Giles Sam, Rücklin Martin, Donoghue Philip C J
School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, UK.
J Morphol. 2013 Jun;274(6):627-44. doi: 10.1002/jmor.20119. Epub 2013 Feb 2.
The vertebrate dermal skeleton has long been interpreted to have evolved from a primitive condition exemplified by chondrichthyans. However, chondrichthyans and osteichthyans evolved from an ancestral gnathostome stem-lineage in which the dermal skeleton was more extensively developed. To elucidate the histology and skeletal structure of the gnathostome crown-ancestor we conducted a histological survey of the diversity of the dermal skeleton among the placoderms, a diverse clade or grade of early jawed vertebrates. The dermal skeleton of all placoderms is composed largely of a cancellar architecture of cellular dermal bone, surmounted by dermal tubercles in the most ancestral clades, including antiarchs. Acanthothoracids retain an ancestral condition for the dermal skeleton, and we record its secondary reduction in antiarchs. We also find that mechanisms for remodeling bone and facilitating different growth rates between adjoining plates are widespread throughout the placoderms.
长期以来，脊椎动物的真皮骨骼被认为是从以软骨鱼类为代表的原始状态进化而来的。然而，软骨鱼类和硬骨鱼类是从一个祖先有颌类干群进化而来的，在这个干群中，真皮骨骼发育得更为广泛。为了阐明有颌类冠群祖先的组织学和骨骼结构，我们对盾皮鱼（早期有颌脊椎动物的一个多样的类群或演化支）的真皮骨骼多样性进行了组织学调查。所有盾皮鱼的真皮骨骼主要由细胞性真皮骨的蜂窝状结构组成，在最原始的类群（包括褶齿鱼目）中，其上方还有真皮瘤。棘胸鱼目保留了真皮骨骼的原始状态，我们记录了褶齿鱼目中其真皮骨骼的二次退化。我们还发现，重塑骨骼以及促进相邻骨板之间不同生长速率的机制在整个盾皮鱼中广泛存在。
