Diversity and disparity
Mammals and their closest fossil relatives are unique among tetrapods in expressing a high degree of pectoral girdle and forelimb functional diversity associated with fully pelagic, curso- rial, subterranean, volant, and other lifestyles. However, the earliest members of the mammalian stem lineage, the “pelycosaur”-grade synapsids, present a far more limited range of morphologies and inferred functions. The more crownward nonmammaliaform therapsids display novel forelimb morphologies that have been linked to expanded functional diversity, suggesting that the roots of this quintessentially mammalian phenotype can be traced to the pelycosaur–therapsid transition in the Permian period.
We quantified morphological disparity of the humerus in pelycosaur-grade synapsids and therapsids using geometric morphometrics. We found that disparity begins to increase concurrently with the emergence of Therapsida, and that it continues to rise until the Permo-Triassic mass extinction. Further, therapsid exploration of new regions of morphospace is correlated with the evolution of novel ecomorphologies, some of which are characterized by changes to overall limb morphology. This evolutionary pattern confirms that nonmammaliaform therapsid forelimbs underwent ecomorphological diversification throughout the Permian, with functional elaboration initially being more strongly expressed in the proximal end of the humerus than the distal end. The role of the forelimbs in the func- tional diversification of therapsids foreshadows the deployment of forelimb morphofunctional diversity in the evolutionary radiation of mammals.
Mammals are the only living members of the larger clade Synapsida, which has a fossil record spanning 320Ma. Despite the fact that much of the ecological diversity of mammals has been considered in light of limb morphology, the ecological comparability of mammals to their fossil forerunners has not been critically assessed. Because of the wide use of limb morphology in testing ecomorphological hypothesis about extinct tetrapods, we sought: (1) to estimate when in synapsid history modern mammals become analogs for predicting fossil ecologies; (2) to document examples of ecomorphological convergence; and (3) to compare the functional solutions of distinct synapsid radiations.
We quantitatively compared the forelimb shapes of the multiple fossil synapsid radiations to a broad sample of extant Mammalia representing a variety of divergent locomotor ecologies. Our results indicate that each synapsid radiation explored different areas of morphospace and arrived at functional solutions that reflected their distinctive ancestral morphologies. This work counters the narrative of non-mammalian synapsid forelimb evolution as a linear progression towards more mammalian morphologies. Instead, a disparate array of early-evolving shapes subsequently contracted towards more mammal-like forms.
Current postdoctoral project
I am working to quantify cranial and postcranial morphology of identified species of sphenacodontid pelycosaurs for comparison to unidentified specimens. Historical species-level descriptions within sphenacodontids use a variety of different and often non-overlapping characters for species delimitation, with preservational issues playing a central role in the process. Taking into account the importance of body size and stratigraphic occurrence in the taxonomy of spehnacodontids, I hypothesize that the species-level taxonomy of this group is over-split.
To help unify the taxonomy of sphenacodontids, I am executing geometric morphometric analyses on both cranial and postcranial elements. The use of postcrania (commonly used for delimitation in sphenacodontids and very abundant in the group’s fossil record) in combination with crania (instrumental in the taxonomy of many synapsid clades) will shed light on correlations of morphological differentiation between skeletal elements, providing a more consistent basis for sphenacodontid taxonomy. Preliminary data I collected (canonical variates analysis, above) shows potential distinction in proximal humerus shape among species. However, specimens lacking species-level identifications (gray dots) obscure this pattern. Consideration of additional skeletal elements may help to assign these unknown specimens to species, while facilitating a clearer understanding of whether sphenacodontid species can be diagnosed by appendicular morphologies. Furthermore, because geometric morphometric analyses provide rigorous ways to isolate the effects of size on shape, my analyses will be able to determine whether supposed sphenacodontid species complexes are instead better interpreted as an ontogenetic series.
Forelimb Shape, Disparity, and Functional Morphology in the Deep Evolutionary History of Synapsida
Mammals and their closest fossil relatives use their shoulders and forelimbs for many functions, which is reflected by the great range of mammalian forelimb shapes. Little work has been done to quantify this diversity as it relates to deep mammalian evolutionary history. Using geometric morphometric techniques on the humerus and ulna, I sought to quantify morphometric disparity, functional diversity, and the phylogenetic influence of the two across the 300-million year evolution of this clade. I found that forelimb shape diversity in the early mammalian lineage (Synapsida) began to increase about 270 million years ago, with the emergence of a group called Therapsida, and is accompanied by new forelimb functions. The functional diversification of therapsid forelimbs was curtailed by the Permo-Triassic mass extinction, but eventually continued as more mammal-like therapsids evolved new ecologies. The analyses presented in this dissertation characterize the deep time origin of a quintessential part of the mammalian body plan: evolutionarily labile forelimbs that can be deployed in a wide range of functional and ecological roles.
Continuing this research on the origins and the recent forms of synapsid forelimb structure, I undertook a critical assessment of the ecological comparability of mammals to their fossil forerunners. Three interrelated goals are addressed: (1) to estimate when in synapsid evolutionary history modern mammal morphologies become effective for predicting fossil ecologies; (2) to investigate examples of morphological convergence within our geometric morphometric framework; and (3) to compare the functional solutions of distinct synapsid radiations in light of their shared phylogenetic history. I found that mammal limb shapes are not analogous to fossil synapsids until very close to the origin of crown Mammalia. These results suggest that phylogenetic placement strongly influences how an organism can respond to functional pressures, emphasizing that each synapsid radiation explored distinct areas of morphospace and arrived at functional solutions that reflected their separate ancestral morphologies.
Building upon this work, I quantified the influence of shared ancestry upon the macroevolution of synapsid forelimbs. Using a composite phylogenetic tree including 218 genera across 220 million years of synapsid evolution, I compared the phylogenetic signal and phenotypic rate change among forelimb metrics between phylogenetic groups and across anatomical forelimb elements. This work points to a critical but previously under-appreciated feature of the synapsid forelimb: that individual forelimb elements are undergoing independent evolutionary pressures and responding to those pressures at different rates. The work presented here challenges the traditional narrative of synapsid forelimb evolution as clear progression towards increasingly mammalian morphologies, and instead reveals a broad diversification of forelimb shapes early in synapsid history. This mosaic evolution of the synapsid forelimb reveals the complexity of forelimb evolutionary history, highlights the importance of forelimb morphometry to functional interpretation, and presents an increasingly dynamic picture for the forelimb evolution of Mammalia’s deepest fossil ancestors.
Lungmus and Angielczyk, 2019
FMNH Press Release
"Mammals’ unique arms started evolving before the dinosaurs existed"
"Bats fly, whales swim, gibbons swing from tree to tree, horses gallop, and humans swipe on their phones—the different habitats and lifestyles of mammals rely on our unique forelimbs. No other group of vertebrate animals...."
Lungmus and Angielczyk, 2019
Altmetric score of 178
(top 5% of all research outputs)
Lungmus and Angielczyk, 2021
Altmetric score of 23
Jones et al., 2018
Altmetric score of 207
(top 5% of all research outputs)
Lungmus, J.K. 2020, Evolutionary rate analysis reveals dynamic and variable patterning of forelimb evolution across the deep history of Synapsida. Journal of Vertebrate Paleontology, Program and Abstracts, 2020. Finalist for Romer Prize for Best Student Presentation at SVP Meeting.
Lungmus, J.K., Angielczyk, K.D., Luo, Z.X., 2020, Limb ecometrics show limited applicability for quantifying ecological novelty in the deep evolution of Synapsida. Society for Integrative and Comparative Biology, Austin, Texas, USA.
Lungmus, J.K., Angielczyk, K.D., 2019. Can geometric morphometric analyses of limb shape reveal ecomorphological patterns across the evolutionary history of Synapsida? International Congress on Vertebrate Morphology, Prague, Czech Republic.
Lungmus, J.K., Angielczyk, K.D., 2018. Morphological disparity across the synapsid forelimb: suborder-level patterns across 80 million years of synapsid evolution. Journal of Vertebrate Paleontology, Program and Abstracts, 2018, 172.
Lungmus, J.K., 2017. Increased disparity in Therapsida corresponds with the emergence of novel ecomorphologies - Cistecephalidae (Therapsida:Anomodontia) as a case study. Paleontological Association Annual Conference. London, UK
Lungmus, J.K., Increased limb morphological disparity coincident with the emergence of major synapsid clades and shifts to new morphofunctional types. Journal of Vertebrate Paleontology, Program and Abstracts, 2017, 154.
Small, B.J., Pardo, J.D., Lungmus, J.K., Douglass, R.J., Schlotterbeck, T., Huttenlocker, A.K., The first vertebrate body fossils from the Carboniferous-Permian Maroon Formation, Colorado, USA. Journal of Vertebrate Paleontology, Program and Abstracts, 2017, 195.
Lungmus, J.K., Angielczyk, K.D., Morphometric analysis of pelycosaur-grade synapsid pectoral elements reveals decreasing disparity towards Therapsida. Journal of Vertebrate Paleontology, Program and Abstracts, 2016, 178.
Lungmus, J.K., Angielczyk, K.D. 2016. Functional morphology of the pectoral girdle and forelimbs of a new burrowing cistecephalid dicynodont (Therapsida: Anomodontia). International Congress on Vert. Morphology. Washington, D.C.
Knaus, P. L., Sander, P., Van Heteren, A. H., Lungmus, J. K., Flow index of basal Eupelycosauria suggests elevated metabolic rates since the Carboniferous. Journal of Vertebrate Paleontology, Program and Abstracts, 2016, 167.
Lungmus, J.K., Angielczyk, K.D., Sidor, C.A., Nesbitt, S.J., Smith, R.M., Steyer, J-S., Tabor, N.J., Tolan, S., A new cistecephalid dicynodont (Therapsida: Anomodontia) from the Mid-Zambezi Basin (Zambia) and its fossorial adaptations Journal of Vertebrate Paleontology, Program and Abstracts, 2015, 169. Winner of Colbert Student Poster Prize (see Awards and Fellowships).