Progalesaurus
| Progalesaurus Temporal range:Induan
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|---|---|
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| Progalesaurusdentary in right lateral view | |
Scientific classification
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Clade: | Cynodontia |
| Family: | †Galesauridae |
| Genus: | †Progalesaurus Sidor & Smith, 2004 |
| Type species | |
| Progalesaurus lootbergensis Sidor & Smith, 2004
| |
Progalesaurusis an extinct genus ofgalesauridcynodontfrom the earlyTriassic.Progalesaurusis known from a single fossil of the speciesProgalesaurus lootsbergensis,found in theLystrosaurusAssemblage Zoneof theBalfour Formation.Close relatives ofProgalesaurus,other galesaurids, includeGalesaurusandCynosaurus.Galesaurids appeared just before thePermian-Triassic extinction event,and disappeared from the fossil record in the Middle-Triassic.
The name “Progalesaurus” is derived from Greek, “pro” meaning before, “gale” meaning weasel or cat, and “saurus” meaning lizard or reptile (Sidor and Smith). The name refers to the relationshipProgalesaurushas to the more derivedGalesaurus.[1]
Discovery and history
[edit]Progalesauruswas originally discovered by Roger M. H. Smith in 1998. The specimen was found in the Sneeuberg mountains near New Lootsberg Pass in the Karoo Basin of South Africa.Progalesauruswas first described in 2004 byChristian A. Sidorand Roger M. H. Smith in their paper titled, “A New Galesaurid (Therapsida: Cynodontia) From the Lower Triassic of South Africa.”
Although no other specimen ofProgalesaurushas been found as of yet, Sidor and Smith's findings have been included in many papers on the Permian-Triassic extinction event, cynodont diversity, and the paleoenvironment of South Africa.[2][3]
Description
[edit]Progalesauruswas a relatively small mammal-like creature, with the skull of itsholotypemeasuring 9.35 cm in length.[1]It likely closely resembled its early cynodont relatives, walking on four legs and covered in fur.[4]
Skull
[edit]Progalesaurus,likeGalesaurus,has remarkably large nares compared to other early cynodonts. The nares are formed externally by the premaxilla, the maxilla, and the nasal. The septomaxilla resides inside the nares, on top of the junction between maxilla and premaxilla.
The orbit faces anteriorly and is formed by the lacrimal, prefrontal, jugal, and post orbital. The post orbital notably has a deeply forked posterior margin. This characteristic is seen in some other basal cynodonts, but is widely variable.[1]
The maxilla forms a good portion of the side of the face and is dotted with small foramina, mostly above the canines. These foramina likely housed nerves, and were perhaps associated with whiskers.[4]The nasal is also dotted with tiny foramina.[1]
Progalesaurushas a parietal foramen, which is used for light sensing in extant taxa.[5]Posterior to the parietal foramen the parietals are fused, forming asagittal crest.The crest narrows posterior to the foramen likeGalesaurus and Cynosaurus,and unlike more derived cynodonts.
Progalesaurus,likeGalesaurus, Cynosaurus,andThrinaxodon,possesses a largezygomatic arch.Under this arch, in posterior view, lies a foramen associated with the outer ear tube. Compared to cynognathians such asCynognathusorDiademodon,the foramen is relatively shallow.
Progalesaurusdoes not have a fully-formedsecondary palate,[1]which serves to separate the airway from food-processing.[6]
Dentition
[edit]The mandible ofProgalesaurusis very similar to that ofGalesaurus,with its teeth setting it apart from other cynodonts.Progalesaurushas a dental formula of I4/3, C1/1, PC7?/9. The upperincisorsare long and thin, with a circular cross-section. The lower incisors are shorter than their upper counterparts. The incisors have an oval cross-section and longitudinal striations. Their upper canine’s edges are preserved well enough to conclude they lack serration, but the lower canines are not still sharp enough to make any conclusions about their serration. The lower canines are slightly longer than the upper canines.
The post-canine teeth are, as of now, the most distinct feature ofProgalesaurus.The recurved main cusp resemblesGalesaurus, Cynosaurus,andProbelesodon,however the number and placement of the accessory cusps are unique. The upper post-canines are poorly preserved, but the teeth that are well-enough preserved to see accessory cusps have at least one posterior to the main recurved cusp each. The bottom post-canines are extremely well preserved. The teeth get progressively lower and anteroposteriorly longer from front to back. The buccal surface of each post-canine is smooth. The teeth are also slightly angled so that the posterior of one tooth contacts the anterior of the next. The posterior accessory cusps of teeth 2 and 3 curve upwards towards the top of the tooth. The 4th tooth shows posterior accessory cusps as well as at least one cusp mesial to the main cusp. The 5th tooth only shows one posterior accessory cusp, but the lack of other accessory cusps is “probably due to wear.” The 6th tooth on to the 9th tooth have multiple posterior accessory cusps as well as at least one mesial cusp.[1]
Post-cranial skeleton
[edit]Very little post-cranial skeleton is preserved in the holotype forProgalesaurus.Only the rightscapulaand the left atlantal neural spine were recovered. Each of these elements closely resemble those ofThrinaxodon.[1]
Classification
[edit]Progalesaurusis a galesaurid, belonging to the cladeEpicynodontia.As an epicynodont,Progalesaurusbelongs to the greater cladeCynodontia.Cynodonts are therapsids, which in turn belong to the greater groupSynapsida,and the even broaderAmniota.[1]
Paleobiology
[edit]Early cynodonts likeProgalesauruslikely had large litters, as more derived cynodonts likeTritylodontidhave been found with litters far larger than modern mammals. Early cynodonts have also been preserved with juveniles, suggesting they provided parental care to their young after birth or hatching.[7]
Progalesauruslikely burrowed, as closely related taxa likeThrinaxodonandGalesaurushave been found in burrows of their own making. Burrowing probably helped Triassic cynodonts to avoid harsh above-ground conditions shortly after the Permian-Triassic extinction event.[8]Early cynodonts have even been found in burrows with other taxa, indicating they may have cohabitated interspecifically.[9]
Based on tooth shape, paleontologists believe that early cynodonts likeProgalesauruswere insectivores and carnivores.[10]Coprolites,or fossilized feces, of cynodonts have also been found and can be used to investigate their diet. One coprolite of a 240 million year old cynodont even preserved parasitic nematode eggs, the earliest evidence of pinworms ever found.[11]
Paleoenvironment
[edit]Progalesauruslived very soon after the devastatingPermian-Triassic extinction eventin what is modern South Africa. Other cynodonts and potentially even other galesaurids, likeCynosaurus,crossed the extinction boundary.[1]Cynodonts may have been able to survive the mass extinction due to their burrowing behavior,[3]as perhaps living mostly underground would have pre-conditioned these burrowers to the high levels of carbon dioxide and low levels of oxygen present during the extinction event.[8]Cynodont diversity increased relatively rapidly after the extinction event.[2]
The earlyTriassicperiod was one of the hottest in the history of the Earth, however the climate in the areas cynodonts have been discovered was more temperate. There were high levels of carbon dioxide in the atmosphere.[3]In the Karoo Basin, whereProgalesauruswas discovered, there is evidence to suggest the area was a moderately damp open woodland.[12]
In the early Triassic of South Africa,Progalesauruswas accompanied by "survivor fauna," and "recovery fauna." A few examples of (vertebrate) survivor fauna, creatures that crossed the extinction boundary, includeLystrosaurus,Tetracynodon,Moschorhinus,andIctidosuchoides.Recovery fauna include small amphibians such asMicropholis,Galesaurids, someprocolophonoids,and some archosauromorphs such asProterosuchus.[8]
See also
[edit]References
[edit]- ^abcdefghiSidor, Christian A.; Smith, Roger M. H. (May 2004)."A new galesaurid (Therapsida: Cynodontia) from the Lower Triassic of South Africa".Palaeontology.47(3): 535–556.doi:10.1111/j.0031-0239.2004.00378.x.ISSN0031-0239.
- ^abSmith, Roger; Botha, Jennifer (September 2005). "The recovery of terrestrial vertebrate diversity in the South African Karoo Basin after the end-Permian extinction".Comptes Rendus Palevol.4(6–7): 623–636.doi:10.1016/j.crpv.2005.07.005.ISSN1631-0683.
- ^abcAbdala, Fernando; Ribeiro, Ana Maria (February 2010). "Distribution and diversity patterns of Triassic cynodonts (Therapsida, Cynodontia) in Gondwana".Palaeogeography, Palaeoclimatology, Palaeoecology.286(3–4): 202–217.doi:10.1016/j.palaeo.2010.01.011.ISSN0031-0182.
- ^abBenoit, J.; Manger, P. R.; Rubidge, B. S. (2016-05-09)."Palaeoneurological clues to the evolution of defining mammalian soft tissue traits".Scientific Reports.6(1): 25604.doi:10.1038/srep25604.ISSN2045-2322.PMC4860582.PMID27157809.
- ^Benoit, Julien; Abdala, Fernando; Van den Brandt, Marc J.; Manger, Paul R.; Rubidge, Bruce S. (2015-11-04). "Physiological implications of the abnormal absence of the parietal foramen in a late Permian cynodont (Therapsida)".The Science of Nature.102(11–12): 69.doi:10.1007/s00114-015-1321-4.ISSN0028-1042.PMID26538062.
- ^Rubidge, Bruce S.; Sidor, Christian A. (November 2001). "Evolutionary Patterns Among Permo-Triassic Therapsids".Annual Review of Ecology and Systematics.32(1): 449–480.doi:10.1146/annurev.ecolsys.32.081501.114113.ISSN0066-4162.
- ^Hoffman, Eva A.; Rowe, Timothy B. (2018-08-29). "Jurassic stem-mammal perinates and the origin of mammalian reproduction and growth".Nature.561(7721): 104–108.doi:10.1038/s41586-018-0441-3.ISSN0028-0836.PMID30158701.
- ^abcSmith, Roger; Botha, Jennifer (2005-09-01). "The recovery of terrestrial vertebrate diversity in the South African Karoo Basin after the end-Permian extinction".Comptes Rendus Palevol.4(6): 623–636.doi:10.1016/j.crpv.2005.07.005.ISSN1631-0683.
- ^Jasinoski, Sandra C.; Abdala, Fernando (2017)."Aggregations and parental care in the Early Triassic basal cynodonts Galesaurus planiceps and Thrinaxodon liorhinus".PeerJ.5:e2875.doi:10.7717/peerj.2875.ISSN2167-8359.PMC5228509.PMID28097072.
- ^ABDALA, F.; CISNEROS, J. C.; SMITH, R. M.H. (2006-10-01). "Faunal Aggregation in the Early Triassic Karoo Basin: Earliest Evidence of Shelter-Sharing Behavior Among Tetrapods?".PALAIOS.21(5): 507–512.doi:10.2110/palo.2005.p06-001r.ISSN0883-1351.
- ^Hugot, Jean-Pierre; Gardner, Scott L; Borba, Victor; Araujo, Priscilla; Leles, Daniela; Stock Da-Rosa, Átila Augusto; Dutra, Juliana; Ferreira, Luiz Fernando; Araújo, Adauto (2014-11-13)."Discovery of a 240 million year old nematode parasite egg in a cynodont coprolite sheds light on the early origin of pinworms in vertebrates".Parasites & Vectors.7(1): 486.doi:10.1186/s13071-014-0486-6.ISSN1756-3305.PMC4236488.PMID25495824.
- ^Retallack, G.J. (2004). "Vertebrate extinction across Permian-Triassic boundary in Karoo Basin, South Africa: Reply".Geological Society of America Bulletin.116(9): 1295.doi:10.1130/b25614.1.ISSN0016-7606.
