''Martharaptor'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

therizinosauroid Therizinosaurs (once called segnosaurs) were large herbivorous theropod dinosaurs whose fossils have been found across the Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs, skull and pelvis unite t ...

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

from the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

of the

Cedar Mountain Formation The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah, spanning most of the early and mid-Cretaceous. The formation was named for Cedar Mountain (Utah), Cedar Mountain in northern Emery Coun ...

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

. They can be distinguished from other therizinosauroids by means of several features of the skeleton (particularly the hands and feet) which were intermediate between early therizinosaurs such as ''

Falcarius ''Falcarius'' (meaning "sickle cutter") is a genus of primitive therizinosaur dinosaur that lived during the Early Cretaceous period in what is now North America. Its remains were first collected in the Cedar Mountain Formation in 1999, with su ...

'' and '' Beipiaosaurus'', and more "advanced" members of the group like

therizinosaurids Therizinosauridae (meaning 'scythe lizards')Translated paper
is a family of derived (advanc ...

. The deep and homogeneous hand claws clearly differ from the case in early therizinosauroids, but the foot has not yet acquired the robust morphology of therizinosaurids.

Discovery and naming

The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

specimen, UMNH VP 21400, hails from the Hayden-Corbett site of the

, approximately eight miles southeast from the city of

Green River Green River may refer to: Rivers Canada * Green River (British Columbia), a tributary of the Lillooet River *Green River, a tributary of the Saint John River, also known by its French name of Rivière Verte *Green River (Ontario), a tributary of ...

. The specimen was unearthed from a higher stratigraphic level (upper Yellow Cat Member) than ''

''. The generic name, ''Martharaptor'', is in honor to the

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

assistant Martha C. Hayden who helped in the discovery of the site, and the specific name, ''greenriverensis'', is a reference to the Green River. The specimen includes fragments of

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

, a

scapula The scapula (plural 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 eithe ...

, forelimb and hindlimb bones, and an

ischium The ischium () form ...

. It also includes well-preserved manual unguals. Manual and pedal morphology show that the specimen is distinct from other theropods from the Cedar Mountain Formation and from other previously described therizinosauroids.

Description

Forelimbs

A pair of fragmentary elongated bones preserved next to each other may represent the

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

and

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

of the antebrachium. Hand and finger bones are more well-preserved, with strongly ginglymoidal (pulley-shaped) joint surfaces. The manual unguals (hand claws) are very distinctive. Their height is greater than their length, and they are strongly curved. One of the preserved unguals is larger than the others, and it may represent the claw of the first finger. Other unguals are as large as each other, indicating that the second and third fingers had claws of equal size. The deep unguals of similar shape differs from the condition in other early therizinosauroids, which have longer unguals which differ in shape between different fingers.

Hindlimbs

Several bones of the left foot are preserved. The first metatarsal thins towards the ankle, similar to most theropods but unlike therizinosaurids, indicating that the first toe did not contact the ground. In conjunction with this, the claw of the first toe is smaller than those of the other toes. On the other hand, the toe claws are all deep and curved, as in other therizinosauroids. The

fourth metatarsal The fourth metatarsal bone is a long bone in the foot. It is smaller in size than the third metatarsal bone and is the third longest (and smallest) of the five metatarsal bones. The fourth metatarsal is analogous to the fourth metacarpal bone in t ...

is beveled (slightly slopes to the side) compared to the rest of the foot. This is intermediate between ''Falcarius'', which has no slope, and therizinosaurids, which have a fourth metatarsal angled at 90 degrees to the rest of the foot. None of the

metatarsals The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medi ...

are ginglymoidal, but the toe bones are.

Other bones

The only preserved bone of the pectoral girdle is the left

(shoulder blade). This bone has a hatchet-like shape, expanded near the shoulder as in other therizinosauroids which preserve a scapula and measures about long. The pelvis (hip) preserves fragments of the pubis and part of the

ischium The ischium () form ...

, which is very flattened (from the side) near the hip socket. Three vertebral fragments are preserved. These include a strip of bone from the upper portion of a cervical (neck) vertebra, the centrum (main body) of a dorsal (back) vertebra, and the lower portion of a vertebra believed to be a distal caudal (i.e. from the tip of the tail). The cervical fragment shows that the

prezygapophysis The articular processes or zygapophyses (Greek ζυγον = "yoke" (because it links two vertebrae) + απο = "away" + φυσις = "process") of a vertebra are projections of the vertebra that serve the purpose of fitting with an adjacent vertebr ...

(front joint plate) is not flexed, indicating that the specimen was not a

dromaeosaurid Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...

. Each side of the dorsal vertebra possessed a hypapophysis (rib facet) at its lower front corner and a pit located at the center of the side.

Classification

Phylogenetic analysis placed ''Martharaptor'' within Therizinosauroidea as the sister taxon to the ''

Alxasaurus ''Alxasaurus'' (; meaning " Alxa lizard") is a genus of therizinosauroid theropod dinosaurs from the Early Cretaceous (Albian age) Bayin-Gobi Formation of Inner Mongolia. History of discovery The fossil remains were first discovered in 1988 a ...

'' +

Therizinosauridae Therizinosauridae (meaning 'scythe lizards')Translated paper
is a family of derived (advanc ...

group, although support for this placement is weak. Nevertheless, Hartman ''et al.'' (2019) performed a phylogenetic analysis for the

Therizinosauria Therizinosaurs (once called segnosaurs) were large herbivorous theropod dinosaurs whose fossils have been found across the Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs, skull and pelvis unite the ...

corroborating the initial placement of ''Martharaptor.'' Left cladogram shows the probable placement of ''Martharaptor'' within Therizinosauroidea performed in the original description.

References

{{Taxonbar, from=Q2986383 Therizinosaurs Fossil taxa described in 2012 Early Cretaceous dinosaurs of North America Taxa named by James I. Kirkland Paleontology in Utah