Pisanosaurus

Taxobox
name = "Pisanosaurus"
fossil_range = Fossil range|228|216.5 Late Triassic
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo =
genus = "Pisanosaurus"
genus_authority = Casamiquela, 1967
subdivision_ranks = Species
subdivision = "P. mertii" Casamiquela, 1967

"Pisanosaurus" (meaning "Pisano lizard") 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 one partially complete skeleton. The fossils were discovered in Argentina's Late Triassic Ischigualasto Formation, from around 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 ornithischian, part of a diverse group of dinosaurs which lived during nearly the entire span of the Mesozoic Era.

Description

Based on the known fossil elements, "Pisanosaurus" was a small, lightly-built dinosaur approximately convert|1|m|ftin|abbr=on|lk=on in length and convert|30|cm|in|abbr=on|lk=on in height. Its weight was between convert|2.27|-|9.1|kg|lb|0|abbr=on|lk=on.Holtz, Thomas R. Jr. (2008) "Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages" [http://www.geol.umd.edu/~tholtz/dinoappendix/DinoappendixSummer2008.pdf Supplementary Information] ] These estimates vary due to the incompleteness of the fossil. The tail of "Pisanosaurus" has been reconstructed as being as long as the rest of the body, based on other early ornithischians,cite web| last = Holtz| first = Thomas R. Jr.| authorlink = | title = The Dinosaur Family Tree: What is a dinosaur?| work = | publisher = University of Maryland Department of Geology| date = 2006| url = http://www.geol.umd.edu/~tholtz/G104/10417what.htm| format = | doi = | accessdate = 2008-08-10] but as a tail has not been recovered, this is speculative. It was bipedal and, like all ornithischians, was probably exclusively herbivorous.

Discovery and naming

"Pisanosaurus mertii" was described by Argentine paleontologist Rodolfo Casamiquela in 1967. The name "Pisanosaurus" honors Juan A. Pisano, an Argentine paleontologist, while "saurus" is derived from the Greek _gr. σαυρος, meaning "lizard".cite book | author = Liddell, Henry George and Robert Scott | year = 1980 | title = A Greek-English Lexicon (Abridged Edition) | publisher = Oxford University Press | location = United Kingdom | id = ISBN 0-19-910207-4] "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.cite journal| last = Butler| first = Richard J.| authorlink = | coauthors = Upchurch, Paul and Norman, David, B.| title = The phylogeny of the ornithischian dinosaurs| journal = Journal of Systematic Palaeontology | volume = 6| issue = 1| pages = 1–40| publisher = | location = | date = 2008| url = http://journals.cambridge.org/production/action/cjoGetFulltext?fulltextid=1702324| doi = 10.1017/S1477201907002271| id = | accessdate = 2008-08-09]

Classification

clade| style=font-size:90%;line-height:80%
label1= Ornithischia
1=clade
1= "Pisanosaurus"
label2=
2=clade
label1= Heterodontosauridae
1=clade
1= "Abrictosaurus"
2= "Heterodontosaurus"
label2= Genasauria
2=clade
1=Thyreophora
2=Neornithischia
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.cite journal| last = Sereno| first = P.C.| authorlink = Paul Sereno| title = "Lesothosaurus", "fabrosaurids", and the early evolution of Ornithischia| journal = Journal of Vertebrate Paleontology| volume = 11| issue = | pages = 168–197| publisher = | location = | date = 1991| url = | doi = | id = | accessdate = ] However, recent studies suggest that the fossils belong to a single specimen.cite journal| last = Irmis| first = R.B. | authorlink = | coauthors = Parker, W.G., Nesbitt, S.J. and Liu, J.| title = Early ornithischian dinosaurs: the Triassic record| journal = Historical Biology| volume = 19| issue = | pages = 3–22| publisher = | location = | date = 2007| url = | doi = | id = | accessdate = ]

"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".cite journal| last = Casamiquela| first = R.M.| authorlink = | title = Un nuevo dinosaurio ornitisquio triásico ("Pisanosaurus mertii"; Ornithopoda) de la Formación Ischigualasto, Argentina| journal = Ameghiniana| volume = 4| issue = 2| pages = 47–64| publisher = | location = | date = 1967| url = | doi = | id = | accessdate = ] The Pisanosauridae family has fallen into disuse, as a 1976 study considered the group synonymous with the already named Heterodontosauridae.

Paleoecology

The fossils of "Pisanosaurus" were discovered in Argentina's Ischigualasto Formation. Originally dated to the Middle Triassic,cite journal| last = Bonaparte| first = J.F.| authorlink = Jose Bonaparte| title = "Pisanosaurus mertii" Casamiquela and the origin of the Ornithischia| journal = Journal of Paleontology| volume = 50| issue = 5| pages = 808–820| publisher = | location = | date = 1976| url = http://www.jstor.org/pss/1303575| doi = | id = | accessdate = 2008-08-09] 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 rhynchosaurs, cynodonts, dicynodonts, prestosuchids, ornithosuchids, aetosaurs, and primitive dinosaurs. The early carnivorous dinosaur "Herrerasaurus" lived in this area and at this time, and may have fed upon "Pisanosaurus".

References

*Casamiquela, R.M. (1967). "Un nuevo dinosaurio ornitisquio triásico ("Pisanosaurus mertii"; Ornithopoda) de la Formación Ischigualasto, Argentina". "Ameghiniana" 4(2):47–64

External links

* [http://www.dinoruss.com/de_4/5a7b967.htm "Pisanosaurus" in The Dinosaur Encyclopaedia] at Dino Russ' Lair
* [http://paleodb.org/cgi-bin/bridge.pl?action=checkTaxonInfo&taxon_no=38729&is_real_user=1 "Pisanosaurus"] from the PaleoBiology Database
* [http://www.dinodata.org/index.php?option=com_content&task=view&id=7227&Itemid=67 "Pisanosaurus"] at DinoData.com