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An Aptian-age Lower Cretaceous pterosaur known as Sinopterus (meaning "Chinese wing") is a genus of tapejarid pterodactyloid pterosaurs found in the Jiufotang Formation of Chaoyang, Liaoning, China. It was initially identified and characterized by Zhou Zhonghe and Wang Xiaolin. Several species have been assigned to the genus in the past, but only one is thought to be genuine. The proportionately large skull of Sinopterus is characterized by its pointed beak like a bird, a long bony crest that extends from the tall premaxilla down the center of the skull to a point that protrudes from the back of the skull, and the absence of teeth.

Description

The articulated, virtually complete skeleton IVPP V13363 serves as the foundation for the type species, S. dongi. This person's estimated wingspan measured 1.2 meters (3.9 feet), and their skull measured 17 centimeters (6.7 inches) in length. The first tapejarid recorded outside of Brazil, as well as the earliest and most complete tapejarid, led the authors to hypothesize that it was an omnivore. This pterosaur's maximal adult wingspan was estimated to be 1.9 meters (6.2 feet), and its weight would have been 2.87 kg (6.3 lb).

Classification

Numerous specimens, some of which have been attributed to distinct species or even other genera throughout time, are known to exist for Sinopterus. One specimen, described in 2003, is all that is known about the type species, Sinopterus dongi. In 2003, Li, Lü, and Zhang also reported a second specimen, BPV-077, placing it in the S. gui species. Its reduced size (about half that of S. dongi) and the existence of a notarium were thought to be its primary differences from S. dongi, albeit these claims were later refuted. S. gui was thought to be only a younger S. dongi specimen in some subsequent research, however a thorough investigation conducted in 2014 revealed that S. gui was actually a more ancient tapejarid. In 2007, a third specimen was reported to Sinopterus and was once more identified as a new species, with the designation S. jii. Lü & Yuan originally identified this species in 2005 as the type species of a newly created genus they called Huaxiapterus. In reality, H. jii was more closely linked to Sinopterus than to "H." corollatus and "H." benxiensis, the two additional species both placed to Huaxiapterus, according to two further studies conducted in 2007 and 2011. The two study groups came to the conclusion that the other two "Huaxiapterus" species need a new genus name, and that Huaxiapterus jii should be reclassified as Sinopterus jii. More thorough phylogenetic research, however, revealed that Sinopterus could really represent a step in between H. jii and the other two Huaxiapterus species, making Sinopterus paraphyletic if H. jii is taken into account. S. lingyuanensis, a different species, was identified in 2016. The proportions of its nasoantorbital fenestra, rostral index, femur and tibia relative sizes, and first and second wing digit sizes were said to set it apart from the other species. Huaxiapterus atavismus was named in the same study that described this species. Xinjun Zhang and associates, on the other hand, reclassified H. atavismus to Sinopterus in 2019 after ruling that Huaxiapterus was an invalid genus. This resulted in the creation of the new combination Sinopterus atavismus. Darren Naish and colleagues' 2021 study on variation within pterosaur growth stages found that many species had been assigned to the Sinopterus or "Huaxiapterus" genus, with the majority of these classifications based only on a single specimen. These species were primarily distinguished from one another by characteristics such as wing proportions, skull length, and crest size and shape. All of these traits are known to vary within a single species as a result of growth, as noted by Naish et al., and if there were a high diversity of remarkably similar species in the same ecosystem, their differences would most likely result from variation within a small number of species. They recommended that more research be done to clarify the issue of how many different species of pterosaurs that resembled Sinopterus truly existed in the Jiufotang environment and how they are connected to one another. According to their early assessment, "Huaxiapterus" corollatus may be a legitimate second species of Sinopterus according to its distinct wing and leg dimensions, but there is probably only one recognized species of Sinopterus, S. dongi. Rodrigo V. Pêgas et al. examined the tapejarid taxonomy history in 2023. They equated S. gui and S. lingyuanensis with S. dongi in their article. Moreover, H. jii and H. atavismus were reclassified as synonyms of S. dongi, and "H." corollatus was reclassified to the new genus Huaxiadraco, with which Huaxiapterus benxiensis became synonymous. As a consequence, the genus Huaxiapterus was synonymized with Sinopterus.

Relationships

The cladogram that follows, which places two Sinopterus species ("S." gui and S. dongi") inside the clade Tapejaromorpha, is based on a study conducted in 2014 by Brian Andres and colleagues.

Tapejaromorpha
Bennettazhia oregonensis
Eopteranodon lii
"Sinopterus" gui
Nemicolopterus crypticus
Huaxiapterus jii
Tapejaridae
Sinopterus dongi
Tapejarinae
"Huaxiapterus" benxiensis
"Huaxiapterus" corollatus
Tapejarini
Tupandactylus navigans
Tupandactylus imperator
Bakonydraco galaczi
Europejara olcadesorum
Tapejara wellnhoferi

2019 saw the recovery of Sinopterus inside the Tapejarinae, a subfamily within the wider Tapejaridae group. Sinopterus is a sister taxon to both Huaxiapterus and Eopteranodon. This investigation was conducted by Alexander Kellner and colleagues. Below is the cladogram resulting from their analysis:

Tapejaromorpha
Keresdrakon vilsoni
Tapejaridae
Thalassodrominae
Thalassodromeus sethi
Tupuxuara leonardii
Tapejarinae
Caupedactylus ybaka
Aymberedactylus cearensis
Eopteranodon lii
"Huaxiapterus" benxiensis
"Huaxiapterus" corollatus
Sinopterus dongi
Tapejarini
Europejara olcadesorum
Caiuajara dobruskii
Tapejara wellnhoferi
Tupandactylus imperator

Paleobiology[]

Growth

Because scientists have access to several specimens of Sinopterus at different phases of growth, they are able to examine the changes these creatures underwent over their lives. It has been determined that at least one extremely tiny juvenile—possibly a hatchling—specimen belongs to Sinopterus. 2008 saw the first classification of this species as Nemicolopterus crypticus, a separate genus. The Greek terms "Nemos" (for forest), "ikolos" (for resident), and the Latinized word "pteron" (meaning "wing") are the sources of the name Nemicolopterus. "Kryptos" means "hidden" in Greek, and this is where the particular term "crypticus" originates. Therefore "Nemicolopterus crypticus" translates to "Hidden flying forest dweller". N. crypticus type specimen IVPP V-14377, catalog number IVPP, is kept at the Institute of Vertebrate Paleontology and Paleoanthropology's collection in Beijing, China. Like other adult Sinopterus specimens, the fossil was obtained from the Jiufotang Formation. It was found in the northeastern Chinese region of western Liaoning Province in the Luzhhouou locale of Yaolugou Town, Jianchang County, Huludao City. With its somewhat smaller wingspan of less than 25 centimeters (10 in), it is smaller than all but a few hatchling pterosaur specimens.

SinopterusLifeRestoration

Sinopterus and Huaxiadraco restoration.

SinopterusFossil

Sinopterus fossil.


Sources

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