Welcome to an exciting exploration of the evolution of synapsids and the fascinating anatomy of mammals. This journey takes us to Harvard’s Museum of Comparative Zoology, where Dr. Kenneth Angielczyk, the Associate Curator of Fossil Mammals at the Field Museum of Natural History, guides us through an intriguing study of fossil mammals.
Before diving into the details, let’s clarify what synapsids are. Synapsids are a group of animals that include all living mammals and their extinct relatives. A defining feature of synapsids is a unique opening in the skull, located just behind the eye socket. This opening is where the jaw muscles attach, and it’s a characteristic shared by all synapsids.
To illustrate, consider Eothyris, one of the most primitive synapsids. Its skull looks quite different from that of modern mammals, yet both share the synapsid temporal opening. As synapsids evolved, their skulls and other features underwent significant changes. For example, Massetognathus, a more advanced synapsid, has a skull that closely resembles those of living mammals.
Our focus today is on the evolution of the backbone in synapsids. Modern mammals have a distinct vertebral column with specialized regions serving different functions. In contrast, primitive synapsids had a more uniform backbone. To understand how these structures evolved, we study both fossils and living animals, examining how their backbones function with attached soft tissues like muscles.
In the Preparation Lab at Harvard’s Museum, Dr. Katrina Jones, a researcher in mammalian anatomy and evolution, introduces us to a fisher cat. Despite its name, the fisher cat is neither a fish nor a cat but resembles a large ferret or otter. The dissection of its vertebral column provides valuable insights into mammalian anatomy.
During the dissection, we observe the thoracic vertebrae and muscles, noting the absence of ribs in the lumbar region. This feature distinguishes modern mammals from some ancient ancestors that had ribs along their entire trunk, potentially limiting their range of motion. The shape and fit of vertebrae are crucial for determining mobility at each joint.
As we proceed, we remove a forelimb, revealing how muscles attach to bones and to each other through connective tissue called fascia. This intricate system enables various functions, such as flying or swimming. We also encounter the brachial plexus, a network of nerves responsible for muscle movement and sensation.
Further dissection reveals the atlanto-occipital joint, which allows for head movement, and the ball-and-socket joint formed by the femur and acetabulum. These structures highlight the complexity and adaptability of mammalian anatomy.
Examining the vertebral column, pelvis, and ribs, we hypothesize that early synapsids had less flexible spines. The evolution of specialized joints likely facilitated the development of asymmetric gaits in mammals. This division of the vertebral column is controlled by hox genes, which play a crucial role in spine morphology evolution.
Exploring the genetic research on animals that lived millions of years ago is an exciting endeavor. By studying both fossils and living specimens, we gain a deeper understanding of the evolutionary journey that led to the diverse and adaptable mammals we see today.
Engage in a virtual lab where you can examine 3D models of synapsid fossils. Compare the skull structures of primitive synapsids like Eothyris with those of modern mammals. Identify the synapsid temporal opening and discuss its evolutionary significance with your peers.
Participate in a hands-on workshop where you will reconstruct the vertebral column of a synapsid using provided models. Analyze the differences between primitive and modern vertebral structures and present your findings on how these changes might have influenced mammalian movement and flexibility.
Join a virtual dissection of a fisher cat to explore mammalian anatomy. Focus on the thoracic and lumbar regions, observing the absence of ribs in the lumbar area. Discuss how this anatomical feature contributes to the flexibility and mobility of modern mammals.
Engage in an interactive session where you simulate the attachment of muscles to bones using digital tools. Explore the role of fascia and the brachial plexus in movement. Experiment with different muscle arrangements to understand their impact on various functions like flying or swimming.
Participate in a debate on the role of hox genes in the evolution of the vertebral column. Research and present arguments on how genetic changes may have led to the development of specialized joints and asymmetric gaits in mammals. Collaborate with classmates to explore different evolutionary hypotheses.
**Sanitized Transcript:**
[Warning: This episode contains material that may not be suitable for all audiences. Viewer discretion is advised.]
This series of episodes is brought to you by the Field Museum, the Harvard Museum of Comparative Zoology, and the National Science Foundation.
– Hey! We’re here at Harvard’s Museum of Comparative Zoology with Dr. Kenneth Angielczyk.
– I am the Associate Curator of Fossil Mammals at the Field Museum of Natural History.
– And we’re here today to conduct some experiments on some specimens to learn more about fossil mammals. It’s going to be great. Let’s go!
[Before we start the dissection, we have to explain synapsids.]
– In the episodes that we’ve been doing so far, we’ve talked a lot about synapsids, but you might not know what they are. A synapsid is a member of a group of animals that includes living mammals as their living relatives, as well as a number of fossil forms that can look quite different. All synapsids are characterized by one feature: an opening in the back of the skull, just behind the eye socket. This area is where jaw muscles attach to the skull, and all synapsids have this feature.
– If you compare an animal like Eothyris, one of the most primitive synapsids we know about, to a living mammal, you can see that the skull looks very different. However, they both have that same synapsid temporal opening. This is an animal called Massetognathus, which is a more advanced kind of synapsid. You can see that its skull is much more similar to our living mammals.
– Synapsids have undergone a massive amount of evolutionary change over their history, and there are very few features other than that opening that you can point to in all synapsid specimens.
– That’s kind of why we’re here today, right? We’re going to be looking at some of the changes in the other parts of the skeletons of these animals. What are we primarily going to be looking at?
– We’re interested in the evolution of the backbone of synapsids. Living mammals have distinct vertebral columns or backbones that have different regions with specific functions. In contrast, more primitive synapsids have a much more uniform backbone. We can only get so much information from fossils, so we need to look at living animals that have their soft tissues, like muscles, attached to the backbone. By studying how the backbone functions in those animals, we can model how the vertebral columns of fossils would have worked when they had all their soft tissues attached.
– So, we’re going to the Prep Lab.
[43 minutes later]
– We are here in the Preparation Lab at Harvard’s Museum of Comparative Zoology with Dr. Katrina Jones.
– Hi Emily. I’m a researcher here at the Museum, and I study the anatomy and evolution of mammals.
– And what do we have here in this bag in front of us?
– This is a fisher cat. Today, we’re going to dissect its vertebral column for our experiments.
– But it’s not a fish or a cat; it’s more like a large ferret or otter. The skin and organs have been removed, and now we need to take off the head and limbs to access the vertebral column.
– Let’s do it!
– [After some dissection] You can already see the ribs, thoracic vertebrae, and muscles contained in that area, but there’s nothing in the lumbar region.
– Mammals have a lumbar region that is free of ribs, which is different from some ancient mammal ancestors that had ribs along their entire trunk.
– This might have limited their range of motion. The shape of the vertebrae and how they fit together is also important for determining mobility at each joint.
– First, we’re going to remove a forelimb.
– [After some dissection] So, this muscle attaches to bones to move them, but some muscles attach to other muscles through connective tissue called fascia, which helps them move.
– It’s fascinating to think about all the different functions mammals perform with their arms, like flying or swimming.
– [Continuing the dissection] This is the brachial plexus, a dense web of nerves that transmits impulses to move muscles and sensation.
– [After further dissection] Now we can work on the head. There are important connections between the head and body, including the atlanto-occipital joint, which allows for head movement.
– [After some effort] We’ve removed the head along with the neck muscles.
– [Continuing with the dissection] Now, let’s remove the baculum.
– [After some dissection] This is the head of the femur, which fits into the acetabulum, forming a ball-and-socket joint.
– [After further dissection] Now we have the vertebral column, pelvis, and ribs left. Before we conduct our experiment, we will also remove the pelvis and ribs.
– [After some time] We can see long strips of muscle running along the back, which is a unique mammal feature. This allows for flexion and extension, which is important for movement.
– [Discussing evolution] We hypothesize that early synapsids had a less flexible spine, and the evolution of specialized joints allowed for the development of asymmetric gaits in mammals.
– The division of the vertebral column is controlled by a set of genes called hox genes, which play a crucial role in the evolution of spine morphology.
– [Concluding] It’s exciting to explore the genetic research on animals that lived millions of years ago.
[End of Transcript]
Synapsids – A group of animals that includes mammals and their extinct relatives, characterized by a single temporal opening in the skull behind the eyes. – Synapsids are crucial to understanding the evolutionary transition from reptiles to mammals.
Evolution – The process by which different kinds of living organisms are thought to have developed and diversified from earlier forms during the history of the earth. – The theory of evolution provides a scientific explanation for the diversity of life on Earth.
Anatomy – The branch of biology concerned with the study of the structure of organisms and their parts. – Comparative anatomy allows scientists to trace the evolutionary history of different species.
Mammals – A class of warm-blooded vertebrates characterized by the presence of mammary glands, hair, and three middle ear bones. – Mammals have evolved a wide range of adaptations to survive in diverse environments.
Vertebral – Relating to the vertebrae or the vertebral column, which is the backbone of vertebrates. – The vertebral column is a key feature that supports the body structure of vertebrates.
Fossils – The preserved remains or traces of organisms that lived in the past, often found in sedimentary rock. – Fossils provide critical evidence for understanding the evolutionary history of life on Earth.
Muscles – Tissues composed of fibers capable of contracting to effect bodily movement. – The study of muscles in different species helps biologists understand the mechanics of movement and evolution.
Movement – The act or process of changing position or place, often facilitated by the muscular and skeletal systems. – Evolution has led to a variety of movement strategies in animals, from flying to swimming.
Joints – The locations at which two or more bones make contact, allowing for movement and flexibility. – The evolution of complex joints has enabled mammals to perform a wide range of movements.
Genes – Units of heredity that are transferred from a parent to offspring and determine some characteristics of the offspring. – Genetic mutations can lead to evolutionary changes by introducing new traits into a population.
