Lab 1: Alex Valigosky and Jeff Walker

We ALL know that REPTILES are cool, but...

What is a reptile? A reptile is a scaly creature with somewhere in the range of zero and four legs that may or may not lay eggs of varying hardness.  Eh.  In all seriousness, though, reptiles are derived tetrapods sharing a common ancestor with amphibians, and evolutionarily more recent ancestor with mammals; reptilian ancestors diverged from amphibians during the carboniferous period as they moved onto dry land.  This move forced them to adapt morphologically in ways that can still be seen in extant reptiles today:

Reptiles and early mammals both laid cleidoic eggs (also called amniotic eggs); a chicken egg (as birds are highly derived reptiles) is an excellent example of an amniotic egg.  Amniotic eggs are much more complex than anamniotic eggs (gelatinous amphibian eggs that can rely on simple diffusion due to their aquatic environments).  Amniotic eggs have crystalized calcium carbonate shells that retain water while allowing diffusion of gasses through small pores.  Everything that the embryo needs to survive early development can be found within the egg; an incredible terrestrial adaption - this includes the yolk, an early food source, and other functional membrane layers.  But how does the hatchling emerge from this hard-shelled cage?! Duhh - an egg-tooth (seen above-right on the snout of this ageless young turtle)

Reptilian skin has several layers, but is most often covered by scales, or feathers (in the case of birds, which we don't really care about - lol). There are several different types of scales and each type can be found in various places on any one specimen’s body. However, not all reptiles have scales, like our friend Zagnut, the soft-shelled turtle. 

Here is an example of large rectangular scales on a cayman (right)

The skeleton of tetrapods, in the case of most reptiles and mammals, evolved to endure a less aquatic life. This required beefing up the pelvic and pectoral girdles and strengthening the vertebral column (fusing many bones). Other notable adaptions include a more derived atlas-axis complex (pictured to the left), where the skull attaches to the start of the spine. This adaption allowed freer movement of the head for feeding.  This is beneficial as pressure differences of air and water present different adaptational challenges.

This is a fine example of a tetrapod skeleton! (crocodilian)

The skulls of extant reptiles (those living today) are characterized as either diapsid skulls (snakes, lizards, crocodiles) or anapsid skulls (in the case of turtles). Reptile skulls may differ in the shapes of fused bones; however, the major differences lie in the presence or absence of fenestre - these are gaps or holes on the skull in certain places.  Excluding the nose and eye holes, anapsid skulls completely lack fenestra (as did the skulls of the ancestral reptiles), while diapsid skulls exhibit both a supratemporal (just above and behind the eye socket) and infratemporal fenestre (just below and to the outside of the supratemporal)

Lab 1: Reptile Anatomy (Kelly and Maggie)

The first lab of the semester was designed to introduce the class to the basic anatomy of reptiles. These anatomical characteristics helped us to determine the definition of a reptile. In this blog, we will cover the following characteristics: eggs, embryos, and development; skin, scales, and glands; and the skeleton.

Anatomy of a cleidoic egg: (A) albumin, (B) yolk, (C) chalaza, (D) shell

Eggs, Embryos, and Development:
The shell of a reptile egg is composed of two distinct layers: a hard, calcareous outer layer and a fibrous inner layer. Pores in the outer layer of the shell allow for gas exchange while the embryo is growing.
Inside the shell, we find the internal anatomy of the egg. In a fertilized egg, the embryo is encased in a nutrient-providing yolk; the yolk is anchored inside of the shell by the chalaza and is supported by the layers of the albumin ("egg white" in layman's terms).

Clockwise from bottom: snapping turtle, emu, ostrich

While the internal anatomy of the cleidoic egg is similar among reptile species, the actual appearance of the egg varies greatly! Some, like birds, have a very hard shell, while others, like snakes, have a more flexible shell. Check out some of the different eggs to the left. 

Egg tooth of late stage turtle embryo

Reptiles exhibit direct development. This means that, when the embryo hatches from its egg, it looks like a mini-version of the adult. Many hatching reptiles have an adaptation called an egg tooth: this structure aids in breaking open the shell.







Skin, Scales, and Glands:

Dr. Sheil instructs the class on the different scale types

The skin of a reptile is comprised of three distinct layers. The Stratum corneum is the layer of skin that is composed of dead skin cells. The second important layer, which is composed of living cells of the deep epidermis, is called the stratum germinativum. The last distinct layer discussed in lab is the dermis. The dermis forms the armor-like protective layer of some lizards, turtles, and some crocodilians.

Scales are important to pay attention to when attempting to distinguish specimens. Scale types range from smooth to keeled; some may overlap, and others may have pits. Different scale types can vary over the surface of individual bodies. Important scales to note are granular, small rectangular, large rectangular, cycloid, smooth juxtaposed, and keeled. Combinations of the types can occur. For example, some species may have keeled cycloid scales.

Glands of reptiles do not come close to the number amphibians have. Femoral glands are located on the inside of the upper hindlimbs and are visible to the naked eye, particularly in males. They manufacture chemicals that are used for communication and for marking territories. 

Cleared and stained chameleon. Red is bone, and blue is cartilage

Skeleton:

When observing the skeleton of an alligator we see four distinct regions of the vertebral column. These include the cervical, dorsal, sacral, and caudal regions. An important anatomical feature of some reptiles is gastralia. Gastralia aid in the respiration of these particular reptiles. 

Another important feature to point out in the skeleton is the skull. Reptiles can be classified as either anapsid or diapsid. These terms refer to the presence of (or lack of) a supratemporal fenestra and/or a subtemporal fenestra. Both are present in a diapsid skull, but none are present in an anapsid skull. Mammals have a synapsid skull, meaning that only the subtemporal fenestra is present.

Left to right: anapsid, synapsid, and diapsid skull conditions

Learning about these characteristics helped us to further understand about what defines a reptile, particularly with regards to reptilian anatomy.

Stay tuned for our next adventure in BL 526 Biology of the REPTILIAAAAAA. Until next time...

KG & MH

Things get a little dangerous in the lab sometimes.

Lab 1: Reptile Development and Anatomy: Dan Paluh and Sean Harrington

The general purpose of this lab was to become familiar with aspects of reptile development and anatomy. The main topics that were discussed include cleidoic eggs and development, scale structure, and skeletal anatomy.

Cleidoic eggs: There are two main layers to the shell of a cleidoic egg, an outer and inner organic layer. The calcium carbonate outer layer is made up of crystalline, columnar shell units that are separated by pores. These pores allow gas exchange to take place. The shell membrane is an inner organic layer made up of protein fibers. Cleidoic eggs also contain an external, middle, and internal albumin, as well as a yolk, chalaza, and an air cell.

Cleidoic eggs are variable in flexibility and thickness. The egg of Chelydra serpentina, the common snapping turtle, is hard and thick (traits that are often found in birds and many turtles). The eggs of Elaphe, as well as the eggs of all snakes, lizards, crocodilians, dinosaurs, and some turtles, are soft and leathery.

Embryos and Development: Reptiles exhibit oviparity or ovovivipairy during development. Oviparous reptiles hatch from eggs laid by the mother, and ovoviviparous reptiles emerge from eggs retained within the mother (a form of live birth). All reptiles exhibit direct development, where embryos form into miniature versions of the adult. Cleared and double stained specimens of Trachemys scripta embryos were examined. Cartilage is stained blue, bone is stained red, and soft tissues are cleared in these specimens.

Hatching: An egg tooth is commonly used by reptiles to assist them in the process of hatching. An eggtooth attached to a late stage embryo of Geochelone emys was observed.

Skin: The skin of reptiles is usually covered in scales or feathers, and has few glands when compared to amphibians. The three layers found in reptilian skin are the stratum corneum, the stratum germinativum, and the dermis. The stratum corneum is the outer layer made up of dead cells, the stratum germinativum is the deep epidermis made up of living cells, and the dermis is made up of the nerves, blood vessels, and sometimes osteoderms.

Scale Morphology: One of the diagnostic features that can be used to identify reptile species is external scale morphology. There are number of different scale types, including, but not limited to: granular, rectangular, keeled, cycloid, and juxtaposed. Many species of reptile exhibit variation in scalation, with different scale types present on different areas of the body, such as the ventral and dorsal surfaces. Many lizards and snakes also have distinct patterns of enlarged scales on their heads that are useful in identification.

Shed snake skin (cycloid)

Glands: Many lizards have glandular pores present anterior to the cloaca (precloacal pores) or on the underside on the hind leg (femoral pores). These pores are typically found on male lizards, and, if present, will smaller in females than males of a species.

General Skeletal Anatomy: We also examined the basic skeletal anatomy of reptiles. We examined the general body regions of a reptileon a dried alligator skeleton. The vertebral column is broken up into the cervical region (the neck vertebrae anterior to the pectoral girdle), the trunk (vertebrae between the pectoral girdle and the sacrum), and the caudal region (vertebrae posterior to the sacrum). The forelimb and hind limb of reptiles are anchored to the body by the pectoral and pelvic girdles, respectively.

Skull Morphology and Temporal Fenestration: We also examined crocodilian skulls, which demonstrate the diapsid condition present in all extant reptiles, excluding turtles. This means that there are two temporal fenestrae, which are openings in the temporal region of the skull that allow for muscle attachment. Diapsid skulls have both a supratemporal fenestra and a lower subtemporal fenestra.

This is in contrast to the anapsid condition seen in turtles, in which there are no temporal fenestrae, but rather deeply inscribed temporal emarginations at the posterior of the skull to allow space for muscle attachment. Mammals and their ancestors exhibit the synapsid condition, in which there is a single subtemporal fenestra. Although all extant reptiles except for turtles possess a phylogenetically diapsid skull, in many cases the skull is highly derived, such that these fenestrae have been variously modified or lost.

Dan Paluh & Sean Harrington

Lab 1: General Anatomy of Reptiles. Chalaza, Cloacal plates, and Ecdysis, Oh my! (Michele and Brad)

The first lab for the Biology of the Reptilia focused on cleidoic eggs, embryonic development, reptile integument, and the regions of a reptile’s skeleton.

Cleidoic Eggs and Development

First we looked at the cleidoic eggs of reptiles. We noticed how variable the thickness and texture of reptile eggs are, depending on the composition of the outer layer of the shell. One of the first characteristics we noticed was that the Rat Snake egg’s shell had a leathery texture.

The Snapping Turtle eggs resembled ping-pong balls and had a harder shell than the snake eggs.

Next, we observed a broken Chicken egg shell and the internal anatomy of the egg. The outer layer of the

shell (1) is made of units of calcium carbonate, containing pores that allows for gas and water exchange. The inner organic layer (2) is made up of a fibrous layer and is easily seen after the egg has been broken.

After looking at the exterior components of the chicken egg, we looked at the internal anatomy of the egg.

The external albumin was much more runny than the more firm middle albumin. The chalaza is present on both sides of the yolk membrane and serves to anchor the yolk to the center of the egg shell. The air cell was visible on the inside of the empty egg shell and it looked like a bubble on one end of the egg

During development in the egg, many structures of the embryo become visible. The cleared and double-stained turtle embryo (below, on the left) is blue where cartilage has developed and the soft tissue has been cleared. It is easy to see the egg tooth on the late-stage turtle embryo (below, right) which is used to pierce through the membranes and egg shell. The yolk is still visible and attached to the ventral side of the turtle embryo, supplying it with nutrients while developing.

Integument: Skin, Scales and Glands

The skin of reptiles is composed of the Stratum corneum (the outer layer of dead cells), the Stratum germinativum (deep epidermis), and the dermis (contains nerves, blood vessels and osteoderms). The folding of the dermis and epidermis yields scales. There are many different types and arrangements of scales, which help herpetologists identify different species of reptiles.

Below, are the scales of the Eastern Massasauga Rattlesnake (Sistrurus catenatus) which have a prominent ridge down the middle and are called keeled scales. These scales are shingle-like because they overlap.

Keeled scales (Below, Left) are also visible on the shed skin of snakes (the shedding of skin is called ecdysis). We observed 2 apical scale pits on a shed (Below, Right).













Below (Left) is a picture of the cloacal plate, and the ventral and subcaudal scales of the S. catenatus. Venemous snakes generally have a complete cloacal plate and complete subcaudals. Brad and I noticed that a few of the subcaudal scales right beneath the cloacal plate were divided, but most of the scales were complete further down the tail. Below (Right) is a picture of S. catenatus' rattle (which is unique to genera Crotalus and Sistrurus), and by counting the sections, we can tell that this snake has gone through 8 sheds.








An example of a non-venomous Rat snake's divided cloacal plate and divided subcaudal scales:

One of the specimens had a body similar to a snake because it didn't have legs, but it is actually a glass lizard (Ophisaurus). The features that give it away are the ear openings and the presence of eyelids, which are characteristic of lizards. We also noticed the glass lizard had a really long tail. The glass lizard has small rectangular scales on the dorsal half of it's body.


To the left is a picture of
small rectangular, juxtaposed scales of an Iguana.









To the right is a picture of a gecko's femoral pores, which males develop when they are sexually mature, the glands secrete hormones.






Skeletal system

To the right is a cleared and stained chameleon. This staining makes it easy to see where the skeletal system is (red) and where the cartilage is (blue). Below is a clear and stained Horned lizard. It is easy to see the vertebral column and regions of the skeleton in stained specimens.













Snakes have a large thoracic region (the region where ribs are present) and a smaller caudal region (absent of ribs).






To the left is an alligator skeleton, focusing on the Gastralia, where the ribs connect at the ventral midline. This whole picture shows the trunk region of the skeleton. The trunk region includes the lumbar region (lacking ribs) and the thoracic region (with ribs).









To the right are some of the different skulls of Amniota, and different modifications that either strengthen or lighten the skull with temporal fenestration, which are openings between bones.
1. Diapsid condition, common in reptiles (supratemporal fenestra and subtemporal fenestra)
2.Synapsid condition, often seen in mammalia (subtemporal fenestra)
3. Anapsid condition, without temporal fenestration. Seen in Testudines, Loggerhead turtle pictured here.



And now, a picture of Brad shaking some tail!!

Cha-cha-cha!!

Reptiles Lab 1 - Anatomy (Thompson & Serna)

Where: JCU lab
When: Friday 20 January, 1:30-4:30pm

What We Did: Welcome to the first Reptiles lab of the semester! This week we looked at anatomy of many different reptiles, including snakes, turtles, lizards, and even chickens (yes, birds are reptiles!). Our lab is lucky enough to have various skeletons, eggs, and whole preserved reptiles to learn about different structures. Below is an overview of what we observed.

Eggs: Our lab had snake, snapping turtle, chicken, and ostrich eggs. The snake egg was smooth and leathery while the snapping turtle egg had the consistency of a ping-pong ball; i.e. it was perfectly round and very easy to squish. Not all turtle eggs are like ping-pong balls; ironically, softshell turtles have rigid egg shells.


Snake egg (leathery, easily indented)



Ostrich egg (notice the small indentations, or pores, in the outer shell, used for the embryo's gas exchange). The shell's outer layer is made of shell units, composed of calcium carbonate, and all units are separated by these pores.

We then cracked open a regular chicken egg. After eating eggs for so many years, you would think we would know all there is to know about them, but we learned that eggs are pretty complex. If you have ever peeled a hard-boiled egg, you know that the shell contains 2 layers (outer & inner organic layer). However, the inside is not just yolk and "egg whites"; the albumin, or clear part of the internal egg, has multiple layers - external, middle, and internal albumin. The internal albumin is hard to detect, but if you crack open an egg in a dish, you can "peel" apart the external and middle albumin; the external has a liquid consistency while the middle is gelatinous.

Embryos: We examined some preserved, double-stained turtle embryos. This means the body has been disintegrated down to cartilage and bone, both of which are stained different colors (cartilage is blue, bone is red). The embryos were small and hard to take a picture of, but below is an example of a chameleon that underwent the same staining process.



Hatching: Below is a turtle embryo with an egg tooth (protuberance between forceps). This tooth is used to break through the double-layered eggshell when the offspring is ready to emerge.




Skin: Even reptile skin is complex, with three distinct layers. When the reptile is ready to shed (called ecdysis), the "old" skin is the uppermost layer while new cells are created closer to the body. We had some really nice snake skins to analyze different sizes of scales.


Multiple snake skins (largest is boa skin)


The edge of skin (left) shows the thin inner layer, while the remainder shows both layers of this snake's shed skin.


Scales: Reptiles have scales for thermoregulation (temperature), osmoregulation (water), and protection. Most scales are either rectangular or circular. However, some species can be distinguished by their combinations of shape and position; there exist overlapping circular (called cycloid), adjacent (called juxtaposed; there can be rectangular or circular juxtaposed), and mucronate (i.e., with a ridge down the scale's center) scale types. In addition, scales can be smooth or keeled (raised).

The 5-lined skink (Eumeces fasciatus) displays smooth cycloid scales. The cycloid scales completely line the body.



The gecko that was examined portrays a few different scale types over the body. The dorsal, or back, side of the body is composed of granular scales, which are raised and bump–like. There are rectangular scales on the tail while the ventral, or belly, side is composed of smooth juxtaposed scales.


Rectangular scales were examined on the green iguana (Iguana iguana), spiny tailed iguana (Ctenosaura similis), caiman (family Caimaninae), and the legless lizard (pictured below). The iguanas both have small smooth rectangular scales on their body, while the tail of the spiny-tailed iguana is keeled with larger rectangular scales. The scales of the caiman are large and tough, with some keeled around the tail. The legless lizard has small, keeled rectangular scales throughout its body.




Glands: This view of the gecko (below) shows the femoral (running along the femur, indicated by red circles) and precloacal (above the cloaca, or "all-purpose hole") pores. The femoral pores, more commonly found on males, are used to secrete hormones to mates or to mark territories.


Skeletons: The anatomy of turtles is very unique. Turtles have very short limbs and a short tail. The vertebral column of a turtle is fused to its shell.



This snake skeleton demonstrates even more morphological variation from other reptiles. The skeleton does not contain appendages but is lined with ribs articulating the vertebrae.



Skulls: Reptiles display a variety of temporal fenestration, where fenestrae are large openings between bones in the temple. As a reference, our temples are between our eyes and ears, and can be felt when we open and close our jaws. There are evolutionary trends among fenestrae as modifications were made to the temporal regions of the skull to reduce weight and increase strength.

This turtle skull is anapsid. This is the most ancestral condition, with no temporal fenestrae (the large opening you see once held the organism's eye). The pencil gives you an idea of how big this skull is (it rivals a human's!).

Mammals have synapsid skulls, with only 1 hole posterior (behind) the orbital (eye) fenestra, clearly seen from the drawing below.


Below is a skull of a tuatara with 2 holes (fenestrae) posterior to the orbit, making it diapsid. The top arrow is pointing to the supratemporal fenestra while the bottom points to the subtemporal fenestra.