Pisanosaurus
Encyclopedia
Pisanosaurus is a genus
of primitive ornithischian dinosaur
from the Late Triassic
of what is now South America
. It was a bipedal herbivore
described by Argentine paleontologist Rodolfo Casamiquela in 1967. Only one species, the type
, Pisanosaurus mertii, is known, based on a single partial skeleton. The fossils were discovered in Argentina's Late Triassic
Ischigualasto Formation
, which dates to about 228 to 216.5 million years ago.
The exact classification of Pisanosaurus has been the topic of debate by scientists for over 40 years; the current consensus is that Pisanosaurus is the oldest known ornithischia
n, part of a diverse group of dinosaurs which lived during nearly the entire span of the Mesozoic Era
.
. The tail of Pisanosaurus has been reconstructed as being as long as the rest of the body, based on other early ornithischians, but as a tail has not been recovered, this is speculative. It was bipedal and, like all other known ornithischians, was probably herbivorous.
Rodolfo Casamiquela in 1967. The name Pisanosaurus honors Juan A. Pisano, an Argentine paleontologist, while saurus is derived from the Greek
, meaning "lizard". Pisanosaurus is known from a single fragmented skeleton
found in Argentina
. It is based on
a specimen given the designation PVL 2577, which was discovered in the Ischigualasto Formation
.
Cladogram
of basal Ornithischia after Butler et al. (2008), showing the position of Pisanosaurus as the earliest example of an ornithischian.
Pisanosaurus is very basal within Ornithischia
; the postcrania
seem to lack any good ornithischian synapomorphy
; it was even suggested by Paul Sereno
in 1991 that the fossil is a chimera
. However, recent studies suggest that the fossils belong to a single specimen.
Pisanosaurus has been classified either as a heterodontosaurid
or as the earliest known ornithischian. A 2008 study placed Pisanosaurus outside of (and more basal than) Heterodontosauridae
. In this study, Pisanosaurus is the earliest and most primitive ornithischian.
Pisanosaurus is the type genus of the Pisanosauridae, a family
erected by Casamiquela in the same paper which named Pisanosaurus. The Pisanosauridae family has fallen into disuse, as a 1976 study considered the group synonymous with the already named Heterodontosauridae
.
. Originally dated to the Middle Triassic
, this formation is now believed to belong to the Late Triassic
Carnian
stage
, around 228 to 216.5 million years ago. Pisanosaurus shared its habitat with rhynchosaur
s, cynodont
s, dicynodont
s, prestosuchids, ornithosuchids, aetosaur
s, and primitive dinosaurs. The early carnivorous dinosaur Herrerasaurus
lived in this area and at this time, and may have fed upon Pisanosaurus.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of primitive ornithischian dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
from the Late Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
of what is now South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. It was a bipedal herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
described by Argentine paleontologist Rodolfo Casamiquela in 1967. Only one species, the type
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...
, Pisanosaurus mertii, is known, based on a single partial skeleton. The fossils were discovered in Argentina's Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
Ischigualasto Formation
Ischigualasto
Ischigualasto is a geological formation and a natural park associated with it in the province of San Juan, north-western Argentina, near the border with Chile...
, which dates to about 228 to 216.5 million years ago.
The exact classification of Pisanosaurus has been the topic of debate by scientists for over 40 years; the current consensus is that Pisanosaurus is the oldest known ornithischia
Ornithischia
Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...
n, part of a diverse group of dinosaurs which lived during nearly the entire span of the Mesozoic Era
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
.
Description
Based on the known fossil elements, Pisanosaurus was a small, lightly built dinosaur approximately 1 metre in length. Its weight was between 2.27–9.1 kg (5–20.1 lb). These estimates vary due to the incompleteness of the fossilFossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
. The tail of Pisanosaurus has been reconstructed as being as long as the rest of the body, based on other early ornithischians, but as a tail has not been recovered, this is speculative. It was bipedal and, like all other known ornithischians, was probably herbivorous.
Discovery and naming
Pisanosaurus mertii was described by Argentine paleontologistPaleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
Rodolfo Casamiquela in 1967. The name Pisanosaurus honors Juan A. Pisano, an Argentine paleontologist, while saurus is derived from the Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
, meaning "lizard". Pisanosaurus is known from a single fragmented skeleton
Skeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
found in Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
. It is based on
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
a specimen given the designation PVL 2577, which was discovered in the Ischigualasto Formation
Ischigualasto
Ischigualasto is a geological formation and a natural park associated with it in the province of San Juan, north-western Argentina, near the border with Chile...
.
Classification
Cladogram
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...
of basal Ornithischia after Butler et al. (2008), showing the position of Pisanosaurus as the earliest example of an ornithischian.
Pisanosaurus is very basal within Ornithischia
Ornithischia
Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...
; the postcrania
Postcrania
Postcrania[p] in zoology and vertebrate paleontology refers to all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g...
seem to lack any good ornithischian synapomorphy
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
; it was even suggested by Paul Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
in 1991 that the fossil is a chimera
Chimera (paleontology)
In paleontology, a chimera is a fossil which was reconstructed with elements coming from more than a single species of animal. A now classic example of chimera is Protoavis.-List of paleontological chimeras:*Brontosaurus*Lametasaurus...
. However, recent studies suggest that the fossils belong to a single specimen.
Pisanosaurus has been classified either as a heterodontosaurid
Heterodontosauridae
Heterodontosauridae is a family of early ornithischian dinosaurs that were likely among the most basal members of the group...
or as the earliest known ornithischian. A 2008 study placed Pisanosaurus outside of (and more basal than) Heterodontosauridae
Heterodontosauridae
Heterodontosauridae is a family of early ornithischian dinosaurs that were likely among the most basal members of the group...
. In this study, Pisanosaurus is the earliest and most primitive ornithischian.
Pisanosaurus is the type genus of the Pisanosauridae, a family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
erected by Casamiquela in the same paper which named Pisanosaurus. The Pisanosauridae family has fallen into disuse, as a 1976 study considered the group synonymous with the already named Heterodontosauridae
Heterodontosauridae
Heterodontosauridae is a family of early ornithischian dinosaurs that were likely among the most basal members of the group...
.
Paleoecology
The fossils of Pisanosaurus were discovered in Argentina's Ischigualasto FormationIschigualasto
Ischigualasto is a geological formation and a natural park associated with it in the province of San Juan, north-western Argentina, near the border with Chile...
. Originally dated to the Middle Triassic
Middle Triassic
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...
, this formation is now believed to belong to the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
stage
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
, around 228 to 216.5 million years ago. Pisanosaurus shared its habitat with rhynchosaur
Rhynchosaur
Rhynchosaurs were a group of Triassic diapsid reptiles related to the archosaurs.-Description:Rhynchosaurs were herbivores, and at times abundant , with stocky bodies and a powerful beak...
s, cynodont
Cynodont
Cynodontia or cynodonts are a taxon of therapsids which first appeared in the Late Permian and were eventually distributed throughout all seven continents by the Early Triassic . This clade includes modern mammals and their extinct close relatives. They were one of the most diverse groups of...
s, dicynodont
Dicynodont
Dicynodontia is a taxon of anomodont therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means 'two dog tooth'...
s, prestosuchids, ornithosuchids, aetosaur
Aetosaur
Aetosaurs are an extinct order of heavily armoured, medium- to large-sized Late Triassic herbivorous archosaurs. They have small heads, upturned snouts, erect limbs, and a body covered by plate-like scutes. All aetosaurs belong to the family Stagonolepididae...
s, and primitive dinosaurs. The early carnivorous dinosaur Herrerasaurus
Herrerasaurus
Herrerasaurus was one of the earliest dinosaurs. All known specimens of this carnivore have been discovered in rocks of late Ladinian age in northwestern Argentina...
lived in this area and at this time, and may have fed upon Pisanosaurus.
External links
- Pisanosaurus from the PaleoBiology Database
- Pisanosaurus at DinoData.com