''Astrophocaudia'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of somphospondylan

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...

known from the later part of the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

(

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

stage) of

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

, United States. Its remains were discovered in the

Paluxy Formation The Paluxy Formation is a geological formation found in Texas, Louisiana, Arkansas, Mississippi and Oklahoma, whose strata date back to the Early Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.Weis ...

. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

is ''A. slaughteri'', described in 2012.

Discovery and naming

Fragmentary

remains were among the earliest dinosaurs to be named from North America in the 19th century. In particular, the genera ''

Astrodon ''Astrodon'' is a genus of large herbivorous sauropod dinosaur, measuring in length, in height and in body mass. It lived in what is now the eastern United States during the Early Cretaceous period, and fossils have been found in the Arundel ...

'' and '' Pleurocoelus'' were named based on teeth and isolated limb or vertebral elements. Additional remains would be assigned to these genera over the course of the 19th century, most of which have either been reassigned to their own genera or considered to be dubious. Among the remains assigned to the genus ''Pleurocoelus'' (itself sometimes considered a

junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...

of ''Astrodon'') were the specimens SMU 61732 and SMU 203/73655, which had been discovered and excavated from the

by the paleontologist Robert Slaughter in the 1960s. Wann Langston Jr., a paleontologist who did considerable work on fossils from

, assigned these specimens to ''"Pleurocoelus sp."'' in 1974, and the fossils were not fully described for several decades. The remains were re-examined by the doctoral student Michael D. D’Emic, who was studying at the

University of Michigan The University of Michigan (U-M, U of M, or Michigan) is a public university, public research university in Ann Arbor, Michigan, United States. Founded in 1817, it is the oldest institution of higher education in the state. The University of Mi ...

at the time. His description included a comprehensive review of the sauropod remains from the

of North America including ''

Sauroposeidon ''Sauroposeidon'' ( ; meaning "lizard earthquake deity, god", after the Greek god Poseidon) is a genus of sauropod dinosaur known from several incomplete specimens including a bone bed and fossilized trackways that have been found in the U.S. st ...

'', ''

Cedarosaurus ''Cedarosaurus'' (meaning "Cedar lizard" - named after the Cedar Mountain Formation, in which it was discovered) is a genus of nasal-crested macronarian dinosaur from the Early Cretaceous Period (Valanginian). It was a sauropod which lived in wha ...

'', ''

Brontomerus ''Brontomerus'' (from Greek ''bronte'' meaning "thunder", and ''merós'' meaning "thigh") is a genus of Camarasauromorpha, camarasauromorph sauropod which lived during the early Cretaceous (Aptian or Albian age, approximately 110 million years ag ...

'', and others. In his description, D'Emic erected the new taxon ''Astrophocaudia slaughteri'' to contain both SMU 61732 and SMU 203/73655. The

name was given a twofold meaning: it is derived from several

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

words including ''"stropho-"'' meaning "twisting" or "turning", ''"caud-"'' meaning "tail", and the prefix ''"a-"'', meaning "not". The genus name as a whole therefore means "non-twisting tail", in reference to the closely-connected

hyposphene-hypantrum articulation The hyposphene-hypantrum articulation is an accessory joint found in the vertebrae of several fossil reptiles of the group Archosauromorpha. It consists of a Process (anatomy), process on the backside of the vertebrae, the hyposphene, that fits in a ...

of the

caudal vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

e. The genus name can also be translated to "star tail", using the Ancient Greek word ''"astron"'' and the above mentioned ''"caud"'', meaning "tail". This second meaning is in reference to the shape of the caudal vertebrae when viewed from behind, which have the appearance of a three-pointed star. D'Emic remarks that the name has a third meaning (although not a third translation), which is to pay homage to ''Astrodon'', the first named sauropod from North America. The

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

epithet ''"slaughteri"'' is in honor of Robert Slaughter, the original discoverer of the remains.

Description

The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

of ''Astrophocaudia'' consists of a single tooth (SMU 203/73655) and a partial postcranial skeleton (SMU 61732). The latter specimen contains the following elements: two

cervical vertebra In tetrapods, cervical vertebrae (: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In sauropsid s ...

e, a few fragments of dorsal vertebrae, 24

caudal vertebrae Caudal vertebrae are the vertebrae of the tail in many vertebrates. In birds, the last few caudal vertebrae fuse into the pygostyle, and in apes, including humans, the caudal vertebrae are fused into the coccyx. In many reptiles, some of the caud ...

, 20

rib In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the ...

fragments, two

chevrons Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * '' Eulithis testata'', a moth * Chevron (geology), a fold in rock la ...

, part of a

scapula The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...

, a partial right ilium, and several fragments that were not able to be identified. The roughly proportional size of the bones and the lack of any repeated elements led D'Emic to conclude that all of the preserved remains likely belonged to a single individual. D'Emic did not provide an estimate of the full size of ''Astrophocaudia'' in his description. Rubén Molina-Pérez and Asier Larramendi estimated the full size of this species at long and weighing . ''Astrophocaudia'' is able to be distinguished from all other sauropods by the following

autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...

: a planar orientation of the

s relative to the zygapophyses and the presence of a

lamina Lamina may refer to: People * Saa Emerson Lamina, Sierra Leonean politician * Tamba Lamina, Sierra Leonean politician and diplomat Science and technology * Planar lamina, a two-dimensional planar closed surface with mass and density, in mathem ...

in front of the

neural arch Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

es which contacts a second lamina between, and in front of, the zygapophyses. It is further distinguished from the roughly contemporaneous sauropods ''

'', ''

Venenosaurus ''Venenosaurus'' ( ) is a genus of sauropod dinosaur that lived in what is now Utah during the Early Cretaceous. Its type and only species is ''Venenosaurus dicrocei''. Fossils of ''Venenosaurus'' were first discovered in 1998, by Denver Museum o ...

'', ''

'', and ''

Sonorasaurus ''Sonorasaurus'' is a genus of brachiosaurid dinosaur from the Early to Late Cretaceous (Albian to Cenomanian stages, around 112 to 93 million years ago). It was a herbivorous sauropod whose fossils have been found in southern Arizona in th ...

'' by other characteristics of the caudal vertebrae. ''Astrophocaudia'' also possesses a preacetabular process which is slightly curved when viewed from above.

Classification

In his description of ''Astrophocaudia'', D'Emic conducted a phylogenetic analysis which included all known sauropods from the

of North America. He notably found that fossils of the taxon '' Paluxysaurus'' bore autapomorphies of ''

'', meaning the two taxa were synonymous. He found that ''Astrophocaudia'' belonged in a

polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tree ...

at the base of

Somphospondyli Somphospondyli is an extinct clade of titanosauriformes, titanosauriform sauropods that lived from the Late Jurassic until the end of the Late Cretaceous, comprising all titanosauriforms more closely related to Titanosauria proper than Brachiosau ...

outside of

Titanosauria Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of Sauropoda, sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with tax ...

. An abbreviated version of the cladogram published by D'Emic is shown below next to another, more recent analysis that recovered similar results with greater resolution by Yang Han and colleagues. ;D'Emic, 2012 ;Han ''et al.'', 2024

References

{{Taxonbar, from=Q247092 Macronaria Dinosaur genera Albian dinosaurs Dinosaurs of the United States Fossil taxa described in 2012

Discovery and naming

Description

Classification

See also

References