I seek to understand the mechanisms behind the evolutionary origin of new anatomical features and faunas. The philosophy that underlies all of my empirical work is derived from the conviction that progress in the study of evolutionary biology results from linking research across diverse temporal, phylogenetic, and structural scales. The Origin of Novel Faunas and Anatomical Systems: Much of today's vertebrate diversity was defined by ecological and evolutionary shifts that happened during two critical intervals in the history of the Earth: the Devonian and the Triassic. These periods serve as the focal point for my research because they witness the origin of both new ecosystems and new anatomical designs. My expeditionary research supplies new fossils and a paleoenvironmental context to understand the origin of faunas, whereas our morphological, functional, and developmental studies yield hypotheses on anatomical transformations.
Over the past fifteen years, I have developed expeditionary research programs in Canada, Africa, the continental United States, Asia, and Greenland. These expeditions have led to new insights on the origin of major groups of vertebrates (mammals, frogs, crocodiles, tetrapods, and sarcopterygian fish). Future studies on the origins of pterosaurs, rhizodontid fish, dinosaurs, and salamanders will rely heavily on fossils discovered over the past five years. Examples include the newly discovered adult fin and juvenile skeleton of the fish, Sauripterus. These fossils are providing evidence on the ways that appendage function and skeletal development shifted during the evolutionary radiation of lobe-finned fish. Indeed, this evolutionary radiation is temporally linked to the origin of new freshwater environments. Consequently, the analysis of Sauripterus will place comparative studies of fin structure, development and function in a phylogenetic and paleoenvironmental context.
The goals of the paleontological research dovetail with those of my neontological studies. New fossils, such as Sauripterus, offer tests of hypotheses that derive from our comparative analysis of genetic and morphogenetic processes. For example, the comparison of developmental pathways common to the appendages of all animals suggests genetic mechanisms for parallel evolution and homology. Regularities of variation may reflect the fact that similar regulatory genes are used in the developmental patterning of diverse types of animals.
The Origin of Morphological Variation: The ~400 million year history of terrestrial animals reveals surprising patterns of anatomical stasis and parallel evolution: similar designs crop up in different species living in different environments. Salamanders, for example, arose over 150 million years ago, but have retained a very stable body plan in the face of environmental change and genetic variation. The study of these regularities transcends ecological and paleontological timescales because explanations of larger-scale patterns can be sought in the mechanisms that structure anatomical variation in populations today. Accordingly, my research has involved collecting data on intraspecific variation from diverse populations, developing predictive models of variation based on ontogeny, and comparing developmental processes in diverse salamanders that live in different environmental settings.
Salamander limbs are a model system to approach these issues because of the diversity of their developmental systems and life histories. In addition, the widespread occurrence of parallelism provides us with a window to develop predictive rules about the origin of variation in populations. Over the past seven years, colleagues and I have composed a database of limb variation and ontogeny in populations of diverse salamanders. Virtually all of the species analyzed to date possess variant conditions that both restore ancient features and anticipate more derived conditions seen in distantly-related species. Much of the observed intraspecific variation is predictable from a knowledge of phylogenetic history or development. Ultimately, if these historical and developmental effects resulted in long-term evolutionary patterns, they must have acted over geological timescales. Tests of this hypothesis will come from the study of the Chinese Cretaceous where, in collaboration with colleagues, I am studying variation of salamanders in a Cretaceous pond that were killed in a single mass-mortality event.
Phylogenetic analysis of ontogenetic trajectories in salamanders affords critical assessments of the role of historical, ecological, and structural factors in evolution. Analysis of development in salamanders with different life histories suggests certain aspects of early limb development are highly sensitive to variation in larval biology. I intend to explore this link between ontogenetic diversity and anatomical variation in the future by using experimental and comparative studies of ontogeny.
University of Pennsylvania
A.M. - Biology
Ph.D. - Organismal and Evolutionary Biology
A.M. - Organismal and Evolutionary Biology
New York City, NY
A.B. - Biology
Ontogeny of the anuran urostyle and the developmental context of evolutionary novelty.
Senevirathne G, Baumgart S, Shubin N, Hanken J, Shubin NH. Ontogeny of the anuran urostyle and the developmental context of evolutionary novelty. Proc Natl Acad Sci U S A. 2020 02 11; 117(6):3034-3044.
Fin ray patterns at the fin-to-limb transition.
Stewart TA, Lemberg JB, Taft NK, Yoo I, Daeschler EB, Shubin NH. Fin ray patterns at the fin-to-limb transition. Proc Natl Acad Sci U S A. 2020 01 21; 117(3):1612-1620.
The evolutionary origins and diversity of the neuromuscular system of paired appendages in batoids.
Turner N, Mikalauskaite D, Barone K, Flaherty K, Senevirathne G, Adachi N, Shubin NH, Nakamura T. The evolutionary origins and diversity of the neuromuscular system of paired appendages in batoids. Proc Biol Sci. 2019 11 06; 286(1914):20191571.
Feeding kinematics and morphology of the alligator gar (Atractosteus spatula, Lacépède, 1803).
Lemberg JB, Shubin NH, Westneat MW. Feeding kinematics and morphology of the alligator gar (Atractosteus spatula, Lacépède, 1803). J Morphol. 2019 10; 280(10):1548-1570.
Chemokine C-C motif ligand 33 is a key regulator of teleost fish barbel development.
Zhou T, Li N, Jin Y, Zeng Q, Prabowo W, Liu Y, Tian C, Bao L, Liu S, Yuan Z, Fu Q, Gao S, Gao D, Dunham R, Shubin NH, Liu Z. Chemokine C-C motif ligand 33 is a key regulator of teleost fish barbel development. Proc Natl Acad Sci U S A. 2018 05 29; 115(22):E5018-E5027.
A conserved Shh cis-regulatory module highlights a common developmental origin of unpaired and paired fins.
Letelier J, de la Calle-Mustienes E, Pieretti J, Naranjo S, Maeso I, Nakamura T, Pascual-Anaya J, Shubin NH, Schneider I, Martinez-Morales JR, Gómez-Skarmeta JL. A conserved Shh cis-regulatory module highlights a common developmental origin of unpaired and paired fins. Nat Genet. 2018 04; 50(4):504-509.
Gene regulatory networks and network models in development and evolution.
Shubin N. Gene regulatory networks and network models in development and evolution. Proc Natl Acad Sci U S A. 2017 06 06; 114(23):5782-5783.
Open data and digital morphology.
Davies TG, Rahman IA, Lautenschlager S, Cunningham JA, Asher RJ, Barrett PM, Bates KT, Bengtson S, Benson RB, Boyer DM, Braga J, Bright JA, Claessens LP, Cox PG, Dong XP, Evans AR, Falkingham PL, Friedman M, Garwood RJ, Goswami A, Hutchinson JR, Jeffery NS, Johanson Z, Lebrun R, Martínez-Pérez C, Marugán-Lobón J, O'Higgins PM, Metscher B, Orliac M, Rowe TB, Rücklin M, Sánchez-Villagra MR, Shubin NH, Smith SY, Starck JM, Stringer C, Summers AP, Sutton MD, Walsh SA, Weisbecker V, Witmer LM, Wroe S, Yin Z, Rayfield EJ, Donoghue PC. Open data and digital morphology. Proc Biol Sci. 2017 Apr 12; 284(1852).
Digits and fin rays share common developmental histories.
Nakamura T, Gehrke AR, Lemberg J, Szymaszek J, Shubin NH. Digits and fin rays share common developmental histories. Nature. 2016 09 08; 537(7619):225-228.
Regulatory evolution of Tbx5 and the origin of paired appendages.
Adachi N, Robinson M, Goolsbee A, Shubin NH. Regulatory evolution of Tbx5 and the origin of paired appendages. Proc Natl Acad Sci U S A. 2016 09 06; 113(36):10115-20.