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.

A Cretaceous eutriconodont and integument evolution in early mammals


The Mesozoic era (252–66 million years ago), known as the domain of dinosaurs, witnessed a remarkable ecomorphological diversity of early mammals. The key mammalian characteristics originated during this period and were prerequisite for their evolutionary success after extinction of the non-avian dinosaurs 66 million years ago. Many ecomorphotypes familiar to modern mammal fauna evolved independently early in mammalian evolutionary history. Here we report a 125-million-year-old eutriconodontan mammal from Spain with extraordinary preservation of skin and pelage that extends the record of key mammalian integumentary features into the Mesozoic era. The new mammalian specimen exhibits such typical mammalian features as pelage, mane, pinna, and a variety of skin structures: keratinous dermal scutes, protospines composed of hair-like tubules, and compound follicles with primary and secondary hairs. The skin structures of this new Mesozoic mammal encompass the same combination of integumentary features as those evolved independently in other crown Mammalia, with similarly broad structural variations as in extant mammals. Soft tissues in the thorax and abdomen (alveolar lungs and liver) suggest the presence of a muscular diaphragm. The eutriconodont has molariform tooth replacement, ossified Meckel’s cartilage of the middle ear, and specialized xenarthrous articulations of posterior dorsal vertebrae, convergent with extant xenarthran mammals, which strengthened the vertebral column for locomotion.

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

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Prices vary by article type



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

Figure 1: New Early Cretaceous gobiconodontid Spinolestes xenarthrosus.
Figure 2: New gobiconodontid S. xenarthrosus, holotype counter slab (MCCMLH30000B) and integumentary structures.


  1. Alibardi, L. Perspectives on hair evolution based on some comparative studies on vertebrate cornification. J. Exp. Zool. 318B, 325–343 (2012)

    Article  Google Scholar 

  2. Ji, Q. et al. The earliest known eutherian mammal. Nature 416, 816–822 (2002)

    Article  CAS  ADS  Google Scholar 

  3. Ji, Q. et al. A swimming mammaliaform from the Middle Jurassic and ecomorphological diversification of early mammals. Science 311, 1123–1127 (2006)

    Article  CAS  ADS  Google Scholar 

  4. Meng, Q.-J. et al. An arboreal docodont from the Jurassic and mammaliaform ecological diversification. Science 347, 764–768 (2015)

    Article  CAS  ADS  Google Scholar 

  5. Meng, J. et al. A Mesozoic gliding mammal from northeastern China. Nature 444, 889–893 (2006)

    Article  CAS  ADS  Google Scholar 

  6. Vullo, R. et al. Mammalian hairs in Early Cretaceous amber. Naturwissenschaften 97, 683–687 (2010)

    Article  CAS  ADS  Google Scholar 

  7. Zhou, C.-F. et al. A Jurassic mammaliaform and the earliest mammalian evolutionary adaptations. Nature 500, 163–167 (2013)

    Article  CAS  ADS  Google Scholar 

  8. Meng, J. & Wyss, A. R. Multituberculate and other mammal hair recovered from Palaeogene excreta. Nature 385, 712–714 (1997)

    Article  CAS  ADS  Google Scholar 

  9. Chernova, O. F. Evolutionary aspects of hair polymorphism. Biol. Bull. 33, 43–52 (2006)

    Article  Google Scholar 

  10. Storch, G. Eurotamandua joresi, ein Myrmecophagide aus dem Eozän der “Grube Messel” bei Darmstadt (Mammalia, Xenarthra). Senckenbergiana Lethaea 61, 247–289 (1981)

    Google Scholar 

  11. Ting, S.-Y. A Paleocene edentate from Nanxiong Basin, Guangdong. Palaeontol. Sin. New Series C 17, 85–118 (1987)

    Google Scholar 

  12. Rose, K. D. & Emry, R. J. in Mammal Phylogeny: Placentals (eds Szalay, F. S., Novacek, M. J. & McKenna, M. C. ) 81–102 (Springer, 1993)

    Book  Google Scholar 

  13. Luo, Z.-X. & Wible, J. R. A Late Jurassic digging mammal and early mammalian diversification. Science 308, 103–107 (2005)

    Article  CAS  ADS  Google Scholar 

  14. Linnaeus, C. Systema Naturæ per Regna Tria Naturæ, Secundum Classes, Ordines, Genera, Species, cum Characteribus, Differentiis, Synonymis, Locis Vol. 1 (Regnum Animale) editio decima, reformata (Laurentius Salvius, 1758)

    Google Scholar 

  15. Kermack, K. A. et al. The lower jaw of Morganucodon. Zool. J. Linn. Soc. 53, 87–175 (1973)

    Article  Google Scholar 

  16. Chow, M. & Rich, T. H. V. A new triconodontan (Mammalia) from the Jurassic of China. J. Vertebr. Paleontol. 3, 226–231 (1984)

    Article  Google Scholar 

  17. Fregenal-Martínez, M. A. & Meléndez, N. in Lake Basins through Space and Time (eds Gierlowski-Kordesch, E. H. & Kelts, K. ) AAPG Studies in Geology Vol. 46, 303–314 (2000)

    Google Scholar 

  18. Buscalioni, A. D. & Fregenal-Martínez, M. A. A holistic approach to the palaeoecology of Las Hoyas Konservat-Lagerstätte (La Huérgina Formation, Lower Cretaceous, Iberian Ranges, Spain). J. Iber. Geol. 36, 297–326 (2010)

    Article  Google Scholar 

  19. Rougier, G. W. et al. An Early Cretaceous mammal from the Kuwajima Formation (Tetori Group), Japan, and a reassessment of triconodont phylogeny. Ann. Carnegie Mus. 76, 73–115 (2007)

    Article  Google Scholar 

  20. Gao, C.-L. et al. A new mammal skull from the Lower Cretaceous of China with implications for the evolution of obtuse-angled molars and ‘amphilestid’ eutriconodonts. Proc. R. Soc. B 277, 237–246 (2010)

    Article  Google Scholar 

  21. Ji, Q. et al. A Chinese triconodont mammal and mosaic evolution of the mammalian skeleton. Nature 398, 326–330 (1999)

    Article  CAS  ADS  Google Scholar 

  22. Luo, Z.-X. et al. A new eutriconodont mammal and evolutionary development in early mammals. Nature 446, 288–293 (2007)

    Article  CAS  ADS  Google Scholar 

  23. Meng, J. et al. Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont. Nature 472, 181–185 (2011)

    Article  CAS  ADS  Google Scholar 

  24. Jenkins, F. A. & Schaff, C. R. The Early Cretaceous mammal Gobiconodon (Mammalia, Triconodonta) from the Cloverly Formation in Montana. J. Vertebr. Paleontol. 8, 1–24 (1988)

    Article  Google Scholar 

  25. Kielan-Jaworowska, Z. & Dashzeveg, D. Early Cretaceous amphilestid (“triconodont”) mammal from Mongolia. Acta Palaeontol. Pol. 43, 413–438 (1998)

    Google Scholar 

  26. Li, C.-K. et al. A new species of Gobiconodon (Triconodonta, Mammalia) and its implication for the age of Jehol Biota. Chin. Sci. Bull. 48, 1129–1134 (2003)

    Google Scholar 

  27. Hu, Y.-M. Postcranial Morphology of Repenomamus (Eutriconodonta, Mammalia): Implications for the Higher-Level Phylogeny of Mammals. Dissertation, City Univ. of New York (2006)

  28. Luo, Z.-X. Developmental patterns in Mesozoic evolution of mammal ears. Annu. Rev. Ecol. Syst. 42, 355–380 (2011)

    Article  Google Scholar 

  29. Kielan-Jaworowska, Z. et al. Mammals from the Age of Dinosaurs. Origins, Evolution, and Structure (Columbia Univ. Press, 2004)

    Book  Google Scholar 

  30. Gaudin, T. J. The morphology of xenarthrous vertebrae (Mammalia: Xenarthra). Fieldiana Geol. New Series 41, 1–38 (1999)

    Google Scholar 

  31. Lessertisseur, J. & Saban, R. in Traité de Zoologie Tome 16, Fascicule 1 (Mammifères, Téguments et Squelette) (ed. Grassé, P. P. ) 709–1078 (Masson et Cie, 1967)

    Google Scholar 

  32. Kusuhashi, N. et al. New triconodontids (Mammalia) from the Lower Cretaceous Shahai and Fuxin formations, northeastern China. Geobios 42, 765–781 (2009)

    Article  Google Scholar 

  33. Gaetano, L. C. & Rougier, G. W. New materials of Argentoconodon fariasorum (Mammaliaformes, Triconodontidae) from the Jurassic of Argentina and its bearing on triconodont phylogeny. J. Vertebr. Paleontol. 31, 829–843 (2011)

    Article  Google Scholar 

  34. Cuenca-Bescós, G. & Canudo, J. I. A new gobiconodontid mammal from the Early Cretaceous of Spain and its palaeogeographic implications. Acta Palaeontol. Pol. 48, 575–582 (2003)

    Google Scholar 

  35. Sweetman, S. C. A gobiconodontid (Mammalia, Eutriconodonta) from the Early Cretaceous (Barremian) Wessex Formation of the Isle of Wight, southern Britain. Palaeontology 49, 889–897 (2006)

    Article  Google Scholar 

  36. Lovell, J. E. & Getty, R. The hair follicle, epidermis, dermis, and skin glands of the dog. Am. J. Vet. Res. 18, 873–885 (1957)

    CAS  PubMed  Google Scholar 

  37. Whiteley, H. J. Giant compound hair follicles in the skin of the rabbit. Nature 181, 850 (1958)

    Article  CAS  ADS  Google Scholar 

  38. Evans, H. E. & de Lahunta, A. Miller’s Anatomy of the Dog (Elsevier Saunders, 2012)

    Google Scholar 

  39. Spencer, B. & Sweet, G. The structure and development of the hairs of monotreme and marsupials. Q. J. Microsc. Sci. 36, 549–588 (1899)

    Google Scholar 

  40. Hausman, L. A. The cortical fusi of mammalian hair shafts. Am. Nat. 66, 461–470 (1932)

    Article  Google Scholar 

  41. Rudnicka, L. et al. in Atlas of Trichoscopy: Dermoscopy in Hair and Scalp Disease (eds Rudnicka, L., Olszewska, M. & Rakowska, A. ) 11–46 (Springer, 2012)

    Book  Google Scholar 

  42. Vincent, J. F. V. & Owers, P. Mechanical design of hedgehog spines and porcupine quills. J. Zool. 210, 55–75 (1986)

    Article  Google Scholar 

  43. Montandon, S. A. et al. Two waves of anisotropic growth generate enlarged follicles in the spiny mouse. EvoDevo 5, 33 (2014)

    Article  Google Scholar 

  44. Weibel, E. R. et al. Design of peripheral airways for efficient gas exchange. Respir. Physiol. Neurobiol. 148, 3–21 (2005)

    Article  Google Scholar 

  45. Dal Sasso, C. & Signore, M. Exceptional soft tissue preservation in a theropod dinosaur from Italy. Nature 392, 383–387 (1998)

    Article  CAS  ADS  Google Scholar 

  46. Bramble, D. M. & Jenkins, F. A. Mammalian locomotor-respiratory integration: implications for diaphragmatic and pulmonary design. Science 262, 235–240 (1993)

    Article  CAS  ADS  Google Scholar 

  47. Campione, N. E. & Evans, D. C. A universal scaling relationship between body mass and proximal limb bone dimensions in quadrupedal terrestrial tetrapods. BMC Biol. 10, 60 (2012)

    Article  Google Scholar 

  48. Foster, J. R. Preliminary body mass estimates for mammalian genera of the Morrison Formation (Upper Jurassic, North America). PaleoBios 28, 114–122 (2009)

    Google Scholar 

  49. Kirk, E. C. et al. Intrinsic hand proportions of eucharchontans and other mammals: Implications for the locomotor behavior of plesiadapiforms. J. Hum. Evol. 55, 278–299 (2008)

    Article  Google Scholar 

  50. Stanley, W. T. et al. A new hero emerges: another exceptional mammalian spine and its potential adaptive significance. Biol. Lett. 9, 20130486 (2013)

    Article  Google Scholar 

Download references


Research funds were provided by Spanish MINECO, Project CGL-2013-42643 P and Junta de Comunidades de Castilla-La Mancha. We thank J. L. Sañudo for finding the specimen, M. Llandres and O. Dülfer for preparation, D. Kranz for artwork, O. Sanisidro for the lifelike reconstruction of S. xenarthrosus, G. Oleschinski for photography, M. Furió and A. Valera for SEM, K. Jäger for three-dimensional reconstructions, and T. McCann for improving the English. R. L. Cifelli is thanked for review and B. Mähler for discussion on actuo-taphonomical experiments on rat carcasses.

Author information

Authors and Affiliations



A.D.B. designed the Las Hoyas research project; J.M.-L., R.V., H.M.-A., and A.D.B. participated in the fieldwork; T.M., J.M.-L., R.V., H.M.-A., Z.-X.L., and A.D.B. organized and conducted the research (preparation, computed tomography scan, light microscopy, and SEM imaging) and analysed data; Z.-X.L. performed phylogenetic analyses; and T.M., J.M.-L., R.V., Z.-X.L., and A.D.B. wrote the manuscript.

Corresponding authors

Correspondence to Thomas Martin, Zhe-Xi Luo or Angela D. Buscalioni.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 New gobiconodontid S. xenarthrosus, holotype transferred slab MCCMLH30000A.

Skull exposed in ventral aspect. Inset: left calcaneus in dorsal view on the same slab somewhat apart from the skeleton. Arrow points to skin patch preserving hair bundles between dorsal vertebrae 11 and 14.

Extended Data Figure 2 Dentition and xenarthrous vertebrae of Spinolestes.

a, SEM images (stereo pair) of right lower mandible and right upper maxilla with molariforms. b, SEM image of anterior portion of skull and mandibles with dentition. c, SEM image of penultimate (m3) and ultimate (m4) right lower molariforms in lingual view. Abbreviations: C/c, upper/lower canine; I/i, incisor; M/m, molariform; P/p, premolar; D/d, deciduous tooth; R/r, replacing tooth. d, SEM images (stereo pair) of dorsal vertebrae D 12 to D 19 in lateral aspect with ribs.

Extended Data Figure 3 Phylogenetic relationships of Spinolestes and patterns of mammalian integumentary structure in early mammalian evolution.

a, Position of Spinolestes within Eutriconodonta (Bremer index/bootstrap values on the key clades of this study). b, Evolution of mammalian integumentary structures (simplified tree). Data sets and full analyses are presented in Supplementary Information.

Extended Data Figure 4 Skin structures of S. xenarthrosus.

a, SEM image of skin surface showing compound hair follicles (FO), epidermal cells (keratinocytes), and pores (P). b, Schematic drawings of scale-like skin folds (SCF) with compound hair follicles (FO) of the dog with primary (PH) and secondary (SH) hairs of three ontogenetic stages (redrawn from ref. 38). c, Skin surface of Spinolestes with scale-like wrinkles. d, Schematic diagram of scale-like wrinkled skin folds with hair follicles of a dog (redrawn from ref. 38). e, SEM image of epidermal cells (keratinocytes) of a hair follicle. f, SEM images of skin surface with polygonal epidermal cells (keratinocytes) and pores. g, Detail of the keratinocytes.

Extended Data Figure 5 SEM images and interpretative line drawings of cuticular scale patterns.

ac, Primary (a, b) and secondary (b, c) hairs.

Extended Data Figure 6 Hair structures of S. xenarthrosus.

a, c, d, Patch of skin located between dorsal vertebrae 11 and 14 (arrow in Fig. 1 and Extended Data Fig. 1) on slab MCCMLH30000A under translucent light. b, SEM image of an orifice of a compound follicle (FO) with primary hair (PH) and three broken secondary hairs (SH). e, SEM image of a fraying hair of S. xenarthrosus showing fusiform cortical cells (FCC). f, Schematic diagram of human hair bulb (B) with cuticular scales (CU) and fusi (F) of the hair shaft (HS). g, Schematic diagram of a human head hair with fusiform cortical cells (FCC) and fusi. f, g, Redrawn from ref. 40. Abbreviations: C, cuticula; HB, hair bulb.

Extended Data Figure 7 External pinna of S. xenarthrosus.

a, b, Comparison with pinna and scalp of decaying rat (Rattus norvegicus): a, on transferred slab MCCMLH30000A; b, on counter slab MCCMLH30000B on original limestone rock matrix. c, d, Pinna and scalp of decaying rat (Rattus norvegicus) for comparison. c, Head of decaying rat after 274 days in water at room temperature. The skull is detached from the scalp and has fallen to the bottom. Scalp and right pinna are still intact and connected to the torso of the floating carcass. d, Detail of c with well-preserved right pinna in original position at the scalp. The mandible is displaced and loosely hanging down from the skin.

Extended Data Figure 8 Keratinous dermal scutes (SC) of S. xenarthrosus.

a, Oval dermal scutes dorsally of dorsal vertebra 20. b, Oval dermal scute dorsally of left ischium (ISC-L). c, Oval dermal scute from dorsal region with tubules (T) merging to homogeneous keratinous matrix.

Extended Data Figure 9 Visceral cavities of S. xenarthrosus with internal organs.

a, Detail of the visceral cavities of MCCMLH30000B with separation of the anterior thoracic cavity (TC) containing the lungs (LU), and the posterior abdominal cavity (AC) containing the liver (LI). Dashed line represents the diaphragm. SE, sternal elements. b, Lung tissue in the anterior part of the thoracic cavity. c, Peripheral conducting and acinar airways of the lungs with typical dichotomous structure of the bronchial tree. d, Peripheral conducting and acinar airways of the lungs from transferred slab MCCMLH30000A under translucent light. e, f, Details of the peripheral conducting airway dichotomies (DI) and acinar structures (ACI) of the lungs.

Extended Data Figure 10 Lifelike reconstruction of S. xenarthrosus.

Supplementary information

Supplementary Information

This file contains Supplementary Text and Data, see contents page for details. (PDF 2988 kb)

CT reconstruction of right maxilla of Spinolestes xenarthrosus with heavily worn DM3 and DM4 still in place labially of replacing M3 and M4.

CT reconstruction of right maxilla of Spinolestes xenarthrosus with heavily worn DM3 and DM4 still in place labially of replacing M3 and M4. (MP4 12294 kb)

CT reconstruction of right mandible of Spinolestes xenarthrosus with wide Meckel´s groove (ossified Meckel´s cartilage fallen off).

CT reconstruction of right mandible of Spinolestes xenarthrosus with wide Meckel´s groove (ossified Meckel´s cartilage fallen off). (MP4 12361 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Martin, T., Marugán-Lobón, J., Vullo, R. et al. A Cretaceous eutriconodont and integument evolution in early mammals. Nature 526, 380–384 (2015).

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