Li, Wang and Jiang 2021 report
on a new slab filled with small Early Cretaceous pterosaur tracks (Figs. 1–3).
The authors report,
“IVPP V 26281.2, which is a greyish green sandstone block (125 cm × 25 cm) with 114 natural casts (convex hyporelief) of small pterosaur tracks was collected from Huangyangquan Reservoir tracksite 1, Wuerho region, northwestern Junggar Basin, Xinjiang, China.”
Coeval (Early Cretaceous) pterosaur taxa known from bones
include two slender dsungaripterids, Noripterus (Fig. 3) and Dsungaripterus. These two were derived from sharp-snouted Late Jurassic Solnhofen germanodactylids in the large pterosaur tree (LPT, 258 taxa). The authors suggested the tracks were made by Noripterus (Fig. 3), which is chronologically and geographically reasonable, until one notices a mismatch in proportions and size.
Li, Wang and Jiang report,
“There is no preservation of impressions formed by the fifth metatarsal and digit V.” …and that’s how these two ichnites were scored individually in the LPT.
Even so, after phylogenetic analysis
both ichnites surprisingly nested within the Late Jurassic genus Rhamphorhynchus (Figs. 4–6), though millions of years after Rhamphorhynchus fossils were buried in Solnhofen strata.
It is worthwhile to take a closer look at the Wuerho pedal impressions
(Fig. 2). The medial metatarsals appear to be slightly elevated because their impressions disappear as if the sole of the foot was arched (see Peters 2011 for more details and examples). Such a pedal arch would put more weight (= creating deeper impressions) on the medial and lateral digits. The impression of the lateral digit appears to have an unexpected joint not found in pterodactylid or ctenochasmatid ichnites. That ‘bend’ was also drawn by Li, Wang and Jiang (Figs. 2, 3) producing an unexpected lateral bump. Given the present data, the ichnites appear to document metatarsal 4 resting upon pedal digit 5 in this trackmaker (Fig. 3), thus obscuring the appearance of a straight metatarsal 4 that would have been sitting on top of that bent digit 5.
If this is incorrect,
and the Wuerho trackmakers had no pedal digit 5, that would also be in accord with, and convergent with, other post-Jurassic pterosaur descendants of Middle to Late Jurassic dorynathids and scaphognathids in the LPT. These also greatly reduce pedal digit 5 and so produce four convergent clades of ‘pterodactyloid’-grade pterosaurs in the Latest Jurassic and Cretaceous. As mentioned above, scoring in the LPT assumed no long pedal digit 5.
I traced several pedal trackways in the slab
(Fig. 1), but only a few left and right manus impressions are associated with each pedal trackway. That indicates bipedal locomotion with an occasional manus touch to the substrate for these trackways. The authors counted 57 manus imprints and 57 pes imprints, but only a few of these are associated with pedal tracks in typical pterosaur fashion. A collection of manus only tracks appears at mid-slab. Thus the matching numbers (57 and 57) are coincidental.
Other Solnhofen and pre-Solnhofen taxa gave rise to Cretaceous taxa in the LPT. Rhamphorhynchus was the sole exception until now. The present evidence suggests that Rhamphorhynchus-derived taxa also survived into the Early Cretaceous Wuerho refugium of China along with the last stegosaur, Wuerhosaurus.
According to Wikipedia,
“Wuerhosaurus is a genus of stegosaurid dinosaur from the Early Cretaceous Period of China and Mongolia. As such, it was one of the last genera of stegosaurians known to have existed, since most others lived in the late Jurassic.”
So… there’s at least one more late surviving taxon
that somehow survived into the Junggar Basin of Wuerho and nowhere else (so far).
In an effort to make pterosaur tracks more easily identified,
Peters 2011 produced a catalog of dozens of pterosaur pedes and ichnospecies, but that work was not cited by Li, Wang and Jiang.
The LPT scores relatively few pedal traits
and ichnites can be difficult to trace and interpret. Given that proviso, surprisingly these two ichnite taxa would rather nest within the genus Rhamphorhynchus than closer to the genus Noripterus or any other of 258 taxa in the LPT. Even with a scoring handicap.
So, let’s keep an open mind
with regard to this wonderful new slab from the Early Cretaceous of China (Fig. 1). Let’s not exclude any taxa a priori, nor attempt to force fit the ‘pterosaur next door’. The slab may preserve evidence of an overlooked late survivor from the Late Jurassic, the only Rhamphorhynchus descendants that left clues to their existence in the Early Cretaceous refugium of Wuerho, China.
Li Y, Wang X and Jiang S 2021. A new pterosaur tracksite from the Lower Cretaceous of Wuerho, Junggar Basin, China: inferring the first putative pterosaur trackmaker. PeerJ 9:e11361 DOI 10.7717/peerj.11361
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification.Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605.