Жоғалған қырқыш құйрықты динозаврлар тұқымдасы

Extinct family of dinosaurs

Therizinosauridae (meaning 'scythe lizards') is an extinct family of derived (advanced) therizinosauroid dinosaurs whose fossil remains have been found in mostly Late Cretaceous boundary. Even though representative fossils have only been found throughout Asia and North America, the range of Therizinosauridae is believed to have spanned much of the supercontinent of Laurasia based on several footprints and isolated remains in Europe and Africa. Currently, Therizinosauridae comprises eight described and named taxa. Therizinosauridae was named in 1954 by paleontologist Evgeny Maleev after the large, claw bearing unguals of the type species Therizinosaurus cheloniformis. Therizinosaurids were generally large and very robustly built animals that had a near convergent body plan with the more recent (and also extinct) ground sloths. The largest genera of the group are Therizinosaurus and Segnosaurus, which were about and long, respectively. The physiology of therizinosaurids include a broad and rounded belly supported by a wide and robust pelvis with thick hind limbs composed of very stout, four toed feet, a strong arm build with enhanced hand flexibility, elongated hand claws, and a highly derived, nearly avian inner ear. Traits that are also well known include an elongated neck, a prominent keratinous beak and a prosauropod like dentition that differs from all theropods. In addition, therizinosaurids are estimated to have had more advanced feathers in comparison to primitive therizinosaurs (Beipiaosaurus or Jianchangosaurus). The unique and bizarre features of the group has encouraged research into the paleobiology and paleoecology of the family. A fair portion of modern research has concentrated on the feeding patterns of these dinosaurs, as they are considered to be the best regarded theropod candidates for herbivory. While other theropod groups are fully carnivorous, members of Therizinosauridae diverged and adopted an herbivorous and possibly omnivorous lifestyle. This is even more supported by their unusual morphology. As indicated by their feet morphology and several footprints from Asia, Africa and Europe, they probably were plantigrade walkers, but further examination may be required. Therizinosaurids were oviparous animals that nested in colonies and laid egg clutches. In fact, therizinosaur eggs are particularly common in Late Cretaceous formations, mainly in Asia. The oofamily Dendroolithidae is often attributed to therizinosaur grade dinosaurs. Some of the first dendroolithid eggs were found on the Bayan Shireh and Nanchao formations. Their relationships were confusing and obscure on the early years of research mainly because of the unusual traits among members. Several alternative classifications were proposed (such as the naming of Segnosauridae in 1979) until more complete specimens and other taxa were described during the 1990s, which confirmed them as theropods. Many of the shared characters within the group also showed that Segnosauridae was a junior synonym of the much earlier family Therizinosauridae. The current phylogenetic consensus is that therizinosaurids evolved from small, bird like maniraptorans, and thus they fall within the coelurosaurian clade called Maniraptora. Moreover, most of the traits of therizinosaurids (such as the ear structure) were inherited by smaller, agile, carnivorous ancestors. Extensive phylogenetic analyses have concluded that within Maniraptora, therizinosaurs were the first of five major groups to diverge.

The first definitive therizinosaurid discovered was Therizinosaurus. The fossil remains were discovered in 1918 during Mongolian field expedition on the Nemegt Formation of the Gobi Desert. Several claws were unearthed by the team and later described by the Soviet paleontologist Evgeny Maleev in 1954. The claws were unusually large, approximately long if restored, very straight and flattened. Maleev considered that the claws belonged to a giant marine turtle and named the new genus and species Therizinosaurus cheloniformis, also erecting the Therizinosauridae to include the new species. The Mongolian paleontologist Altangerel Perle described and named the new genus Segnosaurus in 1979, based on lower jaws and much of the hindlimbs. He also coined the newer Segnosauridae (now synonym of Therizinosauridae) to contain this species. In the same year, paleontologist Dong Zhiming described the genus Nanshiungosaurus, but wrongly interpreted the remains to have pertained to some kind of dwarf sauropod. In the following year, Barsbold and Perle coined the family Segnosauria (now Therizinosauria) to contain the Segnosauridae and kin. Also, they named and briefly described Erlikosaurus, a new genus smaller than Segnosaurus. Confusingly, Perle redescribed Erlikosaurus treating the taxon as a new genus and species in 1981. Also, Perle described another specimen of Therizinosaurus in 1982, this time a partial hind limb. He referred the hindlimb to the genus based on the similarities with Segnosaurus. In 2001, the new therizinosaurids Neimongosaurus and Nothronychus (N. mckinleyi) were described and named, and in the following year Erliansaurus was also described and named. Although a new species of Nothronychus (N. graffami) was named in 2009. With this, both species make Nothronychus the most complete therizinosaurid known.

Therizinosaurids were quite advanced and robustly built animals that reached multi ton dimensions which make them among the largest maniraptorans. The smallest known therizinosaurids are Erliansaurus, Erlikosaurus and Neimongosaurus which were around long, furthermore the holotype skull of Erlikosaurus is about Segnosaurus and the possible therizinosaurid Suzhousaurus were about the same size, in length and weighing Slightly smaller members are represented by Nanshiungosaurus and Nothronychus, estimated at long and in weight, respectively. The related "Nanshiungosaurus" bohlini was similar in size (about long), however, its assignment to Nanshiungosaurus is unlikely and it may or not represent another species or specimen of the better known Suzhousaurus. Therizinosaurus were the largest representatives, reaching the top dimensions of the group, they grew up to long weighing over These dimensions that make the genus among the largest known theropods. Skin impressions from Beipiaosaurus and Jianchangosaurus indicate that primitive therizinosaurs were covered with a coat of down like, sparse feathers similar to those seen in the compsognathid Sinosauropteryx, as well as longer, simpler, quill like feathers that may have been used in display. However, while the earliest known example of primitive, stage I feathers are found among early therizinosaurs, more advanced members are thought to have possessed more developed, avian like feathers. Although typically associated with flight, the feathers which covered these animals were not used for that purpose, instead, they assisted in either metabolism or display.

Therizinosaurids had more specialized skulls compared to primitive members such as Falcarius, which had a generalist, beak less snout. They had relatively elongated snouts and the tip was covered with a rhamphotheca (keratinous beak) used during feeding. Although the extension of the beak on the dorsal surface of the snout is unknown, it is estimated that it slightly overlapped the nasal cavity as in some modern day birds. The dentary (lower jaw) also developed a rhamphotheca, seen on the edentulous (without teeth) anterior most end. This extension was supplied by neurovascular foramina (small pits) found on the lateral surfaces. The known specimens of the therizinosaurids Erlikosaurus, Neimongosaurus and Segnosaurus preserve numerous neurovascular foramina (more notorious on Erlikosaurus), indicating that a well developed beak was present in life.

In therizinosaurids, the shoulder girdle was robustly specialized than in other maniraptorans and less bird like. The scapula (shoulder blade) was very straight and flattened at the upper end being fused to the coracoid bone, forming the scapulocoracoid. Near the region of the scapulocoracoid suture, on the coracoid, a large foramen is present. The coracoid is a wide and broad element that is slightly convex and thickened near of the scapulocoracoid suture. The humerus (upper arm) was exceptionally robust and flexible with wide lower ends as seen on the humeri of the therizinosaurids Nothronychus and Therizinosaurus. Not only that but the biceps muscle was prominently well developed in Therizinosaurus. The vertebral column was highly pneumatized (air spaced) and is relatively well documented from several badly to well preserved elements among genera but specimens of Nanshiungosaurus and Nothronychus preserve the most complete series of vertebrae. Parallel to this, the newly and also described Nanshiungosaurus was assigned to the Titanosaurinae by Dong Zhiming based on the assumption it was a sauropod genus. In 1988 he suggested a segnosaurian classification for the therizinosaurids Therizinosaurus. In a review article on the book The Dinosauria in 1990, Barsbold and Teresa Maryańska considered Segnosauria to be an enigmatic group of saurischians with a position subject to change. They, however, disagreed with Therizinosaurus as a segnosaurian taxon since it was known from forelimb material; they corroborated the referred hindlimb material as segnosaurian though. Lastly, Barsbold and Maryańska noted the striking similarities between the pelvises of Nanshiungosaurus and Segnosaurus, such as the opisthopubic condition and large iliac blade. They concluded that the former was part of the Segnosauridae. With the description of the therizinosauroids Alxasaurus in 1993 by Dale A. Russell and Dong Zhiming, the affinities of the group were fairly more clear. This new taxon represented the most complete member and was known from multiple specimens with numerous theropod traits. Moreover, the preserved hindlimbs in some specimens showed that the assignment of segnosaurian hindlimbs to Therizinosaurus was correct and "segnosaurs" were in fact theropods. Russell and Dong also noted the extreme similarities between Therizinosauridae and Segnosauridae and considered that the latter was a synonym of the former due to priority. However, Alxasaurus was a fairly more primitive genus and the superfamily Therizinosauroidea was coined to contain it and related species. Posterior to this year, Clark and colleagues redescribed the holotype skull of Erlikosaurus and found more theropod traits than when first described. They concluded that therizinosaurs were more likely to be classified as maniraptoran theropods. Therizinosauria itself, was erected in 1997 by Rusell in order to contain all of these theropods. This new infraorder was composed of Therizinosauroidea and the more advanced Therizinosauridae. The family Therizinosauridae was first given a phylogenetic definition by Paul Sereno in 1998, who defined it as all dinosaurs closer to Erlikosaurus than to Ornithomimus. In 2010, Lindsay Zanno conducted the most detailed phylogenetic analysis of the Therizinosauria to that point. She cited the inaccessibility, damage, potential loss of holotype specimens, scarcity of cranial remains, and fragmentary specimens with few overlapping elements as the most significant obstacles to resolving the evolutionary relationships within the group. The position of Segnosaurus and those of some other Asian therizinosaurids was affected by these factors; Zanno stated more well preserved specimens and the rediscovery of missing elements would be necessary. Zanno also revised Therizinosauroidea to exclude Falcarius and retained it in the wider clade Therizinosauria, which became the senior synonym of Segnosauria. In addition, she defined Therizinosauridae as the least inclusive clade containing Erlikosaurus, Nothronychus, Segnosaurus and Therizinosaurus. Falcarius and Jianchangosaurus are now regarded as the most primitive therizinosaurs while therizinosauroids are considered to be more derived that these two taxa, but less derived than therizinosaurids.

In 2009, Zanno and colleagues stated therizinosaurs were the most widely regarded candidates for herbivory among theropods based on the small, densely packed, coarse serrations; lance shaped teeth with a relatively low replacement rate; a well developed keratinous beak; long neck for browsing; relatively small skulls; a very large gut capacity as indicated by the rib circumference at the trunk and the outwards flaring processes of the ilia; and the notable lack of cursorial adaptations in the hind limbs. All of these features suggest that members of this family feed on vegetation, as well as pre processing it within their mouths to begin the breakdown of cellulose and lignin. This is perhaps even more so true for therizinosaurids, which seem to have further exploited these characters. One of the most notable adaptations in advanced therizinosaurids are the four toed feet, which had a fully functional, weight bearing first digit that was likely adapted to slow life style. Zanno and colleagues found that Ornithomimosauria, Therizinosauria, and Oviraptorosauria had either direct or morphological evidence for herbivory, which would mean either this diet evolved independently multiple times in coelurosaurian theropods or that the primitive condition of the group was at least facultative herbivory with carnivory only emerging in more derived maniraptorans. As indicated by their respective dental morphologies, the contemporaneous therizinosaurids Erlikosaurus and Segnosaurus were separated by niche partitioning. These differentiations include the relatively indistinct and symmetrical teeth with moderate serrations (denticles) in Erlikosaurus, and the enlarged serrations in Segnosaurus composed of additional carinae and folded carinae with denticulated front edges, which together created a roughened, shredding surface near the base of the tooth crowns that was apparently unique to Segnosaurus and suggest they consumed unique food resources or used highly specialized feeding strategies, and had a higher degree of oral food processing than other therizinosaurids. During the same year, Ali Nabavizadeh concluded that most therizinosaurs were mainly orthal feeders (moving their jaws up and down and not to the sides) and raised their jaws isognathously whereby the upper and lower teeth of each side contacted each other at once. However, advanced Late Cretaceous therizinosaurids had relatively weak bite forces compared to primitive therizinosaurs. In 2013 the paleontologist Stephan Lautenschlager performed digital reconstructions for the cranial musculature in Erlikosaurus and found the bite force of Edmontosaurus being greater than that for the former. The lesser bite force for Erlikosaurus better served in stripping and cropping leaves, rather than active mastication. On a newer study with more therizinosaur taxa, Lautenschlager found similar conclusions. The evolutionary trends in jaw mechanics of therizinosaurs noticed a change in bite force through time, from higher bite forces in early members to lesser ones in the advanced therizinosaurids. Therizinosaurids were aided by the down turned tip and symphyseal regions (union between bones) of the dentaries, and probably also by beaks. By contrast, the straighter and more elongated dentaries of primitive therizinosaurs had the highest magnitudes of stress and strain. A downwards pulling motion of the head while gripping vegetation was more likely than a sideways or upwards movement, though such behavior would be more likely in therizinosaurids with their stress mitigating jaws.

Among therizinosaurids, the forelimbs were increased in robustness and the flexibility of the wrist was increased as well, with this, the presumed reach for foraging is likely to have lengthened. Moreover, the pectoral girdle has been modified to further augment upright reach, however the grasping ability of the animals is thought to have decreased. These adaptations are more linked to assist with their herbivorous lifestyle, as they have specialized the ability to harvest and collect vegetation. In 2014, Lautenschlager tested the biomechanical function of multiple therizinosaur claws. He noted that the hands of some therizinosaurids (such as Nothronyhus or Therizinosaurus) were more effective when piercing or pulling down vegetation. The arms would have had to be able to extend the range of the animal to a point that could not be reached by the head if they were used for browsing and pulling down vegetation. In genera where both neck and forelimb elements are preserved, however, the necks were equal in length or longer than the forelimbs, so pulling vegetation would only be likely if lower parts of long branches were pulled down to access out of reach vegetation. Lautenschlager also found that therizinosaurid claws would not have been used for digging, which would have been done with the foot claws because, since as in other maniraptorans, feathers on the forelimbs would have interfered with this function. Additionally, this action leads to a higher stress tension on the dorsal area of the claw−this is more evident in Therizinosaurus. However, he could neither confirm nor disregard that the hand claws could have been fully used for sexual display, self defense, intraspecific competition, mate gripping during mating or grasping stabilization when foraging.

The group is also notable for adaptations to the structures of their ear. The structure of their inner ear is almost avian, with bird like semicircular canals and an extended cochlea. For birds, an extended cochlea allows them to hear across an increased range of frequencies, suggesting a similar function in the ponderous therizinosaurids and also allowing them a good hearing and balance, which indeed, are traits better associated with carnivorous theropods. Furthermore, the lengthening of the cochlea, an adaptation which has independently evolved in a number of other theropod groups, is thought to further improve auditory acumen. The forebrain of therizinosaurids was fairly enlarged and developed with elongated olfactory bulbs. The adaptations to the inner ear and forebrain of therizinosaurids likely served a number of functions, such as well developed senses of smell, complex social behavior, increased alertness to the vocalizations of juveniles or even communicating with conspecifics, moreover, the large pneumatic chambers on the sensorial areas in the skulls of therizinosaurids (Erlikosaurus or Nothronychus mckinleyi) indicates that the tympanic systems would result in increased and optimal low frequency sound reception, possibly infrasound. Such is the case of N. mckinleyi, which had an average hearing frequency of 1100 to 1450 Hz and possible upper limits between 3000 and 3700 Hz. Features include not only extensive basicranial pneumaticity, but also the development of a basisphenoid bulla (hollow bony structure). In addition, the orientation of the horizontal semicircular canal relative to the horizontal orientation of the occipital condyle gave therizinosaurids a horizontal head posture that enabled binocular vision with overlapping visual fields. A vast majority of these senses were also well developed in earlier coelurosaurs and other theropods, indicating that therizinosaurids inherited many of these traits from their small, carnivorous maniraptoran ancestors and retained the ancestral, carnivorous ear configuration to be used for their different and very specialized dietary purposes.

In 1964, Zakharov described and named the particular ichnogenus Macropodosaurus, which is represented by a series of four toed footprints. These tracks were found in beds of the Cenomanian age at Tajikistan, noting that they were made by a bipedal four toed dinosaur and the toes were webbed or at least, very fleshy. It is unlikely that these were made by a quadrupedal animal since no manual footprints were found in association. The footprints are about long and wide. Since the research of therizinosaurs started posterior to these findings, Zakharov was not able to determine the exact type of dinosaur. Sennikov in 2006 re examined these footprints and concluded that a therizinosaurid grade dinosaur could have made those tracks. He compared Macropodosaurus with the articulated feet of Erlikosaurus and the referred one from Therizinosaurus revealing that when articulated in a plantigrade position they fit in the morphology of Macropodosaurus. Therefore, he considered these tracks to be more associated with therizinosaurids and was one of the first in propose a plantigrade stance in therizinosaurids. An additional Macropodosaurus grade footprint was discovered in Poland and first reported in 2008. This footprint is reminiscent of the tracks described by Zakharov and therefore assigned to Macropodosaurus sp. These tracks could indicate the presence of therizinosaurs in Europe. In 2017 Masrour with colleagues reported Macropodosaurus footprints in what is now Morocco. They are similar to the original description with some degree of semiplantigradism. However, several other footprints may indicate a more digitigrade stance. Such is the case the footprints from the Cantwell Formation labelled under the numbers DMNH 2010 07 01, 2013 08 04, 2013 08 06 and 2014 11 05. These impressions are composed by four toes with the first digit slightly smaller than the others which is attributed to therizinosaurids. At least one footprint, DMNH 2010 07 01, was directly compared to the relatively complete right pes of Erlikosaurus revealing a consistent morphology. However, most of the footprint was made (apparently) by the fingers and a foot pad, indicating a more upright position of the metatarsals. Nevertheless, Botelho and colleagues have also considered a plantigrade stance for therizinosaurids in 2016. Accordingly, members of the Therizinosauridae (such as Neimongosaurus or Nothronychus) re evolved a fully functional first digit that articulates to the ankle.

Some of the first dendroolithid eggs—which are attributed to therizinosaurs—were reported from the Bayan Shireh and Nanchao formations on the same year, 1997. These consisted of several egg clutches (a group) with an average composition of 7 or more eggs. In addition, the Bayan Shireh Formation has produced fully grown, specific therizinosaurid taxa, such as Erlikosaurus and Segnosaurus. However, in 2007 these were described by paleontologist Martin Kundrát and colleagues and tentatively identified as therizinosaurids based on anatomical features such as the tooth less premaxilla with a downturned edge, dentary with a lateral shelf, teeth with leaf shaped crowns, humerus with a prominent deltopectoral crest, ilium with an expanded anterior end, and the elongated, sharply pointed manual unguals. Most eggs have an average size of and given these dimensions, they likely were laid by a medium sized female. Although several egg clutches were found, one was found containing 7 eggs of which 3 of them were preserving the embryos. In 2019, Hartman and colleagues were the first authors to include these embryos in a phylogenetic analysis and as expected, the embryos were recovered as therizinosaurids. This nesting site was formally described in 2019 by Kohei Tanaka and colleagues. In this comprehensive description, the amount of egg clutches was corrected to at least 15, noting that the eggs were laid in clutches composed of 3 to 30 eggs and hatched in the same single nesting season. The eggs have an average diameter of with some variations between and Based on the smooth outer surface, both inner and outer portions, and several irregular shaped pore canals of these eggs, they were corroborated to pertain to the Dendroolithidae. Approximately the 50% of the nesting area has been eroded, and based on the egg clutches distribution, the nest density can be estimated around 1 nest per 10 m2. This indicates that up to 32 nests were originally present. The habitat that the parents nested in was a semi arid flood plain and the egg clutches were covered in organic rich material during incubation as some extant archosaurs do today (crocodiles and megapode birds). In addition, the egg shell fragments association indicates that many of the clutches hatched before the site was buried by a flood event. Out of a total of 15 clutches, at least 9 successfully hatched, which represents a nesting success rate of at least 60% for the entire site. The prominent nesting site of the Javkhlant Formation indicates that colonial nesting first evolved in non avian dinosaur species to increase hatching success in ecosystems subject to high nest predation pressure (such as this formation). Lastly, though dendroolithid eggs are also attributed to megalosauroids, and therizinosaurids are not known from the Javkhlant Formation, it overlies the Bayan Shireh Formation, where other dendroolithid eggs and the therizinosaurs Enigmosaurus, Erlikosaurus and Segnosaurus were found. Moreover, the absence of megalosauroids on these formations is notable. As reflected by at least 31 therizinosaurid footprints at the Cantwell Formation of Alaska, some species formed small herds, which is consistent with the complex brain and ear structure in these theropods. The co occurrence with hadrosaurids on this area may also indicate that these very different dinosaurs benefited from an ecological interaction, just as some animals today congregate for mutual beneficial reasons, such as augmented resource acquisition or lesser predation pressure. It is also possible that a herd of hadrosaurids and therizinosaurids walked across this terrain at different times and did not encounter each another. Regardless of these explanations, the therizinosaurid trackway reflects a gregarious behaviour in these theropods. the relatively complete remains of Nothronychus have been found outside Asia in North America. Though the fossil record of therizinosaurids indicates that the family flourished near the Turonian stage of the Late Cretaceous, by the Barremian stage there was already a pan Laurasian distribution of therizinosauroids. Since Laurasia was beginning to break apart during the Cretaceous, two theories have arisen to explain how therizinosaurs could have spanned across Laurasia. One theory is that primitive members were already present in both Asia and North America before it began to drift apart, suggesting an emergence for therizinosaurs of at least the Late Triassic. A second theory is that the group dispersed between Asia and North America via a "Cretaceous" Beringian land bridge during the Berriasian Valanginian stages. This last proposal is supported by the presence of therizinosaurids in North America during the early Late Cretaceous such as Nothronychus. Nevertheless, therizinosaurid grade footprints are known from remote locations such as Europe or Africa. Several four toed tracks were found in Poland, and a series of footprints dating back to the Late Cretaceous were found in Morocco. Both findings may indicate that therizinosaurids were far more disperse than previously thought. The idea of a land bridge is even more supported by the multiple co occurrence of hadrosaurid and therizinosaurid footprints at the lower Cantwell Formation of the Denali National Park, which reflects an important faunal exchange between landmasses. These tracks show the dominant presence of hadrosaurids and a reduced concentration of therizinosaurids in the same location at potentially the same time. As indicated by the discovery of a waterlily like impression representing a single fossil leaf from the same site, the trackway was made by the dinosaurs as they crossed a shallow body of water away from the main river channels, which is curious given that during the Late Cretaceous this part of North America was a semi arid habitat. This occurrence at this single locality within the lower Cantwell Formation has not been documented elsewhere in North America and these trackways represent the first reported encounter between notoriously different dinosaurs from North America. The diversity of the ichnotaxa in this site supports the idea of similar dinosaur faunas between Alaska and Asia during the Late Cretaceous period, specifically with the Nemegt Formation which had relatively wet environments. Fiorillo and colleagues suggested that Alaska represented a "gateway" for faunal exchange between the two continental landmasses and the existence of a "Cretaceous" Beringian land bridge further allowed this mixing of faunas, which was encouraged as similar habitats were present within Asia and North America.