ZOOLOGY OF CHORDATES: STUDY GUIDE - Zakharenko M.O. - 2015

CHAPTER 4. SUPERCLASS TETRAPODA. LOWER TERRESTRIAL VERTEBRATES

4.3. Identification of Amphibian Representatives.

1 [2] Tail absent. Tailless. Anura.

2 [1] Tail present.

3 [4] Maximum body width fits into its length (excluding tail) more than three times. Larvae ("tadpoles") of tailless amphibians. Salientia.

4 [3] Maximum body width fits into its length more than three times. Tailed. Caudata.

Order Tailless. Anura.

Identification key for tailless amphibians

1 [34] Teeth present on the upper jaw (test with a fingernail).

2 [19] Tongue deeply notched at the posterior margin, appearing as if with two lateral lobes.

3 [18] Dorsolateral folds present.

4 [13] A dark temporal Λ-shaped spot extending from the eye across the tympanum and almost to the shoulder; color never green; males with vocal sacs hidden beneath the throat Skin, or entirely without vocal sacs.

5 [6] Inner metatarsal tubercle high.

Moor frog - Rana arvalis.

6 [5] Inner metatarsal tubercle relatively low, fitting 2–4.5 times into the length of the inner toe of the hind limb.

7 [8] Distance from the snout tip to the anterior margin of the eye equals or is even slightly greater (maximum 117%) than the distance between the dark stripes at the anterior margin of the eyes; width of each eyelid approximately equals the interorbital space.

Common frog - Rana temporaria.

8 [7] Distance from the snout tip to the anterior margin of the eye significantly exceeds (112–144%) the distance between the dark stripes at the anterior margin of the eyes; eyelid width typically greater than the interorbital space.

9 [12] Outer metatarsal tubercle present, belly never red-spotted (if red, the coloration is uniform).

10 [11] Dorsolateral folds on the anterior part of the back rather weakly developed; tympanic membrane equals 0.4–0.5 of the eye length.

11 [10] Dorsolateral folds well developed along the entire length; tympanic membrane equals 0.5–0.6 of the eye length.

13 [4] Temporal spot absent, or if present, the dorsal color is green; males with external vocal sacs in the form of pouches near the corners of the Mouth.

14 [15] A fairly large number of longitudinal skin ridges present between the dorsolateral folds.

15 [14] Longitudinal ridges between the dorsolateral folds absent.

16 [17] Inner metatarsal tubercle high, contained 1–3 times in the length of the inner hind toe, and 5–10 times in the shank length; vocal sacs white.

Pool frog - Pelophylax lessonae.

17 [16] Inner metatarsal tubercle low, contained 2.5–4.5 times in the length of the inner hind toe, and 9–14 times in the shank length; vocal sacs gray or almost black.

Marsh frog - Pelophylax ridibundus.

18 [3] Dorsolateral folds absent, skin quite tuberculate, giving a toad-like appearance.

19 [2] Tongue without a notch at the posterior end, or if notched, the fingertips are expanded into disks.

20 [23] Fingertips expanded into disks.

21 [22] Shank length, when folded along the back, fits 2 times into the distance from the cloaca to the line connecting the nostrils or the anterior margins of the eyes.

European tree frog - Hyla arborea.

22 [21] Shank length, when folded along the back, fits 2 times into the distance from the cloaca to the line connecting the posterior margins of the eyes.

23 [20] Fingertips not expanded.

24 [27] Inner metatarsal tubercle spade-shaped, very large: approximately equal in length to the first hind toe.

25 [26] A prominent longitudinal Swelling on the forehead and crown.

Common spadefoot toad - Pelobates fuscus.

26 [25] Forehead between the eyes flat.

27 [24] Inner metatarsal tubercle relatively small: several times smaller than the first hind toe.

28 [29] Webbing on the hind legs very poorly developed, present only at the Base of the toes; pupil not triangular; subarticular tubercles present.

29 [28] Webbing well developed; pupil triangular; subarticular tubercles absent.

30 [31] Shank length less than FOOT length; fingertips dark or barely lightened.

European fire-bellied toad - Bombina bombina

31 [30] Shank length greater than or equal to foot length; fingertips distinctly light-colored.

32 [33] Belly (in life!) with red patches; skin on the ventral side smooth.

Yellow-bellied toad - Bombina variegata.

34 [1] Teeth absent in the upper jaw.

35 [38] A single tubercle on the underside of the third joint (counted from the tip) of the fourth (longest) hind toe.

36 [37] The tip of the fourth (outermost) toe of the forelimb extends beyond the first (terminal) joint of the third toe.

Green toad – Bufo viridis.

37 [36] The tip of the fourth toe of the forelimb does not reach the first joint of the third toe.

35 [35] There are two tubercles on the underside of the third joint of the fourth toe of the hind limb.

39 [40] The inner margin of the tarsus has a longitudinal skin fold.

Natterjack toad – Bufo calamita.

40 [39] The inner margin of the tarsus lacks a longitudinal skin fold.

Common toad – Bufo bufo. 4.4. ORIGIN AND EVOLUTION of Amphibians. In the Late Devonian, the first amphibians—Ichthyostegalia—diverged from freshwater lobe-finned Fishes (Sarcopterygii). Possibly as early as the Late Devonian, they gave rise to two amphibian subclasses: Lepospondyli and Apsidospondyli, which dominated the terrestrial fauna of the Carboniferous period and displaced freshwater lobe-finned fishes from shallow Water bodies. Paleozoic amphibians, regardless of their taxonomic affiliation, are commonly referred to as stegocephalians or armored-headed amphibians. They were covered in a continuous armor of dermal (skin) bones. The armor possessed only openings for the nostrils, eye sockets, and parietal organ. In some stegocephalians, the body was covered with fish-like scales, while in others, dermal ossifications were retained only on the underside of the body, forming a ventral shield (protecting the belly when moving on land). In many species, the Pelvic Girdle was not connected to THE Vertebral Column, and the Pectoral Girdle sometimes retained a connection to the occipital region of the Skull. Their paired limbs were relatively weak.

Paleozoic apsidospondyl amphibians are grouped into the superorder Labyrinthodontia, named so because the outer surface of their teeth exhibited complex folding, forming a labyrinth of enamel loops in transverse cross-section. This superorder includes four orders. At the end of the Devonian, the order Ichthyostegalia gave rise to numerous amphibian groups; it also branched off the Lineage leading to reptiles. The order Rachitomi and the order Stereospondyli separated from it in the Carboniferous and were represented by species of various sizes (the largest reaching 5 m in length). They likely inhabited the banks of massive rivers and lakes, lying in wait for prey (mainly fish) in shallow waters. In some large-headed species, the heavy trunk and tail were noticeably shortened. Labyrinthodonts began to die out at the end of the Paleozoic (in the Permian) and only a few survived into the mid-Triassic. The jumping tailless amphibians—superorder Salientia—presumably arose from some primitive rachitomes. Remains of primitive anurans found in Lower Triassic deposits (about 10 cm long, with up to 15 trunk vertebrae, short Ribs, a Femur longer than the Tibia, and possibly a short tail) are grouped into the order Proanura. Species appearing around the Middle Jurassic (with about 10 trunk vertebrae and a tibia no shorter than the femur) are classified under the order Anura, which includes all modern tailless amphibians.

At the end of the Devonian and the beginning of the Carboniferous, the order Anthracosauria (or Embolomeri) diverged from certain ichthyostegalians or primitive rachitomes. In their lifestyle (fairly large piscivorous predators) and General Structural Features, they were similar to primitive rachitomes, differing only in some details of the vertebrae and skull Structure (notches on its posterior margin, The formation of a single occipital condyle). In the middle of the Carboniferous, seymouriamorphs diverged from them. A number of zoologists and paleontologists tend to classify them within the Class Amphibia, assigning them to the subclass Batrachosauria. At the end of the Devonian, the Lepospondyli—lepospondyl amphibians—branched off from ichthyostegs. Paleozoic lepospondyl stegocephalians are divided into three orders. The order Microsauria is represented by small forms (up to 50 cm in length) that externally resembled modern newts and salamanders. Currently existing amphibian orders—Caudata (remains known from the mid-Cretaceous) and Gymnophiona (fossil remains not yet discovered)—diverged from certain, possibly Permian, microsaurs. The order Nectridea unites larger (up to 100 cm in length) newt-like amphibians that led a predominantly aquatic lifestyle. The order Aistopoda encompasses small animals (20-50 cm in length) with a snake-like body and reduced limbs. They were previously thought to be aquatic; a more plausible assumption now suggests that the loss of limbs was associated with dwelling in dense grassy vegetation along the banks of water bodies. The latter two orders went extinct without leaving descendants.

Thus, the adaptive radiation of Paleozoic amphibians took place during the Carboniferous and partly during the Permian periods. In the latter period,

most groups went extinct, and only isolated forms of certain groups survived into the middle of the Triassic. This rapid extinction was perhaps driven by biotic rather than climatic causes. In the Early Permian, as in the Carboniferous, a warm and humid climate prevailed over most of the land. Only in the Late Permian and Triassic, after the extinction of most Paleozoic amphibians, did the climate become hotter and drier. Seymouriamorphs and primitive amphibians retained significant amphibian traits and inhabited the same biotopes as amphibians. Possessing high mobility and, presumably, complex behavior, seymouriamorphs—which diverged from them in the Late Carboniferous and Permian—along with other reptile groups, gradually displaced (through food competition and direct predation) amphibians from their occupied habitats. Strictly aquatic amphibians survived the longest, but they too retreated under pressure from reptiles during the Triassic, with some forms recolonizing aquatic biotopes by secondarily transitioning to an aquatic or semi-aquatic lifestyle.

Control Questions

1. General characteristics of amphibians.

2. STRUCTURE OF THE amphibian skin.

3. The amphibian Skeleton.

7. The Digestive System of amphibians.

5. The Respiratory system of amphibians.

6. The excretory system of amphibians.

7. The Circulatory system OF amphibians.

8. The Nervous system of amphibians.

9. The Reproductive System of amphibians.

10. Reproduction and development of amphibians.

13. The Significance of amphibians in nature and human life.

14. Classification of amphibians.

15. Comparative CHARACTERISTICS OF THE respiratory Organs in amphibians and fish.

16. Comparative characteristics of the nervous system in amphibians and fish.

17. Comparative characteristics of the excretory organs in amphibians and bony fish.

18. Sense Organs of amphibians.

19. Lifestyle of bony fish.

20. Comparative characteristics of the skeleton in amphibians and fish.

21. Ecological groups of amphibians.

22. Parental care in amphibians.

23. Aquatic and terrestrial amphibians.

24. Feeding habits of amphibians.

25. The Role of amphibians in nature and human life.

26. Exotic amphibians.

27. Amphibians of the Red Data Book of Ukraine.

28. Systematics of amphibians.

29. The role of sound in the life of amphibians.