The slab and counterslab of the holotype specimen of H. lingyuanensis were given to different groups of researchers in Beijing, one from the Institute of Vertebrate Paleontology and Paleoanthropology and the other from the Beijing Natural History Museum.
Each team described the taxon and published their results independently in January 1999, giving the animal two different names: Hyphalosaurus lingyuanensis and Sinohydrosaurus lingyuanensis.
It was quickly recognized that Sinohydrosaurus and Hyphalosaurus were mirror images of one another and in fact represented different halves of the same specimen.
The ICZN, which governs the naming of animals, mandates that the older name is valid.
However, in June 2001 paleontologists Joshua Smith and Jerry Harris noted that since both were published at almost exactly the same time, a third party needed to select which name would better serve as the objective senior synonym.
Smith and Harris took the opportunity to do so, selecting Hyphalosaurus as the senior synonym because the manuscript for its description had apparently been submitted (though not published) earlier.
They therefore made Sinohydrosaurus a junior synonym of Hyphalosaurus.

Hyphalosaurus is related to the large, crocodile-like Champsosaurus and the smaller, lizard-like Monjurosuchus.
Its closest relative was the similarly built species, Shokawa ikoi, from the Early Cretaceous of Japan.
 The choristoderes were a clade of aquatic reptiles that survived the end-Cretaceous extinction along with crocodilians, turtles, lizards and snakes.
The choristoderes became extinct by the Miocene.
The slab and counterslab of the holotype specimen of H. lingyuanensis were given to different groups of researchers in Beijing, one from the Institute of Vertebrate Paleontology and Paleoanthropology and the other from the Beijing Natural History Museum. Each team described the taxon and published their results independently in January 1999, giving the animal two different names: Hyphalosaurus lingyuanensis and Sinohydrosaurus lingyuanensis. It was quickly recognized that Sinohydrosaurus and Hyphalosaurus were mirror images of one another and in fact represented different halves of the same specimen. The ICZN, which governs the naming of animals, mandates that the older name is valid. However, in June 2001 paleontologists Joshua Smith and Jerry Harris noted that since both were published at almost exactly the same time, a third party needed to select which name would better serve as the objective senior synonym. Smith and Harris took the opportunity to do so, selecting Hyphalosaurus as the senior synonym because the manuscript for its description had apparently been submitted (though not published) earlier. They therefore made Sinohydrosaurus a junior synonym of Hyphalosaurus.
Hyphalosaurus is related to the large, crocodile-like Champsosaurus and the smaller, lizard-like Monjurosuchus. Its closest relative was the similarly built species, Shokawa ikoi, from the Early Cretaceous of Japan.  The choristoderes were a clade of aquatic reptiles that survived the end-Cretaceous extinction along with crocodilians, turtles, lizards and snakes. The choristoderes became extinct by the Miocene.
Hyphalosaurus