Fossil bone histology reveals ancient origins for rapid juvenile growth in tetrapods

Abstract

Patterns of growth throughout the lifetime of an animal reflect critical life history traits such as reproductive timing, physiology, and ecological interactions. The ancestral growth pattern for tetrapods has traditionally been described as slow-to-moderately paced, akin to modern amphibians, with fast growth and high metabolic rates considered a specialized physiological trait of amniotes. Here, we present bone histology from an ontogenetic series of the Early Carboniferous stem tetrapod Whatcheeria deltae, and document evidence of fibrolamellar bone—primary bone tissue associated with fast growth. Our data indicate that Whatcheeria juveniles grew rapidly and reached skeletal maturity quickly, allowing them to occupy a large-bodied predator niche in their paleoenvironment. This life history strategy contrasts with those described for other stem tetrapods and indicates that a diversity of growth patterns existed at the origins of tetrapod diversification. Importantly, Whatcheeria marks an unexpectedly early occurrence of fibrolamellar bone in Tetrapoda, both temporally and phylogenetically. These findings reveal that elevated juvenile growth is not limited to amniotes, but has a deep history in the tetrapod clade and may have played a previously unrecognized role in the tetrapod invasion of land.

On the origins of endothermy in amniotes

“…This tetrapodomorph, which lived during the Carboniferous Period, was inferred as being ectothermic in our study, based on canal size. However, it displays FLC in its femoral cross section, 44 a type of tissue frequently used as evidence for endothermy by numerous studies, including Grigg et al. 4 However, † Whatcheeria ’s HMC is in accordance with big erythrocytes, suggesting its cardiovascular system did not attain a sufficient efficiency to sustain tachymetabolism ( Figure 3 ).…”

Ancient Diseases in Vertebrates: Tumours through the Ages

“…Studies in dry bone lesions have shown promising results in differentiating between some tumour types. Immunohistochemistry and molecular analysis methods have provided insights into ancient tumours' cellular and molecular characteristics [36]. Although a powerful tool in paleo-oncology, this technique does have its limitations.…”