Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:


Hummingbird-sized dinosaur from the Cretaceous period of Myanmar

A Retraction to this article was published on 22 July 2020

This article has been updated


Skeletal inclusions in approximately 99-million-year-old amber from northern Myanmar provide unprecedented insights into the soft tissue and skeletal anatomy of minute fauna, which are not typically preserved in other depositional environments1,2,3. Among a diversity of vertebrates, seven specimens that preserve the skeletal remains of enantiornithine birds have previously been described1,4,5,6,7,8, all of which (including at least one seemingly mature specimen) are smaller than specimens recovered from lithic materials. Here we describe an exceptionally well-preserved and diminutive bird-like skull that documents a new species, which we name Oculudentavis khaungraae gen. et sp. nov. The find appears to represent the smallest known dinosaur of the Mesozoic era, rivalling the bee hummingbird (Mellisuga helenae)—the smallest living bird—in size. The O. khaungraae specimen preserves features that hint at miniaturization constraints, including a unique pattern of cranial fusion and an autapomorphic ocular morphology9 that resembles the eyes of lizards. The conically arranged scleral ossicles define a small pupil, indicative of diurnal activity. Miniaturization most commonly arises in isolated environments, and the diminutive size of Oculudentavis is therefore consistent with previous suggestions that this amber formed on an island within the Trans-Tethyan arc10. The size and morphology of this species suggest a previously unknown bauplan, and a previously undetected ecology. This discovery highlights the potential of amber deposits to reveal the lowest limits of vertebrate body size.

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Photograph, computed tomography scans and interpretive drawings of the HPG-15-3 holotype of O. khaungraae.
Fig. 2: Proportions of the eye socket relative to the skull in HPG-15-3, compared to extant birds.
Fig. 3: A star plot illustrating the functional morphospace of scleral-ring and orbit morphology of modern saurians in the context of their diel activity pattern.
Fig. 4: Simplified results of the strict consensus of 2,044 trees depicting the phylogenetic relationships of O. khaungraae relative to other known Mesozoic birds.

Similar content being viewed by others

Data availability

Owing to their size, the raw computed tomography data are available upon request from L.X. ( All other materials are included in the Supplementary Information or are available at

Change history


  1. Xing, L. et al. Mummified precocial bird wings in mid-Cretaceous Burmese amber. Nat. Commun. 7, 12089 (2016).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  2. Xing, L. et al. A feathered dinosaur tail with primitive plumage trapped in mid-Cretaceous amber. Curr. Biol. 26, 3352–3360 (2016).

    Article  CAS  PubMed  Google Scholar 

  3. Daza, J. D. et al. An enigmatic miniaturized and attenuate whole lizard from the Mid-Cretaceous amber of Myanmar. Breviora 563, 1–18 (2018).

    Article  Google Scholar 

  4. Xing, L.-D. et al. A mid-Cretaceous enantiornithine (Aves) hatchling preserved in Burmese amber with unusual plumage. Gondwana Res. 49, 264–277 (2017).

    Article  ADS  Google Scholar 

  5. Xing, L.-D. et al. A flattened enantiornithine in mid-Cretaceous Burmese amber: morphology and preservation. Sci. Bull. (Beijing) 63, 235–243 (2018).

    Article  ADS  Google Scholar 

  6. Xing, L. et al. A fully feathered enantiornithine foot and wing fragment preserved in mid-Cretaceous Burmese amber. Sci. Rep. 9, 927 (2019).

    Article  ADS  PubMed  PubMed Central  CAS  Google Scholar 

  7. Xing, L., McKellar, R. C., O’Connor, J. K., Niu, K. & Mai, H. A mid-Cretaceous enantiornithine foot and tail feather preserved in Burmese amber. Sci. Rep. 9, 15513 (2019).

    Article  ADS  PubMed  PubMed Central  CAS  Google Scholar 

  8. Xing, L. et al. A new enantiornithine bird with unusual pedal proportions found in amber. Curr. Biol. 29, 2396–2401.e2 (2019).

    Article  CAS  PubMed  Google Scholar 

  9. Hanken, J. & Wake, D. B. Miniaturization of body size: organismal consequences and evolutionary significance. Annu. Rev. Ecol. Syst. 24, 501–519 (1993).

    Article  Google Scholar 

  10. Westerweel, J. et al. Burma Terrane part of the Trans-Tethyan Arc during collision with India according to palaeomagnetic data. Nat. Geosci. 12, 863–868 (2019).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  11. Shi, G. et al. Age constraint on Burmese amber based on U-Pb dating of zircons. Cretac. Res. 37, 155–163 (2012).

    Article  Google Scholar 

  12. Field, D. J. et al. Complete Ichthyornis skull illuminates mosaic assembly of the avian head. Nature 557, 96–100 (2018).

    Article  ADS  CAS  PubMed  Google Scholar 

  13. Smith, R. D. A. & Ross, A. Amberground pholadid bivalve borings and inclusions in Burmese amber: implications for proximity of resin-producing forests to brackish waters, and the age of the amber. Earth Environ. Sci. Trans. R. Soc. Edinb. 107, 239–247 (2018).

    Google Scholar 

  14. Lovette, I. J. & Fitzpatrick, J. W. The Handbook if Bird Biology 3rd edn (Princeton Univ. Press, 2004).

  15. Dalsgaard, B. et al. Trait evolution, resource specialization and vulnerability to plant extinctions among Antillean hummingbirds. Proc. R. Soc. Lond. B 285, 20172754 (2018).

    Google Scholar 

  16. Glaw, F., Köhler, J., Townsend, T. M. & Vences, M. Rivaling the world’s smallest reptiles: discovery of miniaturized and microendemic new species of leaf chameleons (Brookesia) from northern Madagascar. PLoS ONE 7, e31314 (2012).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  17. Yeh, J. The effect of miniaturized body size on skeletal morphology in frogs. Evolution 56, 628–641 (2002).

    Article  PubMed  Google Scholar 

  18. Griffith, H. Miniaturization and elongation in Eumeces (Sauria: Scincidae). Copeia 1990, 751–758 (1990).

    Article  Google Scholar 

  19. Chiappe, L. M., Ji, S., Ji, Q. & Norell, M. A. Anatomy and systematics of the Confuciusornithidae (Theropoda: Aves) from the Late Mesozoic of northeastern China. Bull. Am. Mus. Nat. Hist. 242, 1–89 (1999).

    Google Scholar 

  20. Elzanowski, A. Embryonic bird skeletons from the Late Cretaceous of Mongolia. Palaeontologica Polonica 42, 147–179 (1981).

    Google Scholar 

  21. Jollie, M. T. The head skeleton of the chicken and remarks on the anatomy of this region in other birds. J. Morphol. 100, 389–436 (1957).

    Article  Google Scholar 

  22. Edinger, T. Über Knöcherne Scleralringe (Fisher, 1929).

  23. Schmitz, L. Quantitative estimates of visual performance features in fossil birds. J. Morphol. 270, 759–773 (2009).

    Article  PubMed  Google Scholar 

  24. Schmitz, L. & Motani, R. Morphological differences between the eyeballs of nocturnal and diurnal amniotes revisited from optical perspectives of visual environments. Vision Res. 50, 936–946 (2010).

    Article  PubMed  Google Scholar 

  25. Schmitz, L. & Motani, R. Nocturnality in dinosaurs inferred from scleral ring and orbit morphology. Science 332, 705–708 (2011).

    Article  ADS  CAS  PubMed  Google Scholar 

  26. Rauhut, O. W. M. The Interrelationships and Evolution of Basal Theropod Dnosaurs (Special Papers in Palaeontology 69) (The Palaeontological Association, London, 2003).

  27. O’Connor, J. & Chiappe, L. M. A revision of enantiornithine (Aves: Ornithothoraces) skull morphology. J. Syst. Palaeontology 9, 135–157 (2011).

    Article  Google Scholar 

  28. Xu, X. & Norell, M. A. A new troodontid dinosaur from China with avian-like sleeping posture. Nature 431, 838–841 (2004).

    Article  ADS  CAS  PubMed  Google Scholar 

  29. O’Connor, J. K. The trophic habits of early birds. Palaeogeogr. Palaeoclimatol. Palaeoecol. 513, 178–195 (2019).

    Article  ADS  Google Scholar 

  30. Rittmeyer, E. N., Allison, A., Gründler, M. C., Thompson, D. K. & Austin, C. C. Ecological guild evolution and the discovery of the world’s smallest vertebrate. PLoS ONE 7, e29797 (2012).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  31. Hu, H. et al. Evolution of the vomer and its implications for cranial kinesis in Paraves. Proc. Natl Acad. Sci. USA 116, 19571–19578 (2019).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  32. Bout, R. G. & Zweers, G. A. The role of cranial kinesis in birds. Comp. Biochem. Physiol. A Mol. Integr. Physiol. 131, 197–205 (2001).

    Article  CAS  PubMed  Google Scholar 

  33. Rayfield, E. J. Aspects of comparative cranial mechanics in the theropod dinosaurs Coelophysis, Allosaurus and Tyrannosaurus. Zool. J. Linn. Soc. 144, 309–316 (2005).

    Article  Google Scholar 

  34. Degrange, F. J., Tambussi, C. P., Taglioretti, M. L., Dondas, A. & Scaglia, F. A new Mesembriornithinae (Aves, Phorusrhacidae) provides new insights into the phylogeny and sensory capabilities of terror birds. J. Vertebr. Paleontol. 35, e912656 (2015).

    Article  Google Scholar 

  35. Holliday, C. M. & Witmer, L. M. Archosaur adductor chamber evolution: integration of musculoskeletal and topological criteria in jaw muscle homology. J. Morphol. 268, 457–484 (2007).

    Article  PubMed  Google Scholar 

  36. Witmer, L. M. The evolution of the antorbital cavity of archosaurs: a study in soft-tissue reconstruction in the fossil record with an analysis of the function of pneumaticity. J. Vertebr. Paleontol. 17, 1–73 (1997).

    Article  Google Scholar 

  37. O’Connor, J. K., Chiappe, L. M. & Bell, A. in Living Dinosaurs: the Evolutionary History of Birds (eds Dyke, G. D. & Kaiser, G.) 39–114 (John Wiley & Sons, 2011).

  38. Bailleul, A. M., Li, Z., O’Connor, J. & Zhou, Z. Origin of the avian predentary and evidence of a unique form of cranial kinesis in Cretaceous ornithuromorphs. Proc. Natl Acad. Sci. USA 116, 24696–24706 (2019).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  39. Zhou, Z. & Zhang, F. A long-tailed, seed-eating bird from the Early Cretaceous of China. Nature 418, 405–409 (2002).

    Article  ADS  CAS  PubMed  Google Scholar 

  40. Xu, X. Mosaic evolution in birds: brain vs. feeding apparatus. Sci. Bull. (Beijing) 63, 812–813 (2018).

    Article  ADS  Google Scholar 

  41. Goloboff, P. A., Carpenter, J. M., Arias, J. S. & Esquivel, D. R. M. Weighting against homoplasy improves phylogenetic analysis of morphological data sets. Cladistics 24, 758–773 (2008).

    Article  Google Scholar 

  42. Xing, L.-D., McKellar, R. C. & O’Connor, J. An unusually large bird wing in mid-Cretaceous Burmese amber. Cretaceous Res. 110, 104412 (2020).

    Article  Google Scholar 

  43. Chen, R.-C. et al. PITRE: software for phase-sensitive X-ray image processing and tomography reconstruction J. Synchrotron Radiat. 19, 836–845 (2012).

    Article  PubMed  Google Scholar 

  44. Symonds, M. R. E. & Blomberg, S. P. in Modern Phylogenetic Comparative Methods and their Application in Evolutionary Biology (ed. Garamszegi, L. Z.) 105–130 (Springer, 2014).

  45. Jetz, W., Thomas, G. H., Joy, J. B., Hartmann, K. & Mooers, A. O. The global diversity of birds in space and time. Nature 491, 309–316 (2012).

    Article  CAS  Google Scholar 

  46. Jetz, W. et al. Distribution and conservation of global evolutionary distinctness in birds. Curr. Biol. 24, 919–930 (2014).

    Article  CAS  PubMed  Google Scholar 

Download references


This research was funded by the National Natural Science Foundation of China (no. 41888101, 41790455 and 41772008), the National Geographic Society (no. EC0768-15) and the Natural Sciences and Engineering Research Council of Canada (2015-00681). We thank BL13W of the Shanghai Synchrotron Radiation Facility for beamtime access based on proposal 16ssrf 01737, and the Beijing Synchrotron Radiation Facility for supplying the high MTF imaging detector. We thank S. Abramowicz for assistance with figures and D. Blackburn, D. Steadman and E. Stanley for making the computed tomography scan of M. minima accessible.

Author information

Authors and Affiliations



L.X. and J.K.O. designed the project, L.X., J.K.O., L.M.C., L.S., R.C.M., Q.Y. and G.L. performed the research: G.L. and Q.Y. performed computed tomography scanning of the specimen and processed the data. L.S. performed the eye-scaling statistical analyses. J.K.O. performed the cladistic analysis. J.K.O., L.M.C., L.S., L.X. and G.L. wrote the manuscript. L.X., J.K.O., L.S. and G.L. contributed equally.

Corresponding author

Correspondence to Jingmai K. O’Connor.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Close-up photographs of HPG-15-3.

a, Entire skull in left lateral view. b, Left eye. c, Maxillary dentition. The black arrows in a indicate decay products from the soft tissue of the dorsal surface of the skull and the original position of skull, which drifted before the resin hardened; the black arrow in b indicates the position of decay products released from the left eye. Scale bars, 2 mm (a), 500 μm (b), 200 μm (c).

Extended Data Fig. 2 Computed tomography scan of HPG-15-3 in palatal view, with the mandibles removed, and an isolated quadrate.

a, Full palatal view. b, Close-up of the preserved lingual papillae of the roof of the mouth. c, Isolated left quadrate in lateral view. d, Quadrate in caudal view. Dashed square box in a indicates the region enlarged in b. bp, basipterygoid process; bs, basisphenoid plate; bsr, basisphenoid rostrum; ch, choana; dt, developing tooth; pt, pterygoid; pp, papillae; pmc, medial contact of the palatal processes of the premaxillae.

Extended Data Fig. 3 Raw computed tomography slices showing the anatomy of important cranial sutures of HPG-15-3.

a, Interparietal suture, cranial portion (closed). b, Interfrontal suture (closed). c, Palatal processes of the premaxilla (open). d, Frontoparietal suture (open). e, Interparietal suture, caudal portion (open). f, Image of the entire skull, showing position of the slices shown in ac, e (image shown in d is a sagittal slice through the middle of the skull). Boxes outlined in dashed pink lines show the region enlarged in the insets, to clearly demonstrate the morphology of the suture or contact.

Extended Data Fig. 4 Rendering of the cranial endocast of HPG-15-3.

a, Dorsal view. b, Ventral view. c, Caudal view. d, Cranial view. e, Right lateral view. f, Left lateral view. g, Interior view of the brain cavity, showing the bivalve boring that intrudes through the ventral surface. Because the ventral surface of the cranium is damaged by a bivalve boring and the bones supporting the cranial margins of the brain are not preserved, only the dorsal surface of the endocast reveals reliable information. The white dashed lines indicate the portions of the endocast that probably were not occupied by brain tissue. The cerebrum appears to be prominent but a distinct optic lobe—as seen in other birds—cannot be identified. bb, bivalve boring; c, cerebrum; ot, part of the olfactory tract and/or olfactory lobe.

Extended Data Fig. 5 Isolated mandible of HPG-15-3.

a, Right mandible in (from top to bottom) ventral, dorsal, medial and lateral views. b, Left mandible in (from top to bottom) ventral, dorsal, medial and lateral views. c, Articulated mandibles in ventral (left) and dorsal (right) views. cor, coronoid process; mds, mandibular symphysis; mf?, possible mandibular foramen; nf, nutrient foramina.

Extended Data Fig. 6 Skull size in HPG-15-3 compared to other birds.

The skull of HPG-15-3 is small compared to those of extant birds (total of n = 213 extant bird species sampled), here illustrated through a box plot of log10-transformed postnasal skull length (as a proxy for the braincase), measured from the craniofacial hinge to the caudal end of the cranium. Each box plot illustrates the median (thick line) the 1st and 3rd quartiles (the hinges), and the distance from the upper and lower hinge to the largest and smallest value no further than 1.5× the interquartile range (the whiskers). HPG-15-3 is smaller than swifts (n = 12), passerines (n = 23) and hummingbirds (n = 22)—and may even be smaller than the smallest hummingbird, M. helenae.

Extended Data Fig. 7 Scleral ring of HPG-15-3.

a, As preserved. b, After retrodeformation.

Extended Data Fig. 8 Scleral rings of selected neornithines.

a, Asio flammeus, short-eared owl. b, Buteo jamaicensis, red-tailed hawk. c, Cerorhinca monocerata, rhinoceros auklet. d, Dendrocopus villosus, hairy woodpecker. e, Chordeiles minor, common nighthawk. f, Selaphorus sasin, Allen’s hummingbird. g, Cypseloides niger, American black swift. h, Megaceryle alcyon, belted kingfisher.

Extended Data Fig. 9 Summary of the slope estimates obtained from phylogenetic generalized least squares with the Ericson and the Hackett backbone tree sets, containing 1,000 trees each.

a, Ericson backbone tree set. b, Hackett backbone tree set. The x axes represent the estimated slope values, and the y axes represent the number of the tree sampled from the entire set of 1,000 trees. Dots signify the actual slope estimate, and grey bars visualize the s.e. of the slope estimates. The blue dashed line is the slope value obtained from ordinary least square regression, and the red dashed line represents the slope of isometry. Results from the phylogenetic generalized least squares iterations (n = 1,000) suggest the presence of negative allometry (slope < 1) in the relation between eye socket and skull length (P < 0.001).

Extended Data Fig. 10 Results of analysis using a priori weights and the unsimplified cladogram depicting the results of the phylogenetic analysis.

For further discussion, see Supplementary Information. a, A priori weighting results in a polytomy consisting of all taxa more derived than Archaeopteryx. b, Results of the analysis using implied weighting with a k value of 16; results were the same for k values of 12–20 and of 25; k values between 2 and 11 differed only from higher k values in the relative placement of some derived enantiornithines. Here Nanantius valifanovi is considered a junior synonym of Gobipteryx minuta (thus the operational taxonomic unit name is given as ‘Gobipteryx_N_valifanovi’).

Supplementary information

Supplementary Information

Combined PDF containing supplemental text and ethical statement regarding the amber provenance. Additional supplemental files (scripts for all analyses in the manuscript and 3D interactive model of HPG-15-3) can be found online:

Reporting Summary

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Xing, L., O’Connor, J.K., Schmitz, L. et al. Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature 579, 245–249 (2020).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing