Hypsilophodontidae

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Hypsilophodontidae
Temporal range:
Ma
↓
Hypsilophodon skeleton
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Clade: †
Clypeodonta
Family: †Hypsilophodontidae
Dollo, 1882[1]
Subgroups[2]
Synonyms
  • Hypsilophodontinae Nopcsa, 1928
  • Hypsilophodontia Cooper, 1985

Hypsilophodontidae (or Hypsilophodontia) is a traditionally used

phylogenetic analyses from the 1990s and mid 2000s,[3][4] although there have also been many finding that the family is an unnatural grouping which should only include the type genus, Hypsilophodon, with the other genera being within clades like Thescelosauridae and Elasmaria.[5][6][7][8][9][10][11][12][13][14][15] A 2014 analysis by Norman recovered a grouping of Hypsilophodon, Rhabdodontidae and Tenontosaurus, which he referred to as Hypsilophodontia.[2] All other analyses from around the same time have instead found these latter taxa to be within Iguanodontia.[12][16]

Linnaean usage

Othniel Marsh (since named Othnielosaurus and later Nanosaurus
)

Hypsilophodontidae was named originally in

phalanges; the femur was either shorter or longer than the tibia; and dorsal ribs had only a single articulation point.[17]

Thescelosaurus edmontonensis
in display as preserved

The first expansive analysis on the relationships of Hypsilophodontidae was that of Swinton in

Charles M. Sternberg (1940) considered there to be multiple genera within the family, all sharing fully enamelled teeth, divided into two subfamilies, Hypsilophodontinae and Thescelosaurinae. Within Hypsilophodontinae–grouped by a longer scapula, thinner forelimb and femora shorter than tibiae–Sternberg included Hypsilophodon, Dysalotosaurus, and Parksosaurus (renaming of Thescelosaurus warreni). Only Thescelosaurus was included in Thescelosaurinae, as it had a tibia shorter than the femur.[20]

Peter M. Galton in 1972 re-studied the relationships of taxa within Ornithischia. Thescelosaurus was removed from Hypsilophodontidae because of its short limbs, meaning it was probably not cursorial, unlike all other hypsilophodonts. The presence of premaxilla teeth, once used to diagnose the group, was found to be present in unrelated taxa like Heterodontosaurus, Protoceratops and Silvisaurus. Galton made Hypsilophodontidae paraphyletic, as he considered Thescelosaurus to be a hypsilophodont, but excluded it from the family Hypsilophodontidae. The phylogenetic hypothesis of Galton is shown below. Taxa considered hypsilophodontids are enclosed by green.[21]

Ornithischia

Cladistic usage

Question of monophyly

In 1992

David Weishampel and Ronald Heinrich reviewed the systematics and phylogenetics of Hypsilophodontidae. Hypsilophodontidae was supported as a monophyletic clade that encompassed "thescelosaurids", Hypsilophodon and Yandusaurus. The family was diagnosed by the absence of ridges that end as denticles in teeth (reversed in Hypsilophodon); presence of a single central ridge on dentary teeth; ossified sternal plates on torso ribs; and a straight and unexpanded shape of the prepubis. Their resulting cladogram is reproduced below:[4]

Euornithopoda

The following cladogram of hypsilophodont relationships depicts the paraphyletic hypotheses; the "natural Hypsilophodontidae" hypothesis has been falling out of favor since the mid-late 1990s. It is after Brown et al. (2013), the most recent analysis of hypsilophodonts.[16] Ornithischia, Ornithopoda, and Iguanodontia were not designated in their result, and so are left out here. Additional ornithopods beyond Tenontosaurus are omitted. Dinosaurs traditionally described as hypsilophodonts are found from Agilisaurus or Hexinlusaurus to Hypsilophodon or Gasparinisaura.

Skeleton of Convolosaurus (the Proctor Lake hypsilophodont)
unnamed

Norman's Hypsilophodontia

A more recent alternate phylogeny, by Norman in 2014, resolved a monophyletic Hypsilophodontia (the family Hypsilophodontidae was not used because of its history). Hypsilophodon grouped with Rhabdodontidae and Tenontosaurus.[2]

Clypeodonta

Other research

In one analysis in her 2022 review of

sister taxon of Iguanodontia, which consisted of several "traditional" hypsilophodontids, as well as Thescelosauridae. The Bayesian topology of her phylogenetic analyses is shown in the cladogram below:[22]

Clypeodonta
silhouette illustration of Vectidromeus insularis by Nick Longrich
The size of Hypsilophodon and the type specimen of Vectidromeus compared to a human

In 2023, Longrich et al. described Vectidromeus as a new genus of hypsilophodontid. Although they did not perform a phylogenetic analysis, they suggested that, since other taxa previously assigned to Hypsilophodontidae had subsequently been moved to other groups, Vectidromeus and Hypsilophodon remained as the only members of the clade.[23]

References

  1. ^ Dollo, L. (1882). "Première note sur les dinosauriens de Bernissart". Bulletin du Musée d'Histoire Naturelle de Belgique. 1: 161–180.
  2. ^
    doi:10.1111/zoj.12193
    .
  3. ISBN 978-0-520-06727-1
    .
  4. ^
    doi:10.1080/10292389209380426
    .
  5. doi:10.1080/02724634.1998.10011116
    .
  6. doi:10.1080/02724634.1998.10011116
    .
  7. ^ Buchholz, Peter W. (2002). "Phylogeny and biogeography of basal Ornithischia". The Mesozoic in Wyoming, Tate 2002. Casper, Wyoming: The Geological Museum, Casper College. pp. 18–34.
  8. S2CID 86339025
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  9. ISBN 978-0-520-24209-8
    .
  10. PMID 17374596
    .
  11. S2CID 84273584
    .
  12. ^
    PMID 26713260
    .
  13. PMID 26673161
    .
  14. PMID 17567562
    .
  15. S2CID 86728076
    .
  16. ^
    S2CID 129160518
    .
  17. ^
    doi:10.5479/si.00963801.49-2127.591
    .
  18. ^ Zittel, K.A. von (1911). Grundzüge der Paläontologie (Paläzoologie) II. Abtielung Vertebrata (in German) (2 ed.). Berlin and München: Druck und verlad von R. Oldenbourg. p. 289.
  19. doi:10.1111/j.1469-7998.1936.tb08518.x
    .
  20. JSTOR 1298552
    .
  21. S2CID 4196759
    .
  22. doi:10.26879/702
    .
  23. S2CID 261933503
    .
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