Biology of the Reptilia: Laboratory #2: Testudines

by Cait Falasco and Chris Koch
Laboratory #2: Testudines

"Hundred and fifty, and still young, dude. Rock on." Yep some turtles can live up to and beyond 150 years old!

Turtles belong to the order Testudines. Scientists all argue over where they belong on the evolutionary tree, but so far turtles have been broken down into 14 families. They are distributed worldwide and found in many different types of habitats including terrestrial, marine and freshwater. According to the EMBL Reptile Database, there are 323 species of turtles that have been identified which demonstrates a wide range of turtle diversity! The purpose of this lab was to study the anatomy, reproduction and diversity of Testudines.

Skeleton:

The hot and heavy debate first arises over the condition of the turtle’s skull. The skulls of turtles demonstrate the Anapsid condition with No temporal fenestra. Many species of turtles do have deep temporal emargination on the posterior portion of the skull that may resemble and be confused with a different type of skull. It is important to note that all turtles demonstrate the Anapsid condition.
The real ongoing argument is whether or not this means they are

a) ancestral anapsids
OR
b) derived diapsids!

Turtles' unique skeleton makes it difficult to mistake it for any other group of reptiles because of the shell in particular. With a shell on their backs, they are pretty much ready for anything... like say spontaneous relocations, avoiding awkward situations or more importantly, escaping predators. The dorsal portion of the shell is called the carapace and the ventral part of the shell is called the plastron. Both regions of the shell are composed of bones that have been fused or paired to from the unique structure (Carapace=ribs+vertebrae+dermal bones and Plastron=girtles+sternal elements+gastrailia). Covering the carapace and plastron a thin layer of epidermis produces scales called scutes. Scutes are large plate-like scales that can vary in shape from neighboring scales. As a result of the turtle’s shell, a modified pair of girdles are formed for movement. The pelvic and pectoral girdles can be seen in this photo of the ventral side of a turtle.

Reproduction:

Turtles are AMNIOTES, OVIPAROUS and have DIRECT DEVELOPMENT inside a like, CaCO2 shelled cleidoic egg. Turtles basically dig a nest with their hind limbs, lay their babies, bury them up and say goodbye. They don't use vegetation in their nests, like most archosauromorphs.

What's also interesting is the process of reproduction itself!

The 3 C's of Internal Fertilization! (TM: Falasco)

1) Courting : Romance is not dead, even in turtles, they have to have a little knowledge of courtship. Turtle ladies love it when their males "tickle their face" tenderly with their forelimb claws during courtship displays.
2) Concave: Logistically, if these males want to copulate with females, they address the "mounting" issue avoiding slipping off female's bulky shells. One of the solutions is through a concave plastron of males that joins up nicer to the backs of females.
3) Copulatory Organ: This is the true secret of how turtles avoiding shell bulkiness: extending their copulatory organ to compensate for extra distance. It's truly astounding and tenacious.

You can tell the difference between a male and female not only because males have the concave plastron, but also because of the features of the tail!

The position of the vent or cloaca (derived from the word for "sewer" meaning an all purpose hole) on the tail:
In females = at or before the posterior margin of the carapace
In males = well behind the posterior margin of the carapace (end of tail)
AND the size of the tail:
In females = short, less robust
In males = fat, more robust

Last but not least, Diversity:

Turtles have basically formed two group (or suborders): The Pleurodira (right) are more commonly referred to as "Side-neck" turtle group due to the fact that they fold their necks to the right or left when threatened. These turtles also have narrow, spool shaped cervical vertebrae and have 13 scutes on their plastron, one more than the other group. The Cryptodira (left) are more commonly referred to as the "Hidden-necked" turtle group because their posteriorly S-shaped neck tucks backward into their shell when threatened. They have wide and flat cervical vertebrae and 12 scutes on their plastron.

The represented families we saw in Lab were the following:

Cheloniidae: "Hard-shell Sea Turtles" (Crypts)

Chelidae: "Australoamerican Side-neck Turtles" (Pleurs)

Chelydridae: "Snapping Turtles" (Crypts)
**Ohio species: Chelydra serpentina - Common Snapping Turtle

Emydidae: "Cooters, Sliders & American Box Turtles" (Crypts)

**Ohio species: Chrysemys picta marginata - Midland Painted Turtle
Clemmys guttata - Spotted Turtle
Emydoidea blandingii - Blanding's Turtle
(Graptemys geographica - Map Turtle)
Graptemys pseudogeographica - False Map Turtle
(Pseudemys concinna - Hieroglyphica River Cooter)
Terrapene carolina - Eastern Box Turtle
Trachemys scripta - Red-Eared Slider

Kinosternidae "Mud and Musk Turtles" (Crypts)
**Ohio species: Sternotherus odoratus - Stinkpot Turtle