The fourth trochanter is a shared characteristic common to archosaurs. It is a knob-like feature on the posterior-medial side of the middle of the femur shaft that serves as a muscle attachment, mainly for the musculus caudofemoralis longus, the main retractor tail muscle that pulls the thighbone to the rear.
The fourth trochanter is considered homologous with the internal trochanter, an asymmetrical ridge-like structure that extends down from the femoral head and is edged by an intertrochanteric fossa in other reptiles such as lizards. The fourth trochanter can be characterized by its position further down the shaft, symmetrical nature, and lack of an intertrochanteric fossa. The caudofemoralis attachment crest first separated from the femoral head in the Erythrosuchidae, large basal archosauriform predators of the early Triassic period. Shortly afterwards, eucrocopodan archosauriforms (such as Euparkeria) evolved, losing the intertrochanteric fossa and acquiring a symmetrical fourth trochanter.[1][2][3]
This seemingly insignificant detail may have made the evolution of dinosaurs possible as it facilitates a bipedal gait. All early dinosaurs and many later ones were bipeds. It may also have been a factor in the archosaurs or their immediate ancestors surviving the catastrophic Permian-Triassic extinction event [citation needed].
References
[edit]- ^ Nesbitt, S. J.; Stocker, M. R.; Small, B. J. & A. Downs (November 26, 2009). "The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes)". Zoological Journal of the Linnean Society. 157 (4): 814–864. doi:10.1111/j.1096-3642.2009.00530.x.
- ^ Nesbitt, S.J. (2011). "The early evolution of archosaurs: relationships and the origin of major clades". Bulletin of the American Museum of Natural History. 352: 1–292. doi:10.1206/352.1. hdl:2246/6112. S2CID 83493714.
- ^ Ezcurra, Martín D. (2016-04-28). "The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms". PeerJ. 4: e1778. doi:10.7717/peerj.1778. ISSN 2167-8359. PMC 4860341. PMID 27162705.
- Benton, M. J. (2000), Vertebrate Paleontology, 2nd Ed. p.136; (2004) 3rd edition, Blackwell Science Ltd
Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction