| Falcarius | |
|---|---|
 | |
| Reconstructed skeleton,Natural History Museum of Utah | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Maniraptora |
| Clade: | †Therizinosauria |
| Genus: | †Falcarius Kirklandet al.2005 |
| Type species | |
| †Falcarius utahensis Kirklandet al. 2005 | |
Falcarius (meaning "sickle cutter") is agenus of primitivetherizinosaurdinosaur that lived during theEarly Cretaceous period in what is nowNorth America. Its remains were first collected in theCedar Mountain Formation in 1999, with subsequent findings made during the 2000s. The genus is known from multiple specimens ranging from immature to fully-grown individuals.
Falcarius was a 4 m (13 ft) long bipedalherbivore with a small head and an elongated neck and tail. Unlike advanced therizinosaurs,Falcarius had a propubic pelvis and three-toed feet with a reducedhallux (first digit).
Falcarius is the basal most known definitive therizinosaurian genus, and has been considered atransitional form connecting the typical theropod bodyplan to the unusual morphology ofTherizinosauridae. Its description in 2005, following that of the basaltherizinosauroidBeipiaosaurus from theEarly Cretaceous ofChina in 1999, helped clarify the early evolution of the Therizinosauria and its relationships within the larger group of Theropoda.
The remains ofFalcarius were first discovered in 1999 by commercial fossil collector Lawrence Walker at the Crystal Geyser Quarry site inGrand County. He informed paleontologist James I. Kirkland of the find, who with a team of theUtah Geological Survey from 2001 onwards began to uncover the bones that proved to be present in a two-acre (8,000-square-meter) area of Utah'sCedar Mountain Formation (Yellow Cat member).Falcarius thus lived in theEarly Cretaceousperiod. Two extensive bone beds were discovered, including the remains of hundreds, perhaps thousands, of individuals of the new species. The minimum number of individual animals was in 2006 estimated at three hundred.[2] In 2005 over two thousand specimens had been excavated, mostly consisting of disarticulated bones.[3] These included the remains of juvenile animals.[2] In 2008 a second site was reported, the Suarez Quarry, with mainly adult individuals, but of a perhaps slightly different type. In 2010 the number of specimens from the original quarry had increased to over 2,700,[4] and was later that year reported to have risen to over three thousand.[5]
The first remains were partially described and discussed in 2004 on several abstracts bypaleontologistsLindsay E. Zanno, then a doctoral student at the university,James I. Kirkland,Scott D. Sampson, chief curator at theUniversity of Utah'sUtah Museum of Natural History,Donald D. DeBlieux,David K. Smith andR. Kent Sanders.[6][7][8] It was not formally named until a subsequent paper published in the May 2005 issue of the journalNature.[3][9]
Zanno subsequently and informally describedFalcarius as "the ultimate in bizarre: a cross between an ostrich, a gorilla, and Edward Scissorhands."[9] Thegeneric name,Falcarius, is literally taken from theLatin falcarius (meaning sickle cutter) in reference to the large hand claws. Thespecific name,utahensis, reflects the provenance from Utah. Theholotype specimen,UMNH VP 15000, consists of a partial braincase and a large number ofparatypes were assigned.[3]Falcarius has since been described in detail by Zanno in a series of studies, beginning with her thesis in 2004.[10]
Falcarius is known from multiple specimens at different ontogenic stages. While the smallest specimen was approximately less than 1 m (3.3 ft), average adults were about 4–5 m (13–16 ft) in length weighing approximately 100 kg (220 lb).[2][4][11]
The head anatomy ofFalcarius is partially known. The skull was small and elongated. With its long neck,Falcarius could apparently reach about 1.5 m (4.9 ft) off the ground to munch leaves or fruit, possibly higher. The teeth numbered at least sixteen in themaxilla of the upper jaw. Thedentary (part of the lower jaw) carried twenty-eightteeth. Its small leaf-shaped and very finely serrated maxillary teeth indicate that it consumed plant material. The front-most five teeth of the lower jaw are much longer, straighter and more pointed though, and might indicate a partially omnivorous diet including meat, e.g. small animals such aslizards. In the back of the head, the braincase was relatively large. Its lower elements were moderately inflated by pneumatised, hollowed-out, bone tissue. The large skull opening in the snout, thefenestra antorbitalis, is positioned in a depression which reaches the side of thenasal bone. There are at least five pairs of conical teeth in the front of the lower jaws. These teeth are hollowed-out at the inside. On the underside of the vertebrae of the neck there is a depression with at the mid-line a ridge. On the underside of the braincase there is a well-developed depression, therecessus basisphenoidalis. At the back of the head there are deep depressions below theoccipital condyle and on the subotics, each with several pneumatic grooves.[4][12]
The partitioning of the vertebral column followed that of most maniraptorans. The neck was very long with elongated cervical vertebrae. The tail was relatively long. The arm was moderately long with a somewhat robusthumerus. The relatively large, and slightly recurved, pointed ten- to thirteen-centimeter (four- to five-inch) hand claws were likely used in self-defence.[13][4]
Falcarius is known from many specimens, including complete forelimb specimens. Most of the bones of the pectoral girdle and forelimb are known, although sternal bones are not preserved. Both a left and right scapula are preserved, and they are both mostly complete as well. The blades of the scapulae are about 22.5 cm (225 mm) long, and also quite slender, with barely any expansion. They are curved instead of straight. The scapula is placed in a relatively high position. Two coracoids are also preserved, although they differ more than the scapulae in morphology. The right coracoid is the better preserved of the two. The coracoid is not specially enlarged. Thefurcula is elongated and narrow, its branches placed at an angle of 104°. It is V-shaped and possesses a small hypocleidium at the front. The arm as a whole is not especially developed in length but shows signs of an increasing robustness. The humerus has a rather short triangular deltopectoral crest. The epicondyles are exceptionally thick, indicating a strong musculature. Theulna is lightly curved.[13][4]
The hand is rather long but not very robust, with in general an elongatedmetacarpus, although the firstmetacarpal is short. The first finger diverges from the second finger, the longest of the hand. The third finger is very thin. The hand claws are moderately curved, rather pointed, and moderately long. The vertebrae of the back have below their front extensions, theprezygapophyses, a groove which is divided in three smaller depressions. On the thumb claw the raised attachment point for the tendon of the extensor muscle is bordered by deep grooves forligaments. The middle vertebrae of the back have a second ridge extending from the base of the upper rib joint, thediapophysis, to the back of the vertebra. In the arm, the shaft of thehumerus is reinforced by powerful, somewhat obliquely placed, thickenings extending towards thecondyles of the lower joint, which swellings have a hollow front edge. The front edge of the hip joint has a prominent swelling, pointing sideways to the back, on thepubis. In the pelvis theilium was by a moderate inclination partly adapted to a more raised position of the trunk. The pelvis was propubic or mesopubic: thepubic bone pointed more or less forwards. The leg was relatively long and adapted to running, with the lower leg longer than the thighbone. In the foot there were three weight-bearing toes. The first toe did not reach the ground nor did the firstmetatarsal touch the ankle.[13][4]
The describers in 2005 assignedFalcarius to theTherizinosauroideasensu of Zhang, in a basal position.[3] Zanno later placed it as the basalmost taxon in the Therizinosauria, just outside of Therizinosauroideasensu of Sereno.[5]
Because of the primitive position and relative completeness ofFalcarius, it is a good taxon to use to compare to related groups and descendant taxa.Falcarius resembles dinosaurs belonging to theTherizinosauridae, part of the groupManiraptora.Falcarius itself probably does not belong to this former group, although it does belong to the more inclusive groupTherizinosauria. The group is characterized by wider hips, a comparatively largebraincase and long necks typical of plant eaters. The less basal Asian specimens were covered in quill-likefeathers; this is assumed forFalcarius as well.[5] In generalFalcarius can be seen as atransitional form between the original theropod build and the more derivedTherizinosauridae.Falcarius shared some derived traits with the therizinosaurids: it had a long neck, small head with teeth adapted for eating plant material, a more robust arm with large hand-claws and a more vertical position of the body. On the other hand, it resembled more typical theropods in having a long tail, a propubic pelvis, a long lower leg and a foot whose innermost toe did not reach the ground.[4]
Thecladogram below shows the results of a phylogenetic analysis of Therizinosauria performed by Yoshitsugu Kobayashi and team in 2022, based on their description ofParalitherizinosaurus.Falcarius is recovered as the basalmost therizinosaurian taxon:[14]
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