Azendohsauridae is a
family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
of
allokotosauria
Allokotosauria is a clade of early archosauromorph reptiles from the Middle to Late Triassic known from Asia, Africa, North America and Europe. Allokotosauria was first described and named when a new monophyletic grouping of specialized he ...
n
archosauromorphs that lived during the
Middle to
Late Triassic
The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...
period, around 242-216 million years ago. The family was originally named solely for the eponymous ''
Azendohsaurus
''Azendohsaurus'' is an extinct genus of herbivorous archosauromorph reptile from roughly the late Middle to early Late Triassic Period of Morocco and Madagascar. The type species, ''Azendohsaurus laaroussii'', was described and named by Jean- ...
'', marking out its distinctiveness from other allokotosaurs,
but the family now includes four other
genera: the
basal genus ''
Pamelaria'', the large horned herbivore ''
Shringasaurus'',
and two carnivorous genera grouped into the
subfamily-level subclade Malerisaurinae, ''
Malerisaurus'' and ''
Puercosuchus'', and potentially also the
dubious
Doubt is a mental state in which the mind remains suspended between two or more contradictory propositions, unable to be certain of any of them.
Doubt on an emotional level is indecision between belief and disbelief. It may involve uncertainty ...
genus ''Otischalkia''.
Most fossils of azendohsaurids have a
Gondwanan distribution, with multiple species known across
Morocco
Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria t ...
and
Madagascar
Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
in
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
as well as
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
, although fossils of malerisaurine azendohsaurids have also been found in the southwestern
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
of
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
.
Azendohsaurids are notable for the various dinosaur-like traits found in some species, including the
sauropodomorph
Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
-like neck, jaws and teeth of ''Azendohsaurus'', the
ceratopsid
Ceratopsidae (sometimes spelled Ceratopidae) is a family of ceratopsian dinosaurs including ''Triceratops'', ''Centrosaurus'', and ''Styracosaurus''. All known species were quadrupedal herbivores from the Upper Cretaceous. All but one species are k ...
-like horns of ''Shringasaurus'', and
theropod
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
-like teeth of ''Puercosuchus''.
These traits are all
convergently evolved
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
with later dinosaurs, and some similarities are so striking that it is difficult to distinguish isolated azendohsaurid teeth and jaw bones from those of dinosaurs. Indeed, ''Azendohsaurus'' itself was initially described as a herbivorous dinosaur until better remains of its skull and skeleton were found.
Description
Azendohsaurids were robust quadrupeds with sprawled limbs, characterised by their long necks and proportionately small heads, and reached body sizes of up to in length in the largest species.
Although initially characterised as herbivores based solely on ''Azendohsaurus'', azendohsaurids had a diverse diet and lifestyles including large herbivores, insectivores, and carnivores. Consequently, although broadly similar in body form, their skulls varied from short and boxy with leaf-shaped teeth, to long and narrow with recurved, blade-like teeth.
[
Azendohsaurids lack a prenarial process, the bony splint of the ]premaxilla
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...
that otherwise divides the two external nares in typical reptile skulls, giving them a single fused (confluent) opening for their nostrils. Another characteristic of azendohsaurids is that they often possess palatal teeth on the roof of their mouths similar in size and shape to those along the jaw margins, including serrations, compared to the typical tiny and conical palatal teeth of other reptiles. Such large and specialised palatal teeth are known definitively in ''Pamelaria'', ''Azendohsaurus'' and ''Shringasaurus'', while simpler but notably large palatal teeth with coarse serrations are found in ''Malerisaurus''. The palatal teeth of ''Puercosuchus'', however, are simply described as "peg-like".
All known azendohsaurids have long necks, with neck vertebrae very similar in shape and construction to those of early sauropodomorph dinosaurs, and held them raised above their shoulders. The shoulder girdle
The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of t ...
s themselves are tall and very well developed, with long scapula
The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eithe ...
r blades. Azendohsaurids had a sprawling gait like other early archosauromorphs, although their shoulder joint
The shoulder joint (or glenohumeral joint from Greek ''glene'', eyeball, + -''oid'', 'form of', + Latin ''humerus'', shoulder) is structurally classified as a synovial ball-and-socket joint and functionally as a diarthrosis and multiaxial joint. ...
faces back as well as out to the sides, suggesting they may have been able to hold their forelimbs closer to their body. Their bodies are deep, ranging from relatively narrow-bodied in ''Pamelaria'' to barrel-shaped in ''Azendohsaurus'', and their tails are proportionally shorter and stockier compared to other archosauromorphs.
Classification and evolution
Azendohsaurids are one of two or three families included in the clade Allokotosauria, a group of unusual Triassic non-archosaur
Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
archosauromorphs that also includes the families Trilophosauridae
Trilophosaurs are lizard-like Triassic allokotosaur reptiles related to the archosaurs. The best known genus is ''Trilophosaurus'', a herbivore up to long. It had a short, unusually heavily built skull, equipped with massive, broad flattened che ...
and possibly the gliding Kuehneosauridae
Kuehneosauridae is an extinct family of small, lizard-like gliding diapsids known from the Triassic period of Europe and North America. They are distinguished from other diapsids by their 'wings' formed by elongated ribs. These allowed the animal ...
. They have consistently been recognised as the sister taxon
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and t ...
of trilophosaurids, initially united on shared yet differing herbivorous traits. However, as more azendohsaurids have been discovered and recognised, they demonstrate that the group was likely to be ancestrally carnivorous.
A phylogenetic analysis
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
performed by palaeontologist Sterling J. Nesbitt and colleagues in 2021 included all recognised azendohsaurids and other allokotosaurian taxa. Their results found ''Pamelaria'' to be the earliest branching azendohsaurid, with the remaining azendohsaurids divided into two subclades, one containing the herbivores ''Shringasaurus'' and two species of ''Azendohsaurus'', and the Malerisaurinae containing both species of ''Malerisaurus'' and similar larger material (including the material that would be named ''Puercosuchus''). The cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...
below depicts the simplified consensus result of their analysis, where the uncertain relationships within Malerisaurinae are presented as a polytomy
An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...
:
Biogeography
The oldest known azendohsaurids are ''Pamelaria'' and ''Shringasaurus'', both from India and dated to the Anisian
In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from million years ago until million years ago. The Anisian Age succeeds the Olenekian Age (part of the Lower Triassic Ep ...
stage
Stage or stages may refer to:
Acting
* Stage (theatre), a space for the performance of theatrical productions
* Theatre, a branch of the performing arts, often referred to as "the stage"
* ''The Stage'', a weekly British theatre newspaper
* Sta ...
of the 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 in chronostratigraphy. The Middle Triassic spans the time between Ma and ...
. ''Azendohsaurus'' itself has been dated from the end of the Middle Triassic during the Ladinian
The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between Ma and ~237 Ma (million years ago). The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic).
...
(at least for ''A. madagaskarensis'') into the Carnian
The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...
stage of the earliest Late Triassic
The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...
in Morocco and Madagascar. Malerisaurines, including ''Malerisaurus'' and ''Puercosuchus'', are exclusively known from the Late Triassic
The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...
during an interval from the late Carnian into the early Norian
The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.
Stratigraphic defi ...
of both India and North America, and are the latest-surviving azendohsaurids known. This is in spite of their relatively plesiomorphic
In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades.
Plesiomorphy, symplesiomorphy, apomorphy, and ...
(i.e. ancestral) features compared to other azendohsaurids, representing a relictual lineage of early-diverging carnivorous azendohsaurids that survived longer than their more derived herbivorous kin. Malerisaurines disappear from the fossil record in North America at or the near the end of the Adamanian teilzone In biostratigraphy, a local-range zone, topozone or teilzone (German ''teil'' = part + Greek ''zone'') is the stratigraphic range of the rock unit between the first and last appearance datum of a particular taxon in a local area. It is a subset of t ...
(a local biostratigraphic
Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictionary of Bio ...
unit in the southwestern United States) roughly 216 million years ago, marking the extinction of the azendohsaurids globally.
References
{{Taxonbar, from=Q39087053
Allokotosaurs
Prehistoric reptile families
Middle Triassic reptiles
Late Triassic reptiles