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Unit 190: Reptilomorpha |
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The Vertebrates |
400 Cotylosauria |
Abbreviated CladogramTETRAPODA |--TEMNOSPONDYLI `--+--LEPOSPONDYLI `--Reptilomorpha |--Anthracosauroidea | |--Gephyrostegidae | `--Embolomeri `--Batrachosauria |--Seymouriamorpha `--Cotylosauria |--Diadectomorpha `--Amniota |--Sauropsida | |--Mesosauridae | `--Reptilia | |--ANAPSIDA | `--EUREPTILIA `--SYNAPSIDA |
Contents190.000 Overview |
Lungs: complex and in-folded, joined pharynx by trachea with cartilaginous support. Lungs used for CO2 dumping as well as O2 intake due to keratinized skin.
Neck: Often lengthened and more flexible.
Head: Buccal pumping eliminated, so head can be smaller and more domed.
Skull: (Captorhinid) Like "Anthracosaurs" but no otic notch or intertemporal. Postparietal, tabular and supratemporal reduced and on occipital surface only. Supraoccipital supports posterior of braincase, large stapes supports it laterally. Transverse flange on pterygoid. Elimination of large fangs. Basicranial articulation with palate moveable. Basioccipital and exoccipital form occipital condyle. Fits in ring formed intercentra and arches of atlas: ball and socket joint. Palatoquadrate reduced to quadrate and epipterygoid. Lower jaw has 1-2 coronoids and splenial.
Vertebrae: Spool-shaped centra. Small, crescentic intercentra.
Ventral axial muscles: Development of intercostals used to move ribs in respiration.
Ribs: lighter and may be joined ventrally by sternum as specialization for intercostal ventilation. Postural role assumed by epaxial muscles which are no longer primary locomotor muscles.
Limb bones: lighter – possibly reflecting proprioreceptor system. Feet used as levers for propulsion, rather than holdfasts. Ankle forms distinct hinge joint (mesotarsal). Tibiales, other bones of pes fuse to form astragalus. 23453 manus, 23454 pes.
Pelvis: Sacrum expanded from one vertebra to 2-3.
Hearing: convergent development of stapes (hyomandibula) as principal sound conduction mechanism of middle ear (i.e. connects tympanum with inner ear).
Excretion: Duct linking kidney & cloaca. Bladder not used as much for water recovery. This function tends to be performed by kidney.
Amniotic Egg: additional membranes (amnion, allantois chorion) in egg act to permit gas exchange but avoid water loss, permit large amounts of yolk storage, isolate waste products during development.
Temporal Fenestra: Synapsid at squamosal-postorbital-jugal, diapsid add at parietal-squamosal-postorbital. Euryapsid derived independently from diapsid by lack defined lower fenestra – loss of lower temporal bar.
Sauropsida includes most of what was clasically known as "Reptilia" along with birds (which are in effect glorified reptiles) and of course dinosaurs. Sauropsids therefore are the bulk of the reptiles plus birds, while Synapsids are the "mammal-like reptiles" plus mammals.
The
first Sauropsids were probably primitive lizard-like creatures rather similar
(and fairly closely related) to the protorothyrid Hylonomus, shown at
right. They scurried through the Carboniferous
undergrowth. In appearance and behaviour they would have been similar to
modern lizards, although anatomically they were more primitive. At this
time, the world was ruled by stem tetrapods. The only other amniotes around
were a few basal synapsids. Both groups
underwent a rapid evolutionary radiation as the Carboniferous and Permian
proceeded. The synapsid "pelycosaurs" grew into 1 to 3 metre
long predators, including specialized fin-back forms and two herbivorous
lineages. The sauropsids remained small and lizard-like. Thus the dominant
life-form during the Permian
were synapsids, and, during the Late Permian, the therapsids
which evolved from them. The end-Permian extinction, which saw off 95% of
lifeforms on Earth, decimated both synapsids and sauropsids, but the sauropsids
came back faster, with creatures such as the crocodile-like Proterosuchidae.
These sprawling predators were the advance guard of a great army of scaly and
armoured carnivores and herbivores (the Archosauriformes
), as well as the dinosaurs, during
the Triassic period.
Meanwhile the Triassic seas were the home of a variety of Sauropsid marine
reptiles - ichthyosaurs, nothosaurs, and thalattosaurs.
During the Late Triassic
period the dinosaurs well and truly took over. The Synapsids were reduced to the
role of mouse-sized rodents and insectivores; the mammaliforms
and mammals of the Late Mesozoic.
They remained in that lowly station, sharing the microvertebrate niches with a
variety of lepidosaurs (lizards and lizard relatives), until a huge asteroid saw
off the dinosaurs and the marine reptiles (the terminal Cretaceous
extinction event) and the mammals were able to inherit the Earth. The
surviving sauropsids include turtles,
lizards, crocodiles
and birds, all of which are still around
today. The crocodile-like Choristodera were a major group (order) of
reptiles that survive the terminal Cretaceous extinction but became extinct
before the modern era, while the sphenodonts,
the "lizards of the mesozoic" one could call them, are represented by
a single endangered species on a few small islands off New Zealand.
Range: from the Carboniferous.
Phylogeny: Batrachosauria: Seymouriamorpha + *: Diadectomorpha + Amniota.
Characters: $ more derived axis-atlas complex; $ sacrum with at least 2 vertebrae, $ robust claws on pes; $ loss of lateral line system.
Links: Phylogeny of Stegocephalians; AMPHIBIA et REPTILIA NGIANA (Chinese); V The four other mass extinctions. ATW020623.
Diadectomorpha:
Limnoscelis, Diadectes, Tseiajaia.
Range: Late Carboniferous to Early Permian.
Phylogeny: Cotylosauria: Amniota + *.
Characters: 1.5-3 m; some fully terrestrial; "swollen" neural arches; some (Diadectes) herbivorous.
Links: Diadectomorpha; Phylogeny of stegocephalians (note figures of Limnoscelis); Biology 356.
Image: Diadectes. ATW030122.
Range: from the Late Carboniferous.
Phylogeny: Cotylosauria: Diadectomorpha + *: Synapsida + Sauropsida.
Characters: premaxilla with palatal, maxillary & nasal processes [MR05]; frontal contacts orbit; various patterns of fenestration related to additional musculature for jaw from dermal skull and development of musculature to supply static pressure at jaw; squamosal contributes to margin of posttemporal fenestra; hemispherical & ossified occipital condyle; pterygoid with distinct palatal surface, transverse flange and quadrate ramus [MR05]; pterygoid quadrate ramus with separate dorsal flange extending from basicranial articulation to dorsal process of quadrate, supporting elongate epipterygoid [MR05]; loss of labyrinthodont teeth, caniniform tooth present on maxilla; 2 centers of ossification in scapulocoracoid; astragalus present. Numerous additional characters listed above.
Links: Introduction to the Amniota; Amniota; Amniota.
References: Müller & Reisz (2005) [MR05]. ATW051015.
Sauropsida: All amniotes closer to snakes than to St. Patrick.
Range: from the Late Carboniferous.
Phylogeny: Amniota: Synapsida + *: Mesosauridae + Reptilia.
Characters: Little or no specialization along tooth row; $ maxilla separate from quadratojugal; $ single coronoid; some suborbital fenestra present; $ supinator process parallel to humeral shaft; $ 1 centrale in ankle; tail-based locomotion using lateral undulation; frequently bipedal; no glandular skin, uric acid waste, beta keratin.
Links: Sauropsida -- The Dinosauricon; Phylogeny and Classification of Amniotes; Taxonomy browser (Sauropsida); Lecture 8 - Tetrapods; Amniota. ATW010219.
Mesosauridae: Brazilosaurus,
Mesosaurus, Stereosternum
Range: Early Permian of South America & Africa.
Phylogeny: Sauropsida: Reptilia + *.
Characters: secondarily aquatic; elongated snout & neck (~10 vertebrae); nares posterior, near orbits; postorbital contacts the supratemporal; quadratojugal does not extend dorsally and is narrowly exposed on the cheek (primitive); supraoccipital lacks anterior parasagittal flanges (primitive); supraoccipital plate broad & extends farther laterally than postparietal (primitive);.jaw articulation at level of occiput (primitive); ossified dorsal process of stapes (primitive); pterygoid palatal ramus extends anteriorly medial to choanae; teeth thecodont; long teeth (strained plankton?); pachostosed trunk ribs and wide neural arches, long, broad tail; well-developed anterior limbs; iliac blade with long, low posterodorsal process, lacking anterior expansion; large paddle-foot pes.
Image: Stereosternum from Permian Tetrapods. We recommend a visit to this site which has some excellent images in which some of the listed characters can be seen.
Links: Phylogeny and Classification of Amniotes; MESOSAURIA; Nathis Fauna Reptilelen (Dutch). ATW060129.
Reptilia:
LCA Turtles and birds (link).
Range: from the Late Carboniferous.
Phylogeny: Sauropsida: Mesosauridae + *: Anapsida + Eureptilia.
Characters: Tabular small or absent; large posttemporal fenestra; suborbital foramen (small hole near the lateral edge of palate, between the pterygoid, palatine, and ectopterygoid or jugal, when ectopterygoid absent); supraoccipital plate narrow.
Links: Class Reptilia; THE EMBL REPTILE DATABASE; Reptilia - Suite101.com; Introduction to the Diapsids; Reptilia (Reptiles); Nuova pagina 1; BIOSIS | Resource Guide | Reptilia; Class Reptilia; Reptiles; Phylogeny and Classification of Amniotes; Photogallery: Reptilia \ Amphibia. ATW020623.
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