Dinosauria Dinosauria

Dinosauria R. Owen 1842 [M. C. Langer, F. E. Novas, J. S. Bittencourt, M. D. Ezcurra, and J. A. Gauthier], converted name

Registration Number: 194 al. (2008; supplementary Fig. 2) was selected as the primary reference phylogeny. Note that the Definition: The smallest clade contain- definition uses clade addresses (e.g., : ing bernissartensis Boulenger in Megalosauroidea) from Lloyd et al. (2008) to Beneden 1881 (/Euornithopoda) facilitate finding specifiers (e.g., Megalosaurus bucklandii Mantell 1827 bucklandii) on this densely branched supertree. (Theropoda/Megalosauroidea) and Only species, not more inclusive taxa, can be oxoniensis Phillips 1871 (). specifiers in this kind of definition. We accord- This is a minimum-clade definition. Abbreviated ingly do not regard these additional taxon definition: min∇ (Iguanodon bernissartensis names as parts of the formal definition, nor do Boulenger in Beneden 1881 & Megalosaurus we mean to endorse their use for these . bucklandii Mantell 1827 & Cetiosaurus oxoni- ensis Phillips 1871). Composition: According to most phylogenetic hypotheses, Dinosauria is composed of two pri- Etymology: Derived from the ancient Greek: mary subclades—Ornithischia and δεινός = fearful, terrible; σαύρος = -like (this volume)—with the latter composed of (Liddell and Scott, 1882); seemingly in reference Sauropodomorpha (this volume) and Theropoda to the large size of the fossils originally assigned (including Aves, this volume) (e.g., Gauthier et to this group. Indeed, Owen (1842) translated al., 1989; Sereno, 1999; Ezcurra, 2006; Langer δειυός as “fearfully great,” conceivably employ- and Benton, 2006; Irmis et al., 2007; Lloyd et ing the term as “the quality of objects which, al., 2008; Apaldetti et al., 2011; Martínez et al., from their vastness, magnitude, etc., inspire 2011; Sereno et al., 2013; Niedźwiedzki et al., fear, awe, reverence, power, etc.” (Pickering, 2014; Pretto et al., 2015; Cabreira et al., 2016). 1873; in Creisler, 1996). There is some contention over relations of a few very early species—e.g., some have proposed Reference Phylogeny: There are a plethora of that herrerasaurs (e.g., Gauthier et al., 1989; phylogenies depicting relationships within and Novas, 1992; Fraser et al., 2002) and silesaurids among various parts of the host of extinct clades (e.g., Langer and Ferigolo, 2013) are, respec- that diverged from along the avian stem dur- tively, outside and within Dinosauria as defined ing the Mesozoic. More comprehensive stud- here. The composition and relations of those ies (e.g., Sereno, 1999) are rare. No one has yet primary dinosaurian subclades have otherwise attempted to simultaneously analyze a broad been remarkably stable, and alternative topolo- range of species from across the avian total gies proposed among basalmost branches (e.g., clade, which includes more than 11,000 species Cooper, 1985; Baron et al., 2017; but see Langer ranging from mid- to Recent (see Aves, et al., 2017) do not alter the circumscription of this volume). Because it contains the largest Dinosauria as that taxon name is defined here. sample of non-avian , the phylogeny Starting with the compilation of Weishampel derived from the supertree analysis of Lloyd et et al. (2004), Benton (2008) identified 726 Dinosauria

valid species of Mesozoic age. This pelvic and hind-limb modifications thought count includes early winged dinosaurs such to reflect acquisition of an upright striding as Archaeopteryx lithographica, with early bipedal stance and gait (e.g., Gauthier et al., avialans comprising about 10% of Mesozoic 2011) figured prominently in the diagnosis of dinosaur species diversity. The International Dinosauria from Owen’s time to the dawn of Ornithological Union recognizes 10,672 extant the Hennigian (phylogenetic) era (e.g., Bakker species of Aves (Gill and Donsker, 2017); hence, and Galton, 1974; Gauthier, 1986). This col- there are accordingly at least 11,398 species lection of apomorphies remains diagnostic of currently assigned to Dinosauria as that taxon Dinosauria relative to the last ancestor it shared name is defined here. with Alligator mississippiensis (Archosauria, this Starrfelt and Liow (2016) used a Poisson volume). Nevertheless, these distinctly -like sampling model to more accurately estimate “dinosaurian” synapomorphies likely originated species richness among Mesozoic dinosaurs, before the divergence amongst Ornithischia, more than doubling the estimated diversity to Theropoda, and Sauropodomorpha (= Dinosauria around 2,000 species. Considering the episodic as defined here). A growing understanding of nature of deposition on land, the dearth of species diversity and anatomical disparity of dinosaur-bearing beds of Mesozoic age around Triassic dinosaurs and their close kin reveals the world, and the uneven geographic distribu- that many of these traditional “dinosaurian” tion of palaeontologists prospecting for them, apomorphies did indeed evolve earlier on the this is still likely to be an underestimate. Extant avian stem (e.g., Novas, 1996; Sereno, 1999; dinosaurs (Aves) may be far more diverse in Langer and Benton, 2006; Ezcurra, 2006; Irmis terms of species, doubtless reflecting their rel- et al., 2007; Nesbitt, 2011; Cabreira et al., 2016; atively small body size, but large-bodied stem Nesbitt et al., 2017). avians (traditional “dinosaurs”) are far more Several authors have reviewed the synapo- disparate morphologically. Among the aston- morphies of Dinosauria (e.g., Brusatte et al., ishing variety of dinosaurs alive at the end of 2010; Langer et al., 2010; Nesbitt et al., 2010; the , only the very earliest branches Nesbitt, 2011; Nesbitt et al., 2012; Cabreira of crown Aves survived the Chicxulub impact et al., 2016; Baron et al., 2017). They indicate at 66 Ma (Longrich et al., 2011; see Aves this that the precise diagnosis of the clade turns on volume). whether it contains silesaurids (Dzik, 2003; Langer and Ferigolo, 2013; Niedźwiedzki et Diagnostic Apomorphies: With respect to al., 2014; Cabreira et al., 2016) or not. In addi- other “”, Owen (1842) characterized his tion to some uncertainty from character con- three species of Dinosauria—now recognized flict, incomplete preservation in Triassic taxa as two ornithischians and a theropod sauris- (e.g., parringtoni; Nesbitt et al., chian—by their large size and unusual combina- 2012) remains a serious problem in that impor- tion of osteological traits, including a distinctive tant characters of the skull and manus are very sacral construction and an upright limb posture poorly known among non-dinosaur dinosauro- resembling those of “bulky terrestrial mam- morphs (Langer et al., 2013). mals.” Owen’s conception was developed in the A list of traditional dinosaur synapomor- pre-Darwinian era and was burdened further phies based on reviews noted above is presented by there being so few extinct dinosaurs known below. It is mainly composed of uncontrover- in the mid-nineteenth century. Nevertheless, sial dinosaur apomorphies, but it also includes

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some apomorphies with uncertain distributions with ilium and pubis separated by broad con- among a few non-dinosaur dinosauromorphs cave surface** (Irmis et al., 2007); (17) ischia from the Triassic (indicated by *). Others are with extensive contact between their shafts‡ not present in all early dinosaurs, but might (Nesbitt, 2011); (18) femoral head distinctly be synapomorphic for the clade depending off-set at a sharp angle from the shaft‡ (Bakker on assumptions about the frequency of inde- and Galton, 1974); (19) femur with dorsolat- pendent origin vs. secondary loss in evolution eral trochanter‡ (Gauthier, 1986); (20) fourth (indicated by **). Finally, some are also known trochanter with distal margin forming steeper in Nyasaurus parringtoni (indicated by †) and angle relative to femoral shaft** (Langer and in some silesaurids (indicated by ‡), taxa that Benton, 2006); (21) tibia cnemial crest arcs cra- are either sister to, or just inside of, Dinosauria. niolaterally‡ (Benton and Clark, 1988); (22) They nevertheless suffice to distinguish dino- caudal surface of tibia with proximodistally saurs from more distant outgroups near the base oriented ridge** (Nesbitt, 2011); (23) flange on of the avian stem such as talampay- distal portion of tibia overlapping caudally the ensis (= lilloensis) and ascending process of the astragalus‡ (Novas, chanarensis (authorship credited to first explicit 1992); (24) cranial edge of proximal portion identification as an apomorphy): (1) postfron- of fibula tapers to point and arches medially‡ tal absent* (Gauthier, 1986); (2) jugal with (Nesbitt, 2011); (25) broad astragalar ascending bifurcated quadratojugal process* (Sereno and process‡ (Gauthier, 1986); (26) astragalus with Novas, 1992); (3) supratemporal fossa extends fibular facet occupying less than 1/3 of trans- onto frontal rostral to supratemporal fenestra verse width‡ (Langer and Benton, 2006); (27) (Gauthier, 1986); (4) post-temporal opening concave articular surface of the fibula in the much smaller than foramen magnum (Sereno calcaneum‡ (Novas, 1996); (28) calcaneal tuber and Novas, 1993); (5) exoccipitals fail to meet absent** (Gauthier, 1986); (29) distal tarsal IV on the floor of endocranial cavity* (Nesbitt, with flat proximal surface (Nesbitt, 2011); (30) 2011); (6) epipophyses present on cranial cer- metatarsal IV subequal in length to metatarsal vical vertebrae ‡ (Gauthier, 1986); (7) forelimb II‡ (Gauthier, 1986). (humerus+radius) to hindlimb (femur+tibia) ratio less than 0.55** (Gauthier, 1986); (8) del- Synonyms: Pachypodes Meyer 1845, topectoral crest extends for more than 30% Harpagosauria Haeckel 1866, and the humeral length† ‡ (Bakker and Galton, Huxley 1870 are approximate (not defined 1974); (9) humerus with proximal articula- phylogenetically) and partial (did not include tion separated by gap from deltopectoral crest‡ ) synonyms; Eudinosauria Novas 1992 is (Nesbitt, 2011); (10) radius shorter than 80% an unambiguous synonym. In the context of of humerus** (Irmis et al., 2007); (11) reduced the tree of Baron et al. (2017), Saurischia Seeley postaxial digits of hand* (Gauthier and Padian, 1888 as traditionally understood is a partial and 1985); (12) more than two sacral vertebrae** † approximate synonym, and Eusaurischia Padian ‡ (Galton, 1976); (13) concave ventral margin et al. 1999 is an unambiguous synonym. of the acetabulum in the ilium** (Bakker and Galton, 1974); (14) ilium with well-developed Comments: After Owen (1842) coined the brevis fossa** ‡ (Gauthier and Padian, 1985); name Dinosauria, a few more taxon names (15) pubis longer than 70% of femur length‡ entered the literature to designate a similar (Novas, 1996); (16) ischium articular surfaces group of organisms (see Synonyms), but none

1211 Dinosauria gained much traction. Note that Ornithoscelida such as Lagosuchus talampayensis (Romer, 1971; Huxley 1870 has recently been resurrected for a Bonaparte, 1975; Sereno and Arcucci, 1994; proposed clade composed only of Ornithischia Agnolin & Ezcurra, 2019). Because Novas + Theropoda (Baron et al., 2017), and excluding (1992) inferred herrerasaurs to be outside of the Sauropodomorpha, thus rendering Eusaurischia Ornithischia-Saurischia dichotomy, he also coined a junior synonym of Dinosauria and Saurischia the name Eudinosauria for that less inclusive a junior synonym of Theropoda sensu Gauthier clade. Most subsequent analyses have, however, (1986); (see Saurischia and Theropoda, this vol- consistently placed herrerasaurs within the sau- ume.)) Dinosauria was used in most early clas- rischian radiation (Novas, 1996; Sereno, 1999; sification schemes (e.g., Cope, 1866; Huxley, Ezcurra, 2006, 2010; Langer and Benton, 2006; 1870; Marsh, 1882), including that of Seeley Irmis et al., 2007; Nesbitt, 2011; Nesbitt et al., (1888) who, although questioning dinosaur 2012; Apaldetti et al., 2011; Martínez et al., 2011; monophyly, divided “dinosaurs” into ornithis- Sereno et al., 2013; Niedźwiedzki et al., 2014; chians and saurischians, thereby establishing a Pretto et al., 2015; Cabreira et al., 2016). In that nomenclature used in all future works on dino- context, Eudinosauria and Dinosauria (as defined saur . Indeed, most influential works by Novas, 1992) are currently synonymous phy- of the twentieth century (Huene, 1956; Colbert, logenetically. Herrerasaurs have recently been 1964; Romer, 1966) accepted Dinosauria as inferred to lie at the base of Sauropodomorpha, composed of Saurischia plus Ornithischia even with Ornithischia and Theropoda as sisters (Baron though they were generally considered to have et al., 2017) (see Saurischia, this volume), but that arisen independently from “thecodont” ances- still places them within Dinosauria as that taxon tors (e.g., Thulborn, 1975; see Archosauria, name is defined here. this volume). Dinosaur monophyly in the A surprising number of phylogenetic defini- Hennigian sense was first proposed by Bakker tions for the name Dinosauria were proposed and Galton (1974), was firmly established by subsequent to Novas (1992). Although they Gauthier (1986; see also Gauthier, 1984), and agreed on the circumscription of the clade, that hypothesis now represents the consen- tying it to the Ornithischia-Saurischia dichot- sus view emerging from extensive subsequent omy proposed by Seeley (1888), they often study (e.g., Novas, 1996; Sereno, 1999; Langer differed in their choice of internal specifiers and Benton, 2006; Ezcurra, 2006; Irmis et al., (e.g., Padian and May, 1993; Novas, 1996; 2007; Brusatte et al., 2010; Langer et al., 2010; Holtz in Padian, 1997; Sereno, 1998, 2005a,b; Nesbitt, 2011; Nesbitt et al., 2012; Apaldetti et Olshevsky, 2000; Fraser et al., 2002; Kischlat, al., 2011; Martínez et al., 2011; Sereno et al., 2002; Clarke, 2004). Various workers selected 2013; Niedźwiedzki et al., 2014; Bittencourt clades rather than species as specifiers, often et al., 2014; Pretto et al., 2015; Cabreira et al., using avians to represent the saurischian branch 2016; Baron et al., 2017). of Dinosauria. Following the taxonomic orthodoxy of the There are two problems with some of these early time (Gauthier, 1984, 1986; Brinkman and efforts in phylogenetic nomenclature: instead of Sues, 1987; Novas, 1989; Benton, 1990), Novas more inclusive taxa, valid specifiers must be spe- (1992) proposed the first phylogenetic definition cies, specimens or apomorphies (Cantino and de of Dinosauria to include saurischians, ornithis- Queiroz, 2020; ICPN Art. 11.1); and those speci- chians, and herrerasaurs (but see Gauthier et fiers should preserve traditional ideas about the al., 1989), but not near-dinosaur “thecodonts” taxon’s composition (Cantino and de Queiroz,

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2020; ICPN Rec. 11A). Instead of using any Literature Cited avians as specifiers—an approach introduced by Gauthier (1986; see also Gauthier, 1984) Agnolin, F., and M. D. Ezcurra. 2019. The valid- but hardly consistent with the scope of Owen’s ity of Lagosuchus talampayensis Romer, 1971 (Archosauria, ), from the Late Dinosauria (Cantino and de Queiroz, 2010)—we Triassic of Argentina. Breviora 565 (1):1–21. selected three traditional “dinosaurs” to bracket Apaldetti, C., R. N. Martinez, O. A. Alcober, and D. this clade, including the two best-known species Pol. 2011. A new sauropodomorph (Din­ explicitly included by Owen (1842), as suggested osauria: Saurischia) from Quebrada del Barro previously by Holtz (in Padian, 1997), Olshevsky formation (Marayes-El Carrizal Basin), north­ (2000), and Clarke (2004). western Argentina. PLOS ONE 6(11):1–19. Unfortunately, Owen (1842) used only Bakker, R. T., and P. M. Galton. 1974. Dinosaur generic names for the three taxa he included in monophyly and a new class of vertebrates. Nature 248:168–172. his Dinosauria (Megalosaurus, Iguanodon and Baron, M. G., D. B. Norman, and P. M. Barrett. ). We accordingly follow Benson 2017. A new hypothesis of dinosaur relation- et al. (2008) in considering M. bucklandii the ships and early dinosaur evolution. Nature of Megalosaurus (contra Lloyd et al., 2008) 543:501–506. and adopting the subsequently designated I. Beneden, P. 1881. Sur l’arc pelvien chez les dinosau- bernissartensis as the type of Iguanodon (ICZN, riens de Bernissart. Bull. Acad. Roy. Belg., 3 sér. 2000). Owen (1842) possessed scant knowl- 1(5):600–608. edge of sauropodomorph dinosaurs, mistak- Benson, R. B. J., P. M. Barrett, P. Powell, and ing the remains of the sauropod dinosaur D. B. Norman. 2008. The taxonomic sta- tus of Megalosaurus bucklandii (Dinosauria, Cetiosaurus for a gigantic, marine, crocodilian- Theropoda) from the Middle of like “”. But with more specimens he later Oxfordshire, UK. Palaeontology 51:419–424. accepted that Cetiosaurus belonged with the Benton, M. J. 1990. Origin and interrelationships of dinosaurs (Owen, 1875). Because Owen coined dinosaurs. Pp. 11–30 in The Dinosauria (D. B. both names, Dinosauria and Cetiosaurus, and Weishampel, P. Dodson and H. Osmólska, eds.). because C. oxoniensis Phillips 1871 ranks among University of California Press, Berkeley, CA. the earliest discovered, and is by far the best Benton, M. J. 2008. How to find a dinosaur, and known, sauropod from England (Upchurch the role of synonymy in biodiversity studies. Paleobiology 34:516–533. and Martin, 2003), we have added that species Benton, M. J., and J. Clark. 1988. phylog- as a specifier to the definition to preserve the eny and the relationships of the Crocodylia. Pp. traditional inclusion of sauropodomorphs in 289–332 in The Phylogeny and Classification of Dinosauria. Although no bird species is used as Tetrapods, Vol. 1, , Reptiles, Birds an internal specifier, according to nearly every (M. J. Benton, ed.). Clarendon Press, Oxford. phylogeny published since Gauthier (1986; see Bever, G. S., J. A. Gauthier, and G. P. Wagner. also Gauthier, 1984), Aves is part of Dinosauria 2011. Finding the frame shift: digit loss, devel- as defined here (but see James and Pourtless, opmental variability, and the origin of the Evol. Dev. 2009). Archetypical dinosaurs such as the avian hand. 13:269–279. Bittencourt, J. S., A. B. Arcucci, C. A. Marsicano, and horridus, horned ornithischian no M. C. Langer. 2014. Osteology of the Middle less than the winged theropod Archaeopteryx Triassic archosaur admixtus Romer lithographica, can accordingly be regarded as (Chañares Formation, Argentina), its inclusiv- stem birds, even though the former species is far ity, and relationships amongst early dinosauro- more distantly related to Aves than is the latter. morphs. J. Syst. Palaeontol. 13:189–219.

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Sereno, P. C., and F. E. Novas. 1992. The complete Fernando E. Novas; Laboratorio de Anatomía skull and skeleton of an early dinosaur. Science Comparada y Evolución de los Vertebrados; 258:1137–1140. Museo Argentino de Ciencias Naturales Sereno, P. C., and F. E. Novas. 1993. The skull and neck “Bernardino Rivadavia”; Buenos Aires, of the basal theropod ischigualas- C1405DJR, Argentina. Email: fernovas@ tensis. J. Vertebr. Paleontol. 13:451–476. yahoo.com.ar. Starrfelt, J., and L. H Liow. 2016. How many dino- Jonathas S. Bittencourt; Departamento de Geologia, saur species were there? Fossil bias and true Instituto de Geociências; Universidade Federal richness estimated using a Poisson sampling de Minas Gerais; Belo Horizonte-MG, 31270- model. Philos. Trans. R. Soc. Lond. B Biol. Sci. 901, Brazil. Email: bittencourt.paleo@gmail. 371: 20150219 com. Stephanic, C. M., and S. J. Nesbitt. 2019. The evo- Martín D. Ezcurra; Sección Paleontología de lution and role of the hyposphene-hypantrum Vertebrados; Museo Argentino de Ciencias articulation in Archosauria: phylogeny, size and/ Naturales “Bernardino Rivadavia”; Buenos or mechanics? Roy. Soc. Open Sci. 6:190258. Aires, C1405DJR, Argentina. Email: Thulborn, R. A. 1975. Dinosaur polyphyly and the ­[email protected]. classification of archosaurs and birds. Aust. J. Jacques A. Gauthier; Department of Geology and Zool. 23:249–270. Geophysics; ; New Haven, CT Upchurch, P., and J. Martin. 2003. The anatomy 06520-8109, USA. E-mail: jacques.gauthier@ and taxonomy of Cetiosaurus (Saurischia, yale.edu. ) from the Middle Jurassic of England. J. Vertebr. Palaeontol. 23:208–231. Date Accepted: 27 July 2018 Wagner, G. P. 2014. Homology, Genes, and Evolutionary Innovation. Princeton University Primary Editor: Press, Princeton, NJ. Weishampel, D. B., P. Dodson, and H. Osmolska, eds. 2004. The Dinosauria. 2nd edition. University of California Press, Berkeley/Los Angeles/London.

Authors

Max Cardoso Langer; Departamento de Biologia, FFCLRP; Universidade de São Paulo; Ribeirão Preto-SP, 14040-901, Brazil. Email: [email protected].

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