某些動(dòng)物能夠通過(guò)口腔或鼻腔把從喉部產(chǎn)生的超聲波發(fā)散出去,，利用折回的聲音來(lái)定方向，這種空間定向的方法被稱為回聲定位（echolocation）,。我們所熟知具有回聲定位能力的動(dòng)物有蝙蝠、鯨,、海豚等,。而在地面生活具有回聲定位能力的哺乳動(dòng)物僅有北美短尾鼩鼱（Blarina）、栗齒鼩鼱（Sorex）以及馬達(dá)加斯加島的馬島猬（tanrec）,，它們不像蝙蝠那樣利用回聲定位來(lái)尋找食物,，而更多的用于搜尋棲息地。
雷比達(dá)豬齒獸（Hyopsodus lepidus）顱骨化石的三維成像
此次古生物學(xué)家和神經(jīng)學(xué)家發(fā)現(xiàn)了一塊已滅絕的古新世-始新世（Paleocene-Eocene）有蹄類（偶蹄類）哺乳動(dòng)物顱骨化石,，這是科學(xué)家首次發(fā)現(xiàn)史前動(dòng)物回聲定位能力的化石證據(jù),。這塊雷比達(dá)豬齒獸（Hyopsodus lepidus）顱骨化石的相關(guān)研究報(bào)道發(fā)表在公共科學(xué)圖書(shū)館（Public Library of Science）網(wǎng)站上,。
研究人員介紹道：“根據(jù)豬齒獸顱骨化石的顱腔復(fù)原模型形態(tài)學(xué)研究表明：雷比達(dá)豬齒獸的聽(tīng)覺(jué)能力高度發(fā)達(dá),，我們推測(cè)這可能與它們利用地面回聲定位有關(guān)。同時(shí)它是一種行動(dòng)敏捷,，能快速移動(dòng),，通常生活在洞穴里夜行性動(dòng)物，這可能也與它們地面回聲定位能力的演化有關(guān),。像回聲定位如此特化功能的出現(xiàn)也反映了古代豬齒獸應(yīng)具有非常特殊的大腦皮質(zhì)結(jié)構(gòu),。并且，這種史前豬齒獸較大的大腦容量以及大腦各部分的相對(duì)比例都與較進(jìn)化的有蹄類動(dòng)物非常相似,，使得雷比達(dá)豬齒獸的大腦演化在較低級(jí)的有蹄類動(dòng)物中尤為顯著,。”(生物谷 Bioon.com)
doi:10.1371/journal.pone.0030000
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PMID:
Digital Cranial Endocast of Hyopsodus (Mammalia, “Condylarthra”): A Case of Paleogene Terrestrial Echolocation?
Maeva J. Orliac, Christine Argot, Emmanuel Gilissen
We here describe the endocranial cast of the Eocene archaic ungulate Hyopsodus lepidus AMNH 143783 (Bridgerian, North America) reconstructed from X-ray computed microtomography data. This represents the first complete cranial endocast known for Hyopsodontinae. The Hyopsodus endocast is compared to other known “condylarthran” endocasts, i. e. those of Pleuraspidotherium (Pleuraspidotheriidae), Arctocyon (Arctocyonidae), Meniscotherium (Meniscotheriidae), Phenacodus (Phenacodontidae), as well as to basal perissodactyls (Hyracotherium) and artiodactyls (Cebochoerus, Homacodon). Hyopsodus presents one of the highest encephalization quotients of archaic ungulates and shows an “advanced version” of the basal ungulate brain pattern, with a mosaic of archaic characters such as large olfactory bulbs, weak ventral expansion of the neopallium, and absence of neopallium fissuration, as well as more specialized ones such as the relative reduction of the cerebellum compared to cerebrum or the enlargement of the inferior colliculus. As in other archaic ungulates, Hyopsodus midbrain exposure is important, but it exhibits a dorsally protruding largely developed inferior colliculus, a feature unique among “Condylarthra”. A potential correlation between the development of the inferior colliculus in Hyopsodus and the use of terrestrial echolocation as observed in extant tenrecs and shrews is discussed. The detailed analysis of the overall morphology of the postcranial skeleton of Hyopsodus indicates a nimble, fast moving animal that likely lived in burrows. This would be compatible with terrestrial echolocation used by the animal to investigate subterranean habitat and/or to minimize predation during nocturnal exploration of the environment.
