What We Do

Step 1: Basic Information

We start off the collection process by randomly selecting a skull from the shelf, making sure we have not collected that skull before, and bringing it to the work table. We then proceed to examine the skull and type down the basic information that is written on the skull into our database. This information will include the CAS accession number (number assigned to the skull by the team at CAS), RB number (original skull curator number assigned), sex, age (if given), where it was found dead, the date it was found, presence of baculum (if applicable), and standard length of the specimen.

The age classes of the skulls were classified as pup, immature (IM), juvenile (J), subadult (SA), and adult (A). If age was not provided, age was determined by an age categorization table based on the specimen's standard length (Laake et al., 2016). If standard length of the specimen was not provided, we compared skull measurements of others and predicted the age of the specimen based off of the age of similar skull sizes.

Step 2: Measurements

Measurements of the California sea lion skulls is done by a digital caliper that measure up to about 210mm. We take four measurements of the skull: lateral total length, mandible length, medial width, and total height.

The lateral total length is done by starting the measuring at the back near the occipital condyles which is where the spinal cord meets the brain to the frontal tip of the maxilla which is the bone where the teeth connect to the skull. For the mandible length measurement, we measure the tip of the mandible between the front middle incisors back to the open space between the mandibular condyles held in place by a ruler. An example of this type of measurement is shown to the right. The third measurement is the medial width which is where we measure the base of the zygomatic arch which connects to the temporal bone. We specifically measure one side of the zygomatic arch over the zygomatic arch on the other side of the skull. The final measurement we perform is the total height where we put a ruler on top of the highest point of the skull parallel to the ground so we can measure from the same height. We then measure from the ruler to the top of the table surface we are measuring on to get the total height.

Sometimes, the lateral total length measurements we gathered were longer than the calipers are capable of measuring so we use an older wooden caliper which was used to measure most of our skulls.

Step 3: Teeth Examination

The teeth examination process is a process that our team has become extremely familiar with these past few semesters. We examined the teeth and documented any abnormalities and pathologies. We began with the back upper molar, move up to the 4 premolars, then the canine, and finally the three incisors on the upper right section of the skull. We then repeat this same process for the left side of the skull, and both sides of the mandible with one exception being that the mandible has 2 fewer incisors than the ones on the skull do. Often times during our teeth examinations we find abrasion on some of the teeth, but it is also not out of the ordinary when we come across skulls that have an extra set of teeth usually behind the molars.

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