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Thecodontosaurus antiquus

Reptilia

Taxonomy
Thecodontosaurus antiquus was named by Morris (1843). Its type specimen is BCM 1836 and is a 3D body fossil. Its type locality is Durdham Down, Quarry Steps, which is in a Rhaetian fissure fill limestone/breccia in the Magnesian Conglomerate Formation of the United Kingdom. It was considered monophyletic by Yates (2003).

Synonymy list
YearName and author
1843Thecodontosaurus antiquus Morris p. 211
1846Thecodontosaurus antiquus Plieninger p. 150
1850Thecodontosaurus antiquus King p. 238
1852Thecodontosaurus antiquus Quenstedt p. 109
1855Thecodontosaurus antiquus Meyer p. 158
1856Thecodontosaurus antiquus Emmons p. 296
1856Thecodontosaurus antiquus Roemer p. 785
1859Thecodontosaurus antiquus Owen p. 140
1860Thecodontosaurus antiquus Owen p. 248
1861Thecodontosaurus antiquus Gervais p. 251
1861Thecodontosaurus antiquus Owen p. 275
1866Thecodontosaurus antiquus Haeckel p. CXXXIV
1869Thecodontosaurus antiquus Gervais p. 219
1888Thecodontosaurus antiquus Lydekker p. 175
1890Thecodontosaurus antiquus Woodward and Sherborn p. 291
1895Thecodontosaurus antiquus Seeley p. 144
1901Thecodontosaurus antiquus Nopcsa p. 198
1905Thecodontosaurus antiquus Huene p. 349
1907Thecodontosaurus antiquus Sauvage p. 14
1908Thecodontosaurus antiquus Huene p. 13
1909Thecodontosaurus antiquus Allen p. 276
1910Thecodontosaurus antiquus Hay p. 12
1914Thecodontosaurus antiquus Huene p. 12
1918Thecodontosaurus antiquus Haughton p. 469
1920Thecodontosaurus antiquus Van Hoepen pp. 91-92
1929Thecodontosaurus antiquus Huene p. 271
1939Thecodontosaurus antiquus Kuhn p. 61
1941Thecodontosaurus antiquus Huene p. 141
1941Thecodontosaurus antiquus Young p. 206
1957Thecodontosaurus antiquus Robinson p. 262
1964Thecodontosaurus antiquus Tatarinov p. 541
1970Thecodontosaurus antiquus Demathieu p. 154
1970Thecodontosaurus antiquus Steel p. 50
1973Thecodontosaurus antiquus Galton p. 248
1976Thecodontosaurus antiquus Galton and Cluver p. 139
1993Thecodontosaurus antiquus Storrs p. 448
2000Thecodontosaurus antiquus Benton et al. p. 81
2000Thecodontosaurus antiquus Galton p. 267
2000Thecodontosaurus antiquus Schouten p. 73
2003Thecodontosaurus antiquus Yates
2004Thecodontosaurus antiquus Galton and Upchurch p. 236
2005Thecodontosaurus antiquus Galton p. 61A
2005Thecodontosaurus antiquus Yates p. 117
2006Thecodontosaurus antiquus Scanlon p. 276
2007Thecodontosaurus antiquus Galton p. 560
2007Thecodontosaurus antiquus Galton et al. p. 120
2007Thecodontosaurus antiquus Naish and Martill p. 496
2007Thecodontosaurus antiquus Smith and Pol p. 661
2007Thecodontosaurus antiquus Upchurch et al. p. 76
2009Thecodontosaurus antiquus Bittencourt and Kellner p. 9
2010Thecodontosaurus antiquus Langer et al. p. 77
2010Thecodontosaurus antiquus Yates p. 744
2011Thecodontosaurus antiquus Apaldetti et al. p. 4
2012Thecodontosaurus antiquus van den Berg et al. p. 641
2016Thecodontosaurus antiquus Griffin and Nesbitt p. 1
2020Thecodontosaurus antiquus Ballell et al. p. 2
2020Thecodontosaurus antiquus Dalla Vecchia p. 609
2021Thecodontosaurus antiquus Ballell et al. p. 541
2021Thecodontosaurus antiquus Müller and Garcia p. 7
2022Thecodontosaurus antiquus Ballell et al. p. 2

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RankNameAuthor
kingdomAnimalia()
—Bilateria
—EubilateriaAx 1987
—Deuterostomia
phylumChordataHaeckel 1874
subphylumVertebrata
superclassGnathostomata
—Osteichthyes()
subclassSarcopterygii()
subclassDipnotetrapodomorpha(Nelson 2006)
subclassTetrapodomorpha()
—Tetrapoda
—Reptiliomorpha
—Anthracosauria
subclassAmphibiosauriaKuhn 1967
—Cotylosauria()
—Amniota
—Sauropsida
classReptilia
RankNameAuthor
subclassEureptilia()
—Romeriida
—Diapsida()
—Archosauromorpha(Huene 1946)
—Crocopoda
—ArchosauriformesGauthier 1986
—Eucrocopoda
—Archosauria()
informalAvemetatarsalia
—Ornithodira
—Dinosauromorpha
—Dinosauriformes
—Dinosauria()
—Saurischia()
—Eusaurischia
—Sauropodomorpha(Huene 1932)
genusThecodontosaurus
speciesantiquusMorris 1843

If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.

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Diagnosis
ReferenceDiagnosis
M. J. Benton et al. 2000Small, gracile prosauropod (up to 2 m), distinguished primarily on the absence of derived characters seen in other prosauropods. Autapomorphies:
1. Elongate basipterygoid processes in the braincase. The height measured from the top of the parasphenoid to the distal tip of the basipterygoid process is equal to the height of the braincase measured from the top of the parasphenoid to the top of the supraoccipital (Fig. 6B), whereas other prosauropods for which braincases are known share the primitive character of considerably shorter basipterygoid processes. This character is seen also in sauropods (J. Wilson, pers. comm., 1999), but its homology has to be assessed.
2. Dentary less than half length of mandible. The dentary, though damaged (Figs. 3, 4), appears to be relatively complete, and it is short compared to that of other early dinosaurs. If the juvenile specimens from South Wales ascribed to Thecodontosaurus sp. are correctly identified, then the relative shortness of the dentary is confirmed.
3. Posterior process of iliac blade subquadratic. The posterior process of the iliac blade in several specimens of T. antiquus has a distinctly squared termination (Fig. 15A, B), whereas other prosauropods, and other early dinosaurs, have a rounded termination to the posterior process.
A. M. Yates 2003Small, gracile sauropodomorphs with the following derived character states. 1. The basipterygoid processes are elongate and slender, with the length of the process, measured from its tip to the dorsal margin of the parabasisphenoid, being equal to the
height of the braincase, measured from the dorsal margin of the parabasisphenoid to the top of the supraoccipital (convergent in ‘Efraasia diagnostica’). 2. The dentary is short and deep, occupying less than 40% of the total mandibular length, and with a maximum dor-
soventral depth that is greater than 20% of its length (convergent in Saturnalia tupiniquim). 3. The epipophyses of the cranial cervicals are flat plates that
overhang the caudal margins of the postzygapophyseal facets but do not form raised ridges on the dorsal surface of the postzygapophysis. 4. The proximal and mid-caudal neural spines are positioned at the extreme caudal end of their neural arches, filling the
interpostzygapophyseal space (convergent in ‘Efraasia diagnostica’). 5. The ventral furrowing of the caudal centra is reduced so that it is only weakly present in the proximal caudals and is absent altogether from the mid and distal caudals.
P. M. Galton 2007as in Pantydraco caducus, the dentary is short and deep, with a maximum dorsoventral depth that is greater than 20 % of its length, and teeth are plesiomorphic in all being recurved in lateral view. Based on the type Clifton material, Thecodontosaurus antiquus has no autapomorphies or a unique combination of characters and the diagnosis awaits description of the referred material from Tytherington.
A. Ballell et al. 2020A sauropodomorph dinosaur distinguished from other basal sauropodomorphs by the following combination of characters (autapomorphies indicated with an asterisk): absence of a postorbital flange; maxillary and dentary tooth crowns not recurved and with coarse serrations; extensive muscle scar for the origin of M. triceps brachii caput scapulare on the lateral side of the glenoid lip of the scapula*; elaborate humeral cuboid fossa with a bilobate proximal outline and extensively pitted surface*; reduced brevis fossa and shelf; incompletely perforated acetabulum; absence of a femoral trochanteric shelf; and posterolateral descending process of the tibia anteroposteriorly wide and mediolaterally narrow, not reaching the lateral extent of the anterolateral process* (convergent with Anchisaurus, Eucnemesaurus entaxonis, Aardonyx, and Sauropoda).