digit width and divarication angles. Scatter plot of track length against total divarication for the two tracks, small non-avian theropod tracks and Early Cretaceous bird tracks. No statistical tests. Inconsistency in the paper: the length of digit II of FPDM-F-74 is 40 mm in the text but 45 mm in Table 1. The Discussion says FPDM-F-75 “does not exhibit webbing traces”, which appears to mean FPDM-F-74. The Figure 4 caption labels FPDM-F-75 as panels “E–F” (the figure shows D–F).
- **Data type:** New field data: two of seven possible bird tracks collected in 1991 during the 1st Kitadani Dinosaur Excavation Project, newly scanned in 3D (FPDM-F-74 was first shown in photographs in a 1993 dissertation; FPDM-F-75 is new). Existing data: published measurements of other fossil tracks for comparison. The 3D scan files are published as supplementary data.

## Synopsis

### 1. What they did

Fossil bird tracks from the Early Cretaceous are common in South Korea and China, but birds of that age are poorly known in Japan. The Kitadani Formation in Fukui is rich in fossil tracks, and possible bird tracks had been noticed among them.

Seven possible bird tracks were collected from the Kitadani Dinosaur Quarry in 1991. Two showed clear enough relief to be recorded with portable 3D scanners, and the authors described these two in detail:

- Scanning. Both tracks are natural casts (the infill of the original footprint, so they stand up from the rock). The authors scanned them with handheld 3D scanners and turned the scans into contour maps with 0.3 mm contour lines, alongside photographs and line drawings.

- Measuring. They measured track length and width, the length and width of each toe (digits II, III and IV), and the angles between the toes.

- Deciding whether birds made them. They checked the tracks against published criteria for telling bird tracks from those of small meat-eating dinosaurs, and plotted track length against the spread of the toes for their tracks and for published dinosaur and bird tracks.

- Naming the track types. They compared the tracks with known fossil bird track types.

### 2. What they found

The two tracks

- FPDM-F-74 is a left foot, 60 mm long and 94 mm wide, with slender toes ending in sharp claw traces. The outer toes (II and IV) curve slightly outward at the tips. The total spread between digits II and IV is 117 degrees. There is no back toe (hallux) trace and no web trace, and the heel is a shallow U shape. Three toe pads show on digit IV.

- FPDM-F-75 is also a left foot, smaller at 50 mm long and 71 mm wide, with a total spread of 101 degrees and possible claw traces on digits III and IV. There is no back toe trace. It has likely web traces between digits II and III and between III and IV, reaching less than half way along the toes.

Bird or dinosaur?

The authors assign both tracks to birds because they are small compared with most small dinosaur tracks, have slender toes with indistinct pads, a spread between the outer toes of more than 100 degrees, slender claws, and outer claws curving away from the centre of the foot. The web traces on FPDM-F-75 support this, as webs are not known from non-avian dinosaur tracks. On the scatter plot, both tracks fall within the cluster of bird tracks. Another proposed test, comparing footprint length with pace length, could not be used because both are single tracks, not trackways.

Track types

- FPDM-F-74 has the features of the track type Aquatilavipes and is larger than other Aquatilavipes tracks, though not exceptionally large among Early Cretaceous bird tracks. With only one track, the authors cannot confidently assign it to Aquatilavipes, so it is called cf. Aquatilavipes.

- FPDM-F-75 is placed near Gyeongsangornipes (cf. Gyeongsangornipes). It is larger than most webbed fossil bird tracks and differs from Gyeongsangornipes lockleyi from South Korea in its larger size, smaller toe spread and shorter webs.

One bird or two?

The two tracks differ in toe spread and in webbing, but this does not necessarily mean two different birds made them. The toe spread of a living heron can vary by more than 10 degrees either side of the average, and the missing web in FPDM-F-74 may be due to poor preservation. The authors give them different names but say the differences may be an artefact of preservation.

What the web might mean

The web on FPDM-F-75 is small, and its use for swimming is questionable. Some living birds that do not live by water, such as grouse and some domesticated Galliformes, have small webs like this, so a web does not necessarily mean the bird lived near water.

### 3. What they concluded

- The two tracks show that possibly two medium-sized kinds of bird lived in the area of the Kitadani Formation, adding to what is known about Early Cretaceous birds in Japan.

- Web traces on FPDM-F-75 and other late Early Cretaceous bird tracks from Asia suggest that partly webbed feet were not uncommon among birds at the time.

- Because no trackways have been found, the track types and shapes of bird tracks in the Kitadani Formation remain uncertain; further excavation could clarify this.

### 4. How tracking was or was not used

This is a study of fossil footprints (ichnology). The authors identified and measured two isolated footprints, judged whether a bird or a small dinosaur made them from the track shape (size, toe shape, toe spread, claw traces, pads, heel, hallux and web traces), and compared them with published tracks. No trailing was possible: there were no trackways, so stride and pace could not be measured.

### 5. Tracker or observer certification

Not reported. The tracks were described by the authors, palaeontologists at the Fukui Prefectural Dinosaur Museum and Japanese universities. The tracks were found during the 1st Kitadani Dinosaur Excavation Project, and S. Hayashi is thanked for initial data collection and documentation.

### 6. Other technologies, skills or innovations

- Portable 3D scanners (Artec Spider and Artec Eva, Artec 3D) to record the tracks’ surfaces, following an earlier recommendation by Arakawa et al. (2002) to use 3D imaging for footprints.

- Image analysis software (VIVID2Rugle and 3D-Rugle, Medic Engineering Corporation) to turn scans into contour (topographic) images. The authors used 3D imaging to document and describe the tracks objectively.

- The 3D scan files are freely available as supplementary data (STL format) on the museum’s website.

### 8. Implications for tracking (Original Wisdom's observations)

_These are Original Wisdom's observations, not the authors'._

- The features the authors use to tell a bird track from a small dinosaur track (slender toes, wide toe spread, curved outer claws, a web, the heel shape) are the same kinds of features trackers read in modern bird tracks.

- The paper shows the limits of a single track: without a trackway, the authors cannot measure pace or decide whether one or two kinds of bird made the two tracks. Variation within a species and the conditions of preservation can change what a track shows.

## Cite this summary

Lawrence, K. 2026. Summary of: Description of Bird Tracks from the Kitadani Formation (Aptian), Katsuyama, Fukui, Japan with Three-Dimensional Imaging Techniques (Imai and Tsukiji et al., 2018). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/2018-imai-tsukiji-description-bird-tracks-kitadani/