Misplaced Pages

#648351

109-653: Limusaurus is a genus of theropod dinosaur that lived in what is now China during the Late Jurassic , around 161 to 157 million years ago. The type and only species Limusaurus inextricabilis was described in 2009 from specimens found in the Upper Shishugou Formation in the Junggar Basin of China . The genus name consists of the Latin words for "mud" and "lizard", and

218-573: A joint and therefore the presence of a phalanx; it is likely that this was the only phalanx of the fourth finger. The unguals (claw bones) of the fingers were short, stout , and expanded at their base. They had two grooves on their sides, a feature also found in Masiakasaurus . Among the pelvic bones , the ilium was small and tilted towards the midline of the body, as was the case in Elaphrosaurus . As in other ceratosaurians,

327-457: A "frameshift" of the digits; the first digit fails to grow in the first developmental site due to not receiving the necessary signals, which has the effect of shifting digits I-III to the positions of II-IV. Thus, while digits I-III from the ancestral theropod are retained, they do not grow in the same location. A version of the frameshift hypothesis modified to incorporate both elements of BDR and fossil evidence from Limusaurus and other theropods,

436-571: A beak with age. Several of these features were convergently similar to the later ornithomimid theropods as well as the earlier non-dinosaurian shuvosaurids . Limusaurus was the first known member of the group Ceratosauria from Asia. It belonged to the Noasauridae , a family of small and lightly built ceratosaurs , along with its closest relative Elaphrosaurus . The pattern of digit reduction in Limusaurus has been used to support

545-427: A fully-fledged finger, with II-IV taking on the morphologies of the former I-III. In a 2009 response to Xu and colleague's description of Limusaurus , biologist Alexander Vargas, Wagner and Gauthier stated in 2009 that it is plausible that ceratosaurians underwent BDR independent of the tetanurans, and therefore have no bearing on the issue of avian digit homology. Xu and colleagues replied in 2011 that they still found

654-407: A genus is determined by taxonomists . The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. There are some general practices used, however, including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful: Moreover, genera should be composed of phylogenetic units of

763-494: A group) by Dal Sasso and colleagues in 2018 also found that the digit reduction seen in Limusaurus occurred independently from that in tetanurans. According to this analysis, an axis shift from digit position IV to III took place at the basis of Tetanurae after the fourth finger was lost. Specimens of Limusaurus show 78 different anatomical changes that occurred as the animals grew. In particular, their heads became proportionally shallower, their middle hand bones lengthened, and

872-496: A highly viscous sediment and got preserved in their original death positions, the mud pits containing Limusaurus were of a more liquid mud in which the carcasses floated before settling at the bottom. The size of these assemblages can be attributed to the tendency of smaller animals to become trapped in mud. Limusaurus is the most abundant dinosaur found in the mud pits. One of the three pits, TBB2001, contained five Limusaurus individuals while other species are absent. TBB2002, on

981-651: A later homonym of a validly published name is a nomen illegitimum or nom. illeg. ; for a full list refer to the International Code of Nomenclature for algae, fungi, and plants and the work cited above by Hawksworth, 2010. In place of the "valid taxon" in zoology, the nearest equivalent in botany is " correct name " or "current name" which can, again, differ or change with alternative taxonomic treatments or new information that results in previously accepted genera being combined or split. Prokaryote and virus codes of nomenclature also exist which serve as

1090-628: A long time and redescribed as new by a range of subsequent workers, or if a range of genera previously considered separate taxa have subsequently been consolidated into one. For example, the World Register of Marine Species presently lists 8 genus-level synonyms for the sperm whale genus Physeter Linnaeus, 1758, and 13 for the bivalve genus Pecten O.F. Müller, 1776. Within the same kingdom, one generic name can apply to one genus only. However, many names have been assigned (usually unintentionally) to two or more different genera. For example,

1199-419: A matter of debate for almost 200 years, and has been used by paleornithologist Alan Feduccia to support the hypothesis that birds are descended not from theropods but from some other group of archosaurs which had lost the first and fifth digits. The mainstream view of bird origins among paleontologists is that birds are theropod dinosaurs. To explain the discrepancy between morphological and embryological data in

SECTION 10

#1732794138649

1308-415: A more basal position. A 2019 study by paleontologist Max Langer and colleagues, which was based on the same data set used by the 2016 study, also grouped Limusaurus together with Elaphrosaurus and CCG 20011. Argentinian paleontologist Mattia Baiano and colleagues, in 2020, found Limusaurus to form a clade with Elaphrosaurus as well as with the new genus Huinculsaurus . To test the influence of

1417-680: A number of traits, including the beak and the fused sternum, convergently with the later coelurosaurs. A 2012 study by paleontologists Diego Pol and Oliver Rauhut also found Limusaurus and Elaphrosaurus to be basal ceratosaurians in their phylogenetic analysis , while a 2010 study by paleontologist Martin Ezcurra and colleagues placed them in the more derived group Abelisauroidea within Ceratosauria. A 2016 study by paleontologists Oliver Rauhut and Matthew Carrano found Limusaurus to be more derived, grouping together with Elaphrosaurus within

1526-411: A possible land connection between Asia and other continents during that period. Biologist Josef Stiegler and colleagues stated in a 2014 conference abstract that Limusaurus is the earliest known toothless theropod, as well as the only non-bird theropod known to have had strong bilateral reduction of its digits (as the outer fingers were reduced in size). The most basal theropods had five digits in

1635-401: A prominent ridge at its front edge. It also had a comparatively high acromion process . The sternum was fused into a single, large, continuous plate, another feature that evolved independently in coelurosaurs (convergent evolution). Limusaurus also had a furcula , or wishbone, which previously was unknown among ceratosaurians. The head of the humerus (upper arm bone) was bulging, and

1744-477: A reduced first digit, with these researchers hypothesizing that a similar pattern of reduction occurred among the tetanurans (the sister group of the ceratosaurians). Several other hypotheses have been proposed to improve upon and reconcile the LDR and BDR hypotheses. One predominantly favored hypothesis, first developed by evolutionary biologist Günter P. Wagner and paleontologist Jacques Gauthier in 1999, involves

1853-409: A reference for designating currently accepted genus names as opposed to others which may be either reduced to synonymy, or, in the case of prokaryotes, relegated to a status of "names without standing in prokaryotic nomenclature". An available (zoological) or validly published (botanical) name that has been historically applied to a genus but is not regarded as the accepted (current/valid) name for

1962-411: A step-wise shift more plausible than a hidden frameshift. As demonstrated by a teratological analysis by biologist Geoffrey Guinard in 2016, the abbreviation ( mesomelia ) and loss of digits ( hypophalangia ) in the forelimb of Limusaurus is likely the result of a developmental anomaly that appeared exclusively in and persisted throughout the evolutionary lineage of ceratosaurians, and is unconnected to

2071-427: A taxon; however, the names published in suppressed works are made unavailable via the relevant Opinion dealing with the work in question. In botany, similar concepts exist but with different labels. The botanical equivalent of zoology's "available name" is a validly published name . An invalidly published name is a nomen invalidum or nom. inval. ; a rejected name is a nomen rejiciendum or nom. rej. ;

2180-455: A total of c. 520,000 published names (including synonyms) as at end 2019, increasing at some 2,500 published generic names per year. "Official" registers of taxon names at all ranks, including genera, exist for a few groups only such as viruses and prokaryotes, while for others there are compendia with no "official" standing such as Index Fungorum for fungi, Index Nominum Algarum and AlgaeBase for algae, Index Nominum Genericorum and

2289-560: Is comparable to the diet shift experienced by the aforementioned mullets and armored catfish. The paleontologist David A. Eberth and colleagues suggested in 2010 that the large number of Limusaurus specimens in the Shishugou Formation mud pits indicates they were either abundant among the small vertebrate animals in the area, or that the trapped individuals had been drawn there. They found it unlikely that animals were trapped on any basis other than size, and pointed out that it

SECTION 20

#1732794138649

2398-612: Is discouraged by both the International Code of Zoological Nomenclature and the International Code of Nomenclature for algae, fungi, and plants , there are some five thousand such names in use in more than one kingdom. For instance, A list of generic homonyms (with their authorities), including both available (validly published) and selected unavailable names, has been compiled by the Interim Register of Marine and Nonmarine Genera (IRMNG). The type genus forms

2507-502: Is estimated to have been about 1.7 m (5 ft 7 in) in length and the weight of the animal has been estimated at 15 kg (33 lb). One adult specimen is estimated to have been 15% larger than the holotype. Several features of the animal, such as the small head with large orbits (eye openings), toothless jaws, and the long neck and legs, were very similar to those of the Cretaceous ornithomimid theropods, as well as

2616-418: Is in accordance with the presence of genetic signal pathways (molecular processes) which control the formation of teeth in birds. Wang and colleagues analyzed growth rings (visible in bone cross-sections and analogous to the growth rings of trees ) of the tibiae from the various developmental stages of Limusaurus in 2017, and found that the animal was skeletally mature at six years of age. The bone tissue

2725-504: Is known as the external fundamental system), indicating that rapid growth had ceased in these individuals. Anatomical features of Limusaurus such as the small head with toothless jaws and long neck were interpreted as indicating a herbivorous diet by Xu and colleagues in 2009. Paleontologist Lindsay E. Zanno and colleagues found in 2011 that adult specimens of Limusaurus show morphological traits associated with herbivory that are shared with other groups of herbivorous theropods, including

2834-433: Is missing its skull and hands among other elements, and its affinities were long unclear (it was often considered an ornithomimosaur from 1928 well into the 1990s) until the more complete Limusaurus was found. The discovery of Limusaurus allowed the extrapolation of the complete length of Elaphrosaurus , 6.0–6.3 m (19.7–20.7 ft). Wang and colleagues, in 2017, also found Limusaurus and Elaphrosaurus to group in

2943-431: Is no direct contact between bones of separate individuals. This indicates that sediment settled within the mud pits between the burial events. These observations led Eberth and colleagues to conclude that the skeletons must have accumulated within the mud pits over an extended time span rather than during a short-term death event. The completeness and articulation (connectedness) of the skeletons suggest rapid burial, though

3052-781: Is possible Limusaurus lived in groups. Its fossils were discovered in rocks dated to the Oxfordian age. Specimens of Limusaurus (along with other small animals) appear to have been mired in mud pits created by the footprints of giant sauropod dinosaurs. Between 2001 and 2006, a Chinese-American team of paleontologists examining the Wucaiwan locality in the Shishugou Formation , in the northeastern Junggar Basin of Xinjiang , China, discovered three bone beds (numbered TBB 2001, TBB 2002, and TBB 2005, found by T. Yu and J. Mo). The bone beds were dominated by

3161-410: Is present in embryos, and in adult forms of some species; in most species including dinosaurs, centra are more ossified with the notochordal opening closed, improving resistance against compressional forces. Heterocoelous vertebrae allow flexibility while preventing rotation. Procoelous and opisthocoelous centra form concavo-convex ( ball and socket ) joints, where the convex end, the condyle , fits into

3270-460: Is somewhat arbitrary. Although all species within a genus are supposed to be "similar", there are no objective criteria for grouping species into genera. There is much debate among zoologists about whether enormous, species-rich genera should be maintained, as it is extremely difficult to come up with identification keys or even character sets that distinguish all species. Hence, many taxonomists argue in favor of breaking down large genera. For instance,

3379-474: Is the type species , and the generic name is permanently associated with the type specimen of its type species. Should the specimen turn out to be assignable to another genus, the generic name linked to it becomes a junior synonym and the remaining taxa in the former genus need to be reassessed. In zoological usage, taxonomic names, including those of genera, are classified as "available" or "unavailable". Available names are those published in accordance with

Limusaurus - Misplaced Pages Continue

3488-420: Is the most extreme case of tooth morphology changing with age recorded among dinosaurs. Limusaurus is one of the few known jawed vertebrates where teeth are completely lost during growth. The other known examples are the red mullet and striped red mullet , several armored catfish , and the platypus . Meanwhile, its complicated pattern of tooth loss, from both the front and the back, is most similar to that of

3597-449: Is underestimated elsewhere as these animals are generally less likely to fossilize. The known fossil material of Limusaurus consists of large assemblages of individuals mired in mud pits, which were also referred to as "dinosaur death pits" in the 2010 article by Eberth and colleagues that examined the taphonomy of the specimens within them (changes that happened during their decay and fossilization), as well as in media reporting. Two of

3706-436: The deltopectoral crest , a forward-directed bony flange of the humerus that served for muscle attachment, was long and angled; these features were typical for ceratosaurians. In the forearm, the radius was longer than the ulna , and the olecranon process , a bony extension on the upper end of the ulna that served for muscle attachment, was absent in Limusaurus . Both features are considered distinctive features of

3815-518: The Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing : the holotype (a subadult cataloged under the specimen number IVPP V 15923) is an almost complete and articulated (still connected) skeleton, missing only the hindmost tail vertebrae, and is preserved next to another specimen (a large juvenile, IVPP V 20098) which is missing the front part of

3924-621: The International Code of Zoological Nomenclature ; the earliest such name for any taxon (for example, a genus) should then be selected as the " valid " (i.e., current or accepted) name for the taxon in question. Consequently, there will be more available names than valid names at any point in time; which names are currently in use depending on the judgement of taxonomists in either combining taxa described under multiple names, or splitting taxa which may bring available names previously treated as synonyms back into use. "Unavailable" names in zoology comprise names that either were not published according to

4033-824: The International Plant Names Index for plants in general, and ferns through angiosperms, respectively, and Nomenclator Zoologicus and the Index to Organism Names for zoological names. Totals for both "all names" and estimates for "accepted names" as held in the Interim Register of Marine and Nonmarine Genera (IRMNG) are broken down further in the publication by Rees et al., 2020 cited above. The accepted names estimates are as follows, broken down by kingdom: The cited ranges of uncertainty arise because IRMNG lists "uncertain" names (not researched therein) in addition to known "accepted" names;

4142-732: The Ornithomimosauria , Therizinosauria , Oviraptorosauria , and Alvarezsauroidea , along with the troodontid Jinfengopteryx . Wang and colleagues pointed out that adult specimens in particular are characterized by the presence of gastroliths (ingested stones retained in the stomach), with older adults having gastroliths that are larger and more numerous than those of younger adults. The size and quantity of these gastroliths are comparable to those of birds in young adults, and those of ornithomimosaurs and oviraptorosaurs in older adults. These groups of theropods all used gastroliths in processing plant matter, suggesting that Limusaurus did

4251-482: The Triassic non-dinosaurian shuvosaurids , representing a significant case of convergent evolution among these three distinct groups of archosaurs . While Limusaurus has sometimes been depicted with feathers and may have had them, there is no direct evidence of such structures. The skull of Limusaurus was relatively tall and short, roughly half the length of the femur (upper thigh bone). The tip of its jaws

4360-500: The avialan Jeholornis . The early halt in tooth replacement possibly resulted from the regression of the replacement tooth buds during the first year, as in the veiled chameleon . The replacement of teeth by a beak through the growth of Limusaurus suggests that beaks in other lineages of theropods, and indeed beaked animals in general, may have evolved heterochronically , i.e. with beaks first occurring in adults and then gradually appearing in juveniles as these lineages evolved. This

4469-418: The cynodont Yuanotherium ; the mammal Acuodulodon ; the crocodyliform Nominosuchus and another unnamed crocodyliform found with the holotype specimen of Limusaurus ; and the turtles Xinjiangchelys and Annemys . Small theropod dinosaurs are generally rare in the fossil record. According to Eberth and colleagues, the high incidence of Limusaurus indicates that the abundance of small theropods

Limusaurus - Misplaced Pages Continue

4578-419: The nomenclature codes , which allow each species a single unique name that, for animals (including protists ), plants (also including algae and fungi ) and prokaryotes ( bacteria and archaea ), is Latin and binomial in form; this contrasts with common or vernacular names , which are non-standardized, can be non-unique, and typically also vary by country and language of usage. Except for viruses ,

4687-404: The platypus belongs to the genus Ornithorhynchus although George Shaw named it Platypus in 1799 (these two names are thus synonyms ) . However, the name Platypus had already been given to a group of ambrosia beetles by Johann Friedrich Wilhelm Herbst in 1793. A name that means two different things is a homonym . Since beetles and platypuses are both members of the kingdom Animalia,

4796-411: The "hook" of their pubis grew longer. The shaft of the quadrate bone in the skull also straightened in adults, and the tips of their lower jaws became more downturned. The most obvious change that happened during the growth of Limusaurus was the complete loss of teeth from juveniles to adults. Juveniles began with one tooth in each premaxilla, eight in each maxilla, and at least twelve in each half of

4905-467: The "thumbs down" hypothesis of biologist Daniel Čapek and colleagues from 2014, suggests that this frameshift took place after the reduction of both the first and the fourth digits in the theropod lineage. The main alternative hypothesis, supported by Xu and colleagues, known as the "lateral shift hypothesis", considers a partial, step-wise frameshift in which, from a four-fingered hand with reduced digits I and IV, I fully disappears while IV develops into

5014-457: The IVPP. The toothless adults and toothed juveniles were initially thought to be different kinds of dinosaurs, and were studied separately, until it was realized they represent the same species. Limusaurus was a small and slender animal. The holotype (which was originally considered an adult based on the level of fusion of its bones, but later as a subadult when analyzed along with other specimens)

5123-433: The Shishugou Formation hosted a diverse assemblage of animals. More than 35 species of vertebrates are known from fossils, including at least 14 dinosaur species. Contemporaries of Limusaurus in the Wucaiwan locality include the theropods Haplocheirus , Zuolong , Guanlong , Aorun , and Shishugounykus ; the sauropod Mamenchisaurus ; the ornithischians Gongbusaurus , Yinlong , and Hualianceratops ;

5232-554: The Shishugou Formation, a succession of sedimentary rocks that were deposited at the northeastern margin of the Junggar foreland basin and is about 350–400 m (1,150–1,310 ft) in thickness. The formation is dated to the Late Jurassic , around 161 to 157 million years ago. Limusaurus occurs in the upper part of the formation, which represents a variety of environments, including alluvial fans and alluvial plains , streams , wetlands , and shallow lakes . During

5341-532: The abelisauroid family Noasauridae. Together with an as-of-yet unnamed taxon represented by specimen CCG 20011, and not included in other analyses, the two taxa formed the clade Elaphrosaurinae ; Elaphrosaurus and CCG 20011 were closer to each other than to Limusaurus within this group. Laevisuchus and Deltadromeus were placed basal to the group of Noasaurinae and Elaphrosaurinae within Noasauridae. The only known specimen of Elaphrosaurus

5450-442: The base for higher taxonomic ranks, such as the family name Canidae ("Canids") based on Canis . However, this does not typically ascend more than one or two levels: the order to which dogs and wolves belong is Carnivora ("Carnivores"). The numbers of either accepted, or all published genus names is not known precisely; Rees et al., 2020 estimate that approximately 310,000 accepted names (valid taxa) may exist, out of

5559-451: The clade Elaphrosaurinae, within the family Noasauridae. Variants of their analysis also recovered Spinostropheus as a possible additional elaphrosaurine. The Noasauridae was placed in a position outside Neoceratosauria , the group containing Ceratosaurus and Abelisauridae . The Italian paleontologist Cristiano Dal Sasso and colleagues, in 2018, found Limusaurus to be closely related to Spinostropheus , while Elaphrosaurus occupies

SECTION 50

#1732794138649

5668-460: The concave end, the cotyle (also: cotyla ). This configuration allows for greater stability without restricting mobility. In long necks and tails, this stabilization works best when the convex part is pointing away from the body. In sauropods, vertebrae in front of the sacrum are therefore typically opisthocoelous, while those of the tail are procoelous. As a vertebral column can contain different types of central morphologies, transitional centra with

5777-513: The context of bird origins, an alternative scenario to LDR was developed by paleontologists Tony Thulborn and Tim Hamley in 1982. In this scenario, the digits I and V of theropods were reduced in the process of Bilateral Digit Reduction (BDR), with the remaining digits developing to resemble the former digits I-III. Limusaurus was initially considered as evidence for the BDR hypothesis by Xu and colleagues in 2009 due to it—and other ceratosaurians—having

5886-484: The encased dinosaurs could have created the pits themselves can likewise be ruled out given their small size; the largest dinosaur found in the pits, Guanlong , would have been merely 66 cm (26 in) tall. When creating the pits, the footsteps of the sauropods could have led to soil liquefaction , resulting in smaller animals such as Limusaurus becoming stuck. In contrast to other incidences of miring in dinosaurs, where much larger individuals likely became stuck in

5995-528: The extreme anatomical changes with growth in Limusaurus , Wang and colleagues, in their 2017 study, performed separate analyses that were based on only the adult anatomy or on both the adult and juvenile anatomy. In another analysis, each Limusaurus individual was treated as an independent unit. All the juvenile Limusaurus specimens grouped together to the exclusion of adult specimens, showing that their anatomy changed significantly through growth. The inclusion or exclusion of juvenile features had little effect on

6104-463: The femur, and the foot was 1.3 times the length of the femur. The legs were 1.8 times the length of the torso. The upper half of the femur was triangular in cross section, a feature shared with Masiakasaurus . The metatarsals of the three weight-bearing toes were arranged in an arc, with the fourth metatarsal straight and adhering tightly to the third for its entire length; these features are unique to Limusaurus . The hallux (the first toe or dewclaw)

6213-582: The first definite ceratosaur known from Asia to be discovered, Limusaurus is also one of the earliest known members of the group, living during the Oxfordian stage of the Jurassic period (approximately 161-157 million years ago). According to Xu and colleagues, its discovery shows that the Asian dinosaur fauna was less endemic during the Middle to Late Jurassic period than previously thought, and suggests

6322-446: The form "author, year" in zoology, and "standard abbreviated author name" in botany. Thus in the examples above, the genus Canis would be cited in full as " Canis Linnaeus, 1758" (zoological usage), while Hibiscus , also first established by Linnaeus but in 1753, is simply " Hibiscus L." (botanical usage). Each genus should have a designated type , although in practice there is a backlog of older names without one. In zoology, this

6431-737: The generic name (or its abbreviated form) still forms the leading portion of the scientific name, for example, Canis lupus lupus for the Eurasian wolf subspecies, or as a botanical example, Hibiscus arnottianus ssp. immaculatus . Also, as visible in the above examples, the Latinised portions of the scientific names of genera and their included species (and infraspecies, where applicable) are, by convention, written in italics . The scientific names of virus species are descriptive, not binomial in form, and may or may not incorporate an indication of their containing genus; for example,

6540-464: The genus. As in other ceratosaurians, ossified wrist bones were absent. As is typical for ceratosaurs, the arms and hands of Limusaurus were considerably reduced, even more so than in Ceratosaurus . Limusaurus had three fingers (the middle three), as compared to the five fingers of more basal relatives; it was unique in that the first finger was missing entirely, and the first metacarpal

6649-406: The hand. Along the lineage that led to birds the number of digits in the hand decreased; by the emergence of the group Tetanurae , which includes birds, two digits had disappeared from the hand, leaving three. Traditionally, it has been hypothesized that the digits lost were the two outermost digits, i.e. digits IV and V, in a process known as Lateral Digit Reduction (LDR). According to this scenario,

SECTION 60

#1732794138649

6758-478: The hypothesis that the three-fingered hand of tetanuran theropods is the result of the loss of the first and fifth digits from the ancestral five-fingered theropod hand, a contested hypothesis which is relevant to the evolution of birds . The change to toothlessness in adults probably corresponded to a dietary shift from omnivory to herbivory , which is confirmed by the presence of gastroliths (stomach stones) in adults. Since many specimens were found together, it

6867-519: The individuals died in a resting pose within the pits. The typical death poses seen in many other dinosaur skeletons, where the head and tail are drawn above the body, are absent. Eberth and colleagues found it likely that the burial of all individuals occurred in less than a year, based on the seasonality of the local climate and the similarity of the sediments of the three pits. [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Genus The composition of

6976-633: The largest component, with 23,236 ± 5,379 accepted genus names, of which 20,845 ± 4,494 are angiosperms (superclass Angiospermae). By comparison, the 2018 annual edition of the Catalogue of Life (estimated >90% complete, for extant species in the main) contains currently 175,363 "accepted" genus names for 1,744,204 living and 59,284 extinct species, also including genus names only (no species) for some groups. The number of species in genera varies considerably among taxonomic groups. For instance, among (non-avian) reptiles , which have about 1180 genera,

7085-435: The lizard genus Anolis has been suggested to be broken down into 8 or so different genera which would bring its ~400 species to smaller, more manageable subsets. Glossary of dinosaur anatomy#articulated This Glossary explains technical terms commonly employed in the description of dinosaur body fossils . Besides dinosaur -specific terms, it covers terms with wider usage, when these are of central importance in

7194-399: The lower end ("boot") of the pubis was large and expanded. Unique to the genus, it pointed backwards in a hook-like shape and had a ridge on each side. The elongated legs of Limusaurus had proportions that were well-adapted to running, with their lower segments much longer than the femur: the tibiotarsus , the fusion of the tibia (shin bone) and tarsal bones , was 1.2 times the length of

7303-450: The lower jaw (at least 42 teeth in total). At the next stage, the first, sixth, and eighth teeth in each maxilla, as well as the sixth in each half of the lower jaw had all been lost, although the sockets were still present, and there was a small replacement tooth in the socket of the sixth lower tooth (leaving at least 34 teeth in total). During this stage, use of teeth and normal tooth replacement likely ceased or became reduced, since none of

7412-409: The lower jaw was positioned significantly forwards in relation to the hind end of the mandible, similar to other ceratosaurians. Juveniles had nine teeth in each side of the upper jaw and twelve in each side of the lower; they were gradually lost as they grew, disappearing by adulthood. The cervicals (neck vertebrae) of Limusaurus were elongated as in the closely related Elaphrosaurus , and

7521-416: The more basal theropod Dilophosaurus . Xu and biologist Susan Mackem stated in 2013 that the divergent developmental pathways of ceratosaurians and tetanurans are associated with a difference in forelimb function; tetanurans utilized their hands for grasping prey, while the hands of ceratosaurians almost certainly played no role in predation. An ancestral states analysis (estimation of the original anatomy of

7630-403: The most (>300) have only 1 species, ~360 have between 2 and 4 species, 260 have 5–10 species, ~200 have 11–50 species, and only 27 genera have more than 50 species. However, some insect genera such as the bee genera Lasioglossum and Andrena have over 1000 species each. The largest flowering plant genus, Astragalus , contains over 3,000 species. Which species are assigned to a genus

7739-456: The mud pits containing Limusaurus specimens were found at the same stratigraphic level, while a third was some 6.5 m (21 ft) higher in the stratigraphic column . The mud pits are around 2 m (6 ft 7 in) wide and range in depth from 1 to 2 m (3 ft 3 in to 6 ft 7 in). The mud pits occur within distinctive rock layers that can be followed for hundreds of meters to kilometers. These layers, though not

7848-419: The mudstone layers indicate volcanic events during deposition. The mud pits themselves show a tan-colored, silty to sandy claystone with abundant plant fragments and root traces. At their margins, the laminae of the surrounding mudstone are deformed or truncated, suggesting that the mudstone was partly fluid, plastic, and brittle at the time when the skeletons were deposited. Fragments of the crust topping one of

7957-611: The mudstone layers were found within the pits, indicating that the crust collapsed downwards into the pits. The deformation structures and the consistent size of the pits suggest that they represent the footprints of giant sauropods such as Mamenchisaurus sinocanadorum , which was likewise found in the Shishugou Formation and would have had a mass of over 20 t (22 short tons) and a limb length of over 3 m (9.8 ft). Other possible explanations, including sand volcanoes or sinkholes , can be ruled out because characteristic sedimentological features are lacking. The possibility that

8066-428: The name could not be used for both. Johann Friedrich Blumenbach published the replacement name Ornithorhynchus in 1800. However, a genus in one kingdom is allowed to bear a scientific name that is in use as a generic name (or the name of a taxon in another rank) in a kingdom that is governed by a different nomenclature code. Names with the same form but applying to different taxa are called "homonyms". Although this

8175-426: The neck itself was long. The axis (second neck vertebra) lacked the pleurocoel (excavation) on its front end and the foramina (openings) in its neural arch that are seen in derived ceratosaurians. As in other noasaurids , the neural spines of the cervicals were positioned more towards the front end of their vertebrae than is the case in other theropods. Distinctively, the scapula (shoulder blade) bore

8284-642: The original matrix . Except one, all specimens from this block are mounted in a cast of the block in its semi- prepared state. In 2009, the small ceratosaur was described by paleontologist Xu Xing and colleagues, who named it Limusaurus inextricabilis . The genus name consists of the words limus , Latin for "mud" or "mire", and saurus , Greek for "lizard", and the species name means "impossible to extricate"; both names refer to how these specimens appear to have died after being mired. The name has also been translated as "mire lizard who could not escape". The description incorporated data from two specimens both stored at

8393-407: The other hand, contained five theropod dinosaur skeletons including two Limusaurus , two Guanlong and one individual of a not yet described species. The third pit, TBB2005, contained twelve Limusaurus individuals, including the holotype, but also the tail of a small ornithischian dinosaur as well as two crocodyliforms , two mammals, a turtle and three tritylodontid cynodonts. The completeness of

8502-402: The pattern of digital reduction and frameshift that occurred in tetanurans. Carrano and paleontologist Jonah Choiniere suggested in 2016 that this is supported by the hands of the ceratosaurians Ceratosaurus , Berberosaurus , and Eoabelisaurus having plesiomorphic (i.e. more similar to the ancestral condition of theropods than to derived abelisaurs) metacarpal bones comparable to those of

8611-464: The pits themselves, comprise pale-colored laminated successions of mudstone 0.5 to 2 m (1 ft 8 in to 6 ft 7 in) in thickness. The mudstones probably accumulated either in standing water or a water-saturated substrate; root traces at the top of the layers indicate a marsh -like environment. One of the layers is topped by a crust-like mudstone layer that indicates soil formation and exposure to air. Volcanic minerals found within

8720-401: The placement of Limusaurus in the phylogenetic tree. The cladogram below shows the position of Limusaurus within Noasauridae according to Baiano and colleagues, 2020: Spinostropheus Limusaurus Elaphrosaurus Huinculsaurus Deltadromeus Genusaurus Afromimus Velocisaurus Masiakasaurus Noasaurus Laevisuchus In addition to being

8829-438: The presence of isolated body parts also suggests that some carcasses were exposed to the air for days or months. Evidence for scavenging , such as isolated bones, tooth marks on bones, or shed teeth of theropods, is lacking. However, it is possible that scavengers carried whole body parts away, as feeding at the pits might not have been possible. Eberth and colleagues speculated that the two Guanlong specimens preserved at

8938-541: The provisions of the ICZN Code, e.g., incorrect original or subsequent spellings, names published only in a thesis, and generic names published after 1930 with no type species indicated. According to "Glossary" section of the zoological Code, suppressed names (per published "Opinions" of the International Commission of Zoological Nomenclature) remain available but cannot be used as the valid name for

9047-464: The remains of small theropod dinosaurs, representing at least three genera, with most belonging to a small ceratosaur , the first member of this group found in Asia. Stacked skeletons from these bone beds were removed from the field in blocks, jacketed by plaster, and encased in crates. A resin cast of block TBB 2001 was made, making it available for study after the specimens had been extracted from

9156-470: The same kind as other (analogous) genera. The term "genus" comes from Latin genus , a noun form cognate with gignere ('to bear; to give birth to'). The Swedish taxonomist Carl Linnaeus popularized its use in his 1753 Species Plantarum , but the French botanist Joseph Pitton de Tournefort (1656–1708) is considered "the founder of the modern concept of genera". The scientific name (or

9265-565: The same; the increased number of gastroliths in older adults may be indicative of the gut's ability to process plant matter more finely as they aged. An isotope analysis of the available specimens of Limusaurus likewise showed that adults consistently match the isotope signatures of other herbivorous dinosaurs. In the same analysis, juveniles and subadults were found to vary greatly in their isotopic signatures; this indicates that juveniles were likely omnivorous (feeding on both animals and plants), but switched to strict herbivory as they aged. This

9374-408: The scientific epithet) of a genus is also called the generic name ; in modern style guides and science, it is always capitalised. It plays a fundamental role in binomial nomenclature , the system of naming organisms , where it is combined with the scientific name of a species : see Botanical name and Specific name (zoology) . The rules for the scientific names of organisms are laid down in

9483-626: The skeleton. The other (an adult, IVPP V 15304, inaccurately referred to by the number IVPP V 16134 in the original description) is a likewise almost complete and articulated specimen that is missing only the skull, and is larger than the holotype. Seventeen additional Limusaurus specimens were described by paleontologist Shuo Wang and colleagues in 2017, excavated from the same blocks as those described in 2009. These specimens include six juveniles (one year in age or less), ten subadults (two to six years in age), and one adult (more than six years in age). These specimens are also stored at

9592-455: The skeletons is variable; at least half of the theropod skeletons are complete, with missing parts due to recent erosion. Rear parts of the skeletons tend to be more common than front parts. Most individuals were embedded laying on their sides, though some lie on their backs or undersides. In pits TBB2001 and TBB2002 the skeletons lie one above the other. Bones pertaining to the same individual often lie upon each other in direct contact, while there

9701-489: The species name means "impossible to extricate", both referring to these specimens possibly dying after being mired. Limusaurus was a small, slender animal, about 1.7 m (5 ft 7 in) in length and 15 kg (33 lb) in weight, which had a long neck and legs but very small forelimbs (with reduced first and fourth fingers). It underwent a drastic morphological transformation as it aged: while juveniles were toothed, these teeth were completely lost and replaced by

9810-497: The specific name particular to the wolf. A botanical example would be Hibiscus arnottianus , a particular species of the genus Hibiscus native to Hawaii. The specific name is written in lower-case and may be followed by subspecies names in zoology or a variety of infraspecific names in botany . When the generic name is already known from context, it may be shortened to its initial letter, for example, C. lupus in place of Canis lupus . Where species are further subdivided,

9919-412: The standard format for a species name comprises the generic name, indicating the genus to which the species belongs, followed by the specific epithet, which (within that genus) is unique to the species. For example, the gray wolf 's scientific name is Canis lupus , with Canis ( Latin for 'dog') being the generic name shared by the wolf's close relatives and lupus (Latin for 'wolf') being

10028-459: The still-erupted teeth bear any wear marks or resorption . As the specimens grew, the transformation became more radical. In subadult and adult specimens older than one year, all the teeth were missing. CT scanning shows that only five empty tooth sockets remained in the adult maxilla; all the sockets in the lower jaw were fused into a single, hollow canal, and the rest of the tooth sockets were obliterated. The loss of teeth with age in Limusaurus

10137-402: The study of dinosaurs or when their discussion in the context of dinosaurs is beneficial. The glossary does not cover ichnological and bone histological terms, nor does it cover measurements. Amphicoely is the primitive condition tetrapods. In fishes, the ends of the centra are deeply excavated and connected via a small opening, the passage for the notochord . In reptiles, this type of centrum

10246-403: The taxon is termed a synonym ; some authors also include unavailable names in lists of synonyms as well as available names, such as misspellings, names previously published without fulfilling all of the requirements of the relevant nomenclatural code, and rejected or suppressed names. A particular genus name may have zero to many synonyms, the latter case generally if the genus has been known for

10355-443: The three fingers retained by tetanurans were therefore homologous (evolutionary corresponding to) with digit I, II, and III of basal theropods, which would have implications for the evolution of birds . However, the hypothesis of LDR is in contradiction to some embryological studies on birds which show that, from five developmental sites, the digits that develop are the three middle digits (II, III, IV). This inconsistency has been

10464-559: The time when Limusaurus lived, the environment would have been relatively warm and dry, judging by the abundance of coal and carbon-rich deposits. The climate was probably highly seasonal due to monsoonal influences, with warm, wet summers and dry winters. The climate enabled the growth of a richly forested environment; the forest would have been dominated by Araucaria trees, with the undergrowth being occupied by Coniopteris , Anglopteris and Osmunda ferns, Equisetites horsetails, and Elatocladus shrubs. The environment of

10573-421: The top and on the side of the skull's rear, respectively). As in other ceratosaurians, parts of the bony nostril were formed by the maxilla (upper jaw bone); also, the antorbital fenestra was proportionally small, and the rear part of the nasal bone formed parts of the cavity which contained this opening. The external naris was large and located in a hindwards position, similar to tetanuran theropods. The orbit

10682-451: The top of pit TBB2002 could have been scavenging on the mired carcasses before getting mired themselves. The horizontal orientation of the skeletons within the pits suggests that the mud was soft. The neck and tail of one specimen are bent upwards, suggesting that the carcass was pushed down towards the bottom of the pit by trampling of another animal that became trapped at a later time. Specimens typically show flexed hind limbs, indicating that

10791-576: The values quoted are the mean of "accepted" names alone (all "uncertain" names treated as unaccepted) and "accepted + uncertain" names (all "uncertain" names treated as accepted), with the associated range of uncertainty indicating these two extremes. Within Animalia, the largest phylum is Arthropoda , with 151,697 ± 33,160 accepted genus names, of which 114,387 ± 27,654 are insects (class Insecta). Within Plantae, Tracheophyta (vascular plants) make up

10900-429: The virus species " Salmonid herpesvirus 1 ", " Salmonid herpesvirus 2 " and " Salmonid herpesvirus 3 " are all within the genus Salmonivirus ; however, the genus to which the species with the formal names " Everglades virus " and " Ross River virus " are assigned is Alphavirus . As with scientific names at other ranks, in all groups other than viruses, names of genera may be cited with their authorities, typically in

11009-423: Was covered by a beak , a feature that was previously unknown in non- coelurosaurian theropods like Limusaurus (the coelurosaurs include the most bird-like dinosaurs). As in most dinosaurs, the skull featured five principal fenestrae (openings): the external naris (bony nostril), orbit, antorbital fenestra (between the nostril and eye), as well as the upper and lower temporal fenestra (on

11118-412: Was difficult to explain why herbivores like Limusaurus would be attracted to sites where other animals were mired, so they considered it most likely that the larger number of Limusaurus fossils was due to their abundance. These authors also suggested that the abundance of Limusaurus inferred for the area and the evidence for successive, rapid burials of each individual made it possible that Limusaurus

11227-404: Was especially large, accounting for 40% of the length of the entire lower jaw, a distinguishing feature of the genus. The dentary (tooth-bearing bone at the front of the lower jaw) was short compared to the rest of the lower jaw, as in other ceratosaurians. The front end of the dentary was down-turned and had a convex inner margin, similar to the related Masiakasaurus . The angular bone of

11336-566: Was gregarious, living in groups. There is some evidence for gregariousness in many small theropods and that there may have been social behaviours related to age, but it remains unknown whether the bone beds containing Limusaurus specimens preserve evidence of sociality and segregation related to age. Paleontologist Rafael Delcourt agreed in 2018 that since both Limusaurus and Masiakasaurus have been found in assemblages of multiple specimens each, this suggests these small ceratosaurs lived in groups. All known Limusaurus fossils were recovered from

11445-430: Was large, while the lateral temporal fenestra was not as large as would be expected from more derived (or "advanced") members of the Ceratosauria. Uniquely to Limusaurus , the inner bottom edge of the premaxilla , the frontmost bone of the upper jaw, was convex. The nasal bone was distinct in having a "shelf" on its side, was short, wide, less than one-third of the length of the skull roof , and twice as long as it

11554-431: Was primarily composed of fibrolamellar bone (where the internal fibres are disorganized), indicating that Limusaurus grew quickly; by contrast, the noasaurines Masiakasaurus and Vespersaurus had parallel-fibred bone indicative of slower growth, possibly due to the drier and more resource-poor environments that they would have lived in. In older specimens, the outermost growth rings are very close together (forming what

11663-460: Was reduced, being only 17% the length of the third metatarsal, another unique feature. As in other ceratosaurians, the unguals of the foot had two grooves on their sides. Limusaurus was classified as a basal member of Ceratosauria by Xu and colleagues in 2009 (who also considered the closely related Elaphrosaurus as such). It had several skull features in common with basal theropods such as other ceratosaurs and coelophysoids , but it also shared

11772-409: Was shorter than the other metacarpals. The second metacarpal was more robust than the other metacarpals, which is another distinctive feature of the genus. The second finger had three phalanges (finger bones). The third finger also only had three phalanges, as opposed to four in other early theropods. Although the fourth finger is not preserved, the tip of the fourth metacarpal indicates the presence of

11881-417: Was wide. The lower part of the lacrimal , the bone that formed the front margin of the eye opening, was unique in being strongly inclined forwards. The jugal bone , which formed the floor of the eye opening, was slender, and its rami (or branches) were rod-like, which is also unique to this genus. The lower jaw of ceratosaurians was pierced by a generally large mandibular fenestra . In Limusaurus , it

#648351