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Mycterosaurus
Mycterosaurus (Greek as mykter/mykteros meaning nose/snout, sauros meaning "lizard") is an extinct genus of amniotes belonging to the family Varanopidae. It is classified in the varanopid subfamily Mycterosaurinae. Mycterosaurus is the most primitive member of its family, existing from 290.1 to 272.5 MYA, known to Texas and Oklahoma. It lacks some features that its advanced relatives have.
Mycterosaurus is a relatively small carnivore, estimated to be around 60 cm (23 inches) long with synonyms of Eumatthevia bolli, and possibly Basicranodon fortsillensis. Restored, Mycterosaurus appears spindly and grotesque in contrast to the majority of "pelycosaurs" in its proportions and especially unlike edaphosaurids, which are commonly stocky in build.
The number of valid Mycterosaurus species have varied over the years, with a total of two classifications of Mycterosaurus longiceps and Mycterosaurus smithae. However, recent analysis has led to a re-description of Mycterosaurus smithae.
Both the holotype and AMNH 7002 "Eumatthevia" have been studied and restudied, with additions and modifications to the cranial description. The nares and orbit of Mycterosaurus are unusually large, with the orbit directed outwardly and circular in manner. The extremely large size of the orbit has been associated with the relatively small size of the animal. Additionally, the surface of the supraoccipital that articulates with the parietals dorsally above are cartilaginous, a condition found in that of crocodiles, lizards, and dinosaurs. The exoccipitals surround the foramen magnum and are loosely attached in a similar fashion to Dimetrodon. The parietal foramen is situated almost at the extreme posterior end of the parietals and is very close to the dermosupraoccipitals. The parietal itself is slightly separated on each side from the squamoso-postorbital arch while the squamosal covers the quadate broadly.
Mycterosaurus possesses 18-20 maxillary teeth that are characteristically different from those of Varanops, Ophiacaodon, Dimetrodon, or Edaphosaurus. The teeth are stout at the base, with slightly recurved and sharp points. The first four to five maxillary teeth (anterior) are the largest at the primitive position of the canines. These teeth are moderately elongated, flattened, and present an obtuse apex. The premaxillary and maxillary teeth are typical thecodont teeth. The prevomers presented with a longitudinal row of small teeth and were long and slender in character. The lower teeth appear to be rather small and isodont, but otherwise unknown due to fossil conditions. In addition to maxillary teeth, Mycterosaurus presents small, but numerous palatal teeth. The pterygoids, on both anterior and middle aspects, show a considerable number of small pointed teeth. The marginal teeth are serrated on the mesial and distal edges.
The vertebrae are similar to that of Varanops, with a thin spine that was no more than 2-3 times in height the centrum. While the cervicals are unknown due to poor fossil records, details from the posterior aspect are somewhat preserved. The neural spine is low and broad in both anterior and posterior direction. The centra has rounded ends and no ventral keel, possessing a characteristic edaphosaurioid spool shape. Additionally, the dorsal centra is moderately elongate (5 units in length). In contrast, the lumbar centras are much shorter.
The scapula is short and not particularly broad, in contrast to the exceptionally broad procoracoid plate, a feature of edaphosaurids. The glenoid surface is short, and the supraglenoid foramen is absent. The pelvis has extreme elongation at the anterior end of the iliac blade with the anterior expansion being greater than the posterior. The humerus and hind leg bones are slender, with no ectepicondylar foramen.
The astragalus is L-shaped and the centrum is circular when viewed in ventral view. These observations are consistent with most pelycosaurian grade synapsids. The fourth distal tarsal is enlarged, with its proximal articular surface facing the convex. The convex is articulated by the astragalus-calcaneum complex. This morphology indicates a highly mobile mesotarsal joint in both Varanops and Mycterosaurus, contrasting earlier beliefs that little movement was present in early synapsids. These observations serve as evidence to suggest that Varanops and Mycterosaurus used a semidigitigrade stance to ambulate.
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Mycterosaurus
Mycterosaurus (Greek as mykter/mykteros meaning nose/snout, sauros meaning "lizard") is an extinct genus of amniotes belonging to the family Varanopidae. It is classified in the varanopid subfamily Mycterosaurinae. Mycterosaurus is the most primitive member of its family, existing from 290.1 to 272.5 MYA, known to Texas and Oklahoma. It lacks some features that its advanced relatives have.
Mycterosaurus is a relatively small carnivore, estimated to be around 60 cm (23 inches) long with synonyms of Eumatthevia bolli, and possibly Basicranodon fortsillensis. Restored, Mycterosaurus appears spindly and grotesque in contrast to the majority of "pelycosaurs" in its proportions and especially unlike edaphosaurids, which are commonly stocky in build.
The number of valid Mycterosaurus species have varied over the years, with a total of two classifications of Mycterosaurus longiceps and Mycterosaurus smithae. However, recent analysis has led to a re-description of Mycterosaurus smithae.
Both the holotype and AMNH 7002 "Eumatthevia" have been studied and restudied, with additions and modifications to the cranial description. The nares and orbit of Mycterosaurus are unusually large, with the orbit directed outwardly and circular in manner. The extremely large size of the orbit has been associated with the relatively small size of the animal. Additionally, the surface of the supraoccipital that articulates with the parietals dorsally above are cartilaginous, a condition found in that of crocodiles, lizards, and dinosaurs. The exoccipitals surround the foramen magnum and are loosely attached in a similar fashion to Dimetrodon. The parietal foramen is situated almost at the extreme posterior end of the parietals and is very close to the dermosupraoccipitals. The parietal itself is slightly separated on each side from the squamoso-postorbital arch while the squamosal covers the quadate broadly.
Mycterosaurus possesses 18-20 maxillary teeth that are characteristically different from those of Varanops, Ophiacaodon, Dimetrodon, or Edaphosaurus. The teeth are stout at the base, with slightly recurved and sharp points. The first four to five maxillary teeth (anterior) are the largest at the primitive position of the canines. These teeth are moderately elongated, flattened, and present an obtuse apex. The premaxillary and maxillary teeth are typical thecodont teeth. The prevomers presented with a longitudinal row of small teeth and were long and slender in character. The lower teeth appear to be rather small and isodont, but otherwise unknown due to fossil conditions. In addition to maxillary teeth, Mycterosaurus presents small, but numerous palatal teeth. The pterygoids, on both anterior and middle aspects, show a considerable number of small pointed teeth. The marginal teeth are serrated on the mesial and distal edges.
The vertebrae are similar to that of Varanops, with a thin spine that was no more than 2-3 times in height the centrum. While the cervicals are unknown due to poor fossil records, details from the posterior aspect are somewhat preserved. The neural spine is low and broad in both anterior and posterior direction. The centra has rounded ends and no ventral keel, possessing a characteristic edaphosaurioid spool shape. Additionally, the dorsal centra is moderately elongate (5 units in length). In contrast, the lumbar centras are much shorter.
The scapula is short and not particularly broad, in contrast to the exceptionally broad procoracoid plate, a feature of edaphosaurids. The glenoid surface is short, and the supraglenoid foramen is absent. The pelvis has extreme elongation at the anterior end of the iliac blade with the anterior expansion being greater than the posterior. The humerus and hind leg bones are slender, with no ectepicondylar foramen.
The astragalus is L-shaped and the centrum is circular when viewed in ventral view. These observations are consistent with most pelycosaurian grade synapsids. The fourth distal tarsal is enlarged, with its proximal articular surface facing the convex. The convex is articulated by the astragalus-calcaneum complex. This morphology indicates a highly mobile mesotarsal joint in both Varanops and Mycterosaurus, contrasting earlier beliefs that little movement was present in early synapsids. These observations serve as evidence to suggest that Varanops and Mycterosaurus used a semidigitigrade stance to ambulate.