Pakasuchus
Encyclopedia
Pakasuchus is a genus of notosuchia
n crocodyliform distinguished by its unusual mammal-like appearance, including mammal-like teeth that would have given the animal the ability to chew. It also had long, slender legs and a doglike nose. Pakasuchus lived approximately 105 million years ago, in the mid-Cretaceous
. Fossils have been found from the Rukwa Rift Basin of southwestern Tanzania
, and were described in 2010 in the journal Nature
. The type species
is P. kapilimai. Pakasuchus means "cat crocodile" (paka meaning "cat" in Kiswahili) in reference to its cat-like appearance and probable behavior.
ns, Pakasuchus had distinctive heterodont
teeth that varied in shape throughout its jaws. There are large, sharp teeth near the front of the jaws, and broad molar
-like teeth at the back of the mouth. While multicuspid teeth are seen in many other notosuchians such as Simosuchus
and Yacarerani
, they are most complex in Pakasuchus. The molar-like teeth show a level of complexity that matches that of mammals, being able to occlude
, or fit with one another, and provide sharp shearing edges for slicing food.
Pakasuchus also differed from modern crocodilians, and many other crocodyliforms, in the reduction of osteoderm
s covering the body. Small, reduced osteoderms overlie the dorsal vertebrae, but fewer in number and are not as large as those of other notosuchians. However, caudal osteoderms still covered the tail. The loss of osteoderms on the body and retention of them on the tail is unique among crocodyliforms.
and the National Geographic Society
as part of the Rukwa Rift Basin Project. Remains from six other individuals were later uncovered. The specific name honors Saidi Kapilima, one of the leaders of the Rukwa Rift Basin Project and who helped in the excavation of the specimens.
The most complete specimen includes a nearly complete skull. Because the jaws were closed in this specimen, some of the teeth were obscured. The describers of the specimens used X-ray computed tomography scanning, or CT scanning, to image the teeth. This provided a detailed view of the animal's dentition that could not normally be observed in the specimen.
modified from O’Connor et al., 2010:
The relative lack of osteoderms on the body may have been an adaptation for an active terrestrial lifestyle, as it would have lightened the animal. However, the retention of osteoderms on the tail is hard to explain, as they would have been quite heavy. The long legs and slender build would also have made Pakasuchus more agile.
Notosuchians were widespread across Gondwana
throughout the Cretaceous. Pakasuchus, as well as many other notosuchians, would have filled ecological niche
s in these areas that were otherwise occupied by mammals in the northern continents. Mammals were relatively uncommon in Gondwana at the time, making it possible for notosuchians to occupy a similar niche.
The Rukwa Rift Basin is known for a rich vertebrate fauna that existed during the Cretaceous. During the Early Cretaceous, the basin was part of a large river system with braided channels
and low-lying vegetated floodplains. Several dinosaurs are known from the basin that would have lived alongside Pakasuchus, including large sauropods and theropods. Aquatic crocodyliforms inhabited the rivers along with turtle
s and fishes.
Notosuchia
Notosuchia is a suborder of primarily Gondwanan mesoeucrocodylian crocodylomorphs that lived during the Cretaceous. Fossils have been found from South America, Africa, and Asia...
n crocodyliform distinguished by its unusual mammal-like appearance, including mammal-like teeth that would have given the animal the ability to chew. It also had long, slender legs and a doglike nose. Pakasuchus lived approximately 105 million years ago, in the mid-Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
. Fossils have been found from the Rukwa Rift Basin of southwestern Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
, and were described in 2010 in the journal Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...
. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
is P. kapilimai. Pakasuchus means "cat crocodile" (paka meaning "cat" in Kiswahili) in reference to its cat-like appearance and probable behavior.
Description
Pakasuchus was around 50 centimetres (19.7 in) long. Like all notosuchians, it was an active terrestrial animal. It probably hunted small prey such as insects. It had a short, broad skull somewhat similar in shape to a cat. Unlike living crocodiliaCrocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns, Pakasuchus had distinctive heterodont
Heterodont
The anatomical term heterodont refers to animals which possess more than a single tooth morphology. For example, members of the Synapsida generally possess incisors, canines , premolars, and molars. The presence of heterodont dentition is evidence of some degree of feeding/hunting specialization...
teeth that varied in shape throughout its jaws. There are large, sharp teeth near the front of the jaws, and broad molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
-like teeth at the back of the mouth. While multicuspid teeth are seen in many other notosuchians such as Simosuchus
Simosuchus
Simosuchus is an extinct genus of notosuchian crocodylomorphs from the Late Cretaceous of Madagascar. It is named for its unusually short skull. Fully grown individuals were about in length. The type species is S. clarki, found from the Maevarano Formation in Mahajanga Province.The teeth of S...
and Yacarerani
Yacarerani
Yacarerani is an extinct genus of Late Cretaceous notosuchian crocodylomorph. Fossils have been found in 2002 from central Bolivia in Amboró National Park and are Turonian-Santonian in age. The genus was recently described in 2009 in the Journal of Vertebrate Paleontology...
, they are most complex in Pakasuchus. The molar-like teeth show a level of complexity that matches that of mammals, being able to occlude
Occlusion (dentistry)
Occlusion, in a dental context, means simply the contact between teeth. More technically, it is the relationship between the maxillary and mandibular teeth when they approach each other, as occurs during chewing or at rest....
, or fit with one another, and provide sharp shearing edges for slicing food.
Pakasuchus also differed from modern crocodilians, and many other crocodyliforms, in the reduction of osteoderm
Osteoderm
Osteoderms are bony deposits forming scales, plates or other structures in the dermal layers of the skin. Osteoderms are found in many groups of extant and extinct reptiles, including lizards, various groups of dinosaurs , crocodilians, phytosaurs, aetosaurs, placodonts, and hupehsuchians...
s covering the body. Small, reduced osteoderms overlie the dorsal vertebrae, but fewer in number and are not as large as those of other notosuchians. However, caudal osteoderms still covered the tail. The loss of osteoderms on the body and retention of them on the tail is unique among crocodyliforms.
Discovery
A complete skeleton of Pakasuchus was found in 2008 in southwestern Tanzania by an international research team funded by the National Science FoundationNational Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...
and the National Geographic Society
National Geographic Society
The National Geographic Society , headquartered in Washington, D.C. in the United States, is one of the largest non-profit scientific and educational institutions in the world. Its interests include geography, archaeology and natural science, the promotion of environmental and historical...
as part of the Rukwa Rift Basin Project. Remains from six other individuals were later uncovered. The specific name honors Saidi Kapilima, one of the leaders of the Rukwa Rift Basin Project and who helped in the excavation of the specimens.
The most complete specimen includes a nearly complete skull. Because the jaws were closed in this specimen, some of the teeth were obscured. The describers of the specimens used X-ray computed tomography scanning, or CT scanning, to image the teeth. This provided a detailed view of the animal's dentition that could not normally be observed in the specimen.
Phylogeny
Below is a cladogramCladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
modified from O’Connor et al., 2010:
Paleobiology
Pakasuchus was probably very mammal-like in behavior as well as appearance. The molariform teeth are well suited to shearing food like modern mammalian carnivores. In fact, the teeth are so similar to those of mammals that it has led paleontologist Greg Buckley to state "If only isolated teeth had been discovered, without the skull, it is very likely that some of the molariform teeth would have been mistaken for a mammal's."The relative lack of osteoderms on the body may have been an adaptation for an active terrestrial lifestyle, as it would have lightened the animal. However, the retention of osteoderms on the tail is hard to explain, as they would have been quite heavy. The long legs and slender build would also have made Pakasuchus more agile.
Notosuchians were widespread across Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
throughout the Cretaceous. Pakasuchus, as well as many other notosuchians, would have filled ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
s in these areas that were otherwise occupied by mammals in the northern continents. Mammals were relatively uncommon in Gondwana at the time, making it possible for notosuchians to occupy a similar niche.
The Rukwa Rift Basin is known for a rich vertebrate fauna that existed during the Cretaceous. During the Early Cretaceous, the basin was part of a large river system with braided channels
Braided river
A braided river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars or, in British usage, aits or eyots. Braided streams occur in rivers with high slope and/or large sediment load...
and low-lying vegetated floodplains. Several dinosaurs are known from the basin that would have lived alongside Pakasuchus, including large sauropods and theropods. Aquatic crocodyliforms inhabited the rivers along with turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s and fishes.