Diplodocoidea

Diplodocoidea is a superfamily of sauropod dinosaurs, which included some of the longest animals of all time, including slender giants like Supersaurus, Diplodocus, Apatosaurus, and Amphicoelias. Most had very long necks and long, whip-like tails; however, one family (the dicraeosaurids) are the only known sauropods to have re-evolved a short neck, presumably an adaptation for feeding low to the ground. This adaptation was taken to the extreme in the highly specialized sauropod Brachytrachelopan. A study of snout shape and dental microwear in diplodocoids showed that the square snouts, large proportion of pits, and fine subparallel scratches in Apatosaurus, Diplodocus, Nigersaurus, and Rebbachisaurus suggest ground-height nonselective browsing; the narrow snouts of Dicraeosaurus, Suuwassea, and Tornieria and the coarse scratches and gouges on the teeth of Dicraeosaurus suggest mid-height selective browsing in those taxa.^[2] This taxon is also noteworthy because diplodocoid sauropods had the highest tooth replacement rates of any vertebrates, as exemplified by Nigersaurus, which had new teeth erupting every 30 days.^[3]

Diplodocoids Temporal range: Middle Jurassic–Late Cretaceous, 174–93 Ma PreꞒ Ꞓ O S D C P T J K Pg N Possible Turonian Record [1]
Six diplodocoids (top left to bottom right): Barosaurus, Apatosaurus louisae, Brachytrachelopan, Nigersaurus, Haplocanthosaurus, Amargasaurus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	†Sauropodomorpha
Clade:	†Sauropoda
Clade:	†Neosauropoda
Superfamily:	†Diplodocoidea Marsh, 1884
Type species
†Diplodocus longus Marsh, 1878
Subgroups
†Haplocanthosaurus †Diplodocimorpha Calvo and Salgado 1995 †Rebbachisauridae †Flagellicaudata Harris & Dodson, 2004 †Dicraeosauridae †Diplodocidae
Synonyms
Rebbachisauroidea Bonaparte, 1997

Most diplodocoids belong to Diplodocimorpha, a name first used by Calvo & Salgado (1995), who defined it as "Rebbachisaurus tessonei sp. nov., Diplodocidae, and all descendants of their common ancestor." The group was not used often, and was synonymized with Diplodocoidea as the groups were often found to have the same content. In 2005, Mike P. Taylor and Darren Naish reviewed diplodocoid phylogeny and taxonomy, and realized that Diplodocimorpha could not be synonymized with Diplodocoidea. Whereas the former was defined node-based, the latter was branch-based.^[4] Haplocanthosaurus and possibly Amphicoelias are non-diplodocimorph diplodocoids.^[5]

Taxonomy

The clade Flagellicaudata was erected by Harris and Dodson (2004) for the diplodocoid clade formed by Dicraeosauridae and Diplodocidae in their paper describing a new genus of sauropod dinosaur, Suuwassea. The authors carried out a phylogenetic analysis and noted that Suuwassea, although more derived than Rebbachisauridae, is in a trichotomy with other families belonging to Diplodocoidea (Diplodocidae and Dicraeosauridae). Flagellicaudata was defined as a node-based clade consisting of the most recent common ancestor of Dicraeosaurus and Diplodocus and all of its descendants. The word "Flagellicaudata" refers to long, whip-like tails of that animals (flagellum is a Latin word meaning "whip" and cauda means in Latin "tail").^[6]

The phylogenetics of Diplodocoidea were reviewed in 2015 by Emanuel Tschopp, Octavio Mateus and Roger Benson with a specimen-level phylogenetic analysis, as well as a species-level analysis. Their cladistic analysis is shown below.^[7]

Diplodocoidea

Haplocanthosaurus priscus Diplodocimorpha Rebbachisauridae Zapalasaurus bonapartei Limaysaurinae Cathartesaura anaerobica Limaysaurus tessonei Nigersaurinae Nigersaurus taqueti Demandasaurus darwini Flagellicaudata Dicraeosauridae Dyslocosaurus polyonychius Suuwassea emilieae Dystrophaeus viaemalae Brachytrachelopan mesai Tharosaurus indicus Amargasaurus cazaui Dicraeosaurus hansemanni Diplodocidae Amphicoelias altus Apatosaurinae ?Apatosaurinae gen. et sp. nov. Apatosaurus ajax Apatosaurus louisae Brontosaurus excelsus Brontosaurus yahnahpin Brontosaurus parvus Diplodocinae ?Diplodocinae gen. et sp. nov. Tornieria africana Supersaurus lourinhanensis Supersaurus vivianae Leinkupal laticauda Galeamopus hayi Diplodocus carnegiei Diplodocus hallorum Kaatedocus siberi Barosaurus lentus

References

• Dinosaurs portal

1. Averianov, Alexander; Sues, Hans-Dieter (2021). "First rebbachisaurid sauropod dinosaur from Asia". PLOS ONE. 16 (2): e0246620. doi:10.1371/journal.pone.0246620. PMC 7904184. PMID 33626060.
2. John A. Whitlock (6 April 2011) Inferences of Diplodocoid (Sauropoda: Dinosauria) Feeding Behavior from Snout Shape and Microwear Analyses
3. Sereno, PC; Wilson, JA; Witmer, LM; Whitlock, JA; Maga, A; et al. (2007). "Structural Extremes in a Cretaceous Dinosaur". PLOS ONE. 2 (11): e1230. doi:10.1371/journal.pone.0001230. PMC 2077925. PMID 18030355.
4. Taylor, M.P.; Naish, D. (2005). "The phylogenetic taxonomy of Diplodocoidea (Dinosauria: Sauropoda)" (PDF). PaleoBios. 25 (2): 1–7.
5. Mannion, Philip D.; Tschopp, Emanuel; Whitlock, John A. (2021-06-16). "Anatomy and systematics of the diplodocoid Amphicoelias altus supports high sauropod dinosaur diversity in the Upper Jurassic Morrison Formation of the USA". Royal Society Open Science. 8 (6): 210377. doi:10.1098/rsos.210377. ISSN 2054-5703. PMC 8206699.
6. JD Harris, P Dodson (2004). "A new diplodocoid sauropod dinosaur from the Upper Jurassic Morrison Formation of Montana, USA". Acta Palaeontologica Polonica. 49 (2): 197–210.
7. Tschopp, E.; Mateus, O.; Benson, R.B.J. (2015). "A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda)". PeerJ. 3: e857. doi:10.7717/peerj.857. PMC 4393826. PMID 25870766.