Dinosaurs and Parental Care

From fossil evidence alone the question of whether or not dinosaurs cared for their young is very difficult to answer. Because behaviors are not preserved in the fossil record, we can only make inferences from indirect evidence. Parental care can be divided into two types of behavior: prehatching (building nests and incubating eggs - for example, sitting on top of them so as to warm the eggs and encourage hatching) and posthatching (feeding the young and guarding the nests). Most of our evidence comes from alleged dinosaur rookeries (places where nests are built). Several have been excavated in eastern Montana, where a large concentration of dinosaur nests was found at a place now called Egg Mountain. Most of these probably belonged to the hadrosaur Maiasaura. Preserved in these nests are the bones of baby dinosaurs. The finds at Egg Mountain and other sites around the world document that dinosaurs laid their eggs in nests.

[p:1]仅根据化石证据，判断恐龙是否照顾其幼崽的问题是非常困难的。由于行为不会被保存在化石记录中，我们只能从间接证据中进行推断。亲代照顾可以分为两类行为：孵化前（筑巢和孵卵 - 例如，坐在卵上以温暖卵并促进孵化）和孵化后（喂养幼崽和守卫巢穴）。我们的大多数证据来自所谓的恐龙繁殖地（筑巢的地方）。在蒙大拿州东部挖掘出几个这样的地方，其中一个地方现在称为卵山，那里发现了大量恐龙巢穴。大多数恐龙巢穴可能属于慈母龙。在这些巢穴中保存了恐龙宝宝的骨骼。卵山和世界其他地方的发现表明，恐龙确实在巢穴中产卵。

The nests at Egg Mountain are reported to be equally spaced, separated by a space corresponding to the length of an adult Maiasaura. From this arrangement scientists have inferred that the nests were separated in this way to allow incubation in a tightly packed nesting colony. Although this interpretation is open to challenge, the discovery of Oviraptor adults on top of Oviraptor egg clutches (as determined by embryos in some eggs) is relatively powerful evidence that at least this dinosaur incubated its nests.

[p:2]据报道，蛋山的巢穴排列均匀，巢穴之间的间距相当于一只成年慈母龙的长度。科学家们从这种排列推测出，这些巢穴是以这种方式分开的，以便在紧密排列的巢群中进行孵化。尽管这一解释仍有争议，但在某些蛋中有胚胎的情况下，发现窃蛋龙成年个体位于窃蛋龙蛋簇之上，这一发现是相对有力的证据，至少证明了这种恐龙孵化它的巢穴

Evidence for parental care following hatching is much more controversial. Behavioral speculation based on indirect fossil evidence is dangerous because the data is not always as unambiguous as might appear. At Egg Mountain, many nests contain baby dinosaur bones. Not all the dinosaurs in the nest are the same size. Many of the small bones found in the nests are associated with jaws and teeth, teeth that show signs of wear. It seems reasonable to assume that the wear was caused by the chewing of the coarse plants that were the hatchlings' diet. Because the young were still in the nest, this food may have been brought to the rookery by foraging adults. This line of reasoning suggests that these animals had an advanced system of parental care. A closer look at the evidence clouds this interpretation. Analysis of dinosaur embryos indicates that worn surfaces are present on the teeth of juveniles even before hatching. Just as a human baby moves inside the mother before birth, modern-day archosaurs also grind their teeth before birth, wearing the surface in some spots. Thus, the fossil evidence for an advanced parental care system in extinct dinosaurs is suggestive but inconclusive, and it is hard even to imagine the sort of paleontologic discovery that could settle this debate for good.

[p:3]在孵化后进行亲代照顾的证据更加具有争议性。基于间接化石证据的行为推测是危险的，因为这些数据并不像看起来那样明确。在蛋山，许多巢穴中包含幼年恐龙的骨骼。巢中的恐龙并不是全都一样大小。巢穴中发现的许多小骨骼与下颚和牙齿有关，这些牙齿显示出磨损的迹象。合理的推测是，这些磨损是因为幼崽咀嚼其饮食中的粗糙植物所造成的。因为这些幼崽仍然在巢中，这些食物可能是由觅食的成体恐龙带回巢地的。这种推理表明这些动物具有发达的亲代照顾系统。但是，仔细观察这些证据，这一解释就不那么清晰了。对恐龙胚胎的分析表明，即使是在孵化之前，幼崽牙齿的某些表面也存在磨损痕迹。就像人类婴儿在出生前会在母体内活动一样，现代的主龙类在出生前也会磨牙，从而在某些部位造成磨损。因此，化石证据表明，灭绝恐龙中存在先进的亲代照顾系统，这虽然具有暗示性，但并不确凿，并且很难想象会有什么样的古生物学发现能够彻底解决这一争论。

The strongest evidence that extinct dinosaurs had some form of advanced parental care system is based on an understanding of the phylogenetic relationships among dinosaurs and their closest living relatives. Birds (which are in essence modern, feathered dinosaurs), even primitive ones such as ostriches and kiwis, exhibit parental care, so some form of parental care can be inferred to have existed in the last common ancestor of all birds. Although unappreciated, crocodiles are reptiles that are also caring parents. They build nests, guard the nests, and in some cases dig their young out of the nest when they hear the chirping young ones hatching. The young even communicate with each other while still in the egg by high-frequency squeaks (as birds do). Some evidence suggests that this squeaking is a cue for the synchronization of the hatching. Since birds and crocodiles share a common ancestor, the simplest explanation for the characteristics they share (such as nest building and some form of parental care) is that they evolved only once - that these attributes were present in their common ancestor and passed on to its descendants. Because extinct dinosaurs also descended from that ancestor, the simplest and most general theory is that extinct dinosaurs also shared these characteristics, even though they cannot be directly observed, and we cannot be sure how elaborate their parental care was.

[p:4]灭绝恐龙具有某种形式的先进亲代照顾系统的最有力证据，是基于对恐龙及其最近的现存亲属之间系统发育关系的理解。鸟类（本质上是现代有羽毛的恐龙），即使是像鸵鸟和几维鸟这样的原始鸟类，也表现出亲代照顾，因此可以推断，所有鸟类的最后一个共同祖先中存在某种形式的亲代照顾。尽管不太被重视，但鳄鱼也是具有亲代照顾行为的爬行动物。它们筑巢、保护巢穴，有时甚至在听到小鳄鱼的鸣叫时挖巢帮助幼崽破壳。幼崽在仍在蛋中时甚至会通过高频鸣叫彼此交流（就像鸟类一样）。一些证据表明，这种鸣叫是同步孵化的提示信号。由于鸟类和鳄鱼共享一个共同祖先，因此它们共享特征（如筑巢和某种形式的亲代照顾）的最简单解释是，这些特征只进化了一次 - 它们存在于其共同祖先中，并传给了后代。由于灭绝恐龙也是该祖先的后代，最简单和最普遍的理论是，灭绝恐龙也共享这些特征，尽管它们不能被直接观察到，我们也不能确定其亲代照顾有多么复杂。