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6261Rhinoptera bonasus - A Living Relative of Potobatis semperei

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  • Neal Robbins
    Nov 21, 2013
         These links have photos of Rhinoptera bonasus.
          Rhinoptera bonasus is a living relative of the Paleocene ray Potobatis semperei. Both are in the order Myliobatiformes and the superfamily Dasytoidea. Rhinoptera bonasus is a member of the family Myliobatidae.
          Rhinoptera bonasus is often called the cownose ray. It is native to the western Atlantic (from New England in the USA to Brazil), the Caribbean Sea, and the Gulf of Mexico. This ray resides in marine and brackish waters as far down as 22 m. (72.2 feet). It is frequently found in bays and estuaries.
          Rhinopterus bonasus is typically about 107 cm. (3.51 feet) in width. It has a disc-like body. Broad wing-like structures are located along the sides. There is a small dorsal fin at the rear of the body. A small, barbed poisonous spine is directly behind this fin. Beyond the spine the body tapers into a long tail that is whip-like. A specialized fin is located beneath the head. This fin is divided into two short rounded lobes. The front of the head features a conspicuous indent. The mouth of Rhinopterus bonasus is on the underside of the head. It has up to 11-13 rows of plate-like teeth. They enable Rhinoptera bonasus to crush hard-shelled prey. The dorsal coloration of Rhinoptera bonasus is light to dark brown. The ventral part is white or yellowish-white. The pectoral fins have brownish edges.
          Rhinoptera bonasus is pelagic and travels in large groups. The cownose ray finds prey by sensing movements and weak electric signals. Rhinoptera bonasus sucks and vents water through its gills and fluidizes the sand. Then it clears the sand by making stirring motions with the pectoral fins. The lobes under the head are used to shift food towards the mouth. The prey is sucked into the mouth and crushed by the teeth. Indigestible parts are emitted from the mouth and edible portions are swallowed. Rhinoptera bonasus eats crabs, lobsters, bottom-dwelling fish, and marine mollusks, for example, clams and oysters. Predators of Rhinoptera bonasus include these creatures:
      Sandbar shark (Carcharhinus plumbeus)
      Cobia (Rachycentron canadum)
      Bull sharks (Carcharhinus leucas)
          Breeding is thought to occur between June and September. The eggs hatch inside the female and the young are born live. After hatching, the offspring get additional nourishment from a nutrient-rich fluid that is produced by the lining of the mother's uterus. A female generally bears one offspring at a time. The width of the newborn is about 36 cm. (1.2 ft.).
          One female was seen carrying a total of six offspring to full term. Gestation takes 11-12 months. Rhinoptera bonasus reaches breeding maturity at4-5 years of age. In the Gulf of Mexico, males live as long as 16 years, though females live up to 18 years. In the Atlantic, the oldest males recorded were 8 years of age. Females in the Atlantic have been recorded to live for 13 years. The reference for this information is this publication:
      J.A. Neer and B.A. Thompson. Life History of the cownose ray, Rhinoptera bonasus, in the northern Gulf of Mexico, with comments on geographic variability in life history traits. Environmental Biology of Fishes 73: 321-331.
          Rhinoptera bonasus goes on long mass migrations that can number thousands of individuals. It goes south in late autumn and north in late spring.
          These publications are references:
      http://www.arkive.org/ Arkive - Rhinoptera bonasus
      Smithsonian Marine Station at Fort Pierce (July, 2009)
      Florida Museum of Natural History (July, 2009)
      D.E. Sasko, M.N. Dean, P.J. Motta, and R.E. Hueter (2006) Prey capture behavior and kinematics of the Atlantic cownose ray, Rhinoptera bonasus. Zooology, 109: 171-181
      IUCN Red List (June, 2009)
      D. Burnie (2001) Animal. Dorling Kindersley, London.
          Neal Robbins