Wikipedia

Dinosauromorpha

Dinosauromorphais acladeofavemetatarsalians(archosaurscloser to birds than to crocodilians) that includes theDinosauria(dinosaurs) and some of their close relatives. It was originally defined to includedinosauriformsandlagerpetids,[3]with later formulations specifically excludingpterosaursfrom the group.[4]Birdsare the only dinosauromorphs which survive to the present day.

Dinosauromorphs
Temporal range:Middle Triassic–Present,247–0Ma(possibleEarly Triassicrecord)
From top to bottom and left to right, different type of dinosauromorphs:Asilisaurus,Borealopelta,TriceratopsandGiganotosaurus.
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Ornithodira
Clade: Dinosauromorpha
Benton,1985[1]
Subgroups

Classification

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Pelvis ofMarasuchus(=Lagosuchus?) specimen PVL 3870

The name "Dinosauromorpha" was briefly coined byMichael J. Bentonin 1985.[1]It was considered an alternative name for the group "Ornithosuchia", which was named byJacques Gauthierto correspond to archosaurs closer to dinosaurs than to crocodilians.[5]Although "Ornithosuchia" was later recognized as amisnomer(sinceornithosuchidsare now considered closer to crocodilians than to dinosaurs), it was still a more popular term than Dinosauromorpha in the 1980s.[3]The group encompassed by Gauthier's "Ornithosuchia" and Benton's "Dinosauromorpha" is now given the nameAvemetatarsalia.[4]

In 1991,Paul Serenoredefined Dinosauromorpha as a node-basedclade,defined by alast common ancestorand its descendants. In his definition, Dinosauromorpha included thelast common ancestorofLagerpeton(alagerpetid),Marasuchus(a possiblejunior synonymofLagosuchus),Pseudolagosuchus(now considered a synonym of thesilesauridLewisuchus), Dinosauria (including Aves), and all its descendants. This definition was intended to correspond to a clade including lagerpetids and crownward bird-line archosaurs, but not pterosaurs or other archosaurs.[3][6]

In 2011, Dinosauromorpha was redefined bySterling Nesbittto be a branch-based clade, defined by including reptiles closer to one group than to another. Under this definition, Dinosauromorpha included all reptiles closer to dinosaurs (represented byPasser domesticus,the house sparrow), rather than pterosaurs (represented byPterodactylus), ornithosuchids (represented byOrnithosuchus), or otherpseudosuchians(represented byCrocodylus niloticus,the Nile crocodile). Nesbitt's study supported the hypothesis that Pterosauromorpha (pterosaurs and their potential relatives) was thesister groupof Dinosauromorpha. Pterosauromorphs and dinosauromorphs together formed the groupOrnithodira,which encompasses almost all avemetatarsalians.[4]

Dinosauriformeswas coined in 1992 by F.E. Novas, who used it to encompass dinosaurs,Lagosuchus,"Pseudolagosuchus"(=Lewisuchus), and theherrerasaurids,which he did not consider to be "eudinosaurs" (true dinosaurs likeornithischiansandsaurischians).[7]Contrary to Novas, most paleontologists since 1992 have considered herrerasaurids to be true dinosaurs, though many other dinosaur-like reptiles still fall within his definition of Dinosauriformes. Novas (1992) defined Dinosauriformes as a node-based clade containing the most recent common ancestor ofLagosuchusand Dinosauria, and all its descendants.[7]Nesbitt (2011) provided a roughly equivalent definition, usingMarasuchusandPasser domesticus(the house sparrow, a representative of dinosaurs). In his analysis, Dinosauriformes included dinosaurs,silesaurids,andMarasuchus,but notlagerpetids,which were considered to be an earlier-branching family of dinosauromorphs.[4]

Phylogeny

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A phylogenetic analysis by Andrea Cau in2018resolved two different topologies for dinosaur origins, depending on whether it was run usingparsimonyorbayesian inference.Cau coined the termDracohorsfor the clade uniting all taxa closer to the theropodMegalosaurus bucklandithan the basal formMarasuchus lilloensis.The name is derived from theLatinwords for "dragon" and "cohort",dracoandcohors.Under parsimony results, Dracohors included onlySilesauridaeandDinosauria,the latter including the groupsHerrerasauria,Sauropodomorpha,TheropodaandOrnithischia,along with the basal formEodromaeus.However, under bayesian results, Herrerasauria placed outside Dinosauria within Dracohors, and Dinosauriformes, Dinosauromorpha, andPan-Aveswere synonyms, withMarasuchusin a clade with lagerpetids.Pisanosauruswas resolved within Silesauridae. Cau identified the synapomorphies of Dracohors as:[8]

The anterior tympanic recess, the axial epipophyses, the centrodiapophyseal laminae in the presacral vertebrae, the relative size enlargement of the postacetabular process of ilium, the elongation of the pubis, the proximal sulcus and the reduction of the ligament tuber in the femoral head, and the further reduction in length of the fourth metatarsal and toe compared to the third.

Skeletal diagram ofIxalerpeton

Following the discovery and description of more cranial and postcranial material of the generaKongonaphon,IxalerpetonandLagerpeton,it was found that lagerpetids shared many features with the basal taxa ofPterosauria.Features of themaxillary bone,teeth,braincaseand forelimb meant that the2020phylogenetic analysis of Ezcurra and colleagues placed Lagerpetidae next to pterosaurs within Pterosauromorpha, removing the family from Dinosauromorpha. The contents of Dinosauromorpha was thus restricted to only Silesauridae, Dinosauria, and individual genera likeLagosuchus.[9]

Simultaneously, Rodrigo Müller and Maurício Garcia published novel results that reduced the family Silesauridae to a grade of basal dinosaurs inOrnithischia.Pisanosaurus,considered by various authors to be either a silesaurid or basal ornithischian, was found to be intermediate between the grade of silesaurids and true ornithischians, explaining its peculiar combination of silesaurid and ornithischian features that has resulted in its phylogenetic inconsistency.Lewisuchus,a carnivorous form, was found to be the most primitive form of ornithischian, which was almost universally considered to be an only-herbivorous clade before. The reclassification of silesaurids left Lagerpetidae andLagosuchusas the only non-Dinosaurians in the Dinosauromorpha.[10] Below are the results of:

A variety of individual species and taxa have at times been found to place within Dinosauromorpha and its subgroups, but outside Dinosauria. The taxonMarasuchushas been consistently recovered as a dinosauromorph between lagerpetids and silesaurids, but may also be a junior synonym of the coexisting formLagosuchus,another dinosauromorph.[11]Pisanosaurus,traditionally considered an ornithischian, was recovered in an unpublished analysis as a dinosauriform outside other clades,[12]but has since been recovered only as a member of Silesauridae or Ornithischia.[10][13][14][15]Saltopus,an enigmatic taxon from theLate TriassicofScotland,has been placed closer to dinosaurs thanMarasuchus,in a polytomy with Silesauridae and Dinosauria,[13]as a sister taxon toMarasuchus,[14][15]or within Dinosauria as a basal saurischian.[10]The British taxonAgnosphityswas originally described as a dinosauriform closer to Dinosauria thanHerrerasaurus,[16]but has also been classified as a dinosauriform more derived than silesaurids but basal toHerrerasauridaeand Dinosauria,[15]a silesaurid,[13]or a basal saurischian.[10][14]The genusNyasasaurusfrom the early Late Triassic ofTanzaniais known only from vertebra and a single humerus, making it difficult to classify. It has been variously found as the direct sister taxon of Dinosauria, the basalmost ornithischian, a basal theropod,[17]or a deeply-nested sauropodomorph.[13][14][15]

Origins

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Dinosauromorphs appeared putatively around 242 to 244 million years ago by theAnisianstage of theMiddle Triassic,splitting from other ornithodires.Early Triassicfootprints reported in October 2010 from theŚwiętokrzyskie (Holy Cross) Mountainsof Poland may belong to a dinosauromorph. If so, the origin of dinosauromorphs would be pushed back into the EarlyOlenekian,around 249 Ma. The oldest Polish footprints are from a small quadrupedal animal namedProrotodactylus,but footprints belonging to theichnogenusSphingopusthat have been found from Early Anisian strata show that moderately large bipedal dinosauromorphs had appeared by 246 Ma. The tracks show that the dinosaur lineage appeared soon after thePermian-Triassic extinction event.Their age suggests that the rise of dinosaurs was slow and drawn out across much of the Triassic.[18]However, other researchers have questioned the dinosauromorph affinities ofProrotodactylusand suggested that the tracemaker may have been a basal archosauriform such as theEuparkeriidae.[19][20]The oldest known definitive dinosauromorph isAsilisaurus,asilesauridwhich may have lived as early as theAnisianage of the middleTriassicperiod, about 245 million years ago,[21]although it is possible thatNyasasaurusis a dinosaur of the same age, pushing the origins of the groups back further.[13]

Putative basal dinosauromorphs includeSaltopus,[22][23]Marasuchus,the perhaps identicalLagosuchus,thelagerpetidLagerpetonfrom theLadinianofArgentinaandDromomeronfrom theNorianofArizona,New Mexico,andTexas(all in the United States),Ixalerpeton polesinensisand an unnamed form from theCarnian(Santa Maria Formation) ofBrazil,[24][25]and thesilesaurids,which includeSilesaurusfrom theCarnianofPoland,Eucoelophysisfrom the Carnian-Norian of New Mexico,Lewisuchusand the perhaps identicalPseudolagosuchusfrom the Ladinian ofArgentina,[26][27]Sacisaurusfrom the Norian ofBrazil,[28]Technosaurusfrom the Carnian of Texas,[29]Asilisaurusfrom theAnisianofTanzania,[30]andDiodorusfrom the Carnian(?) to Norian ofMorocco.[31]

References

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  2. ^Matthew G. Baron; Megan E. Williams (2018). "A re-evaluation of the enigmatic dinosauriform Caseosaurus crosbyensis from the Late Triassic of Texas, USA and its implications for early dinosaur evolution". Acta Palaeontologica Polonica. 63.doi:10.4202/app.00372.2017.
  3. ^abcSereno, Paul C. (1991-12-31)."Basal Archosaurs: Phylogenetic Relationships and Functional Implications".Journal of Vertebrate Paleontology.11(sup004):1–53.Bibcode:1991JVPal..11S...1S.doi:10.1080/02724634.1991.10011426.ISSN0272-4634.
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  6. ^Langer, M. C.; Nesbitt, S. J.; Bittencourt, J. S.; Irmis, R. B. (2013)."Non-dinosaurian Dinosauromorpha"(PDF).Geological Society, London, Special Publications.379(1):157–186.Bibcode:2013GSLSP.379..157L.doi:10.1144/SP379.9.S2CID84303547.
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