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Reptilia - Diplodocidae

Synonymy list
YearName and author
1877Amphicoelias Cope p. 3
1878Amphicoelias Cope p. 76
1878Amphicoelias Williston p. 45
1890Amphicoelias Zittel p. 709
1891Amphicoelias Cope p. 43
1898Amphicoelias Cope p. 69 fig. 22
1902Amphicoelias Hay p. 486
1908Amphicoelias Huene p. 297
1919Amphicoelias Osborn and Mook p. 383
1927Amphicoelias Huene p. 123
1928Amphicoelias Nopcsa p. 184
1929Amphicoelias Huene p. 117
1956Amphicoelias Romer p. 624
1964Amphicoelias Tatarinov p. 549
1966Amphicoelias Romer p. 370
1970Amphicoelias Steel p. 80
1981Amphicoelias Coombs, Jr. and Molnar p. 356
1988Amphicoelias Paul p. 11
1990Amphicoelias McIntosh p. 391
1996Amphicoelias Bakker p. 44
1996Amphicoelias Wilson and Smith p. 73A
1997Amphicoelias McIntosh p. 657
1999Amphicoelias Salgado p. 204
2002Amphicoelias Wilson p. 248
2004Amphicoelias Upchurch et al. p. 265
2005Amphicoelias McIntosh p. 74
2006Amphicoelias Chure et al. p. 236
2010Amphicoelias Galiano and Albersdörfer p. 5
2011Amphicoelias Whitlock
2012Amphicoelias Mannion et al.
2013Amphicoelias Tschopp and Mateus p. 877 fig. 11
2015Amphicoelias Tschopp et al.
2017Amphicoelias Tschopp and Mateus

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phylumChordataHaeckel 1847
subclassDipnotetrapodomorpha(Nelson 2006)
SauriaGauthier 1984
Archosauromorpha(Huene 1946)
ArchosauriformesGauthier 1986
Sauropodomorpha(Huene 1932)

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.

H. Galiano and R. Albersdörfer 2010The genus Amphicoelias differs from other diplodocid genera in the following characteristics of primitive and derived features. Skull microcephalomorph, rostrum long; premaxillae caudally elongate, quadrate rostroventrally inclined; external nares opening dorsally above orbits; basipterygoid processes slender and elongate, occipital condyle ventrally positioned. Upper and lower teeth reduced in number and modified into sub-equal lengths of crown and root that are long and slender, spaced apart and retained in front of jaws; jaws behind preantorbital fenestrae edentulous. mandible long slender with expended symphysis. Fifteen cervical vertebrae, 2nd-15th elongated with 14th process being the longest centrum, ten free dorsals, sacrum normally comprised of one dorsal, two sacral and two caudal vertebrae. First dorsal in the series has the longest centrum, 10th dorsal with neural spine body off alignment with centrum, posterior dorsals, sacrum and anterior caudal vertebrae all with tall neural spines. Sacral vertebrae with ventral keels. three sectioned diverse caudal morphology, anterior caudals with pleurocoels (suppressed or absent in males) and expanded transverse processes; centrum of anterior caudals gradually decreasing posteriorly in size until, at a mid-point, they increase in size and robustness from (16th-20th) before decreasing again in size where they meet the supernumerary whiplash series. the approximately forty or so supernumery caudals are sub-equal in length. the location of enlarged mid caudals or "disproportionately enlarged" transitional series is variable. Caudal fusion is also variable depending on the individual and age, and can occur in singles or in sets of two. Compact bone construction is dense in posterior caudals starting from "disproportionately enlarged" series. Anterior chevrons without anterior processes but remaining posterior ones diversely shaped depending on the location of the tail, starting in mid-tail from a simple elongated paddle then to forked and rod-like “double beam” shape types. Anterior processes become greater in size towards the end, and reach a near equal length with the main chevron body. Forked chevrons usually located below in restricted areas within mid caudal series; ischia distal ends expanded; femur elongated, straight with reduced 4th trochanter and cross section sub circular to ovate. Sternal ribs ossified.
H. Galiano and R. Albersdörfer 2010Amphicoelias differs from all other diplodocids in the extreme microcephalomorph condition of the skull in relation to the length of the axial skeleton in mature individuals. In comparison to other sauropods, the skull in Amphicoelias has proportionately the longest rostrum relative to the post-orbital length. Thus, the premaxillae are caudally elongated and the anterior-posterior length of the nasal and frontal bones are reduced and receded, more so than in other sauropods. The Amphicoelias skull is characterized by a rostral crest formed by the caudal processes of the premaxillae (autapomorphy), and with the premaxillae and maxillae transversely extended and flattened forming a duck billed shaped rostrum. Presence of the external narial openings located posterior-dorsal almost above orbits (synapomorphy). Amphicoelias differs from all sauropods in the development of an interfenestra bridge dividing the preantorbital from the antorbital fenestrae (autapomorphy). In Amphicoelias, Nigersaurus, and Tornieria the preantorbital fenestrae are positioned immediately behind the last maxillary tooth. There are two preantorbital openings present in the maxilla of Nemegtosaurus distinguishing it from Amphicoelias Pterygoid bones in Amphicoelias are sagitally positioned at a steep angle in comparison to other known sauropod skulls. Amphicoelias shares with the diplodocid genera Tornieria, and Dicraeosaurus, the following derived sauropod characters: occipital condyle ventrally positioned; quadrates rostroventrally inclined; basipterygoid processes slender, elongate and oriented rostroventrally; and jaws behind preantorbital fenestra are without teeth.
No measurements are available
Composition: hydroxyapatiteinfrao
Entire body: yesg
Adult length: 10 to < 100infrao
Adult width: 10 to < 100infrao
Adult height: 10 to < 100infrao
Maximum body mass: 100000 kgg
Minimum body mass: 30000 kgg
Thickness: thickinfrao
Architecture: compact or denseinfrao
Form: sphericalinfrao
Ontogeny: accretion, modification of partsinfrao
Grouping: gregariousinfrao
Environment: terrestrialinfrao
Locomotion: actively mobileinfrao
Life habit: ground dwellinginfrao
Diet: herbivoreinfrao
Reproduction: oviparousinfrao
Dispersal: direct/internalinfrao
Dispersal 2: mobileinfrao
Created: 2005-08-24 13:40:53
Modified: 2005-08-24 15:40:53
Source: g = genus, infrao = infraorder
References: Kiessling 2004, Peczkis 1995, Marsh 1875

Age range: base of the Kimmeridgian to the top of the Early/Lower Kimmeridgian or 157.30000 to 150.80000 Ma

Collections (5 total)

Time interval Ma Country or state Original ID and collection number
Late/Upper Oxfordian - Early/Lower Kimmeridgian161.2 - 150.8USA (Wyoming) A. brontodiplodocus (126540)
Kimmeridgian157.3 - 152.1USA (Montana) A. sp. (49624)
Kimmeridgian - Tithonian157.3 - 145.0USA (Colorado) A. altus (48148 48154)
Tithonian152.1 - 145.0Zimbabwe (Mashonaland North) A. sp. (49105)