Dinosauria

DINOSAURIA: Saurischia & Ornithischia

Approximately 315.5 Ma, diapsids (Diapsida) split off from sauropsids, and 307 Ma, Sauria split off from them, which in turn split 265.1 Ma into the ancestors of lizards (Lacertilia) and archosaurs (Archosauria) (2014EzcurraMD_ButlerRJ). The split of turtles (Testudines) from archosaurs occurred at least 255 Ma (2012ChiariY_DelsucF). The oldest archosaur of the avian lineage, Asilisaurus kongwe, which is a sister taxon to Dinosauria, dates back to the interval 247.2-242.0 Ma, designated the Anisian stage of the Middle Triassic (2010NesbittSJ_TsujiLA; 2023CohenKM_CarN). The branch extending to dinosaurs originates from archosaurs. Their oldest remains were found in a rock formed 233.23±0.73 Ma (2018LangerMC_DaRosaÁAS). Among dinosaurs, there are Saurischia and Ornithischia varieties.

Dinosaurs.
Fragment of the exposition of the Darwin Museum (Moscow), photo by the author.

The study of soft tissues of the musculoskeletal system of such early tetrapods is possible only indirectly, focusing on bone markers. In particular, the non-ossified inner wall of the acetabulum is an osteological correlate of the presence of internal ligaments in the hip joint (2015TsaiHP_HollidayCM). A.N. Kuznetsov, A.G. Sennikov (2000) distinguish three types of perforated acetabulums: those with small and large holes, as well as through marginal notches. According to the authors' observations, the non-perforated (closed) acetabulum is the original structure and is found only in primitive forms. Thus, the morphological series of progressive transformation from early thecodonts to birds begins with a non-perforated acetabulum. Subsequently, a small acetabular opening appears (the first type). It gradually increases in size (type II) and reaches its full development (type III), called "open acetabulum". The opening in the acetabulum is found in the following ancient species: Lagosuchus talampayensis (236-234 Ma), Stauricosaurus pricei (233.23 Ma), Herrerasaurus ischigualastensis (237-201 Ma), Terrestrisuchus gracilis (209-201 Ma), Orthosuchus strombergi (209-191 Ma), Tyrannosaurus rex (83.5-66.0 Ma), Ankylosaurus sp. (68-66 Ma) (2000KuznetsovAN_SennikovAG).

Skeleton of a tabrosaurus baby Tabrosaurus bataar (Upper Cretaceous, Mongolia, copy); exhibit of the Darwin Museum (Moscow), photo by the author.

It was established that fossil archosauromorphs had three ligaments in the hip joint: iliofemoral, ischiofemoral, and pubofemoral. The pubofemoral and ischiofemoral ligaments were connected distally, forming the ligamentum capitis femoris (LCF), attached to the fovea capitis. These two ventral ligaments formed an intracapsular double origin of the LCF in the case of a completely perforated acetabulum. In the imperforate acetabulum, the pubofemoral and ischiofemoral ligaments originated at the outer pubic and ischial margins of the acetabulum, respectively. In mature skeletons, the LCF formed a flat or concave fossa on the femoral head. In immature skeletons, the LCF articulated with the cartilage that formed the epiphysis, as in modern juvenile birds and crocodilians. For this reason, the femoral head fossa is not found in fossil bones. Among dinosaurs, distinctly concave or flat fovea capitis have rarely been observed in coelurosaurian theropods. In the saurischian lineage, the femoral head fossa varied from shallow in sauropodomorphs to flat in tyrannosaurids. Basal dinosauromorphs had an indistinct femoral head fossa, suggesting a significant thickness of hyaline cartilage. The evolution of the hip joint in basal dinosaurs is characterized by independent modifications of the two ventral capsular ligaments in the LCF. The pubofemoral and ischiofemoral ligaments in diapsids and sauropodomorphs had a common femoral attachment at the fossa of the femoral head. It was located entirely on the epiphyseal hyaline cartilage, so it did not leave a fossa on the subchondral surface. It is assumed that the LCF was relatively shorter in sauropodomorphs, more basal than mussaurids (2018TsaiHP_HollidayCM). In the illustrations to their work, the cited researchers provided examples of the presence of LCF features: a fossa on the femoral head and a hole in the floor of the acetabulum. Based on the above, we can confidently state that LCF was present in the following extinct species: Allosaurus fragilis (157-145 Ma), Anzu wyliei (67.2-66 Ma), Apatosaurus sp. (161-145 Ma), Asilisaurus kongwe (247-242 Ma), Coelophysis (237-183 Ma), Coelurus fragilis (157-145 Ma), Deinonychus antirrhopus (125-101 Ma), Diplodocus carnegii (157-145 Ma), Falcarius utahensis (139-134.6 Ma), Herrerasaurus ischigualastensis (237-201 Ma), Liliensternus liliensterni (228-201.3 Ma), Mussaurus (228-209 Ma), Piatnitzkysaurus ﬂoresi (180-168 Ma), Plateosaurus engelhardti (228-209 Ma), Tyrannosaurus rex (83.5-66.0 Ma).

View of the hip joint of Diplodocus carnegi Hatcher, Upper Jurassic (161.5-145.0 Ma); exposition of the Orlov Paleontological Museum (Moscow); photo by the author.

Signs of the presence of LCF are noted on the femur and in early dinosauromorphs - contemporaries of dinosaurs and other archosaurs of the late Triassic period (237-201.3±0.2 Ma): Lagerpeton chanarensis, Dromomeron romeri, Dromomeron gregorii. These creatures, unlike dinosaurs, had a groove for attaching the LCF in the form of a barely noticeable gap between the anteromedial and posteromedial tubercles on the head of the femur (2009NesbittSJ_RoweT).

The brief overview of LCF in extinct species indicates that this anatomical element was present in the hip joints of the earliest tetrapods. LCF continued to develop among archosaurs and dinosaurs. While in early tetrapod forms following Tiktaalik roseae, the LCF was located in the upper section of the hip joint, it "migrated" to the lower section after Eryops megacephalus. In dinosaurs, the LCF became significantly more complex, forming a structure of multiple ligaments that functioned together within a perforated acetabulum.

References

Ezcurra MD, Scheyer TM, Butler RJ. The origin and early evolution of Sauria: reassessing the Permian saurian fossil record and the timing of the crocodile-lizard divergence. PLOS ONE. 2014;9(2)e89165. [journals.plos.org]

Chiari Y, Cahais V, Galtier N, Delsuc F. Phylogenomic analyses support the position of turtles as the sister group of birds and crocodiles (Archosauria). Bmc Biology. 2012;10(1)1-15. [link.springer.com]

Nesbitt SJ, Sidor CA, Irmis RB, Angielczyk KD, Smith RM, Tsuji LA. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature. 2010;464(7285)95-8. [nature.com , cienciaescolar.wordpress.com]

Cohen KM, Harper DAT, Gibbard PL, Car N. The International Commission on Stratigraphy (ICS) International Chronostratigraphic Chart. September 2023. [stratigraphy.org]

Langer MC, Ramezani J, Da Rosa ÁAS. U-Pb age constraints on dinosaur rise from south Brazil. Gondwana Research. 2018;57:133-40. [sciencedirect.com]

Tsai HP, Holliday CM. Articular soft tissue anatomy of the archosaur hip joint: structural homology and functional implications. Journal of Morphology. 2015;276(6)601-30. [researchgate.net, onlinelibrary.wiley.com]

Kuznetsov AN, Sennikov AG. On the function of a perforated acetabulum in archosaurs and birds. Paleontological Journal. 2000;34(4)439-48. [researchgate.net]

Tsai HP, Middleton KM, Hutchinson JR, Holliday CM. Hip joint articular soft tissues of non-dinosaurian Dinosauromorpha and early Dinosauria: evolutionary and biomechanical implications for Saurischia. Journal of Vertebrate Paleontology. 2018;38(1)e1427593. [tandfonline.com , researchonline.rvc.ac.uk]

Nesbitt SJ, Irmis RB, Parker WG, Smith ND, Turner AH, Rowe T. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate paleontology. 2009;29(2)498-516. [tandfonline.com]

Keywords

ligamentum capitis femoris, ligamentum teres, ligament of head of femur, doctrine, animals, reptile, dinosauria

The original text in Russian is available at the link: Dinosauria

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BLOG CONTENT

500–1 Mya

Comments

1948EpsteinI

Content [i] Annotation [ii] Original text [iii] Illustration [iv] Source & links [v] Notes [vi] Authors & Affiliations [vii] Keywords [i] Annotation Fragments from the book: Epstein I. Babylonian Talmud. Seder Kodashim. Vol. 2. Hullin (1948). The editor comments on the words of Rabbi Samuel (Shmuel) in the tractate Hullin of the Babylonian Talmud, explaining the location of the ligamentum capitis femoris (LCF) in relation to the joint and its differences from the sciatic nerve. The original in Russian is available at: 1948EpsteinI . [ii] Original text Quote p. 500 Hullin. Chapter 7.89b MISHNAH. [THE PROHIBITION OF] THE SCIATIC NERVE(1) IS IN FORCE BOTH WITHIN THE HOLY LAND AND OUTSIDE IT, BOTH DURING THE EXISTENCE OF THE TEMPLE AND AFTER IT, IN RESPECT OP BOTH UNCONSECRATED AND CONSECRATED [ANIMALS]. IT APPLIES TO CATTLE AND TO WILD ANIMALS, TO THE RIGHT AND LEFT HIP, BUT IT DOES NOT APPLY TO BIRDS BECAUSE THEY HAVE NO SPOON-SHAPED HIP(2). IT ALSO APPLIES TO A F...

1753AstrucJ

Content [i] Annotation [ii] Original text (in French) [iii] English translation [iv] Source & links [v] Notes [vi] Authors & Affiliations [vii] Keywords [i] Annotation Fragments from the book: Astruc J . Conjectures sur les memoires originaux dont il paroit que Moyse s'est servi pour composer le livre de la Genese (Conjectures on the Original Documents Which Moses Apparently Used in Compiling the Book of Genesis, 1753). In analyzing the book of Genesis, the author cites a French text mentioning a hip injury, damage to the ligamentum capitis femoris (LCF), and the consequences of an accident. An Russian translation is available at: 1753AstrucJ . [ii] Original text (in French) Quote p. 176 Genesis. Chap. XXXII A 25. Et quand cest hommeld vid qu’il ne le pouvoit vaincre, il toucha l'enrdroit de l'emboifiement de la hanche d'icelui: ainsi l'emboifiement de l'os de la hanche de Jacob fut entors quand l'homme luictoit avec lui. Quote p. 177...

1845HollsteinL

Fragments from the book Hollstein L. Compendium der Anatomie des Menschen (1865). The author discusses the anatomy of the ligamentum capitis femoris (LCF), and mentions its synonyms. The text is prepared for machine translation using a service built into the blog from Google or your web browser. Quote p. 144 Das Lig am. teres s. rotundum femoris (Fig. 50, 7.) hat eine dreieckige Gestalt, und ist mit seiner Basis in dem Fundus acetabuli, mit seiner rundlichen Spitze in der Fovea capitis ossis femoris befestigt. Es besteht aus einem Bündel Sehnenfasern, und erhält von der Synovialmembran einen scheidenformigen Ueberzug; bisweilen existirt letzterer allein, und manchmal felilt das Band ganz und gar. Fig. 50. Seitliche Ansicht der Bänder des Beckens und Hüftgelenks. Quote p. 145 Die weite Synovialmembran überzieht den Schenkelkopf, geht alsdann als Scheide des Ligam. teres zur Gelenkpfanne über, welche sie ebenfalls auskleidet, und schlägt sich hierauf über die ...

Inferior Portal. Part 1.

Original in Russian is available at the link: Нижний портал. Часть 1. below is a machine translation edited by a non-native speaker ( version dated 03/02/2025 ) . INFERIOR PORTAL FOR HIP ARTHROSCOPY: A PILOT STUDY PART 1. Background and Hypothesis Arkhipov S.V., Independent Researcher, Joensuu, Finland Abstract: The article presents, theoretically and graphically substantiates the technique of a new arthroscopic approach to the central compartment of the hip joint. It is proposed to introduce the optical system of the arthroscope from below through the acetabular notch without traction. Similar approaches were used for puncture, arthroscopy, arthrography, and arthrotomy of the hip joint. Diagnostics using the described lower portal will exclude complications caused by distraction of the leg and compression of the perineal support during surgery. CONTENTS PART 1. Background and Hypothesis [1] . Introduction [2] . Passage through t...

Vertebrates

VERTEBRATES According to the molecular clock, a specific method for dating phylogenetic events, vertebrates (Vertebrata) separated from arthropods (Arthropoda) 976±97 Ma (2004HedgesSB_ShoeJL). The latter began to dominate in species diversity with the Cambrian burst of radiation, which occurred 520 Ma (2010EdgecombeGD). This ratio in the fauna of the Earth is still preserved. Approximately 525 Ma, the phylum Chordates separated from the group of bilaterally symmetrical animals (1995ChenJY_ZhouGQ). In turn, the evolution of chordate organisms led to the formation of the first vertebrates at least 500 Ma, from which the jawed mouths 450-400 Ma descended, becoming the ancestors of the placoderms or "armored" fish (Placodermi) (1979 НаумовНП _ КарташевНН ). Sculptural reconstruction of the placoderm Coccosteus from the order Arthrodires, Middle Devonian, 393.3-382.7 Ma ; exposition of the Orlov Paleontological Museum (Moscow); photo by the author. The first cartilaginou...

LCF in 2026 (May)

LCF in 2026 (May ) (Quotes from articles and books published in May 2026 mentioning the ligamentum capitis femoris) Kim, P. S., Kang, C., Lee, J. K., & Hwang, J. M. (2026). Hip arthroscopy to treat symptomatic paralabral cysts: a retrospective analysis of clinical outcomes. Arthroscopy and Orthopedic Sports Medicine , 13 (1), 27-34. [i] e-aosm.org Ko, H. Y. (2026). Vascular Anatomy of the Extremities and Lungs. In Practical Functional Anatomy for Spinal Cord Injury Rehabilitation: A Guide for Physiatrists and Rehabilitation Specialists (pp. 191-223). Singapore: Springer Nature Singapore. [ii] link.springer.com Aiba, H., Yamaguchi, M., Kimura, H., & Murakami, H. (2026). Advances in limb-salvage surgery and reconstruction for pediatric bone and soft tissue tumors. Frontiers in Pediatrics , 14 , 1817788. [iii] pmc.ncbi.nlm.nih.gov Bajwa, A., Villar, R., ...

Inferior Portal. Part 2.

Original in Russian is available at the link: Нижний портал. Часть 2. below is a machine translation edited by a non-native speaker. INFERIOR PORTAL FOR HIP ARTHROSCOPY: A PILOT STUDY PART 2. Inferior Portal Prototypes Arkhipov S.V., Independent Researcher, Joensuu, Finland CONTENTS PART 1. Background and Hypothesis [1] . Introduction [2] . Passage through the Inferior Portal [3] . Main Advantages of the Proposed Technique [4] . Specific Risks of the Proposed Technique [5] . Main Limitations of the Proposed Technique [6] . References (Part 1) PART 2. Inferior Portal Prototypes [7] . Open Reduction [8] . Puncture and Arthrography [9] . Arthroscopy and Debridement [10] . References (Part 2) [7] . Open R eduction Our idea to reduce the trauma of hip joint surgery through an inferior approach has a rich history. In the spring of 1907, Professor Karl Rudolf Ludloff (1864-1945, photo )...

1943SinzWA

Sinz WA , s culpture Jacob and the Angel (1943). Depicting the circumstances and mechanism of the ligamentum capitis femoris (LCF) injury based on the description in the Book of Genesis: 25 And Ja cob was left alone; and there wrestled a man with him until the breaking of the day. 26 And when he saw that he could not pre vail against him, he struck against the hollow of his thigh ; and the hollow of Jacob's thigh was put out of joint, as he was wrestling with him. … 33 Therefore do the children of Israel not eat the sinew which shrank, which is upon the hollow of the thigh, unto this day; because he struck against the hollow of Jacob's thigh on the sinew that shrank. ( 1922LeeserI , Genesis (Bereshit) 32:25-26,33) More about the plot in our work: Ninth month, eleventh day ( 2024АрхиповСВ. Девятый месяц, одиннадцатый день ). Walter A. Sinz – Jacob and the Angel (1943). Ceramic. Gift of Hilda Kisella (2007.187) ; original in clevelandart.org collect...

Online Journal «ABOUT ROUND LIGAMENT OF FEMUR», May 2026

The journal is dedicated to the ligamentum capitis femoris (LCF) and related topics About the Journal »»» . The online journal « About Round Ligament of Femur » was created based on the scientific blog of the same name. The resource is the English-language part of the project: ONLINE JOURNAL: Ligamentum capitis femoris . Updates: As new materials are prepared. Mission : Popularization and preservation of knowledge about LCF, as well as promoting its practical application. Main goal: Improvement of diagnosis, treatment, and prevention of injuries and diseases of the hip joint. Publisher: Arkhipov S.V., independent researcher, PhD, orthopedic surgeon. Reviewers: G...

1914RickettsCS

Ricketts C.S. , Jacob Wrestling with the Angel (before 1914). Depicting the circumstances and mechanism of the ligamentum capitis femoris (LCF) injury based on the description in the Book of Genesis: 25 And Ja cob was left alone; and there wrestled a man with him until the breaking of the day. 26 And when he saw that he could not pre vail against him, he struck against the hollow of his thigh ; and the hollow of Jacob's thigh was put out of joint, as he was wrestling with him. … 33 Therefore do the children of Israel not eat the sinew which shrank, which is upon the hollow of the thigh, unto this day; because he struck against the hollow of Jacob's thigh on the sinew that shrank. ( 1922LeeserI , Genesis (Bereshit) 32:25-26,33) More about the plot in our work: Ninth month, eleventh day ( 2024АрхиповСВ. Девятый месяц, одиннадцатый день ). Charles S. Ricketts – Jacob Wrestling with the Angel (before 1914). Presented by Miss Katherine Harris Bradley, origina...

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