Nesting Structures of Archelon: The Giant Sea Turtle of Late Cretaceous North America 2004 Gale A. Bishop

Transcription

1 Nesting Structures of Archelon: The Giant Sea Turtle of Late Cretaceous North America 2004 Gale A. Bishop The Late Cretaceous seas contained many swimming marine reptiles that reached gigantic proportions, including 30 footlong mosasaurs, 60 foot-long plesiosaurs, and 15 foot-long sea turtles. These marine reptiles joined toothed diving birds (Hesperorinus and Ichthyornis) and flying reptiles (pterosaurs) to comprise a suite of large animals that fed on the abundant food resources of the Late Cretaceous seas; the bivalves, ammonites, squids, and other invertebrates. The mosasaurs, plesiosaurs, pterosaurs, and diving toothed birds joined the dinosaurs and in the mass extinction at the end of the Cretaceous, an event that killed off 75% of the plants and animals alive during the Cretaceous and set the stage for the evolution of modern life forms. Of all these gigantic reptilian life forms, one that survived was the sea turtles! Nesting of Loggerhead Sea Turtles at St. Catherines Island, Georgia Modern sea turtles inhabit all the world oceans and all are now either endangered or threatened with extinction. Their numbers have rapidly declined dramatically over the last 50 years in response to man s increasing abuse of their habitat and over exploitation of the seas. Modern representatives of these charismatic giants from the ancient past annually crawl onto sandy temperate and tropical beaches to lay eggs to propagate their kind into the future. Their nesting activities can leave a signature that is preservable in the fossil record and attest to their nesting activities in the deep past. 1

2 The possible traces left by sea turtles are limited to nesting structures made by females nesting on sandy beaches in tropical or subtropical regions. Nesting behaviors are strongly imprinted on modern sea turtles and described as a nesting ethogram (Hailman and Elowson, 1992).The ethogram for loggerhead sea turtles (Caretta caretta) includes nine distinct segments each component of which results in characteristic traces of the behaviors that form potential trace fossils. The traces also provide a clue to the evolutionary sequencing of the behavioral segments; the presence of a covering activity (resulting in production of a covering pit) would imply predation pressures existed in the past that led to the development of a hiding strategy. Although the beaches have a low preservation potential, the abundance of nests deposited year after year increases their potential for preservation. The recognition of these structures in the fossil record is difficult due to their small size, cryptic appearance, and lack of experience of geologists with structures of this sort. Crawlways are produced by the female sea turtle ascending and descending the beach and by hatchlings scampering to the ocean. The crawlway morphology (symmetry and nest morphology) allows the sea turtle conservationist to identify the species, which produced the crawlway (Witherington, personal communication; Ga. DNR, personal communication). Individual turtles produce identifiable crawlways due to attached epizoans, flipper pathology, and individual crawling characteristics. The direction the turtle was crawling may often be determined by asymmetrical push marks from rear flippers and by v-shaped drags made by claws on the front flippers that open in the direction of 2

3 crawling. Because of this, entrance and exit crawlways can be readily identified and used in reading the nest. Once on the beach, the turtle may have to wander to find a suitable nesting site or might become disoriented and wander about after nesting trying to find her way back to the ocean; giving rise to a wandering pattern. Upon emergence, hatchlings produce radiating arcs of overlapping crawlways leading from their emergence crater to the ocean. Occasional misorientation, disorientation, or catastrophe can be read in their crawlway patterns. Loggerhead Crawlway A. Alternating comma-shaped flipper marks B. Wavy and smoothed track center with no thin, Straight, and well-defined tail-drag mark C. No regular marking from front flippers a the margins of the track Leatherback Crawlway A. Parallel flipper marks as from a "Butterfly-stroke" crawling pattern B. Ridged track center with a thin, straight, and well-defined tail-drag mark that is punctuated by tail-point marks C. Extensive marking from front flippers at the margins of the track and extending the total track width to 5 6 feet or greater. 3

4 From Georgia Department of Natural Resources handout at Sea Turtle Cooperator's Meeting 4/29/04 Once the nesting sea turtle senses a change in temperature from cool to warm as she passes from tidally-cooled to solarheated sand at the high tide line, she will often attempt to nest. This is initiated by digging a body pit by wallowing and scraping dry surface sand away from and under her body ("wallowing down" to damp sand) so she can excavate an egg chamber in damp sand that will hold vertical wall due to its cohesion. Occasionally the turtle will encounter damp sand from at surface and produce a body pit in it right at the surface forming a distinctive nest morphology (a "sand angel" analogous to "snow angels" produced by children in fresh snow). Sand angels may also be produced by hatchlings if they hang up in vegetation or are flipped on their backs during their rush to the sea. Once the sea turtle has wallowed down to damp sand, she will excavate an egg chamber using her rear flippers (try this yourself next time you visit the beach!) in an alternating scooping motion. The egg chamber is excavated to the depth to which the turtle can reach with her rear flippers and may show a bilateral symmetry in an urn-shaped excavation about cm in diameter. Occasionally turtles will attempt 4

5 nesting multiple times as they encounter subsurface obstructions (logs, wrack, or roots) and may leave several open body pits and egg chambers behind as they scoot forward to try again. Once a suitable egg chamber is constructed the eggs will be extruded nearly to the top of the egg chamber and the egg chamber back-filled, and possibly even tamped, with sand by the turtle's rear flippers. This backfilling is brecciated and in beaches with heavy minerals, will be obvious as a homogeneous, bioturbated sand cutting vertically through the horizontally laminated back beach facies. In horizontal view, if the loose sand of the covering pit is removed, this biogenic sedimentary structure will stand in stark contrast to the contour-like patterns of the back beach facies. The horizontal cross-sectional area of the egg chamber is usually less than 1% of the nest area; clearly an adaptation to protect eggs against predation. Once the egg chamber is backfilled, the turtle enters a covering behavior characterized by front flipper sweeps (Hailman and Elowson, 1992) pushing and throwing sand backwards and propelling the turtle forward. As the turtle moves forward with successive flipper sweeps, she almost always rotates 180 degrees either clockwise or counterclockwise and then exits the covering pit to crawl back to the ocean. The resultant sedimentary structure is a thin bioturbated layer (20-30 cm thick) covering the egg chamber and body pit.the structure exhibits an elliptical shape approximately 3.0 m long and 1.5 m wide bounded by flipper scarps, with an uneven surface, trails of loose, thrown sand, connected to entrance and exit crawlways. The covering pit and crawlways are exceedingly ephemeral structures on the surface, rapidly erased by wind, rain, and tides. 5

6 After approximately sixty days of incubation in the solarheated sand, the eggs will hatch and the hatchling turtles will emerge from their eggshell. The hatchlings begin to dig themselves out by a crawling motion of flippers, loosening the sand around and above them that falls through the mass of hatchlings under the influence of gravity, often forming a "stope" or air chamber above the mass of wiggling little turtles. This mining activity continues as long as the hatchlings are in cool sand beneath the surface. When they near the surface with its solar-heated hot sand, the hatchlings stop their activity and become lethargic, until the sand cools during the night when activity is renewed and the hatchlings emerge from their nest and scamper toward the sea, forming hatchling crawlways. Near the surface the sand is dry and not cohesive, so the surface layer may fall into the stope forming a surface "dimple" announcing an imminent emergence. The final emergence often is en masse, although multiple emerges on successive nights is the norm. Synchronous emergence of large numbers of hatchlings often forms an emergence crater as the surface sand collapses into the void left by the hatchlings. Upon emergence at night the hatchlings head to the sea (downhill, away from the island silhouette, and toward the light and noise of the sea) forming a pie-shaped arc of anatomizing crawlways broadening the sea. Reading these crawlways often allows the documentation of interactions with predators on the beach and an estimate of the number of emergent hatchlings. These are exceedingly ephemeral traces easily destroyed by wind, rain, and tide. Ancient Sea Turtles of the Western Interior Seaway During the Cretaceous Period the seas were inhabited by many types of Cretaceous sea turtles included; including 6

7 small toxichelids, about the size of many modern sea turtles such as loggerheads and giant forms the protostegids, including the genus Archelon. G. R. Wieland described Archelon ischyros in 1895 from a specimen collected in South Dakota and now exhibited in the Yale Peabody Museum (YPM 3000). A more complete Archelon, discovered in 1976, was collected by Frank Watson from southwestern South Dakota, near the Cheyenne River at Buffalo Gap during the mid-1970s, in Shannon County, S.D. Initial preparation and stabilization of the fossil was done by Peter Larson of the Black Hills Institute of Geological Research for Siber & Siber of Zurich, Switzerland. Siber & Siber sold the partly prepared specimen to Naturhistorisches Museum Wien, Austria. Preparation and mounting were completed by Naturhistorisches Museum Wien staff for display as the centerpiece exhibit of the Viennea Museum, where it resides to this day. Dr. Kraig Derstler of the University of New Orleans, who studied this specimen (Derstler, personal communication [1992]), said: "Without exaggeration, the Vienna museum specimen of Archelon ischyros is one of the world's great fossils." Because modern sea turtles are all endangered or threatened and fighting for their survival, Archelon is an especially poignant fossil and serves as a reminder of Earth's many endangered species. This charismatic position is substantiated by the U-Haul SuperGraphics campaign featuring Archelon as the icon for South Dakota. 7

8 Courtesy of National Geographic Society The National Geographic Society included a scaled diagram of Archelon ischros in its "Monsters of the Past" web site. From the diagram above, you can closely estimate the reach of the rear paddles when excavating an egg chamber. Ed Hooks reviewed The systematics of the protostegids (Hooks, 2002) and a cladistic matrix was run based upon morphologic characters. The classification of Archelon ischyros would be: Classification of Archelon ischros Wieland, 1895 Class Reptillia 8

9 Order: Chelonia Suborder: Cryptodira Superfamily: Chelonioidea Family: Protostegidae Genus: Archelon Species: Archelon ischyros NMW xxxxxx Archelon ischyros Wieland Late Cretaceous - 74 MYBP Campanian - Zone of Didymoceras cheyennense? Pierre Shale Shannon County, South Dakota Facts and deductions about the Vienna specimen and other specimens of Archelon have been summarized from the BHIGR < web site, the National Geographic web site, and from the U- Haul International, Inc. web site. The original fossil skeleton of the Vienna Archelon was collected from the Pierre Shale about 45 miles south of Rapid City, South Dakota, USA in the 1970'sand is owned by and displayed at the National Natural History Museum in Vienna, Austria. The Vienna specimen is the largest Archelon ischyros skeleton ever collected, is very nearly complete, the most complete of the Archelon skeletons ever collected, measures about 15'1 (4.5m) long from beak to end of tail (and said to be even longer if the neck were straightened, almost 16 feet! The skeleton measures about 16.5' (5.25m) wide across the carapace from the end of one front flipper to the end of the other outstretched front flipper. The live weight of this Archelon ischyros, is estimated to be more than 4,500 pounds (2200 kilos). Archelon has a hooked beak and, strong musculature, and probably had a very 9

10 powerful bite. This Archelon ischyros, having lived an estimated 100 years (determined by analogy?), probably died while brumating (hibernating) in the sea bottom and was killed and preserved partially buried in the mud of the sea floor. Cast replicas of the original fossil skeleton of Archelon ischyros, owned by the National Natural History Museum in Vienna, Austria, are produced by Black Hills Institute of Geological Research, Inc., under a special agreement with the Vienna Museum. Casts are displayed at Reptile Gardens in the Black Hills and another replica has been on display in Orlando, Florida at Walt Disney World's "Dinosaur Jubilee" since Fossil sea turtle sedimentary structures were discovered in the Fox Hills Sandstone near Limon in Elbert County, Colorado in 1997 see attached paper. The presence of gigantic sea turtles such as Protostega and Archelon raises many questions such as what did they eat, how did they reproduce, and where did they nest. The question of nesting includes what would we expect crawlways, body pits, egg chambers, egg molds, and covering pits of Archelon to look like in the fossil record. To address this question, we are asking you to use your knowledge of modern loggerhead sea turtle traces, the known instances of Cretaceous traces, and extrapolate them to the size of Archelon and to the morphology of traces made by their close relatives, the leatherbacks. 10

11 YPM 3000 Archelon ischyros collected by Dr. Wieland (in photographs) in South Dakota in 1895 and exhibited in the Yale Peabody Museum. Assume Dr. Wieland is six feet tall. Vienna, Austria specimen of Archelon ischyros collected in 1976 in Shannon County, South Dakota. Assume Ms. Marion Zenker is 5"3"" tall. Carnegie Museum specimen of Archelon ischyros no scale. 11

12 The Return of Archelon ischyros Rationale: All extant sea turtles nest on sandy beaches along the oceans they inhabit. The recent discovery of sea turtle nesting structures on an ancient Cretaceous beach (in the Fox Hills Formation near Limon (Bishop et al., 1998)) in Colorado allows sea turtle nesting behavior to be extended into the Late Cretaceous. The presence of giant sea turtles (Archelon and Protostega) in Late Cretaceous seas implies that they nested and produced large-scale nesting structures. By using measurements taken from nearly complete skeletons of these giant creatures and by making analogy to recent and fossil sea turtle nests, it is possible to predict the size and morphology of their nests. This produces a target image for geologists and paleontologists expecting to encounter a nest of a giant sea turtle. Goals and Objectives: This set of activities is presented in three parts: 1) Computing the size of Archelon from published images of the skeleton, 2) Using these measurements to model an Archelon nest, 3) using functional morphology to determine how Archelon deeply Archelon could dig and egg chamber, and 4) using these data to predict what an Archelon nest in the Cretaceous will look like. The students will use a literature search, analogous Recent imagery, proportionality, critical thinking, metric to English conversions, and inventiveness to consider the life modes of these ancient giant creatures. 12

13 Location: To be done preferably on a sandy beach, an open sandy area like a school yard, or in chalk in a large parking lot or classroom. Time Frame: This exercise will take approximately 1/2 to a full day (watch your tides!). Pre/Post-Test Procedure: 1. How Big was BIG! Read the introduction presented with this exercise, measure the following morphologic features on the diagrams presented: Specimen YPM 3000 NMW xxxxxx Carnigie Carapac e length Table of Measurements of Archelon Carapac Flipper e width width Rear Flipper Length Total length Estimated weight 13

14 2. Nesting: Functional Morphology 1. How deep would the body pit of this animal be? 2. Using all of the diagrams, determine the length of "reach" of the rear paddles of Archelon ischyros. 3. How wide would the rear flippers of Archelon ischyros have been? What is your evidence? 4. Construct a scaled map view of the body pit of this great sea turtle. 5. In the bottom of the body pit, sketch the plan view of the egg chamber neck. 6. Now construct a cross-sectional view of the body pit and egg chamber. 7. On an overlay (acetate) of your map view, sketch in the covering pit of a turtle this size, using its extant sea turtles as a model. 8. On your cross-sectional view add the cross section of the covering pit showing the base of the stirred-up (bioturbated) layer made by the covering activity. 9. Write a hypothesis to describe the egg size, morphology, and clutch size for this large sea turtle. 14

15 3. Field Exercise: Constructing an Archelon Nest 1. Read the introduction presented with this exercise. 2. Summarize the symmetry elements and morphology expected in a leatherback crawlway. 3. Calculate the width of the plastron dragway and flipper width (tip to tip) for your Archelon. 4. Lay out the edges of an Archelon crawlway on the beach by taping the proper flipper width and the proper plastron dragway width and mark with stake flags on the back beach and forebeach. 5. Use your ATV to drive a line between the stake flags using your outside wheel to delimitate the outer edges of the crawlway; 6. Repeat for the edges of the plastron drag. 7. Use a shovel or tool of your choice to construct flipper marks and the plastron drag. 8. Construct a body pit, egg chamber, and covering pit at the shoreward end of your crawlway (use a 3:1 ratio to scale off the covering pit).. 9. Repeat to construct an exit crawlway. 10. Photograph and sketch your Archelon nest. 15

16 4. Synthesis: Predicting the Past Now, considering the modeling you have done on the beach at St. Catherines Island, predict what the sedimentary structure suite will look like when an Archelon nest is discovered in the Late Cretaceous. 16

17 Selected References < (from Everhart, Oceans of Kansas < Agassiz, Louis [Remarks on crocodiles of the Green sand of New Jersey and on Atlantochelys]. Proceedings of the Academy of Natural Sciences of Philadelphia. 4:169. Beamon, J. C Depositional environment and fossil biota of a thin clastic unit of the Kiowa Formation, Lower Cretaceous (Albian), McPherson County, Kansas. Unpublished MS Thesis, Fort Hays State University, Hays, KS, 97 p. (oldest Cretaceous turtle remains in Kansas) Case, E. C., Toxochelys. The University Geological Survey of Kansas, Part VI. 4: pls Cope, E. D., Observations on the Reptilia of the Triassic formations of the Atlantic regions of the United States. Proceedings of the American Philosophical Society 11(84): (includes the description of Pneumatoarthrus peloreus, senior synonym of Archelon, Wieland 1896) Cope, E. D., 1872a. [Sketch of an expedition in the valley of the Smoky Hill River in Kansas]. Proceedings of the American Philosophical Society 12(87): (meeting of October 20, 1871) 17

18 Cope, E. D., 1872b. On a new Testudinate from the chalk of Kansas. Proceedings of the American Philosophical Society 12(88): (Cyanocercus incisus ) Cope, E. D., 1872c. A description of the genus Protostega, a form of extinct Testudinata. Proceedings of the American Philosophical Society 12(88): (March 1, 1872) Cope, E. D., 1872d. On the geology and paleontology of the Cretaceous strata of Kansas. Annual Report of the U. S. Geological Survey of the Territories 5: (Report for 1871). Cope, E. D., [On Toxochelys latiremis]. Proceedings of the Academy of Natural Sciences of Philadelphia 25:10. Cope, E. D., The Vertebrata of the Cretaceous formations of the West. Report, U. S. Geological Survey Territories (Hayden). 2:302 p, 57 pls. Cope, E. D., On some new or little known reptiles and fishes of the Cretaceous of Kansas. Proceedings of the American Philosophical Society 17(100): (Toxochelys latiremis Cope: issue of May-Dec., 1877, printed Nov. 20, 1877) Derstler Druckenmiller, P. S., A. J. Daun, J. L. Skulan and J. C. Pladziewicz, Stomach contents in the upper Cretaceous shark Squalicorax falcatus. Journal of Vertebrate Paleont. 13(suppl. to no. 3):33A. 18

19 Hailman, J. P. and A. M.Elowson Ethogram of the nesting female loggerhead (Caretta caretta). Herpetologica 48(1): Hay, O. P., On certain portions of the skeleton of Protostega gigas. Publ. Field Columbian Museum, Zoological Ser. (later Fieldiana: Zoology), 1(2):57-62, pls. 4 & 5. Hay, O. P., On the skeleton of Toxochelys latiremis. Publ. Field Columbian Museum, Zoological Ser. (later Fieldiana: Zoology), 1(5): , pls. 14 &15. Hirayama, R Oldest known sea turtle. Nature 392, Hay, O. P The fossil turtles of North America. Carnegie Institution of Washington, Publication No. 75, 568 pp, 113 pl. Hooks, G. E., III Systematic revision of the Protostegidae, with a redescription of Carcarichelys gemma Zangerl, Journal of Vertebrate Paleontology, 18(1): Kear, B. P First gut contents in a Cretaceous sea turtle. Biol. Lett. (2006) 2, [Published online 2 November 2005]. Kear, B. P., W. E. Boles, and E. T. Smith Unusual gut contents in a Cretaceous ichthyosaur. Proc. R. Soc. Lond. B (Suppl. ) 270, S206 S208. Kear, B. P.. W. E. Boles, and E. T. Smith Unusual gut contents in a Cretaceous ichthyosaur. Proc. R. Soc. Lond. B (Suppl. ) 270: S206 S

20 Lane, H. H., 1946, A survey of the fossil vertebrates of Kansas, Part III, The Reptiles, Kansas Academy Science, Transactions 49(3): , 7 figs. Lehman, T. M., and S. L. Tomlinson Terlinguachelys fischbecki, a new genus and species of sea turtle (Chelonioidea: Protostegidae) from the Upper Cretaceous of Texas. Journal of Paleontology 78: Leidy, J., Cretaceous reptiles of the United States. Smithsonian Contributions to Knowledge 14(192):1-135, pls Manning, E. M., Dr. William Spillman ( ), pioneer paleontologist of Mississippi. Mississippi Geology. 15(4): Nicholls, E. L., New material of Toxochelys latiremis Cope, and a revision of the genus Toxochelys (Testudines, Chelonoidea). Journal of Vertebrate Paleontology, 8(2): Russell, D. A Vertebrates in the Western Interior Sea. Pages in Caldwell, W. G. E. and E. G. Kaufmann, eds., Evolution of the Western Interior Basin, Geological Association of Canada. Special Paper 39. Raidal, S. R., P. L. Shearer, and R. I. T. Prince Chronic shoulder osteoarthritis in a loggerhead turtle (Caretta caretta). Australian Veterinary Journal Volume 84, No 7: Shimada, K. and G.E. Hooks III Shark-bitten protostegid turtles from the upper cretaceous Mooreville Chalk, Alabama. J. Paleontology 78:

21 Shimada, K., M. J. Everhart, and G. E. Hooks, Ichthyodectid fish and protostegid turtle bitten by the Late Cretaceous lamniform shark, Cretoxyrhina mantelli. Journal of Vertebrate Paleontology 22(suppl. to 3):106A. (Abstract) Sternberg, C. H., Directions for collecting vertebrate fossils. Kansas City Review of Science and Industry 8(4): Sternberg, C. H., Protostega gigas and other Cretaceous reptiles and fishes from the Kansas chalk. Kansas Academy Science, Transactions 19: Stewart, J. D., Earliest record of the Toxochelyidae. Kansas Academy of Science, Transactions 81(2):178 (abstract). Stewart, J. D., Niobrara Formation vertebrate stratigraphy, pages 19-30, In Bennett, S. C. (ed.), Niobrara Chalk Excursion Guidebook, The University of Kansas Museum of Natural History and the Kansas Geological Survey. Wieland, G. R., Archelon ischyros: a new gigantic cryptodire testudinate from the Fort Pierre Cretaceous of South Dakota. American Journal of Science, 4th Series 2(12): , pl. v. Wieland, G. R Some observations on certain wellmarked stages in the evolution of the testudinate humerus. American Journal of Science, 4th Series, 9(54): , with 23 text fig. 21

22 Wieland, G. R Notes on the Cretaceous turtles, Toxochelys and Archelon, with a classification of the marine Testudinata. American Journal of Science, Series 4, 14:95-108, 2 text-figs. Wieland, G. R., A new Niobrara Toxochelys. American Journal of Science, 4th Series, 20(119):343, pl. x, 8 text-figs. Wieland, G. R., The osteology of Protostega, Memoirs of the Carnegie Museum, 2(7): Wieland, G. R Revision of the Protostegidae. American Journal of Science, Series 4. 27(158): , pls. ii-iv, 12 text-figs. Williston, S. W., A new turtle from the Benton Cretaceous. Kansas. University Quarterly 3(1):5-18, with pls. ii-. Williston, S. W., Turtles. The University Geological Survey of Kansas, Part VI. 4: pls Williston, S. W., A new turtle from the Kansas Cretaceous. Kansas Academy Science, Transactions 17: Williston, S. W., On the hind limb of Protostega. American Journal of Science, Series 4, 13(76): , 1 fig. Williston, S. W., Water reptiles of the past and present. Chicago University Press. 251 pp. (Free, downloadable.pdf version here) 22

23 Zangerl, R., The vertebrate fauna of the Selma formation of Alabama, Part IV, the turtles of the family Toxochelyidae. Fieldiana (Geol. Mem.): 3(4): Zangerl, R Patterns of phylogenic differentiation in the toxochelyid and chelonid sea turtles. American Zoologist 20: Zangerl, R. and R. E. Sloan A new description of Desmatochelys lowi (Williston). A primitive cheloniid sea turtle from the Cretaceous of South Dakota. Fieldiana, Geology Memoirs 14:7-40. Return to previous page Go to Table of Contents Go to the next page 23

24 Evaluation: yes no 1. Was constructing the mock Archelon nest fun? Comments? 2. Was constructing a mock Archelon nest a good learning activity? Comments? 3. Did you personally have to construct new thoughts is this exercise? Comments? 4. Can you modify this activity to use in your curriculum? Comments? 5. Would your students find this exercise (modified to grade level and discipline) fun? Comments? 6. Can you address performance standards within the context of teaching this exercise about charismatic sea turtles? 24

25 Comments? Open Ended Question: What needs to be added, deleted, or changed to make this a functional learning experience for your curriculum? [Answer on the back of this page] Thank you for your input! 25

26 26