Stamford Museum and Nature Center, Stamford, CT, USA.
Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, USA.
BMC Ecol Evol. 2022 Jul 12;22(1):90. doi: 10.1186/s12862-022-02043-4.
A major challenge to understanding how biodiversity has changed over time comes from depauperons, which are long-lived lineages with presently low species diversity. The most famous of these are the coelacanths. This clade of lobe-finned fishes occupies a pivotal position on the vertebrate tree between other fishes and tetrapods. Yet only two extant species and fewer than 100 extinct forms are known from the coelacanth fossil record, which spans over 400 million years of time. Although there is evidence for the existence of additional genetically isolated extant populations, a poor understanding of morphological disparity in this clade has made quantifying coelacanth species richness difficult.
Here, we quantify variation in a sample of skulls and skeletons of the Triassic eastern North American coelacanth †Diplurus that represents the largest assemblage of coelacanth individuals known. Based on the results of these quantitative comparisons, we identify a diminutive new species and show that multiple lacustrine ecosystems in the Triassic rift lakes of the Atlantic coastline harbored at least three species of coelacanths spanning two orders of magnitude in size.
Conceptions about the distribution of species diversity on the tree of life may be fundamentally misguided when extant diversity is used to gauge signals of extinct diversity. Our results demonstrate how specimen-based assessments can be used to illuminate hidden biodiversity and show the utility of the fossil record for answering questions about the hidden richness of currently species-poor lineages.
理解生物多样性随时间变化的一个主要挑战来自于久存物种，这些是现今物种多样性较低但寿命较长的谱系。其中最著名的是腔棘鱼。这些有肺鳍的鱼类在脊椎动物树中处于其他鱼类和四足动物之间的关键位置。然而，腔棘鱼化石记录中仅知道两个现存物种和不到 100 个已灭绝的形式，其跨度超过 4 亿年的时间。尽管有证据表明存在其他遗传上隔离的现存种群，但对该谱系中形态差异的理解不足，使得量化腔棘鱼物种丰富度变得困难。
在这里，我们量化了来自三叠纪东北美腔棘鱼†Diplurus 的样本的头骨和骨骼的变异，这代表了已知的最大腔棘鱼个体集合。基于这些定量比较的结果，我们确定了一个微小的新物种，并表明三叠纪大西洋海岸线裂谷湖中存在至少三个物种的腔棘鱼，大小跨越两个数量级。
当使用现生物种多样性来衡量灭绝多样性的信号时，关于生命之树中物种多样性分布的概念可能会从根本上产生误导。我们的结果表明，基于标本的评估可以用来阐明隐藏的生物多样性，并展示化石记录在回答目前物种较少的谱系隐藏丰富度问题方面的效用。
