Fact Sheet: Pakasuchus kapilimai
Patrick M. O'Connor
Associate Professor of Anatomy
Ohio University College of Osteopathic Medicine
- Pakasuchus kapilimai is known from multiple specimens, with the holotype (the specimen on which a taxonomic name is based) represented by a virtually complete skull and skeleton.
- Pakasuchus was a small crocodyliform, with a skull length of ~7 cm and a total body length estimated at 55 cm.
- Micro-computed tomography (μCT) scanning was used to reveal high-resolution detail of the small skull, dentition, and skeleton, some of which is still completely embedded in rock.
- When compared to other crocodyliforms, the skull and dentition are among the most unusual features of Pakasuchus, particularly the occluding upper and lower molar-like teeth that have shearing surfaces.
- Unerupted replacement teeth in the jaws of Pakasuchus already exhibit characteristic shearing ridges, indicating that this morphology (shape) is determined by genetics and not merely as a result of one tooth wearing against another.
- The forward-facing opening to the Pakasuchus nasal cavity suggests the animal had a primarily terrestrial (land-living) existence, rather than the aquatic one that is typical of crocodylians today.
- Notosuchian crocodyliforms, the group to which Pakasuchus belongs, diversified during the Middle and Late Cretaceous Period and are known primarily from former Gondwanan landmasses such as Africa, Madagascar and South America.
- The amazing diversity of small-bodied notosuchians on southern continents, along with an apparent paucity of mammals from these same places, suggests that notosuchians may have been exploiting a ‘mammalian’ niche in Gondwana during the Cretaceous.
- Notosuchia refers to a group of Cretaceous crocodyliforms characterized by small body size and a variety of skull and dental specializations that may have allowed them to exploit niches different from those occupied by living crocodylians today.
- The Cretaceous Period spanned from 144 to 65 million years ago and ended with a mass extinction event that eradicated many plant and animals species, including non-avian dinosaurs.
- The holotype skeleton of Pakasuchus is one of the best preserved and most complete land-living vertebrate fossils recovered from Cretaceous-age deposits on continental Africa.
- The Rukwa Rift Basin Project (RRBP) team initiated reconnaissance field surveys in 2002. Since then, annual expeditions have focused on exploring for fossils and characterizing the geology of the Rukwa Rift Basin in southern and western Tanzania.
- The Rukwa Rift Basin is approximately 300 km long by 50 km wide and is part of the Western Branch of the East Africa Rift System (EARS).
- Specimens of Pakasuchus have been recovered from several localities, in sedimentary rocks from the Namba Member of the Galula Formation, which belongs to a larger rock unit known as the Red Sandstone Group, exposed throughout the Rukwa Rift Basin.
- Sedimentological analyses reveal that the paleoclimate transitioned from tropical semiarid to tropical humid conditions during deposition of the Galula Formation during the Middle Cretaceous.
- The RRBP has provided field and laboratory training to 19 graduate students and 11 undergraduate students to date, representing eight universities in five countries.
- The research team has created a bilingual traveling exhibit in English and Kiswahili on the RRBP. The exhibit has been displayed in the Tanzania National Museum, at Ohio University in Athens, and at the Michigan State University Museum.
- The RRBP is also documenting and characterizing the only known late Oligocene (~25 million-years-old) terrestrial fauna below the equator. Near the Paleogene-Neogene boundary, a dramatic change occurred in African faunal composition, when a collision between Afro-Arabia and Eurasia resulted in large-scale replacement of much of the endemic African fauna by immigrant taxa. Fossils from the Rukwa Rift are important for documenting the sequence and timing of this faunal replacement.
- Late Oligocene deposits in the Rukwa Rift have revealed a diverse fauna including new species of anthropoid and strepsirrhine primates, sengis (elephant shrews), hyraxes, and rodents, as well as a range of other taxa including anthracotheres, birds, squamates, frogs, fishes and invertebrates.
Key References Related to the Rukwa Rift Basin Project:
O'Connor, P.M., J.J.W. Sertich, N.J. Stevens, E.M. Roberts, M.D. Gottfried, T.L.
Hieronymus, Z.A. Jinnah, R. Ridgely, S.E. Ngasala, and J. Temba. In Press. The
evolution of mammal like crocodyliforms in the Cretaceous of Gondwana. Nature: DOI
Roberts, E.M., P.M. O’Connor, N.J. Stevens, M.D. Gottfried, Z.A. Jinnah, S.E. Ngasala, and
R.A. Armstrong. Sedimentology and depositional environments of the Red Sandstone
Group, Rukwa Rift Basin, southwestern Tanzania: New insight into Cretaceous and
Paleogene terrestrial ecosystems and tectonics in sub-equatorial Africa. African Journal of Earth Sciences 57 (Presidential Review Paper 15):179-212 (2010).
Stevens, N.J., M.D. Gottfried, E.M. Roberts, S. Kapilima, S. Ngasala, and P.M. O’Connor.
Paleontological exploration in Africa: A view from the Rukwa Rift Basin of Tanzania,
pp. 159-180, in Developments in Primatology: Progress and Prospects, Tuttle, R. H. (ed.),
O’Connor, P.M., M.D. Gottfried, N.J. Stevens, E.M. Roberts, S. Ngasala, S. Kapilima, and R.
Chami. A new vertebrate fauna from the Cretaceous Red Sandstone Group, Rukwa Rift
Basin, southwestern Tanzania. Journal of African Earth Sciences Vol. 44:277-288 (2006).
Artist’s rendering of Pakasuchus kapilimai.
A photograph of the postcranial skeleton of Pakasuchus kapilimai
as it appears partially prepared out of the red sandstone matrix. The researchers used a sandbox and foam padding (in blue) to position the separate fragments of the fossil prior to photographing the specimen.
This line-drawing draft of Pakasuchus kapilimai
was completed by Ohio University graduate student Haley O'Brien. The drawing simplifies the complexity of the partial skeleton presented in the above photograph, delineating the position of the vertebral column, the tail (at the top, covered with osteoderms), and limb elements.
Saidi Kapilima (foreground,
and for whom Pakasuchus kapilimai
is named) and graduate student Sifa Ngasala (background) take a short break while hand-quarrying for fossils.
Artist’s rendition of Pakasuchus kapilimai
dentition, highlighting the mammal-like motions the jaw may have produced during eating.
Nile crocodile in Queen Elizabeth National Park, Uganda, illustrating modern crocodile dentition.
Ohio University graduate students Erin Simons (top right) and Verne Simons (foreground right) apply plaster bandages to a small dinosaur jacket at the field site in the Rukwa Rift Basin of southwestern Tanzania.
Eric Roberts (left), Nancy Stevens (second from left), Verne Simons (second from right) and Tobin Hieronymus (right) hand-quarry for fossils in the Rukwa Rift Basin of southwestern Tanzania.
Patrick O'Connor and Sifa Ngasala excavate a dinosaur limb bone out of a cliff face on the Mtuka River, while Nancy Stevens and Erin Simons collect fossils along the edge of the riverbed.