Related Experiment Video
Updated: Jun 24, 2026
08:02
Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton
Published on: May 7, 2016
Stem sarcopterygians have primitive polybasal fin articulation
1Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, PO Box 643, Beijing 100044, People's Republic of China. zhumin@ivpp.ac.cn
Biology Letters
|March 28, 2009
Summary
Early sarcopterygian fishes possessed polybasal pectoral fin articulation, similar to basal actinopterygians. This finding reveals the origin of the tetrapod limb
Area of Science:
- Paleontology
- Evolutionary Biology
- Comparative Anatomy
Background:
- Osteichthyan paired fins exhibit diversity in endoskeletal components and shoulder girdle articulation.
- Basal actinopterygians have polybasal fins (pro-, meso-, metapterygia), while sarcopterygians have monobasal fins (metapterygium).
- The transition from polybasal to monobasal fins is crucial for understanding the evolution of tetrapod limbs, but fossil evidence has been lacking.
Purpose of the Study:
- To investigate the shoulder girdle morphology of early sarcopterygians.
- To determine the phylogenetic and temporal context of the fin-limb transition.
- To elucidate the evolutionary origins of the tetrapod stylopod.
Main Methods:
- Analysis of three-dimensionally preserved shoulder girdles from stem sarcopterygians (Psarolepis and Achoania).
- Comparative anatomical study with basal actinopterygians and other sarcopterygians.
- Phylogenetic analysis to constrain the timing of evolutionary events.
Main Results:
- Stem sarcopterygians Psarolepis and Achoania exhibit polybasal pectoral fin articulation, similar to basal actinopterygians.
- This indicates that the polybasal condition predates the origin of monobasal fins in sarcopterygians.
- The loss of propterygium and mesopterygium occurred within the stem sarcopterygian lineage.
Conclusions:
- The transition to monobasal fins in sarcopterygians occurred later than previously inferred.
- The origin of the tetrapod limb's proximal segments (stylopod and zeugopod) is rooted in the polybasal fin condition of stem sarcopterygians.
- This study provides critical fossil evidence for the fin-to-limb transition in vertebrate evolution.
Related Concept Videos
01:25Fascicle Arrangement in Skeletal Muscles
Fascicles are bundles of muscle fibers in a skeletal muscle. Muscle fascicle arrangement is directly associated with the power and range of motion of various muscles. The configuration of these fascicles can vary, leading to different functional outcomes.
The four primary types of muscle based on fascicle arrangement are:
The four primary types of muscle based on fascicle arrangement are:
01:54Convergent Evolution
Evolution shapes the features of organisms over time, ensuring that they are suited for the environments in which they live. Sometimes, selection pressure leads to the rise of similar but unrelated adaptations in organisms with no recent common ancestors, a process known as convergent evolution.The structures that arise from convergent evolution are called analogous structures. They are similar in function even if they are dissimilar in structure. Further, structures can be analogous while also...
01:09Overview of the Axial Skeleton
The skeleton is subdivided into two major divisions—the axial skeleton and the appendicular skeleton. The axial skeleton forms the vertical, central axis of the body. It includes all of the bones of the head, neck, chest, and back. It protects the brain, spinal cord, heart, and lungs. It also serves as the attachment site for muscles that move the head, neck, and back and for muscles that act across the shoulder and hip joints to move their corresponding limbs.
The axial skeleton of the adult...
The axial skeleton of the adult...
01:08The Sarcomere
A sarcomere is a microscopic segment repeating in a myofibril. The sarcomere fundamentally consists of two main myofilaments: thick filaments called myosin and thin filaments called actin. These filaments interact by sliding past each other in response to stimulus. In addition to myosin and actin, several other proteins, such as tropomyosin, troponin, titin, nebulin, myomesin, α-actinin, and dystrophin, play crucial roles in regulating, structuring, and functioning of the sarcomere.
Each myosin...
Each myosin...
01:09Changes in the Appendicular Skeleton with Age
The upper and lower limb initially develops as a small bulge called a limb bud, which appears on the lateral side of the early embryo. The upper limb bud appears near the end of the fourth week of development, with the lower limb bud appearing shortly after.
Initially, the limb buds consist of a core of mesenchyme covered by a layer of ectoderm. The ectoderm at the end of the limb bud thickens to form a narrow crest called the apical ectodermal ridge. This ridge stimulates the underlying...
Initially, the limb buds consist of a core of mesenchyme covered by a layer of ectoderm. The ectoderm at the end of the limb bud thickens to form a narrow crest called the apical ectodermal ridge. This ridge stimulates the underlying...
01:18Classification of Bones
The bones of the human skeletal system are of varied shapes, sizes, and functions. They can be classified based on their shape and function into four major classes: long bones, short bones, flat bones, and irregular bones. Some classifications include a fifth type, the sesamoid bones, as a separate class, whereas others categorize them under short bones.
Long and Short Bones
The appendicular skeleton, particularly the upper and lower limbs, is primarily made of long and short bones. The long...
Long and Short Bones
The appendicular skeleton, particularly the upper and lower limbs, is primarily made of long and short bones. The long...