Brasilodon and Riograndia (Triassic cynodonts) jaw and middle ear evolution (free pdf)
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Ben Creisler
Sep 25, 2024, 12:49:03 PMSep 25
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Ben Creisler
A new paper:
Free pdf:
James R. G. Rawson, Agustín G. Martinelli, Pamela G. Gill, Marina B. Soares, Cesar L. Schultz & Emily J. Rayfield (2024)
Brazilian fossils reveal homoplasy in the oldest mammalian jaw joint
Nature (advance online publication)
doi: https://doi.org/10.1038/s41586-024-07971-3
https://www.nature.com/articles/s41586-024-07971-3
The acquisition of the load-bearing dentary–squamosal jaw joint was a key step in mammalian evolution. Although this innovation has received decades of study, questions remain over when and how frequently a mammalian-like skull–jaw contact evolved, hindered by a paucity of three-dimensional data spanning the non-mammaliaform cynodont–mammaliaform transition. New discoveries of derived non-mammaliaform probainognathian cynodonts from South America have much to offer to this discussion. Here, to address this issue, we used micro-computed-tomography scanning to reconstruct the jaw joint anatomy of three key probainognathian cynodonts: Brasilodon quadrangularis, the sister taxon to Mammaliaformes, the tritheledontid-related Riograndia guaibensis and the tritylodontid Oligokyphus major. We find homoplastic evolution in the jaw joint in the approach to mammaliaforms, with ictidosaurs (Riograndia plus tritheledontids) independently evolving a dentary–squamosal contact approximately 17 million years before this character first appears in mammaliaforms of the Late Triassic period. Brasilodon, contrary to previous descriptions, lacks an incipient dentary condyle and squamosal glenoid and the jaws articulate solely using a plesiomorphic quadrate–articular joint. We postulate that the jaw joint underwent marked evolutionary changes in probainognathian cynodonts. Some probainognathian clades independently acquired ‘double’ craniomandibular contacts, with mammaliaforms attaining a fully independent dentary–squamosal articulation with a conspicuous dentary condyle and squamosal glenoid in the Late Triassic. The dentary–squamosal contact, which is traditionally considered to be a typical mammalian feature, therefore evolved more than once and is more evolutionary labile than previously considered.
****
News:
Brazilian fossils reveal early evolution of mammalian jaw and middle ear
===
Free pdf:
James R. G. Rawson, Agustín G. Martinelli, Pamela G. Gill, Marina B. Soares, Cesar L. Schultz & Emily J. Rayfield (2024)
Brazilian fossils reveal homoplasy in the oldest mammalian jaw joint
Nature (advance online publication)
doi: https://doi.org/10.1038/s41586-024-07971-3
https://www.nature.com/articles/s41586-024-07971-3
The acquisition of the load-bearing dentary–squamosal jaw joint was a key step in mammalian evolution. Although this innovation has received decades of study, questions remain over when and how frequently a mammalian-like skull–jaw contact evolved, hindered by a paucity of three-dimensional data spanning the non-mammaliaform cynodont–mammaliaform transition. New discoveries of derived non-mammaliaform probainognathian cynodonts from South America have much to offer to this discussion. Here, to address this issue, we used micro-computed-tomography scanning to reconstruct the jaw joint anatomy of three key probainognathian cynodonts: Brasilodon quadrangularis, the sister taxon to Mammaliaformes, the tritheledontid-related Riograndia guaibensis and the tritylodontid Oligokyphus major. We find homoplastic evolution in the jaw joint in the approach to mammaliaforms, with ictidosaurs (Riograndia plus tritheledontids) independently evolving a dentary–squamosal contact approximately 17 million years before this character first appears in mammaliaforms of the Late Triassic period. Brasilodon, contrary to previous descriptions, lacks an incipient dentary condyle and squamosal glenoid and the jaws articulate solely using a plesiomorphic quadrate–articular joint. We postulate that the jaw joint underwent marked evolutionary changes in probainognathian cynodonts. Some probainognathian clades independently acquired ‘double’ craniomandibular contacts, with mammaliaforms attaining a fully independent dentary–squamosal articulation with a conspicuous dentary condyle and squamosal glenoid in the Late Triassic. The dentary–squamosal contact, which is traditionally considered to be a typical mammalian feature, therefore evolved more than once and is more evolutionary labile than previously considered.
****
News:
Brazilian fossils reveal early evolution of mammalian jaw and middle ear
https://www.bristol.ac.uk/news/2024/september/brazilian-fossils.html
https://phys.org/news/2024-09-brazilian-fossils-reveal-early-evolution.html
https://www.sci.news/paleontology/brazil-cynodonts-13286.html
https://phys.org/news/2024-09-brazilian-fossils-reveal-early-evolution.html
https://www.sci.news/paleontology/brazil-cynodonts-13286.html
Gregory Paul
Sep 27, 2024, 4:41:07 AMSep 27
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Might anyone know the specimen number for the titanosaur from the Aguja Formation described by Rivera-Sylva, H.E., Guzman-Gutierrez, J.R., and Palomino-Sanchez, F.P., 2006,
Preliminary report on a vertebrate fossil assemblage form the Late Cretaceous of Chihuahua, Mexico: Hantkeniana, v. 5, p. 66-68.
GSPaul
Gregory Paul
Sep 27, 2024, 4:45:37 AMSep 27
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And what level of the Aguja the tibia is from. Are there any other titanosaur fossils from the formation?
Stephen Poropat
Sep 27, 2024, 5:01:41 AMSep 27
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Hi Greg,
This paper will help re Aguja Formation sauropod records, but not (as far as a very brief skim is concerned) specimen number or level within the unit:
Ramírez-Velasco, A.A., Hernández-Rivera, R., 2015. Diversity of Late Cretaceous dinosaurs from Mexico. Boletín Geológico y Minero 126, 63–108. (https://www.researchgate.net/publication/278018238_Diversity_of_late_cretaceous_dinosaurs_from_Mexico)
PBDB lists only three occurrences for sauropods in the Aguja Formation, all listed in the relevant table in this paper, with references.
Cheers,
Steve
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Dr Stephen F. Poropat
Research Fellow
Western Australian Organic and Isotope Geochemistry Centre
School of Earth and Planetary Sciences
Curtin University
Bentley, Western Australia
Australia 6102
Ben Creisler
Sep 28, 2024, 4:49:30 PM (13 days ago) Sep 28
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Ben Creisler
"At another Javelina Formation outcrop in northeast Chihuahua, the most complete sauropod reported for Mexico was collected. Although it belongs to a private collection, it is on display in the Museo de Paleontología de Delicias, in Delicias, Chihuahua (Fig. 9.7). The specimen has not been formally described. It consists mainly of postcranial material, including vertebrae, a femur, a proximal fragment of a tibia, and one ulna. This material shows the size of the animal of about 22 m in length.The greater trochanter on the lateral margin of the right femur is below the proximal level of the femoral head, and the procoelic vertebrae are autapomorphic characteristic for the titanosauridae. One of the large dorsal vertebrae is similar to Alamosaurus sanjuanensis. This specimen could be the first record of this species in Mexico."
Note that Rivera-Silva and Carpenter (2014) say the specimen is from a private collection, so it may not have a formal specimen number.
"At another Javelina Formation outcrop in northeast Chihuahua, the most complete sauropod reported for Mexico was collected. Although it belongs to a private collection, it is on display in the Museo de Paleontología de Delicias, in Delicias, Chihuahua (Fig. 9.7). The specimen has not been formally described. It consists mainly of postcranial material, including vertebrae, a femur, a proximal fragment of a tibia, and one ulna. This material shows the size of the animal of about 22 m in length.The greater trochanter on the lateral margin of the right femur is below the proximal level of the femoral head, and the procoelic vertebrae are autapomorphic characteristic for the titanosauridae. One of the large dorsal vertebrae is similar to Alamosaurus sanjuanensis. This specimen could be the first record of this species in Mexico."
H.E. Rivera-Silva & Kenneth Carpenter (2014)
Mexican saurischian dinosaurs.
In: Dinosaurs and Other Reptiles from the Mesozoic of Mexico, edited by Héctor E. Rivera-Sylva, Kenneth
Mexican saurischian dinosaurs.
In: Dinosaurs and Other Reptiles from the Mesozoic of Mexico, edited by Héctor E. Rivera-Sylva, Kenneth
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