Botha-Brink Jennifer, Modesto Sean P
Karoo Palaeontology, National Museum, PO Box 266, Bloemfontein 9300, Republic of South Africa.
Proc Biol Sci. 2007 Nov 22;274(1627):2829-34. doi: 10.1098/rspb.2007.0803.
Living species of mammals, crocodiles and most species of birds exhibit parental care, but evidence of this behaviour is extremely rare in the fossil record. Here, we present a new specimen of varanopid 'pelycosaur' from the Middle Permian of South Africa. The specimen is an aggregation, consisting of five articulated individuals preserved in undisturbed, close, lifelike, dorsal-up, subparallel positions, indicating burial in 'life position'. Two size classes are represented. One is 50% larger than the others, is well ossified, has fused neurocentral sutures and is distinguished by a coat of dermal ossifications that covers the neck and shoulder regions. We regard this individual to be an adult. The remaining four skeletons are considered to be juveniles as they are approximately the same size, are poorly ossified, have open neurocentral sutures and lack dermal ossifications. Aggregates of juvenile amniotes are usually siblings. Extant analogues of adult and juvenile groupings suggest that the adult is one of the parents, leading us to regard the aggregation as a family group. The Late Middle Permian age of the varanopid family predates the previously known oldest fossil evidence of parental care in terrestrial vertebrates by 140 Myr.
现存的哺乳动物、鳄鱼和大多数鸟类都表现出亲代抚育行为，但这种行为的证据在化石记录中极为罕见。在此，我们展示了一个来自南非中二叠世的恐头龙类“盘龙目”新标本。该标本是一个聚集体，由五个关节相连的个体组成，它们以未受干扰、紧密、逼真、背部朝上且近乎平行的姿势保存，表明是在“生前姿势”下被掩埋的。标本中有两个大小等级。其中一个比其他个体大50%，骨骼化程度良好，神经中央缝已融合，其特征是覆盖颈部和肩部区域的一层皮内成骨。我们认为这个个体是成年个体。其余四个骨架被认为是幼年个体，因为它们大小大致相同，骨骼化程度较差，神经中央缝未愈合，且没有皮内成骨。幼年羊膜动物的聚集体通常是兄弟姐妹。成年和幼年个体组合的现存类似物表明，成年个体是其中一个亲代，这使我们将这个聚集体视为一个家庭群体。恐头龙类家族的中二叠世晚期比此前已知的陆地脊椎动物亲代抚育的最古老化石证据早1.4亿年。
