Biology of the Reptilia: Lab #2: Testudines (Nick Spies and Alex Murray)

Lab #2: Testudines

There are currently 327 identified extant species of Testudines, placed into 14 families. In this specific lab, 8 of these extant Testudines families were examined and described. The eight specific Testudine families that were examined in this lab are as follows:

Podocnemidae (Madagascan Big-Headed Turtles & American Side-Neck Turtles)
Chelidae (Australoamerican Side-Neck Turtles)
Trionychidae (Soft-Shell Turtles)
Cheloniidae (Hard-shelled Seaturtles)
Chelydridae (Snapping Turtles)
Kinosternidae (Mud and Musk Turtles)
Testudinidae (Tortoises)
Emydidae (Cooters, Sliders, American Box Turtles)

Figure 1: Phylogenetic Relationships of Turtle Families

Pleurodira and Cryptodira Testudines

Within the Testudines, there is a basil split between Pleurodira and Cryptodira. The two following terms refer to how Testudines hide their heads when they are frightened. Pleurodiran turtles fold their head either to the right or to the left, and cannot pull their heads into their shells (Fig. 1)(Fig. 2). Cryptodiran turtles pull their heads into their shells within a pocket, during this process, the turtle's neck curves posteriorly in an "S" shape(Fig. 1)(Fig. 2).

Figure 2: Pleurodira vs. Cryptodira Neck Retraction

Two Pleurodira Testudine Families Examined in Lab:

1) Podocnemidae (Madagascan Big-Headed Turtles & American Side-Neck Turtles)

Location: South America & Madagascar

Characteristics:

3 Genera, 8 Species

Moderately Large

River Turtles

Broad, domed, streamlined shells

Active Swimmers

Herbivores/Opportunistic carnivores

Nest in sand along river

2) Chelidae (Australoamerican Side-Neck Turtles)

Location: South America, Australia, Indonesia

(Southern Hemisphere only)

Characteristics:

Flattened Skull and Shell

Primarily Aquatic

Omnivores

Some leave water to forage during rains near water

(Gulp Feeding)

Six Cryptodira Testudine Families Examined in Lab:

1)Trionychidae (Soft-Shell Turtles)

Location: Africa, Asia, New Guinea, SE Asia, Indonesia, North America

Characteristics:
Snorkel-like snout
Flattened "Pancake"
Reduced Carapace/Plastron
Lack epidermal scutes
Possess thick, leathery skin
Long Necks
Some Possess femoral flaps on plastron

Characteristics:

Lattice-like plastron, either fused or separate, hyoplastron and hypoplastron

Opportunistic carnivores

Cutaneous Respiration (from not having scales)

2)Cheloniidae (Hard-shelled Seaturtles)

Location: Tropical to Subtropical Oceans

Characteristics:

Flat streamlined shells with epidermal scutes

Forelimbs flipper like

Hind limbs webbed for steering

Emerge on beaches only to nest

Require 25 years for sexual maturity

3)Chelydridae (Snapping Turtles)

Location: Eastern North America, Mexico & Central America, Northern South America
Characteristics:
2 Genera, 2-5 Species
Large Heads (relative to body)
Skull roof deeply emarginated
Broad, flat Carapace
Reduced Plastron (cruciform)
Longest tail of any Testudine
Aquatic, only on lad to lay eggs
Opportunistic carnivores
Primarily Herbivores

**Two genera of Chelydridae are Chelydra (common snapping turtles) and Macrochelys Alligator Snapping Turtle**

Biggest difference between the two species is that Macrochelys has four marginal scutes, whereas Chelydra

4)Kinosternidae (Mud and Musk Turtles)

Location: North America, Central America, and Northern South America (New World Only)

Characteristics:

24 + species

Smallest Testudines

Oblong, moderately domed carapace

Large heads compared to body size

Plastron commonly hinged

Reduced plastron

<10 epidermal marginal scutes

Entoplastron sometimes present

Generally aquatic

Bottom walkers

Hibernate on land

Can forage on land

Occupy underground retreats/nest communally

Occasionally nest below vegetation

5)Testudinidae (Tortoises)

Location: North/South America, Galapagos, Africa, Madagascar, Seychelles, Europe, Asia, Indonesia

Characteristics:

15 Genera, 45+ Species

Almost all have domed shells

Columnar/Elephantine feet

Terrestrial (Desert, Grassland, Scrub)

100 days incubation to 18 months

6)Emydidae (Cooters, Sliders, American Box Turtles)

**two Testudine subfamilies within this Testudine family, Emydinae (Fig. 3) and Deirochelinae (Fig. 4)

Figure 3: Subfamily: Emydinae, Genus: Clemmys

Figure 4: Subfamily: Deirochelinae Genus: Graptemys

Location: North America, Central America, Parts of South America, Europe, Asia, North Africa

Characteristics:

42 species

Medium Sized Turtles

Plastron large, occasionally hinged

Semi-aquatic/terrestrial

Sexual Dimorphism common (females 2X larger than males)

Omnivores or strongly herbivorous

Two Subfamilies:

1) Emydinae: conservative diets, diversity of habitats, some plastrons hinged

2) Deirochelinae: Diversity of diets, conservative habitats, aquatic, diet specialists, epipubes do not ossify

Testudine Anatomy

Skeletons of Testudines are the most unique skeletons of any other type of reptile, because of the presence of a sell structure. The shell structure is formed by two main skeletal structures, the carapace and the plastron. The carapace (Fig. 5 & 6) is formed of broadly expanded and fused ribs and vertebrae in the trunk region, as well as a layer of dermal bones that span the spaces between these bones. The plastron (Fig. 5 & 6) is composed of several paired bones that are remnants of the sternal elements and perhaps the gastralia. Positioned within the shell structure are the pectoral girdle and forelimb, and the pelvic girdle and hind limb.

Bones of the Carapace: (Fig. 5 & 6) Bones of the Plastron: (Fig. 5 & 6)

Nuchal Epiplastron

Peripheral Endoplastron

Neural Hyoplastron

Costal Mesoplastron

Suprapygal Hypoplastron

Pygal Xiphilplastron

Figure 5: Bones of Carapace and Plastron

Figure 6: Bones of Carapace and Plastron examined in Lab 2: Testudines

Overlaying the bony skeleton of Testudines is a thin layer of epidermis. This epidermis produced large plate-like scale, referred to as scutes (Fig. 7 & 8).

Scutes of the Carapace (Fig. 7 & 8): Scutes of the Plastron (Fig. 7 & 8):

Cervical Intergular

Marginal Gular

Supramarginal Axillary

Vertebral Humeral

Pleural Pectoral

Abdominal

Inframarginal

Inguinal

Femoral

Anal

Figure 7: Scutes of the Carapace and Plastron

Figure 8: Scutes of the Carapace and Plastron examined in Lab 2: Testudine

Girdle of Testudine

Figure 9: Pelvic Girdle of Testudine

Figure 10: Pectoral Girdle of Testudine

Testudine Skull

Testudines have the skull condition known as an Anapsid skull (Fig. 11 &12). Although Testudines demonstrate the Anapsid skull condition, many Testudine species have a deep temporal emargination on the posterior margin of the skull.

Figure 11: Anatomy of Testudine Skulls examined in Lab 2: Testudines

Figure 12: Skull Anatomy of Testudine

Reproduction

Exhibit internal fertilization

Direct Development of embryos inside a cleidoic egg

Shell is hard or pliable and composed of calcium carbonate shell units

All are Oviparous

Males

1.Typically have a concave or slightly concave plastron to prevent them from sliding off females (Fig. 13)

2. Males typically have longer forelimb claws (Fig. 14)

3. Males have a very large copulatory organ, the intromittent organ, its purpose is like a penis to transfer sperm (Fig. 15)

A good way to tell difference between male and female Testudines is by examining the tail. Males tales will be fatter and more robust than the females, and when the tail is gently straightened, the cloaca will be exposed, clearly behind the posterior edge of the carapace, while the female cloaca is positioned at or before the posterior edge of the carapace (Fig. 16).