The larger specimen of Sinopterus atavismus enters the LPT basal to dsungaripterids

Many pterosaur fossils attributed to Sinopterus
have been described. They vary greatly in size and shape.

Presently four Sinopterus specimens have been added
to the large pterosaur tree (LPT, 253 taxa). They are all sister taxa, but as in Archaeopteryx, no two are alike, one is basal to the others, which are, in turn, basal to large clades within the Tapejaridae.

  1. Sinopterus dongi (the holotype) nests basal to the Tupuxuara clade.
  2. Sinopterus liui nests in the Tupuxuara clade.
  3. Sinopterus jii (aka Huaxiapterus jii) nests basal to the Tapejara clade.
  4. Sinopterus atavisms (Figs. 1-4; Zhang et al. 2019; IVPP V 23388) nests basal to the Dsungaripterus (Fig. 4) clade, outside the Tapejaridae.
Figure 1. Sinopterus atavismus in situ.

Figure 1. Sinopterus atavismus in situ. IVPP V 23388

From the Zhang et al. 2019 abstract:
“Here, we report on a new juvenile specimen of Sinopterus atavismus from the Jiufotang Formation of western Liaoning, China, and revise the diagnosis of this species.”

Zhang et al. note that several elements are unfused including a humeral epiphysis. Several pits and grooves in the distal ends of the long bones are also pitted and grooved. Normally these would be good indicators in archosaurs and mammals, but pterosaurs are lepidosaurs and lepidosaurs follow distinctly different ‘rules’ for growth (Maisano 2002). As an example, some pterosaur embryos have fused elements. Some giant pterosaurs have unfused elements. Here the new specimen (IVPP 23388) is considered an ontogenetic adult as its size is similar to other phylogenetic relatives.

“Sinopterus atavismus does not present a square-like crest. Moreover the feature that groove in the ventral part of the second or third phalanx of manual digit IV is not diagnostic of the species.”

Zhang et al. are comparing the new larger IVPP specimen to the smaller, previously described (Lü et al. 2016) XHPM 1009 specimen (then named Huaxiapterus atavismus), which they considered conspecific. The XHPM specimen has wing phalanx grooves while the IVPP specimen does not. The shapes of the skulls do not match (Fig. 3) and we know that pterosaurs grew isometrically. Thus these two specimens are not conspecific.

“In the new material, the skull preserves a pointed process in the middle part of the dorsal marginof the premaxillary crest, which is different from other Chinese tapejarids. Considering the new specimen is known from a large skeleton that differed from the holotype, this difference may be related to ontogeny, as the premaxillary crest of the holotype is short and does not extend as long as that of the new specimen.”

These two specimens are not conspecific, so ontogenetic comparisons should not be made.

Figure 2. Sinopterus atavismus reconstruction.

Figure 2. Sinopterus atavismus reconstruction.

From the Zhang et al. 2019 discussion:
“Except for D 2525 which represents an adult individual of Sinopterus (Lü et al. 2006b), all Chinese tapejarid pterosaurs known so far were immature individuals at the time of death. The new specimen (IVPP 23388) shares some features with the holotype of Sinopterus atavismus. The wingspan of the new material is about twice as long as that of the holotype of S. atavismus.”

As mentioned above, the IVPP V 23388 specimen is here considered an adult with unfused bone elements. It needs both a new generic and specific name. The XHPM 1009 specimen (Fig. 3) requires further study.

Figure 3. Sinopterus atavismus size comparison

Figure 3. Sinopterus atavismus size and shape comparison.

The present confusion about the ontogenetic status of pterosaurs 
could have been largely resolved with the publication of “The first juvenile Rhamphorhynchus recovered by phylogenetic analysis” and other papers suppressed by pterosaur referees. Sorry, readers, we’ll have to forge ahead with the venues we have.

Figure 3. Sinopterus atavismus skull restored (gray areas).

Figure 4. Sinopterus atavismus skull restored (gray areas).

Figure 4. Sinopterus atavisms compared to Dsungaripterus to scale.

Figure 5. Sinopterus atavisms compared to Dsungaripterus to scale.

Sinopterus atavismus (Zhang et al. 2019; Early Cretaceous; IVPP V 23388) was originally considered a juvenile member of the Tapejaridae, but here nests as a small adult basal to Dsungaripteridae. The antorbital fenestra is not taller than the orbit. The carpals are not fused. No notarium is present. The antebrachium is robust. The distant pedal phalanges are longer than the proximal pedal phalanges. An internal egg appears to be present (but half-final-size adults were sexually mature according to Chinsamy et al. 2008,)

Sinopterus dongi IVPP V13363 (Wang and Zhou 2003) wingspan 1.2 m, 17 cm skull length, was linked to Tapejara upon its discovery, but is closer to Tupuxuara.

Sinopterus? liui (Meng 2015; IVPP 14188) is represented by a virtually complete and articulated specimen attributed to Sinopterus, but nests here at the base of Tupuxuara longicristatus.

Sinopterus jii (originally Huaxiapterus jii, Lü and Yuan 2005; GMN-03-11-001; Early Cretaceous) is basal to the Tapejara in the LPT, distinct from the other sinopterids basal to Tupuxuara.

Figure 5. Click to enlarge. The Tapejaridae arise from dsungaripterids and germanodactylids.

Figure 5. Click to enlarge. The Tapejaridae arise from dsungaripterids and germanodactylids.

The present LPT hypothesis of interrelationships
appears to be a novel due to taxon inclusion, reconstruction and phylogenetic analysis. If not novel, please let me know so I can promote the prior citation.

Traditional phylogenies falsely link azhdarchids with tapejarids
in an invalid clade ‘Azhdarchoidea‘. The LPT has never supported this clade (also see Peters 2007), which is based on one character: an antorbital fenestra taller than the orbit (that a few sinopterids lack). Pterosaur workers have been “Pulling a Larry Martin” by counting on this one character and by excluding pertinent taxa that would have shown them this is a convergent trait ever since the first cladograms appeared in Kellner 2003 and Unwin 2003.

Figure 1. Gene studies link swifts to hummingbirds. Trait studies link swifts to owlets. Trait studies link hummingbirds to stilts.

Figure x. Gene studies link swifts to hummingbirds. Trait studies link swifts to owlets. Trait studies link hummingbirds to stilts.

Unrelated update:
The stilt, Himantopus (Fig. x) has moved one node over and now nests closer to the hummingbird, Archilochus. Both arise from the Eocene bird, Eocypselus, which also gives rise to the hovering seagull, Chroicocephalus. The long, mud probing beak of the stilt was adapted to probing flowers in the hummingbird. All these taxa nested close together in the LRT earlier.


References
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Kellner AWA 2003. 
Pterosaur phylogeny and comments on the evolutionary history of the group. Geological Society Special Publications 217: 105-137.
Lü J and Yuan C 2005. 
New tapejarid pterosaur from Western Liaoning, China. Acta Geologica Sinica. 79 (4): 453–458.
Maisano JA 2002. The potential utility of postnatal skeletal developmental patterns in squamate phylogenetics. Journal of Vertebrate Paleontology 22:82A.
Maisano JA 2002.
Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Unwin DM 2003. On the phylogeny and evolutionary history of pterosaurs. Pp. 139-190. in Buffetaut, E. & Mazin, J.-M., (eds.) (2003). Evolution and Palaeobiology of Pterosaurs. Geological Society of London, Special Publications 217, London, 1-347.
Wang X and Zhou Z 2003. A new pterosaur (Pterodactyloidea, Tapejaridae) from the Early Cretaceous Jiufotang Formation of western Liaoning, China and its implications for biostratigraphy. Chinese Science Bulletin 48:16-23.
Zhang X, Jiang S, Cheng X and Wang X 2019. New material of Sinopterus (Pterosauria, Tapejaridae) from the Early Cretaceous Jehol Biota of China. Anais da Academia Brasileira de Ciencias 91(2):e20180756. DOI 10.1590/0001-3765201920180756.

wiki/Sinopterus

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