Heleosaurus
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Heleosaurus Temporal range: Middle Permian, 270–290 Ma |
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| Fossils | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Family: | †Varanopidae |
| Subfamily: | †Mycterosaurinae |
| Genus: |
†Heleosaurus Broom, 1907 |
| Type species | |
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†Heleosaurus scholtzi Broom, 1907 |
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Heleosarus scholtzi is an extinct basal synapsid, known as pelycosaurs, in the Varanopidae family during the middle Permian. At first H. scholtzi was mistakenly classified as a diapsid. Members of this family were carnivorous and had dermal armor, and somewhat resembled monitor lizards. This family was the most geologically long lived, widespread, and diverse group of early amniotes. To date only two fossils have been found in the rocks of South Africa. One of these fossils is an aggregation of five individuals.
H. scholtzi was first described by Broom in 1907 who originally placed it as an early diapsid. It is named for his student, T.J.R Scholtz, and was originally called Galechirus scholtzi. Later work placed it as a Eosuchian in the family Younginidae and even proposed as an ancestor for Archosauria. More recent work has placed it where it is now as a Mycterosaurinae in the Varanopidae family. The closely related Elliotsmithia longiceps has been placed in a sister taxon to H. scholtzi.
The exact locale of the holotype is uncertain due to Broom’s inexact description, but work by Reisz and Modesto (2007) places it in the Tapinocepholous Assemblage Zone exposures in Victoria West. This makes the horizon the Abrahamskraal formation, Beaufort Group, in the Karoo Basin. The discovery of the second fossil in that locale confirmed this as the horizon.
Basal Varanopids are small, slender animals specialized for a specific feeding niche. H. scholtzi have six main features that are Varanopid autapomorphies, placing them firmly in the family. These are their slender, elongated quadratojugals, anterodorsal sloping of the quadrate, parasphenoid dentition, elongate hyoids, plate-like interclavicle heads, and their recurved and serrated teeth with a labiolingual compression. They also have three main autapomorphies unique to the species, these are the trunk osteoderms, ornamentation on the surangular and angular, and a longitudinal median groove ventrally placed on the dorsal centra surface.
The holotype fossil, SAM-PK-1070, is preserved in negative relief and has a partial skull, mandibles, axial skeleton, pectoral and pelvic girdles, osteoderms, and femur elements. The preserved femurs include a complete left and partial right. Partial skull elements present are the maxilla, quadrate, parabasisphenol, jugal, quadratojugal, mandible, and the palate. Little of the skull roof remains in this specimen. The alveolar region of the mandible has five teeth preserved in it.
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Wikipedia