Hypselorhachis is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of extinct reptile

Reptile

Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

, possibly a ctenosauriscid archosaur

Archosaur

Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...

 related to Ctenosauriscus

Ctenosauriscus

Ctenosauriscus is an extinct genus of sail-backed poposauroid archosaur from Early Triassic deposits of Lower Saxony in northern Germany. It gives its name to the family Ctenosauriscidae, which includes other sail-backed poposauroids such as Arizonasaurus...

. It lived during the Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 Period. It is currently known only from a single vertebra found from the Middle Triassic

Middle Triassic

In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...

 Manda Beds in Tanzania

Tanzania

The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...

.

The type species

Type species

In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...

 is H. mirabilis, mentioned but never fully described by English paleontologist

Paleontology

Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...

 Alan J. Charig

Alan J. Charig

Alan Jack Charig was an English palaeontologist and writer who popularised his subject on television and in books at the start of the wave of interest in dinosaurs in the 1970s....

. Hypselorhachis was assigned to the Ctenosauriscidae

Ctenosauriscidae

Ctenosauriscidae is an extinct family of pseudosuchian archosaurs within the clade Poposauroidea. Ctenosauriscids existed in Africa, Asia, Europe and North America during the Early Triassic to the Middle Triassic period . All species had large "sails" on their backs...

, a group of sail-backed archosaurs, in 1988. It was formally described by Richard J. Butler and co-workers in 2009.

Hypselorhachis is known from a single anterior dorsal vertebra found from the Lifua Member of the Manda Beds, which is thought to have been deposited during the Anisian

Anisian

In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...

 stage. The only characteristic that diagnoses the genus is a feature seen in the prezygapophysis. Because of the lack of any other material, comparisons between it and other early archosaurs can only be based on features seen in the vertebrae, making any current phylogenetic classification tentative. Because the neural spine of the holotype is elongate, being over five times the height of the centrum

Centrum

Centrum means center in Latin.Centrum may refer to:* The central portion of a vertebra*Centrum , a Washington state performing arts organization* Centrum , metro station in Warsaw, Poland...

, Hypselorhachis may be a ctenosauriscid. Other ctenosauriscids such as Arizonasaurus

Arizonasaurus

Arizonasaurus was a ctenosauriscid archosaur from the Middle Triassic . Arizonasaurus is found in the Middle Triassic Moenkopi Formation of northern Arizona. A fairly complete skeleton was found in 2002 by Sterling Nesbitt. The taxon has a large sailback formed by elongate neural spines of the...

and Ctenosauriscus possessed characteristically large sails that were formed from elongate neural spines.