Open Paleo

Alvarezsauridae

Bonaparte, 1991 Type genus Alvarezsaurus

Its genera lived 93.9–66.0 million years ago Late Cretaceous
Late Cretaceous stages

Alvarezsauridae is a family of small, long-legged maniraptoran theropods known from the Late Cretaceous of South America, North America, and Asia, from the Cenomanian to the uppermost Maastrichtian (Fowler and colleagues, 2020). Though once interpreted as flightless birds, they are now placed outside Avialae among the coelurosaurs (Qin and colleagues, 2019). The family includes the large-bodied Patagonykinae of Patagonia, the South American Alvarezsaurus, and the miniaturized Parvicursorinae, which some authors treat as the senior synonym of Mononykinae (Agnolín and colleagues, 2012). Alvarezsaurids have long legs and exceptionally short, robust forelimbs bearing a hypertrophied claw on the first finger, with the other fingers lost or greatly reduced in derived forms (Fowler and colleagues, 2020). Their simple teeth have prompted comparisons with living ant-eaters and an insect diet, the stout forelimbs perhaps used to tear apart vegetation or insect nests (Fowler and colleagues, 2020), though Agnolín and colleagues (2012) find no unambiguous evidence for ant-eating.

Diagnosis

  1. Presacral vertebrae with ball-and-socket (opisthocoelous) intercentral joints
  2. Humerus with a figure-of-eight cross-section
  3. Hypertrophied olecranon process of the ulna
  4. Symmetrical iliac blade
  5. Fully procoelous caudal vertebrae

Clades within Alvarezsauridae

Genera placed directly in Alvarezsauridae

  • Achillesaurus Disputed Martinelli & Vera, 2007 Santonian (85.7–83.6 Ma)Argentina
  • Albertonykus Longrich & Currie, 2009 Maastrichtian (72.2–66.0 Ma)Canada
  • Alvarezsaurus Bonaparte, 1991 Santonian (85.7–83.6 Ma)Argentina
  • Heptasteornis Nomen dubium Harrison & Walker, 1975 Maastrichtian (72.2–66.0 Ma)Romaniaunder dispute
  • Nemegtonykus Disputed Lee et al., 2019 Maastrichtian (72.2–66.0 Ma)Mongolia
  • Qiupanykus Lü et al., 2018 Maastrichtian (72.2–66.0 Ma)Chinaunder dispute

References

  1. Bonaparte, J. F. (1991). Los vertebrados fósiles de la Formación Río Colorado, de la Ciudad de Neuquén y Cercanías, Cretácico Superior, Argentina [The vertebrate fossils of the Rio Colorado Formation, from the city of Neuquén and surrounding areas, Upper Cretaceous, Argentina]. Revista del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" e Instituto Nacional de Investigación de las Ciencias Naturales: Paleontología 4(3): 17-123. bonaparte1991a
  2. Qin, Z.; Clark, J.; Choiniere, J.; Xu, X. (2019). A new alvarezsaurian theropod from the Upper Jurassic Shishugou Formation of western China. Scientific Reports 9(1). Springer Science and Business Media LLC. doi:10.1038/s41598-019-48148-7

    Described a Jurassic alvarezsaurian from China, reviewing the group's earlier interpretation as flightless birds and its placement outside Avialae.

    qin2019a
  3. Agnolín, F. L.; Powell, J. E.; Novas, F. E.; Kundrát, M. (2012). New alvarezsaurid (Dinosauria, Theropoda) from uppermost Cretaceous of north-western Patagonia with associated eggs. Cretaceous Research 35: 33-56. Elsevier BV. doi:10.1016/j.cretres.2011.11.014

    Described Bonapartenykus and named Patagonykinae for it and Patagonykus, noting Parvicursorinae is treated by some as the senior synonym of Mononykinae.

    agnolín2012a
  4. Fowler, D. W.; Wilson, J. P.; Freedman Fowler, E. A.; Noto, C. R.; Anduza, D.; Horner, J. R. (2020). Trierarchuncus prairiensis gen. et sp. nov., the last alvarezsaurid: Hell Creek Formation (uppermost Maastrichtian), Montana. Cretaceous Research 116. Elsevier BV. doi:10.1016/j.cretres.2020.104560

    Described Trierarchuncus from the uppermost Maastrichtian Hell Creek Formation, the youngest known alvarezsaurid.

    fowler2020b