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Ranjeev’s research on speciation in Tanzanian gastropods is published!

Ranjeev’s research on speciation in Tanzanian gastropods is published!

Congratulations to Ranjeev Epa (MS ’17)!  The research paper based on his MS thesis on systematics and morphology of Oligocene gastropods is now published in Papers in Paleontology.

Epa, Y.R., Stigall, A.L., Roberts, E.M., O’Brien, H., Stevens, N.J. 2018. Morphological diversification of ampullariid gastropods (Nsungwe Formation, late Oligocene, Rukwa Rift Basin) is coincident with onset of East African rifting. Papers in Palaeontology, 4:327-348.


A new freshwater gastropod fauna is described from the late Oligocene Nsungwe Formation of the Rukwa Rift Basin, Tanzania. Six new species of ampullariids are established including five species of Lanistes (L. microovum,L. nsungwensis, L. rukwaensis, L. songwellipticus and L. songweovum) and one species of Carnevalea (C. santiapillaii). These taxa occupy a morphospace region comparable to nearly half of extant Lanistes, a common and widespread genus in Africa and Madagascar. Palaeoecological evidence indicates that Nsungwe ampullariids inhabited fluvial, pond and paludal environments. Among these species are the oldest high‐spired and fluvially adapated Lanistes taxa. We suggest that Nsungwe Lanistes rapidly diversified in concert with habitat heterogeneity associated with the initiation of rifting along the western branch of the East African Rift System (EARS). Taxonomy, evolution and the biogeographical affinities of Nsungwe Formation freshwater gastropods contributes significantly to expanding the undersampled Palaeogene invertebrate fossil record of continental Africa.


Here is the university writeup about Ranjeev’s paper:

Paleontologists Find New Snail Species with Evolutionary Speed – Ohio University | College of Arts & Sciences

Snails may be physically rather slow, but the six new species identified by Ohio University researchers put on plenty of evolutionary speed when they had to. Ohio University paleontologists analyzing snail fossils from 24 to 26 million years ago have identified six new species-and published the first documentation of rapid …


Nilmani’s study of Ames Limestone Paleocommunities is published!

Nilmani’s study of Ames Limestone Paleocommunities is published!
So many beautiful brachiopods

Congratulations to Nilmani Perera (MS ’17)!  Her thesis project, which identified hierarchical biogeographic patterns in the paleo communities of the Pennsylvanian Ames Limestone has been published in Palaeogeography, Palaeoclimatology, Palaeoecology.

Perera, S.N. and Stigall, A.L. 2018. Identifying hierarchical spatial patterns within paleocommunities: An example from the Late Pennsylvanian Ames Limestone of the Appalachian basin. Palaeogeography, Palaeoclimatology, Palaeoecology, 506:1-11.

Abstract: Identifying ecological mechanisms that produce hierarchically arrayed spatial variation in community structure can be difficult in the fossil record due to conflation of spatial and temporal patterns. However, this difficulty can be mediated by minimizing the temporal duration of deposition within the unit examined. In this study, the fauna of the Upper Pennsylvanian Ames Limestone (Conemaugh Group) was analyzed to explore whether Ames paleocommunities exhibited hierarchical structure in a spatial dimension. This widespread carbonate unit was deposited during the maximum flooding interval of a glacio-eustatically influenced fifth order sea level cycle, and preserved taxa are contemporaneous within only a few thousand years. Paleocommunity structure and variability was assessed at multiple spatial scales using samples collected from seven outcrops of the Ames Limestone throughout southeastern Ohio which form a northeast to southwest trending transect parallel to the paleoshoreline. Abundance data were collected using quadrat sampling for brachiopods, bivalves, gastropods, bryozoa, corals, crinoids, echinoids, trilobites and foraminifera. Paleocommunity structure was analyzed via cluster, ordination, guild, and abundance analyses at multiple spatial scales (within a single locality, among localities and within the total study area) to provide insight on geographic partitioning of paleocommunity variation. Multiple levels of paleocommunity organization were recovered within the Ames fauna. All levels exhibited spatial partitioning, but the inferred proximate controls shifted from abiotic environmental controls at higher hierarchical levels to biotic controls at the lowest level. At the highest level, differentiation into a northern and southern regional paleocommunity was controlled primarily by substrate consistency and habitat heterogeneity related to variation in fluvial input within the basin. Local paleocommunity differentiation reflects biotic responses to topographic and environmental conditions that were geographically distributed within the region; whereas within outcrop variation was due largely to biotic feedback mechanisms.

Key points:


  • Paleoecology of a widespread, but temporally-restricted marine fauna was analyzed
  • Community analyses identified hierarchical constraints on spatial structure
  • Abiotic environmental controls were paramount at regional scales
  • Biotic interactions were primary at local scales
  • Hierarchical structure should be considered in paleocommunity analyses


Here is the university writeup about Nilmani’s paper:

Perera and Stigall Publish Study Detailing Ecological Structure of Local Fossil-Rich Limestone – Ohio University | College of Arts & Sciences

Generations of geology students at Ohio University have studied the Ames Limestone, the most fossiliferous rock layer in the Athens area, for class field trips and projects. This unit preserves skeletal remains of marine animals-corals, snails, brachiopods, trilobites, sharks- that inhabited a shallow sea that covered Athens about 300 million …

Two new publications on the Great Ordovician Biodiversification Event

Hot off the presses!  

The Stigall Lab has two new articles published in the Lethaia special issue “Contextualizing the Great Ordovician Biodiversificaiton Event”. This special issue derives from the IGCP 653 opening meeting in Durham in October 2016, and includes papers on many aspects of the GOBE and related topics.  You can access the entire issue online here.

Our lab has two contributions:

Stigall, A.L. 2018. How is biodiversity produced? Examining speciation processes during the Great Ordovician Biodiversification Event. Lethaia, 51 (2), 165-172. https://doi.org/10.1111/let.12232.

–In this paper, I make the case that it is critical to consider biological aspects of speciation, not only aggregate diversity counts, when seeking the causes of diversification events, such as the GOBE.

Trubovitz, S., & Stigall, A.L. 2018. Ecological revolution of Oklahoma’s rhynchonelliform brachiopod fauna during the Great Ordovician Biodiversification Event. Lethaia, 51(2), 277-285. https://doi.org/10.1111/let.12233.

–This is the second half of Sarah Trubovitz MS thesis, which examines community structure and body size in brachiopod communities across the GOBE in the Simpson Group of Oklahoma.

Bayesian estimation of Ordovician dispersal pathways


Today was an exciting day for the lab.  The paper on Ordovician dispersal pathways led by Adriane Lam which incorporates her primary MS thesis research came out. This paper is exciting for several reasons.  First, it’s always great when a student gets their research published! Second, this is the first use of bayesian biogeographic modeling with Paleozoic taxa.  Third, this project represents an evolution beyond a MS thesis project, through collaboration and improvements with additional authors at other institutions, namely Nick Matzke.  I am really so thrilled with how this paper came out.  It is a landmark is methods and has important implications for understanding Ordovician biogeography.  The only downside…Adriane titled it “Dispersal in the Ordovician” as  play on “Pirates of the Carribean” so I can’t get the Pirates theme song out of my head….

Lam, A.R., Stigall, A.L, Matzke, N.J. 2018. Dispersal in the Ordovician: Speciation patterns and paleobiogeographic analyses of brachiopods and trilobites. Palaeogeography, Palaeoclimatology, Palaeoecology, 489: 147-165. Online

Key Points:

  • Bayesian and ML methods were successfully implemented with Ordovician taxa.
  • Founder event speciation was important in the evolution of Paleozoic taxa.
  • Taxa with different larval strategies responded similarly to climate shifts.
  • Ocean currents were key influences on invertebrate dispersal patterns.
  • Results indicate most evolution within clades occurred during climate shifts.


Review paper on BIMEs: Biotic Immigration Events

Review paper on BIMEs: Biotic Immigration Events

I am extremely pleased to announce the latest paper from my research group.  This is a review of Biotic Immigration Events, which we term BIMEs, in the fossil record focusing on the ecological and evolutionary impacts that fossil large scale invasion events.  We consider examples from the Ordovician through Cenozoic in both marine and terrestrial systems.  The fossil data supports a two-phase diversity cycle in which the immigration event itself reduced speciation and causes faunal homogenization; whereas the subsequent basinal isolation is characterized by increased speculation and diversity accumulation at multiple levels.  We think this model has great potential as a null model to compare and contrast diversification patterns in the fossil record.  Perhaps my favorite part of this study, though, was working with Adriane, Davey, and Jen–former students that are now talented early career paleontologists in their own right.

Stigall, A.L., Bauer, J.E., Lam, A.L., Wright, D.A. 2017. Biotic immigration events, speciation, and the accumulation of biodiversity in deep time. Global and Planetary Change, 148: 242-257. Online

New paper showcasing current trends in biogeography

My colleagues and I recently published a horizon scan, a review of the current state of the field, of modern biogeography based on the International Biogeography Meeting held in Bayreuth, Germany in 2015.  Some of the key threads in this paper are the increasing prominence of large databases, integrated analyses, and inclusion of paleodata.

Dawson, M.N., Axmacher, J.C., Beierkuhnlein, C., Blois, J., Bradley, B., Cord, A.F., Dengler, J., He, K.S., Heaney, L.R., Jansson, R., Mahecha, M.D., Myers, C.E., Nogués-Bravo, D., Papadopoulo, A., Reu, B., Rodgríguez-Sánchez, F., Steinbauer, M., Stigall, A.L., Tuanmu, M-N. & Gavin, D.G. 2017. A Second Horizon Scan of Biogeography: Golden Ages, Midas Touches, and the Red Queen. Frontiers in Biogeography, 8(4), e29770. Online

It’s great to have this paper out, and just in time to revisit this concepts and explore how the field has changed at the upcoming International Biogeography Meeting in Tucson, Arizona next month.

Eochonetes revision published

The final section of Jennifer Bauer’s MS thesis research, a substantial phylogenetic and morphometric analysis of the Late Ordovician brachiopod genera Eochonetes and Thaerodonta has (finally) been formally published in the Journal of Paleontology.

Bauer, J.E. & Stigall, A.L. 2016. A combined morphometric and phylogenetic revision of the Late Ordovician brachiopod genera Eochonetes and Thaerodonta. Journal of Paleontology, 90 (5): 888-909. Online

Cliff notes version: most of the species previously referred to either genus belong within Eochonetes, Thaerodonta is not a valid genus, and some of the previously referred species don’t belong to this clade at all.  Bonus fun: Jen named some new species including one for her amazing grandmothers and another for a character in her favorite book series.

I’m really very proud of Jen for her really excellent work on this project. I am also very pleased that we could clear up some of the confusing nomenclature around Cincinnati fossils.  The species variably known as Thaerodonta clarksvillensis and Eochonetes clarksvillensis is now definitively Eochonetes clarksvillensis.


*until someone else revises the genus at a later time

New volume on Speciation in the Fossil Record

by Alycia Stigall

Just in time for GSA, an excellent new volume Species in the Fossil Record edited by Warren Allmon and Peg Yacobucci is now available.  There are many excellent conceptual chapters as well as clade-specific overviews. It’s a worthy volume for anyone interested in macroevolution in general and/or systematics in the fossil record.

My contribution synthesizes some of my work over the past decade.

Stigall, A.L. 2016. Invasive species and speciation, p. 340-365. In Allmon, W. and Yaccobucci, M.M., Species in the Fossil Record. Chicago University Press. Publisher link.

Species-level diversity curve for Middle Ordovician Laurentian brachiopods published in GEOLOGY

Congratulations to alumnus Sarah Trubovitz on the publication of her MS thesis research in GEOLOGY!   **clicking this link bypasses the paywall, so click here!

Also, this is the first official publication of IGCP 653: Onset of the Great Ordovician Biodiversification Event. Our project is off to a great start!


Synchronous diversification of Laurentian and Baltic rhynchonelliform brachiopods: Implications for regional versus global triggers of the Great Ordovician Biodiversification Event

The profound global impact of marine radiations during the Great Ordovician Biodiversification Event (GOBE) is widely appreciated; however, diversification varied among paleocontinents and these individual trajectories are less understood. Here we present a new species-level diversity curve for rhynchonelliform brachiopods from midcontinental Laurentia based on bed-by-bed analysis of the Simpson Group of Oklahoma (USA).