Thursday, February 2, 2012

Lab 2: Testudines (Brad and Michelle)

Lab 2: Testudines!

General Objectives: Observe the skeletal and reproductive anatomy of turtles; and to witness the overall diversity of Testudines.

This week for Biology of the Reptilia Lab 2 we focused on one of the most diverse clades of reptiles, Testudines. Testudines is split into 14 families with over 323 from habitat ranges spanning worldwide (except Antarctica). These fascinating organisms are one of the most distinct reptiles and cannot be mistaken otherwise...mainly due to their prominent anatomy.

Turtle Anatomy:
The major feature that makes a turtle a turtle is its shell. No other extant organism on Earth has this distinctive physical makeup. A turtle shell can be broken down into two main components: the carapace and the plastron. The carapace comprises the dorsal portion of the shell while the plastron is ventral. Essentially, the carapace and plastron are made up from a series of dermal bones. Overlaying the dermal bones of the shell are epidermal structures known as scutes. Turtles have modified their ribs, vertebrae (forming the carapace), sternum, and girdles (forming the plastron) providing a heavy duty means of protection. Living life within a shell has made for a highly modified skeleton paired with relatively specialized girdles.

Turtle skeleton

In terms of skull anatomy, turtles are a perfect candidate showing form meeting function. In this lab we were lucky enough to witness some really cool turtle skulls including some from Chelydridae, Trionychidae, and even Testudinidae. The Chelydrid (snapping turtle) skull showed very prominent sutures, perfect in identifying some of the main bones in the skull associated with representatives of Testudines.

While the carapace and plastron serve as a great means of protection it has made reproduction rather interesting. Turtles, like other amniotes, are equipped for internal fertilization (see photo of intromittent organ below) and have offspring that undergo direct development (a “mini-adult”) in a cleidoic egg (made of calcium carbonate).

Generally, without laproscopically probing the hatchlings/juveniles, it is hard to tell the difference between females and males. However, as the organisms reach sexual maturity there are some tell-tale signs in distinguishing among the sexes. Typically all you have to do is look to the posterior end of the animal; the tail. In males the cloaca is positioned distally behind the carapace (Left photo below). In females, the cloaca is positioned at or before the end of the carapace(Right photo below). (Observe differences below)

Another characteristic is the shape of the plastron. The male plastron is typically more concave, allowing for the male to mount the female more easily during courtship (see photo below -concave male plastron on left).

A large portion of the lab was dedicated to observing the biodiversity of turtles. Turtles can be broken down into 2 main groups: Pleurodira and Cryptodira. The difference between these groups has to do with the how the turtle brings its neck into the shell. The Pleurodirans, appropriately known as the "side-neck turtles", when frightened, fold their head into the side of the shell, but cannot bring it completely inside. Interestingly enough we also learned that some are lefties and some are righties. The Cryptodirans, known as the "hidden neck turtles", can completely bring their head inside of the shell due to an S-shaped vertebral column in the neck. Essentially, these turtles can extend their necks (lessening the S-shape) and when they pull their head in the S-shape is formed.

Some of the major families representing the Cryptodiran condition:

• Chelydridae (Snapping Turtles)*
• Cheloniidae (Hard-Shelled Seaturtles)*
• Dermochelyidae (Leatherback Seaturtle)
• Carrettochelyidae (Pig-Nose Turtles)
• Trionychidae (Softshell Turtles)*
• Dermatemydidae (Mesoamerican River Turtles)
• Kinosternidae (Mud & Musk Turtles)*
• Platysternidae (Big-Headed Turtle)
• Emydidae (Cooters, Sliders, American Box Turtles & Allies)*
• Geomydidae (Asian River Turtles, Leaf & Roofed Turtles, Asian Box Turtles & Allies)
• Testudinidae (Tortoises)*

(* = Representatives actually seen in lab)


The Soft-shell Turtles are a relatively distinct family of turtles ranging from Africa, parts of Asia, Indo-pacific Islands, and North America. They have very leathery skin (used partially for cutaneous respiration) and typically burrow into soft substrate on the bottoms of rivers. They utilize their snorkel like snout and very long necks to stealthily acquire oxygen/air from the water surface. Photographed below is an Ohio species Apalone spinifera. Another species also native to Ohio (but not pictured) is Apalone mutica.

One of the only lineages that makes its existence mainly on land, tortoises are commonly found throughout sea level-1000m elevations. Most have high domed shells and exhibit robust elephantine feet. Fifteen genera have been described with over 45+ species. Pictured below is the one and only Geochelone sulcata (SAMSON!!!!)

This family has some of the smallest turtles (representing only 24+ species). They generally exhibit an oblong, domed carapace and have large heads (relative to their body). Although generally aquatic, they hibernate on land and have been known to terrestrially forage as well. Pictured below is an Ohio species: Sternotherus odoratus (Stinkpot Turtle)

Broken up into two sub-families: Emydinae and Deirochelinae, this family is one of the most diverse groups providing upwards of 15% of all turtle diversity. Emydidae also represents the greatest diversity among Ohio turtles. Observe the diversity below (most of what we saw in lab came from this clade. Pictured on the left below is the rare Ohio species, Clemmys guttata. Pictured on the right below is Graptemys.

Some of the Ohio species represented in this clade include:
- Chrysemys picta marginata
- Clemmys guttata
- Emydoidea blandingii
- Graptemys geographica
- Graptemys pseudogeographica
- Pseudemys concinna
- Terrapene carolina
- Trachemys scripta

One of the coolest, but unfortunately not so speciose families, the Chelydrids or Snapping Turtles, represent one of the largest (in size) species of turtle in Ohio (Chelydra serpentina - pictured on
left below). The larger of the 2 genera is Macrochelys (the alligator snapping turtle). These mean looking BAMFs have large, robust heads, broad, flat carapaces, and a cruciform plastron. The tell tale difference between the 2 species is the 3-4 supramarginal scutes found on the carapace of Macrochelys (pictured on right below).

The Hard-Shelled Seaturtles represent one of the only families that we witnessed in lab that reside primarily in marine environments. The forelimbs are flipper-like and hind-limbs are webbed. All 6 species emerge on beaches only to nest and will return to the same spot every couple of years during their reproductive age (takes ~25 years to reach reproductive age). Hatchlings and small juveniles will commonly "disappear" into the pelagic zone.

Some of the major families representing the Pleurodiran condition:
• Chelidae (Australoamerican Side-Neck Turtles)*
• Pelomedusidae (African Mud Terrapins)
• Podocnemidae (Madagascaran Big-Headed Turtles & American Side-Neck Turtles)*

Another representative showing the Pleurodira condition, these omnivorous turtles are primarily aquatic and have relatively flattened skulls and shells. The Chelids are common to tropical/subtropical habitats throughout Australia and parts of South America.

Another represenative showing the Pleurodiran condition (note the side-neck anatomy), the classic river turtle (pictured below) has a sleek, wide, domed shell perfect for cruisin. They have relatively large heads and jaws helping them take big bites out of aquatic vegetation or other prey items.

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