Lab 2: Testudines (Kelly and Maggie)

Turtles belong in the Order Testudines. According to the EMBL Reptile Database, 323 extant species have been identified in the world; these species have been organized into 14 families. They occupy a variety of habitats, including terrestrial, marine, and freshwater. A turtle is not an organism to be confused with anything else, as its magnificent shell makes it stand out from all other animal groups.

The skeleton of a turtle is so unique that it would be hard to confuse it with anything else. The dorsal region of a turtle is called the carapace, while the ventral region is called the plastron. The carapace and the plastron are composed of bone. Overlaying the skeleton are not typical reptile scales, but large plate-like scales termed scutes. Between the carapace and the plastron lie the pectoral and pelvic girdles of the turtle.

(A) Scutes of carapace. (B) Note the pectoral (1) and pelvic (2) girdles. (C) Bones  of carapace. (D) Scutes of plastron. (E) Scutes of carapace.

(A) Macrochelys temminckii (B) Aldebrachelys gigantea

Having no temporal fenestra, turtles demonstrate the anapsid condition. Not all turtles display this trait clearly though. Some turtles have deep temporal emarginations, which have the appearance of temporal fenestra. Note the deep temporal emargination in Aldebrachelys gigantea.

Because of the shell, reproduction between a male and female turtle becomes an interesting topic. Males typically have a concave plastron, which allows the male to remain mounted upon the female. Male turtles also have a large copulatory organ that is used to transfer sperm to the reproductive tract of the female. Like other amniotes, turtles display internal fertilization and direct development. 

While the phylogenetic origins of turtles is a hot topic for discussion, it is clear that there are two distinct suborders of turtles: Pleurodiran (Side-Neck) and Cryptodiran (Hidden Neck) turtles. Let's explore the differences between these two groups...

PLEURODIRA

-when retracting head into the shell, the neck folds to either the right or left side

PODOCNEMIDAE (Madagascan Big Headed Turtles and American Side Neck Turtles)

- Range: South America,Madagascar

- moderately large river turtles

- nest communally

 

PELOMEDUSIDAE (African Mud Terrapins)


- Range: African, Arabian Peninsula, Seychelles, Madagascar
- large heads
- primarily carnivorous
- aestivate in heat, hibernate in cold

CHELIDAE (Australoamerican Side-Neck Turtles)

- Range: South America; Australia; Indonesia
- primarily aquatic
- tropical/subtropical

CRYPTODIRA

-cervical vertebrae folds into an S-curve inside the carapace

CHELYDRIDAE (Snapping Turtles)

- Range: Eastern North America, Central America, Northern South America

- longest tails of any turtles

- greatly reduced plastron

- aquatic turtles

- Ohio native:

          - Chelydra serpentina (far left and far right in picture) 

CHELONIIDAE (Hard-shelled sea turtles)

-Range: tropical to subarctic oceans

- move on land to nest

- many are dietary specialists

TRIONYCHIDAE (Softshell turtles)


- Range: Africa, SE Asia, New Guinea, North America
- carapace and plastron lack epidermal scutes
- thick, leathery skin
- cutaneous respiration
- aquatic bottom dwellers
- Ohio natives:
            - Apalone spinifera
            - Apalone mutica 
 

TESTUDINIDAE (Tortoises)

- Range: North America, South America, Africa, Europe, Asia

- columnar/elephantine feet

- terrestrial deserts, grasslands, scrub

- high domed shell

 KINOSTERNIDAE (Mud turtles and Musk turtles)

- Range: North America, Central America, North South America

- domed carapace

- large heads 

- generally aquatic

- Ohio natives:

         - Sternotherus odoratus

EMYDIDAE (Cooters, Sliders, American Box Turtles)

- Range: North America, Central America, South America, Europe, Asia, North Africa

- Two subfamilies: EMYDINAE and DEIROCHELINAE

- medium-sized turtles

- generally have a hinged plastron, which allows for complete closure of carapace and plastron

- semi-aquatic and terrestrial

- sexual dimorphism is common

- Ohio natives:

           - Chysemys picta marginata

           - Clemmys guttata

           - Emydoidea blandingii

           - Graptemys geographica

           - Graptemys pseudoheographica

           - Pseudemys concinna

           - Terrapene carolina

           - Trachemys scripta

Learning about the different types of turtles, particularly those native to Ohio, will be very helpful when we get into the field as the weather warms. We can't wait to trap some turtles! Because we all like turtles. Like this kid. 







KG & MH