Marivaux Laurent, Ramdarshan Anusha, Essid El Mabrouk, Marzougui Wissem, Khayati Ammar Hayet, Lebrun Renaud, Marandat Bernard, Merzeraud Gilles, Tabuce Rodolphe, Vianey-Liaud Monique
Laboratoire de Paléontologie, Institut des Sciences de l'Évolution de Montpellier (ISE-M, UMR-CNRS 5554), Université Montpellier 2, Montpellier, France.
PLoS One. 2013 Dec 4;8(12):e80778. doi: 10.1371/journal.pone.0080778. eCollection 2013.
Molecular clock estimates of crown strepsirhine origins generally advocate an ancient antiquity for Malagasy lemuriforms and Afro-Asian lorisiforms, near the onset of the Tertiary but most often extending back to the Late Cretaceous. Despite their inferred early origin, the subsequent evolutionary histories of both groups (except for the Malagasy aye-aye lineage) exhibit a vacuum of lineage diversification during most part of the Eocene, followed by a relative acceleration in diversification from the late Middle Eocene. This early evolutionary stasis was tentatively explained by the possibility of unrecorded lineage extinctions during the early Tertiary. However, this prevailing molecular view regarding the ancient origin and early diversification of crown strepsirhines must be viewed with skepticism due to the new but still scarce paleontological evidence gathered in recent years.
METHODOLOGICAL/PRINCIPAL FINDINGS: Here, we describe new fossils attributable to Djebelemur martinezi, a≈50 Ma primate from Tunisia (Djebel Chambi). This taxon was originally interpreted as a cercamoniine adapiform based on limited information from its lower dentition. The new fossils provide anatomical evidence demonstrating that Djebelemur was not an adapiform but clearly a distant relative of lemurs, lorises and galagos. Cranial, dental and postcranial remains indicate that this diminutive primate was likely nocturnal, predatory (primarily insectivorous), and engaged in a form of generalized arboreal quadrupedalism with frequent horizontal leaping. Djebelemur did not have an anterior lower dentition as specialized as that characterizing most crown strepsirhines (i.e., tooth-comb), but it clearly exhibited a transformed antemolar pattern representing an early stage of a crown strepsirhine-like adaptation ("pre-tooth-comb").
CONCLUSIONS/SIGNIFICANCE: These new fossil data suggest that the differentiation of the tooth-comb must postdate the djebelemurid divergence, a view which hence constrains the timing of crown strepsirhine origins to the Middle Eocene, and then precludes the existence of unrecorded lineage extinctions of tooth-combed primates during the earliest Tertiary.
冠狐猴型灵长类动物起源的分子钟估计通常支持马达加斯加狐猴型和亚非懒猴型具有古老的历史，接近第三纪开始，但大多可追溯到晚白垩纪。尽管推断它们起源较早，但这两个类群（马达加斯加指猴谱系除外）在始新世大部分时间的后续进化历史都呈现出谱系多样化的空白期，随后从中始新世晚期开始多样化相对加速。这种早期进化停滞现象曾初步解释为第三纪早期可能存在未记录的谱系灭绝。然而，鉴于近年来新发现但仍然稀少的古生物学证据，关于冠狐猴型灵长类动物古老起源和早期多样化的这种主流分子观点必须受到质疑。
方法/主要发现：在此，我们描述了可归属于Djebelemur martinezi的新化石，这是一种来自突尼斯（杰贝勒尚比）的约5000万年前的灵长类动物。基于其下齿列的有限信息，该分类单元最初被解释为一种cercamoniine类狐猴型原猴。新化石提供了解剖学证据，表明Djebelemur不是狐猴型原猴，而是狐猴、懒猴和婴猴的远亲。颅骨、牙齿和颅后骨骼遗骸表明，这种小型灵长类动物可能是夜行性、食肉动物（主要食虫），并以一种普遍的树栖四足行走方式为主，频繁进行水平跳跃。Djebelemur没有像大多数冠狐猴型灵长类动物那样特化的下前齿列（即齿梳），但它明显呈现出一种转变的前臼齿模式，代表了类似冠狐猴型适应的早期阶段（“前齿梳”）。
结论/意义：这些新的化石数据表明，齿梳的分化必定晚于Djebelemur的分化，这一观点因此将冠狐猴型灵长类动物起源的时间限制在中始新世，进而排除了最早第三纪期间存在未记录的齿梳灵长类动物谱系灭绝的可能性。
