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quinta-feira, 17 de novembro de 2016

[PaleoMammalogy • 2016] 

Echovenator sandersi • The Origin of High-Frequency Hearing in Whales


Echovenator sandersi 
Churchill, Martinez-Caceres, de Muizon, Mnieckowski & Geisler, 2016

  DOI: 10.1016/j.cub.2016.06.004 

Highlights
• An ancient toothed whale is described, which possesses a well-preserved inner ear
• Features associated with ultrasonic hearing are preserved in the ear of this whale
• Ultrasonic hearing evolved with echolocation in the first toothed whales
• Hearing at higher frequencies began in the ancestors of toothed whales

Summary
Odontocetes (toothed whales) rely upon echoes of their own vocalizations to navigate and find prey underwater. This sensory adaptation, known as echolocation, operates most effectively when using high frequencies, and odontocetes are rivaled only by bats in their ability to perceive ultrasonic sound greater than 100 kHz. Although features indicative of ultrasonic hearing are present in the oldest known odontocetes, the significance of this finding is limited by the methods employed and taxa sampled. In this report, we describe a new xenorophid whale (Echovenator sandersi, gen. et sp. nov.) from the Oligocene of South Carolina that, as a member of the most basal clade of odontocetes, sheds considerable light on the evolution of ultrasonic hearing. By placing high-resolution CT data from Echovenator sandersi, 2 hippos, and 23 fossil and extant whales in a phylogenetic context, we conclude that ultrasonic hearing, albeit in a less specialized form, evolved at the base of the odontocete radiation. Contrary to the hypothesis that odontocetes evolved from low-frequency specialists, we find evidence that stem cetaceans, the archaeocetes, were more sensitive to high-frequency sound than their terrestrial ancestors. This indicates that selection for high-frequency hearing predates the emergence of Odontoceti and the evolution of echolocation.



Description

Systematics

Order Cetacea Brisson 1762.
Suborder Odontoceti Flower 1867.

Family Xenorophidae Uhen 2008.

Echovenator sandersi gen. et sp. nov.

Etymology: From Latin for “echo hunter,” referring to its use of echolocation while foraging. Species name is in honor of Albert Sanders, former curator of The Charleston Museum, for his contributions to our knowledge of Oligocene Cetacea.

Holotype: Georgia Southern Museum (GSM) 1098, a nearly complete skull with 39 teeth, mandible, and atlas, presumed to represent a single individual (Figures 1 and 2; see also Figures S1 and S2, Table S1, and Supplemental Experimental Procedures, part I).




 Locality and Age: Drainage ditch associated with Limehouse Branch Creek, Berkeley County, South Carolina. Approximate coordinates are: N 33°01′53′′; W 80°06′06′′. Basal bed of the Chandler Bridge Formation, late Oligocene (ca. 24–27 Ma) in age. This bed is a probable equivalent of the marine or marginal marine lithofacies, which was deposited in a nearshore marine or restricted bay environment.

Diagnosis: Echovenator has the following synapomorphies of Xenorophidae: premaxilla underlies the ascending process of the maxilla, a frontal window that exposes the maxilla and premaxilla, and an elongate ventrolateral tuberosity of the periotic. Echovenator differs from all xenorophids in having fused, or partially fused, fronto-nasal and maxillo-premaxillary sutures and in having a paranaris fossa; it differs from Xenorophus sloanii and Albertocetus meffordorum in having a postnarial fossa and a depressed internasal suture; and it differs from Cotylocara macei in having an undivided postnarial fossa and in having larger dorsal exposures of parietals.


Morgan Churchill, Manuel Martinez-Caceres, Christian de Muizon, Jessica Mnieckowski and Jonathan H. Geisler. 2016. The Origin of High-Frequency Hearing in Whales. Current Biology.    DOI: 10.1016/j.cub.2016.06.004

  


wesome Ancient Whale 'Echovenator' Had Ultrasonic Hearing by @jacsrons http://inv.rs/GdQ via @inversedotcom
Echo hunter: Researchers name new fossil whale with high frequency hearing http://phy.so/389523432 via @physorg_com

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