[中文]蜥螈

动物档案：

名字：蜥螈（Seymouria），又名西蒙龙、西蒙螈

含义：来自西蒙（蜥螈的发现地，在美国得克萨斯州）

时期：二叠纪早期

分类：四足动物总纲（西蒙螈亚目）

体长：60厘米（2英尺）

体重：10-15千克（22-23磅）

食性：小型动物

化石分布地：北美洲、欧洲

人们在得克萨斯州的红层中发现了这种肉食性动物的化石，其中大多数都还保存得十分完整。得克萨斯州的红层可上溯至二叠纪。除了蜥螈，这里的红层还保存了许多了不起的生物遗体，比如说“背上有帆”的异齿龙（本章后面有介绍）。有一部分蜥螈的化石发掘于得克萨斯州的西蒙城，因此蜥螈也有西蒙螈之名。这种动物看起来像是一只巨大的蜥蜴，甚至大得像是一只鳄鱼。它有一张硕大的嘴巴，长着许多尖牙，用来抓捕猎物。与本章之前已介绍过的许多动物一样，蜥螈是一种两栖的四足动物。其更进一步的分类名称是石炭蜥目，前一页介绍的始螈也属于这一级分类。与蜥螈一同被发掘出来的动植物化石表明，它们当时的栖息地是相当干燥的，湖泊与河流只是点缀。蜥螈固然有两栖的能力，但考虑到当时的环境，它应该主要生活于陆地。

科学家们在刚开始研究蜥螈的化石时，认为它们可能是一种爬行动物。因为它们的确有许多爬行动物的特征，包括肩骨以及胯骨的结构、颅骨与颈椎的连结处（颈部的脊梁骨）。然而，它们同时也有一些爬行动物所不具备的小特征，比如说它们幼体的颅骨上存在细线。这通常意味着它们是有侧线的动物，在水中运动时会用侧线来感知水流。在鱼的身体两侧就可以清晰地看到各有一条线，那就是侧线。人们现已发现了数种蜥螈，生活于二叠纪的各个时期。

右图 这是来自得克萨斯州的一个蜥螈化石样本，很好地展现了蜥螈的坚固骨架。正是这样厚实的骨骼才支撑起蜥螈那颇有分量的身体。

下图 蜥螈是一种强壮的四足动物。它们拥有爬行动物的外观，十分适应陆地生活。但它们也保留了两栖动物的特征，比如说侧线，也就是分布在它们身体上部的那条从头到尾的线条。在潜入水中时，它们可以通过侧线来感知水流的变化。

[/中文]

[外文]Seymouria

ANIMAL FACTFILE

Seymouria

Meaning: Of Seymour (its discovery site)

Pronunciation: see-moor-ee-ah

Period: Early Permian

Main group: Tetrapoda (Seymouriamorpha)

Length: 60 centimeters (2 feet)

Weight: 10–15 kilograms (22-23 pounds)

Diet: Smaller animals

Fossil sites: North America, Europe

Many excellently preserved fossils of this

60-centimeter (2-foot) predator have been

found in rocks in Texas known as the Red

Beds. The rocks, which date back to the

Permian period, have also yielded remains of

many other impressive creatures, such as the

“sailback” Dimetrodon (described later in this

chapter). Seymouria was named after the town

of Seymour, Texas, where some of its fossils

were uncovered. It resembled a large lizard or

even a crocodile, with a wide mouth and

sharp teeth for grabbing prey. Seymouria was a

member of the amphibious group called the

tetrapods, like other creatures shown so far in

this chapter. Within this main group, it

is placed in the anthracosaur subgroup, like

Eogyrinus (on the previous page). Fossils of

other animals and also plants found with

those of Seymouria show that the habitat of

the time was fairly dry upland, here and there

dotted with rivers and lakes. Although

Seymouria was able to live on both land and

in water, it probably dwelled mostly on land.

The scientists who first studied the remains

of Seymouria thought that it might be a

reptile. It had reptilian features, including the

structure of its shoulder bones and hipbones,

and the joints between the skull and the

cervical vertebrae (neck backbones).

However, there were small details that were

not reptilian, such as the presence of lines on

the skulls of young specimens. These usually

accommodated the lateral line sense that

detects waterborne vibrations, clearly seen as

a line along each side of the body in fish.

Several types of Seymouria are known from

most of the Permian period.

RIGHT A fine specimen of Seymouria from Texas

showing the sturdy or robust construction of the

skeleton, with thick-set bones for carrying

considerable weight on land.

BELOW Seymouria was a tough, reptilian-looking

tetrapod well adapted to dry land. But it

retained amphibious features such as the lateral

line, seen as a stripe along length of the upper

body, which detects ripples and vibrations when

submerged in water.[/外文]