The Jurassic pachycormid osteichthyan Leedsichthys problematicus is renowned for having been able to achieve
prodigious size for a bony fish. Building on work of MARTILL (1986a), a thorough examination of all known
material was conducted in order to constrain estimates of the size of this animal and examine its rate of growth.
Important specimens of Leedsichthys are described for the first time. The histology of Leedsichthys is reviewed, and
the presence of growth annuli is used to establish ages for five specimens. Age and growth data were obtained
from gill rakers (n = 4) and lepidotrichia (n = 2). Lepidotrichia show upward curvilinear growth profiles and
ages ranging from 21 to 40 annuli, which are assumed to represent years. Both growth profiles start at a small
size (0.26 and 0.33 mm radial distance), which is assumed to represent age 1. However, annuli can be lost near
the margins of the elements. Gill rakers exhibit a sigmoidal growth profile. Age of gill rakers was estimated by
adjusting the alignment of the inflection points of the growth profiles thereby giving adjusted ages. Gill rakers
ranged in age from 19–38 annuli, but all show evidence of reabsorption of annuli near the focal points and at the
margins of most elements. Sizes for the five individuals range from 8.0-16.5 m for ages of 19-40 years. Growth
rate (0.01-0.05 K) was relatively slow as expected for a large, long-lived fish. At age 1, individuals were 1.6 m in
length. Estimates for the length of L. problematicus compare well with published lengths of other large suspension
feeders such as those for basking and whale sharks
