Kuqaia, Li, 1993

Peng, Jungang, Slater, Sam M., McLoughlin, Stephen & Vajda, Vivi, 2023, New species of Kuqaia from the Lower Jurassic of Sweden indicates a possible water flea (Crustacea: Branchiopoda) affinity, PLoS ONE (e 0282247) 18 (6), pp. 1-20 : 12

Kuqaia is recorded sporadically across Laurasia including, from east to the west, the Yangtze Gorge Area, Qaidam Basin, Yanqi Basin, Junggar Basin and Tarim Basin in China, southern Sweden, offshore central Norway, and the northern North Sea ( Fig 8 ). Owing to their wide distribution and, until recently, uncertain systematic placement, we suspect that many examples of this genus have gone unreported in surveys of microfossil assemblages, or have been included as miscellaneous organic remains under categories such as acritarchs [ 22]. Examples referable to Kuqaia quadrata , K. concentrica and K. radiata are widely distributed in both eastern and western Laurasia [ 18, 26 – 29]. Kuqaia yangii and K. yanqiensis were documented in the Yanqi and Tarim basins in western China [ 25, 27], whereas K. cucuma is confined to the Yangtze Gorge Area [ 19]. Thus far, K. scanicus is known only from southern Sweden (this study).

The geological ranges of these fossils have been explored at generic level ([ 22, 27]; Fig 8 ), since species of Kuqaia , especially the widely distributed Kuqaia quadrata , K. concentrica and K. radiata , are normally associated in previously studied samples [ 18, 22, 24 – 27].

The oldest records of Kuqaia are from Hettangian strata of offshore Norway [ 28] where they are encountered in continental, freshwater deposits. The genus was not found in Triassic strata of that region. This accords with the records from the Yanqi Basin, where Kuqaia occurs slightly above the basal Jurassic strata [ 25]. The youngest occurrences of Kuqaia are in lower Middle Jurassic strata based on records from various sections in the Tarim, Yanqi, Junggar and Qaidam basins [ 23, 25, 26, 39]. The youngest occurrence of Kuqaia is in the northern North Sea succession within lower Bajocian strata [ 29]. Overall, Kuqaia is an index taxon of Lower to lower Middle Jurassic (Hettangian–Bajocian) strata.

A general change in the abundance of Kuqaia has been proposed based on quantitative data from stratigraphic successions in the Tarim, Yanqi and Junggar basins, northwestern China ([ 22, 25, 39]; Fig 8 ). Kuqaia appears in the Ahe and Badaowan formations (lower Lower Jurassic) in low abundances, is more common in the overlying Yangxia and Sangonghe formations (upper Lower Jurassic), and decreases in the succeeding Kezilenur and Xishanyao formations (lower Middle Jurassic). However, these quantitative trends are equivocal given that yields of Kuqaia -sized fossils, e.g., mesofossils, vary greatly between samples (e.g., from 1 to more than 200 specimens) as a consequence of taphonomic sorting.

Figures

Fig 8. Geological ranges, palaeogeographic distributions, and apparent abundance pattern of Kuqaia. The base and top of Kuqaia stratigraphic ranges from each starred locality were tentatively calibrated based on material from offshore mid-Norway and the northern North Sea.The palaeogeographic map was modified after [38] under the Creative Commons Attribution 4.0 International License.