Araeoscelidia or
Araeoscelida is a
cladeA clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.[The term "monophyletic group" is used in this article...]
of extinct
diapsidDiapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...
reptiles superficially resembling lizards, extending from the Late
CarboniferousThe Carboniferous is a geologic period and system that extends from the end of the Devonian period, about 359.2 ± 2.5 Ma , to the beginning of the Permian period, about 299.0 ± 0.8 Ma ....
to the Early
PermianThe Permian
[The term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named...]
.
The group contains the
generaIn biology, a genus is a taxonomic unit used in the classification of living and fossil organisms. The term comes from Latin genus "descent, family, type, gender" , cognate with – genos, "race, stock, kin" ..In addition, genus is a taxonomic rank in the hierarchy In biology, a genus (plural:...
AraeoscelisAraeoscelis is an extinct genus of reptile, and one of the earliest diapsids. Fossils have been found in the United States, dating from the early Permian period.Araeoscelis was around long, and superficially resembled a modern lizard...
,
PetrolacosaurusPetrolacosaurus was a small, long, reptile, and the earliest diapsid known. It lived during the late Carboniferous period, the Joggins strata where it was found are dated to 302 million years old....
, the possibly aquatic
SpinoaequalisSpinoaequalis is an extinct genus of diapsid reptile.The 30 cm long creature, known from fossils found in Kansas, USA, was one of the first diapsids, along with Petrolacosaurus. It was also the first reptile to return to the water, evolving shortly after Hylonomus, the oldest confirmed reptile...
, and less well-known genera such as
Kadaliosaurus and
Zarcasaurus.
This clade is considered to be the sister group to all (currently known) later diapsids.
Araeoscelidans were small animals (less than one meter in length) looking somewhat like lizards, though they are only distantly related to true lizards.
Araeoscelidia or
Araeoscelida is a
cladeA clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.[The term "monophyletic group" is used in this article...]
of extinct
diapsidDiapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...
reptiles superficially resembling lizards, extending from the Late
CarboniferousThe Carboniferous is a geologic period and system that extends from the end of the Devonian period, about 359.2 ± 2.5 Ma , to the beginning of the Permian period, about 299.0 ± 0.8 Ma ....
to the Early
PermianThe Permian
[The term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named...]
.
The group contains the
generaIn biology, a genus is a taxonomic unit used in the classification of living and fossil organisms. The term comes from Latin genus "descent, family, type, gender" , cognate with – genos, "race, stock, kin" ..In addition, genus is a taxonomic rank in the hierarchy In biology, a genus (plural:...
AraeoscelisAraeoscelis is an extinct genus of reptile, and one of the earliest diapsids. Fossils have been found in the United States, dating from the early Permian period.Araeoscelis was around long, and superficially resembled a modern lizard...
,
PetrolacosaurusPetrolacosaurus was a small, long, reptile, and the earliest diapsid known. It lived during the late Carboniferous period, the Joggins strata where it was found are dated to 302 million years old....
, the possibly aquatic
SpinoaequalisSpinoaequalis is an extinct genus of diapsid reptile.The 30 cm long creature, known from fossils found in Kansas, USA, was one of the first diapsids, along with Petrolacosaurus. It was also the first reptile to return to the water, evolving shortly after Hylonomus, the oldest confirmed reptile...
, and less well-known genera such as
Kadaliosaurus and
Zarcasaurus.
This clade is considered to be the sister group to all (currently known) later diapsids.
Description
Araeoscelidans were small animals (less than one meter in length) looking somewhat like lizards, though they are only distantly related to true lizards. They differ from other, earlier sauropsids by their slender limbs, their elongated tail, and of course by the presence of two temporal openings, the feature defining the
diapsidDiapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...
condition. In
AraeoscelisAraeoscelis is an extinct genus of reptile, and one of the earliest diapsids. Fossils have been found in the United States, dating from the early Permian period.Araeoscelis was around long, and superficially resembled a modern lizard...
, only the upper temporal opening remains, thus resulting in a derived euryapsid condition.
Genera
Araeoscelida includes well-known genera such as
AraeoscelisAraeoscelis is an extinct genus of reptile, and one of the earliest diapsids. Fossils have been found in the United States, dating from the early Permian period.Araeoscelis was around long, and superficially resembled a modern lizard...
(Williston, 1910; Vaughn, 1955; Reisz et al., 1984),
PetrolacosaurusPetrolacosaurus was a small, long, reptile, and the earliest diapsid known. It lived during the late Carboniferous period, the Joggins strata where it was found are dated to 302 million years old....
(Lane, 1945; Peabody, 1952; Reisz, 1981) and
SpinoaequalisSpinoaequalis is an extinct genus of diapsid reptile.The 30 cm long creature, known from fossils found in Kansas, USA, was one of the first diapsids, along with Petrolacosaurus. It was also the first reptile to return to the water, evolving shortly after Hylonomus, the oldest confirmed reptile...
(deBraga & Reisz, 1995; deBraga & Rieppel, 1997), known from virtually complete skeletons.
Zarcasaurus (Brinkman et al., 1984),
Aphelosaurus (Gervais, 1859; Thévenin, 1910; Falconnet & Steyer, 2007) and
Kadaliosaurus (Credner, 1889) belong to this clade, but are known only from post-cranial remains and a mandible fragment for
Zarcasaurus.
The genus
Dictybolos has been included in Araeoscelidia by Olson (1970), but this inclusion has been criticized e.g. by Evans (1988), especially since Olson also included distantly related groups such as
protorosaursProtorosaurus , a lizard-like reptile of the order Prolacertiformes, is the earliest known archosauromorph. It lived during the Late Permian period in Germany....
and
mesosaurMesosaur were an order of small marine reptiles that lived during the early Permian period, roughly 320 to 280 million years ago. Mesosaurs were the first aquatic reptiles, having returned to a watery way of life after evolving on land....
s.
New specimens have been discovered in Oklahoma, United States (May & Hall, 2002; Swanson & Carlson, 2002) but so far lack a scientific description.
Phylogeny
Araeoscelidia
├─?
Dictybolos
├─o
SpinoaequalisSpinoaequalis is an extinct genus of diapsid reptile.The 30 cm long creature, known from fossils found in Kansas, USA, was one of the first diapsids, along with Petrolacosaurus. It was also the first reptile to return to the water, evolving shortly after Hylonomus, the oldest confirmed reptile...
└─o Araeosceloidea
├─o Petrolacosauridae
│ └─o
PetrolacosaurusPetrolacosaurus was a small, long, reptile, and the earliest diapsid known. It lived during the late Carboniferous period, the Joggins strata where it was found are dated to 302 million years old....
│
└─o Araeoscelidae
├─o
Zarcasaurus
└─o Araeoscelinae
├─o
Kadaliosaurus
└─o
├─o
AraeoscelisAraeoscelis is an extinct genus of reptile, and one of the earliest diapsids. Fossils have been found in the United States, dating from the early Permian period.Araeoscelis was around long, and superficially resembled a modern lizard...
└─o
Aphelosaurus
Phylogenetic relationships after deBraga and Reisz (1995) and Falconnet and Steyer (2007).
Stratigraphic and geographic distribution
Araeoscelida are known from the Late Carboniferous in the United States (
Petrolacosaurus,
Spinoaequalis) to the Early Permian in France (
Aphelosaurus), Germany (
Kadaliasaurus) and the United States (
Dictybolos,
Zarcasaurus,
Araeoscelis). Apart from araeoscelidans, only one other diapsid is known before the Late Permian:
Apsisaurus from the Early Permian of Texas (Laurin, 1991).