Biology of the Reptilia

By: Megan Landon, Cameron Eddy, and Vince Ziccardi

Laboratory #2: Testudines

Key Points Covered in Lab:

1. Turtle Anatomy of the skeleton

Sea turtle skull exhibiting anapsid
condition and keratinized beak.

2. Reproduction of Turtles

3. Turtle Diversity

Let’s Get a Quick Glimpse on Testudines!

· There are 327 species of turtles categorized into 14 Families

· Turtle distribution is everywhere worldwide except for Antarctica

· Can live in habitats of marine, terrestrial, and freshwater

· Special morphology of the carapace and plastron (will be discussed later)

· Turtles lay eggs and are therefore oviparous

· Mothers typically bury their eggs into a nest and never return to it!

· Extant turtles lack teeth but have keratinized beak

· Skull is anapsid (no temporal fenestra)
· Testudines emerged in Triassic period (210-220 mya)

Extinct Ancestors of Modern Turtles:

1. Proganochelys quenstedti: note that they possessed teeth, carapace, plastron, long tail with turtles and limbs held inside the ribcage

2. Odontochelys semitestacea: They possessed teeth, a plastron but no carapace!

The Turtle Skeleton: Unlike most reptiles, the turtle skeleton is very unique due to its two parts: the carapace and plastron!

Carapace and Plastron Bones

a. Carapace Bones

i. Formed by fused ribs (costal bones) and vertebrae in trunk region (neural bones)

ii. Note the outermost bones (peripheral bones), the base of the spine (sacral bone), the posterior end (pygal), the anterior end near the neck (nuchal bone), and the suprapygal bone which is between the sacral and pygal bones

Bones of the carapace: A) Nuchal B) Neural C) Costal D) Sacral E) Suprapygal F) Pygal G) Peripheral

b. Plastron Bones

i. Most anterior lateral pair of bones (epiplastron), posterior lateral pair of bones (xiphiplastron), the median plate on anterior side (entoplastron)

ii. Note how the hyoplastron is above the hypoplastron with the mesoplastron in-between the two lateral pairs of bones

Bones of plastron: A) Epiplastron B) Entoplastron
C) Hyoplastron D) Hypoplastron E) Xiphiplastron

Carapace and Plastron Scutes

a. Carapace Scutes

i. Note that the vertebral scutes cover the spinal region, the pleural scutes cover the ribs, and the marginal are the outermost scutes

ii. Also note how the supramarginal scutes fall in-between the marginal and pleural; the cervical scute covering the neck region of the turtle

Scutes of the carapace: A) Vertebral B) Pleural C) Marginal D) Cervical

Supramarginal scutes present on carapace of Macrochelys temminkii, but not Chelydra serpentina

b. Plastron Scutes

i. Note the intergular scutes covering the throat of the turtle (anterior) and the anal scutes (posterior); the gular scutes are first lateral pair followed by the humeral scutes which are underneath

ii. The pectoral scutes are laterally paired near the pectoral girdle (note how the axillary scutes cover the pectoral girdle), the abdominal scutes cover the abdomen (inframarginal scutes are outside abdominal scutes), and the femoral scutes covering the femur of the turtle

Plastron scutes: A) Gular B) Humeral C) Pectoral D) Abdominal E) Femoral F) Anal G) Inframarinal H) Axillary

***A note on Carapace/Plastron Scutes vs. Carapace/Plastron Bones

Vs.

(The scutes covering the bones and both the carapace and plastron do not directly align with each other.)

Girdles of Turtles

a. Pectoral Girdle

i. contains two parts of the scapula and a coracoid

Turtle pectoral girdle: A) Dorsal process of scapula
B) Ventromedial process of scapula C) Coracoid

b. Pelvic Girdle

i. the ilium (sticking out in the back), the ischium (the two posterior bones on pelvic girdle), and the pubis (the two anteiror bones of the pelvic girdle)

Turtle Pelvic girdle: A) Ilium B) Pubis C) Ischium

Turtle girdles: A) Pectoral B) Pelvic

Here’s a different look by showing the entire skeleton of the turtle. Try to see if you can identify the bones associated with the pectoral and pelvic girdles.

Turtle Skulls

a. Note the prefrontal, frontal, parietal, and postorbital bones on the dorsal view of the turtle skull

b. On the ventral view, note the premaxilla, maxilla, pterygoid, palatine, vomer (separating the right and left nasal cavities), supraoccipital, basioccipital and exoccipital

c. On the lateral view of the turtle, note the jugal, quadratojugal, quadrate

Dorsal, ventral, and lateral view Chelydra seprentina skull. A) Supraoccipital B) Squamosal C) Exoccipital D) Parietal E) Postorbital F) Frontal G) Prefrontal H) Maxilla I) Premaxilla J) Jugal K) Quadratojugal L) Quadrate M) Pterygoid N) Basioccipital O) Vomer P) Palatine

Reproduction

Both sexes of turtle have anatomical characteristics, unique from both each other and from other reptiles, that allow scientists to differentiate between sexes as well as aid in the act of reproduction. In determining the sex of the turtle, the easiest way is to look at the tails. Males have a larger, fatter, overall more robust tail than females who have shorter less robust tails.

Comparing the tail sizes of female (left) and male (right) turtles

When these tails are laid straight, the cloaca of the male turtle can be found well beyond the posterior margin of the carrapace whereas the cloaca of the female is found before/ as the posterior margin of the carrapace(Fig. X).

Ventral view of the male plastron and female plastron

Posterior view of the male (right) and female (left) plastron

The unique reproductive characteristics of turtles are found mainly in males. Males have a concave plastron to keep them from sliding off the female during copulation, they have longer forelimb claws which are used during courtship to "tickle" the face of the female

Images comparing forearm claws (left) and cloaca position (right) of both male and female turtles

and they have a intromittent organ, a large appendage similar to a penis that functions to transfer sperm.

Copulatory organ in male turtles

Turtles are typical amniotes and oviparous wherein they have internal fertilization resulting in a cleidoic egg laid outside the body. These cleidoic eggs have hard calcium carbonate shells to protect the embryo inside from the outer environment while also allowing gas exchange. The embryos inside the egg have direct development, meaning that when the babies hatch, they will be minature versions of their parents. (Check last week's lab for images)

Diversity

About 200 to 250 million years ago, the order Testudines split between two groups: Cryptodira and Pleurodira. Turtles that belong to Cryptodira are more commonly known as "hidden neck turtles" meaning they pull their heads straight back into their shells when frightened.
Turtles that belong to Pleurodira are more commonly known as "side-neck turtles", so when they are frightened they pull their head to the side under the edge of their shells.

Cryptodira

Pleurodira

Ohio Diversity

Out of the multiple families and species of turtle that are found worldwide, Ohio is home to only 4 families and 12 species.
Chelydridae - Chelydra serpentina (Common Snapping Turtle)