# Late Ediacaran Trackways Produced by Bilaterian Animals with Paired Appendages

> More than 540 million years ago, a small animal crossed the sea floor in what is now South China and left two rows of tracks, each only 1 to 2 mm across. These are the oldest known trackways made by an animal with paired legs. By reading the tracks the way a tracker would, the authors show the animal may have walked on top of the mat and then burrowed beneath it.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/2018-chen-chen-late-ediacaran-trackways-produced/

## Citation and access

- **Authors:** Zhe Chen, Xiang Chen, Chuanming Zhou, Xunlai Yuan and Shuhai Xiao
- **Year published:** 2018
- **Journal or source:** Science Advances
- **Full citation:** Chen, Z., Chen, X., Zhou, C., Yuan, X. and Xiao, S. 2018. Late Ediacaran trackways produced by bilaterian animals with paired appendages. Science Advances 4(6): eaao6691.
- **DOI:** 10.1126/sciadv.aao6691
- **Access status:** Open access (CC BY-NC 4.0)
- **PDF:** https://www.originalwisdom.com/wp-content/uploads/2026/11/2018_Chen_and_Chen_etal_late-ediacaran-trackways-produced-by-bilaterian-animals-with-paired-appendages.pdf

## Tags

- **Species:** Invertebrates
- **Region:** Asia > China
- **Tracking:** Burrows; Track measurements; Track photographs; Tracking; Tracks; Tracks and signs identification
- **Behaviour and ecology:** Behaviour; Movement
- **Data type:** New field data
- **Observer qualification:** Not reported
- **Discipline:** Behaviour and ecology; Ichnology
- **Year published:** 2018

## Detailed keywords

- **Species:** Studied: unknown trace makers, probably millimetre-sized bilaterian animals (animals with left and right sides) with paired appendages; their phylum is unknown. The authors consider an arthropod-like animal possible, but also animals similar to modern annelids (segmented worms such as polychaetes), onychophorans (velvet worms) or tardigrades. Other trace fossils on the same surface: Lamonte trevallis and a possible new species, Lamonte sp. Body fossils in nearby beds: Hiemalora, Rangea, Aspidella, Pteridinium and Wutubus. Comparison trackways: Danstairia congesta (Early Devonian, Old Red Sandstone, Scotland), Pterichnus (interpreted as made by myriapods or isopods) and Diplichnites (interpreted as made by many-legged arthropods such as myriapods, euthycarcinoids and trilobites).
- **Location and habitat:** Wuhe, Yangtze Gorges area, South China (30°47′23.1″N, 111°3′22.9″E). Shibantan Member of the upper Dengying Formation, about 70 m above the base of the member; ca. 551 to ca. 541 million years ago (late or terminal Ediacaran Period). Dark grey, thin-bedded, bituminous limestone laid down in a shallow sea below the fair-weather wave base but above the storm wave base, in beds with microbial mats.
- **Topics:** trace fossils; ichnology; oldest known trackways; early animal evolution; origin of paired appendages; trackways versus trails and burrows; undertracks (imprints pressed through a microbial mat) versus overtracks; undermat burrows; walking and burrowing by the same animal; microbial mats; track series, sets and stride; gait; comparison with Paleozoic arthropod trackways.
- **Statistics or models:** None
- **Data type:** New field data: two trackways (TW1, TW2) and three burrows (UB1 to UB3) excavated in situ on one slab (NIGP-166148), with part and counterpart, plus a second slab with Lamonte (NIGP-166149) and a previously published specimen (NIGP-154193). Collection dates are not given. Specimens are held at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences. Inconsistency in the paper: the trace makers are called millimetre-sized, yet the trace maker is also said to be probably more than 13.8 mm wide, based on trackway width.

## Synopsis

### 1. What they did

Molecular evidence suggests that most groups of bilaterian animals (animals with a left and right side, such as arthropods and worms) arose in the Ediacaran Period, 635 to 541 million years ago. Yet hardly any Ediacaran body fossils can be firmly linked to these groups, and none clearly has paired appendages (legs or leg-like parts). Ediacaran trace fossils have so far been simple surface trails and shallow burrows. Trackways, rows of imprints left by legs or leg-like parts, were unknown before the Cambrian.

The authors excavated a slab of limestone from the Shibantan Member at Wuhe in the Yangtze Gorges area of South China, dated to about 551 to 541 million years ago. It held two possible trackways (TW1 and TW2) and three burrows (UB1 to UB3). Because they collected the slab in place, with both the top and bottom surfaces, they knew which way up each impression was. They photographed the specimens under natural light and low-angle light from different directions, made a latex mould of the bottom surface, and measured each trackway and burrow. They compared the trackways with younger trackways and with other trace fossils on the same surface.

### 2. What they found

Why these are trackways

- Each trackway is two rows of shallow pits on the top surface, matched by two rows of bumps on the bottom surface.

- The sediment between and beside the rows is undisturbed, and TW2 crosses two burrows (UB1 and UB2) without cutting into them. Trails or burrows would have disturbed that sediment and cut into the burrows they crossed.

- The authors conclude the impressions are most likely tracks made by paired appendages. They may be undertracks: imprints pressed into the sediment below a microbial mat by an animal walking on top of it.

The trackways

- TW1: about 70 mm long, 13.8 mm wide on the outside and 4 mm on the inside. Tracks are 1 to 2 mm across and about 1 mm deep. At least four sets of tracks can be vaguely made out. Each set has two opposite series at about 15° to the midline, each series 17 to 18 mm long with four or more tracks. The apparent stride is about 13.7 mm. Faint marks along the midline and oblique scratches on one side may be present, but this is uncertain.

- TW2: about 91 mm long, 16 mm wide on the outside and 4 mm on the inside, with tracks of similar size. The two rows are clear, but series are not. Repeated groups of five imprints seem to appear, and small dimples run along the inner side of one row, making the trackway lopsided. Groups and dimples are spaced about 8 to 10 mm apart. There are no midline marks.

- The tracks are much less regular than most later trackways of arthropods and annelids. They look most like Danstairia, an irregular trackway from Early Devonian rocks in Scotland.

The burrows and possible connections

- The burrows are 9.5 to 11.5 mm wide; UB1 is 133 mm long and curved, UB2 and UB3 are 42 and 21 mm long and fairly straight. They were dug beneath microbial mats and are filled with carbonate sediment.

- TW2 seems to join UB3, and TW1 seems to join UB1, with the same direction and width, though with a slight offset at each join.

- Two other trace fossils on the same surface (Lamonte sp.) also seem to show possible trackways turning into burrows.

### 3. What they concluded

- These are the oldest known trackways made by bilaterian animals with paired appendages.

- The discrete tracks rule out legless worms moving by muscle waves. The lack of a body drag mark, and the way TW2 crosses burrows without cutting them, suggest the animal held its body up on its appendages (or pushed its appendages through a microbial mat).

- The trace maker was probably wider than 13.8 mm and may have had at least four, perhaps five, pairs of appendages. The authors caution that false series or groups of tracks can sometimes appear.

- The irregular tracks suggest poorly coordinated leg movements, unlike the smooth wave-like leg rhythm of modern arthropods. Modern arthropods are useful comparisons, but the trace maker cannot be placed in any phylum: all that can be said is that it was probably a bilaterian with paired appendages.

- If the links between trackways and burrows are confirmed, the same animal may have walked on top of microbial mats and burrowed beneath them, a moderately complex behaviour.

- Small bilaterian animals with paired appendages were beginning to play a growing role in shaping their environment through their interactions with microbial mats.

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

The study is a careful reading of fossil tracks and signs. The authors identified the impressions as trackways rather than trails or burrows from what the sediment showed: undisturbed sediment between the two rows, no drag mark, pits on the top surface matched by bumps on the bottom, and a trackway crossing burrows without cutting them. They measured trackway width, track size and depth, the angle and length of track series, and stride, and they read track groups to estimate the number of appendage pairs. They photographed the tracks with low-angle light from several directions to bring out faint imprints. They used Trewin’s (1994) system for describing arthropod trackways. No trailing in the modern sense was involved.

### 5. Tracker or observer certification

Not reported. The interpretations were made by the authors (Zhe Chen and Shuhai Xiao), who are palaeontologists; no test or certification of track-reading skill is described.

### 6. Other technologies, skills or innovations

- Photography with a Nikon D700 camera under natural light and low-angle light with controlled lighting directions.

- A latex mould of the bottom surface, photographed the same way.

- Excavation in place, with both top and bottom surfaces, so there was no doubt about which way up each impression was.

- Petrographic thin sections (shown in the supplementary materials) of other burrows in the Shibantan Member.

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

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

- The authors’ reasoning is the reasoning of any tracker: is this a line of separate footfalls, or a body dragged or pushed through the ground? Undisturbed ground between the two rows and no drag mark point to an animal carried on its legs.

- The study shows the value of low, raking light from several directions for bringing out faint tracks, a technique trackers also use when reading tracks in poor conditions.

- Undertracks, imprints that show up in a layer below the surface the animal walked on, are a reminder that what is visible can be a softened version of the true track, so fine detail and regular patterns may be lost.

## Cite this summary

Lawrence, K. 2026. Summary of: Late Ediacaran Trackways Produced by Bilaterian Animals with Paired Appendages (Chen and Chen et al., 2018). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/2018-chen-chen-late-ediacaran-trackways-produced/