Eryops megacephalus

ERYOPS MEGACEPHALUS

Eryops megacephalus Cope 1877 is an early tetrapod from the Permian (298.9-251.9 Ma), apparently showing strong similarities to salamanders (2022HerbstEC_HutchinsonJR; 2023CohenKM_CarN). Adults reached an advanced degree of terrestrial habitation and a size of about three meters from head to tail (2002SchochRR).

Eryops megacephalus (Lower Permian); top – reconstruction of the skeleton; bottom – appearance of the animal, sculptor Ya.M. Eglon; exposition of the Orlov Paleontological Museum (Moscow); photo by the author.

Anatomical evidences of the ligamentum capitis femoris (LCF) in Eryops megacephalus is suggested by certain features in fossilized pelvic and femoral bones. Notable LCF indicators on the femur include the fovea capitis, the groove on the femoral head, and the femoral head’s tuberosity. In the pelvic bone, signs of LCF presence include acetabular notches, an acetabular fossa, perforations, and irregularities on the acetabular surface. We used these features to identify LCF in the first amphibians and land species.

According to E.D. Cope (1880) the pelvic bones of Eryops megacephalus resemble «… in their compression below, the corresponding parts in the Anura. The ilia are, however, shorter and worn as in the Urodela. They are flat, and stand at right angles to the line of the ischiopubic symphysis. There is an open concavity of their inferior posterior free border, and a facet-bearing elevation on the inferior border, or that entering into the formation of the acetabulum. The latter is large and half as long again as deep. The anterior and posterior borders of the pelvis descend regularly to the inferior edge, forming with it a triangle. The ischiadic or posterior border is but little thickened; the anterior, or pubic is flat in front and presents a reverted edge outwards. This expands prominently where it is joined by a ridge which bounds the acetabulum below; it there contracts to an inferior apex. Beneath the anterior point of the acetabulum it is pierced by the usual foramen, which issues on the inner edge of the anterior face, just above the symphysis.» (1880CopeED).

Pelvis of Eryops megacephalus; lower center – lateral view, cranial end on the left (1880CopeED, no changed).

A.S. Romer (1922) described the pelvis of early tetrapods as follows: «A constant feature is the presence of a prominent wedge above the acetabulum, merging gradually into the general surface of the bone anteriorly, but posteriorly dropping back sharply as a distinct supra-acetabular notch. This is found practically the same in almost every form examined, from Eryops to the highest therapsids. As suggested by Broili, who first noticed it in dicynodonts (1908, p. 3), it indicates the position of a ligament similar to that found in the cotyloid notch of the ischium of mammals; the changed position of the mammalian femur would account for a shifting ventrally of the notch.»

Right pelvic bone of Eryops megacephalus, lateral view, cranial end on the right; legend: SAN – supra-acetabular notch, TRL – transverse line, F. OBT – obturator foramen, attachment zones of the ilio-ischiadic ligament – lig. il-isch, ilio-puboiliac ligament – lig. il-pub (1922RomerAS, no changed).

Common morphological features between Eryops megacephalus and modern salamanders include a shallow acetabulum (2022HerbstEC_HutchinsonJR). A large notch is clearly visible in the posterosuperior region of the acetabulum.

Pelvis of Eryops megacephalus, modified from Pawley & Warren (Pawley and Warren 2006); illustration from 2018AhlbergPE, no changed).

The acetabular notch is designed to accommodate and attach the LCF. Although the precise positioning of the LCF remains unknown, it is hypothesized to have functioned as a flexible support element activated during terrestrial movement. It is most plausible that the proximal end of the LCF was attached within the supra-acetabular notch, resembling the attachment observed in one of the paired femoral head ligaments in salamanders (1934FrancisETB). The distal end of the LCF in Eryops megacephalus might have attached to the upper edge of the femoral head. In this configuration, LCF tension would restrict medial pelvic tilt during walking, reducing the load on abductor muscles. From our perspective, the LCF in Eryops megacephalus likely did not facilitate pelvic rotation within the horizontal plane.

View of the bones forming the hip joint of Eryops megacephalus, we have marked the supposed localization of LCF; exposition of the Orlov Paleontological Museum (Moscow); photo by the author.

References

Herbst EC, Manafzadeh AR, Hutchinson JR. Multi-joint analysis of pose viability supports the possibility of salamander-like hindlimb configurations in the Permian tetrapod Eryops megacephalus. Integrative and Comparative Biology. 2022;62(2)139-151. [academic.oup.com]

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

Schoch RR. The evolution of metamorphosis in temnospondyls. Lethaia. 2002;35(4)309-27. [idunn.no]

Cope ED. Second Contribution to the History of the Vertebrata of the Permian Formation of Texas. Proceedings of the American Philosophical Society. 1880;19(107)38-58. [jstor.org]

Romer AS. The locomotor apparatus of certain primitive and mammal-like reptiles. Bulletin of the AMNH. 1922;46, art.10:517-647. [digitallibrary.amnh.org]

Broili F. Ein Dicynodonttierreste ausderKarooformation. Neuen Jahrb. Fur Min., Geol., und Paliiont. 1908, I:1-15, P1. I.

Ahlberg PE. Follow the footprints and mind the gaps: a new look at the origin of tetrapods. Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 2018;109(1-2)115-37. [cambridge.org]

Francis ETB. The anatomy of the salamander. Oxford: The Clarendon Press, 1934. [archive.org]

Keywords

ligamentum capitis femoris, ligamentum teres, ligament of head of femur, doctrine, animals, amphibian

The original text in Russian is available at the link: Eryops megacephalus

NB! Fair practice / use: copied for the purposes of criticism, review, comment, research and private study in accordance with Copyright Laws of the US: 17 U.S.C. §107; Copyright Law of the EU: Dir. 2001/29/EC, art.5/3a,d; Copyright Law of the RU: ГК РФ ст.1274/1.1-2,7

BLOG CONTENT

500–1 Mya

Comments

1851HyrtlJ

The author expresses a classic view on the functions of the ligamentum capitis femoris (LCF): a conductor of blood vessels and a limiter of adduction of the femur. J. Hyrtl believed that it was impossible to completely dislocate the hip without tearing the LCF. Hyrtl J. Lehrbuch der Anatomie des Menschen, mit Rücksicht auf physiologische Begründung und praktische Anwendung. Wien: W. Braumüller, 1851. [fragment] Quote p. 265 In der Höhle des Gelenks liegt das runde Band des Schenkelkopfes (Lig. teres), welches an der Incisura acetabuli entspringt, und bei richtiger Neigung des Beckens, senkrecht zur Grube des Schenkelkopfes aufsteigt. Es beschränkt dieses Band die Zuziehung des Schenkels, und schreibt zugleich den durch die Incisura acetabuli eindringenden Blutgefässen den Weg vor, den sie zum Oberschenkelkopfe zu nehmen haben. Da das Band, wenn es in die Höhle des Gelenkes vorragen würde, durch Reibung viel zu leiden hätte, so...

1902RilkeRM

Works of art that mention ligamentum capitis femoris (LCF) are extremely rare. One such work is the poem «Der Schauende» ( He Who Visions, The Seer, The Man Watching, The Beholder) b y Rainer Rilke. Below is the original text in German. Der Schauende 1. Ich sehe den Bäumen die Stürme an, die aus laugewordenen Tagen an meine ängstlichen Fenster schlagen, und höre die Fernen Dinge sagen, die ich nicht ohne Freund ertragen, nicht ohne Schwester lieben kann. 2. Da geht der Sturm, ein Umgestalter, geht durch den Wald und durch die Zeit, und alles ist wie ohne Alter: die Landschaft, wie ein Vers im Psalter, ist Ernst und Wucht und Ewigkeit. 3. Wie ist das klein, womit wir ringen, was mit uns ringt, wie ist das groß; ließen wir, ähnlicher den Dingen, uns so vom großen Sturm bezwingen, - wir würden weit und namenlos. 4. Was wir besiegen, ist das Kleine, und der Erfolg selbst macht uns klein. Das Ewige und Ungemeine will nicht von uns gebogen sein. Das ist der Enge...

1823CooperA

According to the author, the ligamentum capitis femoris (LCF) is intended to prevent dislocations in all directions. A. Cooper discusses traumatic obturator dislocation of the hip joint and LCF injury in more detail. Cooper A. Abhandlung über Luxationen und Fracturen der Gelenke des Unterkiefers, der obern Extremitäten und der Knochen des Rumpfes. Aus dem Englischen. Weimar : Landes-Industrie-Comptoir, 1823. [fragments] Quote p. 1 4 8 Das ligamentum teres hat die Bestimmung, Luras tionen nach allen Richtungen hin zu verhindern, besonders aber nach abwärts, denn wenn die Schenkel weit ausein andergespreizt werden, wie z. B. bei'm Fechten, so würde der Kopf des linken Oberschenkelknochens in Gefahr feyn, aus seiner Gelenkhöhle zu schlüpfen, was aber durch dieses Ligament verhindert wird. The ligamentum teres is designed to prevent dislocations in all directions, especially downwards, because when the thighs are widely ab...

A Novel Technique for Proximal Fixation

Arkhipov SV. A Novel Technique for Proximal Fixation of Ligamentum Capitis Femoris Reconstruction: The Gifts of the Magi for Orthopedic Surgeons. About Round Ligament of Femur. January 14, 2026. DOI: 10.13140/RG.2.2.25269.33763 https://roundligament.blogspot.com/2026/01/the-gifts-of-magi-for-orthopedic.html Abstract Purpose: To describe an experimental technique for proximal fixation in ligamentum capitis femoris (ligamentum teres femoris; LCF) reconstruction using pubic and ischial portions anchored in corresponding pelvic bone tunnels, tested on synthetic hip joint models, and to propose it’s for arthroscopic application with visualization via an inferior portal and femoral tunnel. Methods: Synthetic polyurethane bone analogs (Synbone) of the pelvis and proximal femur were used to fabricate hip joint models. Acetabular cartilage analogs were created from self-curing plastic compound. Femoral tunnels were drilled along the neck axis from the subtrochanteric region below the tub...

Human Children. Retelling of Chapter 13

Short retelling of chapter 13 of the essay: Arkhipov S.V. Human Children: The Origins of Biblical Legends from a Physician's Perspective. Joensuu: Author's Edition, 2025. [In Russian] Chapter 13. PROPHETIC DREAMS After his wanderings and battles, Abraham settles in “Mamre’s oaks in Hebron.” Following these events, he experiences a divine “word in a vision” and a dream promising him lands “from Egypt’s river to the great river, Euphrates.” His family relocates to a desert along the Shur road, near the well “Beer-Lahai-Roi,” between Kadesh and Bered. In another divine appearance, Abraham is commanded to circumcise all males’ foreskins, rename Sarai as Sarah, and is told he’ll father a child at 100, despite Sarah’s barrenness at 89. That day, Abraham circumcises his son Ishmael, household males, and, at 99, himself. In Mamre’s oaks, during “daytime heat,” a mirage foretells fatherhood. The dream shifts, showing Sodom and Gomorrah’s destruction and Lot’s miraculous rescue. ...

LCF in 2025 (July)

LCF in 2025 ( July ) (Quotes from articles and books published in July 2025 mentioning the ligamentum capitis femoris.) Tekcan, D., Bilgin, G., & Güven, Ş. Evaluation of Risk Factors for Developmental Dysplasia of the Hip. HAYDARPAŞA NUMUNE MEDICAL JOURNAL , 65 (2), 99-103. [i] jag.journalagent.com Domb, B. G., & Sabetian, P. W. (2025). Greater Trochanteric Pain Syndrome: Gluteal Tendinopathy, Partial Tear, Complete Tear, Iliotibial Band Syndrome, and Bursitis. In Orthopaedic Sports Medicine (pp. 1-17). Springer, Cham. [ii] link.springer.com Kuhns, B. D., Becker, N., Patel, D., Shah, P. P., & Domb, B. G. (2025). Significant Heterogeneity in Existing Literature Limits Both Indication and Outcome Comparability Between Studies Involving Periacetabular Osteotomy For Acetabular Dysplasia With or Without Arthroscopy Despite Improvement for Both: A Systematic Review. Arthroscopy . [iii] ...

1730CheseldenW

Fragments from the book Cheselden W. The Anatomy of the Human Body (1730). The author draws attention to the role of ligamentum capitis femoris (LCF) in counteracting hip dislocation and maintaining the femoral head in the joint. The work notes that the LCF is “powerful” and “short” - “about two inches” i.e. approximately 5 cm! This error will be corrected in a subsequent treatise ( 1733CheseldenW ) . Quote pp. 43 - 44 Chap. VII. Of the Ligaments At the upper part of the articulation of the Os Femoris and Os Innominatum, is a strong ligament of great consequence; it contributing very much to preserve that joint from being luxated by the weight of the body. And from the lower edge of the Acetabulum of the Os Innominatum, runs a ligament to the middle of the head of the Os Femoris, about two inches long (which the Motion in this joint requires) called Teres, or Rotundum, whose use is to prevent the Os Femoris from being luxated upwards, but down wards it will le...

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., ...

Human Children. Retelling of Chapter 14

Short retelling of chapter 14 of the essay: Arkhipov S.V. Human Children: The Origins of Biblical Legends from a Physician's Perspective. Joensuu: Author's Edition, 2025. [In Russian] Chapter 14. ESAU AND JACOB At 40, Isaac marries Rebekah, his cousin’s daughter. Their marriage is long childless until Rebekah conceives twins, detected prenatally, possibly by her large belly or palpation. Genesis states that at 60, Isaac fathers the twins, born naturally after 20 years of marriage. The first, Esau, emerges “red, all hairy like a cloak,” followed by Jacob, unremarkable but grasping Esau’s heel. Over time, their differences deepen: Esau, a skilled hunter, roams fields; Jacob, gentle, stays in tents. Famine forces the family from “Beer-Lahai-Roi” in the Negev to “Gerar’s Philistine king,” then to “Gerar’s valley,” and finally to Beersheba. At 40, Jacob, urged by Rebekah, deceives blind Isaac to steal Esau’s inheritance, sparking enmity. Rebekah advises Jacob to flee to rela...

1877MorrisH

An excerpt from the article by Morris H. Dislocations of the Thigh: their mode of occurrence as indicated by experiments, and the Anatomy of the Hip-joint (1877, pp. 161-170). The author noted that the ligamentum capitis femoris (LCF) is stretched during flexion, adduction, and external rotation. It was found that the LCF is always damaged in hip dislocations, is more often torn from the femur, and is rarely ruptured. Discussion of article see article 1877BrookeC . DISLOCATIONS OF THE THIGH: THEIR MODE OF OCCURRENCE AS INDICATED BY EXPERIMENTS AND THE ANATOMY OF THE HIP-JOINT. BY HENRY MORRIS, M.A., M.B., F.R.C.S., ASSISTANT SURGEON TO, AND LECTURER ON ANATOY1 AT, THE MIDDLESEX HOSPITAL. Received January 9th-Read February 13th, 1877. RECENTLY, whilst making various dissections of the hip-joint, the usually accepted doctrine that dorsal and ischiatic dislocations of the femur occur when the thigh is in a position of adduction appeared to me as very improbable, on anatomi...

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