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research in evolutionary morphology

Paleohistology: The study of Ancient Tissues

& their Evolution

Does bone histology explain the success of nonmammalian synapsids and coexisting tetrapods during the Permo-Triassic mass extinction?

While ectotherms have a limited range of bone tissue textures, reflecting their modest growth rates and energetics, little effort has been made to database histomorphology in the mammal-stem lineage (also known as synapsids). My Master’s work provided insights into the physiology of Carboniferous-through-Triassic synapsids by showing that the earliest synapsids, such as the iconic sail-backed Dimetrodon, adopted a diversity of reptile-like and mammal-like tissues in the early stages of their evolution, including woven-fibered bone tissues, and revealed considerable histologic diversity in pioneering terrestrial tetrapods (right).

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Starting during my PhD (2008-2013), I've investigated the relationship between major environmental changes in Earth’s history and growth patterns recorded in the bones of fossil synapsids. My aim is to better understand the effects of long-term environmental instability on vertebrate life histories. Continued work with Jennifer Botha (National Museum, Bloemfontein) and Colleen Farmer (U of U) aims to elucidate patterns shared between synapsids and archosauromorphs in order to identify whether growth, reproduction, and physiologic innovations may have conferred a selective advantage on some tetrapod clades in the harsh, unpredictable conditions of the Permo-Triassic mass extinction (~252 million years ago). My research has been the first to identify size- and histology-related selectivity during a major extinction while accounting for phylogenetic relatedness.

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Using Histology & 3d Virtual imaging to investigate Bone adaptation & Behavior IN MAMMALS & their Extinct kin

To what extent does terrestrial activity (walking/climbing/digging) influence bone tissue structure & function in

the synapsid skeleton?

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The converging fields of ‘paleohistology’ and virtual morphology are revolutionizing paleontology; giving life to ancient bones and making important contributions to physiology’s two central questions: mechanism and origin. How is bone histology optimized for mechanical use in long bones? From the elongated spines of Dimetrodon, to the primate clavicle (left), is shape or tissue properties more important in determining bone function? Has tissue structure become more important over time as mammals adopted more complex and active terrestrial behaviors?

Combining recent and fossil evidence, our lab has become interested in the functional evolution of the highly mobile mammalian shoulder girdle and acromioclavicular joint. To test how bone shape and tissue organization are adapted to forelimb loading, we are investigating forelimb histology in closely-related terrestrial and arboreal didelphid marsupials (opossums) with different locomotor modes. The primary goal of this study is to contrast bone adaptation in the shoulder girdle of ground- and tree-dwelling didelphids by investigating clavicle microstructure in a comparative framework. We are additionally exploring changes in pectoral girdle anatomy and range of motion using 3D virtual imaging of Permo-Triassic synapsid fossils to reconstruct the diversification of forelimb function and behavior.

Related publications & Abstracts

  • Cubo, J., and A. K. Huttenlocker. (in press for 2020). Introduction to Vertebrate Palaeophysiology. For Philosophical Transactions of the Royal Society.

  • Huttenlocker, A. K., and C. Shelton. (in press for 2020). Bone histology of varanopids (Synapsida) from Richards Spur, Oklahoma, sheds light on growth patterns and lifestyle in early terrestrial colonizers. For Philosophical Transactions of the Royal Society.

  • Kato, K. M., E. A. Rega, C. A. Sidor, and A. K. Huttenlocker. (in press for 2020). Investigation of a bone lesion in a gorgonopsian (Synapsida) from the Permian of Zambia and periosteal reactions in fossil nonmammalian tetrapods. For Philosophical Transactions of the Royal Society.

  • Crane, M. A., K. M. Kato, B. A. Patel, and A. K. Huttenlocker. (2019). Histovariability in clavicular cortical bone microstructure and its mechanical implications. Journal of Anatomy 235:873–882. doi:10.1111/joa.13056 [Featured Cover Article, volume 252, issue 5]

  • Huttenlocker, A. K., and C. G. Farmer. 2017. Bone microvasculature tracks red blood cell size diminution in Triassic mammal and dinosaur forerunners. Current Biology 27:48–54. doi:10.1016/j.cub.2016.10.012

  • Botha-Brink, J., D. Codron, A. K. Huttenlocker, K. D. Angielczyk, and M. Ruta. 2016. Breeding young as a survival strategy during Earth’s greatest mass extinction. Scientific Reports 6:srep24053. doi:10.1038/srep24053

  • Huttenlocker, A. K., and J. Botha-Brink. 2014. Bone microstructure and the evolution of growth patterns in Permo-Triassic therocephalians (Amniota, Therapsida) of South Africa. PeerJ 2:e325. doi:10.7717/peerj.325

  • Huttenlocker, A. K. 2014. Body size reductions in nonmammalian eutheriodont therapsids (Synapsida) during the end-Permian mass extinction. PLOS ONE 9:e87553. doi: 10.1371/journal.pone.0087553

  • Huttenlocker, A. K., and J. Botha-Brink. 2013. Body size and growth patterns in the therocephalian Moschorhinus (Therapsida) before and after the end-Permian extinction in South Africa. Paleobiology 39:253–277. doi:10.1666/12020

  • Huttenlocker, A. K., H. N. Woodward, and B. K. Hall. 2013. Chapter 1: Biology of Bone. In Bone Histology of Fossil Tetrapods: Issues, Methods, and Databases – Eds., K. Padian and E.-T. Lamm. University of California Press.

  • Lee, A. H., Huttenlocker, A. K., K. Padian, and H. N. Woodward. 2013. Chapter 8: Analysis of Growth Rates. In Bone Histology of Fossil Tetrapods: Issues, Methods, and Databases – Eds., K. Padian and E.-T. Lamm. University of California Press.

  • Rega, E. K. Noriega, S. S. Sumida, A. Huttenlocker, A. Lee, and Brett Kennedy. 2012. Healed fractures in the neural spines of an associated skeleton of Dimetrodon: Implications for dorsal sail morphology and function. Fieldiana: Life and Earth Sciences (2012):104–111.

  • Sigurdsen, T., A. K. Huttenlocker, S. P. Modesto, T. Rowe, and R. Damiani. 2012. Reassessment of the morphology and paleobiology of the therocephalian Tetracynodon darti (Therapsida), and the phylogenetic relationships of Baurioidea. Journal of Vertebrate Paleontology 32:1113–1134. doi:10.1080/02724634.2012.688693

  • Huttenlocker, A. K. & E. Rega. 2012. Chapter 4: The paleobiology and bone microstructure of pelycosaurian-grade synapsids. Pp. 90-119 in A. Chinsamy-Turan (ed.) The Forerunners of Mammals: Radiation, Histology and Biology. Indiana University Press.

  • Huttenlocker, A. K., D. Mazierski, & R. Reisz. 2011. Comparative osteohistology of hyperelongate neural spines in the Edaphosauridae (Amniota: Synapsida). Palaeontology 54:573-590.

  • Huttenlocker, A. K., E. Rega, & S. Sumida. 2010. Comparative anatomy and osteohistology of hyperelongate neural spines in the sphenacodontids Sphenacodon and Dimetrodon (Amniota: Synapsida). Journal of Morphology 271:1407-1421.

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