Late Cretaceous vertebrate faunas of Sudan
The Late Cretaceous sediments of Sudan are known to yield a fascinating variety of micro- and macrovertebrates, ranging from small salamanders up to giant crocodiles and dinosaurs. Also, some of the oldest and most diverse snake faunas have been reported from these deposits. Detailed information, however, has remained fragmentary, and only little is known about the environment in which these animals lived. In a collaborative field project together with David Evans (Royal Ontario Museum Toronto), Nicole Klein (Uni Bonn), Robert Bussert (TU Berlin) and our partner institutions in Sudan (Al Neelain University, Museum of Natural History Khartoum) we have been prospecting and excavating at various sites and formations in the Saharan desert of Sudan. We have so far completed two successful field seasons, during which we discovered new fossil-bearing localities and several new taxa. Whereas fossils from Sudan were previously only known from bonebeds, we now also discovered sites that preserve completely articulated skeletons.
Pleistocene vertebrate faunas of Sudan
Starting in 2018, our team has been exploring fossil deposits in the upper reaches of the Atbara River valley. Previous work had documented the presence of Middle to Late Pleistocene fauna and stone tools near Khashm el Girba, and our surveys have extended the range of Pleistocene sites in the region over 100 km up the Atbara and Setit Rivers. These deposits document the transition from Acheulean to Middle Stone Age technologies and the evolution of modern African ecosystems during the time of emergence of our species, Homo sapiens. This project comprises an international team led by Faysal Bibi, with Johannes Müller and Robert Bussert (TU Berlin), and in collaboration with colleagues at Al Neelain University, Khartoum University, and African University. It has been supported by a National Geographic Explorer’s Grant and the German Research Foundation (DFG).
Late Miocene vertebrates of Arabia
Exposed in the Al Gharbia (western) region of the United Arab Emirates are late Miocene rocks of around 7 million years age. Work in the 1980s and 90s led by Andrew Hill (Yale University) and the late Peter Whybrow (Natural History Museum, London) led to the discovery and description of a wide range of animal fossils from this region. Since, 2002, a team led by Faysal Bibi (MfN), Brian Kraatz (Western Univ.), Andrew Hill (Yale), and Mark Beech (Abu Dhabi Department of Tourism and Culture) has more than doubled the previous findings and greatly expanded the number of sites. Our findings include skeletal remains of diverse mammals, fish, birds, and herps which are all in different stages of analysis, and are providing new information on the ancient climate, ecology, and biogeographic relationships of what is today the Arabian desert region. You can read preprints of the upcoming monograph Sands of Time: Ancient Life in the Late Miocene of Abu Dhabi, United Arab Emirates (Springer, 2022), here.
Evolution of lacertid lizards
The Old-World clade of Lacertidae gained recently attention as a result of their newly discovered sistergroup relationship with the legless, burrowing Amphisbaenia. Lacertids can be subdivided into a Palearctic and an African radiation, with the latter showing an inverse latitudinal diversity gradient having the highest species numbers in arid and semiarid regions on both sides of the Equator. Our research focuses especially on the African clade, which we investigate both morphologically and ecologically and with special emphasis on the desert lacertids from the Sahara and the Kalahari/Namib. Desert lacertids show a remarkable degree of ecomorphological convergence, which might be induced, among other things, by changes in their life history as an evolutionary response to climate and habitat. Also, we are interested in the fossil history of the Lacertidae, which we use as additional evidence to decipher the clade’s patterns of diversification and to gain new calibration points for molecular clock studies.
Origin and evolution of the Amphisbaenia
The burrowing amphisbaenians are one of the greatest enigmas of Squamata, and only recently – also through studies from our lab – was it revealed that they share a common ancestry with the four-limbed, fully terrestrial lacertid lizards (see above). Next to working on their evolutionary origin, we are also concentrating on the ingroup evolution of Amphisbaenia. Current research in this area involves detailed osteological studies of all modern amphisbaenian genera, which we investigate using CT technology, and a careful reassessment of the amphisbaenian fossil record. In collaboration with the lab of Hussam Zaher in Sao Paulo, we combine this morphological information with molecular data in order to unravel the clade’s morphological evolution and biogeographic history. Preliminary data suggest that several of the supposedly “unique” amphisbaenian features evolved several times independently within the clade. In this context, we became also interested in other examples of body elongation and limb reduction, and the evolution of plasticity in the vertebral column.
Middle ear evolution in diapsid reptiles
The evolution of the middle ear has been a long-time interest in the lab. While previous research has dealt with parareptiles and early amniotes, our focus is now on the Diapsida. To this day it is still unknown how often an impedance-matching middle ear evolved within the clade, which is why we track the evolution of this complex from the base of the clade up to its modern members. In this respect, we have also taken advantage of the great fossil vertebrate collection at the Museum für Naturkunde Berlin, particularly the Tendaguru dinosaurs, and recently studied in detail the braincase and inner ear structure of the ornithischian dinosaur Dysalotosaurus lettowvorbecki. So although dinosaurs are normally blacklisted in the lab, we are sometimes moving over to the dark side.
Diversification of caenophidian snakes
Caenophidian snakes are the most speciose clade of Serpentes, and include all species that people would normally consider a “typical” snake. The Caenophidia appear to have diversified dramatically since the Oligocene, but the reasons for this diversification are poorly understood and have largely remained speculative. In a collaborative project with Jason Head from the University of Cambridge, we are currently assessing the fossil record of modern snakes in a quantitative framework, and try to test the different hypotheses that have been put forward to explain Caeonophidia’s apparent boost in Neogene diversification. In addition, we are investigating the morphology and evolution of selected clades of Colubroidea.
Evolution and paleoecology of African Bovidae
Antelopes (Bovidae) are the most diverse family of terrestrial large mammals and theyare typically abundant in fossil assemblages from the Neogene of Eurasia and Africa. The adaptation of different bovid clades to particular vegetational and climatic habitats means that they are of great use in the reconstruction of past environmental conditions and ecological relationships. This is particularly the case in Africa, where bovids are often the most abundant mammal found at sites where fossil hominins are discovered. We use the fossil bovid record to reconstruct changes in local habitat and ecological community structure are fossil sites ranging from the late Miocene to late Pleistocene across Africa.
Ruminant phylogenetics and diversification
Physical environmental change has been proposed as one of the main drivers of mammalian evolution. Ecological traits modulate the response of organisms to such changes, potentially affecting their capability to shift their geographic distributions, the composition of community assemblages and even their speciation and extinction rates. We use ruminants — e.g. deer, antelopes, giraffes — as a model faunal set for exploring the connections between environmental change, ecological traits, and evolution. This includes a synthesis of both fossil and extant taxa into a single phylogenetic framework, and the calculation of phylogenetic community structure metrics to reconstruct the diversity dynamics (e.g. speciation, extinction patterns) of paleo-communities. The timing of main evolutionary and ecological events can then be compared to the ever-growing record of physical environmental change in order to establish correlations and test existing hypotheses on the relationships of environment and mammalian evolution.
3D Geometric Morphometrics
Quantitative comparisons of cranial shape of extant and fossil species using landmarks digitized on 3D scans provide detailed insights on morphological differences both within and among species, including investigations of size-shape allometry and disparity through time. The Museum für Naturkunde has a state-of-the-art visualization lab with micro-CT and surface (ARTEC) scanners and our group has several ongoing projects on lizards, snakes, bovids, and hippopotamus.
Museum DNA and Integrative Taxonomy
Many species that are endangered or extinct today are preserved in zoological collections – many such specimens retain genomic information (DNA) that can be extracted and sequenced, illuminating the evolutionary history of these species and populations going back into the Pleistocene. Several ongoing projects use DNA from museum specimens in order to analyze ranges of genomic diversity and phylogeographic structure in extinct or extirpated populations, and the correspondence between molecular and morphological distances (integrative taxonomy).
ecoClimate Database and Species Distribution Modeling
Sara Varela is part of a team that developed ecoClimate.org, a new open-access database that enables researchers to use homogeneous climatic layers for working in macroecology and paleobiogeography. In ecoClimate.org there are GIS layers from 9 different climatic models with a cell resolution of 0.5 degrees, for the past (Pliocene, Late Glacial Maximum, Holocene), present (pre-industrial, historic, present), and future (4 different rcps) climatic scenarios. Ecological Niche Models (ENM) allow us to map the species geographic ranges and investigate the effects of climate changes and human impact on species potential distributions. We are collaborating with different international researchers to implement ENM at local and global scales for understanding extinction processes, migrations and the impact of current global changes.