An Ornithopod-Dominated Tracksite from the Lower Cretaceous Jiaguan Formation (Barremian-Albian) of Qijiang, South-Central China: New Discoveries, Ichnotaxonomy, Preservation and Palaeoecology

Abstract

The historically-famous Lotus Fortress site, a deep 1.5-3.0-meter-high, 200-meter-long horizonal notch high up in near-vertical sandstone cliffs comprising the Cretaceous Jiaguan Formation, has been known since the 13th Century as an impregnable defensive position. The site is also extraordinary for having multiple tetrapod track-bearing levels, of which the lower two form the floor of part of the notch, and yield very well preserved asseamblages of ornithopod, bird (avian theropod) and pterosaur tracks. Trackway counts indicate that ornithopods dominate (69%) accounting for at least 165 trackmakers, followed by bird (18%), sauropod (10%), and pterosaur (3%). Previous studies designated Lotus Fortress as the type locality of Caririchnium lotus and Wupus agilis both of which are recognized here as valid ichnotaxa. On the basis of multiple parallel trackways both are interpreted as representing the trackways of gregarious species. C. lotus is redescribed here in detail and interpreted to indicate two age cohorts representing subadults that were sometimes bipedal and larger quadrupedal adults. Two other previously described dinosaurian ichnospecies, are here reinterpreted as underprints and considered nomina dubia. Like a growing number of significant tetrapod tracksites in China the Lotus Fortress site reveals new information about the composition of tetrapod faunas from formations in which the skeletal record is sparse. In particular, the site shows the relatively high abundance of Caririchium in a region where saurischian ichnofaunas are often dominant. It is also the only site known to have yielded Wupus agilis. In combination with information from other tracksites from the Jiaguan formation and other Cretaceous formations in the region, the track record is proving increasingly impotant as a major source of information on the vertebrate faunas of the region. The Lotus Fortress site has been developed as a spectacular, geologically-, paleontologically- and a culturally-significant destination within Qijiang National Geological Park.

Fig 1. Photograph (A) and proposed future reconstruction (B) of the Lotus tracksite, China.

Illustration by Zhongda Chuang.

Fig 2. Plan view map of the Lotus tracksite (A) and stratigraphic sections of the Qijiang Lotus tracksite (B).

Fig 3. Map of track-bearing levels at QI and II of the Lotus tracksite.

Fig 4. Representative dinosaur tracks from the Lotus tracksite.

An ornithopod track cast (A) and sauropod track cast (B) from QIII, ornithopod track mold and cast (C and D respectively) from QIV, ornithopod track casts (E and F) from QV, ornithopod track casts (G and H) from QVI, ornithopod track casts (F, I–K) from QVII.

Fig 5. Interpretative outline drawing of large-sized ornithopod trackways from QII, Lotus tracksite, Qijiang, China.

Holotype shown in box of trackway QII-O20.

Fig 6. Photographs, interpretative outline drawings and 3D height maps (warm colours are high, cooler colours are low) of well-preserved ornithopod tracks from the Lotus tracksite.

Fig 7. Interpretative outline drawings of small-sized ornithopod trackways from QII, Lotus tracksite, Qijiang, China.

Fig 8. Interpretative map based on drawings of small-sized ornithopod trackways from QIII, Lotus tracksite, Qijiang, China.

Note that specimens UCM 214.258–214.260 are preserved as replicas in the University of Colorado collections.

Fig 9. Scatter diagram of track length and width (A); length and mesaxony (B) in Caririchnium tracks from the Lotus tracksite.

Fig 10. Interpretative outline drawings of Caririchnium drawn to the same scale (modified after Lockley et al.[31]).

A, Carirchnium magnificum [32]; B, Caririchnium leonardii [33]; C, Caririchnium protohadrosaurichnos [46]; D, Caririchnium lotus [2], and E, Caririchnium kyoungsookimi [47].

Fig 11. Interpretative outline drawings of Early Cretaceous Caririchnium tracks from China.

A, Caririchnium isp. from Jiufotang Formation, Luanping tracksite, Hebei Province [–56]; B, Caririchnium type from Tongfosi Formation, Tongfosi tracksite, Jilin Province [57]; C, Caririchnium from Hekou group, Yanguoxia tracksite No. II, Gansu Province; D, Caririchnium type from Hekou group, Yanguoxia tracksite No. I [58]; E, Caririchnium from Hekou group, SS1 site, Gansu Province [59]; F, Caririchnium from Jiaguan Formation, Longjing tracksite, Sichuan Province [76]; G and H, Caririchnium from Feitianshan Formation, Zhaojue tracksites, Sichuan Province [8]; I and J, this text. Scale bar = 10 cm.

Fig 12. Photographs and interpretative outline drawings of ornithopod tracks and undertracks from the Lotus tracksite.

These extramorphological variants of C. lotus formed the basis for two ichnospecies, which we reject here as nomina dubia. See text for details.

Fig 13. Photograph (A), 3D height maps (B–D) and interpretative outline drawing (E) of complexly overprinted ornithopod track series QIII-OI1–9 from the Lotus tracksite.

Fig 14. Photograph (A), 3D height map (B) and interpretative outline drawing (C) of complexly overprinted ornithopod track series QIII-OI10–16 from the Lotus tracksite.

Fig 15. Interpretative outline drawings of sauropod trackway (A) and isolated pes-manus prints (B) from QI.

Photograph (C, D, E and G) of sauropod casts from QVI. Close-up photographs (F, H) show details with striation marks. Dotted line indicates outline of undertracks. Arrow indicates moving direction of tracks.

Fig 16. Interpretative outline drawing of bird trackways from the Lotus tracksite.

Fig 17. Photograph (A and C) and interpretative outline drawings (B and D) of possible theropod tracks from the Lotus tracksite.